BE Computer Engineering (Pokhara University) Instrumentation (PU, ELE 172) Question Paper 2079

(a) With the help of a functional block diagram, describe the generalized configuration of a measurement system, clearly explaining the role of the primary sensing element, variable conversion element, variable manipulation element, data transmission element and data presentation element. [8]

(b) Define accuracy, precision, resolution and sensitivity of an instrument. Distinguish between accuracy and precision with a suitable target-diagram illustration. [6]

(a) Explain the principle of operation of a Linear Variable Differential Transformer (LVDT) with a neat sketch of its construction and output characteristic curve. State two advantages and two limitations of the LVDT for displacement measurement. [8]

(b) A platinum resistance thermometer has a resistance of 100 Ω at 0 °C and a temperature coefficient of resistance α = 0.00385 /°C. It is connected in one arm of a Wheatstone bridge. Determine the resistance of the element at 150 °C and explain how a three-wire connection compensates for lead-wire resistance. [6]

(a) Draw the block diagram of a typical digital data acquisition system (DAS) and explain the function of each block, including the multiplexer, sample-and-hold circuit, ADC and the role of the controller/computer. [7]

(b) State the Nyquist sampling theorem. A signal contains frequency components up to 4 kHz. Determine the minimum sampling frequency required and explain what aliasing is and how an anti-aliasing filter prevents it. [5]

(a) Draw the circuit of an instrumentation amplifier using three operational amplifiers and derive the expression for its overall voltage gain. Explain why a high common-mode rejection ratio (CMRR) is desirable in signal conditioning of bridge transducer outputs. [7]

(b) Explain the operation of a Wheatstone bridge in its balanced and unbalanced (deflection) modes, and state when each mode is preferred. [3]

Classify the errors that occur in measurement systems into gross, systematic and random errors with one example of each. A voltage is measured five times giving readings of 50.1, 49.8, 50.0, 50.2 and 49.9 V. Compute the arithmetic mean, the standard deviation and the probable error of the readings.

Define a transducer and differentiate between active and passive transducers with two examples of each. Explain, with a sketch, the working principle of a piezoelectric transducer and state one practical application.

Explain the working principle of a dual-slope integrating type digital voltmeter (DVM) with the help of a waveform diagram. State two advantages of the dual-slope technique over the ramp (single-slope) type DVM.

Describe the construction and working of a Permanent Magnet Moving Coil (PMMC) instrument with a neat diagram. Explain how a PMMC galvanometer can be converted into (i) an ammeter using a shunt and (ii) a voltmeter using a series multiplier resistance.

(a) Compare Light Emitting Diode (LED) and Liquid Crystal Display (LCD) as digital display devices in terms of power consumption, visibility and operating principle. [4]

(b) Explain how a seven-segment display is used to represent decimal digits. [2]

With a neat block diagram, explain the working of a successive approximation type Analog-to-Digital Converter (ADC). For an n-bit ADC, state the expression for resolution and quantization error, and find the resolution of an 8-bit ADC with a full-scale range of 0 to 5 V.

Explain the principle of a strain gauge and define its gauge factor. A strain gauge with a gauge factor of 2.0 and an unstrained resistance of 120 Ω undergoes a strain of 500 microstrain. Calculate the change in resistance of the gauge.

With the help of a block diagram, explain the working of a cathode ray oscilloscope (CRO). Describe how the oscilloscope is used to measure the frequency and phase difference of two sinusoidal signals using Lissajous figures.