24 questions and answers
Define the terms accuracy, Precision, Resolution, Drift and Relative limiting error.
Accuracy of measurements mean conformity to truth. It is the closeness with which an instrument reading approaches the truth value of the quantity being measured
Explain the difference between Dynamometer type wattmeter and induction type wattmeter.
i. Working torque comparatively weaker. i. Working torque comparatively stronger.
What is phantom loading? Explain with an example how it is more advantageous than testing with direct loading.
A test with actual loading arrangements would involve a considerable waste of power when the current rating of a meter under test is high.
Define gauge factor of a strain gauge & obtain its expression.
It is defined as the ratio of per unit change in resistance to per unit change in length. Expression: Gauge factor \(\left(G_f\right)=\frac{\Delta R/R}{\Delta L/L}\)
Write short note on LVDT
LVDT works under the principle of mutual induction, and the displacement which is a non-electrical energy is converted into an electrical energy.
Write short note on
While most analog meters require no power supply, give a better visual indication of trends and changes, suffer less from electric noise and isolation problems, and, are simple and inexpensive, digital meters offer higher accuracy and input impedance, unambiguous readings at greater viewing distances, smaller size, and a digital electrical output (for interfacing with external equipment) in addition to visual readout.
What are the special features of a high voltage Schering bridge? What is meant by “Wagner’s Earth”?
High voltage supply is obtained from a transformer. Usually at the power frequency and detector used is vibration galvanometer.
What is the function of delay time?
The delay Line retards the arrival of the input waveform at the vertical deflection plates until the trigger and time base circuits start the sweep of the beam.
A single phase kWhr meter makes 500 revolutions per kWhr. It is found on testing that it is making 40 revolutions in 58.1 seconds at 5kW load. Find out the percentage of error.
Energy consumed in 58.1 seconds=\(\frac{5\ast58.1}{3600}\) kWh=0.08069kWh
What are absolute & secondary instruments ? Why is damping required in a measuring instrument ?
These instruments give the magnitude if the quantity under measurement terms of physical constants of the instrument.
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