Question

Four ammeters M1, M2, M3 and M4 with the following specifications are available.

$\begin{array}{cccc}\text{Instrument}& \text{Type}& \text{Full scale}& \text{Accuracy}\\ & & \text{value}& \text{\% of FS}\\ & & \left(A\right)& \\ \text{M1}& 3\frac{1}{2}\text{digit}& 20& \pm 0.10\\ & \text{dual slope}& & \\ \text{M2}& \text{PMMC}& 10& \pm 0.20\\ \text{M3}& \text{Electro-dynamic}& 5& \pm 0.50\\ \text{M4}& \text{Moving-iron}& 1& \pm 1.00\end{array}$


A current of 1 A is to be measured. To obtain minimum error in the reading, one should select meter.

• A. M1
• B. M2
• C. M3
• D. M4

Answer 1

The correct option is D M4

Error in reading of first meter
$=FSD\times accuracy=20\times \frac{\pm 0.1}{100}=\pm 0.02$

Error in reading of second meter
$=10\times \frac{\pm 0.2}{100}=\pm 0.02$

Error in reading of third meter
$=5\times \frac{\pm 0.5}{100}=\pm 0.025$

Error in reading of fourth meter
$=1\times \frac{\pm 1.00}{100}=\pm 0.01$

Fourth meter has least error.