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Electronic Measurements & Instrumentation Question & Answers

GRIET/ECE 1

UNIT-1

1. What are the basic performance characteristics of a system?

Ans:

STATIC CHARACTE RISTICSThe static characteristics of an instrument are, in general, considered for instruments which are used to

measure an unvarying process condition. All the static performance characteristics are obtained by oneform or another of a process called calibration. There are a number of related definitions (or

characteristics), which are described below, such as accuracy% precision, repeatability, resolution,errors, sensitivity, etc.

l.Instrument: A device or mechanism used to determine the present value of the quantity under

measurement.

2. Measurement: The process of determining the amount, degree, or capacity by comparison (direct or

indirect) with the accepted standards of the system units being used.

3. Accuracy: The degree of exactness (closeness) of a measurement compared to the expected (desired)

value.

4.Resolution: The smallest change in a measured variable to which an instrument will respond.

5. Precision: A measure of the consistency or repeatability of measurements, i.e. successive readings

does not differ. (Precision is the consistency of the instrument output for a given value of input).

6. Expected value: The design value, i.e. the most probable value that calculations indicate one should

expect to measure.

7 Error: The deviation of the true value from the desired value.

8. Sensitivity: The ratio of the change in output (response) of the instrument to a change of input ormeasured variable.

DYNAMIC CHARACTERISTICS

Instruments rarely respond instantaneously to changes in the measured variables. Instead, they exhibit

slowness or sluggishness due to such things as mass, thermal capacitance, fluid capacitance or electriccapacitance. In addition to this, pure delay in time is often encountered where the instrument waits for

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some reaction to take place. Such industrial instruments are nearly always used for measuring quantities

that fluctuate with time. Therefore, the dynamic and transient behavior of the instrument is as importantas the static behavior.

The dynamic behavior of an instrument is determined by subjecting its primary element (sensingelement) to some unknown and predetermined variations in the measured quantity. The three most

common variations in the measured quantity are as follows:

l. Step change in which the primary element is subjected to an instantaneous and finite change inmeasured variable.

2. Linear change, in which the primary element is following a measured variable, changing linearly withtime.

3, Sinusoidal change, in which the primary element follows a measured variable, the magnitude ofwhich changes in accordance with a sinusoidal function of constant amplitude

.

The dynamic characteristics of an instrument are (i) speed of response,

(ii) Fidelity, (iii) lag, and (iv) dynamic error.

(i) Speed of Response: It is the rapidity with which an instrument responds to changes in the measured

quantity.(ii) Fidelity: It is the degree to which an instrument indicates the changes in the measured variable

without dynamic error (faithful reproduction).

(iii) Lag: It is the retardation or delay in the response of an instrument to changes in the measuredvariable.

(iv) Dynamic Error: It is the difference between the true values of a quantity changing with time and

the value indicated by the instrument, if no static error is assumed.

When measurement problems are concerned with rapidly varying quantities, the dynamic relations

between the instruments input and output are generally Defined by the use of differential equations

2. What are the different types of static errors in a system?

Ans:

The static error of a measuring instrument is the numerical difference between the true value of a

quantity and its value as obtained by measurement, i.e. repeated measurement of the same quantity givedifferent indications. Static errors are categorized as gross errors or human errors, systematic errors and

Random errors.

1. Gross Errors

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This error is mainly due to human mistakes in reading or in using instruments or errors in recording

observations. Errors may also occur due to incorrect adjustments of instruments and computationalmistakes. These errors cannot be treated mathematically. The complete elimination of gross errors is not

possible, but one can minimize them .Some errors are easily detected while others may be elusive. One

of the basic gross errors that occur frequently is the improper use of an Instrument the error can beminimized by taking proper care in reading and recording the measurement parameter. In general,

indicating instruments change ambient conditions to some extent when connected into a complete

circuit.

2. Systematic Errors

These errors occur due to shortcomings of, the instrument, such as defective or worn parts, or ageing or

effects of the environment on the instrument.

These errors are sometimes referred to as bias, and they influence all

measurements of a quantity alike. A constant uniform deviation of the operation of an instrument is

known as a systematic error. There are basically three types of systematic errors(i) Instrumental, (ii) Environmental, and (iii) Observational

(i) Instrumental Errors

Instrumental errors are inherent in measuring instruments, because of their mechanical structure. For

example, in the D'Arsonval movement friction in the bearings of various moving components, irregular

spring tensions, stretching of the spring or reduction in tension due to improper handling or over loadingof the instrument. Instrumental errors can be avoided by

(a) Selecting a suitable instrument for the particular measurement applications.

(b) Applying correction factors after determining the amount of instrumental error.(c) Calibrating the instrument against a standard.

(ii) Environmental Errors

Environmental errors are due to conditions external to the measuring device, including conditions in the

area surrounding the instrument, such as the effects of change in temperature, humidity, barometric

pressure or of magnetic or electrostatic fields.These errors can also be avoided by (i) air conditioning, (ii) hermetically sealing certain components in

the instruments, and (iii) using magnetic shields.

(iii) Observational Errors

Observational errors are errors introduced by the observer. The most common error is the parallax errorintroduced in reading a meter scale, and the error of estimation when obtaining a reading from a meter

scale.

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These errors are caused by the habits of individual observers. For example, an observer

may always introduce an error by consistently holding his head too far to the left while reading a needleand scale reading.

In general, systematic errors can also be subdivided into static and dynamic Errors. Static

errors are caused by limitations of the measuring device or the physical laws governing its behavior.Dynamic errors are caused by the instrument not responding fast enough to follow the changes in a

measured variable.

3. What is the method used to calculate the errors in an instrument?

Ans:ERROR IN MEASUREMENT

Measurement is the process of comparing an unknown quantity with an acceptedstandard quantity. It involves connecting a measuring instrument into the system under considerationand observing the resulting response on the instrument. The measurement thus obtained is a quantitative

measure of the so-called "true value" (since it is very difficult to define the true value, the term

"expected value" is used). Any measurement is affected by many variables; therefore the results rarelyreflect the expected value. For example, connecting a measuring instrument into the circuit under

consideration always disturbs (changes) the circuit, causing the measurement to differ from the expected

value. Some factors that affect the measurements are related to the measuring instruments themselves.Other factors are related to the person using the instrument. The degree to which a measurement nears

the expected value is expressed in terms of the error of measurement. Error may be expressed either as

absolute or as percentage of error. Absolute error may be defined as the difference between the expectedvalue of the variable and the measured value of the variable, or

e = Yn - Xn

Where e=absolute errors;

Yn=expected value;

Xn=measured value;

Therefore %error = (absolute value/expected value )*100=(e/Yn)*100

Therefore %error=

It is more frequently expressed as an accuracy rather than error.

Therefore A=1-

Where A is the relative accuracy

Accuracy is expressed as % accuracy

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a=100%-%error

a=A*100% (where a=%accuracy)

4. Describe the function of the DC-Voltmeter and multi range voltmeter and explain

their operation?

Ans: DC-Voltmeter

A basic D'Arsonval movement can be converted into a dc voltmeter by adding a series

resistor known as multiplier, as shown in the figure. The function of the multiplier is to limit thecurrent through the movement so that the current does not exceed the full scale deflection value.

A dc voltmeter measures the potential difference between two points in a dc circuit or a circuit

component. To measure the potential difference between two points in a dc circuit or a circuitcomponent, a dc voltmeter is always connected

across them with the proper polarity. The value of

the multiplier required is calculated as follows.

Im: full scale deflection current of the movement

Rm : internal resistance of movementRs : Multiplier resistance

V: full range voltage of the instrument

From the circuit of Fig. 4.1

V= Im *( Rm+ Rs)

Rs = = -

therefore Rs = -

The multiplier limits the current through the movement, so as to not exceed the value of the full scaledeflectionIfsd.

