Diagnosis
Original instructions
Overview of the diagnosis
There are a number of reasons that can lead to the autotuning not starting, being cancelled or failing. In such a case, depending on the cause of failure, it can be possible to supply a parameter set. Every bit of the diagnostic word diag allows for a type of error to be created.
This word contains the current operating mode of the autotuning.
The following cases are explained:
Diagnostic word
This table contains the meaning of the diag elements of the data structure Info_AUTOTUNE
Bit
Meaning
Bit 0 = 1
Autotuning is running
Bit 1 = 1
Autotuning aborted
Bit 2 = 1
Parameter error
Bit 3 = 1
Alteration of parameters, which have just been set automatically
Bit 4 = 1
Stop as a consequence of system error
Bit 5 = 1
Process value saturated
Bit 6 = 1
Alteration too small
Bit 7 = 1
Sampling interval invalid
Bit 8 = 1
Incomprehensible reaction
Bit 9 = 1
Non-stabilized measuring at the start
Bit 10 = 1
Length of actuating pulse Stellimpulses (tmax) too short
Bit 1 1= 1
Too much noise/interference
Bit 12 = 1
Length of actuating pulse (tmax) too long
Bit 13 = 1
Process with significant exceeding of the thresholds
Bit 14 = 1
Process without minimum phase
Bit 15 = 1
Asymmetric process
Bit 16 = 1
Process with integral component
Status of the autotuning
The following bits of the diagnostic word (diag element) show the status of the autotuning.
Bit
Meaning
0
1 = Autotuning running.
1
1 = Autotuning stopped
Bit 0 of the diag element
This Bit indicates that the autotuning is running. On quitting autotuning or terminating using the START Bit, this is set to zero.
Bit 1 of the diag element
This Bit indicates that the user stopped the last control using the START Bit or by setting the operating mode to Tracking.
Causes of a faulty start
The following bits of the diagnostic word (diag element ) indicate a faulty start.
Bit
Meaning
2
1 = Parameter error
7
1 = incorrect sampling interval
Bit 2 of the diag element
The following causes can lead to a faulty start:
Bit 7 of the diag element
If the sampling interval is too large in relation to the length of the actuating pulse (> tmax / 25), then the response test is too imprecise and autotuning will be blocked. This typically occurs during very rapid regular processes (where tmax is larger than the rise time of the process, a matter of a few seconds). In this case tmax can be increased, because the algorithm reacts only slightly to this parameter (in the ratio of 1 to 3), or alternatively, the sampling interval can be set to correspond.