Special module-specific characteristics 141
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
4.8 Sampling Rates
Depending on the modules, the allowed sampling intervals are 1 ms, 2 ms, 10 ms, 20 ms, 50 ms, ..., 1 min
(other modules support faster sampling; for explanation purposes, a base rate of 2 ms is assumed).
Virtual channels derived from functions without data compression have the same sampling rates as their
parameter channels. If the function used to generate the virtual channel supports data compression, the
resultant sampling rate can be smaller than that of the input channels (e.g. Maximum, Minimum,
Average). The resultant sampling rate can never be greater than that of the input channels.
To conserve computational capacity, functions with compressed input data (e.g. sampling rate of 100
ms), are calculated with a time lag. The time lag has the effect that when data compression is present,
more functions can be carried out simultaneously than if all the functions were applied at once to the
same sample. This makes the processing of very involved configurations possible.
Take for instance 10 functions applied to data accumulating at a sampling rate of 10 ms. Instead of all the
functions beginning to work immediately on the sample, one function's value is calculated at each ms
after the sample arrives. This saves on computational exertion for the processor, but causes the results
to be outputted with a time lag.
The larger a function's sampling rate is, the larger the time lag between its calculations can be.
Interdependencies of parameters are, of course, unaffected. No data is lost, only the moment in which
they are processed and in some cases when they are transmitted is delayed.
From a pulse rate of 100 ms onward, this phenomenon can be observed directly in the yellow flashing of
the LED; the red and green components of the LED light flash with a mutual offset. Therefore, it's
recommended to set a maximum sampling time of 50 ms for yellow LED flashing.
If one module has both messages configured with slow data rates and with high rates, it may occur that
the rapid messages are delayed in being transmitted. This happens whenever several messages having a
slow rate are transmitted in rapid succession, which of course takes up much time. This time amount can
also be (significantly) greater than the fastest data rate. The corresponding messages can contain virtual
or physical channels. The problem usually arises whenever very many channels or low Baud rates are set.
One possible remedy might be a higher Baud rate.
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