Yearly Archives: 2026

Class 1 Div 1 vs Div 2: NEC Hazardous Location Guide

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Updated: April 10, 2026

Class 1 Div 1 and Class 1 Div 2 are two NEC hazardous location classifications that define how likely flammable gases or vapors are to be present. The distinction matters because it determines what type of electrical equipment you can install. Div 1 means ignitable concentrations exist under normal conditions. Div 2 means they only appear during abnormal events like leaks or equipment failure. Get the classification wrong, and you risk either an explosion or overspending on equipment rated far beyond what the area requires.

Contents

What Is a Class 1 Hazardous Location?

The NEC (NFPA 70) Article 500 defines Class 1 locations as areas where flammable gases, vapors, or liquids are present or may be present in the air in sufficient quantities to produce ignitable mixtures.

Class 1 covers the broadest range of industrial hazardous environments. Refineries, chemical plants, fuel loading docks, paint spray booths, and gas pipeline facilities all fall under Class 1. The key factor is the presence of flammable gases or vapors—not combustible dusts (that is Class 2) or fibers (Class 3).

Within Class 1, the NEC further divides locations into Division 1 and Division 2 based on the probability and frequency of the hazardous atmosphere. This division directly affects equipment selection, installation cost, and maintenance requirements.

Class 1 Division 1: Definition and Requirements

Per NEC Article 500.5(B)(1), a Class 1 Division 1 location is an area where one or more of these conditions exist:

  • Ignitable concentrations of flammable gases or vapors can exist under normal operating conditions.
  • Ignitable concentrations may exist frequently because of repair or maintenance operations or because of leakage.
  • Breakdown or faulty operation of equipment or processes might simultaneously release ignitable concentrations and cause electrical equipment failure that serves as an ignition source.

In practical terms: the inside of a fuel storage tank vapor space, the area around an open chemical reactor, or the immediate zone around a gasoline dispenser nozzle are all Div 1 locations. The hazardous atmosphere is expected to be there during normal operations.

Equipment installed in Div 1 must use the most stringent protection methods: explosion-proof enclosures (Ex d), intrinsic safety (Ex i), or purged/pressurized systems (Ex p). There is no room for compromise—a single spark can reach an ignitable mixture at any time.

Class 1 Division 2: Definition and Requirements

Per NEC Article 500.5(B)(2), a Class 1 Division 2 location is an area where:

  • Volatile flammable liquids or gases are handled, processed, or used, but are normally confined within closed containers or systems and can only escape through accidental rupture, breakdown, or abnormal operation.
  • Ignitable concentrations are normally prevented by positive mechanical ventilation, and the area might become hazardous only through failure or abnormal operation of the ventilation equipment.
  • The area is adjacent to a Class 1 Division 1 location, and ignitable concentrations might occasionally migrate into it.

Think of it this way: a properly sealed pump room with ventilation where flammable gas only escapes if a gasket fails. Or a laboratory where solvents are stored in sealed containers and only exposed briefly during use. Under normal conditions, the atmosphere is safe. The hazard only appears when something goes wrong.

Div 2 allows less expensive protection methods such as non-incendive equipment (Ex nA), restricted breathing enclosures, or hermetically sealed devices. The lower probability of a hazardous atmosphere means you do not need full explosion-proof housings for every piece of equipment—though you still need certified gear. For more on how pressure transmitters handle hazardous area ratings, see our technical guide.

Class 1 Div 1 vs Div 2: Key Differences

The table below summarizes the main differences between Division 1 and Division 2 classifications:

CriteriaClass 1 Division 1Class 1 Division 2
Hazardous atmosphere presentDuring normal operationsOnly during abnormal conditions
Probability of ignitable mixtureHigh (continuous, intermittent, or periodic)Low (accidental release only)
NEC referenceArticle 500.5(B)(1)Article 500.5(B)(2)
Equipment protection levelExplosion-proof, intrinsically safe, purgedNon-incendive, restricted breathing, hermetically sealed
Div 1 equipment allowed?Yes (required)Yes (over-rated but acceptable)
Div 2 equipment allowed?NoYes
Typical cost impactHigh (premium enclosures and wiring)Moderate (less stringent enclosures)
Example locationsInside tank vapor space, open reactor, fuel dispenser zoneVentilated pump room, solvent storage, area adjacent to Div 1

One rule to remember: equipment certified for Div 1 can always be used in Div 2. But Div 2 equipment cannot be used in Div 1 locations. When in doubt, specifying Div 1-rated equipment eliminates classification risk at the cost of higher upfront expense.

Protection Methods by Division

Division 1 Protection Methods

Explosion-proof (Ex d): The enclosure is built to contain an internal explosion without letting flame or hot gases escape to ignite the surrounding atmosphere. This is the most common method for Div 1 motors, junction boxes, and lighting fixtures. The enclosure must pass hydrostatic and explosion tests per UL 1203 or IEC 60079-1.

Intrinsic safety (Ex i): Electrical energy in the circuit is limited below the minimum ignition energy of the specific gas group. Two levels exist: Ex ia (safe with two faults—suitable for Div 1) and Ex ib (safe with one fault—suitable for Div 2 only). Most 4-20mA transmitters and sensor loops use this method because the power levels are already low.

Purged/pressurized (Ex p): Clean air or inert gas maintains positive pressure inside the enclosure, preventing flammable gas from entering. Used for large control panels or analyzer housings. Requires a continuous purge supply and interlock system per NFPA 496.

Division 2 Protection Methods

Non-incendive (Ex nA): The equipment does not produce arcs or sparks capable of igniting a specific gas under normal operation. This is the most cost-effective method for Div 2. Standard industrial instruments with sealed contacts often qualify.

Hermetically sealed: Components are sealed so that no flammable gas can reach potential ignition sources. Common in relays and switches used in Div 2 areas.

Restricted breathing: The enclosure limits gas exchange to a rate that prevents ignitable concentrations from forming inside. Used for terminal boxes and small enclosures in Div 2 zones.

Understanding these protection methods helps when selecting instruments. For instance, when choosing a pressure transducer wiring configuration, you need to verify whether the wiring method is rated for your specific division.

Gas Groups A, B, C, and D

Within Class 1, the NEC further categorizes gases into four groups based on their explosion characteristics. The group determines the minimum enclosure strength and maximum gap dimensions for explosion-proof equipment:

GroupRepresentative GasMESG (mm)MIC RatioCommon Applications
AAcetylene0.250.40Welding shops, chemical synthesis
BHydrogen0.280.45Refineries, battery charging rooms, electrolysis plants
CEthylene0.650.80Petrochemical plants, polyethylene production
DPropane, Methane0.900.80Oil/gas production, LNG facilities, paint booths

MESG is the Maximum Experimental Safe Gap—the largest gap through which flame cannot propagate. MIC is the Minimum Igniting Current ratio. Group A (acetylene) is the most dangerous and requires the most robust enclosures. Group D covers the most common industrial gases and allows the widest range of certified equipment.

When specifying instruments, always match the equipment group rating to the gases present. An instrument rated for Group D is not safe for Group B environments. In mixed-gas facilities, rate everything for the most hazardous group present.

Choosing Instruments for Hazardous Areas

Selecting the right process instrument for a hazardous area involves three decisions:

  1. Identify the classification: Confirm whether your installation point is Class 1 Div 1 or Div 2, and which gas group applies. This information comes from the area classification drawing prepared by the plant’s electrical engineer per NEC Article 500 or API RP 505.
  2. Select the protection method: For Div 1, you need Ex d or Ex ia rated instruments. For Div 2, Ex nA or Ex ib may be sufficient. Match the instrument’s certification to the area classification.
  3. Verify certifications: Check that the instrument carries the appropriate approval mark: UL/cUL for North America, ATEX for Europe, or IECEx for international sites. The marking should state the class, division, and group—for example, “Class I, Div 1, Groups C & D.”

A common mistake in field projects: installing a Div 2 rated instrument in what turns out to be a Div 1 zone after an area reclassification. Always verify the current classification drawing before procurement. For level measurement in hazardous tanks, guided wave radar and pressure-based level transmitters are popular because Ex ia versions are widely available.

Also consider the wiring method. In Div 1 areas, all conduit must be sealed at boundaries, and only explosion-proof fittings are permitted. In Div 2, standard conduit with seal fittings at the boundary is generally acceptable. For details on wiring practices, refer to NEC Articles 501.10 and 501.15.

Explosion-Proof Instruments from Sino-Inst

Sino-Inst manufactures a full range of Ex d and Ex ia rated process instruments for Class 1 Div 1 and Div 2 installations. All products carry the Ex marking and are available with ATEX or IECEx certification on request.

Explosion-Proof Pressure Transmitter

SI-EP489 explosion-proof pressure transmitter with Ex d IIC T6 housing. Designed for oil & gas wellheads, chemical skids and dust-laden hazardous areas where intrinsic safety is mandatory.

Explosion-proof Ultrasonic Level Meter for Class 1 Div 1

Explosion-Proof Ultrasonic Level Meter

Non-contact explosion-proof ultrasonic level sensor for hazardous areas. Two-wire intrinsically safe version simplifies installation on tanks, sumps and open channels in ATEX zones.

Explosion-Proof Rotameter Flow Meter

Variable-area metal-tube rotameter for liquid, gas and steam in low-flow lines. Local dial plus optional remote 4-20mA transmitter — built for small-flow chemical dosing and utility service.

FAQ

Can I use Class 1 Div 1 equipment in a Div 2 area?

Yes. Equipment rated for Div 1 exceeds the requirements for Div 2 and is always acceptable in Div 2 locations. The reverse is not true—Div 2 equipment cannot be installed in Div 1 areas.

What is the difference between Division and Zone classification?

The Division system (Div 1/Div 2) is the traditional North American method per NEC Article 500. The Zone system (Zone 0/1/2) follows IEC 60079-10-1 and is used internationally and accepted in North America under NEC Article 505. Zone 0 has no direct Division equivalent—it covers areas where ignitable gas is present continuously, while Div 1 groups Zone 0 and Zone 1 together.

Who determines the area classification for a plant?

The facility owner’s electrical engineer or a qualified third-party consultant creates the area classification drawing. Standards like API RP 500 (Division method) or API RP 505 (Zone method) provide guidance on how far each classification zone extends from the source of release.

Does Class 1 Div 2 require conduit sealing?

Yes, but less extensively than Div 1. Per NEC 501.15, seals are required at boundaries between Div 2 and unclassified areas when the conduit enters an enclosure containing ignition-capable equipment. In Div 1, seals are required at every entry to an explosion-proof enclosure.

What certifications should I look for on hazardous area instruments?

In North America, look for UL or cUL listing per UL 1203 (explosion-proof) or UL 913 (intrinsically safe). For international projects, ATEX (EU Directive 2014/34/EU) and IECEx scheme certificates are the standard. The marking plate on the instrument should clearly state the class, division, group, and temperature code. For guidance on selecting the right pressure sensor for your application, check the hazardous area rating on the datasheet before ordering.

What does the temperature code (T-code) mean?

The T-code indicates the maximum surface temperature of the equipment. It must be lower than the autoignition temperature of the gas present. For example, T6 means the surface will not exceed 85°C, which is safe for most common gases. T1 (450°C) is the least restrictive. Always check the autoignition temperature of your specific gas against the equipment T-code.

Need help selecting explosion-proof instruments for your hazardous area project? Our engineering team can review your area classification drawing and recommend the right protection level—whether Div 1 or Div 2. We supply pressure transmitters, flow meters, level transmitters, and temperature sensors with Ex d and Ex ia certifications. Contact us for a technical consultation or quotation.

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How to Calibrate a Flow Meter: 5 Methods & Step-by-Step Guide

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Updated: April 10, 2026

Flow meter calibration is the process of comparing a meter’s output against a traceable reference standard and adjusting it to minimize measurement error. Every flow meter drifts over time due to wear, fouling, or process changes. Without regular calibration, a 1% error on a custody transfer meter handling 10,000 barrels per day means roughly 100 barrels of unaccounted product. This guide covers the main calibration methods, step-by-step procedures, recommended intervals, and field calibration techniques that work without removing the meter from the line.

Contents

What Is Flow Meter Calibration?

Flow meter calibration means running a known quantity of fluid through the meter and comparing its reading to the actual value. The “known quantity” comes from a reference standard—a gravimetric system, volumetric prover, or master meter—that is traceable to national standards (NIST in the US, PTB in Germany, NIM in China).

