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It is possible to monitor several signals at once with an AND-connection within the PLC.

 

ToolScope is able to do this in a better way than an AND-connection, using rules of the Fuzzy-Logic.

 

The ToolScope can be set in the tolerance ranges to monitor several signals. An alarm is only raised if all signals (looked at in union) are far enough outside of the limits.

 

Example:

 

Set Tolerance ranges to monitor more signals

Let the ToolScope learn

Let ToolScope monitor the processes. An alarm will be raised, if the combined signals are outside of the limits. See below example:



Above pictures shows:

- the spindle signal is behaving different than usual
- on first breach of the upper limit, no error is raised (around 3.1sec); Reason: the signal of the Z-axis is showing a very normal signal behaviour
- the alarm is raised about 50ms later, when the spindel signal is far away from its usual behaviour

Recap:

- This method is reducing false alarms, but is also able to mask real alarms. Its defintly better than usual AND or OR combinations of signals.
- Experience shows that its good to have tighter limits than usual when using this method
- This method is implementing a kinf of "common sense" which can reduce the amount of false alarms. It will only work as good as the additional signals are process relevant. If a signal is added that does not behave diffently in case of an error, alarms might be coming later than they should be
- In general, this method makes setting up the monitoring more complicated, since more curves have to be taken care of.