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1 IV SEMESTER FINAL EXAMINATION SUBJECT: BEG232EC, Instrumentation Candidates are required to give their answers in their own words as far as practicable. The figure in the margin indicates full marks. Q. [1] [a] Explain the functions of the sensor, signal conditioner, signal processing and display unit of a measurement system. [6] [b] Discuss the three general classes of measurement errors. Explain how they can be eliminated. [7] [c] A voltmeter whose accuracy is 2% of the full scale reading is used on its 0-150V scale. The voltages measured by meter are 15v and 82v. Calculate the possible percentage error of both readings. Comment upon your answer. [3] Q. [2] [a] Explain principle of operation of linear variable differential transformer (LVDT) displacement transducer. What operational design factors limit the performance of an LVDT in term of linearity, sensitivity and resolution? [8] [b] In order to measure strain in a cantilive veam, a single strain gauge of resistance 1kΩ and gauge factor 2 with a temperature coefficient / o C is mounted on the beam and connected in one arm of the bridge circuit. The adjustment are has a resistor of 1kΩ resistance each. The bridge detector resistance is 100Ω each and its sensitivity is 10mm/ µa. The input voltage to the bridge circuit is 10V. Calculate: (i) (ii) the detector defection for 0.1% strain. The charge in effective strain indicated when the room temperature increases by 10 o C. Q. [3] [a] What are the quantities required to be measured for a vibrating system? Explain how are they measured using seismic transducer. [3+5] [b] A linear resistance pot is 50mm long and is uniformly wound with a wire having a resistance of Ω under normal condition, the slider is at the center of the pot. Find the linear displacement when the resistance of the pot measured by wheatstone bridge for two cases (i) 3850 Ω (ii) 7560 Ω. If it is possible to measure a minimum value of 10 Ω resistance with the above arrangement, find the resolution of the pot. [5] [c] What do you understand by piezoelectric effect? Draw the equivalent circuit of such transducers. [3] Q. [4] [a] Describe how digital to analog conversion is achieved using the weighted binary resistor network. What are the limitations of this method? [6] [b] A 8 bit D/A converter has a reference voltage of 12V. It uses a weighted resistive network. Find the minimum value of R to be connected in the MSB input circuit such that the maximum output current does not exceed 10mA. Also find the smallest value of current. [6] [c] A good quality analog transducer having an input of 0-8V is able to distinguish a change of 1mV in its input signal. Calculate the number of bits the A/D converter should have in order to achieve a resolution not lower than of the analog device. [4] Q. [5] [a] Describe the following types of passive RC filters: (i) low pass (ii) high pass (iii) band pass (iv) band stop. Draw their ideal and practical characteristics. [8] [b] Describe the working and construction of resistance thermometers. Describe the materials used for RTDs, along with their properties. [8] Q. [6] [a] Describe the different methods of data transmission. Explain the block diagram of general telemetry system. [3+5] [b] What is an X-Y recorder? Explain with suitable circuit diagram the working of an X-Y recorder. Describe its application. [1+5+2]

2 IV SEMESTER FINAL EXAMINATION Candidates are required to give their answers in their own words as far as practicable. The figure in the margin indicates full marks. Q. [1] [a] Draw the block diagram of a generalized instrumentation system and explain the functions of each block. [7] [b] Precision is necessary by not sufficient condition for accuracy. Explain this statement. [4] [c] The current passing through a resistor of (100±0.2)Ω is (0.00±0.01)A. Using the relationship P = I 2 R, calculate dissipation and the limiting error in the computed value. Q. [2] [a] Explain the theory and working principle of Wheatstone bridge for measurement of medium resistance. [7] [b] What are gross errors and how can they be eliminated? [3] [c] An ac bridge is in balance with the following constants: arm AB: R =450Ω, arm BC; R =300Ω in series with C = µf, arm CD known, arm DA: R-200Ω is series with L =15.9mH. If the oscillator frequency is 1 khz, find the constants of arm CD. [6] Q. [3] [a] Describe the method of measurement of temperature with the use of [i] RTD and [ii] Therimistors with neat diagrams. Describe their advantages and limitations. [4+4] [b] What are active and passive transducer? Give suitable examples. [3] [c] A strain gauge is bonded to a beam 0.1m long and has a corss-sectional area 4 cm 2. Young s modulus for steel is N/m 2. The strain gauge has an unstrained resistance of 240Ω and a gauge factor 2.2. When a load is applied, the resistance of gauge changes by 0.13 Ω. Calculate the change in length of steel beam and the amount of force applied to the beam. [5] Q. [4] [a] What are the uses of LVDT? Describe its construction and working principle. [2+6] [b] A 5-bit converter is used for a dc voltage range of 0-10V. Find the weight of MSB and LSB. Also find the exact range of converter and the error. Find the error if 10-bit converter is used and comment on the result. [6+2] Q. [5] [a] Explain analog to digital conversion process using successive approximation method. [5] [b] Describe with circuit diagram how an Op-AMP acts as (i) a summer and (ii) a differential amplifier. [3+3] [c] A band pass filter consists of two RC networks connected is cascade. The low pass filter consists of R 1 = 10 kω and C 1 = 100nF and the high pass filter consists of R 2 = 1MΩ and C 2 = 0.01 µf. Find the lower and upper cut-off frequencies and the passband gain. [5] Q. [6] [a] Explain a general telemetry system with the help of block diagram. Explain the advantages of digital data transmission over analog data transmission. [4+4] [b] What is strip chart recorder? Why is it called x-t recorder too? Describe the working principles of a basic type of strip chat recorder. Also list its advantages. [8]

