Telemetry

What is Telemetry?

Airborne System

 Data Acquisition

 Multiplexer

 Modulation

 Commutation

 Data Words

 Common Words

 Frame Synchronization Pattern

 Subframe Synchronization Pattern

Data Acquisition & Multiplexer

Data Acquisition

A wide variety of sensors (transducers) are used to measure and acquire a physical property’s value

Signal conditioners serve as the interface of the data acquisition system from the transducers

Multiplexer

Multiplexer is multiple input digital device that can select one of a number of inputs and pass the logic level of that input to the output

Modulation 

It is the technique where the value of each sample (i.e., the modulating signal) systematically changes the characteristics of a carrier signal

Commutation

Commutator is a device used to accomplish time-division multiplexing (TDM) by repetitive sequential switching

Each revolution of the commutator produces a frame of the stream of words containing the value of each measurand. Only the value of a measurand is captured, not its address

There is no way to distinguish the owner of one value from the next,So a unique word called the frame sync is added at the end of each frame to indicate the end of each frame

Data Word

It is a measurement, calculation, counter, command, tag, function, or other information entered into the frame position as a measurand

Common words 

They are filler words that do not contain a measurand and are filled with a common pattern

Frame Synchronization Pattern

Identifying the end of each minor frame period is the synchronization (sync) word, which is a unique sequence of 1's and 0's.

 Subframe Synchronization Pattern

Ground System

 Setup & Control

 PCM Stream Reconstruction

 Frame Synchronization

 Decommutation

 Simulation And Encoding

 Real-time Processing & Displays

 Archiving

 Data Distribution

 Post-test Analysis

Setup and Control

PCM Stream Reconstruction

Frame Synchronization

Decommutation

Decommutator is a unit that reverses the commutation process; separation of information in a commutated data stream into as many independent information channels as were originally commutated. A device that separates (or demultiplexes) commutated signals into its constituent measurands and data

Simulation and Encoding

Real-Time Processing

Real-Time Displays

Telemetry streams can produce too much data for a single person to comprehend as alphanumeric information.

 Displays ease the task of interpreting raw measurands faster than the eye can fathom, depict when measurands are within safe and meaningful limits, show relationships between measurands, and spot trends

Archiving

Telemetry data captured during operation of the ground station must often be archived for post acquisition analysis and to satisfy legal requirements that the vehicle under test was properly certified.

Typically, data is stored immediately in the ground system, as close to the received signal as possible. Data is also archived to disk after decommutation and/or processing and is then backed up to inexpensive cartridge tape

Data Distribution

Ground systems must therefore first convert a measurand’s digital representation to analog; then the recorder digitizes the signal for presentation as an analog wave

LANs and WANs permit distribution of real-time data to multiple client workstations, where separately data can be viewed, analyzed, and archived

Post-Test Analysis

After viewing and interpreting real-time results the original streams were stored on an instrumentation tape recorder, so that data can be played back as originally recorded through a bit synchronizer and decommutator

So archived data can once again be viewed, processed, archived to disk, distributed, or sent to strip chart recorders for reports