The above equation is also used to further extend therange in DC voltmeter'.

Multi range Voltmeter:

As in the case of an ammeter, to obtain a

multi range ammeter, a number of shunts are connected

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GRIET/ECE 6

across the movement with a multi-position switch.

Similarly, a dc voltmeter can be converted into amulti range voltmeter by connecting a number of

resistors (multipliers) along with a range switch

to provide a greater number of workableranges. The below Figure shows a multi range

voltmeter using a three position switch and three

multipliers R1, R2, and R3, for voltage values

V1, V2, and V3. Fig 4.2 can be further modified tomultipliers connected in series string, which is a

more practical arrangement of the

multiplier resistors of a multi range voltmeter. Inthis arrangement, the multipliers are connected in a series string, and the range selector selects the

appropriate amount of resistance required in series with the movement.

This arrangement is advantageous compared to the previous one, because all multi1llier resistances

except the first have the standard

resistance value and are also easilyavailable in precision tolerances. The

first resistor or low range multiplier,

R4, is the only special resistor whichhas to be specially manufactured to

meet the circuit requirements.

5. Explain the working of solid

state voltmeter?Ans:

The below figure shows the circuit of

an electronic voltmeter using an IC OpAmp 741C.This is a directly coupled

very high gain amplifier. The gain of

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GRIET/ECE 7

the Op Amp can be adjusted to any suitable lower value by providing appropriate resistance between its

output terminal, Pin No. 6, and inverting input, Pin No. 2, to provide a negative feedback. The ratio R2/R1 determines the gain, i.e. 101 in this case, provided by the Op Amp. The 0.1 pF capacitor across the

100 k resistance R is for stability under stray pick-ups Terminals 1 and 5 are called offset null terminals.

A 10 k potentiometer is connected between these two offset null terminals with its centre tap

connected to a - 5V supply. This potentiometer is called zero set and is used for adjusting zero output for

zero input conditions.

The two diodes used are for IC protection. Under normal conditions, they are non-conducting, as the

maximum voltage across them is l0 mV. If an excessive voltage, say more than 100 mV appears across

them, then depending upon the polarity of the voltage, one of the diodes conducts and protects the IC. A

A scale of 50 - 1000 A full scale deflection can be used as an indicator. Ro is adjusted to get

maximum full scale deflection.

6. Draw the block diagram of the measuring system and explain the

function of each stage of this system?

Ans:The generalized measuring system consists of three main functional elements. They are,

1. Primary sensing element, which senses the quantity under measurement.

2. Variable conversion element, which modifies suitably the output of the primary sensing element

3. Data presentation element that renders the indication on a calibrated scale.

1. Primary Sensing Element

The measurement first comes into contact with primary sensing element where the conversion takesplace. This is done by a transducer which converts the measurement (or) measured quantity into a usable

electrical output. The transduction may be from mechanical, electrical (or) optical to any related form.

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GRIET/ECE 8

2. Variable Conversion Element

The output of the primary sensing element is in the electrical form suitable for control, recording anddisplay. For, the instrument to perform the desired function, it may be necessary to convert this output to

some other suitable for preserving the original information. This function is performed by the variable

conversion element. A system may require one (or) more variable conversion suitable to it.

(a) Variable Manipulation Element

The signal gets manipulated here preserving the original nature of it. For example, an amplifier accepts asmall voltage signal as input and produces a voltage, of greater magnitude. The output is the same

voltage but of higher value, acting as a voltage amplifier. Here the voltage amplifier acts as a variable

manipulation element since it amplifies the voltage. The element that follows the primary sensingelement in a measurement system is called signal conditioning element. Here the variable conversion

element and variable manipulation element are collectively called as Data conditioning element (or)

signal conditioning element.

(b) Data Transmission Element

The transmission of data from one another is done by the data transmission element. In case ofspacecrafts, the control signals are sent from the control stations by using radio signals.

The stage that follows the signal conditioning element and data transmission element collectively is

called the intermediate stage.

(c).Data Presentation Element

The display (or) readout devices which display the required information about the measurement, formsthe data presentation element. Here the information of the measurand has to be conveyed for,

monitoring, Control (or) analysis purposes.

(a). 1t case of data to be monitored, visual display devices are needed like ammeters; voltmeters and soon are used.

(b)In case of data to be recorded, recorders like magnetic tapes, T.V equipment, and storage type C.R T,

printers and so on are used.

7.Explain the types of test signals used in determining dynamic characteristics ofmeasurements applied to a system.

Ans:

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The a dynamic characteristic (or) analysis is classified with respect to time and frequency as time

domain analysis and frequency domain analysis(a).In time domain analysis the i/p is applied to the system and the behavior of the system is studied as a

function of time.

(b) In frequency, domain analysis the i/p is a sinusoidal one and the behavior of the system is studied asa function of frequency.

The standard test signals used for time domain analysis are as follows.

(i) Step input

(ii) Ramp input

(iii) Parabolic input(iv) Impulse input.

(i) Step Input

The continuous time step input u (t) is defined as the discrete time step input a[n] is defined as,

U (t) = and discrete time step input u[n] is defined as, u (n) =

Therefore, a unit step input represents a signal which changes its level from 0 to I in zero time and. it

reveals a great deal about how quick, the system responds to an abrupt change in the input signal

(ii) Ramp Input

The ramp input is defined in continuous time as

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GRIET/ECE 10

r (t) =

and r[n] =

(iii) Parabolic InputThe parabolic input is defined as,

r (t) =

and the discrete time is defined as,

r[n] =

The signal are given below,

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This signal is also called as acceleration input since the input signal is proportional to represents a

constant acceleration.

(iv) Impulse Input

It is also called as a (delta) function. The continuous time impulse input is given by, square of

time and

(t) =0 for t0

And discrete time impulse input is given by,

(n) =

The unit impulse is defined as the signal which has a zero value everywhere except at t=0.where themagnitude is finite.

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GRIET/ECE 12

In frequency domain analysis, the system behavior is studied through the sinusoidal signal because thetime varying signals such as step, ramp, and parabolic inputs can be expressed in terms of sinusoidal

signal of differential amplitudes and frequencies.

A continuous time sinusoidal signal is given as

X(t)=A sin(t+ )Where A= amplitude

= frequency in radians/sec.

= phase angle in radians.

A sinusoidal signal is an example of a periodic signal, the period of which is T=

The discrete time version of a sinusoidal signal is given by,

X[n] =A sin (n + )

Where, = angular frequency in radians/cycle.

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GRIET/ECE 13

8. Explain the terms

(i). significant figures

(ii). Conformity

Ans:

(i) Significant Figures

The number of meaningful digits used to express a numerical value (measured value of a quantity) are

known as, significant figures. Significant figures indicate the precision of the measurement and themagnitude of the measurements. The measured value should be expressed in more number of significant

figures because the more significant figures the higher will be the precision.Consider an example in which the measured voltage across a resistor in a circuit is specified as

50 V. It indicates that the measured voltage may be close to 49 V or 51 V. This specification has two

significant figures. If the measured voltage is specified as 50.0 V then it indicates that the value may beclose to 49.9 V or 50. 1 V. This specification has three significant figures. From the above illustration, it

can be observed that the specification with three significant figures is more precise than the one with

two significant figures.

(ii) Conformity

Conformity is one of the characteristics which determine the precision. If a measuring instrumentconsistently and repeatedly provides a value as close to the true value (of the measured quantity) as an

observer can estimate the true value from its scale reading then this characteristic refers to the

conformity of the measurement. Let us consider an example of measuring resistance of a resistor whichhas a true resistance of 10,654,739 ). If the multi meter indicates the resistance value as 10.7 MO

consistently and repeatedly, then the condition of conformity is satisfied. But, due to the limitation of

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GRIET/ECE 14

scale reading, there exists an error in the measured value as the scale provides the reading up to one

decimal place only.

