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

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

INSTRUMENTATION

(Electrical & Electronic Engineering)

SET-IV

1. Explain the phenomenon of hysteresis in measurement systems. Alongside explain the terms ‘threshold’, ‘maximum input hysteresis’, ‘maximum output hysteresis’, ‘dead zone’, and ‘Blacklash’, Draw neat diagrams to explain them.

 

2. (a) Explain the spectra of a periodic rectangular pulse train for the following.

i) Amplitude

(ii) Phase spectra when time origin coincides with centre of pulse.

iii) Phase spectra with pulse starting at t=0.

(b) Define line spectra.

 

3. Discuss in detail electrostatic deflection of electron beam.

 

4. (a) On what basis digital voltmeters are classified?

(b) Explain with circuit diagram, the principle of operation of DVM.

 

5. (a) What is a wave analyzer? Mention its significance in measurement system

(b) Explain the working of a Frequency selective wave analyzer with a neat block diagram.

(c) Mention few applications of heterodyne wave analyzers.

 

6. A piezoelectric transducer has a capacitance of 1000pF and a charge sensitivity of

40× 10 – 3 C/m. The connecting cable has a capacitance of 300pF while the oscilloscope used for readout has an input resistance of 1M and a parallel capacitance

of 50pF.

(a) what is the sensitivity of the transducer alone?

(b) (V/m) of the entire measuring system?

(c) what is the lowest frequency that can be measured with a 5% amplitude error by the entire system

(d) what is the value of external shunt capacitance that can be connected in order to extend the range of 5% error down to 10 Hz.?

(e) What is the high frequency sensitivity, when the external shunt capacitance calculated in

(f) is connected in the circuit.

 

7. (a) Discuss briefly about piezoelectric accelerometers.

 (b) A piezoelectric accelerometer has a transfer function 61mV/g and a natural

frequency of 4500Hz. In a vibration test at 110Hz, a reading of 3.6V peak is obtained. Find the vibration peak displacement.

 

8. (a) What is a Radiation pyrometer? Explain the principles used for radiation temperature measuring devices.

(b) Explain the black body conditions.

(c) Write a short notes on quartz crystal thermometer.

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