4-20ma Flow Meters

What is 4-20ma Flow Meter?

4-20mA Flow Meters are those flow meters with 4-20mA current signal output function. The signal current of general instruments is 4-20mA. This means that the minimum current is 4mA and the maximum current is 20mA. Our commonly used electromagnetic flowmeters, turbine flowmeters, mass flowmeters, gas flowmeters, etc. all have the function of 4-20mA signal output.

4-20ma Flow Meters

What is a 4-20mA Output?

The signal current of general instruments is 4-20mA, which means that the minimum current is 4mA and the maximum current is 20mA.

The industry generally needs to measure various non-electrical physical quantities. For example, temperature, pressure, speed, angle, etc. They all need to be converted into analog electrical signals before they can be transmitted to the control room or display equipment hundreds of meters away. This device that converts physical quantities into electrical signals is called a transmitter. The most widely used in the industry is to use 4-20mA current to transmit analog quantities.

In the industrial field, to complete signal conditioning and long-term transmission, the following problems will occur:

  1. Since the transmitted signal is a voltage signal, the transmission cable will be interfered by noise;
  2. The distributed resistance of the transmission cable will produce a voltage drop;
  3. How to provide the working voltage of the instrumentation amplifier in the field is also a problem.

In order to solve the above problems and avoid the influence of related noise, we will use current to transmit signals. Because the current is not sensitive to noise.

The 4-20mA current loop uses 4mA to represent the zero signal. Use 20mA to represent the full scale of the signal. The signals lower than 4mA and higher than 20mA are used for various fault alarms.

Why Choose 4-20mA Instead of 0-20mA for the Flowmeter?

Many people will certainly ask: Why choose 4-20mA instead of 0-20mA?
Very simple, if 0 is the smallest, then the open circuit fault will not be detected!

So, why is it 4mA?
During normal operation, the current signal will not be lower than 4mA.
When the transmission cable is broken due to a fault, the loop current drops to zero. 2mA is often used as the disconnection alarm value.
There are two reasons. One reason is to avoid interference. Another reason is that a two-wire system is used at 4-20mA. That is, the two wires are the signal wires. It is also a power cord. And 4mA is to provide the static working current of the circuit to the sensor.

Extended Reading: Mechanical flow meter for diesel

How Does This 4-20mA Control Loop Work?

4-20mA constitutes the basic elements:

  • 24V power supply
  • The transmitter controls the 4-20mA signal to change in proportion to the process variable
  • The indicator converts the 4-20mA signal into the corresponding process variable
  • Indicator or controller I/O input resistance 250Ω shunt generates 1-5V input signal (Ohm’s law: voltage = current * resistance, 4-20 mA X 250 ohms = 1-5V)


  1. They convert the temperature signal of the thermocouple or thermal resistance sensor into a 4-20mA signal and then output;
  2. The controller then translates 4-20mA into a specific temperature value;
  3. Based on this temperature value. The control loop realizes the control of the process terminal control element.

Similarly, the pressure transmitter is in the control loop. Usually used to measure the pressure value of the process medium:

1) The sensor senses pressure. The transmitter converts the signal into 4-20mA signal;
2) The controller then reversely translates the 4-20mA signal into a pressure value;
3) The controller is based on the pressure value. Send instructions to the valve. Control valve opening to realize safety valve control. Ensure that the container does not generate dangerous pressure.

Extended reading: Orifice Plate Flow Meter

Water Flow Meter 4-20ma Output

A Digital Water flow meter is a flow meter that can display the water flow rate, and have the output for the flow rate. Like 4-20mA output, HART, RS 485, and so on. Digital Water Flow Meter is also called Electronic Water Flow Meter. Digital Water Flow Meter is widely used in industrial water and household water measurement. Most of the Sino-Inst flow meters are digital water flow meters. Like the electromagnetic flowmeter, Portable ultrasonic flow meter, Turbine flow meter…..

No matter which WaterFlow Meters you choose. The signal output by WaterFlow Meters, such as 4-20mA. The flow signal can be connected to a paperless recorder. Carry out multi-channel flow signal monitoring.

Read More About: Paperless Recorder Working Principle

Flow Meter with Analog Output

The analog flow meter is a flowmeter with the analog output signal. Analog output is a common function of flow meters. The analog signal is mainly used to output the flow signal to the next control system.

The analog signal refers to the continuous signal of the information parameter in a given range. The characteristic quantity of the information of the analog signal can be transformed into an arbitrary numerical signal in an instant. In the process of transmitting analog signals, the information signals need to be converted into electric wave signals, which are then transmitted through wired or wireless methods.

Analog signal: poor confidentiality, weak anti-interference ability.

Digital signal: strong anti-interference ability and good communication confidentiality.

Read more about Analog Flow Meters.

Turbine Digital Flow Meter

Turbine flow meters are velocity flow meters, also called impeller flow meters. Can be used to measure the instantaneous flow and cumulative flow of liquids and gases.

Turbine flowmeters are widely used in flow measurement: petroleum, organic liquids, inorganic liquids, liquefied gas, natural gas, coal gas, and cryogenic fluids. Turbine flowmeter signals can be divided into pulse signals or current signals (4-20mA). It is suitable for use with secondary display, PLC, DCS, and other computer control systems.

Turbine Flow Meter reference price: USD 200-1700/pc.

4-20ma Air Flow Meter

A digital air flow meter refers to a flow meter that can accurately measure air or compressed air inline. Industrial Digital air flow meters can be divided into mass flow meters or volume flow meters.

Read more about Digital air flow meters.


Help Center

There are many types of flow meters on the market. There are vortex flowmeters, target flowmeters, electromagnetic flowmeters, thermal gas mass flowmeters, etc. Different industries have different choices of flow meters.

Sewage treatment

Sewage is divided into industrial sewage and domestic sewage
Sewage is a solid-liquid mixed fluid. Industrial wastewater is corrosive due to its complex composition. The measurement is difficult. Most meters cannot make measurements.
The main application instruments for sewage treatment are electromagnetic flow and a small number of open channel flowmeters. There are a variety of linings and electrode materials for electromagnetic flowmeters to choose from. High precision and corrosion resistance, it is the main force for measuring the flow of industrial sewage and domestic sewage.

Chemical Industry

The chemical industry is the most widely used industry for flow meters. Almost all types of flow meters are used in the chemical industry.

  1. When measuring air, steam and other gases. The use of vortex flowmeters is the most common. There are also V cones, orifice plates, etc.;
  2. When measuring viscous oily media. Volumetric meters have good application and measurement effects;
  3. Orifice plate and V cone are the most used for ammonia and liquefied gas measurement;
  4. Measure all kinds of light oil. Such as diesel, gasoline, non-corrosive chemical solvents, etc. Turbine flowmeter is the first choice;
  5. Metal rotor flowmeters are also widely used in the chemical industry. Mainly used in the measurement of small flow and process control;
  6. In the measurement of chemical wastewater, electromagnetic flowmeter is currently the only choice.

Food and pharmaceutical industry

Requirements for flow meters in the food and medicine industry:

  1. High measurement accuracy requirements;
  2. The watch body is made of stainless steel, anti-corrosion and anti-rust;
  3. The quick-loading structure is convenient for cleaning and maintenance.
  4. Sanitary electromagnetic flowmeter
    Mainly measure clean water, fruit juice, emulsion, liquid medicine, etc.
    Usually the clamp type connection is convenient for disassembly and cleaning; the material is stainless steel, and the lining is high temperature resistant FEP, PFA, etc. Because there is no dead angle in the structure, it is convenient for high temperature disinfection, and it is the most widely used.
  5. Vortex flowmeter
    Mainly measure steam, water, beer, edible oil, etc.
    The material is stainless steel, and the flange clamp is used, which is convenient to use. The disadvantage is that the accuracy is slightly worse than that of electromagnetic flowmeters.
  6. Turbine flowmeter
    At present, some manufacturers have introduced sanitary turbine flowmeters, most of which are flange-mounted, but also have a clamp-type structure. The measurement accuracy is equivalent to that of electromagnetics. Because of oil prohibition, sealed bearings must be used, and they must be replaced regularly.

Extended reading: 2 inch Water Flow Meter

For different working principle, We offer different types of flow meters, like:

  • Differential Pressure Flow Meters
  • Orifice Plate
  • Venturi Tube
  • Flow Nozzles
  • The Sonic Nozzle – Critical (Choked) Flow Nozzle
  • Calorimetric Flowmeter
  • Ultrasonic Doppler Flowmeter
  • Positive Displacement Flowmeter
  • Variable Area Flowmeter or Rotameter
  • Velocity Flowmeters
  • Pitot Tubes
  • Electromagnetic Flowmeter
  • Turbine Flowmeter
  • Vortex Flow Meter
  • Thermal Flowmeter
  • Coriolis Flowmeter
  • Mass Flowmeters
  • Open Channel Flowmeters

The flowmeter can be used to measure liquid, gas (vapor), and solid (impulse flowmeter). To meet the needs of process control and metering delivery.

