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MELSEC-Q/QnA
5. PID CONTROL PROCEDURE
5.1.2 Sampling cycle
(1) A sampling cycle is the cycle in which PID operation is executed.
The measurement time for one scan is added to the measurement time of up to
the preceding scan each time a PID operation instruction*
1
is executed.
When the cumulative value reaches or exceeds the set sampling cycle, the PID
operation of the corresponding loop is performed.
(2) The measured value of the sampling time used for PID operation is truncated to
units of 10 ms.
For example, if the sampling cycle setting is 50 ms and the measured value is 57
ms, PID operation is executed with a sampling time of 50 ms.If the measured
value is 64 ms, PID operation is executed with a sampling time of 60 ms.
When sampling cycle = 50 ms
PID operation is executed
with set values.
PID operation is executed
with 50 ms sampling
time.
PID operation is executed
with 60 ms sampling
time.
Measured value is changed
to 57 - 50 = 7 ms
Measured value is changed
to 64 - 60 = 4 ms
0
END
PID operation
instruction
0 ms
19 ms
0
END
19 ms
19 ms
0
END
19+19=38 ms
19 ms
0
END
4+19=23 ms
0
END
26+19=45 ms
0
END
7+19=26 ms
19 ms
19 ms
PID control
data setting
instruction
0
END
38+19=57 ms
19 ms
19 ms
0
END
45+19=64 ms
Power ON
Measured
value
Sequence
program
Measured value
< Set value
Measured value
< Set value
Measured value
< Set value
Measured value
> Set value
Measured value
< Set value
Measured value
< Set value
Measured value
> Set value
Measured value
< Set value
PID operation
instruction
PID operation
instruction
PID operation
instruction
PID operation
instruction
PID operation
instruction
PID operation
instruction
PID operation
instruction
POINT
The sampling cycle is measured when the PID operation instruction is executed.
Therefore, a value smaller than the sequence program scan time cannot be set for
the sampling cycle. If a value smaller than the scan time is set, PID operation will
be executed in accordance with the scan time.
REMARK
*1: The following instructions are available as the PID operation instructions.
S.PIDCONT (incomplete derivative)
PIDCONT (complete derivative)
*2: The following instructions are available as the PID control data setting
instructions.
S.PIDINIT (incomplete derivative)
PIDINIT (complete derivative)
Содержание Q Mode
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Страница 18: ...1 4 MELSEC Q QnA 1 GENERAL DESCRIPTION MEMO ...
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