7.2.6 Auto Tune from Below SP - Heat Only

The sequence of operation for a heat only loop is the same as that previously described for a heat/cool loop except that the sequence ends at ‘F’ since there is no need to calculate ‘r2G’.

 

At ‘F’ autotune is turned off and the process is allowed to control using the new control terms.

 

Relative cool gain, ‘r2G’, is set to 1.0 for heat only processes.

 

 

 

For a tune from below setpoint ‘cBLo’ is calculated on the basis of the size of the overshoot (assuming it was not set to Auto in the initial conditions). cBHi is then set to the same value as cBLo.

 

Note:- As with the heat/cool case, Autotune can also occur when the initial PV is above SP. The sequence is the same as tuning from below setpoint except that the sequence starts with natural cooling applied at ‘B’ after the first one minute settling time.

 

In this case cBHi is calculated – cBLo is then set to the same value as cBHi.