BVRIT HYDERABAD College of Engineering for Women Department of Electrical and Electronics Engineering

Hand Out

Subject Name: Electrical and EIectronics Instrumentation Prepared by (Faculty Name): Babita Gupta, Assistant Professor, EEE Year and Sem, Department: III Year- II Sem, EEE

Unit – I: Introduction to Measuring Instruments Important Points / Definitions: Measurement means an act or the result of comparison between the quantity and a predefined

standard. Electrical measuring instrument s are classified as;

1.Indicating instruments. 2.Recording instruments. 3. Intergrating instruments.

The basic requirements of measurement are

1. The standard used for comparison purpose must be accurately defined and should be commonly accepted.

2.The apparatus u sed and the method adopted must be provable.

Calibration is defined as the process by which comparing the instrument with a standard to

correct the accuracy. Static error is defined as the difference between the true value and the measured value

of the quantity. Static error = At – A m

PMMC instrument is used for d.c measurement and used in d.c galvanometer Moving iron instrument is used for both a.c and d.c

The range of PMMC instrument can be extended by connecting a shunt resistor & series resistor

Questions

1. What is meant by measurement? 2. Mention the basic requirements of measurement

3. List the three types of instruments. 4. Classify the instrument based on their functions 5. Give any three applications of measurement systems 6. Why calibration of instrument is important? 7. Write the characteristics of the measurement system 8. Write the main static characteristics? 9. Define static error 10. Define dynamic error

11. Name the types of instruments used for making voltmeter and ammeter.. 12. State the advantages of PMMC instruments 13. State the advantages of moving iron type instruments. 14. State the disadvantages of PMMC instruments. 15. State the applications of PMMC instruments

Fill in the blanks / choose the Best:

1. A null type instrument as compared to a deflected type instrument has more accurate &

high sensitive. 2. The use of absolute instruments is merely confined within laboratories as standardizing

instrument. 3. An Analog ammeter is an indicating instrument.

4. Relative error is same as ratio of absolute error and true value. 5. The moving coil-meters, damping is provided by The aluminium frame of the coil. 6. Moving iron instrument can be used for both A.C and D.C 7. The scale of a permanent magnet moving coil instrument is uniform because it is spring

controlled. 8. When the pointer of an indicating instrument is in the final deflected position damping

torque is zero 9. The best type of meter movement is D’Arsonval movement 10. The controlling torque of an indicating instrument increases as the deflection of moving

system increases

Unit – II Potentiometers and Instrument Transformers Important Points / Definitions: Standardization is the process of adjusting the working current supplied by the supply battery

such that the voltage drop across a portion of sliding wire matches with the standard cell.

A potentiometer is an instrument used to measure an unknown e.m.f which is compared with

known e.m.f.

A.C potentiometer is classify in Polar type and Coordinate type potentiometer.

The materials used in potentiometer are German silver manganin wire

The applications of potentiometers are

1. Measurement of unknown emf 2. Ammeter calibration 3. Voltmeter calibration 4. Wattmeter calibration

The advantages of crompton potentiometer are more accuracy & easy to adjust.

Instrument transformer is used to measure high voltage & high current across the measuring

instruments.

In a current transformer is connected in series and potential transformer is connected in parallel

The types of DC potentiometers are

1. Crompton’s Potentiometer 2. Duo-Range Potentiometer 3. Vernier Potentiometer 4. Brook’s Deflectional Potentiometer

The use of potential transformer are

1. They are used for measurement of high voltage 2. They are used for energizing relays and protective circuits.

Questions

1. What is the basic principle used in potentiometer

2. Name the errors caused in potential transformer.

3. Name the potentiometer material used.

4. Define standardization.

5. State the applications of potentiometer.

6. State the advantages of Crompton’s potentiometer

7. What are the practical difficulties in ac potentiometer?

8. Classify ac potentiometers.

9. How the phase angle is measured in polar type potentiometers.

10. Name some ac potentiometers.

11. State the advantages of ac potentiometers

12. State the advantages of instrument transformers

13. State the disadvantage of instrument transformers

14. Define Instrument transformer.

15. Name the errors caused in current transformer.

16. Define ratio error.

17. How the CT and PT are connected in the circuits

18. How the phase angle error is created.

Fill in the blanks / choose the Best:

1. The transfer instrument which is used for standardization of a polar type AC potentiometer

is a thermal instrument.

