User Manual

Control concept
Closed-loop control strategy
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The PID_CTR block can be configured as a P, PI or PID controller. The following parameter settings are
used to define the control action:
● Gain [Gain]
● Integral action time [Tn]
● Derivative action time [Tv]
As an option, the gain [Gain] can be influenced with the [GainFac] input. It can be useful to correct the
gain factor in this way when controlling outside air dampers, e.g., as the effect of the damper positions can
depend on the outside air temperature. The correction factor is defined with the gain scheduling block
ADAGAIN.
The actuator runtime can be set. Specifying the actual actuator run-times makes it possible to tune the
controller more accurately to the actuator concerned, so improving the control quality of the control system.
Correcting range
The correcting range is limited by specifying the minimum and maximum output variable. In this process,
the minimum of the two values is always set as the maximum value. In other words, the maximum value
may be below the minimum value; there is no need to update the minimum value.
Neutral zone [Nz]
[Nz] is a zone on either side of the setpoint, within which the controller does not respond. As soon as the
difference between the setpoint [Sp] and the measured value [Xctl] is less than half of the [Nz], the output
is driven for a further 7 cycles, so that the measured value [Xctl] is as close as possible to the middle of the
[Nz]. The output signal [Yctr] then remains constant. The output signal is only re-adjusted when the
parameters move outside the [Nz] again.
P/PD controller
If the PID_CTR block is configured as a P-controller or PD-controller, a calibration point (Offset) [YctrOfs]
can be specified, e.g., the P-controller can be calibrated so that the set point is maintained with a 50% load.
With a 0% or 100% load, the P-deviation is then half the amplitude of the proportional range [Gain].
Tracking [Track]
[Track] is used, e.g., where the PI(D) controller, operates as a limit controller, e.g., acting on a valve or
actuator via an intermediary minimum or maximum selector block. The tracking input ensures the
availability of the controller during the period in which it is blocked by the minimum or maximum selector
block. During this time, its integrator (and, hence, its output) is maintained at the value of the signal
received, so that if the limit conditions are violated, it is able to respond immediately. [Track] is also used
in conjunction with special actuators with positioning feedback.
Direct/reverse-acting control action [Actg]