Function Block: Dither Generator; Table 39: Function Block: Nominal Current - WAGO 750-632 Manual

62 Function Description

Table 39: Function Block: Nominal Current

Variable
PA_NOMINAL_CURR
Process value <Current>
Target output current
5.5.5

Function Block: Dither Generator

Using this function block causes a reduction of the influence of static friction. This
enables significant reductions in the response threshold and hysteresis. There
are four parameters provided to use for setting this function:
• #DG_FREQ
• #DG_AMPL
• #DG_RAMP_ON
• #DG_RAMP_OFF
Parameter #DG_FREQ
The frequency of the dither signal can be set using this parameter in a grid from
1 Hz to 250 Hz. The goal is to select the frequency such that the static friction of
the actuator no longer registers.
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
value. Afterwards, the frequency 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 two high, these effects are not as serious; however, the hysteresis can
increase again.
Parameter #DG_AMPL
With this parameter, the amplitude can be specified in a percentage in relation to
the 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 system
becomes noticeable.
Manual
Version 1.3.1, valid from FW/HW-Version 01/01
750-632 Proportional Valve Module
Value
2000
5000
1000
WAGO I/O System 750/753
Unit
mA
0.01%
mA