Extended reading: Vortex Steam Flow Meter

A flow meter (or flow sensor) is an instrument used to measure the linear, nonlinear, mass or volumetric flow rate of a liquid or a gas. When choosing flow meters, one should consider such intangible factors as familiarity of plant personnel, their experience with calibration and maintenance, spare parts availability, and mean time between failure history, etc., at the particular plant site.

It is also recommended that the cost of the installation be computed, only after taking these steps different sensors include dial, in-line, ultrasonic, orifice plate, totalizing meters, variable area, venturi, or with switch output. The different designs of the flow meters have a variety of applications.

Read more about Digital flow meter working principle

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Looking for 4-20ma flow meters? The flow meter is a fast, accurate, and reliable permanent linear motion. In Sino-Inst, you can also find other good deals on measurement and analysis instruments and tools! Keep an eye out for promotions and deals, so you get a big saving of 4 20ma flow meters. You can shop for 4 20ma flow meters at low prices.

Extended reading: How to convert a 4-20mA to 0-10V /1-5V signal?

There is a wide variety of 4-20ma flow meter items you can buy, such as turbine water flow meters, ultrasonic flowmeters. Common materials used for 4 20ma flow meters are stainless steel and carbon steel.

Sino-Inst offers over 50 4-20ma flow meters for flow measurement. About 50% of these are differential pressure flow meters, 40% are the liquid flow sensor, and 20% are Ultrasonic Level Transmitter and mass flow meters.

A wide variety of flow meters options are available to you, such as free samples, paid samples.

Sino-Inst is a globally recognized supplier and manufacturer of flow measurement instrumentation, located in China.

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Ultrasonic Flow Detectors

Ultrasonic flow detectors are an important part of ultrasonic flow meters. Ultrasonic flow detectors are also called ultrasonic transducers. Ultrasonic flow detectors measure the volumetric flow of liquid within closed conduits. Ultrasonic flow meters use transit-time differences for measuring flow rates inside pipes from the outside using electronics and digital signal processing technology.

Featured Ultrasonic Flow Meters Clamp-on

Features of Ultrasonic Flow Detectors

  • Built-in magnet, which can be directly attached to the pipe;
  • Can be used in strong electromagnetic interference occasions;
  • After the junction box is filled with glue, the protection level is IP68;
  • Complete specifications, divided into three models: large, medium, and small;
  • Measuring pipe diameter range DN15-DN6000;
  • The temperature range is -30~90°℃; -30~160℃
  • The measurement liquid is relatively wide, including water, seawater, slurry or oil, acid and alkali, and other homogeneous liquids;
  • Non-contact measurement method, lightweight and small size;
  • The installation of the clamp-on ultrasonic flowmeter probe is simple. And different sizes of probes can detect pipes of different pipe diameters. Under the condition of ensuring accuracy, the clamp-on ultrasonic flowmeter can measure the smallest pipe of DN15. The largest can measure DN6000 pipeline;
  • The external clamp ultrasonic flowmeter does not need to destroy the pipeline in the process of measuring the flow rate. The probe can directly touch the straight pipe section. No pressure loss. The flow measurement can be performed on the already installed pipe;
  • Suitable for measuring pipes of different materials. Common ones are metal pipes: stainless steel, carbon steel, cast iron, etc., plastic pipes, etc. There are also pipes with better sound-permeable materials.

Optional Ultrasonic Flow Detectors

Types Picture Spec. Model Measurement Range Temperature Dimension
Clamp on
Small Size TS-2 DN15~DN100 -30~90℃ 45×25×32mm
Medium Size TM-1 DN50~DN700 -30~90℃ 64×39×44mm
Large Size TL-1 DN300~DN6000 -30~90℃ 97×54×53mm
High Temperature Clamp on Small Size TS-2-HT DN15~DN100 -30~160℃ 45×25×32mm
Medium Size TM-1-HT DN50~DN700 -30~160℃ 64×39×44mm
Large Size TL-1-HT DN300~DN6000 -30~160℃ 97×54×53mm
Mounting Bracket Clamp on Small Size HS DN15~DN100 -30~90℃ 318×59×85mm
Medium Size HM DN50~DN300 -30~90℃ 568×59×85mm
Extended EB-1 DN300~DN700 -30~90℃ 188×59×49mm
High Temperature Mounting Bracket Clamp on Small Size HS-HT DN15~DN100 -30~160℃ 318×59×110mm
Medium Size HM-HT DN50~DN300 -30~160℃ 568×59×110mm
Extended EB-1-HT DN300~DN700 -30~160℃ 188×59×49mm
MoeldX3-φ6.35X3-φ9.53 X3-φ12.7X3-φ15X3-φ20X3-φ25

Ultrasonic Flow Detectors Working Principle

Ultrasonic Flow Detectors are also called ultrasonic transducers. In fact, it is a piezoelectric ceramic whose frequency is the same as its resonant frequency. It uses the piezoelectric effect of the material to convert electrical energy into mechanical vibration.

Under normal circumstances, ultrasonic waves are first generated by an ultrasonic generator. It is converted into mechanical vibration by the ultrasonic transducer. The ultrasonic wave can be generated by the ultrasonic wave deriving device and the ultrasonic wave receiving device.

Ultrasonic transducers mainly include shell, acoustic window (matching layer), piezoelectric ceramic disc transducer, backing, lead-out cable, receiver, and other parts.

Among them, the piezoelectric ceramic disc transducer plays the same role as a general transducer. It is mainly used to transmit and receive ultrasonic waves, and above the piezoelectric ceramic disc transducer is the receiver. It is mainly composed of lead cables, transducers, metal rings, and rubber washers. Used as an ultrasonic receiver. Receive the Doppler dial-back signal generated outside the frequency band of the piezoelectric ceramic disc transducer.

Ultrasonic transducers are piezoelectric ceramics that resonate at ultrasonic frequencies. The piezoelectric effect of the material converts electrical signals into mechanical vibrations. The ultrasonic transducer is an energy conversion device. Its function is to convert the input electric power into mechanical power (ultrasound) and then transmit it out. , It consumes a small part of its own power.

Types of ultrasonic transducers: can be divided into piezoelectric transducers, sandwich transducers, cylindrical transducers, inverted horn transducers, and so on.


Transit Time Ultrasonic Flow Meter adopts the measurement principle of the time difference method. It uses the ultrasonic wave emitted by the sensor to propagate in the flowing fluid. The sound wave propagation speed in the downstream direction will increase, and the backward direction will decrease. In the same propagation distance, there will be different transmission times. According to the difference between the transmission time and the measured The relationship between fluid velocity measures the fluid velocity.

The flow rate of the fluid is different in different positions in the tube. The flow rate in the center of the tube is faster than the flow rate near the wall of the tube. The flow velocity distribution of the fluid in the pipeline can be represented by the flow velocity cross-sectional distribution diagram.

By setting the flowmeter and considering the cross-sectional distribution of the flow velocity, the average flow velocity can be calculated. Then the volume flow of the fluid can be obtained according to the cross-sectional area of the pipe.

Extended reading: Ultrasonic flow detectors types

V measure fluid velocity
M ultrasonic reflection times
D pipe diameter
θ The angle between the ultrasonic signal and the fluid
T up The time when the downstream sensor transmits the signal to the upstream
T down Time from upstream sensor to downstream
ΔT = T up – T down

Guess You’ll Like: Ultrasonic flow meters types & technical guide

Doppler ultrasonic flowmeter uses the physical principle of Doppler frequency shift to measuring the water flow velocity. Therefore, the Doppler ultrasonic flowmeter is suitable for measuring fluids containing solid particles or air bubbles. Not suitable for measuring pure water.

The scope of use includes:
Natural rivers, artificial rivers, farmland channels, urban sewers, corporate sewage outlets, sewage treatment plants, etc.

The products comply with the SL/T 186-1997 standard.

It is suitable for environments that require continuous and accurate measurement of flow rate and flow rate. It has obvious advantages such as convenient installation and maintenance, high reliability, and high precision.

Ultrasonic flow detectors are also called ultrasonic transducers. Or it is often understood by people as an ultrasonic flow sensor.

Ultrasonic flowmeter is an application of ultrasonic, which measures the flow of liquid by applying the speed difference method.

  • Can do non-contact measurement;
  • No flow obstruction measurement, no pressure loss;
  • It can measure non-conductive liquids, which is a supplement to the electromagnetic flowmeter for unobstructed measurement;
  • Except for the pipe section type with measurement, there is generally no need for actual flow calibration;
  • In principle, it is not limited by pipe diameter, and its cost is basically independent of pipe diameter.

