Compares two input signals: if input1 > input2 -> emits upper
output value, if input1 <= input2 -> emits lower output value
The Comparator
Block
Parameters:
| vU |
upper output value |
| vL |
lower output value |
Description:
This block compares two input signals and produces an output event
carrying a value that depends on the result of the comparison. The
user is invited to specify an "upper" and a "lower" output value
(vU and vL). Then, if the first input signal is bigger than the
second one, the output takes the value of vU, and vL
otherwise.
It is the only component that in case of concurrent transitions
(cf. the ModelicaDEVS Theory
section) executes the external transition before the internal one.
This has the following reason: at each event instant, the
comparator estimates the moment when the two input signals will
cross the next time (the estimation makes use of the linear and
quadratic terms of the Taylor series expansion). The chronological
distance between the current and the next event is represented by
the variable sigma. Suppose now the time instant when the two
signals are supposed to cross has arrived. If simultaneously, one
of the signals updates its value, it is of course more advantageous
to use this new, true value instead of relying on the estimated
one. Therefore, in case of concurrent internal and external
transitions, the external transition is more important to process,
because the values on which the scheduling of the internal
transition has been calculated may have become outdated.
Note that because of the reversed priority order of the internal
and the external transition, the Comparator block may not be
connected in a cycle with itself, unless there is another component
in between that breaks the algebraic loop (again, see the Theory section for
details on algebraic loops).
The picture below shows the output of a Comparator (red) that
compares a sine signal (blue) and the output of a Ramp block
(green) run in QSS1-mode, such that there are output events during
the ramp. vU and vL have been set to 2 and 1.5 respectively.
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.ModelicaDEVS.FunctionBlocks.Comparator