# Characteristics of Measuring Instrument MCQ || Measuring Instrument Characteristics Questions and Answers

1. In the measuring instruments, the degree of conformity and closeness to the true value is known as:

1. Precision
2. Deflecting torque
3. Measuring scale
4. Accuracy

Explanation:

• Accuracy is the closeness to the true value; closeness with which an instrument reading approaches the true or accepted value of the variable (quantity) being measured.
• It is considered to be an indicator of the total error in the measurement without looking into the sources of errors.

The most repeatable value (or) the reproducible value out of the set of records is known as precision. It is the measure of consistency. It gives the closeness of individual measured values to the average of all measured values.

For the accuracy of the instrument, both conformity and precision are necessary.

2. If the same measurement process is used among different instruments and operators, over a longer time period, then the variations arising out of it are called

1. Measurement of length
2. Sensitivity
3. Reproducibility
4. Repeatability

Explanation:

Reproducibility is the consistency of measurements by different appraisers using the same measuring equipment. Perfect reproducibility means that the instrument has no drift. No drift means that with a given input, the measured values do not vary with time.

3. An instrument is used to measure a quantity at different time instances, and the expected values of the quantity are to be the same; however, the measured values are different. A set of 5 measurements that were recorded at different time instances are 98, 101, 99, 100 and 102. Find the precision of the third measurement.

1. 0.95
2. 0.1
3. 0.99
4. 0.9

Explanation:

Measurement of consistency or repeatability of measurement i.e., successive reading does not differ.

The average of the measured value is given by,

$\overline {{X_n}} = \sum \frac{{{X_n}}}{n}$

Where Xn is the recorded readings, n is no. of recorded readings.

Precision for particular reading is given by,

Precision $= 1 – \left| {\frac{{Respective\;Reading – \overline {{X_n}} }}{{\overline {{X_n}} }}} \right|$

Calculation:

The average measurement value

$\overline {{X_n}} = \frac{{98 + 101 + 99 + 100 + 102}}{5}$

$= \frac{{500}}{5} = 100$

Given third measurement reading = 99

The 3rd reading precision is given as

$= 1 – \left| {\frac{{99 – 100}}{{100}}} \right|$

$= 1 – \frac{1}{{100}} = 0.99$

4. If meter A requires 100 mA to give full-scale deflection, meter B requires 50 mA to give scale deflection and meter C requires 80 mA to give full-scale deflection, then the

1. Meter A is more sensitive
2. All meter is equally sensitive
3. Meter B is more sensitive
4. Meter C is more sensitive

Answer:3. Meter B is more sensitive

Explanation:

In ammeters, the sensitivity is given as

S = 1/Ifsd

Ifsd is the full-scale deflection in amps

It is expressed in ohm/volt

Calculation:

For Meter A

Ifsd = 100 mA

SA = 1/Ifsd = 1/100 mA

SA = 10

For Meter B

Ifsd = 50 mA

SB = 1/Ifsd = 1/50 mA

SB = 20

Hence, Meter B is more sensitive.

5.  Accuracy is ‘the state of being ‘________’ whereas precision is ‘the state of being ‘________’.

1. Correct, Correct
2. Exact, Correct
3. Exact, Exact
4. Correct, Exact

Explanation:

Accuracy indicates the closeness of a predicted or classified value to its real value. The state of being correct is called Accuracy.

Precision is defined as ‘the quality of being exact‘ and refers to how close two or more measurements are to each other, regardless of whether those measurements are accurate or not. It is possible for precision measurements to not be accurate.

6. Which one of the following is the definition of the dead zone of an instrument?

1. The time required by an instrument to warm up initially
2. The largest change of input quantity for which there is no output of the instrument
3. The time required by the instrument to begin to respond to a change in the measurement
4. The unmeasured quantity which exceeds the maximum range of the instrument

Answer:2. The largest change of input quantity for which there is no output of the instrument

Explanation:

• Dead Zone is defined as the largest change of input quantity for which there is no output of the instrument.
• For example, the input applied to the instrument may not be sufficient to overcome the friction and will, in that case, not move at all.
• It will only move when the input is such that it produces a driving force that can overcome friction forces.
• The term “dead zone” is sometimes used interchangeably with the term hysteresis. However, it may be defined as the total range of input values possible for a given output and may thus be numerical twice the hysteresis.

7. During the measurement of voltage, the voltmeter responded with a 0.18-V change when the input was varied by 0.2 V. Find the sensitivity of the instrument.

1. 0.9
2. 0.18
3. 0.1
4. 0.2

Explanation:

Sensitivity(S) of instrument is defined as change in output with respect to change in input

S = $\frac{dV_0}{dV_i}=\frac{Δ V_0}{Δ V_i}$

Where

V0 = Output voltage of instrument

Vi = Input voltage of instrument

Application:

Given:

ΔV0 = 0.18 V

ΔVi =0.2 V

S = 0.18/2 = 0.9

8. Torque/weight ratio of an instrument indicates

1. Selectivity
2. Accuracy
3. Fidelity
4. Sensitivity

Explanation:

The ratio of torque to the weight of the moving part of an instrument is known as a torque/weight ratio. This indicates the sensitivity of the actuator. The higher value of torque/weight ratio shows that the instrument has good performances.

9. The value of torque/weight ratio  of the instrument should not be less than _____

1. 0.3
2. 0.1
3. 0.5
4. 1

Explanation:

The ratio of torque to the weight of the moving part of an instrument is known as a torque/weight ratio. This indicates the sensitivity of the actuator. The higher value of torque/weight ratio shows that the instrument has good performances.

The value of torque/weight ratio of the moving part of the instrument should not be less than 0.1 if the deflecting torque acts as a force on the apparatus and shows the full-scale deflection.

10. What is the smallest change in applied stimulus that will indicate a detectable deflection in an indicating instrument is called?

1. Accuracy
2. Precision
3. Sensitivity
4. Resolution