assignment with answers

8/6/2019 Assignment With Answers

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BM2203 SENSORS AND MEASUREMENTS

Assignment No.1

UNIT I: SCIENCE OF MEASUREMENTS

2 Marks

1. What is measurement? What are the two basic requirements of any

measurement?

Measurement is an act or the result of comparison between the quantity and a

predefined standard.

Requirements

The standard used for comparison purpose must be accurately defined andshould be commonly accepted.

The apparatus used and the method adopted must be provable.

2. What is measurement and how it is classified.

Direct method measurand value compared with standard quantity

Indirect method- measurand value compared indirectly with standard quantity

3. Draw the block diagram of a measurement system giving the

function of each block.

4. List the advantages of an electronic measurement.

Most of the quantities can be converted by transducers into the electrical or

electronic signals.

An electrical or electronic signal can be amplified, filtered, multiplexed,

sampled and measured.


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The measurement signals can easily be obtained in or converted into digital

form for automatic analysis and recording.

5. How the performance characteristics of an instrument are classified?

Static characteristics for the instruments for the input changes slowly with

time; constant input

Dynamic - characteristics for the instruments for the input changes rapidly

with time

The dynamic characteristics of a measuring instrument describe its behavior

between the time a measured quantity changes value and the time when the

instrument output attains a steady value in response. As with static characteristics,

any values for dynamic characteristics quoted in instrument data sheets only apply

when the instrument is used under specified environmental conditions.

6. Define and explain the following static characteristics of an instrument

Accuracy Degree of closeness with which the instrument reading approaches

the true value of quantity to be measured.

Precision: degree of freedom from random errors (confused with accuracy!)

Repeatability: closeness to output when input is repeated ( same conditions.

e.g. instrument, observer, location)

Reproducibility : repeatability if conditions vary

Static error :Deviation from true value of measured value

Resolution-Smallest measurable change, Minimum input produces detectable

change in output.

Sensitivity-Change in output at a given input change :

scale deflection/value of measurand producing deflection = slope of fitted

line

Threshold smallest measuranle input for which system responds

Zero drift-slow variation in output even when input does not change

Linearity- maximum deviation in output from fitted line (% full scale)

Stability- ability to maintain or retain its performance throughout its life.


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7. Differentiate precision and accuracy of measurement system with

example.

Precision: degree of freedom from random errors (confused with accuracy!)

Accuracy Degree of closeness with which the instrument reading approaches

the true value of quantity to be measured.

8. Differentiate zero drift and span drift.

9. How the instruments are classified? Explain with suitable examples.

Transducers are classified according to their application, method of energy

conversions and nature of the output signal.

Active and passive instruments

Null-type and deflection-type instruments

Analogue and digital instruments

Indicating instruments and instruments with a signal output

Smart and non-smart instruments

10. Define a dynamic response of an instrument.

The dynamic characteristics of a measuring instrument describe its behavior

between the time a measured quantity changes value and the time when the

instrument output attains a steady value in response. Such response is called

dynamic response.

11. What are the two basic factors in specifying the dynamic performance

of an instrumentation system?

Fidelity

Speed of response

Measuring lag


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Rapidly varying input

12. A 0 150V voltmeter has a guaranteed accuracy of 1 percent full scale

reading. The voltage measured by this instrument is 93 V. Calculate the

limiting error in percent.

13. The value of International ampere was based on what phenomenon.

One ampere is the current flowing through two infinitely long parallel

conductors of negligible cross-section placed 1 metre apart in a vacuum and

producing a force of 2 10 7 newtons per metre length of conductor

14. Define a Transducer.

A transducer is a device, usually electrical, electronic, electro-mechanical,

Electromagnetic, photonic, or photovoltaic that converts one type of energy or

physical attribute to another for various purposes including measurement or

information transfer (for example, pressure sensors).

