Omron Sysmac CJ Series, Operation Manual

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80
Troubleshooting Section 5-2
Excessive Overshooting or Undershooting
Excessive Hunting
The same connection and settings problems can cause overshooting, under-
shooting, and hunting. Refer to
Excessive Overshooting or Undershooting on
page 80 for details on possible connection and settings problems.
Step Possible Cause Remedy
Connection The measured temperature is incorrect. Refer to 5-2-1 Troubleshooting from Symptoms: Mea-
surement Errors for troubleshooting directions.
A general-purpose temperature sensor is being
used in a system with a very fast heating
response. Change to a sheathed sensor.
Settings The proportional band is narrow because PID
constant P is too small. • Increase the P constant to a level that produces an
acceptable response delay.
• Perform autotuning.
The integral time is short because PID constant I
is too small. • Increase the I constant to a level that produces an
acceptable response delay.
• Perform autotuning.
The derivative time is short because PID constant
D is too small. • Increase the D constant to a level that produces
acceptable stability.
• Perform autotuning.
ON/OFF control is being used. Use P (proportional) control or PID control.
A long control period has been set in a system
with a very fast heating response. Reduce the control period.
Autotuning was performed, but the Temperature
Control Unit’s PID constants were not refreshed
with the calculated PID constants. Refresh the Temperature Control Unit’s PID constants
with the calculated PID constants. Refer to
3-9 Setting
the PID Constants for details.
Step Possible Cause Remedy
Usage The heater’s output is too large for the controlled
system. Use a heater that is suitable for the controlled system.
Something disturbs the system periodically and
changes it’s heating requirement. Arrange the controlled system to minimize external dis-
turbances.
Autotuning is in progress. The hunting will stop when autotuning is completed.