3 IV SEMESTER BACK-PAPER EXAMINATION Candidates are required to give their answers in their own words as far as practicable. All questions carry equal marks. The marks allotted for each sub-question is specified along its side. Q. [1] [a] Describe the functions of the main components of general instrumentation system. [6] [b] What is signal? Differentiate between analog and digital signal. [1+2] [c] Describe the static and dynamic characteristics of measuring devices. [7] Q. [2] [a] How can you measure unknown inductance using Maxwell s bridge? Explain the demerits of this bridge. [7] [b] What do you mean by loading effects in measurements? How this effect is pronounced while measuring voltage across the circuit? [5] [c] Define error in instrumentation? Classify them and explain any two. [1+2+1] Q. [3] [a] How the differential capacitor arrangement is use to calculate the output voltage for the small change in input displacement. [b] What is piezoelectric effect? Draw the equivalent circuit of such a transducer. [4] [c] What will be the 5000 Ω/V meter read on a 0-5V scale when connected to the circuit of figure below across 100kΩ Q. [4] [a] Explain the operation of LVDT for the measurement of input displacement with necessary diagrams. [6] [b] How analog to digital conversion is possible using successive approximation method? Describe with a flow chart. [4+1] [c] A compressive force is applied to a structural member. The strain is 5 microstrain. Two separate strain gauges are attached to the structural member, one in nickel wire strain gauge having strain gauge-12.1 and the other is nichrome wire strain gauge having gauge factor 3. Calculate the value of resistance of the gauge after they are strained. The resistance before being strained is 115 Ω. [5] Q. [5] [a] What is telemetry? Explain FM/FM radio telemetry system of data transmission with necessary diagram. [2+5] [b] What is fibre optic technology? How it is used in communication system? List the advantages of fiber optic transmission over other forms of transmission. [3+2] [c] A quartz piezoelectric crystal having a thickness 2.5mm and voltage sensitivity of V-m/l subjected to a pressure of 1.8MN/m 2. Calculate the voltage output if the permittivity of quartz is F/m. Calculate its charge sensitivity. [4] Q. [6] [a] Classify types of output devices with suitable example. How x-y plotter can be used as data recording device? [b] Write short notes on (any FOUR): [4 2] [i] Interference in Instrumentation [ii] Types of Signal Conditioning. [iii] Sample and Holds circuits. [iv] Night Vision Helicopter. [v] Shielding and Grounding.

