JNTU
JNTU B.Tech III SIGNAL CONDITIONING CIRCUITS Previous Question Paper (March - 2021 - R13)
Answer any five questions. All questions carry equal marks.
Main
What is ground and ground loops? Describe the methods for reducing interference in instrumentation with neat diagrams.
Answer
Ground is a common reference point in an electrical circuit, ideally at zero potential, providing a return path for current. A ground loop occurs when two or more points in a circuit are connected to ground at different physical locations, creating a potential difference between them. This causes circulating currents to flow through the ground conductor, inducing noise and interference in sensitive instrumentation signals.
Methods to reduce interference include:
- Single-Point Grounding: Connecting all signal grounds to a single physical point to prevent circulating currents.
- Differential Signaling: Using balanced transmission lines to reject common-mode noise.
- Shielding and Isolation: Employing Faraday shields or galvanic isolation (e.g., opto-isolators or transformers) to break the conductive path of the ground loop.
- Cable Routing: Keeping signal cables away from high-power lines and using twisted-pair wiring to cancel electromagnetic interference.
A 350 Ω strain gauge having G = 2.1 is attached to an aluminum strut (E=73 GPa). The outside diameter is 47.5 mm. Calculate the change in the resistance when the strut supports a 1000 kg load.
Answer
Given: Resistance R = 350 Ω, Gauge factor G = 2.1, Young's modulus E = 73 GPa = 73 × 109 N/m2, Load F = 1000 kg × 9.81 m/s2 = 9810 N, Diameter d = 47.5 mm = 0.0475 m.
First, calculate the cross-sectional area A of the strut:
Next, calculate the stress (σ) and strain (ε):
Finally, calculate the change in resistance (ΔR):
Explain the operation of wheat stone bridge when the resistors are in series and parallel. How wheat stone bridge uses in light detector.
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Why use a three op-amp instrumentation amplifier? Draw and explain the practical instrumentation amplifier.
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Sketch and explain simplified resolver to digital converter architecture.
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Justify, why the Circuits often require an integrated AC power source as the optimum strategy to reduce size.
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Suggest a design to reduce the noise and increase the bandwidth in carrier amplifiers in analog devices.
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List the limitations of analog signal conditioning approach and propose an alternative design methodology using digital signal processors.
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Why coupling capacitor should be very large in chopper amplifiers and draw the relevant plots between V and T when both switches are closed and open.
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Specify an example for leakage current measurement repeatability and design a circuit for measurement of integration time for leakage currents.
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Differentiate electrometer and nonvoltmeter characteristics in terms of input offset current and impedance.
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What is a resistor noise? Name and describe various noise standards in terms of low noise resistor.
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Draw and explain the block diagram of digital tachometer to measure velocity of a motor shaft.
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What is an ARCNET bus and specify the features based on three different applications.
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List the electrical characteristics of ultrasonic sensors and describe the construction and operation principle of open structure type.
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Justify MOSFET as a switch and discuss the impact of MOSFET based sensors in manufacturing industry.
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