ME8501 - Metrology and Measurments - Unit-1 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 1st 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.What is Legal Metrology?

Answer

Legal metrology is part of Metrology and it is directed by a National Organisation which is called "National service of Legal Metrology".

2.What is measurement? Give its types.

Answer

It is the process of comparing the input signal with pre-defined standard and it gives out the result. It is a word used to describe about physical quantities such as length, weight, temperature, pressure, force etc. Types: 1.Primary measurements, 2.Secondary measurements, and 3.Teritary measurements

3.Mention the two important requirements of measurement.

Answer

(i) The standards used for comparison must be accurate and internationally accepted, and (ii) The apparatus or instrument and the process used for comparison must be provable.

4.What are the basic components of a measuring system?

Answer

* Units * Scale * Target * Limits * Tool * Process

5.Name the fundamental measuring process in measurement.

Answer

a. Direct comparison. b. Indirect comparison.

6.What are the applications of measurements?

Answer

* Measurement provides the fundamental basis for research and development activities. In research activity, the experimental part is based on the measurement. * Measurement is a fundamental element of any automatic control system. In control system, discrepancy or error between the actual value and described value of a variable is to be determined. * Measurement is used to evaluate the performance of any plant or a process. For example, in modern power plant, temperature, pressure, vibrational amplitudes, etc, must be constantly monitored by the measurement to ensure the proper performance of the system. * Measurement is also the basis for commercial activities such as production, pricing, sale and purchase.

7.How is direct comparison made in measurements?

Answer

In the direct comparison method, the parameter to be measured is directly compared with either a primary or a secondary standard. In this method, the comparison is done with a standard through use of a calibrated system. Direct methods are quite common for the measurement of physical quantities such as length, mass and time.

8.How is indirect comparison done in measurements?

Answer

Indirect comparison makes use of some form of transducing device which converts the quantity to be measured into an analogous signal.

9.What is primary measurement? Give examples.

Answer

In primary measurement, any physical parameters are measured by comparing it directly with reference standards. For example, 1. Matching of two lengths when determining the length of an object with a meter rod. 2. Matching of two weights when determining the mass of the grossary items.

10.Where secondary measurement is used?

Answer

A secondary measurement involves only one translation to be done on the quantity under the measurement.

11.Classify measurements.

Answer

(i) Contact type, and (ii) Non-contact type

12.How does information send through primary sensing elements?

Answer

It is the first element which receives energy from the measured medium and it produces an output depending on the measurand.

13.How energy transfer is made between data processing element and data presentation element?

Answer

It is an element which is used to modify the data before displayed or finally recorded.

14.What are the categories of S.I units?

Answer

(i) Fundamental units. (ii) Supplementary units. (iii)Derived units.

15.Define the standard of measurement.

Answer

Standard is a physical representation of a unit of measurement. A known accurate measure of physical quantity is termed as standard.

16.Classify standards.

Answer

1.International standards 2.Primary standards 3.Secondary standards 4.Working standards.

17.Distinguish between line standard and end standard.

Answer

*Line standard Standards for which the length is indicated by engraved lines on a bar or scale. Ex: Steel rule, tapes *End Standard Standards are in the form of blocks or bas with two faces or ends which are at a defined distance apart. Ex: Gauge blocks.

18.What is the relationship between sensitivity and range?

Answer

The ratio of change in output of the instrument to a change of input or measured variable is termed as sensitivity. Range is the minimum and maximum values of a quantity for which an instrument is designed to measure.

19.What are the facilities that should be provided by the intelligent instrument?

Answer

Good precision, 100% accuracy and repeatability.

20.List out the static characteristics.

Answer

(i) Response (ii) Error (iii)Lag (iv) Fidelity, and (v) Loading effect.

21.Differentiate between sensitivity and range with suitable example.

Answer

*Sensitivity 1.It is the response of the instrument with respect to given input. 2.It is the ratio between output signal and input signal. *Range 1.It is the upper and lower limits of the instruments. 2.It is the difference between maximum value and the minimum value of the instrument.

22.What is meant by static response?

Answer

Response is defined as the rapidity with which a measurment responds to change in the measured quantity.

23.Define measurand.

Answer

The physical, chemical, electrical quantity, property, process, variable or a condition to be measured is referred as measurand.

