ME8501- Metrology and Measurments - Unit-5 Two marks

Subject Name: Metrology and Measurments

Subject Code: ME8501

B.E. Mechanical Engineering - semester 05

Anna University Regulation 2017 Mechanical 5th sem ME8501(Metrology and Measurments) 2 marks for 5th unit is provided below. ME8501 all units 2 marks, Metrology and Measurments all units notes , syllabus are listed down for students to utilize it for scoring maximum marks with our study materials.

1.Define force.

Answer

The mechanical quantity which changes or tends to change the motion or shape of a body to which it is applied is called force.

2.What are the load cells?

Answer

Load cells are the device for the force measurment through indirect methods.

3.What is the function of load cell?

Answer

Load cells are devices for the force measurement through indirect methods. Force is applied to elastic member of the cell results in a proportional displacement or strain sensed by calibrated mechanical or electromechanical means.

4.State any two principles of force measurment.

Answer

1. Direct methods 2. Indirect methods.

5.List of the devices used to measure the force.

Answer

1. Scale and balance 1.Equal arm balance 2.Unequal arm balance 3.Pendulum scale 2. Elastic force meter proving ring 3. Load cell 1.Strain gauge load cell 2.Hydraulic load cell 3.Pneumatic load cell.

6.Differentiate between primary and secondary transducers.

Answer

Primary transducer -It is a mechanical device. -It converts a physical signal into mechanical signal. -Ex. Thermisters and thermocouples. Secondary transducer -It is an electrical device. -It converts analog output into electrical signal. -Ex. Accelerometer and piezoelectric transducer.

7.Give the basic principle of equal arm balance.

Answer

It works on the principle of moment comparison. The beam of the equal arm balance is in equilibrium when clockwise rotating moment is equal to anticlockwise rotating moment.

8.Give the basic principle for elastic force meter (proving ring).

Answer

When a steel ring is subjected to a force (tensile or compressive) across its diameter, it deflects. This deflection is proportional to applied force when it is calibrated.

9.Differentiate between force and torque.

Answer

Force -Force is the linear load acting on the member. -The mechanical quantity which changes or tends to change the motion or shape of a body to which it is applied is called force. Torque -Torque is just a rotational force or force through a distance. It is a moment vector of a force. -It is defined as a measure of the tendency of a force to rotate body on which it acts about an axis.

10.List any two methods employed for measuring torque.

Answer

(i) Torque reaction methods (ii) Proney brake (iii)Torque measurement using strain gauges (iv) Torque measurement using torsion bars.

11.Name the instruments used for measurement of torque.

Answer

1. Mechanical torsion meter (stroboscopic method) 2. Optical torsion meter 3. Electrical torsion meter 4. Strain gauge torsion meter.

12.Give the basic principle of mechanical torsion meter.

Answer

When a shaft is connected between a driving engine and driven load, a twist (angular displacement) occurs on the shaft between its ends. This angle of twist is measured and calibrated in terms of torque.

13.What is the purpose of strain gauge?

Answer

Strain gauges are devices used to measure the dimensional change of components under test. Strain = Change in length / Original length = (mm) / (mm) dimensionless

14.Classify the types of strain gauges.

Answer

1. Unbonded strain gauge 2. Bonded strain gauge 3. Fine wire strain gauge 4. Metal foil strain gauge 5. Piezo-resistive strain gauge.

15.Mention the need for using strain gauge in wheatstone network circuits.

Answer

The change in the resistance due to strain in the gauges Can either be measured or made to give an output which can be easily displayed or recorded.

16.Outline the advantages to be gained by the use of electrical resistance strain gauge factor device in both static and dynamic condition.

Answer

1. High sensitivity 2. Great stability 3. Comparative ruggedness 4. Ease of application The above advantages make electrical resistance strain gauges a very powerful tool for strain determination.

17.Mention a few materials used in binding of strain gauges.

Answer

1. Ceramic cement 2. Epoxy 3. Nitrocellulose.

18.What is meant by pressure?

Answer

Pressure is the force exerted by a medium (fluid) on a unit area due to the interaction of fluid particles among themselves.

19.List out the instruments used to measure pressure.

Answer

1.Elastic transducer (a) Bourdon tube press gauge (b) Elastic diaphragm gauges (c) Bellow gauges 2. Mcleod vacuum gauge 3. Bulk modulus or electrical resistance pressure gauge. 4. Thermal conductivity gauge — Pirani gauge

20.Name any four elements that can be used in elastic pressure transducer.

