Event arcs are able to express the variety of instantaneous actions, one of which is operation of sensor which detects the changes of the plant’s state. Once transition t1 in the model of the process fires, it also switches the sensor ON by means of the event arc. Model of sensor comes first to the transitional state (marking in p2) and after the delay D – to the state with p3=1. Reading of the sensor usually comes to controller as a logic value modeled in our formalism as a condition signal. The sensor itself can have internal dynamics, e.g. delay D, as it is shown in the Figure 1, or an additional “malfunction” state (not shown in the Figure, but similar to the “exception state” considered earlier. Note that in the figure we model the “malfunction free” sensor which always produces the required value upon elapsing the specified time D. Model of sensor can be either simpler (just a bi-stable) or much more complicated, depending on the required results of modeling.
Figure1:
Model of sensing:
sensor detects when the process comes
to the observed state and with delay produces the required
logic value (places p1,p4 of the module “Sensor”).
© 2003,
Martin
Luther University of Halle-Wittenberg, Automation Technology
Lab.
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Document created and maintained by: Valeriy V. Vyatkin