4 IV SEMESTER FINAL EXAMINATION Candidates are required to give their answers in their own words as far as practicable. All questions carry equal marks. The marks allotted for each sub-question is specified along its side. Q. [1] [a] Describe a general instrumentation system with block diagram. [4] [b] Differentiate between analog and digital signals. [4] [c] Explain different types of errors in instrumentation. How can these errors be estimated? [8] Q. [2] [a] How can the unknown inductance be measured using Maxwell s Bridge? Explain the demerits of this bridge. [6+2] [b] In a Wheatstone Bridge the ratio of the resistances (R 2 /R 1 ) of the ratio arms is 10. Under Balanced condition, calculate the value of unknown resistance if the resistance of the balanced arm (R 3 ) is 150 Ω. For the same bride, calculate the deflection of the galvanometer if there is a 5 Ω unbalance in the value of the resistance being measured. Given values: Current Sensitivity of the Galvanometer = 15mm/ µa R 1 = 100 Ω Internal Resistance of Galvanometer = 450 Ω Neglect the internal resistance of the source. Q. [3] [a] is loading error?. [b] Two plates of parallel plate capacitor transducer are 30mm apart and the space is filled with two dielectric materials, one material is 1cm thick with dielectric constant of 4 and the other material is 20mm thick with a dielectric constant of 11. IF the capacitive transducer was to be made up of a single dielectric medium, what is the dielectric constant of that material? [4] [c] A potentiometer has resistance of 5000 Ω and is rated 3W. What is the maximum allowable excitation voltage? If the supply to the potentiometer is maximum allowable voltage, calculate the value of the potentiometer is 0.15m and there are 200 turns. [4] Q. [4] [a] Explain the Linear Variable Differential Transformer (LVDT) transducer with necessary diagram. [8] [b] A resistor is measured by the voltmeter-ammeter method. The voltmeter reading is 123.4V. on the 250V scale and the ammeter reading 283.5mA on 500mA scale. Both meters are guaranteed to be accurate within ±1 percent of full-scale reading. Calculate (a) the indicated value of the resistance and (b) the limits within which you can guarantee the result. [ ] [c] A resistance wire strain gauge having a nominal resistance of 350 Ω is subjected a strain of 500 micro strains. Find the change in the value of resistance neglecting the piezoresistive effect. The gauge factor is 2.5. Q. [5] [a]..are interference signals? eliminated? [4+4] [b] Describe the Ladder Resistive type D/A converters. Show that the weight of MSB is 32 times more than that of LSB in a 6-bit converter. [4+4] Q. [6] [a] Describe the Fiber Transmission System. Explain its merits and demerits. [4+4] [b] Write short notes on any TWO: [4+4] [i] Chart Plotter [ii] Voltage Telemetry System. [iii] X-Y Recorder.

5 IV SEMESTER FINAL EXAMINATION Candidates are required to give their answers in their own words as far as practicable. All questions carry equal marks. The marks allotted for each sub-question is specified along its side. Attempt ALL questions. Q. [1] [a] With the help of block diagram, design a system to maintain the temperature of a room always constant at 20 o C using computer as central control to the output devices. Use block diagram technique for your design and explain each blocks in detail. The design should cover all the climatic conditions. [10] [b] What do you know about the limiting error in instrumentation? Explain the static performance parameter of an instrument. [2+4] Q. [2] [a] Explain the errors in Wheatstone bridge. With the necessary diagrams and derivations, explain the Kelvin Bridge to overcome one of the errors of Wheatstone bridge. [2+4] [b] An AC bridge has in arm AB a pure capacitance of 0.2 µf; in arm BC, a pure resistance of 500Ω; in arm CD, a series combination of R = 500Ω and L = 0.1H arm DA consists of a capacitor C = 0.4 µf in series with a variable resistance Rs. ω = 5000 rad/s. [i] Find the value of Rs to obtain bridge balance. [3] [ii] Can complete balance be attained by the adjustment of Rs? If not, specify the position and the value of an adjustable resistance to complete balance. [3] [c] How can you say that the piezoelectric transducer is an active transducer? Prove that the voltage sensitivity of piezoelectric transducer is the ratio of an electric field strength and an applied pressure. Neglect the internal resistance of the source. [1+3] Q. [3] [a] List at least four transducers that arc-used for-temperature measurement. With the help of necessary diagram and expressions, explain the loading effect due to potentiometric transducer comparing the result with no load condition. Also find out the error due to loading effect. Draw the necessary curves. [2+7] [b] A parallel plate air space capacitor has an effective plate area of m 2, and the distance between the plate is 1mm. If the relative permittivity for air is 1.006, calculate the displacement sensitivity of the device. [3] [c] Why is signal conditioning necessary? With the help of necessary diagrams derive the expression of the cutoff frequency of high pass filter. [1+3] Q. [4] [a] During a final year project, one of the students encountered a problem in using different transducers for the reason that those transducers output voltage is very small to drive the output device and there are other circuits due to which he is unable to collect the information of his interest. With the help of necessary diagrams, derivations and explanations, prove that the above problem can be solved by using an instrumentation amplifier. [6] [b] How can you say that the interference is harmful to the instrumentation system? Explain the types of interference that are generated in the system. [1+4] [c] Explain the steps followed in the process of Analog to Digital conversion technique. [2+3] Q. [5] [a] What is telemetry? Explain the block diagram of telemetry system. [1+4] [b] What is modulation? Why it is necessary? Explain digital modulation techniques. [1+1+3] [c] Explain in detail the X-Y plotter. [6]

Question Paper Code : B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER Third Semester. Electrical and Electronics Engineering

Question Paper Code : B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER Third Semester. Electrical and Electronics Engineering Question Paper Code : 31391 B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2013. Third Semester Electrical and Electronics Engineering EE 2201/EE 33/EI 1202/10133 EE 302/080280016 MEASUREMENTS AND