Thus, conformity is a necessary condition, but not a sufficient condition for the

measurement to be precise.

9. What is ayrton shunt? Describe it with a neat sketch .specify its application?

Ans:

Aryton shunt: It is also known as universal shunt. Figure shows the basic circuit of an arytonshunt.

It avoids the possibility of using the meter in the circuit without a shunt. This is the mostimportant merit of the aryton shunt.

From the above figure, it is noted that the series combination of resistors R2, R3 and the metermovement is in parallel with R1 when the switch (SW) is connected to position "1". Therefore, the

current through the meter movement is less than the current through the shunt, thereby protecting themeter movement. This reduces the sensitivity of meter movement. The series combination of resistor R6and the meter movement is in parallel with resistor R1, R2, when the SW is connected to position "2".

Therefore, the current through the shunt resistance is less than the current through the meter movement.

The resistors R1, R2, and R3, are together in parallel with meter movement. When the switch is in

position "3".Now the current flowing through the shunt is very little whereas the current flowing throughthe meter is very high. Hence the sensitivity of the meter movement is increases.

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10. Explain with a neat block diagram of a dual slope digital voltmeter?

Ans:

Basic Principle:

Initially, the dual slope integrating type DVM integrates the input voltage V i. The slope of the integrated

signal is proportional to the input voltage under measurements .after certain period of time say t1 the

supply of input voltage Vi is stopped, and a negative voltage -Vr of the integrator. Then the outputsignal of integrator will have negative slope, and is constant and also proportional to the magnitude of

the input voltage.

BLOCK DIAGRAM AND WORKING:

The major blocks of a dual slope integrating type

DVM (dual slope analog to digital converter) are,

1. An op-amp employed as an integrator2. A level comparator

3. Oscillator for generating time pulses

4. Decimal counter5. Block of logic circuitry.

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Initially a pulse is applied to reset the counter and the output of flip-flop will be at logic '0'. The switch

Sr is in open condition and the switch, Si is in closed condition. Now, the capacitor 'C' starts to charge.Once the output of the integrator becomes greater than zero, the output state of the comparator changes

which in turn opens the AND gate .When the gate opens the output of the oscillator (clock pulses) are

allowed to pass through it and applied to the counter. Now the counter counts the number of pulses fed

to it. As soon as it reaches its maximum count that is the counter is preset to run for a time period r,, inthis condition the maximum count will be'9999', and for the next immediate clock pulse the count

changes or goes to '0000' and the flip-flop will be activated. Therefore, the output of flip flop becomes

logic 'I' which in turn activates the switch drive circuitry. This makes the switch S i, to open and Sr toclose (i.e., the supply of Vi will be stopped. and the supply of V is applied to the integrator) with this

applied signal the output of the integrator will be a constant negative slope i.e., its output signal linearly

decreases to zero. This again makes the output of the comparator to change its state which in turn closesthe gate. Here, the discharging time t2 of the capacitor is proportional to the input voltage signal Vi

.During this discharging period the counter indicates the count. As soon as, the negative slope reaches

zero volts the comparator changes its output state to 'zero' which in turn locks the gate. Once, the output

of integrator becomes zero (or the input of the comparator is zero) the counter will be stopped. And thecounted pulses are displayed (which directly gives the input voltage).

From the above equation, it is clear that the measured voltage signal's accuracy does not depend on the

time constant of the integrator.

Advantages

1. Depending on the requirement the accuracy and sped can be varied.

2. It can provide the output with an accuracy of +-0.005% in 100ms3. This technique exhibits excel lent noise rejection since the integration process eliminates both noise

and super imposed A.C.

11.Explain the constructional details and differentiate between Ohmmeter series

type and shunt type. ?

Ans: ohmmeter (SERIES TYPE OHM METER)

A D'Arsonval movement is connected in series with a resistance R, and a battery which is connected to apair of terminals A and B, across which the unknown resistance is connected. This forms the basic type

of series ohm meter, as shown in the fig 11.

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The current flowing through the movement then depends on the magnitude of the unknown resistance.

Therefore, the meter deflection is directly proportional to the value of the unknown resistance

referring to the figure 11.R1: current limiting resistance

R2: zero adjust resistance

V= batteryRm =meter resistance

Rx=un know resistance

Calibration of the Series Type Ohmmeter:

To mark the "0" reading on the scale, the terminals A and B are Shorted, i.e. the

Unknown resistance Rx=0, maximum current flows in the circuit and the shunt Resistance R2 is adjusted

until the movement indicates full scale current (Ifsd ). The Position of the pointer on the scale is then

marked "0" ohms. Similarly, to mark the "" reading on the Scale, terminalsA and B are open, i.e., the

unknown resistance Rx=, no current flow in the circuit and there is no deflection of the pointer. The

position of the pointer on the scale is then marked as 0hms.

By connecting different known values of the unknown resistance to terminals Aand B, intermediate markings can be done on the scale. The accuracy of the Instrument can be checked

by measuring different values of standard resistance, i.e., the tolerance of the calibrated resistance, andnoting the readings a major drawback in the series ohmmeter is the decrease in voltage of the internal

battery with time and age. Due to this, the full scale deflection current Drops and the meter does not read"0" when A and B are shorted. The variable Shunt resistor R2 across the movement is adjusted to

counteract the drop in battery Voltage. There by bringing the pointer back to "0" ohms on the scale'

It is also possible to adjust the full scale deflection current without the shunt R2 in

the circuit, by varying the value of R1, to compensate for the voltage drop. Since this value affects the

calibration of the scale, varying by R2 is much better solution. The internal resistance of the coil Rm is

very low compared to R1 When R2 is varied, the current through the movement is increased and the

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GRIET/ECE 18

current through R2 is reduced, thereby bringing the pointer to the full scale deflection position. The

series ohmmeter is a simple and popular design, and is used extensively For general services work,Therefore ,in a series ohmmeter the scale marking on the dial has 0 on the right side ,corresponding to

full scale deflection current ,and "" on the left side corresponding to no current flow as given in the fig

11.1 Values of R1 and R2 can be determined from the value of Rx ,which gives half the full scaledeflection.

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UNIT 2

Q.1) Describe the functioning of standard signal generator

Ans.

STANDARD SIGNAL GENERATOR

A standard signal generator produces known and controllable voltages. It is used as power source

for the measurement of gain, signal to noise ratio (SN), bandwidth standing wave ratio and other

properties. It is extensively used in the measuring of radio receivers and transmitter instrument isprovided with a means of modulating the carrier frequency, which is indicated by the dial setting

on the front panel. The modulation is indicated by a meter. The output signal can be Amplitude

Modulated (AM) or Frequency Modulated (FM). Modulation may be done by a sine wave,Square, rectangular, or a pulse wave. The elements of a conventional signal generator

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The carrier frequency is generated by a very stable RF oscillator using an LC tank circuit, having

a constant output over any frequency range. The frequency of oscillations is indicated by thefrequency range control and the venire dial setting. AM is provided by an internal sine wave

generator or from an external source.

Q.2) how can a sine and square wave be generated using signal generator?

Ans.

The signal generator is called an oscillator. A Wien bridge oscillator is used in this generator.

The Wien bridge oscillator is the best of the audio frequency range. The frequency of oscillationscan be changed by varying the capacitance in the oscillator. The frequency can also be changed

in steps by switching the resistors of different values. The output of the Wien bridge oscillator

goes to the function switch. The function switch directs the oscillator output either to the sinewave amplifier or to the square wave shaper. At the output, we get either a square or sine wave.The output is varied by means of an attenuator.