15. How are transducers, classified based on physical effect?

Types of transducers:

Electromagnetic:

Antenna - converts electromagnetic waves into electric current and viceversa. Cathode ray tube (CRT) - converts electrical signals into visual form

Fluorescent lamp, light bulb - converts electrical power into visible light

Magnetic cartridge - converts motion into electrical form

Photodetector or Photoresistor (LDR) - converts changes in light levels into

resistance changes

Tape head - converts changing magnetic fields into electrical form

Hall effect sensor - converts a magnetic field level into electrical form only.Electrochemical:

pH probes

Electro-galvanic fuel cell

Electromechanical (electromechanical output devices are generically called

actuators):


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Electroactive polymers

Galvanometer ,MEMS ,Rotary motor, linear motor ,Vibration powered generator

,Potentiometer when used for measuring position

Load cell converts force to mV/V electrical signal using strain gauge Accelerometer

Strain gauge

String

Potentiometer

Electroacoustic:

Geophone - convert a ground movement (displacement) into voltage Gramophone

pick-up

Hydrophone - converts changes in water pressure into an electrical form

Loudspeaker, earphone - converts changes in electrical signals into acoustic form

Microphone - converts changes in air pressure into an electrical signal

Piezoelectric crystal - converts pressure changes into electrical form

Tactile transducer

Photoelectric:

Laser diode, light-emitting diode - convert electrical power into forms of light

Photodiode, photoresistor, phototransistor, photomultiplier tube - converts changing

light levels into electrical form

Electrostatic:

Electrometer

Thermoelectric:

RTD Resistance Temperature Detector Thermocouple

Peltier cooler

Thermistor (includes PTC resistor and NTC resistor)

Radioacoustic:

Geiger-Mller tube used for measuring radioactivity. Receiver (radio)

16. Define primary and secondary transducers with application examples.


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The instrument which gives the magnitude of the quantity to be measured in terms

of the physical constants of the instrument,is called primary transducer. Ex.Tangent

galvanometer

The instrument in which the reading shown by the instrument gives directly the

measurement of the quanity to be measured is called secondarytransducer.Ex.Ammeter

17. Differentiate active and passive instruments.

Instruments are divided into active or passive ones according to whether the

instrument output is entirely produced by the quantity being measured or whether

the quantity being measured simply modulates the magnitude of some external

power source. This is illustrated by examples.

An example of a passive instrument is the pressure-measuring device. The pressure

of the fluid is translated into a movement of a pointer against a scale. The energy

expended in moving the pointer is derived entirely from the change in pressuremeasured: there are no other energy inputs to the system.

An example of an active instrument is a float-type petrol tank level indicator. Here,

the change in petrol level moves a potentiometer arm, and the output signal

consists of a proportion of the external voltage source applied across the two ends

of the potentiometer. The energy in the output signal comes from the external

power source: the primary transducer float system is merely modulating the value

of the voltage from this external power source.

In active instruments, the external power source is usually in electrical form, but in

some cases,it can be other forms of energy such as a pneumatic or hydraulic one.

18. A 0-10 A ammeter has an accuracy of 1.5%of full scale reading .The

current indicated by the ammeter is 2.5 A. Calculate the limiting values of

current and percentage limiting error.

20. A 0- 150 V voltmeter reads 90V, find the percentage limiting error if

the instrument has the limiting error if the limiting error of 1%.Find the

limiting error if the meter reads 70V.


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21. Discuss the classes of systematic errors giving suitable example for

each type.

Systematic errors describe errors in the output readings of a measurement

system that are consistently on one side of the correct reading, i.e. either all the

errors are positive or they are all negative. Systematic errors in the output of many

instruments are due to factors inherent in the manufacture of the instrument arising

out of tolerances in the components of the instrument. They can also arise due to

wear in instrument components over a period of time. In other cases, systematic

errors are introduced either by the effect of environmental disturbances or through

the disturbance of the measured system by the act of measurement.

22. Differentiate between electrical and mechanical transducers. Give the

examples of mechanical transducers. Give the merits and drawbacks of

mechanical transducers.

23. Distinguish between transducers and sensors.

The term transducer is commonly used in two senses; the sensor, used to

detect a parameter in one form and report it in another (usually an electrical or

digital signal), and the audio loudspeaker, which converts electrical voltage

variations representing music or speech, to mechanical cone vibration and hence

vibrates air molecules creating acoustical energy.

24. What is the need of a transducer?

To convert non electrical quantities into electrical quantities.25. What is an input device?

An element of an instrument which makes first, the contact with the quantity

to be measured is

Input device and also gives input to the measurement system.


