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.
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:
- 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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Connections
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
On powering, the signal generator starts outputting a 4-20ma Signal, and the current value is shown on the display.
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.
- 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”
Read Part 2 of this article which explains more features of this module here –
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