Diaphragm Seal Pressure Transmitter － Flush Flanged

Posted on January 28, 2026 by KimGuo11

Diaphragm Seal Pressure Transmitter flush flanged

The flush flanged diaphragm seal pressure transmitter uses a diaphragm directly welded to the mounting flange, working in conjunction with an inline pressure transmitter to protect against the effects of high and low temperatures, corrosive, clogging, or erosive processes.

Get a Quote

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

Features
Specifications
Applications

Features of Diaphragm Seal Pressure Transmitter

Flange installation; flange size and standards can be customized.
Diaphragm isolation technology.
Two-wire system, 4-20mA analog output, HART protocol digital communication.
Intelligent LCD display with backlight.
Large diaphragm, fully welded seal, long-term reliability and durability.
Corrosion-resistant diaphragm options available (tantalum, HaC, 316L, 316L PTFE sprayed).
Especially suitable for high-temperature viscous liquids.
HART communication function available.

Specifications of Diaphragm Seal Pressure Transmitter

Measuring medium:	Liquid or gas (compatible with contact material)
Pressure range:	-100kPa～0～10MPa (see range selection table for details)
Pressure method:	Gas pressure, absolute pressure
Medium temperature:	-40～130℃, other high temperatures can be customized up to 60℃
Connection time:	20ms
Accuracy class:	±0.5%FS
Indicator accuracy:	0.05%FS LCD (with backlight) display
Temperature compensation:	-20～80℃
Stability performance:	±0.2%FS/year
Temperature drift:	±0.02%FS/℃ (within temperature compensation range)
Explosion-proof type:	Explosion-proof type ExdbⅡCT6Gb; Explosion-proof dust type ExtbIIICT80℃Db; Intrinsically safe type ExiaⅡCT6Ga (4～20mA/4～20mA HART output only); Dust intrinsically safe type ExiaD20T80℃ (4～20mA/4～20mA HART output only);
Protection class:	IP66;

Applications

The Flush Flanged Diaphragm Seal Pressure Transmitter uses a standard flange as its interface, allowing for on-site flange installation. Because the pressure-bearing diaphragm is exposed and directly senses the pressure, it is easy to clean and meets harsh operating conditions such as moisture resistance, waterproofing, and explosion protection.

This series of products is widely used in industrial process control, petroleum, chemical, and metallurgical industries, as well as in applications involving viscous media containing particles.

High/low temperature fluids;
Highly corrosive/high viscosity fluids;
The fluids which may cause clogging of impulse piping in the low temperature;
Toxic fluids;
The fluids containing suspended solids which are deposited in the impulse piping and may cause clogging.

Extended reading: Featured Diaphragm Seal Pressure Transmitters

Diaphragm flange material selection

The biggest advantage of the Diaphragm Seal Pressure Transmitter is the availability of various diaphragm materials. Commonly used diaphragm materials include SUS316L stainless steel, tantalum, Hastelloy, Monel alloy, pure titanium, and F4 alloy.

Choosing the right material means considering both its corrosion resistance and cost-effectiveness. For example, tantalum and Hastelloy diaphragms offer excellent corrosion resistance but are expensive, making them suitable only for highly corrosive environments; other inexpensive materials are not suitable.

The table below introduces several commonly used corrosion-resistant materials suitable for corrosive media for your reference.

Corrosive medium	Tin bronze (QSn6.5-0.4)	SUS316	Pure tantalum (Ta)	Monel (Ni70Cu30)	Hastelloy (HC)	Polytetrafluoroethylene (F4)
Sulfuric acid (H2SO4)	V	△	○	V	V	V
Nitric acid (HNO3)	╳	V	○	╳	V	V
Hydrochloric acid (HCI)	△	╳	○	╳	V	V
Phosphoric acid (H3PO4)	V	V	○	V	V	V
Acetic acid (CH3COOH)	V	V	○	V	○	V
Caustic soda (NaOH)	△	○	△	○	○	V
Soda ash (Na2CO3)	○	○	○	○	V	V
Baking soda (NaHCO3)	V	○	○	○	○	V
Chlorine (CI)	Dry: V	Dry: V	○	Dry: V	V	V
	Wet: ╳	Wet: ╳	Wet: ╳
Bromine (Br2)	Dry: △	Dry: ╳	○	Dry: ○	○	V
	Wet: ╳	Wet: △	Wet: ╳
Ammonia (NH3)	╳	V	╳	╳	○	V
Seawater (30% NaCI)	V	V	○	○	○	V

Explanation of symbols: ○ ——best; △ ——conditional use; V——can be used;

Extended reading: Common Pressure Sensor Applications

What is a diaphragm seal pressure transmitter?

The diaphragm seal pressure transmitter is a flange-type pressure transmitter. This type of pressure transmitter assembles diaphragm seals to field transmitters for the purpose of measuring pressure, pressure or level.

What is a diaphragm seal?

