During a recent start-up of a desiccant dehumidifier air handling unit, it was noticed that the on-board PLC readout from the remote 0-10Vdc room temp/humidity transmitter signal was very erratic. All other unit transmitters factory installed and wired within the unit were reading steady. This is a short article on A Visual Example of Control Signal Interference.
Electrical interference was immediately suspected and was ultimately the culprit. It was interesting to note however that prior to correction, when using a hand-held meter, the same signal was measured as steady both at the PLC and wire itself. The proper twisted, shielded control wire was used and grounded at one end only.
Watch this short video to witness the interference:
The problem was that about 50 feet of the control wire was run parallel to, and very near, other high-power conduit that created an electrical interference. While the meter did not reflect any abnormal issue, the PLC’s sampling was obviously impacted. Once separated the issue was resolved.
“All other unit transmitters factory installed and wired within the unit were reading steady.”
Factory Mounted OSA Transmitter Applied Mechanical Solutions
Using the hand-held meter was one of the steps that our start-up crew from Applied Mechanical Solutions used to help identify and correct the root cause. Using qualified start-up personnel helps to uncover issues that may otherwise go unnoticed. Q Applied Systems provides start-up service with all major HVAC equipment we represent.
Videos of other equipment and applications can be found at the Q Applied Systems YouTube page.
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About Q Applied Systems, Corp
Q Applied Systems is a manufacturers’ representative of HVAC and moisture control equipment and systems as well as fume and dust collection products throughout Southern California and Baja Mexico. We specialize in the application of engineered systems and equipment for commercial and industrial markets. Click here to view the manufacturers and products that we represent.