JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III BASICS OF SENSORS TECHNOLOGY Previous Question Paper (August/September - 2021 - R18)
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Main
What is RTD? Explain the relationship between resistance and temperature for the RTD with Temperature resistance curve.
Answer
An RTD (Resistance Temperature Detector) is a temperature sensor that operates on the principle that the electrical resistance of a metal changes in a predictable, linear manner as its temperature changes. RTDs are typically constructed from high-purity metals, most commonly platinum, due to its excellent linearity, stability, and wide temperature range.
The relationship between resistance and temperature for an RTD is defined by the following equation:
Where:
- R(T) is the resistance at temperature T.
- R₀ is the resistance at a reference temperature (usually 0°C).
- α is the temperature coefficient of resistance, representing the sensitivity of the material.
- ΔT is the change in temperature from the reference point.
For higher precision, the relationship is expressed using the Callendar-Van Dusen equation, which accounts for non-linearities at higher temperatures:
The temperature-resistance curve is characterized by a positive temperature coefficient, meaning resistance increases as temperature rises. The curve is nearly linear over a wide operating range, making RTDs highly accurate for industrial temperature measurement. The slope of the curve represents the sensitivity of the sensor, where steeper slopes indicate better resolution. In the graphical representation, the x-axis represents temperature (°C) and the y-axis represents resistance (Ω), showing a straight-line progression for standard platinum RTDs (like the Pt100) within their calibrated operating range.
Explain the working principle of electromagnetic sensor.
Answer
An electromagnetic sensor operates based on the principle of electromagnetic induction, specifically Faraday's Law. The sensor detects changes in a magnetic field or the movement of a conductive object within a magnetic field to generate an electrical signal.
The working principle involves the following steps:
- A primary magnetic field is generated, typically by a permanent magnet or an energized coil.
- When a conductive or ferromagnetic target enters this field, it disrupts the magnetic flux lines.
- According to Faraday's Law, the rate of change of magnetic flux through a sensing coil induces an electromotive force (EMF) or voltage across the coil terminals.
- The magnitude and frequency of the induced voltage are proportional to the speed and proximity of the target object.
These sensors are widely used for detecting speed, position, and the presence of metallic objects without physical contact, making them highly reliable in industrial environments.
Give the differences between variable capacitor and differential capacitor sensors.
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What is piezoelectric effect? Explain the construction and working of piezoelectric type sensor. Also give its applications.
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Define thermal sensor. Classify various temperature sensors.
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With a neat diagram explain about the working of thermocouple.
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Explain the method of force measurement using Strain gauge load cell method.
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With a neat diagram, explain the construction and working of accelerometer.
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State different methods to measure viscosity. Explain any one method.
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Explain the interfacing of force sensor.
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Explain how sensors can be calibrated.
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