I've just upgraded from using microswitches as limit/homing switches to LJ12A3-4-Z/BX type inductive proximity sensors. I'm getting some spurious trips from the Z-axis sensor due to interference from the spindle, a Huan Yang 2.2kW water cooled unit fed from a VFD. The spindle and sensor wiring go through the same drag chain for part of the run and I'd like to avoid having to separate them if possible.

One of the symptoms is that the red LEDs on the relevant sensors glow visibly, but very dimly, when the spindle is running. A ferrite ring on the sensor cable makes no difference, neither does a 1uF capacitor between ground and either the +V supply or sensor output.

Has anyone else seen this faint glow before and, if so, how did you fix it?

All help gratefully received.