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Sino-Inst, Manufacturer for Ultrasonic Flow Meters. It can measure a single sound-conducting liquid medium of DN 25—150mm. It can measure even liquids such as water, seawater, oil, and slurry.

Sino-Inst’s Ultrasonic Flow Meter, made in China, Having good Quality, With better price. Our flow measurement instruments are widely used in China, India, Pakistan, the US, and other countries.

What is a Venturi Tube?

what is a venturi tube?

The Venturi Tube is a tubular device commonly used to measure fluid flow rates. It is based on a physical principle, the Venturi effect. This effect states that as a fluid passes through a narrow section of a pipe, its velocity increases and its pressure decreases. The design of the Venturi Tube takes advantage of this principle, with a gradually narrowing entrance and a subsequently expanding exit. As fluid enters the narrowed portion of the venturi, it accelerates, causing the pressure to decrease. This change in pressure can be measured by pressure measuring points on the pipe wall and calculated to determine the flow rate of the fluid.

Venturi Tube is a common flow measurement tool in industry. It is widely used in the measurement of various fluids because of its simple structure, good stability and high accuracy.

Venturi Effect

The Venturi effect describes the increase in velocity and decrease in pressure as a fluid passes through a narrow section of a pipe. When fluid enters a narrow section of a pipe, the flow rate increases and the corresponding pressure decreases. This effect was discovered by Italian physicist Giovanni Battista Venturi, hence its name.

This effect can be explained by Bernoulli’s equation. This equation is a fundamental law of fluid dynamics. Show that in an incompressible fluid without viscosity, the energy of the fluid along the streamline is conserved.

P + 1/2 ρ v^2 + ρ gh = constant

P represents the pressure of the fluid
ρ is the density of the fluid
v is the velocity of the fluid
g is the acceleration due to gravity
h is the height of the fluid

In practical applications, the Venturi effect allows the venturi tube to be used to measure the velocity of a fluid in a pipe, since the velocity of the fluid is proportional to the pressure difference in the pipe.

The Venturi effect is not only used in measurement tools, but is also widely used in many fields such as aircraft wing design, chimney airflow design, and underwater piping systems. It is a very important principle in fluid mechanics and has a profound impact on many branches of engineering and physics.

Venturi tube working principle

The venturi tube is composed of the following parts:

  1. Entrance section: a short cylindrical section with a diameter of D;
  2. Contracting section: the shape is a tapered tube, the cone angle is about 21°±2°;
  3. Throat: a short straight pipe section with a diameter of about 1/3~1/4D and a length equal to the pipe diameter;
  4. Diffusion section: Conical tube with a cone angle of 8°~15°. There is a pressure measuring ring at 0.25-0.75D from the end of the inlet section, with at least 4 pressure measuring holes on it, and the pressure ring leads to the pressure gauge.

In addition, in the center of the throat, there is also a multi-channel pressure measuring ring leading to the pressure gauge. The pressure difference between the inlet section and the smallest section (that is, the throat section) can be measured through the scale of the pressure gauge or the automatic recorder.

Suppose the average velocity, average pressure, and cross-sectional area at the entrance section and the throat are v1, p1, S1, and v2, p2, S2; the fluid density is ρ.

Applying Bernoulli’s theorem and the continuity equation and noting that the streamlines of average motion are of the same height, we can get:

The formula for calculating the flow rate Q can be obtained:

After knowing ρ, S1, S2 and measuring p1-p2, the flow rate Q can be obtained according to the above formula.

The main advantage of the venturi tube is its simplicity of installation. Secondly, due to its diffusion section, the fluid gradually decelerates, reducing the turbulence (see turbulence). Therefore, the pressure head loss is small, no more than 10-20% of the pressure difference between the inlet and the throat.

Venturi tube design

According to the manufacturing process and use, the venturi is divided into standard venturi, general venturi, venturi flow tube, small diameter venturi, rectangular venturi, and other structures. The detailed structure is as follows:

Structure type:

The standard (classic) Venturi tube is composed of an inlet cylindrical section A, a conical contraction section B, a cylindrical throat C, and a conical diffusion section E. The diameter of the cylinder section A is D, and its length is equal to D; the contraction section B is conical and has an included angle of 21º±1º; the throat C is a circular cylinder section with a diameter d, and its length is equal to d; the divergent section E It has a conical shape with a spread angle of 7º~ 15º.

The general-purpose venturi, like the standard venturi, is composed of an inlet cylindrical section A, a conical contraction section B, a cylindrical throat C, and a conical diffusion section E.

The general-purpose venturi adopts the method of changing the contraction angle of the standard venturi and the length of the diffusion section to make it have the advantages of venturi, greatly shortening the length of the body, and effectively reducing the pressure loss.

The Venturi flow tube is also composed of an inlet cylindrical section A, a conical contraction section B, a cylindrical throat C, and a conical diffusion section E. The Venturi flow tube adopts a special pressure method to make it widely used in the flow measurement of dirty media and mixed-phase flow.

The small diameter venturi is composed of an inlet cylindrical section A, a conical contraction section B, a cylindrical throat C, and a conical diffusion section E. The small diameter venturi adopts an integrated mechanical processing method to measure the fluid flow of small diameters. At the same time, it can use a variety of materials to meet the requirements of the on-site working conditions and can meet various connection methods such as welding, flange connection, and threaded connection.

The rectangular venturi is composed of an inlet cylindrical section A, a conical contraction section B, a cylindrical throat C, and a conical diffusion section E. Main technical parameters of rectangular venturi:

  • Nominal diameter: DN=1.13×(WH)0.5≤6000mm
  • Inlet diameter ratio W/H: 0.5≤W/H≤2.0
  • Throat diameter ratio w/h: 0.5≤w/h≤2.0
  • Equivalent β value: 0.44≤β=(w/h)0.5/(W/H)0.5≤0.74
  • Reynolds number range: 2×105≤ReD≤2×107
  • Accuracy: ±1%
  • Repeatability: ±1%
  • Working pressure: 0~25Mpa
  • Working temperature: -100℃~500℃
  • Turndown ratio: 1:10

Rectangular venturi is mainly used in power plant air supply and suction, heating furnace air supply, and suction occasions.

Extended reading: Pitot Tube vs Venturi Meter

How does a Venturi tube measure flow?

Using the Venturi Effect to measure flow, the simple steps are as follows:

  • Install the venturi: First install the venturi in the pipe where the flow is to be measured.
  • Connect the differential pressure sensor:
    • Install a pressure sensor at the wide end and the narrow end of the venturi tube. These sensors measure the pressure difference between the two ends, which is directly related to the fluid velocity.
  • Reading the pressure difference:
    • As fluid passes through a venturi, its velocity increases in the narrow section, causing the pressure there to drop. The differential pressure sensor reads the pressure values at the wide end and narrow end and calculates the pressure difference between the two.
  • Calculate flow velocity:
    • Use Bernoulli’s equation and continuity equation to calculate the velocity of the fluid. v = sqrt(2(P1 – P2)/ρ). where P1 is the pressure at the wide end, P2 is the pressure at the narrow end, and ρ is the density of the fluid.
  • Determine the flow rate:
    • Calculate the flow rate (Q), the formula is: Q = A2 × v. where A2 is the cross-sectional area of the narrow portion of the venturi tube and v is the fluid velocity calculated in the previous step.
  • Recording and monitoring: Continuously monitor pressure difference and flow, and record data for analysis or monitoring system status.

Venturi tube flow meter

A Venturi flow meter is a differential pressure flowmeter. The Venturi flow meter is a combination of a Venturi tube, a differential pressure transmitter, and a valve block. It is often used to measure the flow of pressure pipes.

Venturi flow meters are often used to measure the flow of fluids such as air, natural gas, coal gas, and water. It includes three parts: “constriction”, “throat” and “diffusion”. Install on the pipe where the flow rate needs to be measured.

Venturi flowmeter is a new generation of differential pressure flow measuring instruments. The basic measurement principle is a flow measurement method based on the law of conservation of energy-Berlier equation and flows continuity equation.

The throttling process of fluid flowing through the inner venturi tube is basically similar to the throttling process of fluid flowing through a classic venturi tube and an annular orifice plate.

Extended reading: Fluid flow meter types

Venturi flow meters types:

Classic Venturi:

It is applied to the flow measurement of various media and has the characteristics of small permanent pressure loss, the required long and short front and rear straight pipe sections, and long service life.

Casing type venturi:

It is mainly used in the flow measurement and control of various large-caliber and high-pressure or dangerous media in the petrochemical industry.

Venturi nozzle:

It is suitable for the measurement occasions of various media. It has the characteristics of small permanent pressure loss, a short length of the front and rear straight pipes required, and long life. The installation length of the body is shorter than that of the classic venturi.

Extended reading​: What is a flow nozzle?

