# JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008

JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008

INSTRUMENTATION

(Electrical & Electronic Engineering)

SET-II

1. Draw the block diagram of the measuring system and explain the each stage with their functions.

2. (a) Explain the following processes as applied to pulse code modulation

i. Quantization process

ii. Encoding process.

(b) Describe the following modulation processes:-

i. Pulse amplitude modulation.

ii. Pulse frequency modulation.

3. (a) Give general characteristics of digital voltmeters.

(b) Give the specifications that represent valid information for selecting a digital voltmeter.

4. (a) What would a true rms reading meter indicate if a pulse waveform of 5v peak and a 25% duty cycle were applied? What would the meter indicate if a 5vdc input were applied (assume the meter has dc capability).

(b) To check the distributed capacitance of a coil, the coil is resonated at 10MHZ with 120PF and then is resonated at 15MHZ with 40PF. What is the inductance of the coil and what is the equivalent distributed capacitance

5. (a) A resistive position transducer with a resistance of 5 k and a shaft stroke of 8cm is applied with a voltage of 5V.When the wiper is 3cm from the Reference, what is the value of the output voltage?

(b) A resistance strain gauge with a gauge factor 2.04 is fastened to a beam which is subjected to a strain of 1×10?6.If the original resistance of the gauge is 120  calculate the change in resistance?

6. (a) Explain in detail about photo diode and photo transistors?

(b) Explain in detail about thermocouples?

7. (a) Explain the method of adjacent arm compensating gauge for temperature compensation in strain gauge with a neat circuit.

(b) A single electrical resistance strain gauge of resistance 120 and having a gauge factor of 2 is bonded to steel having an elastic limit stress of 400MN/m2 and modulus of elasticity 200 GN/m2. calculate the change in resistance due to a change of temperature of 200C co-efficient of linear expansion of steel is 12×10?6/0C.

8. (a) What is a torsion bar and how is it used for torque measurement.

(b) Explain how torque can be measured using an inductive transducer. Give the sketch for arrangement of inductive transducers with respect to shaft.