2. Standardization of potentiometer is done in order that, they become accurate and direct reading.

3. A DC potentiometer for the measurement of DC voltage based on null balance technique. 4. In CT transformer is the secondary nearly short circuited under normal operating condition. 5. CT is connected in series and PT is connected in parallel. 6. Instrument transformer cannot be used for DC measurement. 7. The frequency of voltage generated in an alternator depends on no. of poles 8. In synchronous impedance method the value of synchronous method is more than normal

value 9. Synchronous reactance is the combined reactance due to leakage flux and armature

reaction. 10. The leakage reactance of a three phase alternator is determined by performing open-circuit

and zero power factor test.

Unit – III: Measurement of Power and Energy Important Points / Definitions: The electrodynamometer type instrument is known as transfer instrument .

Electrodynamometer type wattmeter can be used for both a.c and d.c.

Electrodynamometer type wattmeter consist of current coil and pressure coil .

The errors caused in Dynamometer type wattmeter are:

1. Error due to pressure coil inductance

2. Error due to pressure coil capacitance

3. Error due to methods of connection

4. Error due to stray magnetic fields

5. Error due to eddy current.

The main parts of induction type energy are:

1. Current coil with series magnet

2. Voltage coil with shunt magnet

3. Al disc

4. Braking magnet

5. Registering mechanism.

Creeping is Slow but continuous rotation of disc when pc is energized and cc is not

energized

Phantom loading is also called fictitious loading.

Phantom loading is used to test the energy meter to avoid power loss.

Trivector meter which measures the KVAh and KVA of the maximum demand.

The meter used to record the maximum power consumed by the consumer during a

particular period are called maximum demand indicators.

Questions

1. Name the constructional parts of induction type energy meter.

2. How voltage coil is connected in induction type energy meter?

3. How current coil is connected in induction type energy meter?

3. Why aluminium disc is used in induction type energy meter?

4. Define Phantom loading

5. State the use of phantom loading

6. Define creeping

7. What is the purpose of braking mechanism?

8. State the reason why holes are provided in Al disc.

9. Define Blondel’s theorem

10. State the advantages of two wattmeter method.

11. What is the basic principle used in potentiometer?

12. Compare the induction type and dynamometer type wattmeters.

13. Write a note on low power factor meter. 14. State the disadvantages of two wattmeter method.

15. Write a short note on polyphase meter.

Fill in the blanks / choose the Best:

1. In A.C. circuits, power consumed is depends on the p.f. of the circuit in addition to voltage and current.

2. A dynamometer type wattmeter consists of potential and current coils. 3. In a Dynamometer type wattmeter, the fixed coil is split into two. 4. When the moving coil in a Dynamometer type wattmeter deflects pointer moves. 5. Pressure coil of a wattmeter has capacitance and inductance. 6. Wattmeter reading has errors induced by mutual inductance. 7. Watt meters are compensated for errors due to inductance by using parallel capacitor. 8. Low power factor watt meters are designed to have a low torque.

9. Driving system in an induction type single phase energy meter consists of two electromagnets.

10. Series electromagnet consists of U shaped laminations. 11. Moving system of the induction type single phase energy meter has light aluminium disc. 12. Braking system consists of permanent magnet. 13. Induction type instruments are used for A.C. measurements. 14. Copper shading bands are placed around central limb. 15. At overloads, magnetic shunt diverts series flux.

Unit – IV: D.C and A.C Bridges Important Points / Definitions: A bridge circuit consists of a network of four impedancearms forming a closed circuit. A source of

current is applied to two opposite junctions. The current detector is connected to other two junctions.