The instrument generates a frequency ranging from 10 Hz to 1 MHz continuously variable in 5

decades with overlapping ranges. The output sine wave amplitude can be varied from 5 mV to 5

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V (rms).The output is taker through a push-pull amplifier. For low output, the impedance is

6000. The square wave amplitudes can be varied from 0 - 20 v (peak). It is possible to adjust thesymmetry of the square wave from 30 -70%. The instrument requires only 7W of power at 220V

50Hz. The front panel of a signal generator consists of the following.

l. Frequency selector: It selects the frequency in different ranges and varies it continuously ina ratio of 1: 11. The scale is non-linear.

2. Frequency multiplier: It selects the frequency range over 5 decades from 10 Hz to 7 MHz

3. Amplitude multiplier: It attenuates the sine wave in 3 decades, x l x 0.1 and x 0.01.

4. Variable amplitude: It attenuates the sine wave amplitude continuously5. Symmetry control: It varies the symmetry of the square wave from 30% to 70%.

6. Amplitude: It attenuates the square wave output continuously.

7. Function switch: It selects either sine wave or square output.8.Output available: This provides sine wave or square wave output.

9.Sync: This terminal is used to provide synchronization of the internal signal

with an external signal.10.On-Off Switch

Q.3) Explain how a Function Generator works?

Ans:

FUNCTION GENERATOR

A function generator produces different waveforms of adjustable frequency. The common outputwaveforms are the sine, square, triangular and saw tooth waves. The frequency may be adjusted,

from a fraction of a Hertz to several hundred kHz lie various outputs of the generator can be

made available at the same time. For example, the generator can provide a square wave to testthe linearity of a rectifier and simultaneously provide a saw tooth to drive the horizontal

deflection amplifier of the CRO to provide a visual display. Capability of Phase Lock the

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function generator can be phase locked to an external source. One function generator can be used

to lock a second function generator, and the two output signals can be displaced in phase byadjustable amount. In addition, the fundamental frequency of one generator can be phase locked

to a harmonic of another generator, by adjusting the amplitude and phase of the harmonic; almost

any waveform can be generated by addition.The function generator can also be phase locked to a frequency standard and its output

waveforms will then have the same accuracy and stability as the standard source. The block

diagram of a function generator is illustrated in fig. Usually the frequency is controlled by

varying the capacitor in the LC or RC circuit. In the instrument the frequency is controlled byvarying the magnitude of current which drives the integrator. The instrument produces sine,

triangular and square waves with a frequency range of 0.01 Hz to 100 kHz.

The frequency controlled voltage regulates two current sources. The upper current sourcesupplies constant current to the integrator whose output voltage increases linearly with time,

according to the equation of the output signal voltage. An increase or decrease in the current

increases or decreases the slope of the output voltage and hence controls the frequency. The

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GRIET/ECE 5

voltage comparator multi-vibrator changes states at a pre-determined maximum level of the

integrator output voltage. This change cuts off the upper current supply and switches on thelower current supply. The lower current source supplies a reverse current to the integrator, so

that its output decreases linearly with time. When the output reaches a pre-determined minimum

level, the voltage comparator again changes state and switches on the Lower current source. Theoutput of the integrator is a triangular waveform whose frequency is determined by the

magnitude of the current supplied by the constant current sources. The comparator output

delivers a square wave voltage of the same frequency.

e = -

The resistance diode network alters the slope of the triangular wave as its amplitude changes and

produces a sine wave with less than 1% distortion.

Q.4) Explain the functioning of Random Noise Generator and explain the

parameters of noise?

Ans:

RANDOM NOISE GENERATOR

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GRIET/ECE 6

The spectrum of random noise covers all frequencies the lower density spectrum tells us how the

energy of the signal is distributed in frequency, but it does not specify the signal uniquely nor

does it tell us very much about how the amplitude of the signal varies with time

The spectrum does not specify the signal uniquely because it contains no phase information. The

method of generating noise is usually to use a semi conductor noise which delivers frequenciesin a band roughly extending from 80 220 KHz The output from the noise diode is amplified

and heterodyned down to audio frequency band by means of a balanced symmetrical modulator.

The filter arrangement controls the bandwidth and supplies an output signal in three spectrum

choices, white noise, pink noise and Usasi noise. From the Fig 4.2 it is seen that white noise isflat from 20Hz to 20 KHz and has upper cutoff frequency of 50 kHz with a cutoff slope of -12

dbs/ octave. Pink noise is so called because the lower frequencies have larger amplitude, similarto red light. Pink noise has a voltage spectrum which is inversely proportional to the square root

of frequency and is used in band analysis. Usasi noise ranging simulates the energy distribution

of speech and music frequencies and is used for testing audio amplifiers and loud speakers.

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GRIET/ECE 7

Q.5 what is a Sweep Generator, explain its functioning?

Ans:

It provides a sinusoidal output voltage whose frequency varies smoothly and continuously overan entire frequency band, usually at an audio rate. The process of frequency modulation may be

accomplished electronically or mechanically. It is done electronically by using the modulating

voltage to vary the reactance of the oscillator tank circuit component, and mechanically by

means of a motor driven capacitor, as provided for in a modern laboratory type signal generator.Figure shows a basic block diagram of a sweep generator. The frequency sweeper provides a

variable modulating voltage which causes the capacitance of the master oscillator to vary. A

representative sweep rate could be of the order of 20 sweeps/second. A manual control allowsindependent adjustment of the oscillator resonant frequency. The frequency sweeper provides a

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GRIET/ECE 8

varying sweep

voltage for

synchronization to drive the horizontal deflection plates of the CRO. Thus the amplitude of theresponse of a test device will be locked and displayed on the screen.

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GRIET/ECE 9

To identify a frequency interval, a marker generator provides half sinusoidal waveforms at anyfrequency within the sweep range. The marker voltage can be added to the sweep voltage of the

CRO during alternate cycles of the sweep voltage, and appears superimposed on the response

curve. The automatic level control circuit is a closed loop feedback system which monitors theRF level at some point in the measurement system. This circuit holds the power delivered to the

load or test circuit constant and independent o frequency and impedance changes. A constant

power level prevents any source mismatch and also provides a constant readout calibration with

frequency.

6. Explain Square and Pulse Generator?ANS:

SQUARE AND PULSE GENERATOR:

These generators are used as measuring devices in combination with a CRO. They provide both

quantitative and qualitative information of the system under test. They are made use of in

transient response testing of amplifiers. The fundamental difference between a pulse generator

and a square wave generator is in the duty cycle.

Duty cycle =

A square wave generator has a 500/o duty cycle.

Requirements of a Pulse

1. The pulse should have minimum distortion, so that any distortion, in the display is solely due

to the circuit under test.

2. The basic characteristics of the pulse are rise time, overshoot, ringing, sag, and undershoot.

3. The pulse should have sufficient maximum amplitude, if appreciable output power is requiredby the test circuit, e.g. for magnetic core memory. At the same time, the attenuation range should

be adequate to produce small amplitude pulses to prevent over driving of some test circuit.

4. The range of frequency control of the pulse repetition rate (PRR) should meet the needs of the

experiment. For example, a repetition frequency of 100 MHz is required for testing fast circuits.

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GRIET/ECE 10

Other generators have a pulse-burst feature which allows a train of pulses rather than a

continuous output.

5. Some pulse generators can be triggered by an externally applied trigger signal; conversely,

pulse generators can be used to produce trigger signals, when this output is passed through adifferentiator circuit.

6. The output impedance of the pulse generator is another important consideration. In a fast pulse

system, the generator should be matched to the cable and the cable to the test circuit. A mismatchwould cause energy to be reflected back to the generator by the test circuit, and this may be re-

reflected by the generator, causing distortion of the pulses.

