Sounds to me like you're getting EMF from a variable speed drive. That could be because your transducer (or transducer wiring) is too close to the motor or the cable feeding the motor. I've even seen noise introduced into the AC control power from drives without input reactors or an isolation transformer affect analog inputs. Is your instrument cable run inside a steel conduit? A shield can only reject so much noise.
currently the wires are only connected from the control cabinet to the machine for testing purposes within the shop, so they are in no conduit at all. although the is quite close to a slew of high voltage AC wire, i will have to rectify that tomorrow.
-are analog output signals just as susceptible to noise? i have an analog output card in the cabinet sending two separate 4-20ma signals to two separate vfds for speed control and watching the drives the HZ stays dead nuts when commanded.
-could i test with a voltmeter how much noise i am seeing on the signal wire? lift the shield from the cabinet, put it on one probe on meter, put other probe on meter to ground? or would i lift the signal wire from the transducer and use that while leaving the shield in place?