Number Of Loops To Be Used And The Number Of Loops To Be Executed In A Single Scan - Mitsubishi Electric MELSEC-Q series Programming Manual

Number of loops to be used and the number of loops to be
executed in a single scan
• 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
loop for which the sampling cycle time reaches or exceeds the set sampling cycle.
• Processing time increases in proportion to the number of loops for which PID operation is executed when the PID operation
instruction is executed.
Operational expression
Processing time = A + B  n
• 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.
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:
• The lowest numbered loop is given the highest priority.
• If there are loops in the preceding scan for which PID operation has not been executed, they are given the
highest priority.
*1 The following instructions are available as the PID operation instructions.
S.PIDCONT (incomplete derivative)
PIDCONT (complete derivative)
*1
is executed. PID operation is executed for the
Meaning of symbols
A: Fixed time for measuring sampling time
B: Time required to execute PID operation for a loop
n = Number of loops
5 PID CONTROL PROCEDURE
49
5.1 PID Control Data
5