FX2N-2LC Temperature Control Block
Auto tuning function
AT (auto tuning)
The AT (auto tuning) function automatically measures, calculates and sets optimal PID con-
stants in accordance with the set temperature.
When the AT execution command (CH1: BFM #20, CH2: BFM #29) is set to "1", auto tuning is
performed. (Auto tuning can start from an arbitrary status at any time immediately after the
power is turned on, while the temperature is rising or while control is stable.)
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 mea-
sured. PID constants are calculated based on the measured values, and stored in each
parameter. When auto tuning normally finishes, control continues with new calculated PID
While auto tuning is performed, b14 of the event (CH1: BFM #1, CH2: BFM #2) is set to "1".
For auto tuning, the AT bias can be set.
(In order to calculate proper PID constants by auto tuning, set the upper limit of the output lim-
iter to 100%, the lower limit of the output limiter to 0%, and the output change ratio limiter func-
tion to OFF.)
1) Auto tuning can be performed when the following conditions are satisfied.
- The control start/stop status shall be set to "control start".
- The operation mode shall be set to the control "mode 2".
- The auto/manual mode shall be set to "auto".
- The input value (PV) shall be normal.
- The upper limit and the lower limit of the output limiter shall not be set to a same value.
- The proportional band shall not be set to "0 (two-position operation)".
Introduction of Functions 5