}. Mid Semester Exam

Electronic Instrumentation (EE370)

Max. Marks: 40

1) Explain with an example the difference between random error and systematic error[2]

2) Can we use Hay's bridge to measure inductance of coils having small Q values?~iscuss.; Q; , [2]

3) ~eatstone bridge, all the four resistances are equal to R ohm. What should bethe voltmeter resistance so that the error is less than one percent? [2]

4) Explain how Schering bridge can be used to measure the dielectric properties of amaterial [2]

5) A liquid level sensor has an input range of 0 to 15 cm. Use the calibration resultsgiven in the table to estimate the maximum hysteresis as a percentage of full scaledeflection [2]

Level (em) 0.0 1.5 3.0 4.5 6.0 7.5 9.0 10.5 12.0 13.5 15.0alP volts 0.00 0.35 1.42 2.40 3.43 4.35 5.61 6.50 7.77 8.85 10.2(h increasing)alP volts 0.14 1.25 2.32 3.55 4.43 5.70 6.78 7.80 8.87 9.65 10.2(h decreasing)

6) The following results were obtained when a pressure transducer was tested in alaboratory under the following conditions:a) Ambient temperature 20°C, Supply voltage 10 V (standard)b) Ambient temperature 20°C, Supply voltage 12 Vc) Ambient temperature 25°C, Supply voltage 10 V

Input (bar)Output a 2 4 6 8 10(mA)a) 4 7.2 10.4 13.6 16.8 20b) 4 8.4 12.8 17.2 21.6 26c) 6 9.2 12.4 15.6 18.8 22Determine the values of KM, KJ, a,K associated with the generalized modelequation: a = (K + KMlM)l + a + KIll [2]

7) A periodic signal is to be measured with a first order instrument having a timeconstant of 3 second. If the dynamic error of ±5% can be tolerated, find the highestfrequency of input signal that can be measured by the instrument. [3]

8) A balloon carrying a first order thermometer with a 15 second time constant risesthrough the atmosphere at 6 m/s. Assume temperature varies with altitude at0.15°C/30 metre. The balloon radios temperature and altitude readings back to the

ground. At 3000 metre, the balloon says the temperature is O°c. What is the truealtitude at which O°Coccurs? What is the correct temperature at 3000 metre? [4+1]

9) A strain gauge with Rg = 350 .n (0.25 Watt) and A = 2.05 is used in arm Rl of aconstant voltage Wheatstone bridge. If the available power supply is limited to 28volt, determine (a)The values of R2, R3, R4 needed to maximize the output voltage (b)sensitivity of the bridge (~) (c) If the strain gauge is subjected to a strain of

flR1/R1

1200 J.linch/inch, determine the output voltage [3+1+1]

10) An ac bridge has in arm AB a pure capacitance of 0.2 J.lF; in arm BC a pure resistanceof 500 .n, in arm CD a series combination of R = 50 .n and L = 0.1 H. Arm DAconsists of a capacitor C = 0.4 J.lF in series with a variable resistor Rs , w =5000 rad/s, (a) Find the value of Rs to obtain bridge balance (b) Can completebalance be attained by the adjustment of Rs ? If not, specify the modificationrequired in the circuit to achieve balance. [3+2]

11) An experiment is conducted to calibrate a copper-constantan thermocouple. With

cold junction at O°C, emf obtained at boiling point of water (100°C) and boiling pointof sulphur (445°C) are 5 mV and 25 mV, respectively. If the relation is assumed to be

et1-t2 = aCtl - t2) + bCtr - tD,(a) Determine the constants a, b [2](b) The above thermocouple indicates 2mV with the cold junction at 40°C.

Determine the unknown hot junction temperature. [2](c) If the cold junction is maintained at 40°C, what would be the emf when hotjunction temperature is at 500°C? [1]

12) The discharge coefficient Cq of an orifice can be found by collecting the water thatflows through during a timed interval when it is under a constant head h. Theformula is Cq = ~ Find Cq and its possible error if:

tpA 2gh

rrd2 mA =4' W = 390 ± 0.25 kg, t = 600 ± 2 s,9 = 9.81 ± 0.1% S2'

kgP = 1050 ± 0.1%-3,h = 3.6 ± 0.03 m d = 12 ± 0.03 mm,

m[5]