Proximity Switch's

[Gordo26 0]

Just wondering if anyone else has ever seen this, and any advice that anyone might have. I have two proximity switches on a conveyor line, one is used as a decel, the other is used to stop the objects movement. For some unknown reason both of these switches are randomly turning on without any metal touching them at all. This happens to mess with the sequence of operation and is becoming quite troublesome. The proxy's go back to a multiport terminal, which is then fed back to a remote input card. Both the multiport, the input card and the multiport cable have been changed out and the problem still persists. Any help would be appreciated. Thanks, Gordo

[OkiePC 14]

Are the cables routed near noisy VFD motor leads, by chance? Edited 15 Mar 2012 by OkiePC

[Shiner 2]

As Okie says, VFD's can be the culprit, either by noisy conductors that are unshielded, or by an improperly grounded motor as well.. Preferably you would want to run them in conduit or shielded SO cord. The housing of the motor will radiate the noise caused by the switching frequency of the drive and I have seen this cause problems like what you are describing. The second possibility, what kind of prox's are you using? If they are a two wire prox wired directly to an input, the current used to operate the prox circuitry could be flirting with the threshold of opening the gate on the input. If two wire devices are used it is always good to have iinterposing relays in the circuit. Edited 19 Mar 2012 by Shiner

[Gordo26 0]

There are several motors running off VFD's in the area and I did notice we use SO cord which runs along the same path as the wires for the proxy's. The proxy's are three wire PNP. As for a bad ground, I'll have to wait for some downtime before I'm able to check that out. Thanks very much for your help! Gordo

[OkiePC 14]

If you can reroute the prox. cables, every inch of separation you can gain will help if this is noise caused by the VFD outputs.