User Manual

Control concept
Closed-loop control strategy
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5.4 Closed-loop control strategy
Controller types
For closed-loop control purposes, two controller blocks are provided in the Desigo system, which cover the
majority of requirements:
● [PID_CTR]
● [CAS_CTR]
PID_CTR stand-alone controller – Sequence controller
The PID_CTR block is used as:
● A universal stand-alone PID controller
● A universal PID controller with external tracking
● An individual sequence-controller element in a sequence controller or sequence cascade controller
The PID_CTR block integrates the following functions:
● Can be programmed for P, PI, PID or PD control action
● Gain, integral action and derivative action can be programmed individually
● Proportional control output with minimum and maximum limit control
● Programmable gain factor
● Programmable neutral zone
● Programmable offset (for P and PD controllers)
● Programmable initial integrator value (for PI or PID controllers)
● Programmable runtime for control variable (0 – 100%, 100 – 0%) and positioning speed
● Type of operation (direct acting or reverse acting) can be selected
A sequence controller can be implemented by interconnecting several PID_CTR blocks. The sequence
linker SEQLINK can also be used, where appropriate. The only function of this block is to enable individual
sequence elements to be deleted without the need to create new connections.
CAS_CTR cascade controller
The PID_CTR block is used:
● As the master controller in a sequence cascade control configuration (e.g., room/supply air cascade).
● In temperature and humidity control loops
The following functions are integrated in the CAS_CTR block:
● Can be programmed for P, PI, PID or PD control action
● Proportional controller output with minimum and maximum limit control
● Setpoints for heating and cooling sequences, and for energy recovery
● Setpoint depending on type of operation, for energy recovery
● Initialization of integrator (initial value)
Universal PID controller
The PID_CTR block can be used as a universal stand-alone controller in a plant for the control of any
control variables, e.g.:
● Temperature, temperature differential
● Pressure, pressure differential
● Velocity
● Absolute humidity, relative humidity
Control action