User Manual

Control concept
Closed-loop control strategy
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Online diagnostics
A diagnostics screen for the PWR_CTL block is available online in Xworks Plus
(XWP).
The following states are displayed:
● Present value: Operating state at the block output pin [PrVal]
● Action: Transient state [TraSta] depending on actual switching conditions:
Up, down or hold
● Present power: Value at the block output pin [PrPwr]
● Status flag: In accordance with the BACnet definition, the value of [StaFlg]
is always Overridden. Alarms may also be displayed here.
● Released aggregate or stage: This shows the current sequence entry, the
released object [RlsObj] and the released object stage
● Last alarm/event message: Value at the block output pin [LstMsg]
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]
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
PID_CTR stand-alone
controller – Sequence
controller