EE-524 TELEMETRYAND SCADA

DEPARTMENT OF ELECTRICAL ENGINEERING

IIT ROORKEE, ROORKEE-247667

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Reference Books

1. D. Patranabis, Telemetry Principles, Tata-McGraw Hill, 2001

2. Stuart A. Boyer, Supervisory Control and Data Acquisition

(SCADA), 4th Edition, International Society of Automation,

2010.

3. Torsen Cegrell, Power System Control Technology, Prentice

Hall, 1986.

4. Wayne Tomasi, Electronic Communication Systems, Pearson

Education, 2008.

5. William Schweber, Electronic Communication Systems,

Prentice Hall, 2005.

6. William Stallings, Data and Computer Communications, 8th

Edition, Pearson-Prentice Hall, 2007.

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Unit-1

Reference Books

Introduction

Meaning and importance of telemetry

Relevance to industry

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Introduction

What is Telemetry?

Two Greek terms: tele and metron, means far off and measure.

Telemetry is the measurement of remote (or far-off) variables or quantities.

Examples of Telemetry system: Centralized control room of Industry,

launching and flight of a rocket are controlled from ground station, a

satellite monitoring etc.

Where is Telemetry Required? Where the conventional measurement or local measurement techniques

cannot work:

(a) Distant location of the measurand: Telemetry uses electrical

communication for transmitting electrical signal representing the value of

the measurand from the location of the measurand to the location of the

user.

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Introduction

(b) Inaccessibility of measurand: In such a situation, the electrical output

of the transducer (or sensor) sensing the measurand, or that of the

associated signal conditioner, cannot be accessed by conventional method

of connecting wires. Therefore, the electrical output is converted to a radio

wave, which is then transmitted to the users location. This type of

telemetry is called Radio Telemetry.

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Introduction

Elements of Telemetry System?

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Introduction

a. Transducer or Sensor: Converts the physical variable to be telemetered (that is, the measurand) into an electrical quantity.

Classification of transducer:

Passive Transducer/ Parametric Transducer

Active Transducer/ Generating Transducer

o Passive Transducer/ Parametric Transducer:

It exhibits a change in one of passive electrical parameters like Resistance,

Capacitance, or Inductance b/c of change of physical quantity to be

measured. These requires an external source of electrical energy to convert in

voltage, current or frequency.

o Active Transducer/ Generating Transducer:

It produce an electrical output that varies b/c of changing quantity to be

measured. 1/17/2014 7

Introduction

b. Signal Conditioner-1:

Converts the electrical output of the transducer (or sensor) into an

electrical signal compatible with the next element, i.e. the transmitter.

Signal Conditioner circuit may be electrical or electronic circuit eg.

Adder, subtractor, multiplier, A/D converters, rectifiers, D.C.

Amplifiers, frequency counter etc.

Differentiator is not commonly used in instrumentation b/c average

noise increases. It is used at very high frequency signal. Normally

integrator is used.

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Introduction

c. Transmitter:

Its purpose is to transmit the information signal coming from the signal

conditioner-1 using a suitable carrier signal to the receiving end. It may

perform one or more of the following functions:

(i) Modulation:

(ii) Amplification:

(iii) Signal Conversion:

(iv) Multiplexing:

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Introduction

d. Signal Transmission Medium: Medium or link that connects the

sending or transmitting end to the receiving end, over which the transmitter

can transmit its output signal to the receiver.

e. Receiver: To receive the signal(s) coming from the transmitter via the

signal transmission medium and recover the information from the same. It

may perform one or more of the following functions:

i. Amplification:

ii. Demodulation:

iii. Signal Conversion:

iv. De-multiplexing:

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Introduction

f. Signal Conditioner-2:

g. End Device: The element is so called because it appears at the end of the system. The end device may be performing one of the following

functions:

i. Analog Indication: PMMC type instruments.

ii. Digital Display: LEDs, LCD, VDU etc.

iii. Digital Storage: Semiconductor memories Eg. ROM, EPROM,

Hard Disk, optical storage etc.

iv. Data Processing: Eg. a microprocessor, digital signal processor or

computer, for analysis etc.

v. Closed-Loop Control:

vi. Print:

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Introduction

Subsystem of Telemetry System:

i. Measurement Subsystem: It comprises the transducer (or sensor), signal

conditioners and the end device, like any conventional measurement

system.

ii. Communication Subsystem: It comprises the transmitter and receiver

along with the transmission medium linking the two, like any

communication system.

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Introduction Types of Signal Transmission Media

Copper Wires:

A pair of copper wires (or conductors) provides a closed-circuit path for the

flow of an electrical signal from the transmitter to the receiver of the

telemetry system.

