Pt100Edit
Pt100 is a widely used platinum-based RTD (resistance temperature detector) that relies on a platinum resistor with a nominal resistance of 100 ohms at 0°C. As a cornerstone of modern temperature measurement, Pt100 sensors combine stability, repeatability, and a robust operating range, making them common in industrial process control, HVAC systems, laboratory instrumentation, and field measurements. The 0°C reference point of 100 ohms provides a straightforward baseline for calibration and interoperability with many instruments that read resistance.
Pt100 sensors belong to the broader family of RTD and are valued for their long-term stability and predictable response. They are frequently chosen over thermocouples in applications where accuracy over time and under steady conditions matters more than the fastest response.
Principle and properties
Temperature alters the electrical resistance of platinum in a highly repeatable way. The basic relationship can be described by a nearly linear increase in resistance with temperature in the common operating range, with a standard reference coefficient around 0.00385 per degree Celsius. In practical engineering, the exact relationship is captured by the Callendar–Van Dusen equation, which provides a precise model of R(T) over a wide temperature span:
- For 0°C ≤ T ≤ 600–850°C: R(T) = R0 [1 + A T + B T^2]
- For −200°C ≤ T ≤ 0°C: R(T) = R0 [1 + A T + B T^2 + C (T − 100)^3]
where R0 is 100 Ω for Pt100, and A, B, C are material constants (typical values: A ≈ 3.9083×10^−3 °C^−1, B ≈ −5.775×10^−7 °C^−2, C ≈ −4.183×10^−12 °C^−3). These equations enable precise conversion from resistance to temperature in both research and industry. The same mathematics underpins the use of Pt100 in ITS-90-based calibrations and many reference instruments.
The platinum element offers excellent stability and repeatability, with low drift over time and resistance to corrosion in many process environments. However, measurement accuracy depends on factors such as excitation current, wiring, and self-heating, which can introduce errors if not properly managed.
Self-heating is a key consideration: when current flows through the Pt100, power dissipates as heat within the sensor. To minimize errors, measurement currents are kept deliberately small (often in the 1–5 mA range, depending on the sensor and application), and higher currents are avoided or compensated in the measurement circuitry. The measurement setup—whether a simple bridge, a dedicated RTD input, or a digital sensor interface—must account for lead resistance and ambient conditions.
Construction and variants
Pt100 sensors come in several form factors and connection schemes to suit different environments and instrumentation. Common configurations include:
- 2-wire RTD: simplest and most economical, but lead resistance adds an error that grows with temperature.
- 3-wire RTD: introduces a compensation path to reduce the effect of lead resistance, improving accuracy in typical installations.
- 4-wire RTD: eliminates lead resistance error entirely, offering the highest accuracy for critical measurements.
The physical form factors range from small probe assemblies for insertion into process vessels to robust, armored sensors for outdoor or harsh environments. Protective sheaths are typically stainless steel or other corrosion-resistant alloys, with materials chosen for mechanical strength and compatibility with process media. Thin-film and coil- or wire-wound constructions are common manufacturing approaches, each with trade-offs in response time, ruggedness, and cost.
Tolerance classes, defined by standards such as IEC 60751, organize Pt100 devices by accuracy. The two most widely used classes are Class A (tighter tolerances) and Class B (broader tolerances). The actual tolerance varies with temperature, so designers select a class based on the required accuracy and budget. In many industrial applications, 3-wire or 4-wire configurations are paired with Class A instruments to achieve reliable performance across changing conditions.
Pt100 sensors can also be specified as Pt100 or Pt1000, indicating the base resistance at 0°C (100 Ω or 1000 Ω, respectively). Pt1000 sensors share the same principle but provide higher sensitivity for certain measurement systems and can reduce current draw for a given electrical readout.
Standards, calibration, and usage
Calibration and performance traceability for Pt100 devices commonly rely on established standards and calibration chains. The core standard for many Pt100 devices is IEC 60751, which defines tolerances, linearity, and methods for classifying thermometer devices. Calibration often references the ITS-90 to ensure consistency across labs and instruments. In practice, technicians and engineers use calibrated instruments, traceable to national or international reference standards, to ensure reliability in process control and test laboratories.
Pt100 sensors are widely deployed in chemical processing, oil and gas, power generation, manufacturing automation, and aviation-ground testing, among other sectors. They are favored where stability, repeatability, and a well-understood transfer function are essential, and where the instrumentation ecosystem already supports RTD-based sensing. Integrating Pt100 with analog or digital readouts often involves dedicated RTD input modules or microcontroller interfaces that implement the appropriate conversion from resistance to temperature, including compensation for lead resistance and self-heating effects.
Applications and integration
In process control, Pt100 sensors monitor temperatures in reactors, distillation columns, furnaces, and heat exchangers. In HVAC systems, Pt100 devices help regulate climate control with stable, predictable readings. In laboratory environments, Pt100 probes provide reliable temperature measurements for experiments, calibration rigs, and thermal chambers. The compatibility of Pt100 with a wide range of instrumentation—bridges, data loggers, PLCs, and dedicated RTD readers—facilitates standardized instrumentation and reduces integration risk.
The choice between Pt100 and alternative temperature sensors—such as thermocouples, thermistors, or optical sensors—depends on the required accuracy, temperature range, environmental conditions, and the existing measurement chain. Pt100’s combination of stability and well-characterized behavior often makes it the preferred option for long-term installations where drift and calibration maintenance are significant considerations.