AMIETE – ET (NEW SCHEME) – Code: AE60
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Subject: INSTRUMENTATION & MEASUREMENTS
Time: 3 Hours Max. Marks: 100
NOTE: There are 9 Questions in all.
· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.
· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.
· Any required data not explicitly given, may be suitably assumed and stated.
Q.1 Choose
the correct or the best alternative in the following: (2
10)
a. Which one of following is an active as well as an inverse transducer.
(A) electrical resistance potentiometer
(B) L.V.D.T.
(C) capacitive transducer
(D) piezo electric crystals
b. A buffer amplifier has gain of
(A) infinity (B) zero
(C) unity (D) dependent upon the circuit parameters
c. X-Y recorder
(A) record one quantity with respect to another quantity
(B) record one quantity on X axis with respect to time on Y axis
(C) record one quantity on Y axis with respect to time on X axis
(D) none of the above
d. A digital voltmeter uses an A/D converter which needs a start pulse, uses an analog comparator and has a relatively fixed conversion time independent of the applied voltage. The A/D converter is
(A) successive approximation converter
(B) digital ramp converter
(C) dual slope converter
(D) all of the above
e. In a Q-meter, the value of shunt resistance connected across the oscillator is typically of the order of
(A) W (B) mW
(C) mW (D) kW
f. A triangular wave shape is obtained
(A) by integrating a square wave (B) by differentiating a sine wave
(C) by differentiating a square wave (D) by integrating a sine wave
g. A vertical amplifier for a CRO can have
(A) high gain only
(B) broad bandwidth only
(C) constant gain times bandwidth product
(D) all of the above
h. The advantage of Hay’s bridge over Maxwell’s inductance-capacitance bridge is that
(A) its equations for balance do not contain any frequency term
(B) it can be used for measurement of inductance of high Q coils
(C) it can be used for measurement of inductance of low Q coils
(D) all of the above
i. A Wheatstone bridge cannot be used for precision measurements because errors are introduced due to
(A) resistance of connecting leads (B) thermo-electric emfs
(C) contact resistances (D) all of the above
j. In measurement systems, which one of the following characteristics are desirable:
(A) accuracy (B) sensitivity
(C) reproducibility (D) all of the above
Answer any FIVE Questions out of EIGHT Questions.
Each question carries 16 marks.
Q.2 a. Define accuracy and precision. Explain why a precise instrument may not necessarily be accurate. (6)
b. Three 250 W, 500 W, and 375 W resistors are connected in parallel. The 250 W resistor has +0.025 fractional error, the 500 W resistor has a -0.036 fractional error, and the 375 W resistor has a +0.014 fractional error. Determine:
(i) the total resistance neglecting errors
(ii) total resistance considering error of each resistor, and
(iii) the fractional error of the total resistance based upon rated value. (6)
c. State the condition for which a second order system response for unit step input is overdamped, underdamped and critically damped. (4)
Q.3 a. A
Maxwell bridge is used to measure an inductive impedance. The bridge constants
at balance are 
,
, 
and 
. Find the series
equivalent of the unknown impedance. (6)
b. (i) Draw the circuit of Schering bridge and derive the balance condition.
(ii) A capacitor is tested by Schering bridge. It forms one arm AB of the bridge. The other arms are : AD – a non-inductive resistance of 100 ohms; DC – a non-reactive resistance of 300 ohms shunted by a capacitor of 0.5mf; BC – a standard loss-free capacitor of 100mf; the supply frequency is 50 Hz. The bridge is at balance with the above components.
Deduce the balance conditions of the bridge and hence find out the capacitance and the power factor of the capacitor under test. (6+4)
Q.4 a. Explain the construction and working of a thermocouple measuring instrument. What are the effects of frequency on the calibration of a thermocouple? (8)
b. Calculate the value of multiplier resistor for a 10 V rms ac range on the voltmeter shown in Fig.1. (8)
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Q.5 a. Explain with the help of a neat block diagram the working of the following:
(i) Ramp Type DVM
(ii)
Q-meter
(62)
b. A circuit consisting of a coil, a resistance and a variable capacitor connected in series is tuned to resonance using a Q-meter. If the frequency is 500 kHz, the resistance 0.5 W and variable capacitor set to 350 pf. Calculate the effective inductance and resistance of coil, if the Q-meter indicates 90. (4)
Q.6 a. With the help of a neat sketch, explain the operation of a cathode-ray tube, commonly used as in cathode-ray oscilloscope. State the difference between this tube and the tube used for T.V. receivers. (8)
b. Discuss with the help of a neat circuit diagram the elements of a standard sweep generator. Draw its output waveform. (8)
Q.7 a. What is a bolometer? How self balancing is achieved in a bolometer bridge?
(8)
b. Where spectrum analysers are commonly used? Explain the working of a basic spectrum analyser. (8)
Q.8 a. Write short notes on:
(i) X-Y recorder
(ii)
Null type recorder (62)
b. The gap of a tape recorder is 0.00625 mm. Determine the speed of the tape so as to have a satisfactory response at 50 Hz. Assume that recorded wavelength must be greater than 2.5 times the gap of the recorder. (4)
Q.9 a. What is the difference between active and passive transducer? Explain the construction and working of linear variable differential transducer (LVDT). (8)
b. A strain gauge bridge shown in the Fig.2 has two fixed resistors R1 and R2 of 120 W each and a variable resistance R4 which is 120 W at zero strain and 120.63 W with a strain of e. The gauge factor is 2.04. Determine the strain where the gauge is attached. (8)
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