Built-in analog I/O noise

[pattyo 0]

On our CP1H-XA we have some analog position sensors feeding into the built-in analog, and outputting 0-5V to two stepper motor drivers. We used shielded twisted pair 24AWG wire and were getting a lot of fluctuations in the motor speed. Motor speed is measured with some 10,000ppr encoders. We fixed the output values (to eliminate the sensor input variable) and still got a lot of fluctuation, like 5-20% depending on my mood and the alignment of the planets. I switched the drivers over to our analog output extension module and now they run perfectly smooth with <.01% fluctuation. Are the built-in analogs inherently noisy, unshielded, or could something be wrong with our unit? Edited 24 Jan 2012 by pattyo