What quality changes with temperature in a PT 100?

• A. Capacitance
• B. Inductance
• C. Dielectric strength
• D. Resistance (0°C = 100 ohms)

Answer: (D)

Resistance is what a PT100 uses to sense temperature. A PT100 is a platinum resistance temperature detector, defined to have 100 ohms at 0°C. As temperature rises, platinum’s resistivity increases, so the resistance goes up in a nearly linear way over the common sensing range. The approximate relationship is R ≈ R0[1 + αT], with α about 0.00385 per °C for platinum, meaning small temperature changes produce measurable resistance changes. This is why the PT100’s reading is all about resistance. Capacitance, inductance, or dielectric strength aren’t what the PT100 measures to determine temperature, so they aren’t the property being used here.