24.Define measuring instruments.

Answer

It may be defined as a device for determining the value of magnitude or quantity of a variable.

25.What are the elements of generalized measurement system?

Answer

(1) Primary sensing element (2) Variable conversion element (3) Variable manipulation element (4) Data transmission clement (5) Data processing element (6) Data presentation element (7) Data storage element.

26.Define primary sensing element.

Answer

It is also called Detector. Measurand is first detected by primary sensor and this act is then immediately followed by the conversion of measurand (input signal) into an analogous electrical signal which acts as transducer.

27.Define variable conversion or transducer element.

Answer

It converts the signal (Output from primary sensing element) from one physical form to another form without changing the information content of the signal. Example: In the system, the output is analog form but the next stage of system accepts only digital form and therefore, A/D converter is used for converting analog to digital form.

28.Define data transmission element with an example.

Answer

It transfers the signal from one place to another place disturbing the signal being transmitted. Example: Shaft to gear --> Short distance From test center to computer --> Medium distance

29.What do you mean by data processing element?

Answer

It alters the data before it is presented on a display or before it is recorded. The main objective is to convert the data to an understandable and useful form. Example: It removes unwanted without disturbances such as noises which come with signal.

30.Define data presentation element with an example.

Answer

Information about the measure quantity is to be presented to a human being for monitoring, control or analysis purpose. Example: 1. Pointer moving over a scale. 2. Recording of pen moving over a chart.

31.What do you mean by Data storage element with an example?

Answer

This element stores the data/information and presents the same when commanded. Example: 1. Magnetic tape recorder - reproducer. 2. Computer.

32.Define units.

Answer

When a particular instrument indicates a reading, to specify the reading and use it in further calculations, it is necessary to specify type and magnitude for that reading. The magnitude is the reading obtained on the instrument. The type of reading is the unit of physical quantity which is measured by instrument. Without unit, only magnitude has no physical meaning.

33.Define standard.

Answer

All the instruments are calibrated at the time of manufacture against a measurement standard. A standard means known accurate measure of a physical quantity.

34.Mention the categories of units.

Answer

1. Fundamental unit 2. Supplementary unit 3. Derived unit.

35.What are the fundamental units?

Answer

Metre (m), Kilogram (kg), Second (s), Ampere (A), Kelvin(K), Mole (mol), Candela (cd).

36.Mention the supplementary units.

Answer

1. Radian for phase angle 2. Steradian for solid angle

37.What are the derived units?

Answer

The units which are derived from fundamental and supplementary units are derived units. 1.Mechanical unit. 2.Electrical and magnetic unit. 3.Thermal unit.

38.Define primary standard.

Answer

These are highly accurate absolute standard which can he used to ultimate reference standards. These primary standards are maintained at national standard laboratories in different countries These standard representing fundamental units as well as some electrical and mechanical derived units are calibrated independently by absolute measurements at each of national laboratories. These are not available for use, outside the national laboratories.

39.State the difference between primary and secondary transducers.

Answer

Transducer is a device which converts the energy from one form to other form. The transducer which does the first stage of energy conversion is called primary transducer. The transducer which converts this form of energy into some other form is called secondary transducer.

40.Define working standard.

Answer

These are the basic tools of measurement laboratory and they are used to check and calibrate the instruments used in laboratory for accuracy and performance.

41.What you mean by sensitivity of a measuring instrument?

Answer

Sensitivity of an instrument is defined as the ratio of the magnitude of output signal to the magnitude of input signal. It denotes the smallest change in the measured variable to which the instrument responds. Sensitivity = Magnitude of output quantity(response) / Magnitude of input quantity(quantity being measured)

42.Define 'precision' and 'accuracy'.

Answer

Accuracy: It is defined as the closeness with which the readiing approaches an accepted standard value or true value. Precision: Term 'precision' refers the ability of an instrument to reproduce its readings again and again in the same manner for constant input signal.

43.Define readability.

Answer

It is a term frequently used for analog type instruments. This characteristic depends on both the instrument and observer. Example: An instrument has a scale span of 200 mm would have higher readability than instrument having a scale span of 100mm.

44.Define the term repeatability.

Answer

Repeatability is defined as the closeness of agreement among the number of consecutive measurement of the output for the same value of input under the same operating conditions. It may be specified in terms of units for a given period of time.

