VISUALISING DATA FRAME FORMATS CONTAINING SUPER COMMUTATION AND VARIABLE WORD LENGTHS
International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada === Compiling a PCM data frame with super commutation poses problems of maintaining constant sample intervals for the parameters whilst keeping within channel bandwidth...
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| Language: | en_US |
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International Foundation for Telemetering
1999
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| Online Access: | http://hdl.handle.net/10150/607299 http://arizona.openrepository.com/arizona/handle/10150/607299 |
| Summary: | International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada === Compiling a PCM data frame with super commutation poses problems of maintaining
constant sample intervals for the parameters whilst keeping within channel bandwidth
limitations. Add an extra requirement of using variable word lengths to optimise the use
of available bit rate and the problem becomes more challenging.
The available telemetry or tape recorder channel bandwidth rather than the capabilities of
the data acquisition system normally govern the amount of data that can be acquired by
the aircraft instrumentation system. The amount of data demanded usually expands to fill
all available bandwidth and the bit rates are operated at the maximum for the particular
channel. The use of variable word lengths can, in some circumstances, increase the
utilisation of a channel bandwidth.
In order to visualise if a particular requirement can be accommodated within a given data
structure a method of sketching PCM data frames containing a wide mixture of sample
rates using an intermediate matrix has been devised.
The method is described in three stages.
1. Compiling a simple PCM frame.
2. Sketching the intermediate matrix to assist in visualising super commutation limits.
3. Mixing variable word lengths and super commutation in the same PCM format.
The method is not guaranteed to be the most efficient but does give a relatively simple,
non mathematical, way to visualise if the required sample rates can be accommodated in
a given data structure. If the requirement will not fit into the data structure then the
method allows the impact of the necessary changes to the structure to be rapidly assessed.
The paper includes comments on the relevant characteristics needed in the aircraft data
acquisition system. These include variable word lengths, frame lengths, incremental bit
rates and coherency of multiple data bus word parameters |
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