Omron CJ Series Operation Manual page 103

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