Sensor physics — RTDs, strain gauges, and many pressure transducers operate on which fundamental effect when used in measurement bridges?

Introduction / Context:
Instrumentation frequently uses passive transducers in Wheatstone bridges or constant-current excitation schemes. Recognizing the underlying transduction principle helps select interfaces and error-compensation strategies. RTDs, strain gauges, and many pressure sensors share a common operating basis in how they change an electrical quantity with the measured stimulus.

Given Data / Assumptions:

• RTD: resistance changes with temperature (positive temperature coefficient).
• Strain gauge: resistance changes with strain via the piezoresistive effect and geometry.
• Many pressure transducers: use resistive strain gauges bonded to diaphragms.

Concept / Approach:
In all three examples, the measurand changes the device’s resistance. Bridge circuits convert minute resistance changes into measurable voltage differences. Although some pressure sensors are capacitive or piezoelectric, the most ubiquitous “foil gauge on diaphragm” pressure transducers are resistive devices at their core. Therefore, categorizing the trio as “resistive” is accurate for typical instructional contexts.

Step-by-Step Solution:

Verification / Alternative check:
Application notes detail linearization for RTDs, gauge factor for strain gauges, and bridge sensitivity for pressure transducers using resistive elements.

Why Other Options Are Wrong:

• Inductive/capacitive: valid for other sensors, but not these three as commonly implemented.
• Solid-state: too broad a label; does not specify the varying electrical property.

Common Pitfalls:
Generalizing from a single pressure sensor technology (e.g., capacitive MEMS) to all pressure sensors; the question groups devices typically taught as resistive.

Final Answer:
Resistive.