A data acquisition system or analog instrumentation recorder may not always be available at the telemetry station to produce PCM data streams for system checkout and operator training. Therefore, it is highly desirable to simulate identical PCM data streams produced by the acquisition subsystem.

Simulators vary in performance; some produce a simple static frame at fixed rates, while others create the most complex frames and data rates to match the decommutator’s capabilities. Describing the frame format for setup may not be required since the telemetry system can produce it from the decommutator’s setup definition. The simulator produces major and minor frames, including super-commutated, sub-, and sub-sub frames; and multiple embedded asynchronous data streams. The PCM output signal is available in any of the standard IRIG codes and levels. Simulators and encoders also provide MSB or LSB word orientation, programmable synchronization words, and support for format switching. Measurands can be simulated statically either as user-defined constants and wave shapes via a CVT or as multiple function generators (square, sine, ramp, triangular) at different data rates and amplitudes. While the data changes, it is not considered dynamic.

Dynamic simulation uses real-time data from external sources and measurand simulators as products of data bus, vehicle, or satellite constellation models. These dynamically simulated streams are desirable for training and system test. A dynamic simulator is, in effect, a PCM encoder. You can produce a new PCM stream by extracting words from incoming PCM stream(s) or external data sources for applications such as commanding or forwarding data to another site. An example of the former is to control the operation of a satellite, while the latter is for an airborne-based ground station to forward key measurands to the ground station during flight tests (see figure below). The airborne ground station not only selects all instances of individual parameters, but may compress them (e.g., averages values or combines multiple measurands, as in processed parameters).

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