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GTU Electrical and Electronic Engineering (Semester 7)
Electrical And Electronics Measuring Instruments
December 2014
Electrical And Electronics Measuring Instruments
December 2014
1 (a)
Explain the construction and working of 1-ϕ induction type energy meter. Also draw the phasor diagram.
7 M
1 (b)
Describe the different controlling methods used in an analog instrument. Compare them and justify scale uniformity for both controlling methods.
7 M
2 (a)
Explain construction and working of PMMC instrument & derive the torque equation.
7 M
Answer any two question from Q2 (b) or Q2 (c)
2 (b)
The inductance of a moving iron ammeter with a full scale deflection of 90° at 1.5 A, is given by the expression: L= (200+40θ-4θ2 -&theta3 ) μH. Where, θ is the deflection in radian from the zero position. Estimate the angular deflection of the pointer for a current of 1.0 A.
7 M
2 (c)
A Dynamometer wattmeter is used to measure the power factor of a 20μF capacitor. The pressure coil of the wattmeter having a resistance 1000Ω and an inductive reactance of 15Ω is connected across a 50Hz supply. The current coil of the wattmeter, a variable resistor R and the capacitor are connected in series across the same supply. The wattmeter deflection is made zero by adjusting the value of R to 1.65Ω. If the current coil resistance is 0.1Ω and its inductance negligible: Determine the power factor of the capacitor.
7 M
Answer any two question from Q3 (a), (b) or Q3 (c), (d)
3 (a)
List various methods of high resistance measurement. Explain Megohm bridge method in detail.
7 M
3 (b)
Derive the equations of balance for the Anderson's bridge. Draw the phasor diagram under the balance condition and give the advantage and disadvantage.
7 M
3 (c)
State the application of modified DeSauty's bridge. Explain its working. Draw the phasor diagram and derive the equation for unknown capacitance.
7 M
3 (d)
In the simple Wheatstone bridge, the values of resistances of various arms are P=1000Ω, Q=100Ω, R=2005Ω and S=200Ω. The Battery has an EMF of 5V and negligible internal resistance. The Galvanometer has a current sensitivity of 10 mm/μA and internal resistance of 100Ω. Calculate the deflection of Galvanometer and the sensitivity of the bridge in terms of deflection per unit change in resistance.
7 M
Answer any two question from Q4 (a), (b) or Q4 (c), (d)
4 (a)
Draw the equivalent circuit and phasor diagram of a current transformer. Derive the expression for its ratio and phase angle error.
7 M
4 (b)
Explain frequency selective wave analyzer with block diagram.
7 M
4 (c)
A Potential transformer, ratio 1000/100 volt, has the following constant:
Primary resistance = 94.5Ω,
Secondary resistance = 0.86Ω,
Primary reactance = 66.2Ω,
Total equivalent reactance = 110Ω,
No load current = 0.02 A at 0.4 power factor.
Calculate:
(i) Phase angle error at no load and
(ii) Burden in VA at unity power factor at which the Phase angle will be zero.
Primary resistance = 94.5Ω,
Secondary resistance = 0.86Ω,
Primary reactance = 66.2Ω,
Total equivalent reactance = 110Ω,
No load current = 0.02 A at 0.4 power factor.
Calculate:
(i) Phase angle error at no load and
(ii) Burden in VA at unity power factor at which the Phase angle will be zero.
7 M
4 (d)
Why are FETs used in differential amplifier type of electronic voltmeter? Draw and Explain the equivalent circuit of such a voltmeter.
7 M
Answer any two question from Q5 (a), (b) or Q5 (c), (d)
5 (a)
What are Lissajous figures? How can you measure the phase difference between two sinusoidal signals using a CRO with this figure?
7 M
5 (b)
Explain the block diagram of a general telemetry system. State different types of telemetry system. Explain land line telemetry system and its application system.
7 M
5 (c)
Write technical notes on active and passive transducers.
7 M
5 (d) (i)
Why platinum is commonly used metal for RTD?
2 M
5 (d) (ii)
Why thermocouple is called active transducer?
2 M
5 (d) (iii)
Core of LVDT is slotted- justify the statement.
3 M
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