ME8501- Metrology and Measurments - Unit-2 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 2nd 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.List the various linear measurements.

Answer

(i) Length (ii) Heights, and (iii) Thickness.

2.What are the various types of linear measuring instruments?

Answer

The various devices used for measuring the linear measurements are as follows. i. Vernier calipers ii. Micrometers iii.Slip gauge or gauge blocks iv. Comparators.

3.List out any four angular measuring instrument used in metrology.

Answer

(i) Angle gauges (ii) Divided scales (iii)Sine bar with slip gauges (iv) Autocollimator (v) Angle dekkor.

4.What is the main difference between linear and angular measurement?

Answer

The main difference between linear and angular measurement is that no absolute standard is required for angular measurement.

5.List down the errors when vernier caliper is used in measurements.

Answer

(i) Errors may arise in manipulation of readings in the vernier caliper. (ii) Jaw movement should be perpendicular to the scale readings. Otherwise, measurements will not be correct. (iii)The contact portion of measuring jaws should be good conditions. So, the wear and tear, and wrapping of vernier caliper jaws should be tested frequently. At the same time, when we close the jaws, it should be tightly together. (iv) During internal measurements, the jaws may become bowlegged. It should be checked frequently.

6.What are precautions to be carried while using vernier calipers?

Answer

(i) The jaws should not be used as a wrench or hammer because the vernier caliper is not a rugged instrument. (ii) These instruments should also be kept in a box and it should not be suddenly dropped and turned up and down. (iii) During measurement, the vernier caliper should not be used with oil, grit and chips in part to he measured. (iv) One hand of operator should be used for stationary jaw and the other hand for supporting the movable jaw while measuring. (v) The operator should wear eye-glass and magnifying glass during measurement because the accuracy of measurement mainly depends on the sensing of sight and sense of touch.

7.Name the different errors involved in measurements due to wear and tear, and incorrect usage.

Answer

1.Backlash: It is the lagging in motion when the thumble rotates. It means that the thimble rotation direction is changed. 2.Total error: It is the maximum difference between the measured value and true value. 3.Cumulative error: It is difference between true value and measuring value at any Point of the measuring range. Range is the difference between maximum scale reading and minimum scale reading. cummulative error is also defined as the sum of all individual errors such as thread error, measuring error, human error etc.,

8.Write short notes on precautions to be taken while using micrometer.

Answer

The accuracy of any measurement depends on the Proper function of individual parts. They are obtained by preserving the equipment cleanly in such a way that it has to be free from dust and other inclusions. During measurement, the spindle should move freely. Holding the instrument is very important while measuring. So, the micrometer should be always held on the right hand and the part to be measured on the left hand. Before measuring the dimensions of work, the range of instrument should be checked by moving the movable jaw far away from the fixed jaw. Mainly, errors occur due to lack flatness and parallelism of anvils and incorrect zero setting.

9.What is floating carriage micrometer?

Answer

The micrometer which has the upper surface of the lower carriage having two 'V' grooves on ball bearings and the upper carriage floating freely on balls is called floating carriage micrometer. It is used to measure the effective diameter of the screw thread.

10.What is wringing of gauge blocks?

Answer

Wringing or slipping is the process combining the faces Of slip gauges one over the other.

11.What are slip accessories?

Answer

(i) Measuring jaw (ii) Scriber and Centre point. (iii)Holder and base.

12.What is a comparator?

Answer

Comparator is one form of linear measurement devices which is quick and more convenient for checking lthe arge number of identical dimensions by comparing the actual dimensions with standard dimensions.

13.Narrate the need for comparators.

Answer

Comparators produce precision measurements with consistent accuracy by eliminating human error. They are used to find out the deviation from set value or standard value fixed by slip gauges from the datum surface. If the indicated deviation is small, a suitable magnification device is selected to obtain the desired accuracy of measurements. In mass production work, the decisions on components against dimensions are made by the set tolerances on comparators. If the indicated deviation is within the set limit, the components will be accepted, if it less than the minimum required dimensions, they will be rejected and if it is more than the set limit, the components will be recommended for rework.

