# Engineering Metrology Questions and Answers – Scales and Gratings

This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Scales and Gratings”.

1. What is the range of line spacings in gratings?
a) 4 to 200 per mm
b) 200 to 400 per mm
c) 10 to 500 per mm
d) 500 to 600 per mm

Explanation: Gratings plays an important role in rotary as well as linear measurements. Gratings have line spacing from 4 per mm to 200 per mm in lengths up 4 meters or so. These are usually employed with photoelectric readouts.

2. What is the alternate name of amplitude grating?
a) Ronchi ruling
b) Prismatic grating
c) Phase grating
d) Index grating

Explanation: Grating which has plane lines is called amplitude grating or Ronchi grating. It is a constant interval bar with equal line and space pattern. These are generally used for optical testing purposes and metrology applications.

3. Which of the following option is true for scales and gratings?
a) Ruling in scales are closely spaced
b) Ruling in gratings is far apart
c) Vernier device is required with scales
d) Ruling in scale forms a periodic pattern

Explanation: Scales have lines marked on them that is rulings. Scales are usually made of steel. Lines in scales are spaced far apart so that interpolating devices e.g. vernier device are used to make accurate settings.

4. What is the length of Prismatic grating?
a) 500 mm
b) 400 mm
c) 300 mm
d) 200 mm

Explanation: Prismatic grating is also known as phase grating. Prismatic grating contains triangularly shaped and contiguous grooves. Prismatic grating has 100 to 200 grooves and its length is limited to 200 mm.

5. Which of the following option is true for the given statements?
Statement 1: Stainless steel has a high thermal coefficient of expansion than cast iron hence used to make scales.
Statement 2: Most of the scales are produced by duplicating from master scale.
a) T, F
b) F, F
c) T, T
d) F, T

Explanation: stainless steel is used for making metal scales. It is stable with time if properly heated, have good finish, resistant to tarnishing but its coefficient of thermal expansion is less than the cast iron and steel.

6. Which type of visual scale line setting against an index is widely used in sophisticated machines?
a) Simple superposition type
b) Alignment of vernier setting
c) Symmetrical forming between two index marks
d) Asymmetrical forming between index marks

Explanation: Index mark is utilized by all scale readouts, with reference to which reading of scale is noted. Symmetrical forming between two index marks is the type which is mostly used in sophisticated machines due to high setting precision.

7. For how much travel length, metal reflecting gratings are used?
a) 600 mm
b) 900 mm
c) 1700 mm
d) Greater than 1800 mm

Explanation: Three types of gratings are commonly used in more fringe system gratings. Phase transmission grating, Metal reflecting grating and line and space transmission grating. Metal reflecting grating is used for travel length more than 1800 mm.

8. What is the condition to obtain fringes of high intensity?
a) Distance between scale and index grating is as far as possible
b) Distance between scale and index grating is minimum
c) Scale and index grating should be overlapped
d) Scale and index grating should be at the right angle

Explanation: Fringes of high intensity means good contrast. It is the essential condition for obtaining good electrical signals. It can be obtained only when the distance between the scale and index grating is minimum.

9. Which of the following is not true for glass scales?
a) Graduations can be produced by depositing material
b) Easily polished
c) Able to work in case of reflected light but not in transmitting light
d) Ordinary glass has 15-30% less thermal coefficient of expansion than steel

Explanation: Glass scales are stable, and are able to work in both transmitting and reflected light. Graduation on these scales can be produced by etching through ruled wax, by depositing material in the form of thin lines and by depositing photographic emulsions.

10. For bi-directional fringe counting, how many detectors are placed for better balance?
a) 3
b) 4
c) 5
d) 6

Explanation: For bi-directional fringe counting, better balance is obtained when four detectors are placed at 0, 90, 180, 270 phase degree of fringe in which counting intervals of one-quarter of the scale interval are provided.

Sanfoundry Global Education & Learning Series – Engineering Metrology.

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