ECKELMANN VS 300, Operating Instructions Manual

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Function of VS 300
51 Doku-Version 2.05 - Firmware 2.10 - 15. September 2017
The P action causes the controller to respond directly to control errors. The I action avoids sustained control er­
rors.
I
Action
I
Action
t
c_Act
t
c_Setp
4
adjust . diff .
Adjusting differential = Definable controller speed
4.5.7 Control algorithm with combined controller
High pressure detected by an A/D converter is compared with the setpoint (see section 4.5.10 Determining the
High-pressure Setpoint).
Depending on the control error, a controller output is calculated to control the fan speed as a 0-10 V signal.
Since the controller acts as a PI controller, both P and I action are calculated.
Calculation of P action:
P action = Control error : 4
Calculation of I action:
The P action acts immediately on the speed in response to a change in pressure. The remaining control error is
minimized by continuously increasing or decreasing the control signal (ramp function). Ramp speed (I action of
controller) is a function of the control error. An excessively high ramp speed results in continuous high pressure
overshoot.
An excessively low ramp speed results in the high-pressure setpoint only being attained with a long delay. The
controller is then too slow. So as to match the I action to the system, the ramp speed can be influenced by
means of the
Adjust Diff. parameter.
I
Action
I
Action
control error adjust . diff .
A positive adjusting differential results in steady state being obtained faster. A negative adjusting differential re­
sults in slower control action.
The I action is attenuated in order to avoid controller hunting at low part load conditions. If only the variable-
speed fan is running, the control signal (0-10 V) is less than 50% and the control error is less than the neutral
zone, the condenser is operated at low part load.
I action is then
I
Action
I
Action
(
control error adjust . diff .)
8
Allowance is made for the pressure change when the control error is small. If the control error is positive and
pressure is falling and lower than the setpoint plus neutral zone in part-load operation or half the neutral zone in
full-load operation, I action is not changed. The I action is also not changed when the control error is negative
and the pressure is rising and greater than the setpoint less neutral zone in part-load operation or half the neu­
tral zone in full-load operation.
So as to prevent speed increasing too fast, increase of the I action is limited to a maximum of 10% of the control
signal (0-10 V). With control errors above or below 1.5 times the neutral zone, the fan runs at maximum or mini­
mum speed.