Diaphragm Seals, also known as Chemical Seals or Gauge Isolators, are used to isolate pressure instrumentation, like pressure gauges, pressure transmitters, pressure switches, level transmitters, and more, from process media that is hot, corrosive, clogging, or otherwise damaging to the pressure instrument.

A diaphragm seal has two primary tasks:

Separation of the measuring instrument from the process medium
Transfer of the pressure to the measuring instrument

What is a remote seal?

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.

Extended reading: SI-703 Flush Diaphragm Pressure Sensor

FAQ

A pressure level transmitter is a device that works on the principle that static pressure is proportional to liquid level height. It is essentially a device that combines the functions of a pressure sensor and a level gauge.

The transmitter uses an advanced isolated diffused silicon sensitive element or a ceramic capacitor pressure sensitive sensor. The measured static pressure of the liquid is converted into an electrical signal.

This process is temperature compensated and linearly corrected, and the final output is a standard electrical signal, common forms are 4~20mA or 1~5VDC, etc.

Extended reading: Flat Pressure Sensor for High Viscosity Fluids

The pressure gauge is an instrument that uses elastic elements as sensitive elements to measure and indicate pressure higher than the ambient pressure. It is used in almost all industrial processes and scientific research fields.

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

The differences between pressure transmitter and pressure gauge are:

The accuracy of the standard instrument required for pressure transmitter calibration is much higher than the accuracy of the standard instrument required for pressure gauge.
The pressure gauge only needs to calibrate a pair of input and output relationships. The pressure transmitter may need to calibrate the relationship between input and communication data.
Pressure gauge calibration must have corresponding metrological qualifications. Pressure transmitters are generally not required except for production and new construction.
The pressure gauge has poor accuracy and no output. It cannot be operated with a hand operator. Generally, 5 points are calibrated. The back and forth difference is different. The intelligent pressure transmitter generally only needs to calibrate the zero point and full scale.
The output of the pressure gauge is a scale indication, and its own display capability. The pressure transmitter is a current output and must be connected to an ammeter display of the corresponding accuracy level.

Extended reading: extrusion melt pressure transducer

A diaphragm seal system consists of a pressure instrument, a fill liquid, and a diaphragm seal, either direct-mount or capillary.

Diaphragm seals are used to seal and protect instruments from process media. The flexibility of the seal lies in the fact that the diaphragm securely seals the contents and penetrates the instrument to accurately measure pressure.

Diaphragm seals are often used in conjunction with pressure transmitters. This combination can be used in extremely harsh environmental conditions.

The fact that they can isolate instruments from any kind of toxic and reactive chemicals makes them particularly useful devices.

Diaphragm-sealed pressure transmitters are used when the medium is corrosive or will corrode the internal parts of the transmitter (for example, ammonia will corrode the copper in the transmitter).

Extended reading: High accuracy pressure transducers

Sino-Inst is Flush Flanged Diaphragm Seal Pressure Transmitters manufacturer in China. We offer all types of Pressure Level Transmitters. Like Direct Mounted, flange-mounted, single flange, double flange, Remote Diaphragm Seals, High Static, Digital Remote.

Most of our Diaphragm Seal Pressure Transmitters are used in oil, liquids, DP transmitters, flow measurement, level measurement (like the ultrasonic level measurement), density, and other process variables.

You can ensure product safety by selecting from a certified supplier with ISO9001, ISO14001 certification. We will share more about instrument calibration, like the flow transmitter calibration.

Request a Quote

Please enable JavaScript in your browser to submit the form

KimGuo11

Wu Peng, born in 1980, is a highly respected and accomplished male engineer with extensive experience in the field of automation. With over 20 years of industry experience, Wu has made significant contributions to both academia and engineering projects.

Throughout his career, Wu Peng has participated in numerous national and international engineering projects. Some of his most notable projects include the development of an intelligent control system for oil refineries, the design of a cutting-edge distributed control system for petrochemical plants, and the optimization of control algorithms for natural gas pipelines.

drurylandetheatre.com

Flange Mounted Differential Pressure Transmitter

Posted on January 26, 2026 by KimGuo11

The Flange Mounted Differential Pressure Transmitter is based on an intelligent differential pressure transmitter and features a flush-mounted or extended flange. It is suitable for measuring the level, differential pressure, and density of liquids that are prone to crystallization or sedimentation. Equivalent to model EJA210E.

Can be directly installed on tanks or pipelines. It is used for measuring high-temperature, easily solidifying or crystallizing, suspended solids-containing, highly viscous, highly corrosive, or other media that require hygienic conditions and cannot be contaminated.

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

More DP Transmitters

Sino-Inst Flange Mounted Differential Pressure Transmitter uses advanced microprocessing technology and digital communication technology. It outputs a 4~20 mA DC signal corresponding to the measured differential pressure. It can also be configured with the HART protocol.

