-4LC User's Manual
Auto Tuning Function
AT (Auto tuning)
The auto tuning function automatically measures, calculates and sets optimal PID constants in accordance
with the set temperature.
The auto tuning function is available in PID control and heating/cooling PID control.
Write "1" to the AT execution command buffer memory to perform auto tuning.
When auto tuning starts, two-position control is performed using the set value (SV). By two-position control,
the output is forcedly hunted and its amplitude and oscillation cycle are measured. PID constants are
calculated based on the measured values, and stored in each buffer memory.
The buffer memories shown below store calculated values.
Applicable buffer memory
Proportional band (P)/
Heating proportional band (P)
Integral time (I)
Derivative time (D)
Loop breaking alarm judgement time
When auto tuning finishes normally, control continues with new calculated PID constants.
The AT bias can be set for auto tuning.
Example of operation (When AT is performed while the temperature is rising)
Measured value (PV)
Set value (SV)
• Before starting auto tuning, confirm that all conditions for performing and aborting auto tuning (refer to
Subsection 6.8.2) are satisfied.
• Before starting auto tuning, set the output limiter upper limit/heating output limiter upper limit to "100%", set
the output limiter lower limit to "0%", and set the output change ratio limiter function to OFF so that optimal
PID constants can be calculated by auto tuning.
• When auto tuning is finished normally, write newly calculated PID constants to the EEPROM using the set
value backup command so that auto tuning becomes unnecessary from the next power ON.
• When auto tuning is finished normally, PID constants and loop breaking alarm judgment time are written to
the buffer memory, and then the AT execution flag turns OFF. Because the AT execution command buffer
memory does not become "0" automatically, write "0" manually.
Less than 0.1%
1000.0% or more
Less than 1 sec.
3600 sec. or more
3600 sec. or more
The calculated integral time multiplied by "2" is automatically written.
However, "0" remains stored when the loop breaking alarm judgment time is set to
"0" when auto tuning is finished.
6 Introduction of Functions
6.8 Auto Tuning Function
Value to be set