The output of calibration is a set of correction factors or K-factors at multiple flow points. These factors tell you exactly how much the meter deviates from true flow at each point across its range. For meters with electronic transmitters, the correction is often programmed directly into the device. For more on K-factors and how they work, see our guide on flow meter K-factor calculation.

Why Calibrate a Flow Meter?

There are four practical reasons to keep flow meters calibrated:

  • Custody transfer accuracy. When fluid changes ownership—oil pipelines, natural gas sales, water billing—the meter reading directly translates to money. API and AGA standards require regular proving.
  • Process control reliability. Batch dosing, chemical blending, and boiler feedwater control all depend on accurate flow readings. A drifted meter throws off the entire control loop.
  • Regulatory compliance. EPA discharge permits, pharmaceutical GMP requirements, and food safety regulations mandate traceable flow measurement with documented calibration records.
  • Troubleshooting baseline. A recent calibration certificate gives you a known reference point. When process issues arise, you can rule out the flow meter as the source of error.

The cost of calibration is small compared to the cost of measurement error. A 2% error on a custody transfer meter processing $1 million in product per month means $20,000 in potential loss or overcharge.

5 Flow Meter Calibration Methods

1. Gravimetric (Weighing) Method

Fluid flows through the meter into a weigh tank on a precision scale. After a timed collection, you divide the collected mass by fluid density to get volume, then compare against the meter reading. This is the primary standard method and achieves uncertainty as low as ±0.02%. National metrology labs use this as their reference.

Limitation: requires stopping and draining the tank between runs. Not practical for large flow rates above about 500 m³/h.

2. Volumetric (Standing Start-Stop) Method

Similar to the gravimetric method, but uses a calibrated collection vessel instead of a scale. Fluid is diverted into the vessel using a fast-acting valve. You read the volume from a calibrated sight glass or level gauge. Achievable uncertainty: ±0.1–0.2%.

This is the most common lab method for water flow meters. Simple to set up but limited to flow rates where the collection time is practical (typically 30 seconds to 5 minutes per run).

3. Pipe Prover (Displacement) Method

A precision sphere or piston travels through a calibrated section of pipe. As the displacer sweeps a known volume between two detector switches, the meter pulses are counted. The ratio of counted pulses to known volume gives the meter factor. Provers achieve ±0.02–0.05% uncertainty.

This is the standard method for custody transfer meters in oil and gas per API MPMS Chapter 4. Bidirectional provers (ball travels both ways) average out timing errors. Compact provers use a piston in a smaller package. Understanding the relationship between flow rate and pressure helps when sizing prover systems.

4. Master Meter Comparison

A pre-calibrated reference meter (master meter) is installed in series with the meter under test. Both meters see the same flow. The master meter reading serves as the reference. Typical uncertainty: ±0.25–0.5%, depending on the master meter’s own calibration.

This method is quick and works well for field verification. The master meter must be the same technology or better than the test meter, and its calibration must be current and traceable.

5. Sonic Nozzle (Critical Flow) Method

Used for gas flow meter calibration. When the pressure ratio across a converging nozzle reaches a critical value (about 0.528 for air), the gas velocity at the throat reaches sonic speed. At this condition, mass flow depends only on upstream pressure and temperature—downstream conditions do not matter. This gives a stable, repeatable reference flow. Uncertainty: ±0.2–0.5%.

Sonic nozzle arrays can be combined in parallel to cover wide flow ranges. This is the standard method in gas meter calibration labs per ISO 9300.

MethodMediumUncertaintyBest For
GravimetricLiquid±0.02%Primary standard, lab calibration
VolumetricLiquid±0.1–0.2%Water meter calibration labs
Pipe ProverLiquid±0.02–0.05%Custody transfer (oil & gas)
Master MeterLiquid/Gas±0.25–0.5%Field verification, quick checks
Sonic NozzleGas±0.2–0.5%Gas meter calibration labs

Step-by-Step Calibration Procedure

This general procedure applies to most flow meter types in a lab or shop setting. Adjust specifics for your meter technology and reference standard.

  1. Prepare the test fluid. Use clean, degassed water (for liquid meters) or dry, filtered air/nitrogen (for gas meters). Record the fluid temperature and pressure—you will need these for density correction.
  2. Install the meter. Follow the manufacturer’s recommended upstream/downstream straight pipe lengths. For most meters, this means 10D upstream and 5D downstream minimum. See our straight pipe requirements guide for details.
  3. Stabilize flow. Run the system at the target flow rate for at least 2–5 minutes before collecting data. Wait until the meter reading is stable and any air pockets have cleared.
  4. Collect data at multiple points. Test at minimum 5 flow rates across the meter’s range: typically 10%, 25%, 50%, 75%, and 100% of maximum flow. At each point, take at least 3 repeat measurements.
  5. Calculate error. At each flow point: Error (%) = [(Meter Reading − Reference Value) / Reference Value] × 100. Record all values.
  6. Adjust if needed. If errors exceed the meter’s specified accuracy, adjust the K-factor, zero, span, or linearization table per the manufacturer’s procedure.
  7. Repeat verification. After adjustment, re-run the calibration at all test points to confirm the meter now reads within specification.
  8. Document results. Issue a calibration certificate showing: meter serial number, test date, reference standard used (with its own calibration traceability), test conditions, as-found and as-left errors at each point.

Calibration Intervals by Application

There is no universal calibration interval. The right schedule depends on the application, fluid conditions, and how much measurement drift your process can tolerate:

ApplicationTypical IntervalDriving Standard
Custody transfer (oil & gas)Monthly proving, annual lab calAPI MPMS Ch. 4, 5, 12
Natural gas fiscal meteringEvery 6–12 monthsAGA Report No. 3, 7, 9
Water utility billingEvery 1–2 yearsAWWA C700 series
Pharmaceutical processEvery 6–12 monthsFDA 21 CFR Part 211
General process controlAnnuallyISO 9001 / plant SOP
HVAC energy meteringEvery 2–3 yearsASHRAE, local codes

Start with the manufacturer’s recommendation, then adjust based on your own drift history. If a meter consistently passes calibration with minimal error, you can extend the interval. If it frequently drifts out of spec, shorten it or investigate root causes like fouling or pipe vibration.

Field Calibration Without Removing the Meter

Removing a flow meter from the line for lab calibration costs downtime and labor. These field methods let you verify or adjust a meter in place:

Clamp-On Ultrasonic Comparison

A portable clamp-on ultrasonic flow meter is temporarily mounted on the pipe next to the installed meter. Both meters read the same flow simultaneously. The clamp-on meter serves as a transfer reference. This method works best when the clamp-on meter has been recently lab-calibrated and the pipe conditions (wall thickness, lining) are well characterized. Achievable field uncertainty: ±1–2%.

Tank Volume Comparison

Run the flow meter and measure the resulting level change in a tank of known dimensions. Multiply the level change by the tank cross-section area to get volume. Compare this to the meter’s totalized reading. Water utilities frequently use clear water reservoir volumes for this check. Uncertainty depends on level measurement accuracy—typically ±1–3%.

In-Line Prover

For custody transfer applications, a permanently installed prover loop allows proving without removing the meter. The prover sphere or piston sweeps a known volume while the meter counts pulses. This is the gold standard for field calibration in oil and gas. For more on flow meter installation requirements that affect accuracy, see our straight length requirements guide.

Calibration vs. Verification

These two terms are often confused. They are different processes with different outcomes:

AspectCalibrationVerification
PurposeDetermine and correct measurement errorConfirm the meter still meets its specification
OutputCalibration certificate with as-found/as-left dataPass/fail statement
AdjustmentYes—meter is adjusted if neededNo—meter is tested only, not adjusted
TraceabilityRequired (NIST, PTB, NIM, etc.)Recommended but not always required
When to useInitial commissioning, after repair, scheduled intervalsPeriodic checks between full calibrations

In practice, many organizations run a verification at 6-month intervals and a full calibration annually. If the verification shows the meter has drifted beyond a warning threshold (e.g., 50% of the allowable error), they pull it for early calibration.

Flow Meters from Sino-Inst

Sino-Inst supplies flow meters with factory calibration certificates traceable to national standards. Each meter ships with a multi-point calibration report covering 5+ flow rates across the operating range.

Magnetic Flow Meter

Electromagnetic (EMF) flow meter for conductive liquids — water, slurry, chemicals, effluent. No moving parts, zero pressure drop, DN3-DN3000 range; the gold standard for wastewater.

Turbine Flow Meter

Turbine-type volumetric flow meter for clean liquids and gases. Proven pulse-output technology used across LPG, hydrocarbons, water and compressed-air billing applications.

Ultrasonic Flow Meter

Transit-time and Doppler ultrasonic flow meters for clean liquids and dirty slurries. Clamp-on, insertion and in-line versions — pick by fluid type, pipe size and accuracy target.

FAQ

How often should a flow meter be calibrated?

It depends on the application. Custody transfer meters in oil and gas are typically proved monthly and lab-calibrated annually. Process control meters are calibrated once a year. Water utility meters every 1–2 years. Start with the manufacturer’s recommendation and adjust based on your drift history.

Can I calibrate a flow meter in the field?

Yes, using three main methods: clamp-on ultrasonic comparison (±1–2%), tank volume comparison (±1–3%), or an in-line prover (±0.02–0.05%). Field calibration is a verification, not a full primary calibration, but it is adequate for most process control applications.

What is the most accurate calibration method?

The gravimetric (weighing) method is the primary standard with uncertainty as low as ±0.02%. Pipe provers are close at ±0.02–0.05% and are the practical standard for custody transfer applications. Both require traceable reference equipment.

Does a magnetic flow meter need calibration?

Yes. Although mag meters have no moving parts and are considered low-maintenance, the electrode surfaces can foul, and the liner can degrade over time. Factory calibration is done on a gravimetric or volumetric test bench. Field verification can be done using the meter’s built-in diagnostic tools (coil test, empty pipe detection) or with a clamp-on reference meter.

What standards govern flow meter calibration?

Key standards include: ISO 4185 (gravimetric method for liquids), ISO 8316 (volumetric method), ISO 9300 (sonic nozzle for gas), API MPMS Chapter 4 (proving), and ASME MFC series. Your local metrology authority may have additional requirements. For flow meters using GPM units, the calibration report should include both GPM and metric equivalents.

What is a calibration certificate?

A calibration certificate is a formal document that records the results of a calibration. It includes the meter identification, test date, reference standard used (with traceability statement), test conditions (fluid, temperature, pressure), and the as-found and as-left readings at each test point. A valid certificate must be issued by an accredited lab or by a lab with demonstrated traceability to national standards.

Need a flow meter with a traceable calibration certificate? Sino-Inst provides factory calibration on all flow meters, with multi-point test data included. We also offer custom calibration at specific flow points matching your process conditions. Contact our engineering team for a quotation or technical consultation.

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What Is a Pressure Sensor? Types, Principles & Selection Guide

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Updated: April 10, 2026

A pressure sensor converts mechanical pressure into an electrical signal. It is the sensing element inside every pressure transmitter, transducer, and switch used in industrial process control. The electrical output—typically a change in resistance, capacitance, or voltage—is proportional to the applied pressure. Pressure sensors measure gauge, absolute, differential, or vacuum pressure depending on the reference. This guide covers the main sensing technologies, how each works, key specifications, and how to select the right type for your application.

Contents

What Is a Pressure Sensor?

A pressure sensor is a device that detects pressure applied to its sensing element and outputs a corresponding electrical signal. The sensing element is usually a thin diaphragm—made of silicon, stainless steel, or ceramic—that deflects when pressure acts on it. That deflection changes a physical property (resistance, capacitance, charge, or frequency) which is measured by the sensor’s internal circuitry.

Pressure sensors are the core component in pressure transmitters and transducers. Without the sensor, there is no measurement. The transmitter adds signal conditioning, temperature compensation, and a standardized output (4-20mA, 0-10V, or digital protocol) on top of the raw sensor signal.

Typical accuracy ranges from ±0.5% to ±0.04% of full scale depending on the technology and price point. Operating temperatures range from -40°C to +125°C for standard silicon sensors, with special designs reaching 300°C or higher for high-temperature applications.