If it can be accurately manufactured in accordance with ASME standards, the measurement accuracy can also reach 0.5%. However, the accuracy of the domestic Venturi flowmeter is difficult to guarantee due to its manufacturing technical problems.

For the working condition of ultra-supercritical power generation, the use of the equalizing ring at the throat is a very dangerous link under high temperature and high pressure. If the equalizing ring is not used, the standard will not be met. The measurement accuracy cannot be guaranteed. This is a contradiction in the manufacture of high-pressure classic Venturi flowmeters.

The pipe is made of the same material as the inlet and outlet. Fluid scouring and abrasion of the throat are severe. Long-term measurement accuracy cannot be guaranteed. The length of the structure must be manufactured according to regulations. Otherwise, the required accuracy will not be achieved.

Due to the strict structural regulations of the classic venturi, its flow measurement range is the largest and the minimum flow ratio is very small, generally between 3 and 5.

This makes it difficult for Venturi flowmeters to meet flow measurements with large flow changes.

Read more about: 5 Factors Affecting Pressure Drop

Venturi tube application

Since its development, venturi products have been successfully applied to the measurement of high-humidity natural gas, low-pressure dirty biogas, coke oven gas, gas, steam, hot water, high-temperature hot kerosene, etc., And the practical application range is rapidly expanding.

Besides, the venturi tube has a unique measurement advantage, for measuring conditions such as long straight pipe installation conditions, special high temperature, high pressure, strong corrosive and dirty media, and non-single phase flow measurement.

Of course, in the sewage and wastewater treatment industry, in addition to venturi flowmeters, electromagnetic flowmeters are also the first consideration for many users.
For example, if you need to measure the flow of wastewater in a 2-inch pipe. Then you can refer to Magnetic Flow Meters Guides.

Extended reading: Hot Water Flow Meters Improve Heating-Boiler System

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Related DP flowmeters

Sino-Inst offers over 50 flow meter products. About 50% of these are differential pressure flow meters (like the Orifice flowmeter), 40% are Magnetic Flow Meters, and 40% are Thermal mass flowmeters.

A wide variety of Annubar flow meter options are available to you, such as free samples, paid samples. 

Sino-Inst is a globally recognized supplier and manufacturer of flow measurement instrumentation, located in China.

The top supplying country is China (Mainland), which supply 100% of the turbine flow meter respectively. Sino-Inst sells through a mature distribution network that reaches all 50 states and 30 countries worldwide.

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

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Flow Transmitter vs Flow Meter

You may have heard of flow transmitters and flow meters. Are flow transmitter and flow meter the same? What is the difference and relationship between them before? Should you buy a flow meter or a flow transmitter? What kind of one to buy?

Let us discuss both flow meter and flow transmitters individually to you understand their concepts thoroughly.

What is a Flow Meter?

A flow meter is an instrument used to measure the flow of fluid in a pipeline or open channel. It measures the flow of fluids, liquids, or gases through a closed transmission system.

Flow meters are divided into differential pressure flow meters, rotor flow meters, throttling flow meters, slit flow meters, volumetric flow meters, electromagnetic flow meters, and ultrasonic flow meters. Classified by medium: liquid flow meter and gas flow meter.

Extended reading: Ultrasonic Flow Meters Types & Technical Guide

These different flow meters have different functional principles. For example, an orifice flowmeter calculates the fluid flow at the entrance cross-section of a narrow, restricted opening (called an orifice) and the exit cross-section of the orifice. On the other hand, a rotameter-type flow meter can measure the volume flow inside multiple tubes placed in different areas of the transfer tube.

The above is a general introduction to the flowmeter. simply put. We can think that the flow meter is composed of two parts: the sensor and the signal processor. This structure can be installed separately or as a whole.
So, the signal processing part here is the Flow Transmitter we are going to talk about next.

Extended reading: How does a rotameter work

What is a Flow Transmitter?

The flow transmitter is an important part of the flowmeter. It is a flow meter with an integrated circuit as its operating system. In the flow transmitter, the flow measurement activity is executed by the electronic circuit after receiving the command from the operator. Since flow transmitters have electronic circuits, these devices can be used to control and monitor fluid flow.

Read more about: Flow Meters With GPM Units

For example, the following picture group is the flow transmitter of our common electromagnetic flowmeter.

Guess you like: What is Reynolds number?

Working Principle of Flow Transmitters

A transmitter (transmitter) is a converter that converts the output signal of the sensor into a signal that can be recognized by the controller. It can also convert the non-electricity input from the sensor into an electrical signal and amplify the signal source for remote measurement and control.

There are many types of transmitters. The transmitters used in industrial control instruments mainly include temperature transmitters, pressure transmitters, flow transmitters, current transmitters, voltage transmitters, and so on. Among various types of instruments, transmitters have the most extensive and common applications.

Therefore, the flow transmitter converts the flow signal collected from the flow sensor into an electrical signal. The various electrical signals that have been converted are used to facilitate the reception and transmission of other instruments or control devices. Through the electronic circuit again. Unify the electrical signals from the sensors. Converted to standard 4-20MA.

For example:
The mass flow meter directly measures the mass value. The flow transmitter displays the volume value. This is the biggest difference! The output of the flow transmitter is 4~20MA, and the pressure can be directly displayed by connecting to the secondary meter.

Read more about What is a Flow Transmitter? on Instrumentation Forum.

Extended reading: rotameter applications

Differences between the Flow Meter and Flow Transmitter

The following are some important differences between flow transmitters and flow meters.

  • The flow meter is designed to measure flow. On the other hand, flow transmitters can not only measure flow. They can also help control and monitor flow.
  • The flow meter is a standard mechanical system, such as an orifice plate, pressure gauge, etc. On the other hand, the flow transmitter has a mechanical body and an electronic function circuit.
  • The flow meter is designed for manual field applications. However, the flow transmitter can be operated remotely.

Extended Reading: Magnetic Battery Operated Flow Meter

Flow transmitter types

In fact, there is no strict classification of flow transmitters. The flow transmitter can be configured according to the customer’s functional requirements.
For example, customers need a digital display, 4-20mA output, integrated.
Or, the customer needs battery power. Digital display. No signal output.

Extended reading: Gas Rotameter Tips

Extended Reading: What Is Metal Tube Flow Meter? Rotameter Manufacturer

Flow transmitter calculation

The calibration methods and calibration requirements of flow transmitters with different functions are different. It is recommended that you check with the manufacturer before calibrating the flow transmitter. For example, the flow transmitter supplied by Sino-Inst has a key calibration function. Simple and easy to operate.

For another example, there are two calibration methods for common electromagnetic flowmeters. You may be reading: Magnetic flow meter calibration

Extended reading: Make Ultrasonic Open Channel Flow Meter Work for You

Applications of Flow Transmitters

Flow transmitters are commonly used in various industries, including but not limited to:

  • Food & Beverage
  • Industrial production process
  • Environmental protection project: Water and wastewater
  • Pulp & paper
  • Pharmaceutical
  • Biotechnology
  • Oil & Gas
  • Energy metering
  • Metals and Mining
  • Marine
  • Power & Utilities
  • Transportation
  • Chemical
  • Textile
  • Building Automation
  • Micro Electronics
  • Biotechnology
  • Marine meteorology, rivers and lakes

Extended reading: Food grade flow meters for Food & Beverage industry

Extended reading: High Pressure Rotameter for Liquids/gas-Upto 25 Mpa

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Sino-Inst offers over 50 Flow Transmitters, with the Best Price.

A wide variety of Flow Transmitters options are available to you, such as free samples, paid samples.

About 13% of these are magnetic flow meters, 14% are Insertion Magnetic Flow Meter, 25% are Venturi flow meters, 13% are ultrasonic flow meters, and others are Liquid Turbine Flow Meters.

Sino-Inst is a Flow Transmitter supplier, located in China. Flow Transmitter s products are most popular in North America, Mid East, and Eastern Europe. The United States, and India, which export 99%, 1%, and 1% of Flow transmitters respectively.

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Point Level Measurement Sensors

What is Point Level Measurement?

Point Level Measurement refers to the use of a point level sensor to detect the material level in a storage tank or silo. Also called point level Indicators, Controls, and Switches. This type of equipment is used when it is not necessary to measure every possible intermediate level. Just like in the case of continuous level measurement.

The point level sensor measures the preset level of liquid, mud, or solid media. And open or close the electrical contact at the desired set point. In some applications, sensors are also used to trigger pumps, valves, or other controls. To return the media to the preset level. Capacitive, ultrasonic, rotary, and vibrating liquid level switches are suitable for almost all applications from bulk solids to liquids and in between.

What is a point level sensor?

Liquid level measurement usually has two forms: continuous liquid level detection and point liquid level detection. In continuous level detection, the sensor continuously measures the level of liquid or solid in the tank. The point level sensor measures the preset level of liquid, mud or solid media, and opens or closes the electrical contact at the desired set point.

