Unit I

BASIC MEASUREMENT CONCEPTS

1. List any four static characteristic of a measuring systems?i) Accuracyii) Precision iii) Conformityiv) Significant figures

2. Define the term accuracy.It is the degree of closeness with which the instrument reading approaches the true value of the quality to be measured.

3. Define the term Precision.It is the degree of closeness with which individual measurements are distributed about the average of number of measured values.

4. What is an error?The algebraic difference between the indicated value and the true value of the quantity to be measured

5. What are the classification of errors in measurements?

6. Mention the different types of standards in measurements?i) International standardsii) Primary standardsiii) Secondary standardsiv) Working standards

7. What is calibration?It is the procedure for determining the correct values of measurements by comparing with the standard one.

8. Distinguish between active and passive instrument

SI.NO Passive Instruments Active Instruments1 Resolution is less Resolution is high2 Simple to design Complicated to design to design3 Addition energy input source is not

required Addition energy input source is required

4 Example: voltmeter , ammeter Example: flow indicator, liquid level

indicator

9. Distinguish between null type and deflection type instrument

SI.NO Null type Instruments Deflection type Instruments1 Not suitable for rapid and dynamic

measurementPreferred for dynamic measurements

2 Accuracy is high Accuracy is less3 High sensitive Less sensitive 4 Example: dc potentiometer Example: Moving coil ammeter

10. What is meant by measurements?It is the act of competition between predefined standard and unknown quantity to be measured.

11. Compare between gravity control and spring control

SI.NOGravity control Spring control

1 Contolling torque can be varied Contolling torque is fixed2 Scale is non uniform Scale is uniform3 Simple and cheap Simple and costly4 Performance is not temperature

dependentPerformance is temperature dependent

12. Mention the advantage of PMMC instrument1.High accuracy2.Not affected by external magnetic field3.Sensitivity is high4.Uniform scale

13. Mention the Disadvantage of PMMC instrument1.Suitable for DC measurements only2.The friction is due to jewel-pivot suspension3.Cost is high

14.List the types of moving iron instruments

1.Moving iron attraction type instruments

2. Moving iron Repulsion type instruments

15.Define Bridge circuit

It is the simplest form of the network with 4 resistance arms forming a closed circuit.

16.Mention the advantage of bridge circuit

(1)Balance equation is independent of magnitude of input voltage

(2) Accuracy is high

(3)Balance equation is independent of Sensitivity of null deflector

17.List the various types of DC bridge circuit

(1)Wheatstone bridge

(2)Kelvin Bridge

18. List the various types of AC bridge circuit

(i)Capacitance comparison bridge

(ii).Inductance comparison bridge

(iii)Maxwells Bridge

(iv)Hay’s Bridge

(v)Wein Bridge

(vi)Anderson Bridge

(vii)Schering Bridge

19.Mention the advantages of Maxwells Bridge

(i)Balance equation is independent of losses associated with inductance

(ii) Balance equation is independent of Frequency of measurement

(iii) Scale of R1 can be calibarated to read the Q value directly

20.Why Schering Bridge is used

(i)Unknown capacitors

(ii).Dielectric loss

(iii)Power factor

21.Define power factor and Loss angle.

Power factor is the series RC combination is defined as the phase angle of the circuit. For a series combination of R and C the angle between the voltage across the series combination and voltage across the capacitor C –Loss angle.

22.Define Dissipation Factor

The quality factor Q=X/R=I/ωRC,Hence the dissipation factor is the reciprocal or Quality factor Q and gives the information about the quality of the capacitor

23.List the sources of errors

(i).Faulty design of instruments

(ii).Due to insufficient knowledge of the quality to be measured

(iii)Unskilled operator of the instrument

(iv)Improper way of using the instrument

24.Define standard

A standard of the measurement is the physical representation of a unique of measurement.Standard means accurate measurement of physical quantity

24.Define zero Drift

It is the deviation in the instrument output with time from its zero value when the variable to be measured is constant.

25.Define Sensitivity Drift

If there exist a proportional change in the indication all along in the uoward stage then the drift from normal characteristics is called sensitivity drift.

