B.Tech VII (Seventh) Semester Examination 2011-12
Course Code: EEC701 Paper ID: 0967117
Digital Instrumentation
Time: 3 Hours Max. Marks: 70 Max Marks: 75
Note: Attempt six questions in all. Q. No. 1 is compulsory.
1. Answer any five of the following (limit your answer in 50 words). (4x5=20)
a) Define the following:
i) Gross Error.
ii) Systematic Error.
iii) Random Error.
iv) Standard deviation.
b) Explain photoelectric effect.
c) Compare effects of circuit loading, when using an ac voltmeter with half wave rectification against those when using an ac voltmeter with full wave rectification.
d) Discuss the principle of operation and circuit diagram of digital oscilloscope.
e) Write short note on the following regarding digital voltmeter:
i) Resolution.
ii) Sensitivity.
iii) Accuracy.
iv) Settling time.
f) What are transducers? Explain different types of transducers.
g) Enumerate the differences between Sampling Voltmeter and Digital Voltmeter.
h) A D/A converter have 6 bits and reference voltage of 10 volts. Calculate the value of R such that maximum value of output current does not exceed 10mA. Find also the smallest quantized value of output current.
2. a) A resistance is determined by voltmeter ammeter method. Voltmeter reads 100 Volts with a probable error of ±12 volt and ammeter reads 10 ampere with a probable error of ±2 ampere. Determine the probable error in the computed value of resistance. (5)
b) An oscilloscope is used for the measurement of phase shift. The phase shift is given by:
Φ= sin-1(B/A).The measurement made are: A= 25±0.5mm, B= 15±0.5 mm. Calculate the nominal value of phase angle and estimate the uncertainty in measurement. (5)
3. a) Which meter has a greater sensitivity: Meter A having a range of 0-10volt and a multiplier resistance of 18 kΩ or meter B with a range of 0-300 volt and a multiplier resistance of 298kΩ ?
Both meter movements have a resistance of 2 kΩ. (5)
b) Explain the working of Megger with neat diagram. (5)
4. What are A/D converters? Explain their types with neat diagrams. (10)
5. a) Describe the phenomenon of synchronization of vertical input signal to its sweep generator in oscilloscope. (5)
b) If the vertical amplifier of an oscilloscope has a bandwidth of 15MHz, what is the fastest rise time that an input may have to be displayed without distortion? (5)
6. Explain different types of probes used in oscilloscopes. (10)
7. The four arms of Maxwell’s capacitance bridge at balance are:
Arm AB, an unknown inductanceL1, having an inherent resistance R1
Arm BC, a non inductive resistance of 1000Ω
Arm CD, a capacitor of 0.5 µF in parallel with a Resistance of 1000Ω.
Arm DA, a Resistance of 1000 Ω
Derive the equation of balance for the bridge and determine the value of R1 and L1. Draw the phasor diagram of the bridge under balance condition. (10)
8. A thermocouple circuit uses a chromel allumel thermocouple which gives an EMF of 33.3 volt when measuring a temperature of 800°C. The resistance of the meter coil, Rm is 50 Ω and a current of 0.1 mA gives full scale deflection. The resistance of junction and leads, Re is 12 Ω. Calculate:
a) Resistance of the series resistance if a temperature of 800 °C is to give full scale deflection.
b) Approximate error due to rise of 1Ω in Re.
c) Approximate error due to rise of 10°C in the copper coil of the meter. The resistance temperature coefficient is 0.00426/ °C. (10)