Electrical and electronics measurements miscellaneous Difficult Questions and Answers

Electrical and electronics measurements miscellaneous

A 4-range milliammeter having ranges of 0 – 10 mA, 0 – 50 mA, 0 – 100 mA and 0 – 500 mA. It is used for measurement of current whose magnitude is not known. In order to prevent damage to the instrument the selector switch of the ammeter should be first placed at

A PMMC instrument produces a deflection of 90° when a current 2 mA passes through its moving coil. The instrument is spring controlled. Supposing the instrument is redesigned with its spring constant as before, and its permanent magnet is replaced with a new permanent magnet which reduces twice the flux density as before, what would be the deflection if a current of 1 mA is passed through the coil? The other features of the PMMC instrument remain the same.

1. high friction loss
1. low friction loss
1. nothing as regards friction loss
1. none of these

The power in a 3-phase, 3-wire load is measured using two 100W full-scale wattmeters W₁ and W₂. W₁ is of a accuracy class ± 1% and reads 100 W. W₂ is of accuracy class ± 0.5% and reads – 50 W. Then the uncertainty in the computation to total power is

An 0 – 10 A ammeter has guaranteed accuracy of 1 percent of full scale deflection. The limiting error while reading 2.5 is

∴ W₁ + W₂ =		50 ±	1.5		× 100 = ± 3%
			50

∴ W₁ + W₂ =		50 ±	1.5		× 100 = ± 3%
			50