There are two types bridges :

1. DC bridge 2. AC bridge

The types of DC bridges are:

1. Wheatstone bridge 2. Kelvin Double bridge

The types of AC bridges are:

1. Maxwell’s Inductance - Capacitance bridge 2. Schering bridge 3. Owen’s bridge 4. Hay’s bridge 5. Anderson bridge 6. Wien bridge

The detectors used in AC bridges are 1. Vibration galvanometers 2. Tunable amplifier 3. Head phones

The sources of errors in AC bridges are:

1. Errors due to stray magnetic fields 2. Leakage errors 3. Eddy current errors 4. Residual errors 5. Frequency and waveform errors. Wien bridge is used for the measurement of unknown and

frequency. Q-factor of the coil is defined as the ratio of power stored in the coil to

the power dissipated in the coil. Faults occur in the cable are:

1.Break down of cable insulation 2.Short circuit fault

3.Open conductor fault

Questions

1. What is a bridge circuit?

2. What are the types of AC bridges

3. What is a bridge circuit?

4. What are the types of bridges?

5. Classify resistance.

6. What are the types of DC bridges?

7. What is the range of medium resistance?

8. Name the methods used for medium resistance measurement

9. State the advantages of Wheatstone bridge method.

10. State the advantages of Kelvin double bridge method.

11. Define megger

12. State the use of Wein bridge.

13. Define: Q-factor of the coil

14. Name the faults that occurs in cables.

15. Name the loop test methods used in location of fault.

16. What is the range of high resistance?

17. Name the methods used for high resistance measurement

18. Name the sources of errors in AC bridge measurements

19. State the advantages of Hay’s bridge

20. How the earth resistance is measured?

Fill in the blanks / choose the Best:

1. Wien’s bridge is used for frequency measurement.

2. Kelvin’s double bridge is used to measure low resistance.

3. Carey-Foster’s bridge is not used for measurement of inductance.

4. Hay’s bridge is used for measurement of inductance.

5. Schering bridge is used for measurement of capacitance.

6. To obtain balance in De sauty’s bridge if both the capacitor are free from dielectric losses

7. Loss of charge method is used for measurement of high resistance.

8. Carey-Foster slide wire bridge is used to measure medium resistance.

9. The range of medium resistance lies between 0.1Ω to 0.1MΩ

10. High resistances are provided with aguard terminals to eliminate the errors caused by

leakage current.

Unit – V: Transducers and Oscilloscopes Important Points / Definitions:

A transducer is a device that converts energy from one form to another.

The process of converting one form of energy to another is known as transduction.

Transducers are often employed at the boundaries of automation, measurement, and control

systems, where electrical signals are converted to and from other physical quantities

The parameters of electrical transducer are:

i. Linearity ii. Sensitivity iii. Dynamic range iv. Repeatability v. Physical size

Thermocouple is type of transducer which converts thermal energy into electrical energy.

Single phase induction motor has low starting torque.

The methods that are used for generating the two electron beams within the CRT are the double

gun tube and split beam method.

The two storage techniques used in oscilloscope are mesh storage and phosphor storage. The Components of CRO are:

1. Cathode ray tube (CRT) along with electron gun assembly 2. Deflection plate assembly 3. Fuorescent screen 4. Glass envelope 5. Base.

Questions 1. State the purpose of a lissajous pattern in CRO.

2. Name the basic circuitry of CRO

3. What is an electon gun

4. Name the components of a CRO.

5. Mention the two storage techniques used in oscilloscope CRTs.

6. Define: Transducer

7. Write the parameters of electrical transducer

8. List the advantages of electrical transducers.

9. What is LVDT.

10. List the advantages of LVDT

11. Define strain guage.

12. List the two physical parameters in strain gauge.

13. In what principles,inductive transducer works?

14. Define thermocoup.le

15. Define thermistor.

Fill in the blanks / choose the Best: 1. A voltmeter using thermocouple measures RMS value

2. In a CRO x-y plates is not a part of electron gun.

3. When a photodiode is operated with a reverse bias voltage, its function as photo conductive

cell.

4. In a CRT, the focussing anode is located between pre-accelerating and accelerating anode

5. Lissajious pattern with equal voltages of equal frequency and zero phase shift is a straight

line.

6. Piezo-electric transducer acts as an inverse transducer.

7. Thermocouple is a primary transducer

8. Peltier effect describes current flow between two junctions formed by two different metals.

9. Thermocouple used for measurement of temperature of liquid.

10. In photo emissive transducers, electrons are attracted by anode

11. Semiconductor layer using silicon and germanium is known as Photo junction diodes

12. Photo resistive cells are Passive device