MEASUREMENT DEVICES

Tutorial 45

Problem 5
The value of resistor is 330Ω, while measurement yields a value of 329 Ω. Calculate (a) relative
accuracy and (b) % accuracy.

Solution

EAbsolute=|330 Ω - 329 Ω| = 1 Ω

%Erelative= EAbsolute x 100% = 1Ω x100% = 0.3%
XExpected 330 Ω

a) Accuracy, A = 1 - % error = 1 - 0.3% = 1 - 0.02 = 0.997

b) %Accuracy = 100% - %Erelative= 100%-0.3% = 99.7%

Problem 6
The value of resistor is 4.7 kΩ, while meter reads a value of 4.66 kΩ. Calculate (a) relative accuracy
and (b) % accuracy.

Solution

EAbsolute=|4.7 kΩ - 4.66 kΩ| = 0.04 kΩ

%Erelative= EAbsolute x 100% = 0.04 kΩ x100% = 0.9%
XExpected 4.7 kΩ

a) Accuracy, A = 1 - % error = 1 - 0.9% = 1 - 0.02 = 0.99

b) %Accuracy = 100% - %Erelative= 100%-0.9% = 99.1%

Problem 7
The voltage across a resistor is supposed to be 5.0 V. Measurement, on the other hand, produces a
result of 4.9 V. Calculate:
(a) Absolute error
(b) Percentage of relative error
(c) Percentage of accuracy
(d) Relative accuracy

Tutorial 46

Solution

a) EAbsolute=|5 V - 4.9 V| = 0.1 V

b) %Erelative= EAbsolute x 100% = 0.1 V x100% = 2%
XExpected 5V

c) Accuracy, A = 1 - % error = 1 - 2% = 1 - 0.02 = 0.98

d) %Accuracy = 100% - %Erelative= 100%-2% = 99.02%

Problem 8
An experiment conducted to measure 5 values of voltage and the results shown in the table below.
Calculate the precision and percentage of the 4th experiment.

No. (V)
1 4.8
2 4.0
3 3.9
45
5 4.7

Table 5 values of Current measured

Solution:

Precision = 1 - �xnx-n̅ x̅n�

xn̅ = ∑ x
n

The average value for the 5 value of measurement is given by

x̅n = ∑x = 4.8+4.0.+3.9+5+4.7 = 4.5
n 5

For the 4th reading,

Precision = 1- �xnx-̅nxn̅ � = 1- �54-4.5.5� = 1- 0.5 = 0.889
4.5

Percentage of 4th reading, % Precision = precision x 100% = 0.899 x 100% = 88.89%

Tutorial 47

Practices
1. The measured value of voltage across a resistor is 2 V and the true value is 3 V. Calculate

absolute error.

2. The measurement yields a current value of 10 mA. While the true value of the current across a
resistor is 30 mA. Calculate absolute error.

3. The measured value of the resistance is 322 Ω. However, the expected value of the resistance
is 330 Ω. Calculate (i) relative error (ii) percentage error in measurement.

4. The value of the voltage across a resistor is 2 V. On the other hand, the measurement yields a
voltage value across a resistor of 1.8 V. Calculate (i) Absolute error (ii) relative error (iii)
percentage of error.

5. An analog voltmeter is used to measure voltage of 4 V across a resistor. The reading value is
3.9 V. Find absolute error, percent error, accuracy or relative accuracy and percent accuracy.

6. An experiment conducted to measure 10 values of currents and the results shown in the table
below. Calculate the precision and percentage of the 4th experiment.

No. (mA)
15
2 6.2
38
47
5 10
6 11
78
89
9 9.8
10 4

Table 10 values of Current measured

7. Given a 500 V voltmeter with accuracy ±2% full scale. Calculate limiting error when the
instrument is used to measure a voltage of 200V?

Tutorial 48

8. A voltmeter is accurate 98% of its full scale reading.
(a) If the voltmeter gives measurement reading of 300V at the range of 500V, calculate the
absolute error of the measurement.
(b) Calculate the percent (%) error for the reading in (a)

Answers
1. 1 V
3. 0.024, 2.42%
5. 0.1 V, 2.5%, 0.975, 97.5%
7. 10 V, 5%

References 49

References

Nor Azura Osman, Khetijah Samat, Munirah Md Nujid (2016). Measurements (1ST), Oxford Fajar.

Kalsi, H. S. (2018). Electronic Instrumentation, 3e. Tata McGraw-Hill Education.
Bird, J. (2017). Electrical and electronic principles and technology. Routledge.
Bell, D. A. (1994). ELECTRONIC INSTRUMENTATION AND MEASUREMENTS 3E.
Bakshi, U. A., & Bakshi, L. A. V. (2020). Electronic measurements and instrumentation. Technical
Publications.