Question

Basically, _____ circuits are Wheatstone Bridge circuits.

• A. Pyrometer
• B. Bimetallic thermometer
• C. Thermocouple
• D. Resistance thermometer

Hint:

RTD sensors are almost always connected in a three-wire or four-wire Wheatstone Bridge configuration to compensate for lead-wire resistance changes, ensuring high accuracy over long distances.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
A Wheatstone Bridge is an electrical circuit configuration used to measure an unknown electrical resistance with high accuracy by balancing two legs of a bridge circuit.
Many temperature sensors operate by converting a temperature change into a variation in electrical resistance, which is then measured using a bridge configuration.

Step 2: Detailed Explation:
Different temperature measuring devices utilize distinct physical principles:
- Resistance Thermometer (or Resistance Temperature Detector - RTD): Operates on the principle that the electrical resistance of fine metal wires (typically platinum, nickel, or copper) changes predictably with temperature.
Because these resistance changes are small, standard ohmmeters lack the sensitivity to measure them accurately.
Therefore, RTDs are integrated into a Wheatstone Bridge circuit, where the changing resistance of the RTD alters the balance of the bridge, producing a measurable output voltage proportiol to temperature.
- Thermocouple: Works on the Seebeck effect, generating an electromotive force (EMF) at the junction of two dissimilar metals when subjected to a temperature gradient.
This voltage is measured directly using a millivoltmeter rather than a Wheatstone Bridge.
- Pyrometer: A non-contact sensor that measures thermal radiation emitted by a hot body to determine its temperature.
- Bimetallic Thermometer: Utilizes the difference in thermal expansion coefficients of two bonded metal strips to produce a mechanical displacement.

Step 3: Fil Answer:
Resistance thermometers (RTDs) rely on Wheatstone Bridge circuits to convert small resistance changes into precise temperature readings.
Hence, the correct option is (D).