Answer

Diaphragms, capsules, bellows and Bourdon or helical tubes.

21.What is a kentometer?

Answer

It is a device for the measurement of absolute pressure.

22.Give the principle of bulk modulus or electrical resistance pressure gauge.

Answer

When an electrical conductor is subjected to direct pressure, its resistance changes. The change in resistance becomes a measure of the applied measure when it is calibrated.

23.What are the instruments used to measure linear velocity?

Answer

(i) Electromagnetic transducer (ii) Digital transducer (iii)Transducers with Doppler Effect.

24.Mention some instruments that measure angular velocity.

Answer

1.Hand speed indicators 2.DC and AC tachogenerator 3.Photoelectric tachometer 4.Stroboscope.

25.Mention the types of dynamometers.

Answer

(i) Absorption dynamometer (ii) Driving dynamometer (iii)Transmission dynamometer.

26.Differentiate between quantity meter and flow meter.

Answer

Quantity meter measures the rate of flow by measuring the total quantity of fluid over a period of time and dividing by the time considered. Flow meter, measures the actual flow rate.

27.Mention the uses of rotameter, hotwire anemometer.

Answer

Both are used to measure flow rate.

28.Mention the types of electrical strain gauges.

Answer

(i) Inductive (ii) Capacitive (iii)Piezo electric (iv) Resistance types.

29.Mention some instruments used to measure negative pressures.

Answer

(i) McLeod gauge (ii) Kundsen gauge (iii)Pirani gauge (iv) Ionization type gauge

30.Discuss the principle of operation of magnetic flow meter.

Answer

The principle of operation of this meter is quite analogous according to Faraday's law of electromagnetic induction of solid conductors. Whenever a conductor cuts lines of magnetic field, an induced emf is generated and the magnitude of this emf is proportional to the rate at which these lines are cut and the emf is perpendicular to the plane of conductor and the magnetic field. The direction of the induced emf is given by Fleming's right hand rule.

31.Give the principle of hot wire anemometer.

Answer

An anemometer is a device for measuring mean and fluctuating velocities in fluid flows. The reduction of temperature of a surface resulting from the heat transferred owing to the fluid flow is related to flow rate.

32.Outline the advantages of venturimeter.

Answer

(i) Low head loss about 10% of differential pressure head. (ii) High coefficient of discharge (0.96 + 0.97) on account of low loss. (iii)Capable of measuring high flow rates in pipes having very large diameter (of the order of a few meters). (iv) Characteristics are well established so they are extensively used in process and other industries.

33.How is the flow measured using ultrasonic flow meter?

Answer

The ultrasonic flow transducer of the flow transducer of the meter has two piezoelectric crystals in the liquid or gas separated by a distance. The crystals in which one acts as transmitter and the other one acts as receiver, either pressed to the exterior of pipe or immersed in the liquid/gas so that the signal from the transmitter is transmitted through the liquid and received at the receiver a little time later. The measure of this transit time determines the velocity of the flow.

34.Why is coefficient of discharge introduced in flow meters?

Answer

In order to account for viscosity effects and eddying motions, the coefficient of discharge is introduced.

35.State the principle of operation of displacement type flow meters.

Answer

The flow of fluid through volume chambers of definite size causes the rotation of an output shaft which measures the flow.

36.Give any two applications of an ultrasonic flow meter.

Answer

1. Measurement of flow between the blades of turbines. 2. Remote seining of wind velocities.

37.Name any four inferential types off flow meters.

Answer

1. A venturi meter 2. A ortice meter 3. A rotameter, and 4. A pitot tube.

38.Name a flow meter that is independent of density.

Answer

Electromagnetic flow meter.

39.What are the unique features of laser anemometers?

Answer

1. Measurement or velocity is direct. 2. There is no physical object need be inserted into the flow. Thus, the flow is undisturbed by measurement. 3. Sensing volume can be very small. 4. A very high frequency response is possible.

40.Give the classification of temperature measuring instruments.

Answer

1. Gas filled temperature measurement 2. Electrical resistance temperature measurement 3. Thermocouple temperature measurement 4. Semiconductor based temperature measurement.

41.List the instruments used for measuring temperature.

Answer

(i)Thermocouple (ii)Electrical thermal resistance (iii)Thermistors (iv)Pyrometers.

42.What are the physical characteristics of temperature measuring sensor?

Answer

(i)Accuracy (ii)Discrimination (iii)Precision (iv)Errors (v)Drift (vi)Sensitivity (vii)Linearity (viii)Hystheresis.

43.What is the use of thermometer and pyrometer?

