Cascade Control - Omron CS1W-LC001 Operation Manual

Examples of Applied Control Types
5-2-1

Cascade Control

Example
162
In the following instances, input the MV of PID1 on the primary loop and the
Remote Set Point of PID2 on the secondary loop, and connect the PC in
series. This configuration is referred to as "cascade control."
1) When there are two controllable processes, and the process to be
controlled is one of the processes (PV of primary loop)
2) When the other (primary loop) can be controlled by controlling the other of
the two (secondary loop)
3) When there is disturbance on the other process (secondary loop), or when
there is dead time until the effect of change on the other (secondary loop)
operated terminal appears in the PV of the other (primary loop)
PID1 of the primary loop indirectly controls the finite control element of the
secondary loop by controlling the setting value of PID2.
By this control, PID2 of the secondary loop absorbs the disturbance on the
secondary loop, and suppresses the influence of the disturbance on the
secondary loop on the primary loop. (The effect on the disturbance on the
secondary loop increases as the response of the secondary loop process
becomes faster than primary loop processes.)
Note 1 This kind of cascade control has no effect on disturbance entering the
primary loop. Cascade control must be combined with feedforward control in
this case.
Function blocks used: Two Advanced PID blocks (Block Model 012)
PV1
MV output of one Advanced PID block is input to the Remote Set Point of the
other Advanced PID block.
MV1
Advanced PID
Block Model 012
RSP
Advanced PID
PV2
Block Model 012
Section
MV2
5-2