Flange Mounted Differential Pressure Transmitter Features:

Used to measure the differential pressure of corrosive and non-corrosive gases, steam and liquids;
Using a stainless steel diaphragm;
Applicable to various hazardous places;
Output linear DC current proportional to the differential pressure value;
Provide various isolation diaphragms to meet special applications, such as liquid level measurement, corrosive media;
High measurement accuracy, 0.1%FS, 0.5%FS;
Extensible measurement range;
Aluminum and stainless steel housing;
With intrinsically safe explosion-proof and isolated explosion-proof capabilities. Can be used in various hazardous places.

Extended reading: Smart Differential Pressure Transmitter

Specification of Flange Mounted Differential Pressure Transmitter

Model	Transmitter type
SMT3151LT	Flange Mounted Differential Pressure Transmitter
Code	Scale range
4	0-4.0～40kPa(0-400～4000mmH2O)
5	0-20～200kPa(0-2～20mH2O)
6	0-70～700kPa(0-7～70mH2O)
7	0-210～2100kPa(0-21～mH2O)
Code	Output form
E	Linear output 4-20mAdc
SF	Linear output 4-20mAdc +HART signal
F	MODBUS-485 signal
Code	Flange standard (high pressure side flange)
A	ANSI American Standard (HG20615)
D	DIN European Standard (HG20592)
Code	Process connection size
ANSI American Standard (HG20615)	DIN European Standard (HG20592)
25	1”	DN25
40	1.5”	DN40
50	2”	DN50
80	3”	DN80
0	4”	DN100
Code	Process connection pressure rating
ANSI American Standard (HG20615)	DIN European Standard (HG20592)
A	150LB	PN16/25
B	300LB	PN40
C	600LB	PN64
D	900LB	PN100
Code	High pressure side diaphragm
A	316 stainless steel
B	Hastelloy C
C	Monel
D	Tantalum
E	Titanium
F	Special Requirements
Code	High pressure side insert tube length	High pressure side insert cylinder material
A	0 mm	None
B	50 mm	316L Stainless steel
C	150 mm	316L Stainless steel
D	200 mm	316L Stainless steel
Code	High pressure side filling fluid
D	General silicone oil （-40~104℃）
F	High temperature silicone oil （-40~304℃）
S	Inert liquid （-40~204℃）
Low pressure side structural material	Flange (joint)	Exhaust/drain valve	Isolation diaphragm	Sensor filling fluid
22	316 Stainless steel	316 Stainless steel	316 Stainless steel	Silicone oil
23	316 Stainless steel	316 Stainless steel	Hastelloy C	Silicone oil
24	316 Stainless steel	316 Stainless steel	Monel	Silicone oil
25	316 Stainless steel	316 Stainless steel	Tantalum	Silicone oil
33	Hastelloy C	Hastelloy C	Hastelloy C	Silicone oil
35	Hastelloy C	Hastelloy C	Tantalum	Silicone oil
44	Monel	Monel	Monel	Silicone oil
S2	A remote transmission device (with a remote transmission device on the low-voltage side)
Code	Shell material	Conduit inlet dimensions
A	Low copper aluminum alloy polyurethane coating	M20×1.5
B	Low copper aluminum alloy polyurethane coating	1/2-14 NPT
C	Stainless steel	M20×1.5
D	Stainless steel	1/2-14 NPT
Code	Optional parts
M1	0～100% Linear indicator head
M4	LCD multi – power digital display head
D1	Side discharge valve at the top (only for the low pressure side of the low pressure side without remote transmission)
D2	Side discharge valve at the top (only for the low pressure side of the low pressure side without remote transmission)
Da	Flameproof ExdIIBT5Gb;(explosion-proof certificate no. : CE16.1163)
Fa	Intrinsically safe ExiaIICT4 / T5 / T6Ga;(explosion-proof certificate no. : CE15.2354X)
CX	With corresponding 316 flushing ring

Extended Reading:

Applications

The Flange Mounted Differential Pressure Transmitter can accurately measure the liquid level and density of various containers. There are two types of flat flange and insert flange. It is suitable for high-viscosity medium or suspended liquid measurement.

Viscous medium at high temperature;
Easily crystallized medium;
Precipitation medium with solid particles or suspended matter;
Strongly corrosive or highly toxic medium;
It can eliminate the leakage of the pressure guiding pipe and pollute the surrounding environment. It can avoid the instability of the measurement signal when the isolation liquid is used. The tedious work of frequently supplementing the isolation liquid is required;
Continuously and accurately measure the interface and density;
The remote transmission device can avoid the mixing of different instantaneous media so that the measurement results truly reflect the actual situation of process changes;
Places with high sanitation requirements;
Such as in the production of food, beverage, and pharmaceutical industries. Not only the transmitter contacting the media parts meet hygienic standards, but also should be easy to wash. To prevent cross-contamination of different batches of media.

Pressure level transmitter is good for level measurement. Most of the time, we use submersible hydrostatic level sensor for the level measurement. When you can not use the probe of hydrostatic level sensor, you can try with this pressure level transmitter. Pressure level transmitter, is one type of DP level measure instrument, with the diaphragm.