4 Types of Pressure Measurement

The “type” of pressure a sensor measures depends on what reference it uses:

TypeReferenceTypical Application
Gauge pressureLocal atmospheric pressureProcess piping, tank pressure, pump discharge
Absolute pressurePerfect vacuum (0 Pa)Barometric, altitude, vacuum systems
Differential pressureAnother pressure inputFilter monitoring, flow measurement, level in pressurized tanks
Vacuum / compoundAtmospheric (negative range)Vacuum pumps, HVAC, packaging machines

Gauge pressure is the most common in industrial applications. When an engineer says “the line pressure is 10 bar,” they almost always mean gauge pressure—10 bar above atmospheric. For more on how static and dynamic pressures interact, see our guide on static pressure vs dynamic pressure.

5 Pressure Sensing Technologies

1. Piezoresistive (Diffused Silicon)

Four resistors are diffused directly into a silicon diaphragm and connected in a Wheatstone bridge. When pressure deflects the diaphragm, the resistors change value due to the piezoresistive effect, producing a millivolt output proportional to pressure. This is the most widely used technology in industrial pressure sensors.

Advantages: low cost, high volume production (MEMS), good linearity, fast response. Limitations: temperature sensitivity requires active compensation; not suitable for highly corrosive media without isolation diaphragm. Standard accuracy: ±0.25–0.5% FS.

2. Capacitive

A metal or ceramic diaphragm forms one plate of a capacitor. A fixed plate sits behind it. Pressure deflects the diaphragm, changing the gap and therefore the capacitance. The electronics measure this capacitance change with high resolution.

Advantages: excellent long-term stability, low power consumption, high overpressure tolerance (up to 100x rated pressure), very low temperature drift. This is the technology used in premium transmitters like the Rosemount 3051 and Yokogawa EJA series. Standard accuracy: ±0.04–0.1% FS.

3. Strain Gauge (Bonded Foil)

Metal foil strain gauges are bonded to a metal diaphragm or beam. Pressure deflects the structure, straining the gauges and changing their resistance. The resistance change is measured with a Wheatstone bridge. This technology works well for high-pressure applications (up to 10,000 bar) because thick metal diaphragms can handle extreme pressures.

Advantages: wide pressure range, robust construction, works at high temperatures. Limitations: lower sensitivity than piezoresistive, requires careful bonding. Standard accuracy: ±0.1–0.25% FS. For details on how pressure transmitters use these sensors, see our guide on how pressure transmitters work.

4. Piezoelectric

Piezoelectric crystals (quartz, PZT) generate an electric charge when mechanically stressed. The charge is proportional to the applied pressure. Unlike the other technologies, piezoelectric sensors only measure dynamic (changing) pressure—they cannot hold a static reading because the charge leaks away.

Advantages: extremely fast response (microseconds), wide frequency bandwidth, no external power needed for the sensing element. Applications: engine combustion analysis, blast pressure measurement, acoustic sensors. Not used for steady-state process control.

5. Resonant (Vibrating Element)

A vibrating wire, beam, or cylinder changes its resonant frequency when stressed by pressure. The frequency shift is measured digitally with very high resolution. This technology offers the best long-term stability and accuracy of any pressure sensing method.

Advantages: frequency output is inherently digital and noise-immune, excellent stability (±0.01% per year), high accuracy (±0.01–0.04% FS). Limitations: expensive, slower response than piezoresistive. Used in fiscal metering, meteorological stations, and calibration reference instruments.

TechnologyAccuracyBest ForLimitation
Piezoresistive±0.25–0.5%General industrial, OEM, HVACTemperature drift
Capacitive±0.04–0.1%Process control, custody transferHigher cost
Strain gauge±0.1–0.25%High pressure, hydraulic systemsLower sensitivity
Piezoelectric±1%Dynamic pressure, combustionNo static measurement
Resonant±0.01–0.04%Fiscal metering, calibrationExpensive, slow response

Sensor vs. Transducer vs. Transmitter

These three terms are often used interchangeably, but they describe different levels of signal processing:

TermWhat It DoesOutput SignalTypical Use
Pressure sensorConverts pressure to a raw electrical changemV (millivolts), pC (picocoulombs)OEM integration, PCB-level
Pressure transducerSensor + basic signal conditioning0–5V, 0–10V, mV/VTest & measurement, lab instruments
Pressure transmitterSensor + full conditioning + standardized output4-20mA, HART, Profibus, ModbusIndustrial process control, DCS/PLC

In practice: a pressure sensor is the raw MEMS chip. A transducer packages it with amplification and outputs a voltage. A transmitter adds temperature compensation, linearization, and a 4-20mA or digital output that can travel hundreds of meters to a control room. When specifying equipment for industrial applications, you almost always want a transmitter. For wiring details, see our pressure transducer wiring guide.

Key Specifications to Consider

When selecting a pressure sensor, these are the specifications that matter most:

  • Pressure range: Select a range where your normal operating pressure falls at 60–75% of the sensor’s full scale. This gives headroom for pressure spikes without sacrificing resolution.
  • Accuracy: Expressed as % of full scale (FS) or % of reading. A ±0.1% FS sensor on a 0–100 bar range has ±0.1 bar error at any point. For custody transfer, look for ±0.04–0.075% FS.
  • Temperature range: Both operating temperature (media touching the sensor) and ambient temperature (electronics). Silicon sensors typically handle -40 to +85°C. High-temperature versions with oil-filled capillary or cooling fins reach 300°C+.
  • Output signal: 4-20mA is the industrial standard for analog. HART adds digital communication over the same wires. For digital-only, Profibus PA and Foundation Fieldbus are common.
  • Media compatibility: The wetted parts (diaphragm, O-ring, process connection) must be compatible with the process fluid. 316L stainless steel handles most applications. Hastelloy, Monel, or tantalum for aggressive chemicals.
  • Process connection: 1/4″ or 1/2″ NPT, G1/2, M20x1.5, or flange-mounted. Match the connection to your existing pipe fittings.
  • Overpressure rating: The maximum pressure the sensor can withstand without permanent damage. Capacitive sensors typically tolerate 100x overpressure; piezoresistive typically 2–3x.

Common Industrial Applications

Pressure sensors are used across every process industry. Here are the most common application categories:

  • Process control: Monitoring and controlling pressure in reactors, distillation columns, heat exchangers, and pipeline systems. The 4-20mA signal feeds directly into a DCS or PLC for closed-loop control.
  • Flow measurement: Differential pressure sensors across an orifice plate, venturi, or flow nozzle measure flow rate. This is still the most common industrial flow measurement method. For GPM-based flow measurement, see our guide on flow meters with GPM units.
  • Level measurement: A pressure sensor at the bottom of a tank measures hydrostatic head, which is proportional to liquid level. Works for open and pressurized tanks (using a differential pressure sensor for the latter).
  • Hydraulic and pneumatic systems: Monitoring pump discharge, accumulator charge, cylinder force, and system pressure in mobile equipment, presses, and injection molding machines.
  • HVAC and building automation: Duct static pressure, chilled water system pressure, filter differential pressure, and refrigerant pressure in chillers.
  • Safety systems: Pressure relief monitoring, burst disc detection, and SIL-rated pressure switches for emergency shutdown systems per IEC 61511.

Pressure Sensors from Sino-Inst

Sino-Inst manufactures over 20 types of pressure sensors and transmitters covering gauge, absolute, differential, and high-pressure applications. All units ship with factory calibration certificates.

Gauge Pressure Sensor

Water pressure sensors for tank, pipe and groundwater measurement. 4-20mA / RS485 output with IP68 sealed housing for drinking water, firefighting and irrigation systems.

Differential Pressure Sensor

Budget-friendly DP sensor for HVAC, filter status and airflow monitoring. Compact diaphragm design keeps unit price low without giving up 0.5% accuracy or 4-20mA output.

Pressure Transmitter (4-20mA)

HH3151 HART smart pressure transmitter with remote zero/span, digital diagnostics and 0.075% accuracy. Drop-in upgrade for plants running HART multiplexers or asset-management systems.

FAQ

What is the difference between a pressure sensor and a pressure transmitter?

A pressure sensor is the raw sensing element that converts pressure into a small electrical change (millivolts). A pressure transmitter packages the sensor with signal conditioning, temperature compensation, and a standardized industrial output (4-20mA, HART, Modbus). For process control, you need a transmitter.

How long does a pressure sensor last?

In normal industrial service, a quality pressure sensor lasts 10–20 years. Silicon MEMS sensors have no moving parts and minimal wear. The main failure modes are diaphragm corrosion (wrong material selection), overpressure damage, and electronics degradation from temperature cycling. Regular calibration checks catch drift before it becomes a problem.

Which pressure sensor technology is most accurate?

Resonant (vibrating element) sensors achieve the best accuracy at ±0.01–0.04% FS, but they are expensive. Capacitive sensors offer ±0.04–0.1% FS at a more reasonable price and are the standard choice for high-accuracy process applications. For general industrial use, piezoresistive sensors at ±0.25–0.5% FS provide the best cost-performance ratio.

Can a pressure sensor measure vacuum?

Yes. Absolute pressure sensors measure from 0 Pa (vacuum) upward. Compound pressure sensors (also called vacuum/pressure sensors) measure both positive and negative gauge pressure in a single range, for example -1 to +10 bar. For deep vacuum applications below 1 mbar, specialized capacitance manometers or Pirani gauges are used.

How do I choose the right pressure range?

Select a sensor where your normal operating pressure is 60–75% of the rated full scale. This gives enough headroom for pressure spikes without sacrificing measurement resolution. For example, if your process runs at 8 bar with occasional surges to 12 bar, a 0–16 bar sensor is a good fit. Never operate a sensor continuously above 90% of its rated range.

What is the temperature effect on pressure sensor accuracy?

Temperature changes affect both the zero point and the span of a pressure sensor. This effect is specified as a temperature coefficient, typically in %FS per 10°C. A good industrial transmitter has a total temperature effect of less than ±0.15% FS over a 10–50°C range after compensation. If your process temperature varies widely, look for a sensor with active digital temperature compensation or use a remote diaphragm seal to keep the electronics at stable ambient temperature.

Looking for a pressure sensor or transmitter for your application? Sino-Inst offers gauge, absolute, differential, and high-pressure models with customizable ranges and outputs. Our engineers can help you select the right technology, material, and connection for your specific process conditions. Contact us for a technical consultation or quotation.

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Pressure Transducer Wiring Diagram: 2-Wire, 3-Wire & 4-Wire Guide

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Updated April 2026 — By Sino-Inst Engineering Team

Wiring a pressure transducer correctly is the difference between a clean 4–20 mA signal and hours of troubleshooting. The three wiring configurations — 2-wire, 3-wire, and 4-wire — each have different power supply requirements, signal routing, and use cases.

This guide provides wiring diagrams for all three types, explains the electrical differences, and covers the most common wiring mistakes.

Contents

2-Wire vs 3-Wire vs 4-Wire: Quick Comparison

Feature2-Wire3-Wire4-Wire
Cables required234
Power & signalShare same 2 wiresShared ground, separate signalFully separate
Common output4–20 mA0–10 V or 4–20 mA4–20 mA, 0–10 V, 0–5 V
Power supply12–36 VDC (loop)12–36 VDC12–36 VDC or 220 VAC
Max cable length1–2 km500 m500 m (voltage) / 1–2 km (current)
CostLowestMediumHighest
Best forProcess control, long runsTest/lab, moderate distanceHigh-accuracy, multi-function

2-Wire Pressure Transducer Wiring Diagram

A 2-wire transmitter is loop-powered. The power supply and the 4–20 mA signal share the same two wires. At zero pressure, the transmitter draws 4 mA. At full scale, it draws 20 mA. The PLC analog input reads this current to determine the pressure.

Wiring steps:

  1. Connect the positive (+) terminal of the 24 VDC power supply to the positive (+) terminal of the transmitter.
  2. Connect the negative (−) terminal of the transmitter to the positive (+) input of the PLC analog module (or across a 250 Ω resistor for voltage conversion).
  3. Connect the negative (−) terminal of the PLC analog module back to the negative (−) terminal of the 24 VDC power supply.

The 2-wire configuration is the industry standard for process control. It uses less cable, is immune to lead resistance errors (current signals are not affected by wire length), and supports HART communication on the same two wires. Over 80% of industrial pressure transmitters use 2-wire 4–20 mA connections.

3-Wire Pressure Transducer Wiring Diagram

A 3-wire transmitter has a dedicated power positive wire, a signal output wire, and a shared ground (common) wire. The power supply and signal output share the negative/ground connection.

