1.

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 %The question was posed to me during an online exam.My query is from Advanced Problems on Indicating Instruments topic in section Extension of Instrument Ranges of Electrical Measurements

Answer»

Correct answer is (c) 3 A ± 1.7 %

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

Thermocouple MEASURE the RMS value of current.

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


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