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-III

1. Distinguish between systematic and random errors in a measurement and how they are usually minimized.

 

2. Distinguish between analog modulation and digital modulation and explain the situations under which each is preferred.

 

3. Write short notes on:

(a) Lumped-parameter delay line.

(b) Distributed-parameter delay line.

 

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 single strain gauge is mounted to measure the axial strain in a simple tensile.

member. If the recorded strain is 380 micro strain what is the axial stress.

i. if the member is steel?

ii. if the member is aluminium?

(b) What are the advantages of electrical transducers?

 

6. (a) Explain in detail the application of RVDT?

(b) Discuss in detail the operation of a synchros?

 

7. (a) What is a load cell? Explain the working of a load cell strain gauge bridge.

(b) A load cell consists of a solid cylinder of steel 40mm in diameter with four strain gauges boned to it and connected in to the four arms of a voltage sensitive bridge. The gauges are mounted to have Poisson’s arrangement. The gauge factor is 2.1 ad each gauge has 1000 ohms resistance. The bridge excitation voltage is 6v. Determine the sensitivity of the cell in V/KN modules of elastic for steel is 200GN/m2 and Poisson ratio is 0.29.

 

8. (a) Explain the principle of measurement of torque using magneto-strictive transducer.

(b) A mild steel shaft is used to connect a motor drive to a constant load torque. A foil strain gauge having a resistance of 120 and a gauge factor 2 is mounted on a shaft with its active axis at angle of 45 degrees to the axis of the shaft. The shear modules of steel is 80GN/m2, the shaft radius is 15mm and the change in strain gauge resistance due to the load 0.24 . Find the load torque.

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