Wiring steps:

  1. Connect V+ (power positive) to the positive terminal of the 24 VDC power supply.
  2. Connect Signal Out to the positive input of your PLC analog module or display instrument.
  3. Connect GND (common) to both the negative terminal of the power supply and the negative terminal of the PLC input.

The 3-wire configuration is common in voltage-output transmitters (0–5 V, 0–10 V). The separate signal wire avoids the voltage drop issue that affects 2-wire voltage transmitters over long cable runs. However, for distances over 500 m, a 4–20 mA current output is still preferred.

4-Wire Pressure Transducer Wiring Diagram

A 4-wire transmitter has completely separate power and signal circuits — two wires for power, two wires for signal. This isolation between power and measurement eliminates ground loops and allows both current and voltage output options.

Wiring steps:

  1. Connect Power + to the positive terminal of the power supply (24 VDC or 220 VAC depending on model).
  2. Connect Power − to the negative terminal of the power supply.
  3. Connect Signal + (current or voltage output) to the positive input of the PLC analog module.
  4. Connect Signal − to the negative input of the PLC analog module.

The 4-wire configuration is used in high-performance transmitters that need more power than a 2-wire loop can provide (the 4 mA minimum in a 2-wire system limits the available power to roughly 36 mW at 24 V). Transmitters with LCD displays, HART modems, or multiple outputs often require 4-wire power. Some 4-wire models accept 220 VAC directly.

Common Wiring Mistakes

Reversed polarity. Connecting + and − backwards. Most modern transmitters have reverse polarity protection, but some older models can be damaged. Always check terminal markings before applying power.

Wrong supply voltage. Applying 220 VAC to a 24 VDC transmitter destroys it instantly. Confirm the rated voltage on the nameplate.

Load resistance too high. A 2-wire 4–20 mA transmitter needs enough voltage to drive the current through the total loop resistance. If your PLC input impedance plus cable resistance exceeds the transmitter’s maximum load, the signal clips at the top end. Check the specification: most 24 VDC transmitters support up to 500–750 Ω total loop resistance.

Ground loops. Connecting the signal ground to the power ground at multiple points creates a ground loop. This adds 50/60 Hz noise to the signal. Use a single grounding point, or use a 2-wire 4–20 mA transmitter (current loops are inherently immune to ground loops).

Mixing up TEST and OUT terminals. Some transmitters have both OUT (operating output) and TEST (factory calibration) terminals. Only connect to the OUT terminals for normal operation.

Featured Pressure Transmitters from Sino-Inst

2-Wire 4–20 mA Transmitter

HH3151 HART smart pressure transmitter with remote zero/span, digital diagnostics and 0.075% accuracy. Drop-in upgrade for plants running HART multiplexers or asset-management systems.

4-Wire DP Transmitter

DP transmitters measure pressure difference across gas, liquid or steam. 4-20mA / 0-5V output drives liquid level, density and flow loops across process plants.

Explosion-Proof Transmitter

SI-EP489 explosion-proof pressure transmitter with Ex d IIC T6 housing. Designed for oil & gas wellheads, chemical skids and dust-laden hazardous areas where intrinsic safety is mandatory.

Browse all pressure transmitters | How pressure transmitters work | Calibration guide

Pressure Transducer Wiring FAQ

What happens if I wire a 2-wire transmitter with wrong polarity?

Reverse polarity on a 2-wire transmitter blocks current flow completely. The loop reads 0 mA, and the PLC/DCS shows an under-range fault. Most modern transmitters have built-in reverse-polarity protection — the device won’t be damaged, but it won’t output a signal until you swap the wires. Always check with a multimeter before powering on.

Can I use a 4-wire transmitter in a 2-wire loop?

No. A 4-wire transmitter needs a separate power supply and has dedicated signal output terminals. You cannot wire it into a standard 2-wire 4–20 mA loop. If your system only supports 2-wire loops, you need a 2-wire transmitter or a signal isolator to convert the 4-wire output.

How long can I run 4–20 mA signal cable?

With standard 18 AWG twisted-pair cable, a 4–20 mA loop typically runs up to 1,500 meters (about 5,000 feet). The limiting factor is total loop resistance — keep it under what the transmitter can drive. For a 24 VDC supply with a 250 Ω sense resistor, a typical transmitter handles around 600 Ω total loop resistance. Longer runs need thicker cable or a higher supply voltage.

Why does my pressure reading drift after wiring?

Common causes: loose terminal connections causing intermittent contact, incorrect grounding creating ground loops, or EMI pickup from running signal wires alongside power cables. Check all connections are tight, verify single-point grounding, and use shielded cable with the shield grounded at one end only.

Do I need shielded cable for pressure transducer wiring?

For 4–20 mA loops in industrial environments — yes. Shielded twisted-pair cable reduces electromagnetic interference from VFDs, motors, and switchgear. Ground the shield at the control room end only. For short runs in electrically quiet environments, unshielded cable works, but shielded is always the safer choice.

What is the minimum supply voltage for a 2-wire transmitter?

Most 2-wire transmitters need 12–36 VDC, but check the specific model’s datasheet. The actual minimum depends on total loop resistance. A rough formula: V_min = 12V + (0.02A × R_loop). With a 250 Ω load resistor and 50 Ω cable resistance, you need at least 18 VDC. A 24 VDC supply handles most installations.

Written by the Sino-Inst Engineering Team — with over 20 years of experience in industrial pressure measurement, installation, and commissioning across oil & gas, water treatment, HVAC, and chemical processing plants worldwide.

Request a Quote or Technical Support

Need help selecting the right pressure transducer for your wiring configuration? Our engineers can recommend the best signal output type — 2-wire, 3-wire, or 4-wire — based on your system requirements.

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Flow Rate and Pressure: How They Relate and How to Calculate

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Updated April 2026 — By Sino-Inst Engineering Team

Flow rate and pressure are the two most measured variables in any piping system. They are connected, but not in a simple linear way. Pressure difference drives flow. No pressure difference, no flow — even if the pipe is full and pressurized.

Contents

This article covers the actual physics behind the relationship, gives you the working formulas, and shows how to calculate one from the other in real piping systems.

How Flow Rate and Pressure Are Related

A common misconception: high pressure means high flow. Not true. A pipe can sit at 150 psi with zero flow if both ends are at equal pressure. Flow happens only when there is a pressure difference (ΔP) between two points.

Once a piping system is fixed (pipe diameter, length, roughness, fittings), flow rate is proportional to the square root of the pressure difference:

Q ∝ √ΔP

Double the pressure difference and flow increases by about 41%, not 100%. This square-root relationship appears everywhere — in Venturi tubes, orifice plates, and control valve sizing equations.

Key Formulas

Bernoulli’s Equation

For an ideal (inviscid, incompressible) fluid flowing along a streamline:

P₁ + ½ρv₁² + ρgh₁ = P₂ + ½ρv₂² + ρgh₂

Where P is static pressure (Pa), ρ is fluid density (kg/m³), v is velocity (m/s), g is gravity (9.81 m/s²), and h is elevation (m). This equation tells you: when velocity goes up, pressure goes down. That is the principle behind every differential pressure flow meter.

Bernoulli applies to clean, low-viscosity fluids at moderate speeds. For real-world pipe systems, you need to account for friction losses.

Darcy-Weisbach Equation (Pressure Drop in Pipes)

The standard formula for friction-based pressure drop in a straight pipe:

ΔP = f × (L/D) × (ρv²/2)

Where f is the Darcy friction factor (dimensionless), L is pipe length (m), D is internal diameter (m), ρ is density (kg/m³), and v is flow velocity (m/s). The friction factor depends on Reynolds number and pipe roughness — use a Moody chart or the Colebrook equation to find it.

Poiseuille’s Law (Laminar Flow Only)

For laminar flow (Re < 2100) in a circular pipe:

Q = π × d⁴ × ΔP / (128 × μ × L)

Where Q is volumetric flow rate (m³/s), d is pipe diameter (m), ΔP is pressure drop (Pa), μ is dynamic viscosity (Pa·s), and L is pipe length (m). This equation works for heavy oils, glycol, and other viscous fluids moving at low velocity.

DP Flow Meter Formula

For an orifice plate, Venturi, or flow nozzle:

Q = C × ε × A₂ × √(2ΔP / (ρ(1 − β⁴)))

Where C is the discharge coefficient, ε is the expansion factor (for gases), A₂ is the bore area, β is the diameter ratio (bore/pipe), and ΔP is measured differential pressure. This is how every DP flow meter converts a pressure reading into a flow rate.

How to Calculate Flow Rate from Pressure

You cannot calculate flow from a single pressure reading. You need pressure difference between two points, plus information about the system. Here is the practical approach:

  1. Measure ΔP — Install pressure taps at two points along the pipe. The difference is your driving force.
  2. Know your pipe — Internal diameter, length between taps, material (roughness), and any fittings or valves.
  3. Know your fluid — Density and viscosity at operating temperature.
  4. Estimate Reynolds number — Start with an assumed velocity, calculate Re = ρvD/μ. This determines if the flow is laminar or turbulent.
  5. Apply the right formula — Laminar: use Poiseuille. Turbulent: use Darcy-Weisbach with the Moody friction factor. Iterate if needed — start with an estimated f, solve for v, recalculate Re, update f, repeat until values converge.

In practice, most engineers skip the manual calculation. Install a differential pressure flow meter and let the transmitter do the math internally. Modern DP transmitters compute flow rate in real-time from the measured ΔP, programmed pipe data, and fluid properties.

Pressure Drop in Piping Systems

Every pipe, valve, elbow, and fitting consumes energy. That energy loss shows up as pressure drop. Two categories:

Friction loss (major loss) — Caused by fluid viscosity against the pipe wall. Proportional to pipe length and the square of velocity. Longer pipes and faster flow mean more pressure drop.

Minor losses — From elbows, tees, valves, reducers, and flow meters. Each component has a loss coefficient (K-factor). In short runs with many fittings, minor losses can exceed friction losses.

Total pressure drop: ΔP_total = ΔP_friction + Σ(K × ρv²/2)

When selecting a flow meter, check its permanent pressure loss specification. An orifice plate typically causes 40-70% permanent loss of the measured ΔP. A Venturi tube recovers most of the pressure — only 5-20% permanent loss. For applications where pumping energy matters, the Venturi tube or V-Cone meter is a better choice.

Quick Reference: Flow-Pressure Formulas

FormulaUse CaseKey Variables
Q ∝ √ΔPGeneral pipe systemsΔP = pressure difference
Bernoulli (P + ½ρv² + ρgh = const)Ideal flow, DP metersP, v, ρ, h
Darcy-Weisbach (ΔP = f·L/D·ρv²/2)Turbulent pipe frictionf, L, D, ρ, v
Poiseuille (Q = πd⁴ΔP/128μL)Laminar flow (Re < 2100)d, ΔP, μ, L
DP meter (Q = CεA√(2ΔP/ρ(1−β⁴)))Orifice, Venturi, nozzleC, ε, A, ΔP, β, ρ

Featured DP Flow Meters from Sino-Inst

Orifice Plate Flow Meter

Accuracy: ±1% | DN15–DN1200
4-20mA/HART | Steam, gas, liquid

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Venturi Tube Flow Meter

Low pressure loss: 5-20% | DN50–DN2000
High accuracy for large pipes

Request Quote

Integral DP Flow Meter

Built-in ΔP transmitter | Compact
4-20mA/HART | Easy install

Request Quote

Browse all flow meters | Use our flow & pressure calculators

Frequently Asked Questions

Does higher pressure always mean higher flow rate?

No. Flow depends on pressure difference, not absolute pressure. A pipe at 200 bar with equal pressure at both ends has zero flow. Increase the pressure at one end while keeping the other constant, and flow begins.

Why is the flow-pressure relationship a square root, not linear?

Friction losses in turbulent flow are proportional to velocity squared (Darcy-Weisbach equation). Since pressure drop goes as v², flow rate (which is proportional to v) goes as the square root of ΔP. Double the flow requires four times the pressure difference.

How do I measure flow rate using pressure?

Use a differential pressure flow meter — an orifice plate, Venturi tube, or flow nozzle installed in the pipe. A DP transmitter measures the pressure drop across the restriction and calculates flow using the square-root relationship. This is the most widely used industrial flow measurement method per ISO 5167.

