Instrument Maintenance

Use an ohmeter and check for floating grounds. Some Daq cards have a floating common or referenced ground. I suspect somewhere in the field panel someone or something has linked them. A check of the previous maintenance records might give you some clues.

I am reminded of a similar problem I ran into many years ago. We had a product which had been field tested for ages with superb results, but suddenly in new installations, the product went to hell in a handbasket. The PC boards worked perfectly on the bench, but in the field, they immediately failed. With serious (and expensive) research, it was discovered that the manufacturers of the card cage had gone from nylon card guides, to metallic card guides, which shorted out our boards.

Bill

1) Is the machine installed for 1st time? if so consult the supplier.

2) If not, What was the 1st reason to remove from the plant? if it is for the same reason as stated above, try to use Ohm-meter and trace the contact of power line with the ground line. Usually it is loose contact then have good time to detect it.

3) if you removed the machine for some another reason, try to inspect all the material and work done. it is probable you commited some error?

A clear answer would require seeing the wiring drawing. But you should be able to float the power supply ground and then use a volt meter to verify the voltage at several points. The re-connect the ground system and watch if the voltage drops off. You may need to look at other components wired into the system and see if they are introducing another voltage source.

Good luck

Jack Beadling

jbeadling@augustaeng.com