Number Of Loops To Be Used And The Number Of Loops To Be Executed In A Single Scan - Mitsubishi QCPU Programming Manual

5. PID CONTROL PROCEDURE
5.1.1 Number of loops to be used and the number of loops to be executed in a
single scan
(1) The number of loops to be used means the number of loops for which PID
operation is executed. The sampling cycle time is measured for the set number
of loops when the PID operation instruction
executed for the loop for which the sampling cycle time reaches or exceeds the
set sampling cycle.
(2) Processing time increases in proportion to the number of loops for which PID
operation is executed when the PID operation instruction is executed.
Processing time = A + B
(3) The number of loops to be executed in a single scan means the number of loops
for which PID operation is executed in one scan when there is more than one
loop for which sampling cycle time reaches or exceeds the set sampling cycle
when the PID operation instruction is executed.
If the number of loops to be executed in a single scan is set, PID operation is
only executed for the set number of loops even if there are a greater number of
loops for which the sampling cycle time reaches or exceeds the set sampling
cycle when the PID operation instruction is executed. PID operation is executed
for the rest of the loops in the next scan.
Sequence program
Execution of the PID operation
POINT
If the number of loops for which sampling cycle time reaches or exceeds the set
sampling cycle is greater than the number of loops to be executed in a single scan,
the PID operation execution priority is as follows:
(1) The lowest numbered loop is given the highest priority.
(2) If there are loops in the preceding scan for which PID operation has not been
executed, they are given the highest priority.
REMARK
*: The following instructions are available as the PID operation instructions.
S.PIDCONT (incomplete derivative)
PIDCONT (complete derivative)
*
is executed. PID operation is
A : Fixed time for measuring sampling time
n B : Time required to execute PID operation for a
loop
n = Number of loops
Execution of
PID operation instruction
END 0
Processing time
= A + B n
5 - 15
MELSEC-Q/QnA
Next PID operation
instruction step
END 0
Processing time
= A + B n
Scan time