What is the difference between pressure drop and pressure loss?

They mean the same thing in practice. Pressure drop is the reduction in pressure as fluid moves through a pipe or component. Some engineers reserve “pressure loss” for permanent, non-recoverable losses (friction, turbulence) and “pressure drop” for the total change including recoverable portions (like in a Venturi).

Can I calculate flow rate from a single pressure gauge reading?

Not directly. You need two pressure readings (upstream and downstream) to get a ΔP, or you need a known flow restriction with calibrated characteristics. A single gauge reading tells you the static pressure at one point — it says nothing about velocity or flow rate.

Which flow meter has the lowest pressure drop?

Among DP meters, the Venturi tube has the lowest permanent pressure loss (5-20% of ΔP). Magnetic flow meters and ultrasonic flow meters cause almost no pressure drop because they have no flow obstruction. Orifice plates have the highest pressure loss (40-70% of ΔP).

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Tell us your application — pipe size, fluid, temperature, pressure, required accuracy. Our engineers will recommend the right flow meter and provide a quote within 24 hours.

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About the Author
Sino-Inst Engineering Team — With over 20 years of experience in industrial process instrumentation, our team specializes in flow, level, pressure, and temperature measurement solutions. We have completed 10,000+ installations across oil & gas, water treatment, chemical, and power generation industries worldwide. Our engineers hold certifications in ISA, IEC, and ISO standards. For technical questions, contact us at rfq@sino-inst.com or call +86-180 4861 3163.

Pressure Transmitter: Working Principle, Types & Selection Guide

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Updated April 2026 — By Sino-Inst Engineering Team

A pressure transmitter converts the mechanical force of fluid or gas pressure into an electrical signal — typically 4–20 mA or a digital protocol like HART. That signal goes to a PLC, DCS, or SCADA system for monitoring, control, and alarms.

Contents

Pressure transmitters are found in nearly every process industry: oil and gas, water treatment, chemical plants, power generation, HVAC, and food processing. They measure gauge pressure, absolute pressure, differential pressure, or vacuum — depending on the application.

This guide explains how they work, the five main sensing technologies, signal output options, and how to select the right one for your application.

How Does a Pressure Transmitter Work?

Every pressure transmitter has three functional blocks:

  1. Sensing element — A diaphragm, piezo crystal, or capacitive cell that physically deforms under pressure.
  2. Signal conditioning — Electronics that convert the raw sensor output (resistance change, charge, or capacitance shift) into a proportional electrical signal.
  3. Output stage — Sends the conditioned signal to the control system via analog (4–20 mA) or digital (HART, Modbus, Profibus) protocol.

The process medium pushes against a diaphragm. The diaphragm deflects — maybe 0.001 mm at full scale. That tiny deflection changes the electrical properties of the sensing element (strain, capacitance, or piezoelectric charge). The transmitter electronics measure the change, compensate for temperature, linearize the output, and produce a calibrated signal.

5 Pressure Sensing Technologies

1. Piezoresistive (Diffused Silicon)

A silicon diaphragm has strain gauges diffused directly into its surface. When pressure deflects the diaphragm, the resistance of these gauges changes — a phenomenon called the piezoresistive effect. A Wheatstone bridge circuit converts this resistance change into a voltage proportional to pressure.

This is the most common sensing technology. It covers ranges from 0–100 Pa to 0–100 MPa. Accuracy is typically ±0.25% to ±0.1% FS. Temperature range: -40 to +125°C. Cost-effective and reliable for general industrial use.

2. Capacitive

Two metal plates sandwich a sensing diaphragm. Pressure deflects the diaphragm, changing the gap between the plates and therefore the capacitance. The electronics measure this capacitance change with high precision.

Capacitive sensors dominate in differential pressure measurement and high-accuracy applications. Accuracy reaches ±0.075% FS in premium models. They handle low pressures (down to 0.1 kPa) better than piezoresistive types. This is the technology used in Rosemount 3051, Yokogawa EJA, and other top-tier DP transmitters.

3. Ceramic (Thick-Film)

A ceramic (Al₂O₃) diaphragm has thick-film resistors printed on its back surface. Pressure bends the ceramic, changing the resistance. The ceramic itself acts as the isolation diaphragm — no fill fluid needed.

Ceramic sensors excel in corrosive media because the sensing element contacts the process directly without an oil-filled cavity. They resist chemical attack from most acids and alkalis. Temperature range: -40 to +135°C. Cost is lower than stainless steel models. Common in water treatment, chemical dosing, and food-grade applications.

4. Piezoelectric

Quartz or tourmaline crystals generate an electric charge when mechanically stressed. The charge is proportional to the applied force. A charge amplifier converts this into a usable voltage signal.

Piezoelectric sensors respond extremely fast — microsecond rise times. They measure dynamic pressure events: combustion chamber pulsations, hydraulic hammer, blast waves. They cannot measure static pressure because the charge leaks away over time. Not used for steady-state process monitoring.

5. MEMS (Micro-Electro-Mechanical Systems)

MEMS pressure sensors use semiconductor fabrication techniques to build the diaphragm and sensing elements on a silicon chip. The result is an extremely small, low-power sensor with good accuracy.

MEMS technology has driven down the cost and size of pressure transmitters. Most consumer and automotive pressure sensors are MEMS-based. In industrial applications, MEMS sensors appear in compact transmitters, portable calibrators, and IoT-enabled wireless pressure monitors.

Types of Pressure Transmitters

Pressure transmitters are classified by what pressure reference they use:

TypeMeasuresReferenceTypical Use
Gauge PressurePressure above/below atmosphereAtmospheric (vented)Pipe pressure, tank pressure, pump discharge
Absolute PressurePressure above perfect vacuumSealed vacuumBarometric, vacuum systems, altitude
Differential PressureDifference between two pressuresSecond pressure portFlow measurement, filter monitoring, level
Vacuum/CompoundPressure below atmosphere or both sidesAtmosphericVacuum pumps, HVAC, process vacuum
Hydrostatic (Submersible)Liquid column pressure = levelAtmospheric (vented cable)Tank level, well depth, open channel

Differential pressure transmitters are the most versatile. With an orifice plate or Venturi, a DP transmitter measures flow. Connected to the top and bottom of a tank, it measures level. Across a filter, it monitors clogging. One instrument, three measurements — that is why DP transmitters account for roughly 40% of all pressure transmitter sales worldwide.

Signal Output Options

OutputSignal RangeMax DistanceBest For
4–20 mA (analog)4 mA = zero, 20 mA = full scale1–2 kmUniversal, noise-immune, long runs
0–10 V (voltage)0 V = zero, 10 V = full scale<15 mShort cable runs, lab/test
HART (hybrid)4–20 mA + digital overlay1–2 kmDiagnostics + analog backup
Modbus RS485Digital, multi-drop1.2 kmMultiple transmitters on one cable
Millivolt (mV)0–100 mV typical<3 mOEM integration, low cost

For most industrial installations, 4–20 mA with HART is the standard. The analog signal is immune to electrical noise and works with every PLC on the market. HART adds digital diagnostics — you can read sensor temperature, configure range, and check health without disconnecting wires. For new digital plants, Modbus or Profibus PA eliminates analog entirely.

How to Select a Pressure Transmitter

Start with these six parameters. Get them wrong and nothing else matters.

  1. Pressure type — Gauge, absolute, differential, or vacuum? This determines the transmitter category.
  2. Pressure range — Select a range where your normal operating pressure falls between 25% and 75% of full scale. Oversizing reduces accuracy; undersizing risks damage.
  3. Process media — What fluid contacts the diaphragm? Corrosive chemicals need Hastelloy or tantalum diaphragms. Food-grade requires sanitary tri-clamp connections. High-viscosity fluids need flush-mount diaphragms.
  4. Temperature — Both process temperature and ambient temperature. Standard transmitters handle -40 to +85°C process temp. High-temp models reach +150°C or higher with remote seals. Electronics rarely survive above +85°C ambient without cooling.
  5. Accuracy — General process control: ±0.5% FS is sufficient. Custody transfer or fiscal metering: ±0.075% FS or better. Remember — accuracy specs apply only at reference conditions. In the field, temperature drift and installation effects add error.
  6. Output and protocol — Match your control system. Most PLCs accept 4–20 mA. HART adds diagnostics at no extra wiring cost. Digital protocols (Modbus, Profibus) need compatible I/O cards.

Other factors: hazardous area certification (ATEX, IECEx, FM), ingress protection (IP65 minimum for outdoor, IP68 for submersible), mounting style (direct, remote seal, flush diaphragm), and response time.

Featured Pressure Transmitters from Sino-Inst

Gauge Pressure Transmitter

HH3151 HART smart pressure transmitter with remote zero/span, digital diagnostics and 0.075% accuracy. Drop-in upgrade for plants running HART multiplexers or asset-management systems.

Differential Pressure Transmitter

DP transmitters measure pressure difference across gas, liquid or steam. 4-20mA / 0-5V output drives liquid level, density and flow loops across process plants.

High-Temperature Pressure Transmitter

High-temperature pressure transducer for media up to 300 °C (further extended with cooling tube). 4-20mA output for boiler drums, reactors and superheated-steam lines.

Browse all pressure transmitters | Pressure transmitter wiring guide | Calibration guide

Frequently Asked Questions

What is the difference between a pressure transmitter and a pressure transducer?

Both convert pressure into an electrical signal. A transducer outputs a raw signal (millivolt or resistance change) that needs external conditioning. A transmitter has built-in electronics that output a standardized signal (4–20 mA, 0–10 V, or digital). In practice, most people use the terms interchangeably. If you need a plug-and-play device for a PLC, you want a transmitter.

How accurate are pressure transmitters?

Standard industrial transmitters achieve ±0.25% of full scale. Premium models (like capacitive DP transmitters) reach ±0.075% or ±0.04% FS. Accuracy specifications apply at reference conditions — in the field, temperature drift, vibration, and mounting position add error. Total performance specs give a more realistic picture than accuracy alone.

Can a pressure transmitter measure flow?

A differential pressure transmitter can measure flow when paired with a primary element — an orifice plate, Venturi tube, or flow nozzle. The DP transmitter measures the pressure drop across the restriction. Flow rate is proportional to the square root of ΔP. This is the basis of all DP flow measurement per ISO 5167.

What is the typical lifespan of a pressure transmitter?

10 to 20 years in normal service. Silicon-based sensors have no moving parts to wear out. The electronics and seals age first. Harsh conditions (high temperature, corrosive media, frequent pressure cycles) shorten life. Annual calibration checks catch drift before it causes process problems.

How do I wire a pressure transmitter?

A 2-wire 4–20 mA transmitter needs only two wires — power and signal share the same loop. Connect the positive terminal to the power supply (+), run the negative terminal through your PLC analog input, then back to the power supply (−). Supply voltage is typically 12–36 VDC. For detailed diagrams, see our pressure transmitter wiring guide.

What is the price range for pressure transmitters?

Entry-level OEM sensors: $30–$80. Standard industrial gauge transmitters: $150–$500. High-accuracy DP transmitters: $500–$2,000+. Premium brands (Rosemount, Yokogawa) cost more; equivalent Chinese-manufactured units offer 70–80% of the performance at 30–40% of the price. For specific pricing, contact our sales team.

Request a Quote

Tell us your pressure range, media, temperature, and output requirement. Our engineers will recommend the right transmitter and provide a competitive quote within 24 hours.

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About the Author
Sino-Inst Engineering Team — With over 20 years of experience in industrial process instrumentation, our team specializes in flow, level, pressure, and temperature measurement solutions. We have completed 10,000+ installations across oil & gas, water treatment, chemical, and power generation industries worldwide. Our engineers hold certifications in ISA, IEC, and ISO standards. For technical questions, contact us at rfq@sino-inst.com or call +86-180 4861 3163.

SMT3151 TGP Gauge Pressure Transmitter

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What is a gauge pressure transmitter? A gauge pressure transmitter is a pressure-measuring instrument specifically designed to measure pressure values ​​relative to atmospheric pressure. The gauge pressure sensor’s back cavity is directly connected to the atmosphere. Its biggest advantage is that it is unaffected by changes in external atmospheric pressure when measuring gauge pressure, but its environmental resistance is relatively weak.

