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POS-123-*-2030
7.8.3
CURRENT (Rated output current)
Command
Parameters
Unit
Group
CURRENT
x
x= 500… 2600
mA
STD
The nominal output current is set. Dither and also MIN/MAX always refer to this current range.
7.8.4
DFREQ (Dither frequency)
7.8.5
DAMPL (Dither amplitude)
Command
Parameters
Unit
Group
DFREQ
x
x= 60… 400
Hz
STD
DAMPL
x
x= 0… 3000
0,01 %
STD
The dither
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can be defined with this commands. Different amplitudes or frequencies may be required
depending on the valve.
The dither amplitude is defined in % (peak to peak value) of the nominal output current
20
(see: CURRENT
command).
The dither frequency is defined in Hz. Depending on the internal calculations, the frequency is adjustable in
steps only
21
.
CAUTION: The PPWM and IPWM parameters influence the effect of the dither setting. These
parameters should not be altered again after the dither has been optimized.
CAUTION: If the PWM frequency is less than 500 Hz, the dither amplitude DAMPL should be set to
zero.
7.8.6
PWM (PWM Frequenz)
Command
Parameter
Unit
Group
PWM
x
x= 61… 2604
Hz
EXP
The frequency can be changed in defined steps (61 Hz, 72 Hz, 85 Hz, 100 Hz, 120 Hz, 150 Hz, 200 Hz, 269
Hz, 372 Hz, 488 Hz, 624 Hz, 781 Hz, 976 Hz, 1201 Hz, 1420 Hz, 1562 Hz, 1736 Hz, 1953 Hz, 2232 Hz and
2604 Hz). The optimum frequency depends on the valve.
Attention: The PPWM and IPWM parameters should be adapted when using low PWM frequencies
because of the longer dead times which forces a reduced stability of the closed loop control.
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The dither is a ripple signal which is superimposed on the current set point and is defined by the amplitude and fre-
quency: the dither frequency and the PWM frequency.
The dither frequency should not be confused with the PWM fre-
quency
.
In some documentations the PWM frequency is described as a dither. This can be recognized by the lack of the
dither amplitude.
20
The dither amplitude is a command signal. Derivations between the commanded amplitude and the real amplitude are
possible, depending on the dynamic of the solenoid.
21
The lower the dither frequency, the smaller the steps. Therefore no practical problems are expected.
