# Engineering Metrology Questions and Answers – Evaluating Uncertainty in Measurement

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This set of Basic Engineering Metrology Questions and Answers focuses on “Evaluating Uncertainty in Measurement”.

1. Which type of distribution approach is not followed by systematic error?
a) U-shaped distribution approach
b) Rectangular distribution approach
c) Triangular distribution approach
d) Normal distribution approach

Explanation: Conventional approach used to evaluate measurement uncertainty is based on random error and systematic error. Systematic error follows Rectangular, Triangular or U-shaped distribution approach.

2. Which approach is accepted as an international procedure in evaluating the uncertainty of measurement?
a) Conventional approach
b) Modern approach
c) Experimental approach
d) Observational approach

Explanation: Modern approach is accepted as an international procedure. It is useful even for those problems where limited observations are possible. It is problem specific and defines the method explicitly.

3. How many methods of evaluation of uncertainty are based upon modern approach?
a) 2 methods namely Type-A and Type-B
b) 2 methods namely Type-1 and Type-2
c) 3 methods namely Type-A, Type-B and Type-C
d) 3 methods namely Type-1, Type-2 and Type-3

Explanation: Modern approach is based on Type A method and Type B method. When observations are taken under same measurement conditions, Type A method is used. In type B method of modern approach, the uncertainty in measurement is evaluated by the judgement of the available information.

4. Which of the following option is correct for given statements about evaluation of uncertainty of measurement?
Statement 1: Principle of evaluation of uncertainty by modern approach is approximately the same as conventional approach.
Statement 2: Conventional approach is problem specific.
a) T, F
b) F, F
c) F, T
d) T, T

Explanation: Modern approach defines the method explicitly and is problem specific. In those problems where only limited observations are possible, modern approach is very useful.

5. Which type of approach is followed by random errors?
a) Poisson distribution approach
b) Binomial distribution approach
c) Gaussian distribution approach
d) Polynomial distribution approach

Explanation: Random errors are those which can be caused by little variation in the standard setting of position, operator errors in reading the display of instrument etc. Random error follows the normal frequency or Gaussian distribution approach.

6. What is the main characteristic of random errors used to determine maximum measuring error?
a) Cumulative error
b) Standard deviation
c) Variance
d) Median

Explanation: Random errors are those which are produced due to large number of fluctuating and unpredictable errors that are non controllable in nature. The main characteristic of random errors is standard deviation, used to determine maximum measuring error.

7. What is the relation between maximum error for a measurement method and standard deviation in the case of random errors?
a) Maximum error equal to standard deviation
b) Maximum error is two times of standard deviation
c) Maximum error is three times of standard deviation
d) Maximum error is four times of standard deviation

Explanation: Spread of possible random error values is determined by the maximum error. The maximum error for a measurement method is three times the standard deviation. The maximum error and standard deviation determine the accuracy of measurement.

8. Which of the following error is not a systematic error?
a) Error induced due to stylus pressure
b) Instrument location errors
c) Error due to parallax
d) Error due to play in the instrument’s linkages

Explanation: Systematic errors can be caused due to calibration errors, Stylus pressure, ambient conditions (Variation from ambient temperature, pressure etc), Avoidable errors (due to the effect of misalignment of centre of workpiece and parallax) and incorrect theory.

9. What is the advantage of statistical methods?
a) Increase the value of (Quality/cost)
b) Increase the value of (Cost/Quality)
c) Decrease the value of (Cost * Quality)
d) Increase the value of (Cost * Quality)

Explanation: The value of (Quality/cost) increases with the help of statistical methods which means offer same quality at low cost or good quality at same cost or both i.e. better quality and less cost. Convention approach which is based upon random errors for evaluating the uncertainty of measurement follow the statistical methods.

10. What is true about random errors?
a) Sign of error can be predicted
b) Probability of occurrence of same absolute value is not equal for negative and positive errors
c) Constant in magnitude
d) Arithmetic mean in a measurement series approaches zero as measurement number increases 