UNIT II

BASIC ELECTRONIC MEASUREMENTS

1. Define electronic voltmeter.

Voltmeter which use rectifier diodes and amplifiers and other supporting electronic circuit to produce a current proportional to the quantity to be measured is called electronic voltmeter

2. List the advantages of electronic voltmeter.

i) Low level signal detection

ii) Low power consumption

iii) Less loading effect

iv) High sensitivity and high input

3. What is meant by form factor?

It is the ratio of the r.m.s. value of the average value of an alternating quantity. For purely sine waveform the form factor is 1.11

4. Mention the disadvantages of rectifier instrument.

i) Readings get affected due to rectifier resistance

ii) Rectifier capacitance may affect the readings of the frequency changes.

iii) It is temperature dependent

5. List the salient features of VOM.

i) It include balanced bridge d.c. amplifier

ii) It include rectifier section

iii) It measure various parameter with the help of indicating meters

iv) It measure various parameter by selecting various function using FUNCTION switch

6. Define Q-factor.

Q-factor is defined as the ratio of power stored in the element to the power dissipated in the element

7. What are the different methods for connecting the unknown component to the testing terminal of Q-factor?

i) Direct connection

ii) Series connection

iii) Parallel connection

8. What are the Different section present in vector voltmeter?

i) Two RF to IF converter

ii) Automatic phase control circuit

iii) Phase control circuit

iv) Voltmeter circuit

9. Mention the application of vector voltmeter?

i) Insertion losses

ii) Complex impedance impedance of mixers

iii) Amplifier gain and phase shift

iv) Filter transfer function

10. Define CRO.

The device which allows the amplitude of such signals to be displayed as a function of

time is called cathode ray oscilloscope

11. Comparison between electrostatic and magnetic deflection

SI.NO Electrostatic deflection Magnetic deflection

1 Deflection is achieved by applying voltage to the plates

Deflection is achieved by applying magnetic field by varying current through the coil

2 Deflection is inversely proportional to accelerating voltage

Deflection is inversely proportional to square root of the voltage

3 Deflection is independent of the ratio q/m Deflection is dependent of the ratio q/m

4 The scheme is used for the general purpose oscilloscope

The scheme is used for the T.V and radar

12. Define magnetic deflection sensitivity

Magnetic deflection sensitivity is defined as the deflection on the screen in meter per tesla of magnetic field density

13. What are the two important requirements of sweep generator?

i) Sweep must be linear in nature

ii) To move the spot in one direction only sweep voltage must drop to zero suddenly after reaching its max.value

14. Why sweep generator is called time base generator?

All the time dependent waveform need x-axis to be calibrated as time axis. The sweep generator produces the movement of spot on the screen such that it act as a time axis or time base for the wave forms to be displayed. Hence sweep generator is called time base generator.

15. Define analog storage oscilloscope.

Conventional CRO has the persistent of the phosphor ranging from few milli second to several seconds. But sometimes it is necessary to retain the image for much long period up to several hours. So it stores the waveform for certain duration.

16. Comparison of mesh and Phosphor storage

SI .NO.

Mesh storage Phosphor storage

1 Continuous persistent storage is possible

Continuous persistent storage is not possible

2 Long CRT life Short CRT life

3 Half tones are possible Half tones are not possible

17. What is meant by colpitts oscillator?

An LC oscillator which uses two capacitance and one inductance in feedback network

18. What is meant by Hartely oscillator?

An LC oscillator which uses two inductance capacitance and one capacitance in feedback network

19. List the specifications of square wave and pulse generator

i) Frequency rage is from 1Hz to 10MHz

ii) Two independent outputs are available

iii) Trigger output pulse are available.

iv) Generator can be operated as free running generator

20.List the features of function generator.

i) Can produce sine ,square triangular waveform

ii) Can be phase locked to external signal source

iii)Distortion is less than one percent for the sine wave

UNIT III

SIGNAL GENERATORS AND ANALYZERS

1) What is a Signal Generator?Signal Generators provides variety of different signals for testing various electronic circuits at low powers. The signal generator is an instrument which provides several different output waveforms including sine wave, square wave, triangular wave, pulse train and an amplitude modulated waveform.

2) What are the various requirements of a signal generator?

*The output frequency of signal generator should be very stable

*The amplitude of the output should be controllable from very small to relatively large values.

