This document discusses telemetry, data transmission systems, and data acquisition systems. It begins with an introduction to telemetry, which involves measuring values remotely and transmitting the data. There are then sections that describe: the basic components and block diagram of a telemetry system; factors that influence system design such as accuracy and data transmission method; different types of telemetry systems including landline, radio frequency, and pulse modulation systems; and applications of data loggers and considerations for choosing one.

1. DATA TRANSMISSION,
TELEMETRY AND DAS
UNIT - II
1

2. INTRODUCTION
 Telemetry is presentation of measured values at
location remote from site of measurement. Greek
words ‘Tele’: remote, ‘meter’: measuring. e.g.,
doctor analyzing data of patient from remote
location
 Telemetry involves three steps:
a. converting measured quantity to signal
b. Transmission of that signal over proper channel
c. Its reconversion to actual data for recording,
displaying(CRT) for graphical analysis and
further computation 2

3. 3
DATA ACQUISITION SYSTEM

4. BLOCK DIAGRAM OF TELEMETRY
SYSTEM
4

5. FACTORS INFLUENCING TELEMETRY SYSTEM
DESIGN
 Primary criteria for choice and design is accuracy.
 System is decided whether transmitted data is in
Analog or Digital domain.
 For digital data to be transmitted, error detection,
recognition and correction capability make system
accurate.
 Selection of apt. bandwidth for data channel and data
link to avoid crosstalk.
 Power levels must be low to reduce noise generation.
 S/N ratio of the system must be high.
5

6. TYPES OF TELEMETRY SYSTEMS
 Landline Telemetry System: Power Lines,
Telephone Lines and Electrical Wires. Distance
ranges from 50m to 1 km e.g., labs, industries.
Types: Current, Voltage & position.
 Radio-Frequency System: Radio links from1 km to
50 km at 4MHz. For distance >50 Km Microwave
links are used 890 MHz to 30GHz. Repeaters are
installed after every 30 to 60 km for long distance
transmission.
6

7. LANDLINE
TELEMETRY SYSTEM
7

8. 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 rvr.
 It is transmitted at the receiver end.
8
Circuit of Voltage Telemetry System

9. CURRENT TELEMETRY SYSTEM
9
Circuit of 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.

10. DEMERITS AND MERITS
Merits:
 Effective for short distance measurement
 V and I can be easily transmitted
 Circuitry required is simple
 Wide variety of primary sensing elements are available to
measure reqd. variable.
Demerits:
 Demands high S/N ratio that is difficult to calibrate.
 Need to be protected from EMI, noises and distortions in
the channel.
 Multiplexing is difficult
 Limited frequency response
10

11. R.F. TELEMETRY
SYSTEM
11

12. R.F. TELEMETRY SYSTEM
 No physical link between telemeter transmitter and
receiver.
 Link is established through radio links.
 Examples : in spacecrafts, rockets and missiles
corrective actions can be taken from stations with
help of R.F. Links
 In instrumentation the o/p of transducer is
considered as modulating signal. 12

13. R.F. TELEMETRY SYSTEM
13
Modulation schemes:
When signal is in continuous form:
Amplitude Modulation
Angle Modulation
When signal is in form of pulses:
Pulse modulation
AM : amp. of high-carrier signal is varied acc. to
instantaneous value of modulating message signal m(t)
Ac

14. 14
t
Frequency
Phase





CALCULATING FM BANDWIDTH
For PM
For FM
t)
ω
sin(
β
(t) m 



 


 dt
t)
ω
sin(
β
(t) m
m
d
f
V
f
β


FM: modulation index, is ratio of deviation, fd
multiplied by amplitude of modulating signal
divided by modulating frequency, fm.
PM : the phase shift is proportional to
instantaneous amplitude of the modulating
signal.
m
p
e
k


ANGLE MODULATION
)
f
(f
2
1)
(β
f
2
B
W
dev
m ax
m ax








15. FREQUENCY TELEMETRY SYSTEM BLOCK
DIAGRAM:
15
THE DISADVANTAGE OF FM TELEMETRY
SYSTEM IS CAPACITY OF CHANNELS OFFERED
IS LESS

16. PULSE TELEMETRY SYSTEM
16
Pam telemetry system: Employs TDM
technique

17. TYPES OF PULSE MODULATION
17
PPM
PWM: Monostable
multivibrator
PAM

18. WHAT IS DATA ACQUISITION SYSTEM ?
• DAQ systems capture, measure, and analyze physical phenomena
from the real world.
• Light, temperature and pressure are examples of the different
types of signals that a DAQ system can measure.
• Data acquisition is the process of collecting and measuring
electrical signals and sending them to a computer for processing.
• • Electrical signals comes from Transducers.

19. THE BUILDING BLOCKS OF A DAQ SYSTEM INCLUDES:
1. Transducer or Sensors: A device that converts a physical
phenomenon such as light, temperature, pressure, or sound into a
measurable electrical signal such as voltage or current.
2. Signal: The output of the transducer.
3. Signal conditioning: Hardware that you can connect to the DAQ
device to make the signal suitable for measurement or to improve
accuracy or reduce noise.
4. DAQ hardware: Hardware you use to acquire, measure, and analyze
data.
5. Software: Application software is designed to help you easily design
and program your measurement and control application.

