Samples a signal at given time instants.
The CommandedSampler
Block
Parameters:
Description:
The CommandedSampler is fairly similar to the SamplerTrigger
block. It takes two inputs where the first input is the signal from
which the samples are taken, and the second input specifies the
time instants when the sampling takes place. The second input is an
arbitrary ModelicaDEVS block that generates a number of events, as
it is in the nature of DEVS models. Usually, it is the values of
the single events that we are interested in, given that they
constitute the output trajectory. In this case however, for the
CommandedSampler block to function correctly, it is only important
to have any events at certain time instants: when the
CommandedSampler receives an event from its second input port, it
immediately takes a sample from the signal coming in through the
first input port and holds this value until the next event is
arriving at its second input port.
Note that both input signals are discrete-time variables in terms
of Modelica, i.e. they are piecewise constant.
Normally, the sampling instants do not coincide with the event
instants of the first port. This means that at a given sampling
instant, the signal from the first port has been updated a certain
amount of time ago and may have changed meanwhile (without
producing an output event). Hence, analogously to the binary
operator blocks (Add, Divider, Multiplier), an approximation of the
first input port's true value is estimated (on the basis of the
linear and quadratic terms of the Taylor series expansion stored in
the second and third entry of the input/output vecors).
The picture illustrating the behaviour of the CommandedSampler
shows a Sine block (blue) and a Ramp block (green) connected to the
input ports of the CommandedSampler. The Sine gives the signal that
has to be sampled, the Ramp block (used in QSS1-mode) determines
the sampling instants: we know that every time the Ramp block
changes its output value, there must have been an event. Hence, at
each of these event instants, the output of the CommandedSampler
block (plotted in red) takes the current value of the Sine signal,
since it has been triggered by the event sent by the Ramp block to
do so.
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.ModelicaDEVS.FunctionBlocks.CommandedSampler