Telemetry is the automatic measurement and wireless transmission of data from remote sources. In general, telemetry works in the following way: Sensors at the source measure either electrical data, such as voltage and current, or physical data, such as temperature and pressure

1. Data Transmission and
Telemetry
Chapter 27

2. Data Transmission and Telemetry: Introduction
In modern measurement systems, various components comprising the systems are
usually located at a distance from each other. It, therefore, becomes necessary to
transmit the data or information between them through some form of
communication channels.
The term data transmission and telemetry refer to the process by which
information regarding the quantity being measured is transferred to a remote
location, perhaps to be processed, recorded and displayed.
The word “Telemetry” is derived from the Greek roots tele, "remote", and metron,
"measure". Telemetry is the technology which enables a user to collect data from
several measurement points at inaccessible or inconvenient locations, transmit
that data to a convenient location, and present the several individual
measurements in a usable form.

3. General Telemetry System
Measurand
Primary
Sensing
Element
Telemeter
Transmitter
Telemeter
Channel
Telemeter
Receiver
End
Device
Intermediate Stage

4. Methods of Data Transmission
Data
Transmission
Hydraulic
Transmission
Pneumatic
Transmission
Electrical and
Electronic
Transmission
Land Line
Telemetry
Voltage
Telemetry
System
Current
Telemetry
System
Position
Telemetry
System
RF Telemetry
Amplitude
Modulation
AM
Frequency
Modulation
FM
Phase
Modulation
PM

5. Methods of Data Transmission
Pneumatic transmission: Pneumatic systems used in
industry are commonly powered by compressed air or
compressed inert gases. Pneumatic transmission is
transfer power by gas pressure or information fluid by
compressed gas as the working medium.
Hydraulic transmission: Means a transmission that
depends on a hydraulic system and in cable flow fluid.
Hydraulic transmission, device employing a liquid to
transmit and modify linear or rotary motion and linear
or turning force (torque).

6. Electrical and Electronic Transmission: Land Line Telemetry
Voltage Telemetry System:
Measured Variable is transmitted in form of voltage
At transmitting end, Slide wire is connected in series with battery.
Slide wire is further connected to Bourdon tube for pressure
measurement.
When pressure changes, slider actuates the slider of potentiometer.
Thus , change in Voltage is transmitted to receiver.

7. Electrical and Electronic Transmission: Land Line Telemetry
Current Telemetry System:
Working is almost same as of Voltage telemetry system
When pressure changes Borden tube moves sliding contact thereby
value of current changes
This current passes through pair of wires and measured by
milliammeter.

8. Electrical and Electronic Transmission: Land Line Telemetry
Current Telemetry System: Motion
Balance System
Current Telemetry System: Force
Balance System

9. Electrical and Electronic Transmission: Land Line Telemetry
Position Telemetry:
A position telemetering system transmits and reproduces the measured
variable by positioning variable resistors or other electrical components in
a bridge circuit form so as to produce proportional changes at both the
transmitter and receiver ends.

10. Electrical and Electronic Transmission: Radio Frequency (R.F.)Telemetry
There is no physical link between the transmitting and receiving stations.
The link between the transmission station and receiving station can only be established through radio
links.
R.F. is suitable for transmission greater than 1 km.
Modulation Methods:
The expression of a carrier wave is:
= sin(2 + )
Where, = amplitude of carrier
= frequency of a carrier
= relative phase shift of the carrier
As a signal can be described by its (i) amplitude(ii) frequency(iii) phase shift .
Accordingly three methods of modulations are
(i) amplitude modulation
(ii) frequency modulation
(iii) phase modulation

11. Radio Frequency (R.F.)Telemetry: Amplitude Modulation
“The amplitude of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal
whose frequency is much lower than that of the carrier.” Which means, the amplitude of the carrier signal
containing no information varies as per the amplitude of the signal containing information, at each instant.
This can be well explained by the following figures.

12. Radio Frequency (R.F.)Telemetry: Amplitude Modulation
If and are the instantaneous values of the carrier signal and modulating signal
voltage respectively, then,
= sin
= sin
The amplitude of the modulated voltage is,
= (1 + sin )
Here, = = modulation index
If upper sideband frequency is fc+fs and lower sideband frequency is fc−fs,
then, Bandwidth, BW=2
The total power , = (1 + )
The maximum total power can be , = 1. ; since maximum value of m=1

13. If the frequency of the carrier wave is varied, in accordance with the instantaneous
value of the modulating signal, then such a technique is called as Frequency
Modulation.
Radio Frequency (R.F.)Telemetry: Frequency Modulation

14. Radio Frequency (R.F.)Telemetry: Summary
Phase Modulation
Amplitude and Frequency Modulation