7. DC coupling of the output circuit is needed, when dc bias level is to be maintained.

The basic circuit for pulse generation is the asymmetrical multi-vibrator. A laboratory typesquare wave and pulse generator is shown in Fig 6.1

The frequency range of the instrument is covered in seven decade steps from 1Hz to 10 MHz,

with a linearly calibrated dial for continuous adjustment on all ranges.

The duty cycle can be varied from 25 - 75%. Two independent outputs are available, a 50source that supplies pulses with a rise and fall time of 5 ns at 5V peak amplitude and a 600

source which supplies pulses with a rise and fall tme of 70 ns at 30 V peak amplitude. The

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GRIET/ECE 11

instrument can be operated as a freerunning genenrator or, it can be synchronized with external

signals.

The basic generating loop consists of the current sources, the ramp capacitor, the Schmitt triggerand the current switching circuit as shown in the fig 6.2

The upper current source supplies a constant current to the capacitor and the capacitor voltage

increases linearly. When the positive slope of the ramp voltage reaches the upper limit set by theinternal circuit components, the Schmitt trigger changes state. The trigger circuit output becomes

negative and reverses the condition of the current switch. The capacitor discharges linearly,

controlled by the lower current source. When the negative ramp reaches a predetermined lowerlevel, the Schmitt trigger switches back to its original state. The entire process is then repeated.

The ratio i1/i2 determines the duty cycle, and is controlled by symmetry control. The sum of i 1

and i2 determines the frequency. The size of the capacitor is selected by the multiplier switch.The unit is powered by an intenal supply that provides regulated voltages for all stages of the

instrument.

7. What is the basic difference between a signal generator and an oscillator?

Discuss fixed and variable AF oscillator?

Ans:Signal generators are the sources of electrical signals used for the purpose of testing and

operating different kinds of electrical equipment. A signal generator provides different types of

waveforms such as sine, triangular, square, pulse etc., whereas an oscillator provides onlysinusoidal signal at the output.

The AF oscillators are divided into two types. They are as follows,

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GRIET/ECE 12

1. Fixed frequency AF oscillator2. Variable frequency AF oscillator.

1. Fixed Frequency AF Oscillator

Many instrument circuits contain oscillator as one of its integral parts to provide output signal

within the specified fixed audio frequency range. This specified audio frequency range can be 1

kHz signal or 400 Hz signal.The 1 kHz frequency signal is used to execute a bridge circuit and 400 Hz frequency signal is

used for audio testing. A fixed frequency AF oscillator employs an iron core transformer. Due to

this a positive feedback is obtained through the inductive coupling placed between the primarywinding and secondary winding of the transformer and hence fixed frequency oscillations are

generated.

2. Variable Frequency AF Oscillator

It is a general purpose oscillator used in laboratory. It generates oscillations within the entire

audio frequency range i.e. from 2O Hz to 20 kHz. This oscillator provides a pure, constant sinewave output throughout this AF range. The examples of variable AF oscillators used in

laboratory are RC feedback oscillator, beat frequency oscillator.

8. With a neat block diagram discuss about an AF sine wave generator?Ans: As the name suggest an AF sine and square wave generator produces either sine wave orsquare wave output. It employee a Wein bridge oscillator, sine wave amplifier, square wave

shaper, square wave amplifier and attenuator. The schematic arrangement of these blocks is

shown below.

The Wien bridge oscillator operates effectively in audio frequency ranges. It produces

oscillations whose frequency can be varied by varying the capacitance value of the capacitor of

the oscillator. Also the frequency value can be varied in steps by switching in different values ofresistors. The oscillations of Wien bridge oscillator are applied to either sine wave amplifier or

sine wave shaper through function key. When the key is connected to position 1, the output

oscillations are connected to sine wave amplifier and then to attenuator. Therefore, theoscillations are amplified and then attenuated and a pure sine wave is available at the output.

Depending on the requirement the amplitude of this sine wave can be varied from 5 mV to 5 V

(r.m.s value).

When the key is connected to position 2, the oscillations are applied to square wave shaper

which converts the oscillations into square wave. The square wave signal is amplified and thenattenuated and finally appears as pure square wave at the output. The amplitude of the square

wave can be varied from 0 V to 20 V (peak value).

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GRIET/ECE 13

This generator produces output in the frequency range of 1 0 Hz to I MHz and it requires power

of 7 W at 220V, 50 Hz. The front panel of the instrument contains

(i) ON/OFF switch.

(ii)FrequencyMultip1ier: To choose the frequency range over 5 decades (from10Hz to1MHz).

(iii) Amplitude Multiplier: To attenuate sine wave output in 3 decades (x 1; x 0.1 and x 0.01).

(iv) Amplitude: To continuously attenuate the amplitude of square wave output.

(v) Variable Amplitude: To continuously attenuate the amplitude of sine wave output.(vi) Frequency Selector: To select different ranges of frequencies and to vary the frequency in a

ratio of 1: 11.

(vii) Function Key: To select either square wave or sine wave output.

(viii) Symmetry Control: To adjust the symmetry of square wave from 30% to 70%

(ix) Sync: To synchronize the internal signal with external signal.

8. What is need for inserting isolation between the signal generator output and oscillator in

a simple signal generator? What are the difference ways in which this can be achieved?

Ans:An oscillator of a simple signal generator needs to be isolated from the

output of the signal generator because any variations in the load (output circuit of signal

generator) will affect the output characteristic (i.e., amplitude, frequency, etc) of an oscillator.

Usually, the frequency of an oscillator should be very stable when the oscillator is operating athigh frequencies of the order of MHz, because even a small variation in the frequency will give

rise to errors. Hence, an isolation of 20 dB or more (based upon the type of oscillator circuit)

should be introduced between oscillator and signal generator output.

The different ways to achieve an isolation of 20 dB or more between oscillator and signal

generator output are,

1. Setting the attenuation of attenuator to 20 dB or more.2. Introducing an isolation amplifier between oscillator and attenuator

1. Setting the Attenuation of Attenuator to 20 dB or More

In a signal generator the output of the oscillator is attenuate d by feeding it to variable attenuator,

in order to obtain a signal of desired amplitude (or power level). So, if the attenuator is set to

provide and attenuate the oscillator output by 20 dB or more, an isolation of 20 dB will beproduced between the oscillator and the load.

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GRIET/ECE 14

2. Introducing an Isolation Amplifier between oscillator and Attenuator

In this method of achieving isolation, the oscillator output is amplified by certain amount using abuffer amplifier. Consecutively, it is attenuated by same amount by a fixed attenuator before

feeding the oscillator output to the variable attenuator of the signal generator. In this way

isolation is achieved without any change in the signal level of oscillator output. To achieve an

isolation of 20 dB or more, a 10 dB gain isolation amplifier followed by a 10 dB fixed attenuatoris introduced between the oscillator and variable attenuator as shown in the following figure. The

gain of the isolation amplifier and thus the attenuation of a fixed attenuator depend on the

amount of isolation required and also on the attenuation of the variable attenuator

9. with respect to construction and circuit configuration, explain how a square

wave generator differs from sine wave generator?

Ans:

Sine Wave Generator

The circuit configuration of a sine wave generator consists of Wien bridge oscillator, sine waveamplifier and attenuator. The block diagram of a sine wave generator is shown in figure 9.1

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GRIET/ECE 15

Wein bridge oscillator produces an oscillating output which is usually a sinusoidal (sine) wave.Thus, half of the operation of a sine wave generator is done by the Wein bridge oscillator. The

frequency of oscillations of this oscillator can be varied by varying its capacitance and thus asine wave of desired frequency can be generated. The remaining elements of sine wave generator

i.e., amplifier, and attenuator are used as signal conditioners to condition the output of Wien

bridge oscillator in order to obtain a sine wave of desired amplitude.