Point level sensor is also called liquid level switch, or liquid level controller. Point level sensor is used for point level detection. The sensor will detect the liquid at a certain point in the tank or chamber. Generally, this applies to processes that need to be managed at a high or low level.

Point level sensor is suitable for liquid, paste, powder, or bulk solid in a silo. You may encounter problems with property changes, turbulence, foam, vibration, or accumulation, but a wide range of sizes, installations and materials make inspection easy.

Common point level sensors, such as photoelectric level switch (SST sensor), horizontal float switch, vertical float switch, ultrasonic level sensor, tuning fork level switch.

Extended reading: Radar level sensor for solids – Dust solid level measurement

What is a continuous level sensor?

The continuous level sensor is designed to provide level detection through every point in the tank or chamber. This means that regardless of the liquid level, it can provide feedback across the entire range of the container. This is very useful for processes where knowing the level is always important and for applications that require increased accuracy.

Common continuous level sensors, such as submersible level sensors, ultrasonic level sensors, capacitive level sensors.

  • Media type (e.g. bulk, powder, liquid, paste, etc.)
  • Media properties (e.g. bulk density, conductivity, viscosity, etc.)
  • Input conditions (e.g. tank material, tank geometry, installation position, installations within the tank, etc.)
  • Process conditions (e.g. pressure, temperature, ambient conditions, explosion protection, hygiene requirements, etc.)

Extended reading: Applicaitons Of Magnetostrictive Level Transmitters

Point level sensor

A sensor designed for point detection will detect liquid at a certain point in the tank or chamber. Generally, this applies to processes that require high-level or low-level management.

In most cases, they act as switches when the tank level rises or falls to a certain level. This could be an alarm or a bonding device. Essentially, the sensor detects when the liquid has reached the desired point, and it acts as a switch to activate the necessary response.

Read more about: Application 3: Level Measurement In Waste Water Treatment Plants

Continuous level sensor

The continuous level sensor is designed to detect the level through every point in the tank or chamber. This means that it provides feedback regardless of the level and the entire container range. This is great for processes where the level is always important, and for applications that require increased accuracy.

Extended reading: Radar Oil Tank Level Sensor

Looking for a specific type or a custom continuous liquid level sensor? Sino-Inst offers High-quality Liquid level sensors for continuous level measurement.

Level sensors are used in process control in many industries and they fall into two categories. Continuous level measurement sensors and Point level measurement sensors. The point level measurement sensor is used to indicate a single discrete level, that is, to indicate a preset level.

The function of this type of sensor is the upper limit alarm, which indicates the overfill condition, or the lower limit alarm condition. Continuous level sensors are more complex, allowing level monitoring of the entire system. They measure the level of the liquid level in a range, not the level of a point. Continuous level sensors produce an analog output that is directly related to the liquid level in the container. To build a level measurement system, this output signal is transmitted to the process control loop and visual indicators.

Read More: Continuous Liquid Level Measurement

Types of Point level measurement

Liquid level measurement is a key link to realize the automated production of industrial processes. According to the difference of its output, it can be divided into Point level measurement and continuous quantity measurement. A wide variety of liquid level switches have caused many obstacles to the correct selection of users. For this reason, the common classifications of liquid level switches are introduced as follows. Hope to be helpful to instrument users.

Extended Reading: What is level transmitter working principle?

After the probe of the capacitive liquid level switch is exposed to liquid, it detects the change of the capacitance value and outputs the contact signal. Generally speaking, capacitive liquid level switches have certain advantages in the measurement of slightly viscous media.

Extended reading: Capacitance level sensor advantages and disadvantages

The electrode type liquid level switch mainly uses the conductivity of the liquid to detect the height of the liquid level. Once the measured medium touches the pole, it will conduct electricity and detect the signal. After the signal is amplified by the controller, it will output a contact signal to realize the control of the liquid level.

The magnetic float of the float level switch rises or falls with the liquid level so that the sensor detects the reed switch chip at the set position in the tube. It sends out contact on/off switch signal. Due to the simple structure of the float level switch, it is economical and practical. It is widely used in the civilian market. But compared with industrial-grade products, its stability is relatively poor.

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The photoelectric liquid level switch mainly uses the principle of light refraction and reflection. It is detected by infrared rays. Because the light will reflect or refract at the interface of two different media. When the measured liquid is at a high level, the measured liquid and the photoelectric switch A kind of interface is formed. When the measured liquid is at a low position, the air and the photoelectric switch from another interface. These two interfaces make the reflected light intensity received by the light-receiving crystal inside the photoelectric switch different. That is to say, there are two corresponding interfaces. Different switch states. Generally speaking, the applicability of photoelectric switches is poor compared with other measuring instruments.

Extended reading: Non contact level measurement

The instrument probe of the ultrasonic external liquid level switch emits ultrasonic waves and detects its after-vibration signal in the container wall. When the liquid flows over the probe, the amplitude of the after-vibration signal will become smaller. The instrument will output a signal after detecting the change Switch signal. Because the ultrasonic external liquid level switch is a non-contact measuring instrument, it is mostly used in the scene where it is not easy to open holes and high risk. But relatively speaking, its cost is relatively high.

Extended reading: The Secret of Ultrasonic Level Measurement

The tuning fork liquid level switch mainly outputs a switch signal by detecting the changes in the frequency and amplitude of the fork vibration. Its versatility is strong, but it is necessary to consult the manufacturer for working conditions with high viscosity. For working conditions that are easy to crystallize, it is not recommended.

Extended reading: ​Solid flow meter | For bulk solids-powder-soybean-cement 

Featured Level switches for point level measurement

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Sino-Inst offers over 10 Point Level Measurement Sensors. About 50% of these are liquid level meters, 40% is the tank level sensor.

A wide variety of Point Level Measurement Sensors options are available to you, such as free samples, paid samples.

Sino-Inst is a globally recognized supplier and manufacturer of Point Level Measurement Sensors instrumentation, located in China.

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Ultrasonic Sludge level sensor

Sludge level sensor is also called sludge level transmitter, sludge level detector, Online sludge interface instrument, or sludge blanket level detector. A sludge level sensor is an instrument used to measure the thickness of the mud layer in the liquid.
The sludge level can be expressed as the distance from the water surface (sludge level depth) or the distance from the bottom of the tank (sludge level height). Sludge level sensor is mostly used in the industrial process of solid-liquid separation. Continuously monitor the mud-water interface of sedimentation tanks or special thickening tanks. A sludge level sensor is an instrument commonly used in the sewage treatment industry (wastewater treatment plant) to monitor the sludge level/sludge bed level in the sedimentation tank or thickening tank.

What is a Sludge level sensor?

Sludge level sensor is an online water quality monitor with a microprocessor. The mud-water interface meter is an industrial online monitoring instrument designed to measure the treatment process of municipal sewage and industrial wastewater.

With the rapid economic development, industrial, agricultural and domestic water use is growing rapidly. More and more sewage is produced, and the problem has become increasingly serious. Therefore, to do a good job in sewage treatment can we ensure the recycling of water resources. In many industrial processes, suspended solids and liquids are separated by sedimentation. This process is usually completed in a sedimentation tank or a special thickening tank. And it is practical, and the mud-water interface must be continuously monitored.

A sludge level sensor is an instrument used to measure the accumulated thickness of sludge at the bottom of the sedimentation tank. It can enable the staff to clearly grasp the amount of sludge at the bottom of the tank at any time. The sludge discharge operation can be carried out in a timely and effective manner.

Ultrasonic Sludge level sensor is designed for long-term reliable operation in industrial and municipal fields. The sensor can work when it is immersed in water 5-10cm. The height of the sludge layer can be determined by ultrasonic emission and echo analysis of suspended solids in the water.

Using ultrasonic to accurately measure the height and thickness of the sludge layer. Effectively grasp the sludge sedimentation characteristics and control the return flow of the sludge. Let the operator make timely evaluations for optimizing the sludge circulation, compensating for the daily fluctuations of wastewater, correcting abnormal state values, and monitoring the separation layer in the pre-concentration tank. It also has a longitudinal profile graph that continuously displays the height of the sludge interface. It is helpful to understand the sludge settlement situation.

