I have a rotary (2000ppr) shaft encoder connected directly to a Cygnal C8051F000 to measure the speed of a medium sized induction motor. The mc counts the number of pulses received every tenth of a second and calculates the shaft speed. A PI control algorithm then outputs a signal to control the motor power electronic drive. The software works at lower drive voltages, the trouble is that the mc becomes unstable when the motor receives increased voltage levels, and resets often causing instability. Scoping the input Channels of the encoder show considerable noise associated with the motor drive, so my question is, which is the best way of preventing the encoder noise from interfering with the MC and causing my problems? Opto or somekind of buffering circuitry?

Thanks

Konrad