14.Classify the comparator according to the principles used for obtaining magnification.

Answer

(i) Mechanical comparator (ii)Electrical comparator (iii)Optical comparator (iv)pneumatic comparator.

15.What are the advantages of mechanical comparator?

Answer

(i) It is usually robust, compact and easy to handle. (ii) There is no external supply such as electricity, air required. (iii)It has very simple mechanism and cheaper when compared to other types. (iv) It is suitable for ordinary workshop and also easily portable.

16.Mention any two disadvantages of reed type mechanical comparator.

Answer

(i) Accuracy of the comparator mainly depends on the accuracy of the rack and pinion arrangement. Any slackness will reduce its accuracy. (ii) It has more moving parts and hence, friction is more and accuracy is less.

17.What are the components of an electrical comparator

Answer

An electrical comparator consists of the following three major parts such as (i) Transducer (ii) Display device as meter (iii)Amplifier.

18.On what basis the transducer works?

Answer

An iron armature is provided between two coils held by a leaf spring at one end. The other end is supported against a plunger. The two coils act as two arms of an AC Wheat stone bridge circuit.

19.what are the major types of an electrical comparator?

Answer

1. Universal electrical comparator 2. Master electrical comparator

20.How is the accuracy of the given work checked with an electrical comparator?

Answer

To check the accuracy of a given specimen or work, first a standard specimen is placed under the plunger. Then, the resistance of wheat stone bridge is adjusted so that the scale reading shows zero. Then the specimen is removed. Now, the work is introduced under the plunger. If there is any deviation in the work, it will be shown in the scale.

21.State the working principle of an electronic comparator.

Answer

In an electronic comparator, transducer induction or the principle of application of frequency modulation or radio oscillation is followed.

22.what are the advantages of electrical and electronic comparator?

Answer

(i) It has less number of moving parts. (ii) Magnification obtained is very high. (iii)Two or more magnifications are provided in the same instrument to use various ranges. (iv) The pointer is made very light so that it is more sensitive to vibration.

23.What are the disadvantages of electrical and electronic comparator?

Answer

(i) Variation of voltage or frequency may affect the accuracy of output. (ii) Due to heating coils, the accuracy decreases. (iii)It is more expensive than mechanical comparator.

24.List the various parts of an optical comparator.

Answer

a. Pivoted lever b. Objective lens c. Scale d. Plunger and table and base.

25.What is the principle of working of pneumatic comparator?

Answer

The word pneumatic is associated with the pressurised air.The pressurized air is used as the working medium in pneumatic comparator. Based on the physical phenomena, the pneumatic comparators are classified into two types. (i) Flow or Velocity type (ii) Back pressure type.

26.Discuss any four applications of pneumatic comparator with schematic diagram.

Answer

(i)Solex air ring gauge (ii)Snap gauge (iii)Height and depth gauges (iv)Plate straightness (v)Tubling straightness (vi)Squareness of bore.

27.How the internal measurement is carried on a solex air gauge?

Answer

An internal measuring head is connected to the flexible pipe. First, the measuring head is inserted to a master gauge (ring gauge). Now, the manometer reading is marked as reference point or zero reading. Then, the measuring head is inserted into the hole of work piece. The water level in the manometer changes depending on the gap between work and measuring head.

28.What are the advantages of pneumatic comparator?

Answer

(i) The wear of measuring heads is avoided due to absence of direct contact. (ii) Friction is less due to less number of moving parts. (iii)Work piece is cleaned by supplying of air During measurement. (iv) High magnification is possible. (iv) There is no interference of measuring head and indicating device because the measuring head is kept away from the indicating device. (iv) It is suitable method to check ovalty and taperness of circular bore.

29.Define tolerance and zero line.

Answer

The maximum allowable error in the measurement is called tolerance. The line at which the measurements are done is zero line. It is simply a reference line for the measurement.

30.Define deviation.

Answer

Deviation is the difference between actual size and the basic size.

31.Differentiate between dimensional and form tolerances.

