Question

A 0 – 10 A ammeter has a guaranteed accuracy of 1 percent of full scale deflection. What will be the limiting error in the reading of 2.5 A?

1. 1 per cent
2. 4 per cent
3. 2 per cent
4. 3 per cent

Answer 1

Correct Answer - Option 2 : 4 per cent

Limiting error:

Limiting error is defined as the difference between the measured quantity (Am) and the true quantity (At).

Limiting error LE = Am - At 

%Limiting error (%LE):

It can be calculated as the ratio of limiting error to the true quantity.

%LE = \(\frac{A_m -A_t }{A_t } \times 100\)

Guaranteed accuracy error (GAE):

It can be calculated as the ratio of limiting error to the full-scale value.

% GAE = \(\frac{Limiting\ error}{Full\ scale\ reading}\times 100=\frac{A_m -A_t }{Full\ scale\ reading} \times 100\)

Calculation:

GIven that,

Full-scale reading =10 A

% GAE = 1 %

True value of ammeter = At

% GAE = \(\frac{Limiting\ error}{Full\ scale\ reading}\times 100=\frac{A_m -A_t }{Full\ scale\ reading} \times 100\)

⇒ 1 = (Limiting error / 10 ) x 100

∴ Limiting error = 0.1 A

% LE = (Limiting error / True value) x 100

⇒ % LE = (0.1 / 2.5) x 100

∴ % Limiting error = 4 %