60 Function Description WAGO-I/O-SYSTEM 750750-632 Proportional Valve ModuleManualVersion 1.3.0, valid from FW/HW-Version 01/01Table 39: Function Block: Nominal CurrentVariable Value UnitPA_NOMINAL_CURR 2000 mAProcess value 5000 0.01%Target output current 1000 mA5.5.5 Function Block: Dither GeneratorUsing this function block causes a reduction of the influence of static friction.This enables significant reductions in the response threshold and hysteresis. Thereare four parameters provided to use for setting this function:• #DG_FREQ• #DG_AMPL• #DG_RAMP_ON• #DG_RAMP_OFFParameter #DG_FREQThe frequency of the dither signal can be set using this parameter in a grid from1 Hz to 250 Hz. The goal is to select the frequency such that the static friction ofthe actuator no longer registers.Basically, the frequency should be set as low as possible until the systemcontrolled by the valve reacts to the dither signal superimposed on the setpointvalue. Afterwards, the frequency should be incrementally increased until thesystem reaction disappears again.At frequencies that are too low, the actuator in the valve increasingly follows thedither signal and the valve output becomes more unstable. At frequencies that aretwo high, these effects are not as serious; however, the hysteresis can increaseagain.Parameter #DG_AMPLWith this parameter, the amplitude can be specified in a percentage in relation tothe nominal current. Values up to 50% are possible.In order to effect a reaction of the valve gate:• the selected amplitude must be large enough, and• the selected frequency must be small enough.If the selected amplitude is too large, then pulsing in the hydraulic systembecomes noticeable.