*The output signal should be free from distortion.

*The amplitude of output signal must be stable.

3) What are the applications of signal generator?

*To provide appropriate signal for calibration, testing and trouble shooting of the amplifier circuits used in communications, electronics such as radio and television amplifiers.

*To be employed as power source for the measurement of gain, bandwidth, signal to noise ratio and standing wave ratio and other properties of circuits.

*To measure the characteristics of antennas and transmission lines.

4) Mention any four Signal generating instruments.

* Low frequency signal generators

*Radio frequency sine wave generators

*Function Generators

*Pulse generators

*Sweep frequency generators.

5)What are the advantages of AF signal generator?

*Stable and simple operation

*Low distortion

*Good amplitude stability

6) What is a function generator?

A function generator is a versatile instrument. It delivers different waveforms whose frequencies are adjustable over a wide range. The most required common output waveforms are the sine, triangular, square and saw tooth waves. The frequencies of these waveforms may be adjusted from a fraction of a hertz to several hundred kilohertz.

7) Write any four features of the function generator.

*The frequency range is 0.01 Hz to 100 Hz.

*It can produce various waveforms such as sine wave, saw tooth wave, triangular wave, square wave etc.

*The accuracy is within ±1% in low frequency range

*It can be phase locked to another external signal source.

8) What are the basic elements of function generator?

*Frequency control network

*Upper and lower constant current source

*Voltage comparator multivibrator

*Output amplifier

9) Define Duty cycle of a pulse value.

The duty cycle is defined as the ratio of the average value of the pulse over one cycle to the peak value. It is defined as ratio of the pulse width to the period of one cycle.

DutyCycle= PulseWidt hPulse Period

10) Define pulse rise and fall time.

The pulse rise time is the time needed for the pulse to go from 10% to 90% of its amplitude. The fall time is the time needed for the trailing edge to go from 90% to 10%. These times are also called leading edge and trailing edge transition times.

11) Define Pulse undershoot.

A distortion of base value immediately following a falling edge is called as pulse undershoot.

12)Define ringing.

The positive and negative peak distortion, excluding overshoot ot undershoot on the pulse top or base line.

13) Define Droop or Sag.

Droop or Sag occurs when the peak value gradually decreases during the pulse.

14)Define pulse repetition rate.

Pulse repetition rate is the rate at which the pulses are produced.

15)Define settling time

The time required for a signal to decrease to a given percentage typically 1% to 5% of its peak value.

16) What are the features of pulse generator?

*The frequency range of the instrument is covered in seven decade steps from 1 Hz to 10 MHz with a linearly calibrated dial for continuous adjustment on all ranges.

*The duty cycle can be varied from 25% to 75%

*Two independent outputs are available

(i) A 50Ω source that supplies pulses with rise and fall times of 5 ns at 5V peak amplitude.

(ii) A 600Ω source supplies pulses with rise and fall times of 70 ns at 30 V peak amplitude.

*The instrument can be operated as a free running generator or it can be synchronized with external signals.

*Trigger out pulses for synchronization are also available.

17) What is RF signal generator?

A radio frequency signal generator has a sinusoidal output with a frequency range between 100 KHz to 40 GHz.

18)What is a sweep frequency generator?

The process of testing the frequency response of amplifiers and filers can be simplified and speeded up by using a signal generator that automatically caries its frequency over a predetermined range. Such an instrument is known as sweep frequency generator.

19) What is frequency synthesized generator?

Frequency synthesized generators produce a very accurate and very stable output frequency derived from either multiples or sub-multiples of one or more crystal controlled oscillator, a process referred to as frequency synthesis.

20)What are the applications of function generator?

*To test the bandwidth of audio frequency amplifier. This method is commonly known as square wave testing.

*It can be used as an important instrument in the trouble shooting of different analog and digital circuits and instruments.

*It can be used to act as a source for the alignment of receiver.

UNIT IV

DIGITAL INSTRUMENTS

1)What is a digital instrument?

The sigital form of measurement can be used to display the measured quantity numerically instead of a deflection. This instrument is called digital instrument.

2) What are the advantages of digital instruments over analog instruments?

