Transducers In Instrumentation Rr

Set No. 1

Code No: RR221002

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007 TRANSDUCERS IN INSTRUMENTATION ( Common to Electronics & Instrumentation Engineering and Electronics & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Classify various transducers and give an example of each and mention their applications. (b) What is the true value of voltage across the 500 KΩ resistor connected between terminals A and B as shown in figure 1b below ? What would a voltmeter with a sensitivity of 20 KΩ/v read on the following ranges: 50, 15,5 volts when connected across terminals C and D. [8+8]

Figure 1b 2. (a) A 2nd order instrument has a natural frequency of 4 Hz and a damping ratio of 0.66. If the excitation frequency of the system is 6 Hz, determine the error due to the proximity of excitation frequency with the natural frequency of the system. (b) Derive the expression for time response of a 2nd order system subjected to unit impulse input. Sketch its response. [8+8] 3. (a) What are the precautions to be taken care while fastening strain gauges on to the specimen explain. (b) A strain gauge is bonded to a beam 0.1 m long and has a cross sectional area 4cm2 Young’s modules for steel is 206 GN/m2 .The strain gauge has an unstrained resistance of gauge changes by 0.013Ω .Calculate the change in length of the steel beam and the amount of force applied to the beam. 4. (a) How the capacitive transducer is useful for the measurement of level of a nonconducting liquid. (b) Explain the principle of capacitive transducer which uses the principle of change in dielectric constant for measurement of displacement. [8+8] 5. (a) Describe the properties of materials used for Piezo-electric transducers. (b) Derive the expressions for voltage and charge sensitivities.

[8+8]

6. (a) With the help of schematic diagram explain about floating mass low range angular velocity transducer. 1 of 2

Set No. 1

Code No: RR221002

(b) Distinguish between Force-balance transducers with electrodynamic and electrostatic servo-actuators. [8+8] 7. (a) Explain briefly the methods used to measure the output from thermocouples. (b) A chromel-alumel thermocouple having a linear relationship between temperature and emf indicates zero at 00 C and 45.14 mV at 11000 C. The thermocouple is exposed to a temperature of 8400 C with cold junction maintained at 250 C, calculate the induced emf. [8+8] 8. Describe the working and construction of resistance thermometers. Describe the materials used for RTDs along with their properties. Sketch this typical characteristic curve. [16] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR221002

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007 TRANSDUCERS IN INSTRUMENTATION ( Common to Electronics & Instrumentation Engineering and Electronics & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define the following static characteristics with necessary examples and graphs: i. ii. iii. iv. v.

Accuracy sensitivity static error Dead space Drift

(b) A voltage has a true value of 1.50 volts. An Analog indicating instrument with a scale range of 0-2.50 volts shows a voltage of 1.46 volts. What are the values of absolute error and correction. Express the error as a traction of the true value and the full-scale deflection. [10+6] 2. (a) Derive the expression for frequency response of a second order system. Draw the magnitude and phase versus frequency plots for damping ratio smaller than 0.707. (b) A first order system which has a time constant of 0.7 sec. is subjected to an input of 5sin 5t + 6 sin 50t. Find the response of the system. [8+8] 3. (a) Differentiate between active and passive transducers. Explain with examples? (b) Derive an expression for loading error for a potentiometer transducer. [8+8] 4. (a) A displacement capacitive transducer uses a differential arrangement with two outer plates which are fixed and a central plate which is movable. The distance between fixed and movable plates is 5mm when no displacement is applied. A voltage of 1000v rms is applied across the fixed plates. Find the differential output voltage of a displacement of 0.01mm is applied to the central plate. Find also the sensitivity of the transducer. (b) Write a detailed a note on capacitive transducer signal conditioning.

[8+8]

5. (a) How the piezoelectric pick-up is useful for measuring torque and explain the same. (b) “Piezoelectric crystal as a measuring element” Explain it clearly.

[8+8]

6. (a) With the help of schematic diagram explain about floating mass low range angular velocity transducer. (b) Distinguish between Force-balance transducers with electrodynamic and electrostatic servo-actuators. [8+8] 1 of 2

Set No. 2

Code No: RR221002 7. (a) Write short notes on Infrared LEDs.

