Siemens 353 User Manual page 195

UM353-1B Operation
Autotuning Considerations:
Figure 8-1 Chart 1, Autotune
Process Noise – could have an effect on the autotuner. Chart 2 illustrates the same process as Chart 1 but more
significant noise. The autotuner settings were the same but the results of this test produced a warning W3 and
recommended settings of P=1.40 & I=0.42. In most cases with warnings, the autotuner will provide tuning
recommendations but they may be more conservative. Manual settings for the %HYS and %DEV can be
considered as described in the section Autotuner Warnings.
Steady State Conditions - must be established for the process and controller prior to starting an autotune exercise.
The autotuner can be initiated while in manual or auto. Steady state is reached when the present valve signal has
brought the process to its present value, and the setpoint is equal to the process. When not at steady state, valve
cycles will not be symmetrical as illustrated in the second tuning exercise in chart 2 or, as a worse case situation, the
valve may not cycle at all. If the valve is does cycle, although not symmetrically, adequate tuning results will still
be obtained.
April 2012 8-5