Connecting multiple Passive 4-20mA sensors to Sigma controller

[Product_Support]

Issue

Multiple passive 4-20mA sensors require an external power supply when connecting to a Sigma controller.
How can this be done correctly and safely?

Product Line

Satchwell BAS & Sigma

Environment

• Sigma UNC Controller
• Passive 4-20mA Sensors
• External Power Supply (12V DC or 24V DC)

Cause

Unlike active 4-20mA sensors, which include an internal power source, passive sensors do not.
Therefore, an external power supply is necessary to operate them when interfacing with a Sigma controller.

Resolution

To connect multiple passive 4-20mA sensors to a Sigma controller:

1. Use a dedicated external power supply for each sensor.

   • Voltage: 12V DC or 24V DC, depending on sensor specifications.

2. Wiring Instructions:

   • Connect the positive terminal of the power supply to the positive input of the Sigma controller.
   • Connect the negative terminal of the sensor to the common ground.

     

3. Configure Sigma Controller:

   • Ensure the Universal Input jumper settings are correctly set to current (mA) mode.
   • Verify input scaling and calibration in the Sigma software to match the sensor's output range.

4. Best Practices:

   • Use shielded cables to minimize electrical noise.
   • Label each sensor connection clearly for maintenance and troubleshooting.
   • Avoid sharing power supplies between sensors unless specifically supported by the sensor manufacturer.
   • Always consult the sensor's datasheet for exact wiring and voltage requirements.