DC supply decoupling

We are refurbishing a machine which uses an inverter to run a motor. This is geared down to a rotating plate. the number of rotations of this plate is counted using an encoder and digital counter.

We are getting a lot of interference on the counter and in certain encoder positions it counts up/down rapidly when no movement is occuring. The old machine is badly wired with motor cables routed alongside control cables.

We have been separating the control cables from the inverter cables but the problem is still happening. It seems now that the inverter is affecting the DC supply to the encoder and that it is this which is causing the interference.

I remember in the past that it has been possible to decouple across DC lines with capacitors to help remove noise. However I can not remember capacitor types/sizes which are most suitable. Does anyone have any ideas on which will be best?

I know that this is not the nest solution and ripping out all the old wiring and replacing it would be better, however at the moment this is the only viable solution due to time scales.

Thanks for your help in advance

Run the encoder off batteries to see if your diagnosis is correct. The noise (assuming it's a noise problem) may be getting in somewhere else besides the dc power supply. If it works properly from the batteries, that supports your present diagnosis. Then you can try fixing the problem with capacitors. I'd start with .01 uf disc ceramic.

Ed

Are you using VFD cable? I have had problemsin th epast with this.

You can also change the carrier frequeb=ncy of the inverter and see what happens.

The drive should have inductors on the output.

Regards Daveb

I have had a similar problem that were causing strange readings from a 24vdc pulsed flow meter. Even though all cables were routed correctly and everything was wired in screend cable.

We found the only solution to the problem was to fit a choke/inductor on the output of the inverter. This cured all the problems we were having.

sQuick..