What do Pt100 and Pt1000 denote in RTD sensors?

• A. Pt100 indicates 100 Ω at 0°C; Pt1000 indicates 1000 Ω at 0°C
• B. Pt100 denotes 100 Hz output; Pt1000 denotes 1000 Hz output
• C. Pt100 refers to platinum grade; Pt1000 refers to platinum grade with higher purity
• D. Pt100 and Pt1000 indicate warranty periods

Answer: (A)

In RTDs, the number in the name tells you the resistance of the platinum element at 0°C. Pt100 means the element is 100 ohms at 0°C, while Pt1000 means it’s 1000 ohms at 0°C. This reference point is what the temperature-resistance relationship is built around: R ≈ R0[1 + α(T − 0°C)], with α about 0.00385 per °C for platinum. So a Pt1000 will show a larger resistance change for the same temperature change compared to a Pt100, which affects signal levels and how you design the measurement circuit (signal voltage, required excitation current, and potential self-heating considerations). The naming has nothing to do with output frequency, platinum purity grades, or warranty.