(b) Draw and explain the characteristics curve of phototransistor and photodiode. [6+10] 8. (a) List the detectors used in radiation and optical pyrometers. (b) Explain the factors affecting the static accuracy of filled in thermometers. [8+8] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: RR221002

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007 TRANSDUCERS IN INSTRUMENTATION ( Common to Electronics & Instrumentation Engineering and Electronics & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define the following static characteristics with necessary examples and graphs: i. ii. iii. iv. v.

Accuracy sensitivity static error Dead space Drift

(b) A voltage has a true value of 1.50 volts. An Analog indicating instrument with a scale range of 0-2.50 volts shows a voltage of 1.46 volts. What are the values of absolute error and correction. Express the error as a traction of the true value and the full-scale deflection. [10+6] 2. (a) Derive the differential equation describing the dynamics of mechanical translational system subjected to a step input force. Draw up a table showing analogy between mechanical and electrical quantities based upon force-voltage analogy . (b) An RC circuit consists of 1 µ F in series with a resistor of 5KΩ . A D.C voltage of 50 volts is suddenly applied across the circuit. Calculate the value of voltage after i. 5 m sec. ii. 25 m sec. [8+8] 3. (a) Explain the construction and operation of thermistors. (b) A thermistor has a resistance of 3980Ω at the ice point (00 C) and 794 Ω at 500 C. The resistance temperature relationship is given by RT = a R0 eb/T . calculate the constants a and b. [8+8] 4. (a) Describe the moving coil microphone system and identify the primary and secondary transducers of the arrangement. (b) Explain the basic principles of operation of variable permeability transducers and show how the phenomenon of permeability enables measurement of certain physical quantities. [8+8] 5. (a) Derive the expressions for frequency response characteristics of piezo electric transducers. 1 of 2

Set No. 3

Code No: RR221002

(b) Describe the uses of piezo electric materials and transducers.

[8+8]

6. (a) With the help of schematic diagram explain about floating mass low range angular velocity transducer. (b) Distinguish between Force-balance transducers with electrodynamic and electrostatic servo-actuators. [8+8] 7. (a) What is a RTD? Where it is used? (b) Explain a 4 lead measurement scheme of temperature measurement using resistance thermometer. [6+10] 8. Describe the working and construction of resistance thermometers. Describe the materials used for RTDs along with their properties. Sketch this typical characteristic curve. [16] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: RR221002

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007 TRANSDUCERS IN INSTRUMENTATION ( Common to Electronics & Instrumentation Engineering and Electronics & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define the following static characteristics with necessary examples and graphs: i. ii. iii. iv. v.

Accuracy sensitivity static error Dead space Drift

(b) A voltage has a true value of 1.50 volts. An Analog indicating instrument with a scale range of 0-2.50 volts shows a voltage of 1.46 volts. What are the values of absolute error and correction. Express the error as a traction of the true value and the full-scale deflection. [10+6] 2. (a) Derive the differential equation describing the time response of a series R-L-C circuit when a step voltage is applied to it. (b) A measuring system has an exponential response to step input. The time constant of the system is 2 sec. what is the time required for reading i. 50% ii. 80% of final steady state reading? [8+8] 3. (a) Explain how a thermo couple is used to measure temperature. (b) List and explain the three laws of thermo couples. (c) What are the common materials used for thermo couples.

[6+6+4]

4. (a) Show how output voltage signals proportional to linear displacements imparted to the movable plate of a parallel plate capacitor. (b) Discuss the problems encountered while measuring small displacements by capacitive transducers. [8+8] 5. (a) Derive the expressions for frequency response characteristics of piezo electric transducers. (b) Describe the uses of piezo electric materials and transducers.

[8+8]

6. (a) What is meant by ‘The Force-balance principle’. (b) List out the advantages and the disadvantages of Force-balance transducers and briefly explain their working with relevant diagram. [6+10] 1 of 2

Set No. 4

Code No: RR221002 7. (a) Write short notes on resistance thermometers.

(b) What are the possible sources of errors in filled in thermometers and how are they minimized. [6+10] 8. (a) List the detectors used in radiation and optical pyrometers. (b) Explain the factors affecting the static accuracy of filled in thermometers. [8+8] ⋆⋆⋆⋆⋆

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