The positioning of standard platinum resistance thermometer (SPRTs)
Standard platinum resistance thermometer (SPRTs) are essential sensors in situations requiring high accuracy temperature measurement. As the name suggests, they utilize characteristic of platinum (Pt) where its electrical resistance changes with temperature, and they truly shine in areas where precise temperature control is required.
Role of National Metrology Institutes and Calibration Laboratories
SPRTs play a crucial role in maintaining and supplying temperature standards at national metrology institutes and calibration laboratories. SPRTs are used as standard instruments for fixed-point calibration and comparative calibration as defined in the International Temperature scale (ITS90), and serve as a benchmark for guaranteeing the accuracy of other thermometers. In Japan's Metrology Traceability System (JCSS), accredited calibration service providers offer calibration services that ensure traceability to national standards, and SPRTs form the core of this system.
Basic knowledge of SPRT and the significance of ITS-90
What is a standard platinum resistance thermometer (SPRT)?
Standard Platinum Resistance Thermometer (SPRT) is a high accuracy temperature sensor that utilizes the characteristic of platinum (Pt), whose electrical resistance changes with temperature. Generally, the electrical resistance of metals changes proportionally with temperature, but platinum has particularly high stability and enables highly reliable measurements over a wide temperature range. Due to its high accuracy and stability, SPRT is used not only for industrial temperature measurement but also as a standard thermometer in a wide range of fields, including scientific research and quality control.
Applicable standards: ITS-90 and defined fixed points
In the International Temperature scale 1990 (ITS-90), the international standard for temperature scale, the SPRT is defined as a standard thermometer for the temperature range from the triple point of mercury (-38.8344°C) to the freezing point of silver (961.78°C). The ITS-90 is an internationally agreed-upon best approximation of thermodynamic temperature, and it reproduces temperature using the phase transition points (defining fixed points) of specific materials. The main ITS-90 defining fixed points are as follows:
- Ttriple point of equilibrium hydrogen: 13.8033 K (-259.3467 °C)
- Triple point of neon: 24.5561 K (-248.5939 °C)
- Triple point of oxygen: 54.3584 K (-218.7916 °C)
- Triple point of argon: 83.8058 K (-189.3442 °C)
- Triple point of mercury: 234.3156 K (-38.8344 °C)
- Triple point of water: 273.16 K (0.01 °C)
- Melting point of gallium: 302.9146 K (29.7646 °C)
- Freezing point of indium: 429.7485 K (156.5985 °C)
- Freezing point of tin: 505.078 K (231.928 °C)
- Freezing point of zinc: 692.677 K (419.527 °C)
- Freezing point of aluminum: 933.473 K (660.323 °C)
- Freezing point of silver: 1234.93 K (961.78 °C)
- Freezing point of gold: 1337.33 K (1064.18 °C)
- Freezing point of copper: 1357.77 K (1084.62 °C)
International standards for establishing calibration and traceability
Japan's metrology traceability system (Japan Calibration Service System: JCSS) is supported by two systems: the "National Standards Provision System" and the "Calibration Laboratory Accreditation System."
Measurement standard supply system
- This system maintains calibrations that are linked to national metrological standards. Calibration service providers designate and registration by the Minister of Economy, Trade and Industry supply metrological standards using specific standards and specific reference materials.
Calibration Service Provider registration System
- This is a system for registration calibration service providers that comply with the requirements of ISO/IEC 17025. registration service providers can issue calibration certificates bearing the JCSS accreditation symbol mark, which are valid overseas through the Mutual Recognition Agreements (MRAs) of ILAC (International Laboratory Accreditation Cooperation) and APAC (Asia Pacific Accreditation Cooperation), of which IAJapan is a member.
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