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35 CPU MODULE BUILT-IN ANALOG FUNCTION
35.5 Function (PID Control Via Instruction)
■Hunting suppression setting
Especially, if the step response method auto-tuning (Page 612 Auto-tuning) is executed in an environment where the
measurement value varies temporarily because of noise of the sensor and analog input, auto-tuning may not be executed
correctly and hunting may occur during PID control operation.
When b8 of (s3)+1 is turned ON and the current input value is less than the previous input value temporarily, auto-tuning is not
completed until the set timeout time has elapsed. Therefore, maximum ramp (R) can be obtained correctly. (See the figure
below.)
To use this function, turn ON b4 of (s3)+1 and OFF b6 of (s3)+1.
The ramp value is obtained with the following formula.
Ramp value = (current input value - previous input value) sampling time
If the hunting suppression setting is not used, the PID control operation with similar performance to the FX3
PLC will be executed.
Set item Description/Setting range
Operation setting (s3)+1: b4 Auto-tuning Make sure to set it to ON
(s3)+1: b6 Auto-tuning mode Make sure to set it to OFF
(s3)+1: b8 Hunting suppression setting ON: Used
OFF: Not used
(s3)+25 Timeout time setting value after
maximum ramp (R) detection
1 to 32767 (second)
(1) Timeout wait after maximum ramp (R) detection
(2) A decrease of ramp caused by temporary deviation of the input
value
(3) Maximum ramp (R) is updated and auto tuning continues
(4) Timeout wait after maximum ramp (R) detection
(5) Maximum ramp (R) detection value at the end of auto tuning
(6) Maximum ramp (R) detection value at the end of auto tuning
when this setting is not used
Time
Ramp value
(1) (1)
(2)
(5)
(6)
(3) (4)
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