537 questions and answers
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.
How can potentiometer be used for
The ammeter to be calibrated is connected in series with a variable resistance R and a standard resistance S. The standard resistance, S should be such of magnitude that with the current to be passed through it, the voltage drop across it does not exceed the range of the potentiometer.
Draw the circuit diagram of DC potentiometer & explain how it works.
Let the standard cell SC be connected with its negative terminal through selector switch S, galvanometer G and key K to the sliding contact J. Since slide wire AB is of uniform cross section, the resistance per unit length r will be constant and equal to R/L. Where R is resistance of whole wire and L is the length of wire.
Deduce the expression of torgue of electrodynamometer type instrument. Why multiplier is used with PMMC instrument? What do you mean by sensitivity of PMMC instrument? Why sensitivity of electrodynamometer type instrument is low? Why the scale of moving iron instrument is cramped at lower end?
Let e= instantaneous voltage across load =\(E_m\) sin (ωt-φ) \(i_t\) =instantaneous load current
Explain how a low resistance is measured by a potentiometer
Let unknown resistor R is connected in series with a standard resistor S. The current through the circuit is controlled with the help of rheostat. A two-pole double throw switch is used.
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