Analog signals wiring

F

Thread Starter

Feg

I have found an installation where four 4-20 mA signals travel inside the same shielded wire. The shield is properly grounded at one end. I would recommend to separate each 4-20 mA signal in an independent shielded wire with its own shield, I had never seen such an installation and I cannot tell of the possible consequences of it.

The fact is that the signals are going to a videographic recorder, the user reports that he replaced the analog input card (6 channels) once as "warranty" with the manufacturer because all the channels were broken and now with a new analog input card he reports that one channel is broken again.

Could this wiring be the problem?
 
M

Michael Griffin

In the same *wire*, or the same *cable*? "Same wire" does not make sense. Multiple pair cables may cause channel to channel noise, but they shouldn't damage the hardware. Check if the card really is "broken", or it is just a noisy signal. If you switch the wiring between channels, does the problem follow the wiring?

If the hardware really is damaged, I would suspect something in the field devices or their connection to the recorder. Check signal conditioners, signal connections, etc.
 
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