Testing 4-20 mA Transducer

Testing a 4-20 mA building space pressure transducer connected to Trane BAS.

1) Measure actual building space pressure at the transducer tubing. If it’s measuring reasonably well based upon your observation, continue troubleshooting. If you have reason to believe the tubing is sampling from a poor location, relocate the sampling tubes’ termination point after verifying the tubing isn’t damaged or plugged.

2) In this case, my dual port manometer verified the building is under a reasonable slight positive pressure of 0.05” wc. I reconnected the transducer tubing and disconnected one of the two transducer signal wires and measured its mA output with my meter in SERIES. It read 0.01 mA or effectively zero.

3) I tested the BAS ability to translate the signal with a signal generator. At 12 mA it read effectively 0.0” wc or a neutral building pressure accurately.

4) My last step is to verify the control wiring integrity. I’ll check for shorts or breaks in the wiring.

5) If the wiring is damaged, we’ll replace the wiring and retest the signal. If the wiring is good, we’ll replace the transducer.