*High accuracy

*High precision

*Better resolution

*No parallax error

*No observational error

*Reading can be stored and retrieved

3) Mention the two types of Ramp type DVM

(i)Linear ramp type DVM

(ii)Staircase ramp type DVM

4) Mention the advantages and disadvantages linear ramp type DVM

Advantages:

(i)Low cost

(ii)Easy circuit Design

(iii)Voltage is converted to time, which can be easily digitized

(iv) As the resolution is directly proportional tp the frequency of the local oscillator, netter resolution can be obtained by adjusting the frequency of the oscillator.

Disadvantages:

(i)Accuracy of the reading depends on slope of the ramp and stability of the local oscillator

(ii)Large errors are possible because of interruption of noise with input signal

(iii)Highly linear ramp signal is required.

(iv)Errors may be produced because of drifts and offsets in the comparator

5)What is a digital voltmeter?

Digital Voltmeters are the instruments which convert the analog signal into digital and display the voltage to be measured as discrete numerical on the digital display instead of pointer deflection. It is called DVM. Digital Voltmeters can be used to measure both a.c .and d.c. voltages.

6)What are the advantages of digital voltmeter?

(i)Highly accurate reading can be taken

(ii)Better resolution

(iii)Higher input impedance

(iv) Digital display eliminates observational errors, interpolation errors and parallax errors

(v) Reading speed is high

7)Mention the advantages and disadvantages of successive approximation type DVM

Advantages:

(i) If noise is introduced in the input m the reading will be inaccurate because of incorrect decisions made by the comparator

(ii) If electromechanical switched are used, speed of measurement is less

Disadvantages:

(i)General ranges of digits is 3 to 5 and irt decides the resolution of the instrument

(ii)Inexpensive method

8) List out the advantages and disadvantages of staircase ramp type DVM.

Advantages:

*Highly accurate than linear ramp type DVM

*Simple in Design

*Cost is cheap

*High input impedance

Disadvantages:

*Accuracy of this meter depends on the accuracy of the D/A converter. Hence a high accuracy D/A Converter should be used.

*Speed of measurement is less

*Introduction of noise in the input will cause error.

9)List out the advantages and disadvantages of a Dual Slope type DVM

Advantages:

*Errors due to noise is very less as it is averaged out by the process of integration

*Time constant of the integrator does not affect the voltage measurement.

*Offset voltage is nil because of electronic switch and auto zero capacitor

*Need of sample and hold circuit is eliminated because of the use of integrator.

*Highly accurate

Disadvantages:

*Slow speed

*Circuit is little bit complex compared to the other types of DVM

10) List out the general characteristics of DVM

(i) Input range

(ii)Absolute accuracy

(iii)Resolution

(iv)Stability

(v)Input resistance

11)Define the resolution of DVM.

Resolution of the digital voltmeter is given by :

R= 110n

Where,

R->Resolution of DVM

n->number of full digits in a digital display

12)Define sensitivity of DVM

Sensitivity is the smallest change in the input which a DVM can detect.

Sensitivity, S=¿)min

where,

SSensitivity

¿)minFull scale value of minimum range

RResolution

13) What is a digital multimeter.

Digital multimeter is an instrument which can be used foe measuring d.c. and a.c. voltages, direct and alternating currents and resistances over several ranges.

14)What are the parts of digital multimeter?

(i)Current to Voltage converter

(ii)DC Voltage attenuator

(iii)AC Voltage attenuator

(iv)AC to DC Converter

(v)Resistance to Voltage Converter

(vi)Analog to Digital Converter

(vii)Display devices

15 ) Give the specifications of a digital multimeter.

(i) Diode Test

(ii) Touch hold

(iii) Peak hold

(iv) Bar graph display

(v) Digital interface

16) What are the advantages of frequency counter?

*Gives accurate reading

*Simple in operation

*Electronic counter has a high speed of operation

*High frequency signal can be measured

17)What are the methods used to increase the frequency range of the frequency counter?

*Pre-scaling

*Heterodyne converter

*Transfer Oscillator

*Automatic divider

18)What is the principle involved in time interval measurement?

In this time interval measurement, the electronic counter used to get the output takes the function of an electronic stop watch thereby measuring the time interval.

19)What is automatic ranging?

