Getting Started with 4 – 20mA Signal Generator Part-1

What is a 4 to 20ma Signal?

4-20mA Signal is commonly used to connect process signals to controllers in industry-grade applications and is a common signal to convey the sensor data. It is basically a current signal which varies from 4 to 20mA depending on the sensor output. Current is used to transmitting the sensor signal as voltage signals are susceptible to noise and difficult to interface with Microcontroller/PLCs operating on different voltages.

For instance, a temperature sensor with 4 to 20ma will output a 4ma signal for 0°C and 20mA for 100°C. The Microcontroller/PLC can measure this current and get the temperature.

Testing of 4-20ma signal Generator using a multimeter

Why are current signals used over voltage/digital signals?

  • A 4-20ma signal works well even through long wires. In industrial environments, sensors and controllers may be installed in different locations which require communication over long distances.
  • It is simple to connect,configure,and requires less wiring.
  • It is easy to troubleshoot for common problems like broken wires, short circuits, etc. 
  • It is able to provide communications over long distances where voltage drop might be an issue.
  • 4-20 mA signal it is easy to scale and calculate the process parameters.

Where is this 4 to 20ma Signal Generator used

Bottom Right: Signal Generator is outputting a current signal. Left: Multimeter reading the output signal.

This signal generator can be used to manually generate a 4 to 20mA signal. A knob on the module, lets users simulate a current signal. It is great if you want to do testing/calibration/etc without having to connect a live sensor.

  • This signal generator is used for calibration of 4-20mA signals..
  • Useful for testing/calibrating the controller. Once the controller is working with the generator, we can then connect a live sensor and start working.

Technical Specifications:

Front panel view of 4-20mA signal Generator
  • Input Voltage :15V-30V
  • Output Range:4-20mA
  • Display mode: Real current value in mA / as percentage 0-100% / 0-50Hz
  • Sampling Resistance:Less than 500Ω
  • Output accuracy:±0.5%
  • Display accuracy:0.01

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How to use this signal generator?

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The Signal Generator has 2 terminals for powering. The signal generator has to be connected in series with a 15-30V DC power supply. The connectors are nonpolarised

Wiring Diagram of 4-20mA signal generator

On powering, the signal generator starts outputting a 4-20ma Signal, and the current value is shown on the display.

Wiring a Signal generator with a multimeter

How to use Menu(Basic)

  • The generator has a knob which can be rotated to adjust the output current. Use the knob to set the desired output current. Turn Clockwise to increase current and anticlockwise to decrease the current.
Rotate the Knob for mode setting
  • The knob can also be pressed to access the onboard settings menu. The module has several advanced features that can be accessed from the settings menu –
    • Change the Knob Adjustment Sensitivity – Coase and Fine Adjustments Settings are available
    • Generate automatic time varying current signals
    • Generate 1Point or multipoint current signals
    • Select between 4-20 Signal or 0-20ma Signal
    • Select Display between Actual Current, Percentage of Current, etc
    • Set predefined current values and steps, instead of linearly varying current signal output.
  • To access settings, press and hold the knob for a few seconds and enter the password. Rotate clockwise for “+”, Rotate anticlockwise for “-”, Press the Knob to “confirm” 
4-20mA signal Generator generating 4-20mA signal

Read Part 2 of this article which explains more features of this module here –

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