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26. What are the types of errors possible in an instrument?

Instrumental error: Due to

Short comings of instrument

Misuse of instrument

incorrect readings

Overloading effects

Environmental error: Due to

Changes in ambient conditions

Observational error: Due to

Misreading

Wrong observations

27. Explain the terms relative error and relative percentage error.

28. What is SI system of units? State the fundamental and supplementary

SI units.

The International System of Units (abbreviated SI from the French language

name Systme International d'Units) is the modern, revised form of the metric

system. It is the world's most widely used system of units, both in everyday

commerce and in science.

The SI was developed in 1960 from the metre-kilogram-second (MKS) system,

rather than the centimetre-gram-second (CGS) system, which, in turn, had manyvariants. At its development the SI also introduced several newly named units that

were previously not a part of the metric system.

There are two types of SI units, base and derived units. Base units are the

simple measurements for time, length, mass, temperature, and amount of

substance, electric current and light intensity. Derived units are made up of base

units, for example density is kg/m3.


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29. Define and explain the term 'Calibration'.

All instruments suffer drift in their characteristics, and the rate at which this

happens depends on many factors, such as the environmental conditions in which

instruments are used and the frequency of their use. Thus, errors due to

instruments being out of calibration can usually be rectified by increasing thefrequency of recalibration.

30. What is standard? Which are the different types of standards?

Standards: Laws to regulate measurement were originally developed to

prevent fraud. Standard is the physical representation of units of measured values.

However, units of measurement are now generally defined on a scientific basis, and

are established by international treaties. In the United States, commercial

measurements are regulated by the National Institute of Standards and Technology

NIST, a division of the United States Department of Commerce.

Types of Standards

International

Primary

Secondary

working

31. What is the difference between international and absolute standards?

International standards are defined as the international agreement-

maintained at the International Bureau of weights and measures and used for

evaluation of primary standards.

Primary standards-accurate absolute standards, used as ultimate reference

standards-maintained at National Standard Laboratories and used for evaluation of

secondary standards.

32. What are primary standards? Where are they used?

Primary standards-accurate absolute standards, used as ultimate reference

standards-maintained at National Standard Laboratories and used for evaluation ofsecondary standards.

33. What is the difference between secondary and working standards?

Secondary standards


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To protect highly accurate primary standards the secondary standards are

maintained, which are designed and constructed from the absolute standards-

maintained by the particular industry to which they belong.

Working standards

These are the basic tools of a measurement laboratory and are used to

check and calibrate the instruments used in laboratory for accuracy and the

performance.

16 Marks

1. Discuss the basic characteristics of measuring device.

2. What is the importance of static characteristics of measurement system?

3. List down the various types of errors in measurement and brief about thesources, causes and prevention of the same.

4. Differentiate random and systematic errors with example.

5. Classify different types of standards used in measurement and explain their

scope of application.

6. Compare the features of various transducers.


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7. List down the various standards used for depicting the parameters such s

capacitance, inductance resistance and electrical safety.

8. How transducers classified and what are are the main characteristics of

pressure transducer.

9. Summarize the possible sources of error in instruments

10. Explain how error compensation is achieved in digital instruments.

11. Define the primary standards for the following with example.

Mass, length, Time, Current, Temperature, Luminous intensity.

12. Explain how secondary standards are derived?

13. List any six basic requirements of transducers?

14. A voltmeter has sensitivity of 1.5 k /volt and it reads 75 volts on its 150V range when connected across an unknown resistor in series with a milli ammeter.

The ammeter reads 20 mA. Calculate the apparent resistance, actual resistance of

unknown resistor, error due to loading effect of voltmeter and percentage relative

accuracy.

15. Write down the various steps involved in the process of calibration.

Assignment No.2

UNIT II: DISPLACEMENT, PRESSURE, TEMPERATURE SENSORS

2 Marks

1. What is strain gauge?

2. Where is strain gauge used?

3. Why strain gauges are called the piezo-resistive strain gauge?

4. What are thermistors?

5. What are Rosettes?


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6. Why thermistor is well suited to precision temperature measurement, control

and compensation.

