The Industry Standard for Precision Temperature Measurement
The PT100 RTD sensor is the most widely used resistance temperature detector in industrial and laboratory applications worldwide. With a nominal resistance of 100.00Ω at 0°C and a standardized temperature coefficient of resistance (TCR) of 0.00385 Ω/Ω/°C, the PT100 provides exceptional accuracy, stability, and interchangeability across manufacturers.
Thermometrics manufactures PT100 sensors using both thin-film and wire-wound platinum elements, each offering distinct advantages. Thin-film elements provide faster response times and smaller package sizes, while wire-wound elements deliver the highest accuracy and long-term stability for reference-grade applications.
- Nominal resistance: 100.00Ω ± tolerance at 0°C
- TCR: 0.00385 Ω/Ω/°C (alpha coefficient)
- Full operating range: -200°C to +850°C
- Conforms to IEC 60751:2022 and ASTM E1137
- Available in 2-wire, 3-wire, and 4-wire configurations
Tolerance Classes per IEC 60751
IEC 60751 defines several tolerance classes for platinum RTDs. The tolerance formula specifies the maximum allowable deviation from the standard resistance-temperature relationship at any temperature within the specified range.
| Tolerance Class | Formula | At 0°C | At 100°C | At -100°C | At 200°C | Valid Range |
|---|---|---|---|---|---|---|
| Class AA (1/3 DIN) | ±(0.10 + 0.0017·|t|)°C | ±0.10°C | ±0.27°C | ±0.27°C | ±0.44°C | -50°C to +250°C |
| Class A | ±(0.15 + 0.002·|t|)°C | ±0.15°C | ±0.35°C | ±0.35°C | ±0.55°C | -100°C to +450°C |
| Class B | ±(0.30 + 0.005·|t|)°C | ±0.30°C | ±0.80°C | ±0.80°C | ±1.30°C | -196°C to +600°C |
| Class C | ±(0.60 + 0.01·|t|)°C | ±0.60°C | ±1.60°C | ±1.60°C | ±2.60°C | -196°C to +600°C |
Important Note on 4-Wire vs. 3-Wire Tolerance
Class A tolerance is only guaranteed in 3-wire or 4-wire configurations. In a 2-wire configuration, lead wire resistance adds directly to the measurement, often exceeding Class B tolerance. For precision applications requiring Class A or better, always specify 4-wire construction.
PT100 Resistance vs. Temperature
Standard PT100 resistance values at key temperature points per IEC 60751 (α = 0.00385 Ω/Ω/°C). Full resistance tables are available in our technical resources section.
| Temperature (°C) | Resistance (Ω) | Temperature (°C) | Resistance (Ω) |
|---|---|---|---|
| -200 | 18.52 | 100 | 138.51 |
| -100 | 60.26 | 200 | 175.86 |
| -50 | 80.31 | 300 | 212.05 |
| 0 | 100.00 | 400 | 247.09 |
| 20 | 107.79 | 500 | 280.98 |
| 25 | 109.73 | 600 | 313.71 |
| 50 | 119.40 | 850 | 390.48 |
Wire Configurations Explained
2-Wire Configuration
The simplest configuration with two lead wires connecting the RTD element to the measurement instrument. Lead wire resistance adds directly to the measured resistance, introducing error proportional to wire length. Suitable only for short cable runs (under 3 meters) or where ±1°C accuracy is acceptable.
Use when: Short cable runs, cost-sensitive applications, lower accuracy needs.
3-Wire Configuration
The most common industrial configuration. A third lead wire enables the measurement instrument to measure and compensate for lead wire resistance. This method assumes all three leads have equal resistance, providing accurate compensation for cable runs up to 100 meters in well-matched cable.
Use when: Industrial process control, PLC/DCS integration, standard industrial measurement.
4-Wire (Kelvin) Configuration
The most accurate configuration, using separate pairs of current-carrying and voltage-sensing leads. This completely eliminates lead wire resistance error regardless of cable length or resistance mismatch. Required for Class A tolerance guarantee and reference-grade measurement.
Use when: Calibration labs, precision measurement, Class A tolerance, long cable runs.
Thin-Film vs. Wire-Wound Elements
Thermometrics offers PT100 sensors with both thin-film and wire-wound platinum elements. The choice depends on your application's requirements for accuracy, response time, vibration resistance, and temperature range.
Thin-Film Elements
- Platinum deposited on ceramic substrate
- Compact size (2mm × 5mm typical)
- Faster thermal response
- Better vibration and shock resistance
- Range: -50°C to +500°C (standard), -200°C to +600°C (extended)
- Lower cost for high-volume production
Wire-Wound Elements
- Platinum wire coiled around ceramic or glass mandrel
- Highest accuracy and long-term stability
- Widest temperature range: -200°C to +850°C
- Preferred for calibration and reference applications
- Best interchangeability between units
- Superior drift characteristics (< 0.05°C/year)
Element Selection Guide
Choose thin-film for industrial applications requiring fast response, compact size, or vibration resistance. Ideal for surface mounting, immersion in flowing media, and high-volume OEM applications.
Wire-Wound for Precision
Choose wire-wound for calibration baths, metrology labs, reference standards, and any application requiring Class AA tolerance or better. Wire-wound elements also perform best at temperature extremes (below -100°C or above 500°C).
Self-Heating Considerations
All RTD sensors experience self-heating from the excitation current. For PT100 elements, use 1 mA or less to keep self-heating below 0.05°C in a well-immersed probe. In still air, self-heating can be 10× higher — consult our engineers for air temperature measurement applications.
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