Temperature sensors — Which device behaves similarly to an RTD (resistance varies with temperature) but exhibits a negative temperature coefficient (resistance decreases as temperature increases)?

Introduction:
Resistive temperature sensors change resistance with temperature. RTDs (often platinum) have a positive temperature coefficient (PTC), while thermistors commonly have a negative temperature coefficient (NTC), making them highly sensitive but nonlinear. Selecting the right sensor requires understanding these characteristics.

Given Data / Assumptions:

• We seek a device similar in principle (resistive sensing) to an RTD.
• Required property: negative temperature coefficient (NTC).
• Focus on common industrial/embedded sensors.

Concept / Approach:

Thermistors are ceramic semiconductor resistors whose resistance falls rapidly with increasing temperature (NTC type). They offer high sensitivity over limited ranges and are well-suited for compensation, inrush limiting, and precise temperature monitoring after linearization. RTDs are metal resistors with near-linear PTC behavior and excellent accuracy over wide ranges.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets classify NTC thermistors (e.g., 10 kΩ at 25 °C) with beta constants describing resistance-temperature curves, confirming the negative coefficient behavior.

Why Other Options Are Wrong:

• Strain gauge: Measures mechanical strain; temperature sensitivity is secondary.
• Negative-type RTD: Not a standard category; RTDs are PTC by definition.
• Thermocouple: Generates voltage from temperature difference, not resistive sensing.
• Hall sensor: Magnetic sensing, not temperature.

Common Pitfalls:

• Assuming all resistive sensors are PTC; thermistors are typically NTC.
• Ignoring nonlinearity of thermistors, which requires linearization for precision measurement.

Final Answer:

Thermistor