For a variety of reasons, the auto-tuning process may
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not be started,
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be aborted during execution,
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fail by setting forth (or not) a set of parameters determined by the cause of failure.
NOTE: It is not possible to perform 2 auto-tuning operations simultaneously on the same channel.
The diagnostics message acknowledgement function is accessible from the Control Expert screen or with the acknowledge commands.
NOTE: The diagnostics message is unique to each process control channel. There is only one message for the 3 loops of the 3 single-loop controllers, or for the 2 loops of the Cascade and Auto-selector loop controllers.
Reasons Why the Auto-Tuning May Not Start
The following errors prevent auto-tuning from starting:
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Parameter error (Bit 2: AT_ERR_PARAM)
Possible causes of a parameter error are as follows:
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Step duration too brief (AT_TMAX < 4 s).
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Amplitude too small (AT_STEP < 1% of output scale).
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Impossible test protocol. If the current output + n times the scaling amplitude (n = 1 for hot auto-tuning, and n = 2 for a cold auto-tuning) falls outside the output scale (OUT_INF, OUT_SUP), the test protocol is no longer applicable. STEP_AMPL must be set to a value compatible with the current function point.
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Incorrect sampling period (Bit 6: AT_TSAMP_HIGH)
If the sampling period is too large in relation to the step duration (greater than AT_TMAX/25), the response analysis will be too imprecise, which in turn inhibits auto-tuning. This case is specific to very fast process controls (AT_TMAX increasing the process stabilization time by a few seconds). TMAX may therefore be increased, as the algorithm is not very sensitive to this parameter (in a ratio from 1 to 3). You may also adjust the sampling period.
Reasons Why Auto-Tuning May Be Aborted