Automatic zeroing is the ability of the digital instrument to change its range for getting a reading with the optimum resolution under all circumstances.

20)What are the four components for a computer test system?

(i)Computer compatible test equipment

(ii)Computer

(iii)Software to perform the desired test and present the data in correct form

(iv)Communication Systems to connect the computer and the test equipment.

UNIT V

DATA ACQUISITION SYSTEMS AND FIBER OPTIC MEASUREMENTS

1)What is Data Acquisition System?

A typical Data Acquisition system consists of individual sensors with the necessary signal conditioning, data conversion, data processing, multiplexing, data handling and associated transmission, storage and display systems.

2) What are the objectives of data acquisition system?

*It must acquire the necessary data at the correct speed and at the correct time

*It must monitor the complete plant operation to maintain on-line optimum and safe operations

*It must be flexible and capable of being expanded for future requirements.

*It must be reliable and should not have a downtime greater than 0.1%

3) What are the classification of data acquisition system?

(1)Analog Data Acquisition system

(2)Digital Data Acquisition system

4) List out the various functional operations of a digital data acquisition system.

(i) It handles the analog signals

(ii) It performs measurement

(iii)It converts analog signal into digital data and handles it.

(iv) It performs internal programming and control

5) What are the various components of the digital data acquisition?

(i) Transducer

(ii)Signal conditioner

(iii)Multiplexer

(iv)Signal Converter

(v) Auxiliary equipments

(vi) Digital recorder

6) What are the factors that decide the configuration of DAS?

(i) Resolution and accuracy

(ii)The number of channels to be monitored

(iii)Sampling rate per channel

(iv)Signal conditioning requirement of each channel

(v)Cost

7) Mention applications of DAS.

*Aerospace application

*Biomedical field

*Telemetry industries

*Industries

8) What is data loggers?

The data loggers is used to automatically make a record of the readings of instruments located at different parts of the plant. It measures and records data effortlessly as quickly as often and as accurately desired.

9) What is IEEE-488 Bus?

The IEEE-488 Bus is also called a general purpose interface bus (GPIB). The Hewlett-Packard Interface Bus (HPIB) is a proprietary version of the IEEE-488 Bus. The main purpose for the IEEE-488 bus is automatic test equipment both generalized and specific.

10) What are the devices in IEEE 488 bus?

1.Controllers

2. Talker only

3. Listener only

4. Talker & Listener

11) Define controllers in IEEE 488 bus.

This type of device act as the brain of the system and communicates device addresses and other interface messages to instruments in the system. Most controllers are programmable digital computers.

12) Define Listener in IEEE 488 bus.

A device capable of listening will receive commands from another instrument, usually controllers, when correct address is placed on the bus. The listener acts on the message received but does not send back any data to the controller.

13) Define Talker in IEEE 488 bus.

The talker responds to the message sent in it by the controller and then sends data back to the controller over the DIO data bus. A frequency counter is an example of a talker.

14) What are the buses in IEEE 488 bus?

Data input/output bus

Data byte transfer bus

General interface management bus

15) What are the signal lines in IEEE 488 bus?

Interface clear (IFC)

Attention (ATN)

Service request (SRQ)

Remote enable (REN)

End or Identify (EOI)

16) What are the types of loss measurements in optical fibers?

Cut-back method

Insertion loss method

Optical Time Domain Reflectometer method

17) Give the advantages of Cut-back method.

It is a simple method for measuring total attenuation loss.

It is a precise and accurate method.

18) Give the merits of OTDR method of measuring loss in optical fibers.

It requires access to one end of the fiber only.

It provides positional information about the properties of fiber.

It is easy to locate the faults.

19) How long would be required for a reflection from a break in a fiber to return to an optical time domain reflectometer if the distance to the break is 1.2km and the index of refraction of the fiber is 1.33.

L=1/2 ( C/n1) t

Where n1 = refractive index of core

C = velocity of light in free space

L=length of break

t=time taken for reflection

t = (2Ln1)/ C

t = (2 x 1.2 x 103 x 1.33)/3 x 108

t = 10.64µs

20) What is optical time domain reflectometer?

An OTDR is a fiber optic tester characterizing fibers & optical networks. The aim of this instrument is to detect, locate and measure events at any location in the fiber link.