Autotune Procedure - Siemens 353 User Manual

Operation

8.3 AUTOTUNE PROCEDURE

If the AUTOTUNE parameter in the controller function block is set to YES, the autotune procedure can be initiated
using the TUNE pushbutton located behind the flip-down door. The Autotuner will substitute an ON_OFF
controller for the PD or PID function. By making +/- step changes to the valve position, the controller will control
the process at the current setpoint while it learns about the process dynamics. The controller then uses this
knowledge to derive recommended P, I, and, D settings.
Press the TUNE button to step through the following parameters and, if desired, initiate autotune:
PG ..................... Proportional Gain setting - (view or change)
TI ...................... Integral Time setting - PID/PIDAG controllers only (view or change)
MR .................... Manual Reset setting - PD controller only (view or change)
TD ..................... Derivative Time setting - (view or change)
% DEV ............. The peak/peak % process deviation that the autotuner will maintain during test
% HYS .............. The % process change needed before the valve output will switch
AUTOTUNE .... Set to YES and STORE to start autotune.
AT PG ............... Proportional Gain setting recommended by the autotuner
AT TI ................ Integral Time setting recommended by the autotuner
AT TD ............... Derivative Time setting recommended by the autotuner
STORE AT ....... Pressing STORE transfers autotuner recommended settings to controller
While autotuning, the controller will continue normal operation. Pressing the A/M button to switch the controller to
Manual will terminate autotune. While in autotune, the alphanumeric display will alternate between 'AUTOTUNE'
and the loop tag name and will stop alternating when the autotune program has been completed. Once completed,
the controller will return to the mode prior to autotune initiation. When the POST AT (in the controller block) is set
to auto transfer, the recommended tuning parameters will automatically be transferred to the controller and it will
return to automatic control. To review the AT parameters before initiating autotune, press TUNE and then press
STORE at the STORE AT prompt to transfer the recommended settings.
Chart 1 (0-100% range) illustrates a typical autotune exercise. The process has a small amount of noise
(approximately 1% P-P). The autotuner was set with fast response, the %HYS was set to A, and the %Dev was set
to A. The autotuner provided recommended settings of P=1.84 and I=0.38. These settings were entered into the
controller and a step change was made to the setpoint to review the response with the new controller settings.
The autotuner will use the initial valve step size (set as % STEP in the controller function block) during the first 1-
cycles to learn the approximate gain of the process. It will then adjust the valve step size during the remainder of
1/2
the autotuning exercise to maintain the % DEV setting. When this test concludes, the recommended settings are
transferred to the controller and a 20% setpoint change is made to illustrate the controller tuning.
When the autotuner is started for the next autotune exercise, it will use the process gain learned during the previous
exercise to determine the valve step size unless: the parameter AT RESET in the controller block has been stored as
YES, warnings occurred during the first test, or the station has been power cycled.
8-4
Press EXIT CONF to return to normal operator faceplate operation.
UM353-1B
April 2012