# Engineering Metrology Questions and Answers – Pneumatic Comparators

This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Pneumatic Comparators”.

1. Which of the following is not correct for pneumatic comparator?
a) Independent of operator skill
b) Loss of accuracy due to gauge wear
c) Speedy operation
d) Total life cost is less

Explanation: In pneumatic comparator, there is no physical contact with setting gauge or part being measured. Due to this reason, there is no loss of accuracy due to gauge wear. It is an accurate, universal, reliable and speedy device.

2. What is the order of magnification in flow type pneumatic gauge?
a) 100 to 1000 times
b) 500 to 5000 times
c) 50 to 500 times
d) 100 to 2000 times

Explanation: Velocity type pneumatic gauge have quick response. It can permit a large clearance between object surface and nozzle which results in less wear in gauging members. Less air consumption. So, the magnification of the order to 500-5000 times is possible.

3. Which of the following is true for Pneumatic sensitivity in pneumatic comparators?
a) Directly proportional to operating pressure
b) Inversely proportion to operating pressure
c) Directly proportional to geometrical area of orifice
d) Independent of area of orifice and operating pressure

Explanation: Pneumatic sensitivity in the pneumatic comparator is directly dependent upon the operating pressure and inversely proportional to the geometrical area of the orifice. It can be represented as dp/dM.

4. What is the formula for overall magnification of pneumatic comparator? (Where, λ is the length of scale of pressure measuring device and La is the average separation between nozzle surface and surface to be gauged)
a) 0.4*λ/La
b) 0.7*λ/La
c) 0.4*λ*La
d) 0.7*λ*La

Explanation: Overall magnification depends upon pneumatic sensitivity, sensitivity of pressure measuring device that is rate of change of reading w.r.t. varying pressure and upon rate of change of geometrical area of orifice w.r.t. ‘L’.

5. What is the relation between overall magnification and pneumatic sensitivity in pneumatic comparators?
a) Independent of each other
b) Overall magnification is directly dependent on the square of pneumatic sensitivity
c) Overall magnification is inversely proportional to the pneumatic sensitivity
d) Overall magnification is directly dependent on the pneumatic sensitivity

Explanation: Overall magnification is the rate of change of linear movement of the pointer to the change in the dimension which produces it and represented as dR/dL. It is directly proportional to the pneumatic sensitivity.
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6. Which of the following option is correct for velocity type pneumatic gauge?
a) Operate by sensing momentary rate of flow of air
b) Response speed is less than back pressure type
c) Low amplification
d) Filter is placed after pressure reducing unit

Explanation: It is operated by sensing momentary air flow rate. This flow can be sensed by a tapered glass tube which is mounted on a graduated scale. Inside this bore a float is present which is lifted by the air flow.

7. Which of the following statement is true for pneumatic gauges?
Statement 1: Can be used to check multiple dimensions.
Statement 2: A float is present inside the bore.
a) T, T
b) F, T
c) F, F
d) T, F

Explanation: It is best suited to check multiple dimensions in the least possible time. While measuring a bore it can reveal complete story of size, straightness, taper, bell mouth etc. It is independent of operator skill.

8. In Back pressure type pneumatic gauge, there are two orifices. What is the relationship between upstream pressure of first orifice and pressure between two orifices?
a) Depends upon the distance between two orifice
b) Depends upon relative size of orifice
c) Only on geometric area of first orifice
d) Distance between pressure source and first orifice

Explanation: Upstream pressure and pressure between both orifices, they both are measured with reference to atmospheric pressure. The relationship between both the pressures depends upon relative sizes of the two orifices.

9. After which frequency range, pneumatic measuring system is not correctly measured displacements?
a) 5 cycles/second
b) 4 cycles/second
c) 3 cycles/second
d) 2 cycles/second

Explanation: Pneumatic measuring system can’t measure displacements correctly after 2 cycles/second because its response spend is slow. Its response is slower than electrical systems. Response time of back pressure type can be improved by using filled system pressure gauge.

10. For which diameter range of parts pneumatic gauges can be used?
a) 50 to 500 mm
b) 0.5 to 900 mm
c) 50 to 700 mm
d) 100 to 600 mm

Explanation: Pneumatic gauge can be used for parts of diameter 0.5 mm to 900 mm having tolerance 0.05 mm or less. It can be easily used for on line measurement of parts.

11. Which of the following is measuring head sensitivity with the variation of diameter (D) of measuring orifice?
a) πD
b) πDL
c) πDL2
d) πD2L

Explanation: Measuring head sensitivity is represented by ‘dM/dL’. ‘M’ is the diameter of measuring orifice which is equal to πDL. By differentiating ‘M’w.r.t ‘L’ we get πD. Hence ‘dM/dL’ = πD.

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