Auto Tuning; Auto Tuning Procedure - Honeywell ST700 User Manual

Auto tuning

Cycle tuning
The PID block supports the Cycle tuning algorithm. In Cycle tuning, the tuning parameter
values are derived from the process response to the resultant action of causing the PV to
oscillate about a SP value. The tuning method uses the measured ultimate gain and period
to produce tuning parameter values, by using the relationship developed by Ziegles Nichols
equations. Cycle tuning does not distinguish between process lags and always results in
gain based on PV amplitude, and calculates the values of Reset and Rate based on time of
the SP crossings using a fixed ratio of 4 to 1. Initially, this method does not require a stable
process. Cycle tuning is applicable to Three Position Step control, and is used for
integrating process.

Auto tuning procedure

There are nine parameters applicable for auto tuning: AT_TYPE, TUNING_CRITERIA,
TUNE_REQ, ATI, AT_MODE, AT_ERR, AT_GAIN, AT_RESET, and AT_RATE.
AT_Type
There are two types of selections, namely Disable and Cycle Tune. When Disable is
selected, AT_MODE becomes inactive. When Cycle Tune is selected, AT_MODE
becomes AT Ready.
TUNING_CRITERIA
There are two types of tuning criteria available for selection: Normal and Fast.
• NORMAL - Conservative tuning designed to reduce overshoot as compared to FAST.
•
FAST - Aggressive tuning designed to provide quarter-dampened response.
TUNE_REQ
TUNE_REQ can be turned ON only in the following modes, namely AUTO, CAS, RCAS,
and ROUT. The ATI value becomes 1, and AT_ERROR shows the status as Run, this
shows that auto tuning is in progress.
If AT_ERROR shows OK, auto tuning is successful. AT_GAIN, AT_REST, AT_RATE
gets updated automatically and same values are copied to GAIN, RESET and RATE
respectively.
Revision 2.0 FOUNDATION Fieldbus ST 700 Pressure Transmitter User's Guide Page 57