User Manual

Control concept

Closed-loop control strategy

90 | 353 CM110664en_07

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.

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].

[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.

[Actg] is a characteristic parameter of the controller and indicates the

relationship between the setpoint deviation and the change in energy flow. A

distinction is made between direct action and indirect [Actg].

● Direct control [Actg]: As the controlled variable rises, the controller output

increases, and as the controlled variable falls, so the controller output

decreases.

Example: Cooling or dehumidification – as the measured value rises above

the setpoint, so the flow of energy is required to increase.

● Indirect control [Actg]: As the controlled variable decreases, the controller

output decreases.

Example: Heating or humidification – as the measured value falls below the

setpoint, so the flow of energy is required to increase.

Neutral zone [Nz]

P/PD controller

Tracking [Track]

Direct/reverse-acting

control action [Actg]