Square Wave Generator

The circuit configuration of a square wave generator consists of the basic elements of a sine

wave generator (i.e., Wien bridge oscillator, attenuator) and square wave shaper and square wave

amplifier. Figure 9.2 shows the block diagram of a square wave generator.

A square wave is obtained by feeding the sinusoidal output of the Wein bridge oscillator to thesquare wave Shaper circuit. The square wave shaper is usually a sine-to-square wave converter.

The square wave is further processed through square wave amplifier and attenuator in order to

obtain a square wave of desired amplitude. The frequency of the square wave can be varied byvarying the oscillation frequency of Wein bridge oscillator.

10. What are the precautionary measures to bee taken in a signal generator

application?

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GRIET/ECE 16

Ans;

A signal generator is an instrument, which can produce various types of wave forms such as sinewave, square wave, triangular wave, saw tooth wave, pulse trains etc. As it can generate a variety

of waveforms it is widely used in applications like electronic troubleshooting anti development,

testing the performance of electronic equipments etc. In such applications a signal generator isused to provide known test conditions (i.e., desired signals of known amplitude and frequency

Hence, the following precautionary measures should be taken while using a signal generator for

an application.

1. The amplitude and frequency of the output of the signal generator should be made stable and

well known.

2. There should be provision for controlling the amplitude of signal generator output from very

small to relatively large values.

3. The output signal of generator should not contain any distortion and thus, it should possess

very low harmonic contents.

4. Also, the output of the signal generator should be less spurious.

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GRIET/ECE1

UNIT-3

1. Draw the Block Schematic of AF Wave analyzer and explain its principleand Working?

ANS: The wave analyzer consists of a very narrow pass-band filter section which canBe tuned to a particular frequency within the audible frequency range(20Hz to 20 KHz)).

The block diagram of a wave analyzer is as shown in fig 1.

The complex wave to be analyzed is passed through an adjustable attenuator which

serves as a range multiplier and permits a large range of signal amplitudes to be analyzed withoutloading the amplifier.

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GRIET/ECE2

The output of the attenuator is

then fed to a selective amplifier, which

amplifiesthe selected frequency. The driver

amplifier applies the attenuated input

signal to a high-Q active filter. This high-Qfilter is a low pass filter which allows the

frequency which is selected to pass and

reject all others. The magnitude of thisselected frequency is indicated by the

meter and the filter section identifies the

frequency of the component. The filter

circuit consists of a cascaded RC resonantcircuit and amplifiers. For selecting the

frequency range, the capacitors generally

used are of the closed tolerancepolystyrene type and the resistances used

are precision potentiometers. The

capacitors are used for range changing andthe potentiometer is used to change the frequency within the selected pass-band, Hence this wave

analyzer is also called a Frequency selective voltmeter. The entire AF range is covered in decade

steps by switching capacitors in the RC section

.The selected signal output from the final amplifier stage is applied to the meter

circuit and to an unturned buffer amplifier. The main function of the buffer amplifier is to driveoutput devices, such as recorders or electronics counters.

The meter has several voltage ranges as well as decibel scales marked on it. It is

driven by an average reading rectifier type detector. The wave analyzer must have extremelylow input distortion, undetectable by the analyzer itself. The band width of the instrument is

very narrow typically about 1% of the selective band given by the following response

characteristics shows in fig.1.2

2. What are the applications of wave Analyzer?

Ans: Application of wave analyzer

1. Electrical measurements

2. Sound measurements

3. Vibration measurements.

In industries there are heavy machineries which produce a lot of sound and vibrations, it is very

important to determine the amount of sound and vibrations because if it exceeds the permissible

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GRIET/ECE3

level it would create a number of problems. The source of noise and vibrations is first identified

by wave analyzer and then it is reduced by further circuitry.

3. Explain the working of the harmonic distortion analyzer?

Ans:Fundamental Suppression TypeDistortion analyzer measures the total harmonic power present in the test wave rather than the

distortion caused by each component. The simplest method is to suppress the fundamentalfrequency by means of a high pass filter whose cut off frequency is a little above the

fundamental frequency. This high pass allows only the harmonics to pass and the total harmonic

distortion can then be measured. Other types of harmonic distortion analyzers based on

fundamental suppressionare as follows

1. Employing a Resonance Bridge

T

h

e

b

ri

dge

s

ho

w

n

in fig 3.1 is balanced for the fundamental frequency, i.e. L and C are tuned to the

fundamental frequency. The bridge is unbalanced for the harmonics, i.e. only harmonicpower will be available at the output terminal and can be measured. If the fundamentalfrequency is changed, the bridge must be balanced again. If L and

CCCCCCCCCCCCCCCCCC are fixed components, then this method is suitable only

when the test wave has a fixed frequency. Indicators can be thermocouples or squarelaw VTVMs. This indicates the rms value of all harmonics. When a continuous

adjustment of the fundamental frequency is desifrequency is desired a Wien bridge

arrangement is used as shown in fig 3.2.

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GRIET/ECE4

2. Wiens Bridge Method

The bridge is balanced for the fundamental frequency. The fundamental energy is

dissipated in the bridge circuit elements. Only the harmonic components reach the outputterminals .The harmonic distortion output can then be measured with a meter. Forbalance at the fundamental frequency

C1=C2=C, R1=R2=R, R3=2R4.

3. Bridged T-Network Method

Referring to the fig 3.3 the L and Cs are tuned to the fundamental frequency, and R

is adjusted to bypass fundamental frequency. The tank circuit being tuned to the fundamentalfrequency, the fundamental energy will circulate in the tank and is bypassed by the resistance.

Only harmonic components will reach the output terminals and the distorted output can

be measured by the meter. The Q of the resonant circuit must be at least 3-5.

One way of using a bridge T-network

is given in Fig. 3.4 The switch S is firstconnected to point A so that the

attenuator is excluded and the

bridge T-network is adjusted for full

suppression of the fundamentalfrequency, i.e. Minimum output

indicates that the bridged T-

network is tuned to thefundamental frequency

and that

fundamental frequenciesis fully suppressed.

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GRIET/ECE5

The switch is next connected to terminal B, i.e. the bridge T- network is excluded. Attenuation isadjusted until the same reading is obtained on the meter. The attenuator reading indicates the

total rams distortion. Distortion measurement can also be obtained by means of a wave analyzer,

knowing the amplitude and the frequency of eachcomponent, the harmonic distortion can be calculated.

However, distortion meters based on fundamental

suppression are simpler to design and less expensive

than wave analyzers. The is advantage is that 1giveonly the total distortion and not the amplitude of

individual distortion components.

4. Draw the block Schematic of a Basic

Spectrum Analyzer and explain its

working?

Ans: The most common way of observing signals isto display them on an oscilloscope with time as the

X-axis (i.e. amplitude of the signal versus time). Thisis the time domain. It is also useful to display signals

in the frequency domain. The providing thisfrequency domain view is the spectrum analyzer.

A spectrum analyzer provides a calibrated graphical display on its CRT, with frequency on the

horizontal axis and amplitude (voltage) on the vertical axis.

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GRIET/ECE6

Displayed as vertical lines against these coordinates are sinusoidal components of which the

input signal is composed. The height represents the absolute magnitude, and the horizontal

location represents the frequency.

These instruments provide a display of the frequency spectrum a given frequency band.

Spectrum analyzers use either parallel filter bank or a swept frequency technique.

In a parallel filter in a parallel filter bank analyzer, The frequency range is covered by a series of

filters whose central frequencies and bandwidth are so selected that they overlap each others, asshown in fig 4.1.

Typically, an audio analyzer has 32 of these filters, each covering one third of an octave.