The SMT3151 TGP Gauge Pressure Transmitter offers stable performance, can be configured for manifold installation, supports local digital display, and provides signal outputs such as 4-20mA, RS485, and HART. It is the preferred gauge pressure transmitter for industrial pressure monitoring!

Sino-Inst offers a variety of Gauge pressure transmitters for industrial pressure measurement. If you have any questions, please contact our sales engineers.

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More Pressure Transmitters

Benefits of Gauge Pressure Transmitter

  • High accuracy: The pressure transmitter can perform high-accuracy measurements within the measurement range of 0~60MPa.
  • Excellent overpressure performance: Can withstand 2 times the pressure range.
  • Intelligent static pressure compensation and temperature compensation protect the transmitter from the influence of temperature, static pressure and overpressure, reducing errors.
  • LCD digital display with backlight
  • Built-in three-button quick operation and local adjustment function
  • Various anti-corrosion materials are available
  • Multi-faceted self-diagnosis function
  • Optional signals 0-10V, 4-20mA, RS485, HART protocol, etc.

Read more about: Common Units Of Pressure

Specifications of Gauge Pressure Transmitter

Use object:Liquid, gas or steam
Measuring range0-3.5～35kPa
0-10～100kPa
0-35～350kPa
0-0.1～1.0MPa
0-0.35～3.5MPa
0-1.0～10MPa
0-2.1～21MPa
0- 4.1～41Mpa
0- 6.0～60MPa
Output signal:4-20mAdc. Output, superimposed HART protocol digital signal (two-wire system)
Power source: External power supply 24V dc. Power supply range 12V ~ 45V
Installation in dangerous placesFlameproof ExdIIBT5Gb; (explosion-proof certificate no. :CE16.1163) Intrinsically safe ExiaIICT4/T5/T6Ga; （explosion-proof certificate no. : CE15.2354X）
Accuracy: ±0.1%, ±0.075%
Stability: ±0.2%/12 months of the maximum
range
Temperature effect：Including zero and range
for maximum temperature error of ±0.2% /
20 ℃
Power supply impact:Less than 0.005% / V of
the output range.
Vibration effect: In any axial direction, the
frequency is 200Hz, and the error is ±0.05% /
g of the maximum range.
Electronic circuit board work in: – 40 ~ 85 ℃;
Sensitive components work in :– 40 ~ 85 ℃;
Storage temperature :– 40 ~ 85 ℃;
With digital display: – 25 ~ 75 ℃ (run);
– 40 ~ 85 ℃ (no damage);
Relative humidity: 0 ~ 95%
Overpressure limit:2~5 times the maximum range
Volume change:Less than 0.16 cm3
Damping:The time constant is adjustable from
0.1 to 32.0s.
Startup time: 3s, no preheating required.

Extended reading: How to calibrate HART pressure transmitters

Gauge pressure transmitter working principle

SMT3151 TGP-Gauge Pressure Transmitter / Transducer is a diffusion silicon pressure transmitter. The working principle of the diffused silicon pressure sensor is based on the piezoresistive effect.

Using the principle of piezoresistive effect, the pressure of the measured medium directly acts on the diaphragm of the sensor (stainless steel or ceramic).

Make the diaphragm produce a slight displacement proportional to the pressure of the medium. To change the resistance value of the sensor. Use electronic circuits to detect this change. And convert and output a standard measurement signal corresponding to this pressure.

More about : Pressure transmitter Working Principle.

Industrial Applications of Gauge Pressure Transmitter

Gauge pressure transmitter is the most commonly used detection instrument in industrial process control, which is widely used in various automatic control systems. Such as aerospace, military industry, petrochemical, chemical industry, oil well, electricity, shipbuilding, building materials, pipelines and many other industries.

It is generally used to measure pressure or absolute pressure in environments where the medium temperature is not too high, the corrosiveness is not strong, the viscosity is not high, and it is not easy to crystallize.

If low temperature, high temperature, corrosive medium measurement is required. Please contact our engineers for customization!

  • Mechanical and plant engineering
  • Chemical industry
  • Medical technology
  • Food and beverage
  • Oil and gas industry
  • Packaging and paper industry
  • Pharmaceutical industry

Read more about: What is industrial pressure transmitter?

Explosion Proof Pressure Transmitter for Hazardous locations

Difference between absolute, gauge, and differential pressure

Comparison of absolute, gauge and differential pressure

Absolute pressure

Absolute pressure is referred to as the vacuum of free space (zero pressure). In practice, absolute piezoresistive pressure sensors, measure the pressure relative to a high vacuum reference, sealed behind its sensing diaphragm.

The vacuum has to be negligible compared to the pressure to be measured. Sino-Instrument’s absolute pressure sensors, offer ranges from 1 bar or even 700 mbar as well as barometric pressure ranges.

Gauge pressure

Gauge pressure is measured relative to the ambient atmospheric. The average atmospheric at sea level is 1013.25 mbar. Changes of the atmospheric, due to weather conditions, or altitude influences the output of a gauge pressure sensor.

A gauge pressure higher than ambient pressure is referred to as positive pressure. If the measured pressure is below atmospheric, it is called negative or vacuum gauge pressure. In general, a vacuum is a volume of space that is essentially empty of matter.

According to its quality vacuum is divided into different ranges such as an e.g. low, high and ultra high vacuum.

Differential pressure

Differential pressure is the difference between any two process pressures p1 and p2. Differential pressure sensors must offer two separate pressure ports, with a tube or thread. Sino-Instrument’s amplified pressure sensors, are able to measure positive and negative pressure differences. i.e. p1>p2 and p1<p2.

These sensors are called bidirectional differential pressure sensors, with ranges of e.g. -1…+1.0 bar or -2.5…+2.5 mbar. In contrast, unidirectional differential pressure sensor only operate in the positive range (p1>p2). E.g. from 0…1.0 bar or 0…2.5 mbar. And the higher has to be applied to the pressure port defined as “high pressure”.

Gauge Pressure VS Absolute Pressure

  1. Gauge pressure refers to pipeline pressure. It refers to the pressure measured with pressure gauges, vacuum gauges, U-shaped tubes and other instruments, also called relative pressure). “Gauge pressure” starts from atmospheric pressure.
  2. The pressure directly acting on the surface of the container or object is called “absolute pressure”. The absolute pressure value starts with absolute vacuum.
    Absolute pressure actually refers to the gauge pressure plus the local atmospheric pressure (generally a standard atmospheric pressure can be 101.3Kpa).

Absolute pressure = gauge pressure + one atmosphere
If the unit is MPa, absolute pressure = gauge pressure + 0.1MPa

Read more about: Absolute Pressure Vs Gauge Pressure Measuring Instruments

Transmitters can convert physical signals into electrical signals.
For example, our pressure transmitter can convert pressure signals into 4-20mA. Liquid level transmitter can convert liquid level signals into 4-20mA.

Gauges are generally mechanical. There is no output of electrical signals. For example, pressure gauges and liquid level gauges. The measurement results can be measured and read intuitively.

When selecting a pressure transmitter, the concept of pressure type is involved: absolute pressure, gauge pressure, negative pressure and differential pressure.

Absolute pressure transmitter measures the absolute pressure of the medium in the equipment. Its reference pressure is an absolute value of 0. It has nothing to do with atmospheric pressure. Therefore, there will be a vacuum sealed cavity on the low-pressure side of the pressure core.

Gauge pressure transmitter measures the pressure based on atmospheric pressure. One side of the pressure transmitter is connected to the atmosphere, and the other side is connected to the measured pressure, so the reference pressure side is open to the atmosphere. It is generally used to measure the liquid level of pipelines and non-pressure tanks.

If you pay close attention to the outer shell of some gauge pressure transmitters, it is not difficult to find some small holes on it. These vents are reserved to keep the reference side connected to the atmosphere.

More Featured Pressure Transmitters and Pressure Measurement Solutions

SI-520 Digital Pressure Sensor
SI-702 High Pressure Sensor
SI-702S Ultra-High Pressure Senors
SI-512H High Temperature Pressure Sensor
Flush diaphragm pressure sensor
Sanitary Pressure Transmitter
Diaphragm Seal Pressure Transmitter
SI-706 Combined Pressure and Temperature Sensor-Dual function

We at Sino-Inst manufacture and supply various types of gauge pressure transmitters for various industries. Customized production is available based on your measurement requirements, including pressure range, temperature, accuracy, signal output, mounting thread, material, etc.

If you need to purchase a gauge pressure transmitter or have any technical questions, please feel free to contact us.

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SMART HART Pressure Transmitter

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What is a HART Pressure Transmitter?

The HART Pressure Transmitter is a two-wire intelligent pressure measurement instrument based on the HART protocol, suitable for precision fluid pressure measurement. The intelligent HART Pressure Transmitter retains a 4~20mA current loop signal while transmitting digital signals. Using a HART handheld device or a smart instrument with HART functionality, users can communicate with the pressure transmitter to perform parameter settings, read diagnostic information, and other operations.

Sino-Inst offers a variety of HART pressure transmitters for industrial pressure measurement. If you have any questions, please contact our sales engineers.

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More Pressure Transmitters

What is hART in a pressure transmitter?

The HART protocol is a backward-compatible smart instrument solution for the transition from analog to digital systems.

A typical HART smart instrument generally consists of a power supply module, sensor interface circuitry, A/D conversion circuitry, MCU, D/A output circuitry, and HART communication circuitry.

HART (Highway Addressable Remote Transducer) is a communication protocol introduced by Rosemount Corporation in 1985 for communication between field smart instruments and control room equipment.

Traditional pressure transmitters only provide a 4-20mA current loop output analog signal. HART smart pressure transmitters retain the 4-20mA current loop signal while transmitting digital signals, playing a crucial role in the transition from analog to digital instruments.

The HART protocol uses FSK frequency shift keying signals based on the Bell202 standard, superimposing a 0.5mA audio digital signal onto a low-frequency 4-20mA analog signal for bidirectional digital communication, with a data transmission rate of 1.2kbps. Since the average value of the FSK signal is 0, it does not affect the magnitude of the analog signal transmitted to the control system, ensuring compatibility with existing analog systems.

In HART protocol communication, the main variables and control information are transmitted via 4-20mA. Additional measurement, process parameters, equipment configuration, calibration, and diagnostic information can be accessed via the HART protocol when needed.

Benefits of HART pressure transmitters

3151 HART pressure transmitter
  • 4～20mA DC current output superimposed HART® protocol digital communication (two-wire system);
  • Adopt digital compensation and nonlinear correction technology;
  • -10℃～80℃ digital wide temperature compensation;
  • With local and remote zero and span adjustment functions;
  • Key operation on site for easy configuration.
  • Shorten troubleshooting time from discovery to problem solving;
  • Continuously verify the integrity of loops and control/automation system strategies;
  • Improve asset efficiency and system availability;
  • Quickly determine and verify control loops and device configurations;
  • Use remote diagnosis to reduce unnecessary on-site inspections.

Featured Industrial HART Pressure Transmitters

HART pressure transmitter is a complete product line of liquid level, differential pressure, gauge pressure and absolute pressure transmitters. Models include flushing diaphragms and sanitary flanges for liquid level measurement, hydrostatic tank metering – HTG. And wetted parts of various materials to suit the process requirements.

Diffused silicon Gauge Pressure Transmitter
Diaphragm Seal Pressure Transmitter
SI-390 Industrial Pressure Transmitter
SI-520 Digital Pressure Sensor
Capacitive Gauge Pressure Transmitter
Hydrostatic pressure transmitter
High-Temperature Pressure Transmitter
Absolute Pressure Transmitter

HART calibrator is our HART communicator for calibrating instruments. For example pressure transmitter, DP transmitter, liquid level transmitter, a flowmeter, and a temperature transmitter.

HART communication protocol (Highway Addressable Remote Transducer) is a hybrid analog + digital industrial automation open protocol. Its most significant advantage is that it can communicate through the traditional 4–20 mA analog instrument current loop, sharing only a pair of wires used by the analog host system.

We use this protocol in the HART calibrator. HART communicator (such as HART 475) is the most common HART calibrator.

The proprietary calibration process ensures optimal temperature compensation. This limits the thermal impact on the sensor output. It is suitable for the global process control industry. It provides a cost-effective solution for the use of conventional HART transmitters (such as the HART 475 field communicator).

No. HART is different from 4-20mA. Their main differences are:

  1. Signal Type

4-20mA: Pure analog signal, transmitting only a single process variable (e.g., pressure, flow rate) via current value (4mA-20mA), unable to carry additional data.