Answer

Thermometer is used to measure the absolute temperatures. The pyrometer is used to measure high temperatures.

44.What is the working principle of bimetallic thermometer?

Answer

Two pieces of metal with different coefficients of thermal expansion are bonded together to form the bimetallic strip. It is in the form of a cantilever beam. When the strip is subjected to a temperature higher than the bonding temperature, it will be bent in one direction.

45.What is the principle involved in fluid expansion thermometer?

Answer

In fluid expansion thermometers, the change in pressure in the bulb is taken as an indication of the temperature.

46.What is thermistor?

Answer

The thermistor is a semiconductor device which has a negative temperature coefficient of resistance.

47.What are the diferent types of bimetallic sensors?

Answer

1. Spiral type 2. helix type 3. Flat type 4. Cantilever type.

48.Give some bimetallic strip metals?

Answer

1. Invar. 2. Brass. 3. Nickel - Iron alloy.

49.What are the different types of thermistor?

Answer

1. Bead type 2. Water type 3. Rod type 4. Washer type.

50.What are the laws of thermocouples?

Answer

1. Law of intermediate metals 2. Law of intermediate temperature.

51.What are the different types of thermocouple materials?

Answer

1. Chromel — alumel 2. Copper — constantan 3. Iron — Constantan 4. Tungsten — Rhenium.

52.Give the composition and useful temperature range of any one commercial thermocouple.

Answer

The method of claim 3 further comprising after step(k) heating the thermocouple at least 100°C above a planned service temperature for at least three hours to stabilize the grain structure. The method of claim 13 wherein the niobium and zirconium alloy is 99% by weigh niobium and 1% by weigh zirconium. The method of claim 9 wherein the niobium and zirconium alloy is 99% by weight niobium and 1% by weight zirconium.

53.What is thermopile?

Answer

When thermocouples are connected in series are called thermopiles.

54.What are the types of pyrometers?

Answer

1. Total radiation pyrometer. 2. Optical radiation pyrometer.

55.Define the principles of electrical resistance thermistor.

Answer

The basic principle involved in thermistor is when it is subjected to a temperature change, the resistance of the thermistor changes. This change in resistance will be the increase in temperature.

56.What are the metals used in thermistor?

Answer

1. Iron 2. Copper 3. Nickel 4. Uranium.

57.What are the liquids used in a fluid expansion thermometer?

Answer

1. Mercury 2. Ethyl alcohol 3. Acetone.

58.Give the basic principle of hydraulic load cell.

Answer

When a force is applied on a liquid medium contained in a confined space, the pressure of liquid increases. The increase in pressure of liquid is proportional to the applied force.

59.What is the general rule used for accelerometers to provide satisfactory performance?

Answer

In order to provide satisfactory acceleration data for an accelerometer, it must be used at forcing frequencies below approximately 40% of its own under damped natural frequency and the instrument damping should be in the order of 70% of critical damping.

60.Define torque.

Answer

Torque can be defined as a measure of the tendency of a force to rotate the body on which it acts about an axis.

61.What is the purpose of torque measurement?

Answer

The main purpose of torque measurement is to determine the mechanical power required or developed by a machine.

62.Name the basic principle of strain gauge load cell.

Answer

When steel cylinder is subjected to force, it tends to change in dimension. On this cylinder, strain gauges are bonded and the strain gauge also is stretched or compressed causing a change in its length and diameter. The change in dimensions of strain gauge causes the resistance to change.

63.What are the differences between orifice and venturimeter

Answer

orifice meter -Loss of head is small. -There is no Wear and tear. -Initial cost is more. -It is difficult to install and replace. -It requires more space. -It is more suitable for large flow of water, process fluids, waste gases and suspended solids. venturimeter -Loss of head is more. -Wear and tear are more. -Low Initial cost. -It is ease of installation and replacement. -It requires less space as compared with venturimeter. -It can be used in wide range of pipe sizes(0.01 m to 1.5 m).

64.Differentiate between quantity meter and flow meter.

Answer

quantity meter -Total quantity of fluid which flows in a given time is measured. -Average flow rate is obtained by dividing the total quantity by time. Flow meter -Quantity of fluid flows per unit time is measured. -Average flow rate is obtained directly from flow meter.

65.Write the working principle of hot wire anemometer.

Answer

When a fluid flows over a heated surface heat is transferred from the surface and so, its temperature reduces. The rate of reduction of temperature is related to flow rate.

66.Name the two types of hot wire anemometer.

Answer

1. Constant current type 2. Constant temperature type.

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