Question

A current of [2 + \(\sqrt{2}\)sin (314t + 30) + 2\(\sqrt{2}\)cos (952t +45)] is measured with a thermocouple type, 5A full scale, class 1 meter. The meter reading would lie in the range?

(a) 5 A ± 1 %

(b) (2 + 3\(\sqrt{2}\)) A ± 1%

(c) 3 A ± 1.7 %

(d) 2 A ± 2.5 %

I have been asked this question in an interview for job.

The doubt is from Advanced Problems on Magnetically Coupled Circuits in section Resonance & Magnetically Coupled Circuit of Network Theory

Answer 1

Correct option is (c) 3 A ± 1.7 %

The explanation: I = [2 + \(\sqrt{2}\) sin (314t +30°) + 2\(\sqrt{2}\) cos (952t + 45°)]

Thermocouple measure the rms value of current.

Irms = \(\Big[2^2 + \left(\frac{\sqrt{2}}{\sqrt{2}}\right)^2 + \left(\frac{2\sqrt{2}}{\sqrt{2}}\right)^2\Big]^{1/2} = \sqrt{9}\) = 3 A ± 1.7%.