HART Protocol: Superimposes a digital signal (FSK modulation) onto the 4-20mA analog signal, enabling dual-channel analog and digital communication, capable of transmitting multiple parameters such as equipment status and diagnostic information.

  1. Communication Capabilities

4-20mA: Unidirectional transmission, supporting only basic measurements, unable to be remotely configured or diagnosed.

HART Protocol: Half-duplex bidirectional communication, supporting remote parameter modification (e.g., range, zero point) and fault diagnosis (e.g., sensor malfunction, loop impedance exceeding limits).

  1. System Compatibility

4-20mA: Requires physical disconnection of the loop for maintenance, cannot be networked with intelligent devices.

HART Protocol: Compatible with traditional analog systems, supports a single-line connection of up to 15 devices, and can be upgraded to WirelessHART or HART IP in the future.

  1. Applications

4-20mA: Suitable for simple applications with limited budgets and only basic measurements required.

HART Protocol: Suitable for high-precision control, smart factories, and other scenarios requiring data interaction, with lower long-term maintenance costs.

The HART protocol extends the functionality of 4-20mA through digital signals, enabling intelligent upgrades, while traditional 4-20mA only retains basic analog transmission capabilities.

You may like: Verabar Flow Meter

How to calibrate a pressure transmitter using HART?

A pressure transmitter is one of the most common instruments in a process plant. To assure its accuracy, it needs to be calibrated.

But what do you need to calibrate it and how is it done?

You may know how to calibrate a pressure transmitter? Or, how to calibrate a differential pressure transmitter? Then, calibrate HART pressure transmitters, kind of like pressure transmitter calibration using a hart communicator. Pressure transmitter manufacturers have improved accuracy and technology, designed into these smart pressure measurement devices.

To calibrate a pressure transmitter, you need:

loop supply (if not connected to the controls system’s loop supply);
a pressure generator to generate input pressure;
an accurate calibrator to measure the input pressure;
an accurate calibrator to measure the output mA current.

Typically, the pressure transmitter is a HART protocol transmitter. So in case, there is any need to adjust/trim it, you will need to use a device supporting HART communication.

How to calibrate HART pressure transmitters?

Explaining how to do the calibration would result in quite a long text. So we have put together a video for you instead. The video shows you how to calibrate and trim a HART pressure transmitter. Please have a look at the video: How to calibrate HART pressure transmitters

Video source: https://www.youtube.com/watch?v=4wLCqH0M9fU&t=9s

HART Pressure Transmitters Calibration Steps

How to calibrate HART pressure transmitters?

Total Time: 20 minutes

1. Isolate the transmitter from the process being measured and its loop wiring.

2. If measuring the mA signal across the transmitter test diode leave the wires intact, but note this method does not give the best mA measurement accuracy.

3. Connect the mA measurement jacks of the 754 to the transmitter.

4. Connect the pressure module cable to the 475, and connect the transmitter test hose from the hand pump to the transmitter.
Press the HART button on the calibrator to see the configuration of the transmitter.

5. Press HART again and the calibrator will offer the correct measure/source combination for the test.

6. If documenting the calibration press As-Found, input the test tolerance and follow the prompts.

7. If the measured mA signal at the test points is found within tolerance the test is complete.
If not, change is required.
Select, adjust, and trim the pressure zero, mA output signal and input sensor.

If you still do not know how to check the pressure transmitter?  Or, how to calibrate a pressure transmitter. Just contact us.

More Pressure Measurement Solutions

Sino-Inst offers over 20 SMART HART Pressure Transmitters. About 50% of these are 4-20ma Low-Pressure Transducers, 40% are Differential Pressure Gauge, and 20% are Diaphragm Seal Pressure transmitters, 20% are 4-20ma differential pressure transmitters.

Sino-Inst sells through a mature distribution network that reaches all 50 states and 30 countries worldwide. HART Pressure Transmitter products are most popular in the domestic market, Southeast Asia, and Mid East.  You can ensure product safety by selecting from certified suppliers with ISO9001, ISO14001 certifications.

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Diaphragm Seal Pressure Transmitters

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Diaphragm Seal Pressure Transmitters work with Diaphragm Seals for those harsh working conditions. The purpose of the diaphragm seal is to isolate the pressure sensor from the process medium.

The diaphragm seal makes measuring pressure safer and more reliable. It is ideal for protecting pressure process transmitters even under harsh working conditions. The diaphragm seal can isolate the pressure sensor from the process medium. No matter absolute pressure or differential pressure measurement. Mounting with capillary and flange, Diaphragm Seal pressure transmitter can measure pressure, liquid level and flow.When the environment is extremely hot or cold, or when the process connection is difficult to connect to the measuring instrument. When the measured medium is corrosive, sticky, sticky or easily cured. Or when the process is not chemically compatible with the instrument material. It is recommended to use a diaphragm seal.

Sino-Inst offers a variety of Diaphragm Seal Pressure Transmitters for industrial pressure measurement. If you have any questions, please contact our sales engineers.

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Featured Diaphragm Seal Pressure Transmitters

Flush diaphragm pressure sensor
Sanitary Pressure Transmitter
Diaphragm Seal Pressure Transmitter
Remote Diaphragm Seal Pressure Transmitter
Flange Mounted Differential Pressure Transmitter
Extended Diaphragm Seal DP Level Transmitter
Remote Seal Differential Pressure Transmitter
Differential pressure(DP) level transmitter

What is a diaphragm seal?

Diaphragm seals, also known as chemical seals or remote seals, are used for pressure measurements when the process medium should not come into contact with the pressurised parts of the measuring instrument.

A diaphragm seal has two primary tasks:

  1. Separation of the measuring instrument from the process medium
  2. Transfer of the pressure to the measuring instrument

You may like: Diaphragm pressure gauge

Advantages of diaphragm seals

Diaphragm seals offer the advantage that the “contact surface” between pressure medium and diaphragm is relatively large. Thus ensuring accurate pressure measurement, especially for very low pressures (< 600 mbar). Furthermore, they can be easily dismounted, e.g. for cleaning or calibration purposes.

Rosemount 1199

Rosemount 1199 remote transmission diaphragm system provides the world’s most extensive product variety and specifications to meet the requirements of various measurements and applications.

There are the following types of remote transmission differential pressure / level transmitters:
1) PFW flat type remote transmission device
2) RTW thread installation type remote transmission device
3) EFW inserted barrel remote transmission device
4) RFW flange mounted remote transmission device
5) SCW hygienic remote transmission device

The 1199 remote diaphragm can be assembled to Sino-Inst differential, gauge, and absolute pressure transmitters and liquid level transmitters.

We can learn more about Rosemount 1199 remote diaphragm.

How do diaphragm seals work?

Basically, diaphragm seals are used in all pressure measurement processes to avoid direct contact between the measuring instrument and the medium during this process.

In addition, if the measuring point cannot be installed or read because the measuring point is located in a hard-to-reach location, a diaphragm seal can also be used.

In both cases, the applied pressure is transferred to the measuring instrument through the system fill fluid in the diaphragm seal housing.

The diaphragm of the seal can be made of different materials, such as stainless steel, Hastelloy, Monel or tantalum. In addition, coatings with ECTFE, PFA or gold can also be used.

We can provide the best diaphragm seal design, materials, system fill fluid and accessories for each application. The combined configuration of the pressure measuring instrument and the diaphragm seal is mainly determined by the special application conditions of the diaphragm sealing system.

You may like: How does a pressure transmitter work?

Differential Pressure Transmitter Installation Guide

Diaphragm type pressure transmitter working principle

Diaphragm pressure transmitter is an automated instrument that measures fluid pressure in the industrial field.

  • It is mainly composed of pressure measuring probe, capillary tube, filling liquid and pressure transmission head.
  • One end of the pressure measuring probe is provided with an elastic metal diaphragm
  • When the pressure acts directly on the surface of the measuring diaphragm, the diaphragm will have a slight deformation.
  • The high-precision circuit on the measuring diaphragm transforms this tiny deformation into a highly linear voltage signal proportional to the pressure and also proportional to the excitation voltage.
  • Then use a special chip to convert this voltage signal into an industry standard 4-2OmA current signal or 1-5V voltage signal.
  • Because the measuring diaphragm adopts standard integrated circuit, which contains linear and temperature compensation circuits, it can achieve high precision and high stability.
  • The transmission circuit adopts a special two-wire system chip, which can ensure the output of a two-wire 4-20mA current signal, which is convenient for field wiring.

Read more about: What is industrial pressure transmitter?

When to use diaphragm seal ?

The diaphragm seal pressure transmitter is suitable for the following working conditions:

  1. The high temperature medium needs to be isolated from the transmitter.
  2. The measuring medium has a corrosive effect on the sensitive components of the transmitter.
  3. Suspended liquid or high viscosity medium.
  4. The measured medium solidifies or crystallizes due to changes in the environment or process temperature.
  5. Replacing the measured medium requires strict purification of the measuring head.
  6. The measuring head must be kept clean and hygienic.
  7. Liquid level measurement of sealed pressure vessel.

Difference between bourdon tube and diaphragm pressure gauge:

SI-D100 Diaphragm Pressure Gauge

Frequently
Asked
Questions

Help Center

The remote seal is used to prevent the medium in the pipeline from directly entering the pressure sensor assembly in the pressure transmitter. It is connected to the transmitter by a capillary filled with fluid. As a result, they’re often used in refining, petrochemical, and chemical plants.

Diaphragm pressure gauge consists of a diaphragm isolator and a universal pressure gauge to form a system pressure gauge. The spring tube is evacuated by special equipment. And fill people with irrigation fluid. Seal it with a diaphragm. When the pressure P of the measured medium acts on the diaphragm, it deforms. The working fluid filled in the compression system makes the working fluid form a △ P equivalent to P, with the help of work. The conduction of the liquid causes a corresponding elastic deformation-displacement at the free end of the elastic element (spring tube) in the pressure meter. According to the working principle of the pressure instrument matched with it, the measured pressure value is displayed.

Diaphragm pressure gauges consist of a system of diaphragms and universal pressure gauges. Diaphragm pressure gauges and equipment are mainly connected with threaded connections, flange connections and sanitary clamps. Diaphragm pressure gauges are suitable for measuring the pressure of medium with strong corrosion, high temperature, high viscosity, easy to crystallize, easy to solidify, and solid floats, as well as occasions where the measurement medium must be avoided from entering the general-purpose pressure meter and to prevent the accumulation of sediment and easy to clean.

The characteristics of the filling fluid determine the performance of the sealing system to a large extent, both in response time and temperature to the heat dissipation conditions.
The initial consideration in choosing a sealed diaphragm to fill fluid is the media compatibility of the process.
Glycerin, silicone oil and halogenated carbon are the most commonly used sealed diaphragm filling fluids.
In general there are three ways to fill a diaphragm seal:
1. Filling a diaphragm seal after assembly of the seal to the instrument
2. Filling a diaphragm seal before assembly of the seal to the instrument
3. Filling a diaphragm seal with a capillary between the seal and the instrument

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Sino-Inst is a manufacturer of Diaphragm Seal Pressure Transmitters.

Sino-Inst offers over 20 Diaphragm Seal Pressure Transmitters at best price. About 50% of these are Pressure level Transducer, 40% are Differential Pressure transmitters, and 40% are Diaphragm Seal Pressure transmitters.
A wide variety of Diaphragm Seal Pressure Transmitters options are available to you, such as free samples, paid samples. 

Sino-Inst is a globally recognized supplier and manufacturer of Diaphragm Seal Pressure Transmitters, located in China. Sino-Inst sells through a mature distribution network that reaches all 50 states and 30 countries worldwide. Diaphragm Seal Pressure Transmitters products are most popular in Domestic Market, Southeast Asia, and Mid East. 

You can ensure product safety by selecting from certified suppliers, with ISO9001, ISO14001 certification.

Request a Quote

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Industrial Pressure Transmitters

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Industrial pressure transmitters for the process pressure measure, monitor and control application.

Industrial pressure transmitters are sensors with electrical transmission output for remote indication of pressure. Process transmitters differentiate themselves from pressure sensors through their increased range of functionality.

They feature integrated displays, offer high measuring accuracies and freely scalable measuring ranges. Communication is via digital signals, and waterproof and explosion-proof certifications are available. Through connection to diaphragm seals, they are suitable for the harshest operating conditions. Ideal for OEMs, process applications, water processing, and industrial pressure applications.

