Page 816 - Basic Electrical Engineering
P. 816
Gross errors are human errors; systematic errors are instrumental errors;
and random errors are because of random variations in measurement
parameters.
Example 11.1 It is intended to measure an unknown resistance by the
ammeter–voltmeter method. For this, a voltmeter is connected across the
unknown resistance and the current flowing through the resistance is
measured by an ammeter as shown in Fig. 11.8.
The voltmeter used has full scale range of 0–100 V and has sensitivity of
1000 Ω/V. The milliammeter has negligible resistance. Assume that the
voltmeter reads a voltage of 80 V across the terminals P and Q. Let us
calculate the value of unknown resistance R and then calculate the error in
measurement due to current drawn by the voltmeter.
Solution:
A voltage of 80 V will also cause a small amount of current flowing through
the voltmeter. Voltmeter resistance, R = 1000 Ω/V × 100 = 100 kΩ
n
Current through the voltmeter,
