User Manual

Control concept
Closed-loop control strategy
5
94 | 351 CM110664en_07
The lowest sequence-controller element (Low) corresponds to control sequence 1, and the highest (High)
to control sequence n.
The lowest sequence-controller element controls a reverse-acting aggregate (if used).
The type of operation may also be reversed during normal operation, (e.g., for energy recovery) but the
order of the sequences must not be affected.
In the sequence controller, the set points [Sp] of sequence-controller elements (1…n) must increase
incrementally:
[Sp]
1
≤ [Sp]
2
≤ [Sp]
3
≤ ... ≤ [Sp]
n
In the transition from one control sequence to the next, continuous control is maintained if all the control
sequences with the same type of operation (direct or reverse acting) also have the same setpoint.
When the type of operation changes, the neutral zone is defined by the set points (e.g., heating setpoint /
cooling setpoint).
Options for connecting sequence controller elements
The PID_CTR blocks can be connected to form a sequence controller via:
● Direct connection
● SEQLINK connection
Direct connection
The individual PID_CTR blocks are connected directly with each other. The [ToLower] pins are connected
to the [FmHigher] pins, and the [FmLower] pins are connected to the [ToHigher] pins.
SEQLINK connection
With this method, the individual PID_CTL blocks are connected via the SEQLINK block. The sequence
linker block SEQLINK is a wiring block with no function other than that of connecting other blocks.