<Toc> <5. Parameters>
5-7
IM 05D01D02-41E 4th Edition: May 31, 2006-00
■ Auto-tuning
Auto-tuning is a function with which the controller automatically measures the process
characteristics to automatically set the optimum PID constants. This function does not work
when the controller is performing on-off control. The UT350/UT320 employ the “Limit Cycle
Method.” As shown in the figure below, the controller temporarily changes its control output
in a step-waveform manner. Then, it calculates the optimum proportional band (P), integral
time (I) and derivative time (D) from the resulting response to set them in their respective
parameters.
PV input value
Control output
Interval of auto-tuning
Auto-tuning is
complete when the
3rd peak arrives.
PID control based on
PID constants determined
by auto-tuning
On
Off
On
Setpoint
Time
Start of
auto-tuning
On
Off
If the Output High Limit (OH) and Output Low Limit (OL) parameters are already config-
ured, the control output turns on and off only between the output’s high and low limits
during auto-tuning.
● Auto-tuning Using Zone PID (see “■ PID Switching (Zone PID)” later in
this chapter)
Setting of
AT Parameter
Auto-tuned Setpoint
OFF - Auto-tuning is turned off (disabled).
1 Determines the values of 1.P, 1.I and 1.D parameters by auto-tuning.
2 Determines the values of 2.P, 2.I and 2.D parameters by auto-tuning.
3 Determines the values of 3.P, 3.I and 3.D parameters by auto-tuning.
4
The setpoints when auto-
tuning is started
Determines the values of 4.P, 4.I and 4.D parameters by auto-tuning.
AUTO Median value of each zone
width
Determines the values of all PID parameters in use by auto-tuning.
Remarks
The AT parameter settings numbered 1 to 4 in the table above are dependent on how many
zones have been set. For example, if you have set two zones, you can use AT parameter
settings 1 and 2. Likewise, if you have set three zones, you can use AT parameter settings
1, 2 and 3.
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