Sino-Inst offers a variety of pressure senors for industrial pressure measurement. If you have any questions, please contact our sales engineers.

CONTACT US

Featured Industrial Pressure Transmitters

Diffused silicon Gauge Pressure Transmitter
A gauge pressure (GP) transmitter compares a process pressure against local ambient air pressure. Gauge pressure transmitters have ports to sample the ambient air pressure in real-time.
Capacitive Gauge Pressure Transmitter
Gauge pressure (GP) transmitters compare process pressure with local ambient air pressure. Gauge pressure transmitters have ports for real-time sampling of ambient air pressure.
Explosion-proof Pressure Transmitter
Explosion-proof Pressure transmitter, or explosion-proof pressure transducer, with the explosion-proof enclosure.
For applications in hazardous areas.
Diaphragm Seal Pressure Transmitter
When the process medium should not come into contact with the pressured parts of the measuring instrument. Diaphragm sealed pressure transmitters are used for pressure measurement.
Hygienic / Sanitary Pressure Transmitter
Also called Hygienic pressure Transmitters, or tri clamp pressure transmitter. Sanitary pressure Transmitters is used to food &beverage or pharmaceutical application.
High-Temperature Pressure Transmitter
High-temperature pressure transmitters with a 4-20mA output.
which has a temperature capability of over 850 °C and is not pyroelectric.

Absolute Pressure Transmitter
Absolute pressure transmitter with 4-20mA output for measuring pressure with absolute type reference. Absolute pressure (AP) transmitter is a measure of the ideal (complete) vacuum pressure.
Hydrostatic pressure transmitter
Hydrostatic pressure transmitter is used for fluid hydrostatic pressure measurement. With working static pressure up to 32Mpa, for liquid, gas or steam .
Remote Diaphragm Seal Pressure Transmitter
Remote seal pressure transmitter, with capillary and diaphragm seal, remote mount. Diaphragm seal systems protect pressure transmitters from hot, viscous, contaminated or corrosive media.

Sino-Inst also provides repair services for Industrial pressure transmitters. Such as WIKA, Rosemount, and other brands of pressure transmitters.

What is a smart pressure transmitter?

Digital smart pressure transmitter is pressure sensor with a 12-bit or higher microprocessor. Smart pressure transmitters are high performance microprocessor-based transmitters with flexibility. Pressure calibration and output, automatic compensation.

Smart pressure transmitter also called intelligent pressure transmitter.

The intelligent Industrial pressure transmitters consist of two parts: a smart sensor and a smart electronic board.

The smart sensor part includes: a capacitive sensor. A measuring diaphragm detection circuit. A temperature sensor, and a temperature compensation circuit.

The smart electronic board includes: a microcomputer controller. And the peripheral circuit, complete the pressure signal to 4 ~ 20mA dc conversion.

Smart Industrial pressure transmitter is used to measure the pressure of liquid, gas or steam. And then convert the pressure signal into 4 ～ 20mA DC signal output. The intelligent pressure transmitter produced by Sino-Inst can communicate with the HART communicator. It is widely used in weakly corrosive liquids in industrial pipelines, Gas and steam measurement and control systems.

Industrial pressure transmitters Working Principle

Principle and Application of Diffusion Silicon Pressure Transmitter

The pressure of the measured medium directly acts on the diaphragm of the sensor (stainless steel or ceramic). Causing the diaphragm to generate a micro-displacement proportional to the pressure of the medium. The resistance value of the sensor changes. The electronic circuit detects this change and converts and outputs a standard measurement signal corresponding to this pressure.

Principle of capacitive pressure transmitter

Capacitive pressure transmitter is mainly composed of capacitance sensor and circuit board. The sensor implements pressure-capacitance conversion. The circuit board converts the capacitance to a two-wire 4-20mA.

When the process pressure is applied to the isolation diaphragm from both sides (or one side) of the measuring chamber, it is transferred to the central diaphragm of the chamber through the silicone oil filling liquid. The central diaphragm is a diaphragm with tensioned edges.

Under the action of pressure, a corresponding displacement is generated. This displacement creates a change in differential capacitance!

And through the adjustment, oscillation and amplification of the electronic circuit board! Converted into 4-20mA signal output! The output current is directly proportional to the process pressure!

How Does a Pressure Transmitter Work?

Types of Pressure Transmitters

Depending on the type of pressure to be measured:

Pressure transmitter types include gauge pressure, absolute pressure, and differential pressure. Gauge pressure refers to the pressure that is less than or greater than atmospheric pressure based on the atmosphere. Absolute pressure refers to the absolute zero pressure as the reference and is higher than the absolute pressure. Differential pressure refers to the difference between two pressures.

According to the working principle of the Industrial pressure transmitters:

  • Strain Gauge Pressure Transducers
  • Capacitance Pressure Transducers
  • Potentiometric Pressure Transducers
  • Resonant Wire Pressure Transducers

Electrical Output of Pressure Transducers

Pressure transmitters are generally available with three types of electrical output. Millivolt, amplified voltage and 4-20mA. Below is a summary of the outputs and when they are best used.

Extended Reading: 4-20ma pressure transducer wiring diagram

Millivolt Output Pressure Transducers

A sensor with a millivolt output is usually the most economical pressure sensor. The output of a millivolt sensor is nominally about 30mV. The actual output is proportional to the input power or excitation of the pressure sensor. If the stimulus fluctuates, the output will change.

Because of this dependence on the level of excitation, a regulated power supply is recommended for millivolt sensors. Because the output signal is so low, the transducer should not be placed in an electrically noisy environment. The distance between the transducer and the reading instrument should also be kept relatively short.

Voltage Output Pressure Transducers

Voltage output transducers include integral signal conditioning, which provides higher output than millivolt transducers. The output is usually 0-5Vdc or 0-10Vdc. Although model-specific, the output of the transducer is usually not a direct function of the stimulus. This means that as long as the regulated power supply falls within the specified power range, it is usually sufficient. Because of their higher output levels, these sensors are not as susceptible to electrical noise as millivolt sensors and can therefore be used in more industrial environments.

4-20 mA Output Pressure Transducers

These types of sensors are also called pressure transmitters. Because 4-20mA signals are least affected by electrical noise and resistance in the signal line, these sensors are best used when signals must be transmitted over long distances. These sensors are typically used in applications where the lead must be 1000 feet or more.

Industrial Applications of Pressure Transmitters

Pressure transmitters are mainly used in the following areas:

  1. Petroleum, petrochemical, chemical. Matching with throttling devices to provide accurate flow measurement and control. Measures pressure and level in pipes and tanks.
  2. Electricity, city gas. And other companies and businesses require high stability and high precision measurement and other places.
  3. Pulp and papermaking are used in places that require chemical-resistant liquids and corrosion-resistant liquids.
  4. Steel, non-ferrous metals, and ceramics are used in furnace pressure measurement and other places that require high stability and high precision measurement. They are also used in places that require stable measurement under strict control (temperature, humidity, etc.).
  5. Machinery and shipbuilding, used to strictly control the place where high precision is required for stable measurement.

Hydrostatic pressure for level measurement:

SI-151 Hydrostatic Level Sensor
SMT3151TR Hydrostatic level transmitter-Rod Type
SI-PCM260 Deep Well Water Level Sensor

Pressure Transmitters VS Pressure Sensors VS Pressure Transducers

A pressure sensor is a device or device that can sense a pressure signal and convert the pressure signal into a usable output electrical signal according to a certain rule.

A pressure sensor usually consists of a pressure-sensitive element and a signal processing unit. According to different test pressure types, pressure sensors can be divided into gauge pressure sensors, differential pressure sensors and absolute pressure sensors. A pressure sensor is the core part of pressure transmitter.

In a pressure transducer, a thin-film or piezo-resistive pressure sensor is mounted on a process connection. The transducer converts pressure into an analog electronic output signal, typically as a millivolt per volt output. These signals are not linearized or temperature compensated.

A pressure transmitter has additional circuitry that linearizes, compensates, and amplifies the signal from a transducer. The different signal types are typically voltage signals (eg, 0 to 5 or 0 to 10 volts), milliamp (eg, 4 to 20 milliamp), or digital. The instrument then can transmit the signal to a remote receiver.

If you still don’t know how to choose the right pressure transmitter. Please feel free to contact our sales engineers. We will provide you with the best pressure measurement and control solution.

Guidelines for Troubleshooting Pressure Transmitters

When this happens, you should consider: Is the pressure source itself stable? The degree of anti-interference ability of the instrument or pressure sensor. Is the sensor wiring normal? The sensor itself is vibrating and the cause of the failure. Is the polarity of the power supply reversed?

Check the degree of pressure variable; make 4-20mA output adjustment.

Check the transmitter’s power supply voltage, calibration equipment and set values (4mA and 20mA points). Check whether the pressure interface is leaking or blocked. Check the wiring mode and power supply. If normal, check if the sensor has zero output. Or Perform a simple pressurization to see if the output changes. If there is a change, the sensor is not damaged.

Check if pressure transmission is blocked; check calibration equipment and adjust sensors; check vehicle damping and electromotive force interference.

Frequently
Asked
Questions

Help Center

1. Do a 4-20mA trimming first to calibrate the D / A converter inside the transmitter. Since it does not involve sensing components, no external pressure signal source is required.

2. Do a full fine-tuning again to make the 4-20mA, digital reading coincide with the pressure signal actually applied. So a pressure signal source is needed.

3. Finally, do the re-ranging, and adjust the analog output 4-20mA to match the external pressure signal source. Its role is exactly the same as that of the zero (Z) and range (R) switches on the transmitter housing.
The communicator can change the range of the intelligent pressure transmitter. And can adjust the zero point and the range without inputting a pressure source. However, this method cannot be called calibration and can only be called “setting the range”. True calibration requires a standard pressure source input to the transmitter.

Adjusting the range (LRV, URV) without using a standard is not calibration. And ignoring the input part (input transmitter pressure) for output adjustment (transmitter conversion circuit) is not a correct calibration. Furthermore, the relationship between the pressure and differential pressure detection components, the A / D conversion circuit, and the current output is not equal. The purpose of calibration is to find the changing relationship between the three.
Emphasize one point:
Only when the input and output (input transmitter pressure, A / D conversion circuit, loop current output circuit) are debugged together, can it be called a true calibration.

First of all, the parameters that must be seen when purchasing a pressure transmitter are:
Pressure range. Range. Measurement medium. Installation method-threaded flange clamps, etc. Installation dimensions. Temperature. Whether with display. Whether with HART protocol. Output type. Current output or voltage output. Explosion-proof level, protection level. Accessories. Mounting bracket.
The above parameters will affect the price of the pressure transmitter.
Sino-Inst, as the manufacturer of pressure transmitter, offer you with the best price.

The input of the pressure transmitter is a pressure signal. The function of the pressure transmitter is to convert the pressure signal input from the outside into a current or voltage signal.

A pressure transmitter is a device that converts pressure into pneumatic or electric signals for control and remote transmission.

It can convert physical pressure parameters such as gas and liquid sensed by the load cell sensor into standard electrical signals (such as 4~20mADC, etc.). Measurement, indication and process adjustment are carried out by supplying secondary instruments such as indicating alarms, recorders and regulators.

Related Products

SI-503K Gas Pressure Sensor
SI-702 High Pressure Sensor
SI-702S Ultra-High Pressure Senors
SI-512H High Temperature Pressure Sensor
High Frequency Dynamic Pressure Sensor
SI-706 Combined Pressure and Temperature Sensor-Dual function
SI-338 Ceramic Pressure Sensor
Cryogenic Pressure Transducer
Extended Diaphragm Seal DP Level Transmitter
Remote Seal Differential Pressure Transmitter
Differential pressure(DP) level transmitter
Flange Mounted Differential Pressure Transmitter

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Sino-Inst offers over 20 industrial pressure transmitters.
A wide variety of industrial pressure transmitters options are available to you. Such as free samples, paid samples.
Sino-Inst is a globally recognized manufacturer of industrial pressure transmitters, located in China.
Sino-Inst sells through a mature distribution network that reaches all 30 countries worldwide.
Industrial pressure transmitters products are most popular in Europe, Southeast Asia, and Mid East. You can ensure product safety by selecting from certified suppliers. With ISO9001, ISO14001 certification.

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