45.Define the term reliability.

Answer

Reliability is the ability of a person or system to perform and maintain its functions in routine circumstances. Reliability is also defined as the consistency of a set of measurements or measuring instrument, often it is used to describe a test.

46.what is hysteresis?

Answer

Hysteresis is defined as the difference in the output for a given input when this value is approached from the opposite direction.

47.Define static characteristics or what is meant by static response.

Answer

Some applications involve measurand (input signal) which are either constant or varying very slowly with time. The set of criteria defined for the instruments which are used to measure the quantities which are slowly varying with time (or) mostly constant.i.e. do not vary with time is called static characteristics.

48.What do you mean by dynamic characteristics?

Answer

As the input varies from instant to instant, the output also varies from instant to instant. The behaviour of system under such conditions is called dynamic response.

49.State the dynamic characteristics of simplified measuring system.

Answer

(i) Speed of response (ii) Lag (iii)Fidelity (iv) Dynamic error.

50.What are the sources of error?

Answer

* Physical nature of components * Linearity, repeatability, hysteresis and resolution * Interpolation * Environmental conditions * Loading * Time variations in the measurand * Calibration * Variation in atmospheric conditions.

51.State any one way of specifying accuracy of an instrument.

Answer

Accuracy can be defined as a percentage of true value. %truevalue = ( (Measurement value — Truevalue) / Truevalue ) * 100

52.Define error. How is it related to accuracy?

Answer

Error can be defined as the difference between the measured value and true value. But the accuracy represents the degree of correctness of the measured value with respect to the true value.

53.What is resolution?

Answer

It is the smallest increment in the measured value which can be detected with certainty by the instrument.

54.What is an instrument error?

Answer

It is the error due to poor design/construction of the instrument.

55.Name the types of both mechanical and electrical tachometer.

Answer

Mechanical Tachometer: Hand speed indicators, Fly ball tachometers. Electrical Tachometer: DC tacho generators, AC tacho generators.

56.What are seismic instruments?

Answer

Seismic instruments are absolute motion measurement devices to indicate or record absolute displacement, velocity and acceleration of a vibrating body.

57.Define calibration.

Answer

Calibration is the process of determining and adjusting an instrument's accuracy to make sure its accuracy is within the manufacturer's specifications.

58.Define international standards.

Answer

It is defined as the international agreement. These standards are maintained at the international Bureau of weights and measures and they are periodically evaluated and checked by absolute measurements in terms of fundamental units of physics.

59.What are different types of standards in measurement?

Answer

1. International standard 2. Primary standard 3. Secondary standard 4. Working standard.

60.What are the Electrical and magnetic, thermal units?

Answer

1. Electrical and magnitude units such as power, energy, ohms, farads, henries magnetic flux in webers, tesla etc. 2. Thermal units such as latent heat, specific heat capacity, sensible heat. calorific value etc.

61.What are the mechanical units?

Answer

Mass, velocity, acceleration, force, weight, torque, work, energy, power etc.

62.What are the derived units?

Answer

The units which are derived from fundamental and supplementary units are derived units. 1. Mechanical unit. 2. Electrical and magnetic unit. 3. Thermal unit.

63.Define Systematic errors?

Answer

A constant uniform deviation of the operation of an instrument is known as systematic error. Instrumentational error, environmental error, systematic error and observation error are systematic errors.

64.Define random errors.

Answer

Some errors result through the systematic and instrument errors are reduced or at least accounted for. The causes of such errors are unknown and hence, the errors are called random errors.

65.Distinguish between relative error and random error.

Answer

Relative error is defined as the results of the absolute error and the value of comparison used for the calculation of absolute error. The comparison may be true value or conventional true value or arithmetic mean for series of measurement. These types of errors occur randomly and reason for this type of errors cannot be specified.

66.Mention the various methods used for limiting temperature errors.

Answer

1. Minimisation through careful selection of materials and operating temperature ranges. 2. Compensation through balancing of inversely reacting elements or effects. 3. Elimination through temperature control.

67.What are the static characteristics and dynamic characteristics?

Answer

1. Static characteristics --> Accuracy, precision, resolution, error, sensitivity, threshold, reproducability, zero-drift, stability and linearity. 2. Dynamic characteristics.

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