Unit -1
Measurement standards and Design of gauges
Q1) Define & explain Metrology.
Ans.
Q2) Define standard & explain its various types.
Ans.
Types of standards
To facilitate measurement at different locations depending upon the relative importance of standard, they are divided into the following four groups:
2. Secondary standards
3. Tertiary standards
4. Working standards
Q3) What are the different types of errors?
Ans.
Systematic error
2. Ambient Conditions
3. Deformation of Workpiece
4. Avoidable Errors
These include the following:
b. Reading errors
c. Errors due to parallax effect
d. Effect of misalignment
e. Zero errors
Radom error
Presence of transient fluctuations in friction in the measuring instrument
Play in the linkages of the measuring instruments
3. Error in operator’s judgement in reading the fractional part of engraved scale divisions
4. Operator’s inability to note the readings because of fluctuations during measurement
5. Positional errors associated with the measured object and standard, arising due to small variations in setting.
Q4) Differentiate between Systematic & Random errors.
Ans.
Systematic error | Random error |
These errors are consistent and | These errors are non-consistent and accidental in nature. |
Not easy to detect | Easy to detect |
They occur due to improper conditions or methods of measurements. | They are inherent in the measuring system or measuring instruments. It is assumed that random error occurrence is bound to be there. |
Cannot be eliminated by repeated measurements | Can be minimized by repeated measurements |
Can be assessed easily | Statistical analysis required |
Minimization of systematic errors increases the accuracy of measurement | Minimization of random errors increases repeatability and hence precision of the measurement |
Calibration helps reduce systematic errors | Calibration has no effect on random errors |
Characterization not necessary | Characterized by mean, standard deviation, and variance |
Statistical methods do not operate on the systematic errors. | Statistical methods only operate on the random errors. |
Q5) Define accuracy.
Ans.
Q6) Define Precision.
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Q7) Differentiate between accuracy & precision.
Ans.
Accuracy | Precision |
Accuracy is the agreement of measured value with the true value of measured quantity. | Precision is the repeatability of measuring process. |
Accuracy is concerned with true value. | Precision is concerned with mean value. Precision has no concern with true value. |
It is difficult and expensive to have good accuracy. | It is much easier and cheaper to achieve precision than to achieve great accuracy. |
High accuracy cannot be obtained with low precision. | High precision can be obtained with low accuracy. |
If true value is 10 mm, then 9.99 mm is more accurate than 9.91 mm. | If true value is 10 mm, and readings obtained are 10.001, 10.002, 10.003, 10.004 and 10.005 mm, then mean value of readings will be 10.003 mm. Therefore, the measurements are said to be precise, because all the readings are very close to their mean value. |
Q8) Define sensibility, readability, repeatability & reproducibility.
Ans.
Sensitivity:
Readability:
Repeatability:
Reproducibility:
Q9) Define calibration & state its procedure.
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Q10) Define traceability.
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Q11) Explain straightness.
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Q12) Explain flatness.
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Q13) Explain roundness.
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Q14) Define tolerance & classify it.
Ans.
Classification of Tolerance
Tolerance can be classified under the following categories:
Unilateral Tolerance
Bilateral Tolerance
Compound Tolerance
Geometric Tolerance
Q15) Define fits.
Ans.
Q16) Define Limits & explain its different types.
Ans.
2. Interference fit
3. Transition fit
Q17) Explain Taylor’s principle.
Ans.
Q18) Write a short note on wear allowance on gauges.
Ans.
Q19) Explain different types of gauges with neat sketches.
Ans.
1. Plain plug gauge
2. Plain ring gauges
prevent against corrosion.
3. Snap gauge
a) Double ended snap gauges: Used to check shaft having diameter in the range of 3 mm to 100 mm.
b) Single ended snap gauges: Used to check shaft having diameter in the range of 100 mm and 250 mm.
4. Limit gauge
Q20) Write a note on gauge materials.
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Q21) Write down considerations of gauge design.
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The following points must be kept in mind while designing gauges:
1. The form of GO gauges should be a replica of the form of the opposed (mating) parts.
2. GO gauges enable several related dimensions to be checked simultaneously and hence are
termed complex gauges.
3. During inspection, GO gauges must always be put into conditions of maximum impassability.
4. NOT GO gauges check a single element of feature at a time.
5. In inspection, NOT GO gauges must always be put into conditions of maximum possibility.