JNTU B.Tech II Semester INSTRUMENTATION Examinations, Apr/May 2008

JNTU B.Tech II Semester INSTRUMENTATION Examinations, Apr/May 2008

(Electrical & Electronic Engineering)

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks


1. (a) What is meant by stability of a measuring system ? Indicate which class of

instruments are required to be more stable.

(b) Distinguish between ‘static’ and ‘dynamic’ characteristics of a measuring system and state the relevance of each in a measuring process. [8+8]


2. Explain how angle modulation of a signal is done. Distinguish between angle and

Phasemodulation. [16]


3. (a) Write the important specifications of CRO for instrumentation applications.

What selection factors are necessary for selecting a CRO.

(b) Calculate the velocity of an electron beam in an oscilloscope if the voltage applied to its vertical deflection plates is 2000v. Also calculate the cut off frequency if the maximum transit time is 1/4th of a cycle. The length of horizontal plates is 50mm. [8+8]


4. With a neat block diagram explain the microprocessor based ramp type digital

voltmeter. [16]


5. (a) Explain the principle and working of peak reading voltmeter with a neat block


(b) A coil of unknown impedance is connected in series with a capacitor of 224?F

and an ammeter of negligible impedance is connected to a variable frequency of constant voltage and negligible impedance. The frequency was adjusted both above and below the resonance frequency till the reading of the ammeter was reduced to 70.7% of its value at resonance. This occurred at the frequencies of 876 and 892 kHz. Determine effective resistance, inductance and Q of the coil. [10+6]


6. Explain the factors that influence the selection of a transducer. [16]


7. (a) Define gauge sensitivity and derive expression for it.

(b) in order to measure strain in a cantilever beam a single strain gauge of resistance 1 K  and gauge factor 2 and temperature coefficient of 10 × 10 – 6/0C is mounted on one beam and connected in one arm of the bridge circuit. The other three arms of the bridge have resistances of 100  each. The bridge detector resistance is 100  and it’s sensitivity is 10mm/?A

i. Calculate deflector’s defletion for 0.1% strain

ii. Calculate the change in effective strain indicated when the room temperature increases by 10 0C.

(c) Mention few devices that are used for the measurement of Rotary displacement. [4+9+3]


8. (a) Describe the principle and operation of Knudsen gauge with a neat sketch.

(b) Describe the operation of Ionization gauges for pressure measurement. [8+8]

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