Extended reading: ultrasonic sludge level meter

Features of Ultrasonic Sludge level sensor

  • Fully intelligent, multi-function, high measurement performance, strong environmental adaptability;
  • Simultaneous display of multiple parameters, height, output current, time, relay status;
  • Dual 4-20mA transmission output, relay high and low alarm control output, RS485 communication output
  • Various variable output;
  • RS485 upload function;
  • Various installation methods such as plug-in type;
  • The cleaning and maintenance are very simple, and the calibration is performed once every three months;
  • A two-point calibration method is adopted to ensure measurement accuracy;
  • Chinese and English menus are optional;
  • Self-set password: The user can set or modify the password to avoid misoperation caused by unrelated personnel entering;

Specifications of Ultrasonic Sludge level sensor

1. Measuring range: 0.4~10 meters; 0.4-25 meters; or expand according to requirements;

2. Display mode: LCD

3. Unit of measurement: meter

4. Resolution: 0.01m

5. Accuracy: ±0.5 %FS

6. Repeatability: ±0.5%

7. Work rate: ≤3W

8. Ambient temperature: -20~50℃; relative humidity: not more than 90%

9. Analog output: two 4~20mA, load 750Ω

10. Switch output: three-way relay, capacity 250VAC/5A

11. Power supply: AC85~265V±10% or 9~36VDC

Application fields of Sludge level sensor

Sludge level sensor has strong practicability and convenient operation. It is an investment-efficient system for water and sewage treatment plants. Consistent sludge level monitoring data can directly improve the quality of the effluent. It can be widely used in sedimentation tanks of water plants and ore washing plants. Power mortar sedimentation tank. Primary sedimentation tank and secondary sedimentation tank of sewage treatment plant. Sludge interface monitoring fields such as thickening tanks and mortar sedimentation tanks in the power industry.

Read more about: Top 5 Ultrasonic Level Sensor Applications

Sludge level sensor Applications

First settling tank, second settling tank, gravity sedimentation tank;
Oil/asphalt separation tank;
Pulp pool
Waste treatment clarifier;
Beverage water clarification tank;
Mining clarifier;
Brine tank
Mud tank
Any container with a liquid/solid interface.

Extended reading: Case Study: Automatic Sludge Blanket Level Detector

Industry development prospects of Sludge level sensor

With the increasing development of domestic water environment management in recent years. The application range of the sludge interface instrument is still expanding. Under the strong attack of market opportunities, the Sludge level sensor market has ushered in another wave of development.

It is understood that the current monitoring of the mud level of sewage plants on the market mainly relies on manual labor. In addition to traditional visual inspection and water sample collection, there are also sludge interface meters or sludge concentration meters. But still, need a handheld instrument to collect and measure. These monitoring methods either require high manpower. Need real-time participation and poor timeliness. Either the monitoring has blind spots and the accuracy is not high. And it requires 24 hours of manual monitoring in the central control room.

In conclusion, in today’s development of the Internet of Things, machines are used to replace humans to achieve real-time and accurate monitoring. It not only brings great convenience to the development of environmental protection work. It also gives entrepreneurs the opportunity to enter the market. In the future, it is believed that with Sludge level sensor, fast, energy-saving, pollution-free, high selection, and other characteristics, it will serve more fields.

Extended reading: Capacitive water level sensor

Sludge blanket level detector working principle

Ultrasonic mud-water interface measurement uses an ultrasonic sensor installed in the water to emit an ultrasonic pulse to the surface of the mud underwater. This pulse signal is reflected back after encountering the muddy water surface. Can be received by the sensor again.

From the ultrasonic transmission to the re-reception. The time is proportional to the distance from the sensor to the surface of the object being measured.

The meter detects this time. And according to the current temperature (measured by the sensor) underwater sound speed. Calculate the distance from the surface of the measured object to the sensor (that is, the spatial distance). Further, convert the level value.

The empty underwater distance W on the surface of the liquid level is proportional to the travel time T of the sound wave: W=V×T/2 (where V is the speed of the sound wave in water).

The user sets the height H from the probe to the bottom of the pool. The instrument automatically converts the pulse travel time T into the corresponding space distance value W. Then calculate the difference of H minus W is the measured value L.


Sludge substances are usually produced in industrial wastewater treatment. It is a mixture of residual organic matter, inorganic particles, bacterial cells, colloids, and other extremely complex substances. According to different sources, sludge can be divided into the following five types:

  1. Primary sedimentation sludge: from primary sedimentation tank.
  2. Wet sludge: from the secondary sedimentation tank after the biofilm process in the secondary sewage treatment.
  3. Residual activated sludge: from the secondary settling tank after the activated sludge method in the secondary sewage treatment.
  4. Digested sludge: from the above three sludge digestion and stabilization processes.
  5. Chemical sludge: it comes from the process of chemical treatment of wastewater.

In addition, sludge can also be divided into organic sludge and inorganic sludge according to the composition of the sludge.

Sludge is a by-product of pollution control technology. This by-product is rich in microorganisms, pathogens, viruses, etc. It has strong pollution properties. If the sludge is improperly disposed of, its pollution spreads through a wide range of ways.

Read more about: Common River Water Level Measurement Methods

The sludge level is the interface between settled down sludge and the above turbid or clear water phase. The sludge level can be given as distance from the water surface (sludge level depth) or as distance to the tank bottom (sludge level height).

In (waste)water treatment and in process control, sludge level is an important parameter. Precise information on sludge level is critical especially in processes regarding phase separation. The WTW sensor can be installed in clear, turbid or even heavily polluted media with high concentrations of suspended solids.

The sludge blanket level can be expressed as the distance from the water surface (sludge level depth) or the distance from the bottom of the tank (sludge level height).

Extended reading: Radar level sensor for solids – Dust solid level measurement

At present, the measurement of sludge mainly uses optical or ultrasonic principles to measure.

  1. Optical sludge interface instrument

Measure the sludge concentration value by using the absorption ratio of sludge to light. Use the cable length to calculate the sludge interface value.

  1. Ultrasonic sludge interface instrument

The distance from the bottom of the pool to the sensor-the distance from the mud layer to the sensor = the sludge interface value

Read more about: The Difference Between Ultrasonic Depth Sensor And Ultrasonic Level Sensor

Calculate the height of the sludge by measuring the distance from the surface of the sensor to the surface of the sludge using ultrasonic waves. Equipped with an advanced ASF (abnormal signal elimination) algorithm, it can be debugged according to the interference situation on the spot. An automatic turning device can be selected according to the site conditions (in the case of a slag scraper). Automatic cleaning devices and wireless transmission devices can meet various complicated working conditions.

Extended reading: Sludge flow meter for sewage treatment return activated sludge system

More Wastewater treatment solutions

Magnetic Water Flow Meter

Magnetic Water Flow Meter is an electromagnetic flowmeter used to measure conductive fluids. Conductive liquids such…

Sino-Inst offers over 10 Ultrasonic Sludge level sensors and transmitters for level measurement. 40% for wastewater treatment, 10% for Mud tank, others for more liquid/solid interface.

A wide variety of Ultrasonic Sludge level sensors and transmitters options are available to you, such as free samples, paid samples.

Sino-Inst is a globally recognized supplier and manufacturer of Ultrasonic Sludge level sensors and transmitters instrumentation, located in China.

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What does intrinsically safe mean?

Intrinsically safe type is an explosion-proof type of electrical equipment. When purchasing electrical equipment, do you often hear about intrinsic safety? For example, when ordering pressure transmitters or flow meters.

Intrinsically safe instruments are intrinsically safe instruments. Also called safety spark type instrument. It means that the instrument is in the normal state and in the fault state. The sparks generated by the circuit and the system and the temperature reached will not ignite the explosive mixture.

What is intrinsically safe?

Intrinsically safe type is an explosion-proof type of electrical equipment. It limits the electric spark or thermal effect energy that may be generated by the inside of the equipment and the connecting wires exposed to the potentially explosive environment to a level that cannot produce ignition.

ia or ib or ic. ia is the highest and ic is the lowest. See GB3836.4-2010 for details.

By controlling the energy level of the equipment itself, it is lower than the critical condition for igniting explosive gas under normal working or fault conditions. It will not produce sparks or higher than the temperature of igniting explosive gas. It does not need to be shielded or blocked by other means.

By limiting the various parameters of the electrical equipment circuit, or taking protective measures to limit the spark discharge energy and thermal energy of the circuit, so that the electric spark and thermal effects generated under normal operation and specified fault conditions cannot ignite the explosive mixture in the surrounding environment. In this way, electrical explosion-proof is realized. The circuit of this kind of electrical equipment itself has explosion-proof performance. That is to say, it is “essentially” safe. So it is called intrinsically safe. Electrical equipment using intrinsically safe circuits is called intrinsically safe electrical equipment.

Because the circuit of intrinsically safe electrical equipment is inherently safe. The sparks, arcs, and heat generated will not ignite the explosive mixture in the surrounding environment. Therefore, intrinsically safe electrical equipment does not require special explosion-proof enclosures. This can reduce the size of the equipment. Volume and weight. Simplify the structure of the device.

At the same time, the transmission line of intrinsically safe electrical equipment can use glue lines and bare wires. It can save a lot of cables.