7. Where is LVDT used?

8. What are the common materials used for piezoelectric transducers?

9. Explain Dynaloy.

10. What are force summing devices?

11. Draw the sketch of a turbine flow meter.

12. Give a schematic equivalent for capacitive interference

13. Draw the sketch of Thermocouple and mention its application.

14. Give the biomedical applications of capacitive transducers.

15. The mechanical elements used to convert the applied force into displaced

are known as what? Give two examples.

16 Marks

1. Explain the construction and working of a strain gauge. Describe the varioususes of this gauge. Discuss its application for force measurements.

2. Compare the three types of strain gauges. Give their merits and demerits.

3. Compare the three types of strain gauges. Give their merits and demerits.

4. Describe the construction and working of vibrating diaphragm pressure

transducer with a neat sketch.

5. What are the various principles of operations of capacitive transducers?

Explain them. Give merits, demerits and applications of capacitive transducers.

6. What is an LVDT? Explain its working with necessary diagrams and

characteristics. What are its advantages and uses?

7. What are passive transducers? How they are classified? Explain its types and

applications.


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8. Explain the principle of working and construction of an electrical resistance

thermometer. In what temperature range it is used.

9. What are thermistors? Explain how thermistors can be used for temperature

measurements.

10. What are the characteristics of thermistor? Explain its application as

incubator.

11. Give construction and explain working of a thermocouple. Give the merits,

demerits and applications of thermocouples.

Assignment No.3

UNIT III: PHOTOELECTRIC AND PIEZOELECTRIC SENSORS

2 Marks

1. What is meant by optoelectronic device?

2. What is the difference between photo emissive, photo c conductive and

photovoltaic cells?

3. What is the disadvantage of multiplier phototubes?

4. What is the main drawback of the photoconductive cells?

5. What are photoconductive cells?

6. Name some devices used for photo detection.

7. What is photodiode?

8. What is photoelectric effect?

9. How phototubes are classified?

10. What is meant by piezoelectric effect?

11. Name some materials used for the construction of piezoelectric transducers.

12. Differentiate photo electric sensors from piezoelectric sensors.

13. What is working principle of ultra sound transducers?


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16 Marks

1. Explain the construction and operation of a multiplier phototube. Draw itstypical anode characteristics, advantages, drawbacks and applications.

2. Describe the construction and working of a photovoltaic cell. Draw its typical

characteristics and give its merits, demerits and applications.

3. What is a photodiode? Give its biasing arrangement and construction. Give its

one or two applications.

4. Describe the construction and working of gas filled phototube. How does it

differ from a vacuum phototube in construction? Draw its anode characteristics

.Give its advantages, drawbacks and applications.

5. How does piezoelectric transducer work? What are the common materials

used for it? Describe an expression for its (i) voltage and (ii) charge sensitivities.

Draw an equivalent circuit for this transducer. Write uses of piezoelectric materials

and transducer

6. Analyze how acoustic sensors are used in ultrasonic scanning equipments.

7. Explain with suitable diagrams the measurement of flow using ultrasonic

sensors.

8. Compare the working principle and biomedical applications of following:Photo conductive cell, Photo voltaic cell, Photo transistor, Photo diodes.

9. With a suitable diagram explain the construction and working of

spectrophotometer with biomedical applications.

Assignment No.4

UNIT IV SIGNAL CONDITIONING & SIGNAL ANALYSER

2 Marks

1. Name the commonly used detectors for ac bridges.

2. Name the detector used for bridge measurements at radio frequencies.


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3. What are the merits and demerits of Maxwell Wein Bridge?

4. What is Wein Bridge? What are its uses?

5. List the factors that may lead to inaccuracies in measurements by Ac Bridge.

6. What is meant by spectrum analyzer?

7. What is MDS in a spectrum analyzer?

8. What is meant by dynamic range of a spectrum analyzer?

9. For measurement of high frequency, what is the function of a transfer

oscillator?

10. List the features of spectrum analyzers.

11. Write down the balancing condition of wheat stone bridge circuit.

12. What is an attenuator? Distinguish it from an amplifier.

13. In a linear device, the output is generally described by. What equation.

16 Marks

1. Describe the working of Hay's bridge for the measurement of inductance.

2. Why is Schering Bridge particularly suitable for measurement at high

voltage?

