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.

How Does This 4-20mA Control Loop Work?

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.

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…..

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.


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.

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.

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.

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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