For wide band narrow resolution analysis, particularly at RF or microwave signals, the swept

Technique is preferred.

Basic Spectrum Analyzer Using Swept Receiver Design

Referring to the block diagram of fig. 4.2, the saw tooth generator provides the saw tooth voltagewhich drives the horizontal axis element of the scope and this saw tooth voltage is the frequency

controlled element of the voltage tuned oscillator. As the oscillator sweeps from fmin to fmaxofits frequency band at a linear recurring rate, it beats with the frequency component of the inputsignal and produce an IF, whenever a frequency component is met during its sweep.

The frequency component and voltage tuned oscillator frequency beats together to produce a

difference frequency, i.e. The IF corresponding to the component is amplified and detected ifnecessary and then applied to the vertical plates of the CRO, producing a display of amplitude

versus frequency.

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GRIET/ECE7

The spectrum produced if the input wave is a single toned A.M is given in figs 4.3, 4.4 and 4.5

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GRIET/ECE8

One of the principal applications of spectrum analyzers has been in the study of the RF spectrumproduced in microwave instruments. In a microwave instrument, the horizontal axis can display

as a wide a range as 2 - 3 GHz for a broad survey and as narrow as 30 kHz, for a highly

magnified view of any small portion of the spectrum. Signals at microwave frequency separatedby only a few KHz can be seen individually.

The frequency range covered by this instrument is from I MHz to 40 GHz, The basic blockdiagram (Fig. 9.13) is of a spectrum analyzer covering the range 500 kHz to 1 GHz, which is

representative of a super heterodyne type.

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GRIET/ECE9

The input signal is fed into a mixer which is driven by a local oscillator. This oscillator islinearly tunable electrically over the range 2 - 3 GHz. The mixer provides two signals at its

output that are proportional in amplitude to the input signal but of frequencies which are the sumand difference of the input signal and local oscillator frequency.

The IF amplifier is tuned to a narrow band around 2 GH4 since the local oscillator is tuned over

the range of 2 - 3 GHz, only inputs that are separated from the local oscillator frequency by

2GHz will be converted to IF frequency band, pass through the IF frequency amplifier, getrectified and produce a vertical deflection on the CRT.

From this, it is observed that as the saw tooth signal sweeps, the local oscillator also sweepslinearly from 2 - 3 GHz. The tuning of the spectrum analyzer is a swept receiver, which sweeps

linearly from 0 to 1 GHz. The saw tooth scanning signal is also applied to the horizontal plates of

the CRT to form the frequency axis. (The spectrum analyzer is also sensitive to signals from 4 -5 GHz referred to as the image frequency of the super heterodyne. A low pass filter with a cutoff

frequency above I GHz at the input suppresses these spurious signals.) Spectrum analyzers are

widely used in radars, oceanography, and bio-medical fields

5. With a neat sketch explain the working of a digital Fourier analyzer?

An:A spectrum analyzer, which uses computer algorithm and an analog to digital conversionphenomenon and produces spectrum of a signal applied at its input is known as digital Fourier or

digital FFT or digital spectrum analyzer.

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GRIET/ECE10

Principle

When the analog signal to be analyzed is applied, the A/D converter digitizes the analog signal

(i.e., converts the analog signal into digital signal). The digitized signal, which is nothing but theset of digital numbers indicating the amplitude of the analog signal as a function of time is stored

in the memory of the digital computer. From the stored digitized data, the spectrum of the signal

is computed by means of computer algorithm.

Description:

The block arrangement of a digital Fourier analyzer is illustrated in the figure above fig 5.The

analog signal to be ana1ysed is applied to the low pass filter, which passes only low frequencysignals and rejects high pass spurious signals. This filter section is used mainly, to prevent

aliasing. The output of low pass filter is given to the attenuator. The attenuator is a voltage

dividing network whose function is to set the input signal to the level of the A/D converter. Theuse of attenuator prevents the converter from overloading. The function of A/D converter is to

convert the samples of analog data into digital i.e. ., to digitize the analog signal. When the

output of A/D converter is applied to the digital computer, the computer analyzes the digitizeddata and adjusts the attenuator setting accordingly in order to obtain the maximum output from

the inverter without any overloading. As soon as the entire analog signal is sampled and digitized

by the A/D converter) computer performs calculations on the data according to the programmed

algorithm and the calculated spectral components are stored in the memory of the computer.

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GRIET/ECE11

If the spectral display is to be viewed on the oscilloscope, the digital values of spectral

components stored in the computer memory are converted into analog by using D/A convertersand then applied to the CRO. Thus the spectral display of the input waveform is obtained on the

CRT screen.

Advantages

1. The use of computer avoids most of the hardware circuitry such as electronic switches.Filters and PLLs. The use of less hardware reduces the cost of the analyzer.

2. More mathematical calculations can be carried-out on the spectral display.3.The rate of sampling analog signal can be modified in order to obtain better spectral

display.

6. Differniate between wave analyzer and harmonic distortion analyzer?

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GRIET/ECE12

Ans:

Wave analyzer Harmonic distortion analyzer1. These are designed to measure the relativeamplitude of each harmonic or fundamental

components separately.

2.They indicate the amplitude of single

frequency component

3.These are tuned to measure amplitude of one

frequency component with in a range of 10Hz

to 40MHz

4.These are also known as frequency selective

voltmeters, selective level voltmeters, carrier

frequency voltmeters

5. These are used with a set of tuned filters anda voltmeter.

6. Wave analyzers provide very high frequency

resolution.

7.These can be used for electrical

measurements, sound ,vibration ,noise

measurement in industries

1. These are designed to measure the totalharmonic content present in a distorted or

complex wave form.

2. They do not indicate the amplitude of single

frequency component

3.These can be operated with in a band of 5Hzto 1 MHz frequency

4.It is general know as distortion analyzer

5. These can be used along with a frequencygenerator.

6. They measure quantitative harmonic

distortions very accurately.7.

7.These can be used to measure frequency

stability and spectral purity of signal sources

7. Explain the two types of spectrum analyzers?

Ans:The two types of spectrum analyzers are,

1. Fliter Bank Spectrum analyzer.

2. Super hetero dyne Spectrum analyzer.

1. Filter Bank Spectrum analyzer

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GRIET/ECE13

2. Super hetero dyne Spectrum analyzer

The modern spectrum analyzers use a narrow band super heterodyne receiver. Super heterodyne

is nothing but mixing of frequencies in the super above audio range. The functional block

diagram of super heterodyne spectrum analyzer or RF spectrum analyzer as shown in theFigure 7.2

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GRIET/ECE14

The RF input to be analyzed is applied to the input attenuator. After attenuating, the signal is fedto low pass filter.

The low pass filter suppresses high frequency components and allows low frequency componentsto pass through it. The output of the low pass filter is given to the mixer, where this signal is

fixed with the signal coming from voltage controlled or voltage tuned oscillator. This oscillator

is tuned over 2 to 3 GHz range. The output of the mixer includes two signals whose amplitudes.are proportional to the input signal but their frequencies are the sum and difference of the input

signal and the frequency of the local oscillator. Since the frequency range of the oscillator is

tuned over 2 to 3 GHz, the IF amplifier is tuned to a narrow band of frequencies of about 2 GHz.Therefore only those signals which are separated from the oscillator frequency by 2 GHz are

converted to Intermediate Frequency (IF) band. This IF signal is amplified by IF amplifier and

then rectified by the detector. After completing amplification and rectification the signal is

applied to vertical plates of CRO to produce a vertical deflection on the CRT screen. Thus, whenthe saw tooth signal sweeps, the oscillator also sweeps linearly from minimum to maximum

frequency range i.e., from 2 to 3 GHz. Here the saw tooth signal is applied not only to the

oscillator (to tune the oscillator) but also to the horizontal plates of the CRO to get the frequencyaxis or horizontal deflection on the CRT screen. On the CRT screen the vertical axis is calibrated

in amplitude and the horizontal axis is calibrated in frequency.