More

The SMT3151LT differential pressure level transmitter is a new type of differential pressure transmitter manufactured using advanced technology and equipment. Equipped with dual remote seals, it can be used for continuous measurement of liquid level, flow rate, and differential pressure. It offers particular advantages in applications involving sealed storage tanks.

More

Flange Mounted Differential Pressure Transmitter Working principle

1. Headcover; 2. Head; 3. Metal bulkhead; 4. Shell; 5. Nameplate label; 6. Explosion-proof joint; 7. Terminal block; 8. Head cover; 9. Drain valve; 10. Bolt; 11. Clamp; 12. Sensor seal; 13. Sensor; 14. Nut; 15. Welded pipe joint assembly

Differential pressure transmitters utilize the pressure difference generated by the liquid’s own gravity to measure the liquid level in a container.

Flange-mounted differential pressure transmitters are directly installed on pre-existing flanges at the bottom of pipes or containers, contacting the liquid through an isolation diaphragm.

When the diaphragm is subjected to pressure, it undergoes slight deformation. The displacement of the diaphragm changes with the differential pressure. This change is precisely converted by an amplification circuit into a 4-20mA DC two-wire current, voltage, or digital HART output signal, thus achieving pressure measurement and transmission.

The high-pressure side measuring tube is always filled with the medium, maintaining constant pressure. The low-pressure side measuring tube forms a communicating vessel with the container, and its pressure changes linearly with the liquid level in the container.

Let △P be the differential pressure signal received by the transmitter, P0 be the internal pressure of the container, P+ be the pressure on the positive pressure side of the transmitter, and P- be the pressure on the negative pressure side of the transmitter. Let ρ be the density of the liquid in the container, g be the acceleration due to gravity, h1 be the height from the process zero point to the upper pressure tap of the container, h2 be the process liquid level in the container, and h be the height from the transmitter to the process liquid level zero point.

Then:
P+ = P0 + ρgh1 + ρgh
P- = P0 + ρgh2 + ρgh
△P = P+ – P- = ρgh1 – ρgh2

When the liquid level changes from h2=0 to h2=h1, the differential pressure measured by the transmitter changes from its maximum value to △P=0. By configuring the transmitter, the output current changes from 4mA to 20mA.

Single flange vs Double flanges differential pressure level transmitter

In principle: all are differential pressure transmitters + flange guide pressure;
In terms of structure: the single flange liquid zd position transmitter has only one flange diaphragm box connected to the high pressure side, and the low pressure side to the atmosphere. The double flange liquid level transmitter is high and low pressure side through oil-filled capillary It is connected with two flanged membrane return boxes. There is also a capillary. The single flange transmitter is installed below, and a capillary is drawn from the low pressure side of the single flange transmitter to the upper flange membrane box.
In terms of engineering applications: all can only measure the liquid level of fixed density. The single-flange transmitter can only be used for the liquid level of atmospheric equipment that can be imagined with the atmosphere. The double-flange transmitter can be suitable. Answer: Use closed equipment kettle to measure liquid level;
From the economical point of view, the double flange is definitely more expensive than the single flange. After all, there is one more flange capsule and capillary.

**Piezoresistive Differential Pressure Transmitter**
Piezoresistive Differential Pressure Transmitter utilizes the piezoresistive effect of semiconductor silicon materials. Realize accurate measurement of differential pressure.

**Smart Differential Pressure Transmitter**
Smart Differential Pressure Transmitter measures industrial differential pressure. Can Works with diaphragm seals, capillary, HART. Outputs standard signals (such as 4 ~ 20mA, 0 ~ 5V).

**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.

**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.

SMT3151DP Smart Differential Pressure Transmitter

Posted on January 26, 2026 by KimGuo11

The SMT3151DP Smart Differential Pressure Transmitter utilizes a single-crystal silicon sensor with German MEMS technology, offering higher measurement accuracy. It outputs standard signals (e.g., 4-20mA, 0-5V) and can also be configured with RS485 Modbus RTU or HART protocols.

The single-crystal silicon sensor core features a dual-beam suspension design, significantly improving accuracy and resistance to unilateral and bilateral overload. A built-in intelligent signal processing module achieves perfect integration of static pressure and temperature compensation. This enhances measurement accuracy and long-term stability across a wide range of static pressure and temperature variations.

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

More DP Transmitters

Features
Specifications
Datasheet
Order Guide

Features

Blue and white custom housing smart differential pressure transmitter

Output signal 4-20mA output+RS485/HART communication;
0.075%FS high accuracy, millisecond-level ultra-fast response;
Built-in three-button quick operation for on-site adjustment;
Self-diagnosis capability;
Range coverage is 0-0.1KPa~41.0MPa;
Good stability, high precision, adjustable damping, strong resistance to one-way overload.
Explosion-proof housing structure.
LCD display;
IP67 protection rating;
Intelligent static pressure compensation and temperature compensation protect the transmitter from the effects of temperature, static pressure, and overpressure, controlling the overall measurement error at the site within the specified parameters;
High static pressure resistance, up to 40MPa;

