Troubleshoot an Equipment Sequence
You can troubleshoot an
Equipment Sequence
by commanding the Equipment Sequence
and executing the logic of the sequence. Failure display indicators are available for the sequence and the individual steps. The failure’s presence can also be observed or indicated in the Quick View, by the icon on the top left corner of the sequence diagram, or on the element generating the issue.
Problem | Possible causes |
Sequence becomes HELD and generates a failure | An Equipment Phase currently running in association with a step executed an Equipment Phase Failure (PFL) instruction. (Phase Failure - PFL instruction executed).Equipment Phase to be run is not in the IDLE state. (Sequence Failure - execution state error). The right to command an Equipment Phase attached to an Equipment Sequence is removed by the Logix Designer application overriding ownership. (Sequence Failure - Right to command is lost).A step becoming active is associated to an Equipment Phase that is inhibited, or is run in a task that is inhibited. (Sequence Failure - execution state error) |
After clearing a failure, the Equipment Sequence immediately fails again | The condition causing the failure must be resolved. The Clear Failures command only resets the steps’ and sequence’s flags for handling failures. |
Sequence does not advance when the transition apparently becomes TRUE | The sequence is in Manual mode.The sequence is waiting for ownership of the next phase to be released. The transition expression includes a step tag or sequencing parameter whose quality of data is FALSE (Valid bit is off). See Quality of data for an explanation of the concept and how it affects sequencing parameters and step tags and their use in transition and parameter expressions in Manual mode.The Equipment Sequence is waiting for active steps above the transition to stop, reset, and return to the IDLE state, and their phases to be released from ownership. The transition expression includes a step tag or sequencing parameter whose quality of data is FALSE (Valid bit is off). See Quality of data <add hyperlink> for an explanation of the concept and how it affects sequencing parameters and step tags and their use in transition and parameter expressions. |
Sequence seems to skip over a step without running it. | The trailing transition expression evaluates TRUE before the phase has a chance to run or finish running. The result is that the step is started and stopped within a scan so you do not see that it executed. The phase logic programming error results in a Phase State Complete (PSC) instruction that prematurely executes and changes the phase’s state to StepName.Complete. |
Sequence execution appears to stall around simultaneous divergences | The transition above a simultaneous divergence will not start any of the steps following it until all the Equipment Phases of all the steps are owned. If this is a problem, use a No phase step to break the dependency between steps and their leading transition above the simultaneous divergence. |
Sequence execution appears to stall around simultaneous converges | The transition below a simultaneous convergence will not start any of the steps following it until all the Equipment Phases of all the steps above it are reset to IDLE and are no longer owned by the sequence. If this is a problem, use a No phase step to break the dependency between steps and their trailing transition below the simultaneous convergence. |
Sequence seems to execute the wrong branch in a selective divergence | Two or more transitions following the selective divergence all evaluate TRUE in the same scan. |
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