Application:

These analyzers are widely used in the field of,

1. Bio medicals

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GRIET/ECE15

2. RADARS

3.Oceangraphy

8. Explain the terms

(i) Distortion in a waveform

(ii) Distortion in a communication signANS:

Distortions may be introduced in a waveform or a communication signal when they aretransmitted from one point to other point through a transmission channel. The transmission

channel consists of various electronic components like amplifier, heterodyning element etc. The

different types of distortions that occur during transmission of an input signal (waveform orcommunication signal) are,

1. Linear distortions(i) Amplitude distortion

(ii) Phase or delay distortion

2. Non-linear distortions(i) Harmonic distortion

(ii) Inter modulation distortion.

l. Linear Distortions

(i) Amplitude Distortion

When different frequency components of the input signal are amplified or attenuated by different

amounts, The output signal consists of distortions, known as amplitude distortions (i.e.,)

amplitude distortion occurs When the amplification or attenuation of the signal is not constantover the useful range of frequencies.

(ii) Phase or Delay Distortion

If the phase of the output signal is different from the phase of input signal then such distortion is

known as phase distortion. Phase distortion leads to delay in the transmission of the signal.

Hence, it is known as delay distortion. If different amounts of phase shifts occur at differentfrequencies of an output signal then it becomes necessary to compensate for such phase

distortions. Whereas if same amount of phase shift occurs at all frequencies then such phase

distortion can be ignored.The phase distortion arises due to the presence of energy storage elements in the transmitting

circuit (i.e. reactive elements such as capacitor and inductor).

2. Nonlinear Distortions

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GRIET/ECE16

The non-linear distortions in the signal arise due to non-linear characteristics of the electronic

components like amplifiers, etc. The two types of non-linear distortions are,

(i) Harmonic Distortion

The non-linear characteristics of an electronic circuit give rise to harmonics in the output signal.

These harmonics produce distortions in the output signal. The distortions caused due to

harmonics are known as harmonic distortions. Harmonic components occur at frequencies 2f1,

3f1, 4f1. (where.f1= Fundamental frequency of signal).

(ii) Inter modulation Distortion

When two signals of different frequencies (f1 and f2) are mixed together (i.e...heterodyned) theresultant signal will be a sum or difference of the actual frequencies of the signal i.e. f1f2, 2f1 f2.....etc. Thus, when the signals are heterodyned additional frequency components are generatedwhich are undesirable and which lead to distortions in the signal. The distortion caused by

heterodyning of different frequency signals is known as inter modulation distortion.

9. Explain how distortion occurs during transmission of a waveform or

Ans

Distortion refers to the deviation in any parameter (like amplitude, frequency. shape) of a signalfrom that of an ideal signal. The non-linear characteristics of the elements of an electronic circuit

give rise to harmonics in the output signal which in turn causes distortion of the output signal.The distortion caused due to harmonics is known as harmonic distortion.

The different types of harmonic distortions caused by an electronic circuit (for example,

electronic amplifier are as follows,

(i) Amplitude distortion

(ii) Frequency distortion(iii) Phase distortion

(iv) Crossover distortion

(v) Inter modulation distortion.

(i) Amplitude DistortionWhen the amplitude of the output signal is not a linear function of the amplitude and inputsignal is distorted under specific conditions then such type of distortion are known as

amplitude distortion. Amplitude distortion occurs when the amplifier gives rise to harmonicsof the fundamental frequency of the input signal.

(ii)Frequency distortion

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GRIET/ECE17

Frequency distortion of a signal takes place when the signal is amplified by different

amounts at different frequencies. This is caused mainly due to the combination of active devices

and components in an amplifier.For Example, the non uniform frequency response of RC-coupled cascade amplifier refers to

frequency distortion

(iii) Phase Distortional: Is different from the phase of the input signal then such distortion is

known as phase distortion.

If different amounts of phase shifts occur at different frequencies of an output signal than

it becomes necessary to compensate for such phase distortions. While if same amount of phase

shift occurs at all frequencies then such phase distortion cannot be ignored .the phase distortionarises due to presence of storage elements in the circuit

(iv)Crossover Distortion

The improper biasing voltages of the electromagnetic components of an amplifier (for

example push-pull amplifier give rise to crossover distortion)

(v) Inter modulation Distortion

When two signals of different frequencies are mixed together (i.e., heterodyned) the

resultant signal will be a sum or difference of the actual frequencies of the signals. Thus, whenthe signals are heterodyned, additional frequencies are generated which are undesirable andthereby leads to distortion. The distortion caused by heterodyning of frequencies is known as

inter modulation distortion.

The various distortions in the signal can be analyzed using a distortion analyzer (for example,harmonic distortion analyzer).

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GRIET/ECE 1

UNIT-4

1. Explain briefly the Basic Features of a CRT?

Ans:

Electrostatic CRTs are available in a number of types and sizes to suit individual requirements.

The important features of these tubes are as follows.

1. Size: Size refers to the screen diameter. CRTs for oscilloscopes are available in sizes of 1, 2,3, 5, and 7 inches. 3 inches is most common for portable instruments

For example a CRT having a number 5GPI . The first number 5 indicates that it is a 5inch tube.

Both round and rectangular CRTs are found in scopes today. The vertical viewing size is8 cm and horizontal is l0 cm.

2. Phosphor: The screen is coated with a fluorescent material called phosphor. This materialdetermines the color and persistence of the trace, both of which are indicated by the phosphor.

The trace colors in electrostatic CRTs for oscilloscopes ale blue, green and But green. White is

used in TVs. and blue-white, orange, and yellow are used for radar Persistence is expressed asshort, medium and long. This refers to the length of time the trace remains on the screen after the

signal has ended.

The phosphor of the oscilloscope is designated as follows.

Pl --Green medium

P2--Blue green medium

P5--Blue very short

P11--Blue short

These designations are combined in the tube type number. Hence 5GPl is a 5 inch tube with a

medium persistence green trace.

Medium persistence traces are mostly used for general purpose applications

Long persistence traces are used for transients, since they keep the fast transient on the screen for

observation after the transient has disappeared.

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GRIET/ECE 2

Short persistence is needed for extremely high speed phenomena, to prevent smearing and

interference caused when one image persists and overlaps with the next one.

P11 phosphor is considered the best for photographing from the CRT screen.

3. Operating Voltages: the CRT requires a heater voltage of 6'3 volts ac or dc at

600mA.

Several dc voltages are listed below. The voltages vary with the type of tube used.

(i) Negative grid (control) voltage 14 V to - 200 V.

(ii) Positive anode no. 1 (focusing anode) -100 V to - ll00 V

(iii) Positive anode no. 2 (accelerating anode) 600 V to 6000 V

(iv) Positive anode no. 3 (accelerating anode) 200 v to 20000 V in some cases

4. Deflection Voltages: Either ac or dc voltages will deflect the beam. The distance through

which the spot moves on the screen is proportional to the dc, or peak ac amplitude. Thedeflection sensitivity of the tube is usually stated as the dc voltage (or peak ac voltage) required

for each cm of deflection of the spot on the screen

5. Viewing Screen: The viewing screen is the glass face plate, the inside wall of which is coated

with phosphor. The viewing screen is a rectangular screen having graticules marked on it. The

standard size used nowadays is 8 cm x l0 cm (8 cm on the vertical and 10 cm on horizontal).

Each centimeter on the graticule corresponds to one division (div). The standard phosphor coloruse d nowadays is blue

2. Exp

Emi Discriptive typeall units material.

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