520 questions and answers
Explain the principle of operation of a digital frequency meter.
A frequency meter has a small device which converts the sinusoidal voltage of the frequency into a train of unidirectional pulses. The frequency of input signal is the displayed count, averaged over a suitable counting interval out of 0.1, 1.0, or 10 seconds.
Explain the worming of Anderson’s bridge with a neat sketch. Derive the required expression for obtaining the unknown inductance.
Let, \(L_1\) = Self-inductance to be measured \(R_1\) = Resistance of self-inductor C = Fixed Capacitor
In a certain current transformer, the following data is obtained. Nominal ratio = 25/5A, Turn ratio = 3, primary terns = 40, secondary turns = 120, secondary resistance = 0⋅16z, secondary reactance = 0⋅195Ω, secondary burden = 15 VA, Burden power factor = 0⋅7, secondary terminal voltage = 3V.
Find ratio & phase angle errors. The magnetising and loss ampere turns corresponding to an emf of 4⋅26V are13 & 10⋅1 respectively.
Secondary burden=15VA, secondary winding current=5A=\(I_s\) Secondary circuit impedance =\(\frac{15}{5^2}=0.6\Omega\)
How that driving torque in a moving iron instrument is given by
Let ‘\(\theta\)’ be the deflection corresponding to a current of ‘I’ amp Let the current increases by di, the corresponding deflection is ‘\(\theta+d\theta\)’ There is change in inductance since the position of moving iron change w.r.t the fixed electromagnets.
Write short notes on
The Q-factor for a series L–C–R circuit is the voltage magnification at resonance, i.e. \(Q-factor = \frac{voltage\ across\ capacitor}{supply\ voltage}\)
What is lissajous pattern? Explain how phase & frequency can be measured using this figures.
Cathode Ray Oscilloscope (CRO) is very important electronic device. CRO is very useful to analyze the voltage wave form of different signals. The main part of CRO is CRT(Cathode Ray Tube). A simple CRT is shown in figure below-
Explain the functional block diagram of CRO with neat diagram.
The cathode Ray Oscilloscope or mostly called as CRO is an electronic device used for giving the visual indication of a signal waveform. It is an extremely useful and the most versatile instrument in the electronic industry.
Describe the process of capacitance measurement using De Sauty’s bridge and draw the relevant phasor diagram. State the limitations of the bridge.
For measurement of capacitance and dissipation factor Schering bridge is widely used. The phasor diagram and circuit diagram of the bridge are as follows:
A Wheatstone bridge has the following resistances : AB = 200Ω, BC = 20Ω, CD = 8Ω & DA = 100Ω. A galvanometer of 40Ω is connected across BD. Find the current through the galvanometer when 20V is applied across A.C.
Resistance of unknown resistor required for balance=\(R_{AD}=\left(\frac{R_{AB}}{R_{BC}}\right)\ast R_{CD}\) \(=\frac{200}{20}\ast8=80\Omega\)
Explain the relevant circuit diagram, the principle of measurement of low resistance by kelvin’s double bridge. Prove that the condition of balance is independent of the read resistance. Up to what low value it can be used?
The kelvin bridge is a notification of the Wheatstone bridge with greater increased accuracy in measurement of low value resistance. Consider the bridge circuit shown in the figure.
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