Extended reading: How to calibrate HART pressure transmitters

Technical Specifications

Measurement Range	1KPa, 4KPa, 40KPa, 100KPa, 400KPa, 4MPa, 40MPa
Single-Side Overpressure	16MPa
Dual-Side Static Pressure	16MPa 25MPa 40MPa
Measurement Accuracy	±0.075%, ±0.1%, ±0.5% (including linearity, hysteresis, and repeatability from zero)
Measured Medium	Gas, Liquid, Steam
Output Signal	4~20mA DC+RS485/HART protocol
Power Supply	General 10.5~45VDC, intrinsically safe explosion-proof 10.5-26VDC
Power Line Spacing	15cm and above (avoid parallel wiring)
Saturation Current	Upper limit 20.8mA, lower limit 3.8mA
Alarm Current	Upper limit 22.8mA, lower limit 3.6mA (mode adjustable)
Adjustment Function	Zero and full-scale points can be adjusted locally via the three buttons on the top of the casing or remotely via configuration software
Zero Shift	Can be shifted within the range of -20% to +20% of the maximum range
Output Method	Linear output Square root output (can be remotely adjusted via configuration software)
Operating Temperature	-40~85℃
Measured Medium Temperature:	-40℃~120℃ (High temperature customizable)
Diaphragm Material	316L stainless steel/Hastelloy alloy/Tantalum diaphragm/Gold-plated diaphragm
Position Effect	Approximately 200Pa between horizontal and vertical positions
Response Time	10ms
Static Pressure Effect	< 0.05%FS/10MPa
Overpressure Effect	< 0.05%FS/10MPa
Stability	≤0.03%FS/year
Power Supply Effect	< 0.005%FS/V
Explosion-Proof Rating:	Exd Ⅱ CT6 Gb, Exia Ⅱ CT6 Ga
Enclosure Protection Rating:	IP67

SMART Differential Pressure Transmitter Datasheet

SM3151DP-Differential-Pressure-Transmitter Download

Order Guide

Use object: liquid, gas, or steam

Model	Transmitter type
DP	Pressure transmitter
HP	Absolute pressure transmitter
Code	Scale range
2	0-0.10～3.5kPa(0-10～350mmH2O)
3	0-0.8～8.0kPa(0-80～800mmH2O)
4	0-4.0～40kPa(0-400～4000mmH2O)
5	0-20～200kPa(0-2000～20000mmH2O)
6	0-70～700kPa(0-0.7～7kgf/cm2)
7	0-210～2100kPa(0-2.1～21kgf/cm2)
8	0-700～7000kPa(0-7.0～70kgf/cm2)
9	0-2.1～21MPa(0-21～210kgf/cm2)
0	0-4.1～41MPa(0-41～4100kgf/cm2)
Code	Output form
E	Linear output 4-20mAdc
SF	Linear/square root output 4-20mAdc +HART signal,，Full function buttons on site
F	MODBUS-485 signal

Structural materials	Flange connector	Exhaust/Drain valve	Isolation diaphragm	Filling liquid
22	316 Stainless steel	316 Stainless steel	316 Stainless steel	Silicone oil
23	316 Stainless steel	316 Stainless steel	Hastelloy C	Silicone oil
24	316 Stainless steel	316 Stainless steel	Monel	Silicone oil
25	316 Stainless steel	316 Stainless steel	Tantalum	Silicone oil
33	Hastelloy C	Hastelloy C	Hastelloy C	Silicone oil
35	Hastelloy C	Hastelloy C	Tantalum	Silicone oil
44	Monel	Monel	Monel	Silicone oil
Code	Shell material	Conduit inlet dimensions
A	Low copper aluminum alloy polyurethane coating	M20×1.5
B	Low copper aluminum alloy polyurethane coating	1/2-14 NPT
C	Stainless steel	M20×1.5
D	Stainless steel	1/2-14 NPT

Code	Pressure connection
L1	1/4NPT-18 Internal thread（excluding waist joint standard）
L2	1/2NPT-14 Internal thread
L3	M20×1.5 External thread
Code	Optional parts
M4	LCD multi – power digital display head
B1	Pipe bending bracket
B2	Plate bending bracket
B3	Pipe mounting bracket
C02	M20×1.5 nut and Φ 14 pressure short tube
C12	1/2NPT-14 external thread and Φ14 pressure short tube
C22	1/4NPT-18 external thread and Φ14 pressure short tube
C32	1/4NPT-18 to M20×1.5 external thread
C42	1/2NPT-14 to M20×1.5 external thread
C43	1/2NPT-14 to 1/4NPT-18 internal thread
C44	1/2NPT-14 to 1/2NPT-14 external thread
C45	1/2NPT-14 to G1/2 external thread
D1	The side discharge valve is on the upper part
D2	The side discharge valve is on the upper part
X1	Oil ban
Da	Flameproof ExdIIBT5Gb;(explosion-proof certificate no. : CE16.1163)
Fa	Intrinsically safe ExiaIICT4/T5/T6Ga;(explosion-proof certificate no. : CE15.2354X)

Working principle of SMART differential pressure transmitter

The intelligent differential pressure transmitter uses a single-crystal silicon piezoresistive sensor as its core component. When pressure is applied to the sensor, the resistance of the single-crystal silicon changes, which is converted into an electrical signal by the circuit, and then digitally processed to output a standard signal (such as 4-20mA or a digital signal).