Answer

An allowance given as a permissible range in the nominal dimensions of a finished magnet is called dimensional tolerance. Form tolerance is a group of geometric tolerances which limit the amount of error in the shape of a feature. Form tolerances are independent tolerances.

32.What are the types bevel protractors?

Answer

(i)Vernier bevel protractor (ii)Universal protractor (iii)Optical protractor.

33.What is the constructional difference between an autocollimator and an angle dekkor?

Answer

The illuminated target used in the autocollimator is replaced by an illuminated scale on a glass screen set in the focal plane of the objective lens.

34.What is interchangeable manufacture?

Answer

Manufacturing process in which the produced parts that go into assembly may be selected at random from a large number of parts.

35.Define interchangeability.

Answer

A part which can be substituted for the component manufactured to the same shape and dimensions is known as interchangeable part. The operation of substituting the part for similar manufactured components of the same shape and dimensions is known as interchangeability.

36.State the advantage of interchangeable manufacturing?

Answer

i) Individual fitting is not necessary. So, less cost of production. ii)Repair of parts is simplified.

37.Write the constructional requirements of the sine bar for accurate measurement.

Answer

(i) The rollers must have equal diameter and equal cylinders. (ii) The rollers should be placed parallel to each other and also to the upper face. (iii)The accurate center to center of rollers must be known. (iv) The top surface of the bar must be flat with high degree of accuracy.

38.Differcntiate between Sine bar and sine center.

Answer

Sine bar is used to measure the taper of vertical surfaces but sine centre is used to the taper of cylindrical surfaces.

39.What are the constructional requirements of a good sine bar?

Answer

1. The rollers must have equal diameter and equal cylinders. 2. The rollers should be placed parallel to each other and also to the upper face. 3. The accurate center to center of rollers must be known. 4. The top surface of the bar must be flat with high degree of accuracy.

40.Write down the applications of limit gauges.

Answer

a. Thread gauges b. Form gauges c. Screw pitch gauges d. Radius and fillet gauges e. Feeler gauges f. Plate gauge and Wire gauge g. Indicating gauges and h. Air gauges.

41.State any two limitations of sine bar.

Answer

1) Sine bars are fairly reliable for angles than 15°. 2) It is physically difficult to hold in position. 3) Slight errors in sine bar cause larger angular errors. 4) A difference of deformation occurs at the point of roller contact with the surface plate and to the gauge blocks. 5) The size of parts to be inspected by sine bar is limited.

42.What the Sources of error in sine bars?

Answer

The different sources of errors are listed below: 1) Error in distance between roller centers. 2) Error in slip gauge combination. 3) Error in checking of parallelism. 4) Error in quality of size of rollers and cylindricity. 5) Error in parallelism of roller axes with each other. 6) Error in flatness of the upper surface of sine bar.

43.What are the disadvantages of Pneumatic Comparator?

Answer

* Accurate pressure regulator are needed. * It is a bulky. So, the portability is difficult. * Various measuring heads are required for different dimensions which increase the cost of comparators. * The scale is not uniform. * High magnification is required to avoid meniscus error due to glass tube as indicating device.

44.What are limit gauges?

Answer

A limit gauge is not a measuring gauge. They are just used as inspecting gauges. The limit gauges are used in inspection by methods of attributes. It gives the information about the products which may be either within the prescribed limit or not.

45.State "Taylor's principle of gauge design".

Answer

It states that GO gauge should check all related dimensions. Simultaneously, NOGO gauge should check only one dimension at a time. Maximum metal condition: It refers to the condition of hole or shaft when maximum material is left on i.e. high limit of shaft and low limit of hole. Minimum metal condition: If refers to the condition of hole or shaft when minimum material is left on such as low limit of shaft and high limit of hole.

46.What are the different taper measurments?

Answer

a. Slip gauges b. Sine bar c. Autocollimator d. Alignment telescope e. Angle dekkor f. V-block g. Bevel protactor h. Angle gauges i. Taper plug gauges. j. Rollers k. Dovetail slides.

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