We recently had some problems with noise making is way into the CW and CCW stepper motor controller signal and thus making the motor rotate when it should have been stationary . We discovered various noise sources including 24V clutches and an impoperly grounded shield; however,we were unable to remove all of the noise. The motor would turn each time when the machine got to a particular step; therefore, we assumed it was another motor/supply generating the noise. When I placed a homemade Spectrum Analyzer (limited to 50kHz)on the CW and CCW, no noise was seen (but could be seen on an oscilloscope). I suspected that the noise was probably beyond this range and suggested tying in some capacitors from the CW and CCW to ground to allow the high frequency content to drain off. My suggestion was not easily accepted but when we tried it, it worked. The controller has an input resistance of 230 ohms and I selected a 0.1uF capacitor to allow the content to roll off above 20kHz. Although this is working and this is the third week it has been working, other people are starting to doubt this technique. I need feedback on this and any short comings I should expect. Thanks for your time.