3. Explain how Maxwell's inductance-capacitance bridge is used for the

measurement of inductance of a coil. What are the advantages and disadvantages

of the bridge?

4. Describe how Schering Bridge can be used for measurement of unknown

capacitance and its loss angle. Derive the conditions of balance and draw the

phasor diagram of the bridge circuit under conditions of balance.

5. Draw the block diagram of spectrum analyzer and explain its working with anapplication example.

6. What is Wein-network? Determine the condition for zero phase shift between

its input and output.

7. With a neat circuit diagram explain the generation of variable Frequency sine

generator with amplitude stabilization.


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8. Draw the block diagram of logic analyzer and explain its working with an

application example.

9. Explain the working of the following with neat sketches

i. Kelvin bridge

ii. Schering bridge

Assignment No.5

UNIT V: DISPLAY AND RECORDING DEVICES

2 Marks

1. What is a recorder?

2. What is the necessity of the recorders?

3. What is the main recording requirement?

4. What are strip chart recorders?

5. Why strip chart recorders are also called the x-t recorders?

6. What is a CRT?

7. What is a CRO?

8. What are the major components of a CRO?

9. Mention the two applications of DSO.

10. Mention different types of probes used in CRO.

11. What is a digital voltmeter? What are its advantages?

12. What is the principle of operation of a DVM?

13. Name the different types of DVMs.

14. What is DMM?

15. What are the advantages of LCDs over LEDs?

16. What is the display devices used in digital instruments?


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17. List two guarding techniques used in digital instruments.

18. What are the merits of digital meters over analog meters?

19. Describe the working principle of sampling oscilloscope.

20. Define deflection sensitivity and band width of CRO.

21. Define guarantee error and confidence level.

22. The performance of a beat frequency oscillator depends on what factors.

23. Distinguish the types of motors used in analog X-Y recorder and digital X-Y

recorder respectively.

24. The laser printer is comparatively faster than line, dot matrix and inkjet

printers. Why?

25. Define deflection sensitivity of Cathode Ray Oscilloscope.

26. What are various elements of magnetic tape recorder?

27. How are digital meters classified as?

28. For reading punched cards in the data processing industry, what types of

transducers are deployed and why are they preferred.

29. What are known as Lissajous patterns w.r.t. CRO.

30. Why Oscilloscope probe compensation adjusted?

16 Marks

1. Draw the block diagram of 3 digit multimeter and explain the function of

each block.

2. How is it used for A.C. voltage and current measurements?

3. What is an X-Y recorder? How it is different from X-t or Y-t recorder? Describe

its functioning giving suitable circuit diagram. Give its merits, demerits and

applications.

4. Explain with the suitable diagram the CRT recorder.

5. Describe with the help of suitable diagrams, the basic components of

magnetic tape recorder. Give its operating principle, advantages and applications.


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6. How do you maintain the accuracy in DVM? Also how is automation in

voltmeters established?

7. Note down the specifications of a digital multi meter and state the principle of

coherent sampling and incoherent sampling and how they are used in digital

instrumentation.

8. Discuss the functioning of a multichannel column display oscilloscope with

suitable sketches.

9. How is digital data recording performed by synchronous digital; recoding?

What are its merits and demerits?

10. What is a digital voltmeter (DVM)? What are its advantages? List different

types of DVMs.How can a DVM be used for measurement of (i) current and (ii)

resistance.

11. Enlist the advantages of the special oscilloscope over a conventional type.Also discuss the working of a sampling scope.

12. Write brief notes on

a. Magnetic recorder

b. Multichannel column display oscilloscope

13. Describe the working of storage oscilloscope with a neat sketch.

14. Write a not on Lissajous figures.

15. Discuss in detail with necessary diagrams the construction and working of

magnetic tape recorder.

16. What is the limiting frequency for a magnetic tape recorder which has a gap

of width 5 micro-meters and is used with a tape speed of 95.5mm/s.

17. Describe the working of cathode ray oscilloscope with a neat sketch.

18. Explain how Lissajous figures help in making phase measurements.

19. Discuss the construction and working of servo type recorder in detail with

necessary diagrams. How does it help to record bio signals?


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