Matching Transducers and Their Measurement Applications

This question asks us to match different types of transducers with their typical applications. Transducers are devices that convert one form of energy into another, often used to convert physical quantities (like pressure, displacement, level) into electrical signals for measurement or control.

Analyzing Each Transducer and its Application

Let's examine each transducer listed in List I and determine its common application from List II.

• (A) Pirani gauge: A Pirani gauge is a type of thermal conductivity gauge used for measuring the pressure of a gas in a vacuum system. It works by sensing the change in thermal conductivity of the gas, which is related to its pressure. While primarily a pressure gauge for vacuum, its operation depends on gas properties and is often used in contexts related to managing gas flow in low-pressure environments. Therefore, matching it with 'Gas flow' makes sense in this context, likely implying flow measurement or control indirectly linked to pressure.
• (B) Dielectric gage: A dielectric gauge typically measures properties related to the dielectric constant of a material. A common application of measuring changes in dielectric constant is in determining the level of a liquid. As the liquid level changes, the medium between capacitor plates changes (e.g., from air to liquid or different liquids), altering the overall dielectric constant and thus the capacitance, which can be measured to find the level. This is a common method for capacitance level sensing. Thus, 'Liquid level' is a suitable application.
• (C) Magnetostriction gage: Magnetostriction is a property of ferromagnetic materials that causes them to change shape or dimensions when subjected to a magnetic field (Joule effect) and, conversely, to change their magnetization when subjected to mechanical stress (Villari effect). Magnetostrictive transducers are used in various applications including sensing position, force, and generating/detecting ultrasonic waves. One significant application related to vibrations or waves is the generation and detection of sound, particularly ultrasonic sound, making 'Sound' a plausible application, possibly in sonar or ultrasonic testing.
• (D) Variable capacitance pressure gage: A variable capacitance pressure gauge uses a diaphragm that deflects under pressure. This deflection causes a change in the capacitance between the diaphragm (or a plate attached to it) and a fixed plate. While it measures pressure, the fundamental principle involves the mechanical displacement of the diaphragm changing the capacitance. Therefore, this type of gauge directly relates a pressure input to a displacement output (of the diaphragm), which is then converted to a capacitance change. Thus, it can be considered a device that measures displacement caused by pressure, or more broadly, capacitance change due to displacement, making 'Displacement' a relevant match.

Summary of Matches

Based on the analysis, the probable matches are:

• (A) Pirani gauge → (III) Gas flow
• (B) Dielectric gage → (I) Liquid level
• (C) Magnetostriction gage → (IV) Sound
• (D) Variable capacitance pressure gage → (II) Displacement

Let's compare this with the provided options.

This set of matches corresponds to option 4.

Revision Table: Transducers and Applications

Additional Information: Exploring Transducer Types

Transducers are essential components in measurement systems and automation. They bridge the gap between physical phenomena and electrical signals that can be processed by computers or other electronic devices. Here are some key points about the types mentioned and related concepts:

• Pirani Gauge: Suitable for pressures typically ranging from 0.5 torr down to $10^{-4}$ torr. Higher pressures reduce its sensitivity.
• Capacitance Transducers: Highly versatile, used for measuring displacement, pressure, level, and even humidity. They offer good sensitivity and frequency response. The change in capacitance $\Delta C$ is often related to a change in distance between plates or a change in dielectric material.
• Magnetostrictive Transducers: Known for their robustness and ability to operate in harsh environments. Applications include non-destructive testing (NDT) using ultrasonic waves, and level sensing in tanks containing volatile liquids.
• Pressure Transducers: Devices like the variable capacitance pressure gauge are crucial in many industries. They convert pressure into an electrical signal. Other types include strain gauge-based, piezoelectric, and resonant pressure transducers. The choice depends on the required pressure range, accuracy, and environmental conditions.
• Displacement Transducers: Used to measure linear or angular position. Besides variable capacitance, common types include LVDT (Linear Variable Differential Transformer), potentiometers, optical encoders, and ultrasonic sensors.

Understanding the operating principles of various transducers is key to selecting the appropriate one for a specific measurement task.