Code: AE12                                      Subject: INSTRUMENTATION AND MEASUREMENT

Time: 3 Hours                                                                                                     Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1       Choose the correct or best alternative in the following:                                         (2x10)

            a.   The error due to the constant zero offset in a meter can be classified as

(A) Random error                                      (B) Systematic error

(C) Standard error                                     (D) Uncontrollable error

            b.   Kelvin bridge is used mainly for measurement of 

(A) Very small values of resistances

(B) Very high values of resistances that cannot be measured by Wheatsone’s

                        bridge

      (C) Inductance of  transformer windings

(D) Capacitances used in tuning  circuits

            c.   The  value nearest to the resonant frequency of  a Wien bridge of an  

                                                                        audio frequency generator having its resistors of 10 KΩ each and capacitors of 0.1µF each is

(A) 15.9 Hz                                   (B) 159 Hz      

(C) 1.59 kHz                                 (D) 15 kHz

            d.  The triggered horizontal sweep is a CRO is generated by

(A) Pulsing a trigger circuit manually

      (B) The signal being measured

(C) A Hall probe

      (D) A differentiating circuit at the signal input terminal

            e.   The frequency range of a frequency counter can be increased by

(A) Increasing the clock speed

(B) Increasing the number of digits in the display unit

(C) using a prescaler or divide-by-N counter

(D) An A/D converter of suitable number of output bits

            f.    A thermocouple RF ammeter measures a transmitter line current of 1A    

                                                                        into a load of 50 . The power delivered to the load is

(A) 50 W                                       (B) 500 W      

(C) 5 W                                         (D) 5 mW

            g.   Quieting method is a technique used in

(A)  AM alignment                                    

(B)  FM alignment

(C)  Transmitter output impedance measurement

(D)  Receiver sensitivity measurement

            h.  The principle of working of harmonic distortion analyzer is based on

(A)  Heterodyning of two frequencies

(B)  amplification of fundamental frequency

(C)  Suppression of fundamental frequency

(D)  Suppression of harmonics

            i.    Which of the following material may be used for obtaining output of   

                 electrical potential by applying the mechanical force ?

(A)  Ferrite                                                (B) Alloy of Rhodium and Platinum

      (C)  Rochelle Salt                           (D) Tungsten

            j.    A 12-bit successive approximation A/D converter uses a clock of            

                  2  kHz.   Its conversion time is

(A) 3.6 ns                                      (B) 4.8 ms       

(C) 2.4 ms                                     (D) 6ms

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Distinguish between ‘passive’ and ‘active’ transducers. Give two examples of each.                        (6)

             b.   Explain the following terms as understood in measurement practice :

(A) Accuracy                                      (B) Static error

(C) Repeatability                                 (D) Uncertainty                                          

(E) Resolution                                                                                                 (10)

Q.3     a.   Draw the circuit diagram of amplified current and voltage meter and         describe its operation. What are its limitations?                                                      (8)

             b.   Write the circuit of Maxwell’s bridge. Derive the conditions for its           balance, and solve the problem given below.

                   A Maxwell Bridge is used to measure an inductive impedance Zx

                   composed of Rx and Lx in series. The bridge shows balance for 

                   R1 = 450 kΩ, C1 = 0.012 µF, R2= 5 kΩ and R3= 100 kΩ. Find the values of Rx and Lx.                                   (8)

Q.4     a.  Explain ‘indirect’ method of frequency  synthesis’ using phase-locked loop.          (8)

             b.  Write block schematic of digital frequency meter and explain its operation.           (8)

Q.5     a.   Show the circuit of a 10-to-1 probe of an oscilloscope and describe its           operation. Explain the effects of incorrect setting of the probe taking the                                                              

example of a fast risetime pulse.                                                                         (8)

             b.  Explain how modulation characteristics of a modulated waveform may

                   be measured using oscilloscope.                                                                         (8)

Q.6     a.   Delineate, using a circuit schematic, how hysterisis loop of a ring specimen

                   of magnetic material can be traced  using a CRO.                                               (8)

             b.   How may the RF power be measured by measurement of load voltage?

                   Explain by drawing a circuit scheme.               (8)

Q.7     a.   Define `sensitivity’ of a receiver.  Explain with diagrams, any one method

                   of measuring  receiver sensitivity.                                                                        (8)

             b.   Show a set up of equipments and circuits for FM receiver sweep alignment

                   and describe the procedure for alignment.                                                           (8)

Q.8     a.   What is the function performed by a wave analyzer? Draw a block diagram

                   of heterodyning wave analyzer and explain its working.                                       (8)

             b.   Draw a circuit of 4-bit digital-to-analog converter based on R-2R ladder

                   network. Deduce the value of the output voltage as a fraction of the

                   reference voltage for a digital input 0100                                                             (8)

Q.9     a.   Define the ‘gauge factor’ of a resistive strain gauge. Show a Wheatstone

                   bridge circuitry for strain measurement with the facility  for ‘zero’ and

                                                                              ‘sensitivity’– adjustment, and describe its operation.                   (2+6)

             b.   Explain the basic principle of working of thermocouples. Give examples

                   of at least two metal pairs useful in constructing thermocouples.                           (8)