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Ground
System
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 database
- Specifying, 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.
