Dither

Dither is a rapid, small movement of the spool about the desired shift point. It is intended to keep the spool moving to avoid stiction and to average out hysteresis. Dither must be large and slow enough to make the spool move and small and fast enough not to cause pulsing or resonance in the system. Use dither when fine control of a proportional valve is necessary or when the user has an input device with a fine degree of labeling such that they are troubled by hysteresis. Dither is not usually required when using EDC or Servo valves. It is often hard to know if dither is required until after machine commissioned. Dither can cause problems if not applied correctly and can be hard to adjust. The HA valve drivers with dither generators allow turning off the dither so that it is available as cheap insurance if it is needed, but does not cause trouble if it is not.

Dither waveform examples.