Radio Link:

A radio link between the two ends of the telemetry system by allowing the

propagation of radio waves (high frequency electromagnetic waves)

generated by the transmitting antenna through it.

Optical-Fibre Link:

An optical fibre, acting as a waveguide for the optical beam (in infra-red

wavelength band) generated by the transmitter, delivers the same to the

receiver.

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Introduction Telemetry Classification Based on

Signal Transmission Medium

Wire-Link or Wire Telemetry

Radio Telemetry or Wireless Telemetry

Optical-Fibre Telemetry or Fibre-Optic Telemetry

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Introduction

Necessity of Modulation in Telemetry

The information signal is very often not suitable for transmission from the

transmitter to the receiver and therefore, used to modulate a carrier signal

compatible with the given transmission medium.

Reasons for using modulation in telemetry:

o To achieve compatibility with the given transmission medium:

o To improve signal-to-noise ratio:

o To achieve multiplexing:

Two exceptions

o In very simple situations of short range wire telemetry, the information

signal itself can be transmitted and no modulation would, therefore, be

required.

o In some complex situations, two or even three stages of modulation are

employed for better performance of the communication subsystem of the

telemetry system.

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Introduction Telemetry Classification Based on

Modulation Method

Three categories of telemetry systems as follows:

DC Telemetry Systems o Direct voltage telemetry system

o Direct current telemetry system

AC Telemetry Systems o Amplitude modulation (AM) telemetry system

o Frequency modulation (FM) telemetry system

Pulse Telemetry System

o Pulse amplitude modulation (PAM) telemetry system

o Pulse width modulation (PWM) telemetry system

o Pulse phase modulation (PPM) telemetry system

o Pulse frequency modulation (PFM) telemetry system

o Pulse code modulation (PCM) telemetry system

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Introduction Telemetry Classification Based on Type

of Information Signal

Analog Telemetry Systems

o Direct voltage telemetry system

o Direct current telemetry system

o Amplitude modulation (AM) telemetry system

o Frequency modulation (FM) telemetry system

o Pulse amplitude modulation (PAM) telemetry system

o Pulse width modulation (PWM) telemetry system

o Pulse phase modulation (PPM) telemetry system

o Pulse frequency modulation (PFM) telemetry system

Digital Telemetry System OR Pulse Code Modulation

(PCM) telemetry system

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Introduction Single and Multi-Channel Telemetry

Systems

A telemetry system may be a single-channel or a multi-channel

telemetry system depending on the number of physical variables

(measurands) telemetered by it.

Type of multiplexing is used in multi-channel:

o Time Division Multiplexing (TDM): It can be used with all types of

signal transmission links.

o Frequency Division Multiplexing (FDM): It can be used with copper

wire links and radio links

only.

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Introduction Frequency Division Multiplexing

(FDM):

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Introduction

Frequency Division Multiplexing

(FDM):

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Introduction Time Division Multiplexing (TDM):

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Introduction Telemetry Error

Definition:

Telemetry is the difference between the telemetered value of the

measurand and its true value.

Telemetered value True value Percent telemetry error = ---------------------------------------- x 100

True value

Components of Telemetry Error

o Measurement Error:

o Transmission or Communication Error:

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Introduction Sources and Control of Telemetry

Error

A. Main sources or causes of the measurement error are: o Improper choice of the measurement components (sensor,

signal conditioners and end device):

o Improper design of the measurement components:

o Drifts in the measurement components.

B. Measurement error resulting from the above causes can be

controlled (minimized) by resorting to the following measures:

o Proper selection of the measurement components.

o Proper design of the measurement components.

o Periodic calibration of the telemetry system on the whole or

that of the critical components in the system.

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Introduction Sources and Control of Telemetry

Error

C. Main sources or causes of the transmission or

communication error are:

o Attenuation of the transmission signal, if information is

contained in its amplitude or magnitude.

o Distortion of the transmission signal, if information is

contained in its wave-shape.

o Noise in communication, both internally generated and

externally induced.

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Introduction Sources and Control of Telemetry

Error

D. Transmission or communication error resulting from the above

causes can be controlled (minimimized) by resorting to

following measures:

o Proper choice of the transmission signal.

o Proper choice of the modulation method

o Proper choice of the signal transmission medium.

o Proper design of the transmitter and receiver.

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Introduction Relevance to Industry

Commercial Solution provided by the Industries:

o SIEMENS: Supervision of plants using telemetry systems, Telecontrol

o HALLIBURTON

o CAMPBELL SCIENTIFIC

o CANNON WATER TECHNOLOGY, INC.

o ABB AUTOMATION INC.: etc.

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