Therefore, intrinsically safe electrical equipment has the characteristics of safety and reliability, simple structure, small size, lightweight, low cost, convenient manufacturing, and maintenance, etc. It is an ideal explosion-proof electrical equipment.

However, since the maximum output power of intrinsically safe electrical equipment is about 25W, the range of use is limited.

Intrinsically safe electrical equipment is mainly used in communication, monitoring, signal, and control systems, as well as instruments and meters.

Extended reading: How To Install The Pressure Sensor When Measuring The Flow Pipeline?

What are the specifications and guidelines for intrinsic safety?

ATEX (Europe)

The European Union Directive 94/9/EC often referred to as ATEX (“Atmospheric Explosion”). It is the main European regulation for protection systems and equipment used in potentially explosive atmospheres.

The purpose is to serve as a unified directive to lay the foundation for the necessary health and safety requirements. Replace existing different national and European legislation.

The directive is mandatory for electrical and electronic equipment sold in Europe on July 1, 2003 and used in environments affected by explosion hazards.

The ATEX directive has now been adopted all over the world.

NEC (United States)

The National Electrical Code (NEC) is the basis for all electrical codes in the United States. NEC 500 and 505 cover the classification of hazardous areas and related product identification.
NEC 500 explained that it is a long-term regulation. It has been adopted all over the world, except in Europe. NEC 505 is similar to ATEX.

Intrinsically safe symbol

After evaluation, each approved intrinsic safety device should meet ATEX and NEC or Factory Manual standards. Through the corresponding grade system, you can know which areas, protection types, gas groups, and temperature grades the instrument has been approved for.

Example: Fluke 707ex conforms to ATEX II 2 G Ex ia IIC T4

The ATEX examination mark. This sign is required on all devices for use in European hazardous areas.
II 2 GRegional classification. “II” indicates that the tool has been approved for use in all non-mining areas. “2” indicates the category of the device. In this example, the device is evaluated for use in a ** category* hazardous area. “G” designates the environment, in this case, gas, steam, and moist environment.
ExExplosion protection is based on European Ex regulations.
iaExplosion protection type, in this case, the energy in the device or connector has been reduced to a safe value.
IICGas group. The “IIC” grade indicates the suitability of the * hazardous gas group.
T4The temperature category is the maximum temperature that may exist on the surface.
Example of Factory Mutual classification: Fluke 707ex is N.I.Class 1, Div 2, Groups A-D, T4 classified by FM.
The Factory Mutual approval mark.
N.I.A non-flammable instrument with limited internal energy, so it will not ignite the specified environment during use.
Class ICan be used with gas, steam, and liquid (except for dust, fiber, or filing).
Div 2It is certified to be used in “Area 2”, and the explosive gas environment that does not usually exist may exist for a short time in rare cases.
Groups A-DAfter evaluation, it can be used with explosive gases defined in Group A-D. These gases include acetylene, hydrogen, acetylene, and propane.

Read more about: What Is the Difference Between Class 1 Div 1 and Class 1 Div 2 ?

Definitions of Hazardous Areas

According to the frequency and duration of the explosive environment, the hazardous area is divided into different areas.
The gas field is divided into three areas: Zone 0, Zone 1, and Zone 2.

Zone 0Places where the explosive mixture in an explosive environment continuously appears in the form of gas, vapor, or mist or exists for a long time.
Zone 1During normal operation, a place where an explosive mixture in the form of gas, vapor, or mist may occur in an explosive environment.
Zone 1 is a typical application place for explosion-proof electrical equipment.
Zone 2During normal operation, it is unlikely that explosive mixtures in the form of gas, vapor, or mist will appear in an explosive environment, and if they occur, they will only occur occasionally and exist for a short time. Normally, “short time” means that the duration is not more than 2 hours.

The dust site is divided into three areas: Zone 20, Zone 21, and Zone 22:

Zone 20During normal operation, combustible dust appears continuously or frequently, and its quantity is sufficient to form a mixture of combustible dust and air and/or may form an uncontrollable and extremely thick dust layer and inside the container.
Zone 21During normal operation, there may be places where the amount of dust is sufficient to form a mixture of combustible dust and air but is not classified into Zone 20. This area includes places that are directly adjacent to filled or discharged dust, where dust layers appear and places where flammable concentrations of combustible dust and air mixture may be produced under normal operating conditions.
Zone 22Under abnormal conditions, places where combustible dust clouds occasionally appear and only exist for a short period of time, or combustible dust occasionally accumulates or there may be a dust layer and generate combustible dust-air mixtures but are not classified into Zone 21. If it cannot be guaranteed to exclude combustible dust accumulation or dust layer, it should be divided into 21 zones.

Intrinsically safe certification

Intrinsically safe explosion-proof certification technology is currently standardized and suitable for zone 0 technology. For automation instruments, the most commonly used explosion-proof types are intrinsically safe, explosion-proof, and increased safety.

However, due to the rapid development of electronic technology and the continuous birth of low-power electronic devices. So that the promotion and application of intrinsically safe explosion-proof technology has a broader space. Especially because the intrinsically safe explosion-proof type is compared with other explosion-proof types. It not only has a simple structure but also has a wide range of applications. It also has the characteristics of easy operation and convenient maintenance. Therefore, this kind of intrinsically safe explosion-proof, which suppresses the ignition source energy as an explosion-proof method, has been accepted by instrument manufacturers and users.

  1. Basic principles of intrinsically safe explosion-proof certification technology

Electric sparks and thermal effects are the main sources of ignition that cause explosive hazardous gas explosions. Intrinsic safety is achieved by limiting the energy of two possible ignition sources: electric spark and thermal effects.

Under normal working and fault conditions, when the energy of the electric spark or thermal effect that the meter may produce is less than this energy. It is impossible for the instrument to ignite explosive dangerous gas and cause an explosion.

The principle is to start with limiting energy. Reliably limit the voltage and current in the circuit to an allowable range. In order to ensure that the electric spark and thermal effects generated by the instrument in normal operation or short-circuit and component damage, etc., will not cause the explosion of dangerous gases that may exist around it.

  1. Features of intrinsically safe explosion-proof certification technology

Intrinsically safe explosion-proof technology is actually a low-power design technology. Usually, for hydrogen (IIC) environment, the circuit power must be limited to about 1.3w.

It can be seen that intrinsically safe technology can be well applied to industrial automation instruments.

Compared with any other explosion-proof type. The use of intrinsically safe explosion-proof technology can bring the following technical and commercial features to industrial automation instruments:

  • No complicated design and manufacturing process is required. A bulky and heavy flameproof enclosure. Therefore, the intrinsically safe instrument has the characteristics of simple structure, small size, light weight and low cost. According to data, the cost ratio of establishing an intrinsically safe and flameproof switch transmission circuit is about 1:4.
  • Maintenance, calibration and replacement of some parts of the instrument can be carried out under electrified conditions.
  • High safety and reliability. The intrinsically safe instrument will not reduce the safety and reliability of the instrument due to the loss of the fastening bolts or the corrosion of the casing joint surface, scratches and other man-made reasons
  • Because intrinsically safe explosion-proof technology is a kind of “weak current” technology. Therefore, the use of intrinsically safe instruments can avoid the occurrence of electric shock accidents of on-site engineering and technical personnel.
  • Wide application range. Intrinsically safe technology is the only explosion-proof technology applicable to hazardous locations in Zone 0.
  • For simple devices like thermocouples. No special certification is required to access the intrinsically safe explosion-proof system.

In summary, for automated instruments, intrinsically safe explosion-proof technology is an ideal explosion-proof technology. It will also be widely used in the design of Fieldbus intelligent instruments and their systems.

Intrinsically safe vs explosion-proof

It is often necessary to use explosion-proof instruments in industrial sites. The general industrial explosion-proof instruments are mainly explosion-proof and intrinsically safe. So, how to understand the difference between them?

Read more Intrinsically Safe vs Explosion Proof Pressure Transmitters

Choose the right intrinsically safe device for your application

Explosion Proof Pressure Transmitter

SIEP489 Explosion proof pressure Transmitter is a microprocessor-based high-performance transmitter. SIEP489 has flexible pressure calibration, push button configuration, and programmable using HART® Communication. We also supply industrial pressure sensors, and explosion proof differential pressure transmitter.

All our electronic pressure transducers can be offered with Explosion-proof. Select explosion-proof pressure transmitters with Ex d certification and 4-20mA output signals for installation. These installations require the use of equipment and enclosures designated as containing internal explosives. This prevents ignition of the explosive environment surrounding the equipment ( Specified) Flameproof area.

Intrinsically Safe Flow Meter

When do I need to choose an explosion-proof or intrinsically safe flowmeter?

Please remember that when you need to measure the medium is flammable and explosive. Be sure to tell the flowmeter manufacturer. Choose intrinsically safe or explosion-proof flow meters.

