INTRODUCTION
What Is Telemetry?
Telemetry is the process by which an object’s characteristics are
measured (such as velocity of an aircraft), and the results transmitted to a distant station where they are displayed, recorded, and analyzed.
Several Good Definitions:
The measurement of some quantity with the aid of intermediate means
which permit the measurement to be interpreted at a distance from the primary detector.
The process that measures a quantity and then transfers the
measurement data to a remote location to be recorded, displayed, or to control a process. [Streich, p 1].
FCC Definition: "use of telecommunication for automatically indicating or
recording measurements at a distance from the measuring instrument." [Horan, p 1]
Strictly speaking, "telemetry" is the information that is collected, and
TELEMETRY SYSTEMS OVERVIEW
A telemetering system includes all
components that are used to measure, transfer, and analyze the data.
A telemetry system is often viewed as
Data acquisition begins when sensors
(transducers) measure the amount of a physical attribute and transform the measurement to an engineering unit value.
Sensors attached to signal conditioners provide
power for the sensors to operate or modify signals for compatibility with the next stage of
acquisition.
Since maintaining a separate path for each source
is cumbersome and costly, a multiplexer
TRANSDUCER
Transducers are used to transform a
physical parameter into an electrical signal. There are several major
classifications of transducers [Horan, p 15, 16]:
Optical or Visual
Pressure, Strain, Force
Environmental
AMPLIFIER
An instrument amplifier is used to
amplify the (usually) very small
MULTIPLEXER
The multiplexer is used to combine
several measurement signals into a single signal to be transmitted to the base station.
There are two primary types of
multiplexing--Time Division Multiplexing (TDM) and Frequency Division
PULSE CODE MODULATOR
PCM encodes the amplitude of the
multiplexer output in digital form and then transmits that signal.
Ability to add error correction codes
TRANSMITTER
Transmits the signal that is generated
by the multiplexer.
The transmission can take place via
