J
I've been experiencing issues with Woodward Governor SPC's not following demand. On two separate SPC's, the analog position being fed by the SPC back to a ControlLogix is very quickly (30 to 100 mS) deviating by over 25% for several seconds, which trips the process. The SPC's are configured to use both devicenet and analog as demand with devicenet as the primary signal and are returning their position as both devicenet and analog. The PLC looks at demand verses analog feedback and trips the process if there is a deviation greater than 25% between its demand and the analog feedback. The demand may not even be changing, but the SPC suddenly reports that the servo is off sufficiently to trip. The servos themselves are typical servos with a bias current and 2 AC lvdt's per servo. This problem only appears every few hours. Otherwise, the servos appear to behave correctly. Can anyone provide direction as to what to even look for.