For example, to measure diesel oil, turbine flowmeters are used. The explosion-proof model must be selected.
Another example is measuring hydrogen. Use vortex flowmeter. The intrinsically safe model must be selected.

Sino-Inst offers a variety of Intrinsically Safe vs Explosion Proof Pressure-Level-Flow Transmitters for industrial pressure measurement. If you have any questions, please contact our sales engineers.

Molasses Flow Meters-High Viscosity Liquids Solution

Molasses flow meters are a type of flow meter used for molasses flow measurement. Molasses are common high viscosity liquids. So Molasses flow meters are flow meters that can be used to measure various high viscosity liquids. Can common electromagnetic flowmeters be used to measure high viscosity liquids? What about the Coriolis mass flow meter?

Perhaps after the introduction of this article, you will understand.

Viscosity is a value obtained by measuring the inherent frictional force of a fluid.
Viscosity is a physical and chemical property of a substance.
It is defined as a pair of parallel plates with an area of A and a distance of dr. The plates are filled with a certain liquid. Now a thrust force F is applied to the upper plate to generate the force required for a degree of speed change.
Due to the effect of viscosity, the object is subjected to frictional resistance and differential pressure resistance when moving in the fluid, resulting in loss of mechanical energy.
Essentially, the more viscous a liquid is and the more resistant it is to flow, the higher its viscosity.

Due to the viscosity of the liquid, this force layer is transmitted layer by layer. Each layer of liquid also moves accordingly. A velocity gradient du/dr is formed. Called the shear rate, expressed by r’.
F/A is called the shear stress and is represented by τ.
The relationship between shear rate and shear stress is as follows:


The proportional coefficient η is defined as the shear viscosity of the liquid.
In addition, extensional viscosity and shear viscosity are usually used more often. Generally speaking, when it is abbreviated as viscosity without distinction, it usually refers to shear viscosity.

Therefore, η=(F/A)/(du/dr)=τ/r′.

Immerse two plates with an area of ​​1 square meter in the liquid, and the distance between the two plates is 1 meter. If a 1N shear stress is applied to a certain board. If the relative speed between the two plates is 1m/s, the viscosity of the liquid is 1Pa·s.

Newtonian fluid:

a fluid that conforms to Newton’s formula. Viscosity is only related to temperature, not to shear rate.

Extended reading: Fluid flow meter types

Non-Newtonian fluid:

does not conform to the Newtonian formula τ/D=f(D). Express the viscosity under a certain (τ/D) with ηa, which is called the apparent viscosity.

Viscosity changes significantly with temperature but usually changes little with pressure.

Liquid viscosity decreases with increasing temperature, while gas viscosity increases with increasing temperature.

For solutions, the relative viscosity μr is often used to indicate the ratio of the solution viscosity μ and the solvent viscosity μ. which is:
The relationship between relative viscosity and concentration C can be expressed as:


In the formula, [μ] is the intrinsic viscosity of the solution.

K’ is the coefficient. [Μ], K’have nothing to do with concentration.

The viscosity of different fluids varies greatly.

At a pressure of 101.325kPa and a temperature of 20°C, the dynamic viscosity and kinematic viscosity of air, water and glycerin are:

Air μ=17.9×10^-6Pa·s, v=14.8×10^-6m²/s
Water μ=1.01×10^-3Pa·s, v=1.01×10^-6m²/s
Glycerin μ=1.499Pa·s, v=1.19×10^-3m²/s

More about Viscosity

You may find examples of high and low viscosity fluids- Honey, syrup, glue

Dynamic viscosity unit conversion

1 poise (1P)=100 centipoise (100cP)
1 centipoise (1cP) = 1 mPa·s (1mPa·s)
1 mPa·s (1mPa·s)=1000 microPascal·s (1000μPa·s)

Conversion of dynamic viscosity and kinematic viscosity
Where μ--- dynamic viscosity of sample (mPa·s)
ν--- Kinematic viscosity of sample (mm²/s)
ρ--- The density of the sample at the same temperature as the measured kinematic viscosity (g/cm³)

Extended reading: Liquid mass flow controller for process liquid -Sino-Inst

The so-called high-viscosity liquid means that the liquid is viscous and thick. It is different from general liquids and non-Newtonian fluids (mud, pulp). The activity is slow and it is very difficult to filter with simple methods.

What’s more, the liquid contains some dust in addition to it. It also contains colloidal particles that are not completely dissolved.

For example solutions of rubber, paraffin, cellulose acetate, viscose, polyacrylonitrile, paint and animal glue.

Read more about: Coriolis Mass Flowmeter Working Principle

Properties of molasses

What is molasses:

Molasses is a viscous, dark brown, semi-liquid object. It mainly contains sucrose. The content of pantothenic acid in sucrose is higher, reaching 37mg/kg. In addition, the biotin content is also considerable. It is easy to be mixed into soybean molasses and molasses fermentation liquid.

Molasses characteristics

  1. Molasses is a brownish yellow viscous liquid, with the fragrance of yeast and the sweetness of molasses;
  2. The content of CP is high, 3-6%;
  3. High sugar content, generally 42-50%. Low energy density, good taste. Fast digestion and absorption, and the price is lower than corn (2346, 2.00, 0.09%).
  4. Contain vitamins, minerals, bacterial proteins, nucleic acids, surface active substances and growth-promoting factors (biologically active substances) and other ingredients.
  5. Anti-acid and alkali, anti-oxidation, strong chelating ability to divalent cations. It can form organic chelating trace elements with metal ions. Promote the absorption and utilization of minerals by livestock and poultry.

The above is a detailed introduction to what molasses is.

Choosing right molasses flow meters

For the properties of molasses. There are 4 types of flow meters that can be used as molasses flow meters.

The electromagnetic flowmeter is a flow measuring instrument. In the working conditions that require flow measurement, electromagnetic flowmeters are inseparable.

When measuring the flow of low-viscosity and high-viscosity liquids, many people think of electromagnetic flowmeters. In fact, it is right, although I dare not say that the electromagnetic flowmeter is omnipotent. But almost all conductive liquids can be solved by electromagnetic flowmeters.

For diluted molasses. Good liquidity. It can be measured with an electromagnetic flowmeter.

Extended reading: Sludge flow meter for sewage treatment return activated sludge system

Spur Gear Flowmeter is our brand new product. Measure small flow rates. As low as 0.01L/min.

The gear flow meter is a common positive displacement flow meter. The gear flow sensor has built-in double gears to operate. The volume of the medium is calculated by the volume of the gear. The flow rate of the small fluid medium is measured.

Gear flow meters can be used for resin and glue flow measurement. Flow measurement of hydraulic oil, lubricating oil, and grease. Maltose, syrup. Fuel oil flow measurement. Flow measurement of ink and asphalt. Flow measurement of liquid nitrogen, freezing liquid, and solvent. Edible oil, fish oil, and food filling measurement. Chemical and anti-corrosion requirements fluid measurement. A fluid quantitative control system, etc.

Read more about Gear flow meter for Microflow

If the flow rate of molasses is large, how to measure the flow rate of the liquid with high viscosity?

Oval gear flowmeter is a positive displacement flowmeter, also known as displacement flowmeter. It is a type of flowmeter with high measurement accuracy among flow meters, and it is very good at measuring liquids with high viscosity.

The oval gear flowmeter can measure liquids up to Viscosity: 1000-2000mPa.s.

The measurement of the oval gear flowmeter has nothing to do with the flow state of the fluid. The higher the viscosity of the medium, the smaller the leakage from the gear and the metering gap. Therefore, the higher the viscosity, the more advantageous it is for measurement.
Measurable medium: fuel, diesel, gasoline, heat transfer oil, hydraulic oil, kerosene, tar, petroleum, crude oil, asphalt, resin, and other liquids. Especially suitable for the measurement of high viscosity liquids.

Coriolis mass flowmeter has the characteristics of high measurement accuracy, good stability, and easy operation. It is an ideal instrument for measuring the flow of high-viscosity media such as high temperature, high viscosity, and easy crystallization.

The flow and temperature of the high-viscosity medium form a cascade control system. Install an automatic regulating valve on the inlet pipe to automatically cut off and adjust the size of the oil volume according to the reaction temperature. Ensure a fast response state and reduce pure lag time.

After using the mass flowmeter, the flow of the high-viscosity medium is uniform and stable, which reduces the labor intensity of the operators. The pure lag time is shortened, and the quality of the product is guaranteed. Improved economic efficiency.

Extended reading: U-series Liquid Mass Flow Meter | Liquid-slurry flow measure

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Sino-Inst, Manufacturer for Molasses Flow Meters-High Viscosity Liquids Solution

Sino-Inst’s Molasses Flow Meters, made in China, Having good Quality, With better price. Our flow measurement instruments are widely used in China, India, Pakistan, the US, and other countries.