Its intelligent feature lies in its built-in microprocessor, which can perform temperature compensation, linear correction, and fault diagnosis, ensuring high measurement accuracy and stability.

The SMT3151DP intelligent differential pressure transmitter integrates differential pressure measurement, display, and signal output functions. This intelligent differential pressure transmitter is used to measure the level, density, flow rate, and pressure of liquids, gases, or vapors.

Smart Differential Pressure Transmitter Applications

SMT3151DP smart differential pressure transmitter is suitable for applications like:

Flow measurement;
- The differential pressure transmitter is combined with the throttling device (like the orifice plate). To convert the flow rate according to the differential pressure value, generated before and after the throttling device.
Level monitoring;
- Measuring the height of the liquid by the pressure difference, generated by the gravity of the liquid itself.
Steam measurement;
Filter or pump differential pressure;
For Monitoring Hydronic HVAC Systems.
Critical process monitoring.

https://www.drurylandetheatre.com/wp-content/uploads/2019/03/SMT3151DP-smart-differential-pressure-transmitters-manufacturer.mp4?_=1

Generally used in liquid, gas or steam differential pressure, flow measurement. The medium temperature is not too high, corrosion is not strong, viscosity is not high, not easy to crystallize and other environments.

If the working static pressure exceeds 16MPa, a high static differential pressure transmitter should be selected.

FAQ

Help Center

Smart transmitters work on the function of microprocessors for signal transmission.

Smart pressure transmitter consists of two parts: smart sensor and smart electronic board.

The intelligent sensor part includes: capacitive sensor, measuring diaphragm detection circuit, temperature sensor and temperature compensation circuit.

The part of the intelligent electronic board includes: a microcomputer controller and peripheral circuits. It completes the conversion of the pressure signal to 4-20mA dc.

Extended Reading: Digital Pressure Sensor-RS485

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 pressure transmitter:

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

Extended reading: Silicon Pressure Sensor

Simply put, a differential pressure transmitter is a device that measures two opposing pressures in a pipe or vessel. Differential Pressure (DP) transmitters measure the difference between two pressures. They use a reference point called the low-side pressure and compare it to the high-side pressure. Ports in the instrument are marked high-side and low-side. The DP reading can be either negative or positive depending on whether the low-side or high-side is the larger value. A DP transmitter can be used as a gauge pressure transmitter if the low-side is left open to the atmosphere.

Extended reading: Featured Diaphragm Seal Pressure Transmitters

The most common and useful industrial pressure measuring instrument is the differential pressure transmitter. This equipment will sense the difference in pressure between two ports and produce an output signal with reference to a calibrated pressure range.

The differential pressure transmitter can be used in combination with other accessories and can be used to measure liquid level and flow.

Differential pressure transmitters and pressure transmitters have many similarities. It can be mixed and used most of the time. As long as it is within the range of the differential pressure transmitter, it can measure not only positive pressure but also negative pressure. When measuring positive pressure, the negative port is open to atmosphere, and when measuring negative pressure, the positive port is open to atmosphere.

Differential pressure transmitters can also measure flow, pipeline pressure difference, tank liquid level, bubble water level, dust, or medium that is easy to crystallize and viscous and fluidity is not good.

DP Level Transmitter for Tank Level Measurement

Posted on January 16, 2026 by KimGuo11

The DP level transmitter works on the principle that the hydrostatic pressure difference of a liquid is directly proportional to the liquid level height. It calculates the liquid level by measuring the pressure difference of the medium inside the container and outputs a standard electrical signal. The dual-flange capillary structure provides mechanical and thermal isolation, allowing it to handle complex corrosive and high-temperature media in various industrial processes and tank level monitoring applications.

Sino-Inst offers a variety of DP Level Transmitters for industrial pressure measurement. Connection with diaphragm seals. If you have any questions, please contact our sales engineers.

More DP Transmitters

Features

Exd II CT6 Gb/ Exia II CT6 Ga, suitable for direct use in hazardous areas and outdoors;
All sensor components are made of 316L stainless steel;
316 stainless steel diaphragm, convenient installation with movable flange;
6 diaphragm materials available: 316L diaphragm, HC276 diaphragm, tantalum diaphragm, 316L fully coated diaphragm, gold-plated diaphragm, PTFE diaphragm, etc., customizable;
High-precision configuration, optional 0.1%FS, 0.075%FS;
Extremely high anti-interference and stability;
275-point temperature, pressure, and current compensation;
LED LCD display, 0-100% percentage display, and real-time liquid level value display;
Output: 4-20mA + HART/RS485;
Nitrogen pressurized base, superior sealing performance, nitrogen pressurization prevents leakage.

