How a PT100 (RTD) Works

PT100 is a platinum resistance temperature detector (RTD). "PT" = platinum; "100" = 100 Ω at 0°C.

Working principle

Platinum's electrical resistance changes predictably with temperature. The PT100’s resistance increases when temperature rises. A transmitter or measuring instrument reads that resistance and converts it to °C or °F.

Resistance examples

• 0°C → 100.00 Ω
• 100°C → ≈ 138.50 Ω
• 200°C → ≈ 175.80 Ω

Wiring types (accuracy vs cost)

• 2-wire – simple, lowest cost, affected by lead resistance (short runs).
• 3-wire – most common in industry; compensates for lead resistance and gives good accuracy.
• 4-wire – best accuracy (lab use); completely cancels lead resistance.

Typical use with transmitter

Often RTD → temperature transmitter → converts to 4–20 mA for PLC/DCS/HMI. This gives robust, noise-immune transmission.

Advantages

• Accurate and stable
• Good repeatability and linear-ish response
• Wide usable temperature range (depending on sensor construction)

Quick note on installation

Use correct wiring (3- or 4-wire for long runs), ensure good thermal contact (use probe/immersion wells as required), and calibrate if high accuracy is needed.

Quick comparison: PT100 (RTD) vs Thermocouple

Feature	PT100 (RTD)	Thermocouple
Accuracy	High accuracy	Moderate, lower accuracy
Stability / Drift	Very stable over time	Can drift, needs recalibration
Temperature Range	-200°C to +600°C (depends on sensor)	Very high range (up to 2300°C depending on type)
Linearity	More linear response	Non-linear (needs linearization)
Output Signal	Resistance (Ω), needs transmitter	Millivolts (mV), needs CJC
Response Time	Moderate	Fast response
Cost	Higher (sensor + transmitter)	Lower sensor cost
Typical Use	Industrial process, labs, high accuracy	High temperature, furnaces, fast detection