20. BLOCK DIAGRAM OF DAS

21. • COMMON ANALOG SENSORS
Sensor Physical Variable
Accelerometer Acceleration
Microphone Pressure
Pressure gauge Pressure
Resistive temperature device (RTD) Temperature
Strain gauge Force
Thermocouple Temperature

22. • SIGNAL CONDITIONING
• To measure signals from transducers, you must convert them into a
form a Signal Conditioning measurement device can accept.
• Common types of signal conditioning include amplification,
linearization, transducer excitation, and isolation.
• Sensor signals are often incompatible with data acquisition
hardware. To overcome this incompatibility, the sensor signal must
be conditioned.
 Common ways to condition signals include –
• Amplification
• Filtering
• Electrical isolation
• Multiplexing
• Excitation source

23. WHAT TYPE OF DEVICE TO USE?
• The trade-off usually falls between
1- Resolution (bits)
2- Sampling rate (samples/second)
3- Number of channels, and data transfer rate
(usually limited by “bus” type: USB, PCI, PXI, etc.)

24. RESOLUTION
• Precision of the analog to digital conversion process
is dependent upon the number (n) of bits the ADC of
the DAQ uses.
• The higher the resolution, the higher the number of
divisions the voltage range is broken into (2^n), and
therefore, the smaller the detectable voltage changes.
• An 8 bit ADC gives 256 levels (2^8) compared to a
12 bit ADC that has 4096 levels (2^12).

25. SAMPLING RATE
• The data is acquired by an ADC using
a process called sampling.
• Sampling an analog signal occurs at
discrete time intervals.
• The rate at which the signal is
sampled is known as the sampling
frequency.

26. • The two important features of a data acquisition
system :
• Signals are input to a sensor, conditioned, converted
into bits that a computer can read, and analysed to
extract meaningful information.
• Data from a computer is converted into an analog
signal and output to an actuator.

27. BASIC DATA ACQUISITION SYSTEM
Physical
Paramete
r
Transduc
er
Active
Filter
Analog
Multipl
exer
Amplifie
r
Sample
hold
A/D
converter
Co
mp
uter
Dat
a
Bus

28. DATA LOGGERS
 A data logger is an electronic
device that records data over
time or in relation to location
either with a built in instrument
or sensor or via external
instruments and sensors.
 They generally are small,
battery powered, portable, and
equipped with a
microprocessor, internal
memory for data storage, and
sensors.
 Data Logger Cube Storing
technical & sensor data.

29. • Different types of data loggers and
their operation
• The differences between various data loggers are based on
the way that data is recorded and stored. The basic
difference between the two data logger types is that one
type allows the data to be stored in a memory, to be
retrieved at a later time, while the other type automatically
records the data on paper, for immediate viewing and
analysis. Many data loggers combine these two functions,
usually unequally, with the emphasis oneither the ability to
transfer the data or to provide a printout of it.

30. APPLICATIONS
 Environmental monitoring
 Road traffic counting.
 Unattended soil moisture level recording.
 Motor Racing
 Temperature, Humidity and Power use for Heating
and Air conditioning efficiency studies.
 Unattended weather station recording
 Measure temperatures (humidity, etc) of perishables
during shipments
 Tank level monitoring.

31. DATA RECOVERY AND TRANSFER
• Data can be recovered from data acquisition systems in
various ways :
▫ Serial comms interface via direct connect, modem, cell
phone, radio, satellite
▫ PCMCIA - modem, cell phone, LAN, memory card, USB
memory device
▫ Network port - Ethernet, field bus, proprietary, etc
▫ Universal Serial Bus (USB)
• Data can be transferred and published using :
▫ Local Ethernet network
▫ Intranet - email, web pages
▫ Internet - email, world wide web pages

32. TYPES OF DATA
ACQUISITION SYSTEMS
 Data acquisition systems can be of a number of
forms:
 Pocket loggers - small, battery powered, stand alone
devices with simple functionality
 Intelligent data loggers - stand alone devices with own
intelligence, sophisticated data manipulation, alarms,
backed up power supply, displays, etc. Accessed
continuously or periodically by a PC.
 Plug in cards - plugged into the ISA bus or USB port of a
PC to provide basic data acquisition functionality.
The PC provides power, control, data storage, etc.

33. CHOOSING A DATA LOGGER:
When choosing a data logger the following parameters should
be considered
 AC Voltage/Current
 Light On/Off
 Shock/Acceleration
 Bridge/Strain/Load/Pressure
 Motor On/Off
 Sound
 Dew point
 PH Pressure
 Temperature

34. PICTURES OF DATA LOGGERS:

35. TYPES OF DATA LOGGERS:
• Miniature Single Input Data Loggers
Miniature single input data loggers are generally
low cost loggers dedicated to a specific input type.
These types of data loggers are often used in the
transportation industry. A typical application would
be to include a temperature data logger in a
shipment of food products to insure that the food
temperature does not exceed acceptable limits. In
addition to temperature miniature data loggers are
available for a large variety of input types.

36. TYPES OF DATA LOGGERS:
 Fixed Mount Multi-Channel Data Loggers
Fixed input loggers have a fixed number of input
channels which are generally dedicated for a specific
type of input. OMEGA offers fixed input data loggers
ranging from one to 8 channels.
 Modular Data Loggers
A modular data logger is configurable and expandable
through the use of plug-in modules. The modules are
normally field configurable and the user has the option
of adding as many channels to satisfy the application
requirement.

37. ADVANTAGES:
• Data logging devices can be sent to places that humans can
not easily get to. e.g. to the planet Mars, in to the bottom of
a volcano and on to a roof of a tall building to get to a
weather station.
• Graphs and tables of results can be produced
automatically by the data logging software.

38. DISADVANTAGES:
 The main disadvantage of using a data logging
system is the initial cost of purchasing the
equipment. While a thermometer can be purchased
for less than one pound, the price of the
components of a data logging system to record the
temperature will be considerable.

39. DATA ACQUISITION VS DATA LOGGING
• Data loggers typically have slower sample rates
than Data Acquisition System.
• Data loggers are implicitly stand-alone devices,
while typical data acquisition system must remain
tethered to a computer to acquire data.
• data loggers must be extremely reliable than Data
Acquisition System

40. 40