Chapter 10 Built-in PID Functions
10 - 7
10.4.2 PID instruction group
The PID instruction group includes 5 instructions: PIDRUN, PIDCAS, PIDINIT, PIDPRMT, and PIDPAUSE. In
fact, all operations of the PID function are performed by the PIDRUN or PIDCAS instruction. The three other
additional instructions (PIDINIT, PIDPRMT, PIDPAUSE) operate normally when the PIDRUN or PIDCAS
instruction also exists on the ladder program. They are for the convenience in using the PIDRUN or PIDCAS
instruction.
(1) PIDRUN
PIDRUN is the most basic PID control instruction that is responsible for single PID loop control.
Operand S has the range 0 ~ 31 (constants) and means the loop number.
(2) PIDCAS
PIDCAS is a instruction to implement a cascade control using two loops.
Operand M is the master loop with the range 0 ~ 31 (constants) and means the loop number.
Operand S is the slave loop with the range 0 ~ 31 (constants) and means the loop number.
Note
Operands M and S in PIDCAS cannot be the same.
Operand M means the number of the master loop during cascade PID operation, while
operand S means the number of the slave loop.
Basically, the master loop inputs its MV into SV of the slave loop during operation, while the
slave loop executes its operation using the SV value input thorugh the master loop.
In addition, the two loops observe each other’s operation information (wind-up, manual
mode, auto mode shift, etc).
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