User Manual

Control concept
Closed-loop control strategy
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The connection is made between the pins of block PID_CTL and a location on the SEQLINK block. The
order in which the PID_CTR blocks are connected must be the same as that of the sequence. The
connections to the SEQLINK block need not be continuous: connected pins and unused pins may be
interspersed.
For example, 1 = Re-heater, 2 = Pre-heater, 3 = Dampers, 6 = Cooling coil.
This method of connection is used to interconnect PID_CTR blocks on different charts, or in cases where
individual project-specific sequence-controller elements or aggregates are to be deleted from an off-the-
shelf solution (CAS library).
Communication between one sequence controller element and another flows via the pins [ToLower] →
[FmHigher] and [ToHigher] → [FmLower].
The block recognizes configuration errors and shows these at the Token State output [TknSta]. If, e.g., the
control action [Actg] of an individual sequence-controller element is incorrectly set, the associated
sequence controller element is disabled and an error message is displayed.
Example: Output from elements 4 and 6 [TknSta] = HEL_CSEQ Output from elements 3 and 5 [TknSta] =
CEL_HSEQ:
Examples of automatically deactivated sequence elements:
In all the examples illustrated, several aggregates are deactivated. This is a precaution, as the sequence
elements cannot determine which of the aggregates has incorrectly set parameters. For this reason, the
aggregates are disabled one after the other until there is a clear transition to the next sequence.
Cascade control
The CAS_CTR block integrated into the Desigo system is a PI master controller for room supply air cascade
control. It delivers three supply air set points on the basis of the difference between the measured room
temperature and the room setpoint.
The following functions are integrated into the block:
● Facility to select P or PI control
● Gain and integral action time (can be configured)