Specifications of DP level transmitter

Measuring Medium:	Gases, Vapors, Liquids
Measuring Range	-100kPa…0~6kPa…7MPa
Accuracy:	±0.075%, ±0.1%, ±0.2% (including linearity, hysteresis, and repeatability from zero point)
Stability:	±0.2%/year
Power Supply:	10–36V DC (24V DC recommended)
Reference Accuracy for Range Adjustment:	If TD > 10 (TD = Maximum range / Adjustable range), then: ±(0.075 × TD)%
Ambient Temperature:	-40℃ ~ 85℃
Measuring Medium Temperature:	-40℃ ~ 400℃ (higher/lower temperatures can be customized)
Storage Temperature:	-40℃ ~ 85℃
Display:	LCD, OLED
Display Module Temperature:	-20℃ ~ 70℃ (LCD), -40℃ ~ 80℃ (OLED)
Measuring Diaphragm:	316L, Hastelloy C, Tantalum, Titanium, Nickel, Monel, Duplex Stainless Steel, PFA, Gold Plating
Process Connection:	Stainless steel 316L, 304
Filling Fluid:	Silicone oil, fluorinated oil, etc.
Transmitter Housing:	Aluminum alloy material, epoxy resin coating on the surface
Housing Seal:	Nitrile rubber
Nameplate:	Stainless steel 304
Enclosure Protection Rating:	IP67
Explosion Protection Rating:	Exd Ⅱ CT6 Gb, Exia Ⅱ CT6 Ga
Measuring Range Limits	Within the upper and lower limits of the range, it can be set arbitrarily, as long as the calibrated range ≥ the set range. It is recommended to choose a range with the lowest possible range ratio to optimize performance.
Influence of Mounting Position	Changes in installation position will cause zero point influence, which can be corrected by zero adjustment; there is no range influence.
Output	Two-wire 4-20mA, compliant with NAMUR NE43 standard, superimposed digital signal (Hart protocol)
Output Signal Limits	Imin (minimum): 3.9mA Imax (maximum) = 21.0mA
Alarm Current	Low alarm mode (minimum): 3.9mA High alarm mode (maximum): 21mA (user pre-settable)
Default Alarm Current Setting	High alarm mode
Fault Warning	If the sensor or circuit fails, the automatic diagnostic function automatically outputs 22.0mA
Response Time	Amplifier component damping constant is 0.1s; sensor time constant is 0.1–1.6s, depending on the range and range ratio. Additional adjustable time constant: 0–100s
Warm-up Time	<15s

There are 5 types of remote transmission devices for remote differential pressure transmitters:

Flat type
Thread mounting type
Flange mounting type
Extended Diaphragm Seal
Wet legs/Dry legs

SM3151LT liquid level pressure-differential pressure transmitter Download

Applications of DP level transmitters

The differential pressure liquid level transmitter can prevent the measured medium from directly contacting the sensor diaphragm of the transmitter. It is suitable for the following situations:

When the measured medium has a corrosive effect on the transmitter connector and sensitive components;
When the high temperature measured medium needs to be isolated from the transmitter;
When there are solid suspended solids or high viscosity in the measured medium, it is easy to block the transmitter connector and the pressure chamber;
When the measured medium is easily cured or crystallized by the pressure tube;
When changing the measured medium needs to be rinsed and not to be mixed;
Hygienic conditions must be maintained to prevent pollution. .
Changing the measured medium requires strict purification of the measuring head
Suspended liquid or high viscosity medium
Measurement of sealed pressure vessel.

DP level transmitter working principle

The differential pressure level transmitter is an instrument that uses the pressure generated by the liquid column to measure the height of the liquid level. When the liquid level changes, the pressure received by the diaphragm at the high-pressure side flange will change accordingly. The differential pressure value calculated by the transmitter will also change accordingly. There is a linear relationship between them.

Normally, the high-pressure side (H side) and the low-pressure side (L side) cannot be installed reversely. Generally, the H side is installed at the lower part of the equipment, and the L side is installed at the higher part of the equipment. Before installation, the flange surface of the equipment should be cleaned and the gasket should not be placed off-center to prevent the diaphragm from being punctured or deformed, causing distortion of the transmitter.

SMT 3151 Differential Pressure Level Measurement

Differential pressure transmitter level measurement calculation

When using a Differential pressure (DP) level transmitter to measure the liquid level as shown in the figure below.

The measured liquid density in the figure is ρ.
The working medium density in the capillary of the double flange differential pressure transmitter is ρ0.
The measuring range of the measured liquid level is H.
The center distance of the sampling tube of the measured liquid level is h.

It can be seen from the figure that the maximum measurement range of the liquid level △ P = P + — P- = H × ρ × g – h × ρ0 × g.

It can be seen from the formula that the dual-flange differential pressure transmitter should perform negative migration. The migration amount S is h × ρ0 × g. And the installation position of the double flange differential pressure transmitter has no effect on the migration amount and the measurement result.

