All the
robust features of a ground system are for naught if you cannot easily
set up and control it. This is where the term "user-friendly" takes
on importance. Setting up a telemetry ground station includes:
- Creating the definition for the data acquisition system, including
sensor characteristics and signal conditioners. Defining the telemetry frame(s) to accommodate sampling rate requirements
as well as limitations of the acquisition hardware. The stream is defined
down to the word and bit level if results will be displayed or data
analyzed in real time. (Wizards are available to automatically create
the frame definition based on constraints and requirements.)Defining data for appropriate words in the stream to drive the PCM
simulator for system checkout and training.Entering calibration information for every sensor if data will be
evaluated in engineering units, or using information from the airborne
systems databaseSpecifying, and where necessary, creating algorithms and their coefficients
required for deriving parameters or engineering unit conversion.Creating displays for each display terminal, including objects, their
size, attributes, and location, as well as measurands to be displayed.Defining data to be archived to disk.
- Allocating measurands and derived parameters destined for strip chart
recorders and other output devices.
The time required to set up and check out telemetry
systems is significant. Since the setup files for both the airborne and
ground system contain a large subset of common data it can be helpful
to utilize file translation tools or a common database system. Chapter
9 of the IRIG-106
Standard defines an intermediate structure to specify a telemetry
stream along with information about the data acquisition system and real-time
processing . Use of the TeleMetry Attributes
Transfer Standard (TMATS) is an increasingly popular method to transfer
files between non-compatible ground systems. Since each system uses a
different internal format, translators are required to convert data to
and from the TMATS intermediate format.
Other,
more elaborate alternatives utilize a relational database management
system (RDBMS) such as Microsoft Access or Oracle to maintain setup
files
for airborne, flight line, and ground systems. Information regarding
the calibrations, data streams, etc. requires entry only once. Not
only can
these systems produce the complete set of setup files — from airborne
sensors to ground station displays — but they can maintain historical
files to recreate any specific test scenario. Generally, these are one-of-a-kind
projects tailored to specially configured airborne and ground systems
and they adhere to the methodology of the ground center. Recent vendor
alliances and acquisitions offer purchasers a single source like L-3
Communications for an integrated system to set up and manage all
telemetry system components.
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