Dither Generator Function Block; Figure 29 Dither Generator Function Block - WAGO 750 Product Manual

Functions

4.4.2.6 Dither Generator Function Block

This function block can be used to reduce the influence of static friction. Thus even small
changes in the valve position can be controlled precisely. This enables significant reduc-
tions in the response threshold and hysteresis. This function can be adjusted with the fol-
lowing parameters:
• DG_FREQ (dither frequency)
• DG_AMPL (dither amplitude)
• DG_RAMP_ON (dither startup ramp)
• DG_RAMP_OFF (dither switch-off ramp)
• DG_WAVEFORM (dither signal form)
• DG_AUTO_AMPL_ADJ (dither – automatic amplitude adjustment)
• DG_DC_CORRECTION (dither – DC correction)
The dither function can be switched on and off with the dither bit in the control byte
(Vx_CTRL).
The parameters are set in
Dither Frequency (DG_FREQ Parameter)
The frequency of the dither signal can be set with the DG_FREQ parameter. The goal is
to select the frequency in such a way that the static friction of the actuator no longer reg-
isters. However, the dither frequency should not affect the hydraulic circuit controlled by
the valve.
Basically, the frequency should be set as low as possible until the system controlled by
the valve reacts to the dither signal superimposed on the setpoint. Afterwards, the fre-
quency should be incrementally increased until the system reaction disappears again.
At frequencies that are too low, the actuator in the valve increasingly follows the dither
signal, and the valve output becomes more unstable. At frequencies that are too high,
these effects are not as serious; however, the hysteresis can increase again.
Dither Amplitude (DG_AMPL Parameter)
Using the DG_AMPL parameter, the amplitude can be specified as a percentage in rela-
tion to the nominal current. Values up to 50 % are possible. To cause a reaction of the
valve spool, the amplitude chosen must be high enough and the frequency chosen low
enough.
If the selected amplitude is too large, then pulsing in the hydraulic system becomes no-
ticeable.
Dither Startup Ramp and Dither Switch-off Ramp (DG_RAMP_ON or
DG_RAMP_OFF Parameter)
The dither signal is only gradually supplied to the actual value during on and off switch-
ing. The temporal progression is determined by a startup ramp and a switch-off ramp.
50 Product manual | Version: 1.1.0
Proportional Valve Module 2-3-4
8 Parameter Tables 162 and 163
750-1632/000-100
Figure 29: Dither Generator Function Block
[} 41].