The dual-flange differential pressure transmitter requires negative migration.

When the measured liquid level is 0, the pressure difference between the positive and negative measurement chambers of the remote differential pressure transmitter is the largest. The output current of the double flange differential pressure transmitter is 4mA.

As the measured liquid level rises, the pressure difference between the positive and negative measurement chambers of the transmitter gradually decreases.

When the measured liquid level rises to the highest Hmax. The pressure difference between the positive and negative measurement chambers of the transmitter is the smallest. The output current of the double flange differential pressure transmitter is 20mA.

DP level transmitter calibration

The differential pressure liquid level transmitter has been calibrated in the range, accuracy, linearity and other parameters according to customer requirements at the factory. And mark the range, accuracy, etc. on the nameplate of the differential pressure liquid level transmitter. As long as the density and other parameters of the measured medium meet the requirements of the nameplate, generally no adjustment is required.

If the customer needs to adjust the range or zero position, please adjust according to the following methods. Assuming that the range of the differential pressure liquid level transmitter is 0 ~ 10 meters:

Unscrew the protective cover of the differential pressure liquid level transmitter. It can be adjusted by connecting an external standard 24VDC power supply and ammeter (requires accuracy of 0.2% or above).
When there is no liquid in the differential pressure liquid level transmitter. Adjust the zero potentiometers. Make it output a current of 4mA.
Pressurize the differential pressure liquid level transmitter to full scale (10 meters). Adjust the full-scale resistor. Make it output a current of 20mA.
Repeat the above steps two or three times until the signal is normal.
Please input 25%, 50%, and 75% signals to check the error of the differential pressure liquid level transmitter.
For non-aqueous media. Differential pressure level transmitters are calibrated with water. It should be converted according to the pressure generated by the actual density of the medium. For example, when the medium density is 1.3, the 1.3m water level should be used to calibrate the 1m range.
After adjustment, tighten the protective cover.
The verification cycle of the differential pressure liquid level transmitter is once a year.
HART intelligent differential pressure liquid level transmitter of Sino-Inst instrument can be selected. It is convenient to adjust the range of the differential pressure liquid level transmitter.

Extended reading: How to calibrate HART pressure transmitters

Professional Partner for Measure & Control

Monthly Archives: January 2026

Diaphragm Seal Pressure Transmitter － Flush Flanged

Features of Diaphragm Seal Pressure Transmitter

Specifications of Diaphragm Seal Pressure Transmitter

Applications

Diaphragm flange material selection

What is a diaphragm seal pressure transmitter?

What is a diaphragm seal?

What is a remote seal?

More Pressure Measurement Solutions

FAQ

Flange Mounted Differential Pressure Transmitter

Flange Mounted Differential Pressure Transmitter Features:

Specification of Flange Mounted Differential Pressure Transmitter

Applications

Flange Mounted Differential Pressure Transmitter Working principle

Single flange vs Double flanges differential pressure level transmitter

More Pressure and Level Measurement Solutions

SMT3151DP Smart Differential Pressure Transmitter

Features

Technical Specifications

SMART Differential Pressure Transmitter Datasheet

Order Guide

Working principle of SMART differential pressure transmitter

Smart Differential Pressure Transmitter Applications

FAQ

More Featured Pressure Measurement Solutions

DP Level Transmitter for Tank Level Measurement

Features

Specifications of DP level transmitter

Applications of DP level transmitters

DP level transmitter working principle

Differential pressure transmitter level measurement calculation

DP level transmitter calibration

More Featured DP Transmitters

More Pressure and Level Measurement Solutions

Features of Diaphragm Seal Pressure Transmitter

Specifications of Diaphragm Seal Pressure Transmitter

Applications

Diaphragm flange material selection

What is a diaphragm seal pressure transmitter?

What is a diaphragm seal?

What is a remote seal?

More Pressure Measurement Solutions

FAQ

What is a pressure level transmitter?

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

What is the use of diaphragm seal in pressure transmitter?

When do I need to use a diaphragm-sealed pressure transmitter?

Flange Mounted Differential Pressure Transmitter Features:

Specification of Flange Mounted Differential Pressure Transmitter

Applications

Flange Mounted Differential Pressure Transmitter Working principle

Single flange vs Double flanges differential pressure level transmitter

More Pressure and Level Measurement Solutions

Features

Technical Specifications

SMART Differential Pressure Transmitter Datasheet

Order Guide

Working principle of SMART differential pressure transmitter

Smart Differential Pressure Transmitter Applications

FAQ

What is a smart pressure transmitter?

What are the types of pressure transmitters?

What is differential pressure transmitter?

What does a differential pressure transmitter do?

When would you use a differential pressure transmitter?

More Featured Pressure Measurement Solutions

Features

Specifications of DP level transmitter

Applications of DP level transmitters

DP level transmitter working principle

Differential pressure transmitter level measurement calculation

DP level transmitter calibration

More Featured DP Transmitters

More Pressure and Level Measurement Solutions