Pt100 Sensors Principles and Industrial Applications Explained

In industrial environments where precise temperature measurement is critical, one technology stands out for its reliability and accuracy: the Pt100 platinum resistance temperature sensor. Known for its excellent linearity, stability, and corrosion resistance, this sensor plays a vital role in industrial temperature measurement applications.

The designation "Pt100" reveals key information about this sensor type. "Pt" stands for platinum, the noble metal used as the sensing element, while "100" indicates a resistance of 100Ω at 0°C. Similar naming conventions apply to other resistance temperature detectors (RTDs), such as Cu100 (copper) or Ni120 (nickel).

Among various RTD types, Pt100 remains the most widely used. Platinum's exceptional physical and chemical properties make platinum-based RTDs (often called platinum resistance thermometers or PRTs) the preferred choice for precision measurements.

The Pt100 operates on a fundamental principle: as temperature increases, so does the platinum element's electrical resistance. A standard Pt100 sensor shows 100Ω at 0°C and 138.5Ω at 100°C, demonstrating a consistent change of approximately 0.385Ω per degree Celsius.

All Pt100 specifications—including resistance values, temperature coefficients, tolerances, and cable color codes—conform to the international standard BS EN 60751:2008. This standardization ensures interchangeability between sensors from different manufacturers.

Despite being a precious metal with higher material costs, platinum offers unmatched linearity and stability for temperature sensing. Its exceptional corrosion resistance and chemical inertness, combined with high-temperature stability, make it ideal for demanding applications. Beyond RTDs, platinum also serves in high-temperature thermocouples.

Notably, the actual platinum content in a Pt100 sensor is minimal, keeping material costs a small fraction of the total sensor price.

Industrial Pt100 sensors typically employ one of two sensing technologies: thin-film elements or wire-wound elements.

Thin-film technology dominates high-volume, cost-sensitive industrial applications. These elements feature a laser-trimmed platinum grid deposited on a ceramic substrate, with automated production ensuring consistent quality. Common in automotive and appliance applications, thin-film sensors offer:

• Robust construction withstands significant shock and vibration
• Standard operating range of -70°C to +500°C
• Typical tolerances of Class B or Class A (some achieving 1/3 DIN accuracy)

However, limitations exist. Higher accuracy requirements reduce the usable temperature range. Thermal cycling can cause stress accumulation between the platinum grid and ceramic substrate, potentially affecting long-term accuracy.

Wire-wound elements, though more expensive due to manual production, deliver superior reliability—particularly in long-term stability. These sensors feature hand-wound platinum coils inserted into porous ceramic insulators, allowing free thermal expansion without stress buildup.

Key advantages include:

• Extended temperature range up to 650°C
• Higher tolerance classifications
• Only viable option for cryogenic applications down to -200°C

The trade-off comes in mechanical robustness—wire-wound elements aren't suitable for high-vibration environments due to their minimally supported platinum coils.

Regardless of sensing technology, Pt100 probes share similar construction principles. Most feature protective metal sheaths—typically 316 stainless steel for general use, with alternatives like 310 stainless or Inconel for specialized applications.

Bare or ventilated elements may measure dry gases, but exposure to liquids must be avoided. Connection methods vary from direct cabling to terminal boxes or industrial connectors, depending on installation requirements.

Measuring Pt100 output is straightforward with commercial instruments that handle both signal acquisition and linearization. For long cable runs, temperature transmitters convert the resistance signal to industry-standard 4-20mA outputs, enabling reliable long-distance transmission. Transmitters mount in junction boxes or on DIN rails as needed.

Pt100 represents a specific RTD type with 100Ω at 0°C and 138.5Ω at 100°C. Its stability and accuracy make it the industrial standard for process and laboratory temperature measurement.

The sensor operates on platinum's predictable resistance-temperature relationship, described by the Callendar-Van Dusen equation. This linear change enables precise temperature measurement across industrial and scientific applications.

As an IEC 60751-compliant RTD, Pt100 sensors combine measurement robustness with accuracy. Their platinum elements exhibit low hysteresis and excellent corrosion resistance, often housed in stainless steel or specialty alloy sheaths for harsh environments.

With temperature ratings exceeding 600°C, these sensors serve demanding applications from industrial furnaces to exhaust gas monitoring. Various lead wire options (copper, nickel, etc.) and standardized connectors ensure compatibility across measurement systems.