Exception Conditions; Notes Concerning Pv Out-Of-Range (Result Code 3) - Siemens SIMATIC S7-200 System Manual

Exception Conditions

Three warning conditions can be generated during tuning execution. These warnings are reported
in three bits of the ASTAT field of the loop table and, once set, these bits remain set until the next
auto-tune sequence is initiated.
Warning 0 is generated if the deviation value is not at least 4X greater than the hysteresis
-
value. This check is performed when the hysteresis value is actually known, which depends
upon the auto-hysteresis setting.
Warning 1 is generated if there is more than an 8X difference between the two peak error
-
values gathered during the first 2.5 cycles of the auto-tune procedure.
Warning 2 is generated if the measured average peak error is not at least 4X greater than
-
the hysteresis value.
In addition to the warning conditions several error conditions are possible. Table 15-3 lists the
error conditions along with a description of the cause of each error.
Table 15-3 Error Conditions during Tuning Execution
Result Code (in ARES)
01 aborted by user
02 aborted due to a zero-crossing watchdog
timeout
03 aborted due to the process out-of-range
04 aborted due to hysteresis value exceeding
maximum
05 aborted due to illegal configuration value
06 aborted due to a numeric error
07 PID instruction was executed with no
power flow (manual mode)
08 auto-tuning allowed only for P, PI, PD, or
PID loops

Notes Concerning PV Out-of-Range (Result Code 3)

The process variable is considered to be in-range by the auto-tuner if its value is greater than 0.0
and less than 1.0.
If the PV is detected to be out-of-range during the auto-hysteresis sequence, then the tuning is
immediately aborted with a process out-of-range error result.
If the PV is detected to be out-of-range between the starting point of the tuning sequence and the
fourth zero-crossing, then the output step value is cut in half and the tuning sequence is restarted
from the beginning. If a second PV out-of-range event is detected after the first zero-crossing
following the restart, then the tuning is aborted with a process out-of-range error result.
Any PV out-of-range event occurring after the fourth zero-crossing results in an immediate abort of
the tuning and a generation of a process out-of-range error result.
PID Auto-Tune and the PID Tuning Control Panel
EN bit cleared while tuning is in progress
Half-cycle elapsed time exceeds zero-crossing watchdog
interval
PV goes out-of-range:
S during the auto-hysteresis sequence, or
S twice before the fourth zero-crossing, or
S after the fourth zero crossing
User-specified hysteresis value, or
automatically determined hysteresis value > maximum
The following range checking errors:
S Initial loop output value is < 0.0 or > 1.0
S User-specified deviation value is <= hysteresis value ,
or is > maximum
S Initial output step is <= 0.0 or is > maximum
S Zero-crossing watchdog interval time is < minimum
S Sample time value in loop table is negative
Illegal floating point number or divide by zero encountered
PID instruction executed with no power flow while
auto-tuning is in progress or is requested
Loop type is not P, PI, PD, or PID
Chapter 15
Condition
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