Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 1155

■Number of loops used and number of execution loops in one scan
The number of loops used is the number of loops where PID operation is performed. The sampling period is measured for the
set number of loops when the PIDCONT instruction is executed, and PID operation is performed for the loops that reach the
specified sampling period.
Processing time of the PIDCONT instruction increases in proportion to the number of loops where PID operation is performed.
The number of execution loops in one scan is the number of loops where PID operation is performed in one scan when there
are multiple loops that reach the specified sampling period. If this number is set, PID operation is performed only for the set
number of loops, and PID operation for the rest of the loops that reach the sampling period will be performed in the next scan.
Program
Performing PID operation
A: Time required to measure sampling period
B: Time required to perform PID operation for a single loop
n: Number of loops
When the number of loops that reach the sampling period exceeds the number of execution loops in one
scan, the priority order will be as follows:
• The loop with the smallest loop number is given the highest priority.
• If there are loops where PID operation is performed and not performed in the last scan, the priority is given
to the ones where PID operation is not performed in the last scan.
Executing the
PIDCONT instruction
END 0
Processing time
= A + B × n
Next step of the
PIDCONT instruction
END 0
Processing time
= A + B × n
Scan time
10 PID CONTROL INSTRUCTIONS
10
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10.1 Overview