In industrial systems, accurate measurement requires a reliable way to transmit signals. Listrik Kita is an official distributor of electrical products such as Schneider Electric, Philips, and Socomec, providing original and warranty-backed products. One of the most widely used signal technologies in industrial instrumentation and automation is 4-20 mA. This signal is commonly used to send information from sensors or transmitters to PLCs, DCS systems, and other control equipment.
There are several reasons why 4-20 mA remains widely used. Compared with other signal transmission methods, it offers important advantages for long-distance installations and industrial environments where electrical interference can be present.
Why Is 4-20 mA a Standard in Industry?
What Is a 4-20 mA Signal?
4-20 mA is an analog signal that uses electrical current to represent the value measured by a sensor or transmitter. In this system, 4 mA usually represents the minimum value, while 20 mA represents the maximum value.
For example, a pressure transmitter may have a measuring range of 0 to 10 bar. A signal of 4 mA can represent 0 bar, while 20 mA represents 10 bar. Values between 4 and 20 mA represent the measured pressure between these two limits.
4-20 mA signals are commonly found in instrumentation devices such as pressure transmitters, level sensors, flow transmitters, and temperature measurement systems.
Why Use a 4-20 mA Range?
One important reason is the use of a live zero. The minimum signal does not start at 0 mA but at 4 mA. This allows the control system to distinguish between the minimum process value and a possible fault condition.
If the signal drops close to 0 mA, the system may identify it as a possible problem, such as a broken wire or device failure, depending on the system design and alarm settings.
Why Do Industries Use 4-20 mA Signals?
Easy Detection of Broken Wires
One major benefit of 4-20 mA is that it helps identify problems in the signal loop. Since normal operation starts at 4 mA, a signal close to 0 mA can indicate a fault.
This is different from a 0-20 mA system, where 0 mA can also represent a normal process value. With 4-20 mA, the minimum process value can be separated more clearly from a possible loop failure.
Better Resistance to Installation Interference
Industrial environments often contain many potential sources of electromagnetic interference, including electric motors, inverters, contactors, and high-power equipment.
Current signals such as 4-20 mA are relatively less affected by cable resistance and certain types of electrical interference compared with voltage-based transmission. This makes them suitable for industrial instrumentation systems that require reliable signal transmission.
Reduced Cable and Infrastructure Requirements
In certain configurations, especially with 2-wire transmitters, a single 4-20 mA loop can provide power while also carrying measurement information. This can simplify the installation and reduce the need for additional wiring.
A more efficient wiring arrangement can also reduce installation complexity, especially when many sensors and transmitters are connected to a control panel.
Why Is a Current Signal Better for Long-Distance Transmission?
Current Signal vs Voltage Signal
Voltage signals such as 0-10 V and current signals such as 4-20 mA can both be used to transmit information from sensors to control systems. However, their characteristics are different when used over long cable distances.
With voltage transmission, cable resistance can cause voltage drop. The longer the cable, the more important the effect of cable resistance can become.
Why Can Voltage Signals Be More Challenging Over Long Cables?
Every cable has resistance. When a voltage signal travels through a long cable, some voltage can be lost because of this resistance. If the system is not properly designed, this can affect the voltage received by the control device.
For this reason, voltage-based transmission needs to consider cable length, conductor size, load, and installation conditions.
Why Is 4-20 mA Suitable for Long Distances?
In a 4-20 mA system, information is transmitted as current through a loop. As long as the loop has sufficient voltage and remains within the specified load limits, the current can be transmitted effectively through relatively long cables.
This is one reason why 4-20 mA is widely used in industrial instrumentation. A sensor can be installed some distance away from the control panel without making the signal transmission unnecessarily complicated.
Benefits of Using 4-20 mA Signals
Reliable Signal Transmission
4-20 mA is designed to provide stable signal transmission and can be used across many industrial instrumentation systems.
Easy Detection of Abnormal Conditions
Starting the normal measurement range at 4 mA makes it easier for the control system to recognize conditions outside normal operation, including possible loop faults.
Good Resistance to Electrical Noise
Current signals offer good resistance to certain electrical disturbances, making them suitable for industrial environments containing many electrical devices.
Supports 2-Wire Installation
With compatible transmitters, a 2-wire configuration can use the same loop for power supply and signal transmission. This makes the installation more practical.
Easy Integration with Control Systems
4-20 mA is widely used with PLCs, DCS systems, controllers, and other instrumentation equipment. Its widespread adoption makes integration between devices easier.
Examples of 4-20 mA Applications in Industry
Pressure Measurement
Pressure transmitters can use 4-20 mA signals to send pressure information to a control system. For example, a 0-10 bar measuring range can be represented by a signal from 4 mA to 20 mA.
Level Measurement
In storage tanks, level transmitters can continuously send liquid level information to a PLC or DCS using a 4-20 mA signal.
Flow Measurement
Flow transmitters use 4-20 mA signals to transmit information about the flow rate of fluids moving through a piping system.
Temperature Monitoring
Temperature transmitters can convert temperature measurements into a 4-20 mA signal, allowing the information to be sent to a monitoring or control system.
4-20 mA remains an important standard in industrial instrumentation because it combines reliability, fault detection, resistance to electrical noise, and long-distance signal transmission. It can also make instrumentation systems more practical, especially when used with 2-wire transmitters.
If you need sensors, transmitters, PLCs, control devices, or other electrical products for residential, commercial, industrial, or project applications, Listrik Kita provides electrical products from trusted brands. Find original and warranty-backed products that suit your needs at Listrik Kita.
