Types and structure of elements
High-purity platinum wire is used as the sensing element in SPRT (Standard Platinum resistance) thermometers. The platinum wire is mounted on a quartz or glass support structure and is designed to minimize the effects of mechanical stress caused by thermal expansion. This special structure enables extremely high stability and repeatability.
SPRTs are available in types with nominal resistance values of 25.5 Ω and 100 Ω at 0°C, and are selected based on the measurement temperature range and application.The 25.5 Ω type is widely used by national standards and calibration institutions, while the 100 Ω type is used in research institutions and for calibration applications because it is easy to handle and connect to measurement circuits.
Furthermore, depending on the operating temperature range, SPRTs are classified into low-temperature SPRTs, which can be used in the cryogenic temperature range, and high-temperature SPRTs, which are suitable for calibrating the freezing and melting points of metals. Each structure is optimized to provide the highest stability and accuracy within the target temperature range.
Practical aspects of calibration and traceability
Calibration equipment and standards (comparison method and fixed-point calibration)
SPRT calibration is performed using two main methods, "fixed-point calibration" and "comparative calibration," depending on the application and required accuracy.
- Fixed-point calibration: This calibration method utilizes defined fixed points such as the triple point, freezing point, and melting point of a substance as defined in ITS-90. For example, a triple-point calibration device for water or a freezing point furnace for metals is used. This calibration requires the highest level of precision and is performed by national metrology institutes and some calibration laboratories.
- Comparative calibration: This method involves inserting the SPRT to be calibrated alongside a more high accuracy standard thermometer (e.g., another SPRT or standard thermocouple) in a liquid bath or electric furnace with good temperature distribution and stability, and comparing indicated value of both. Various comparative calibration devices are used depending on the measurement temperature range, such as for low temperatures, medium temperatures, and high temperatures.
JCSS Calibration, MRA, and International Mutual Recognition
JCSS calibration is performed by calibration service providers registration and accredited under the JJapan Calibration Service System (JCSS) based on the Measurement Law.
Calibrations performed within the scope of accreditation are issued with a calibration certificate bearing the JCSS accreditation symbol, which indicates that the calibration service provider meets the requirements of ISO/IEC 17025 and ensures traceability to national metrology standards.
Furthermore, IAJapan, a JCSS-accredited body, is a signatory to the Mutual Recognition Agreement (MRA) between the International Laboratory Accreditation Cooperation (ILAC) and the Asia-Pacific Accreditation Cooperation (APAC). Therefore, calibration certificates bearing the ILAC-MRA mark issued by JCSS-accredited businesses that comply with the international MRA are internationally accepted in member countries and regions.
This system allows for the mutual recognition of the reliability and technical validity of calibration certificates and calibration results issued in different countries, contributing to the smooth operation of international trade and quality assurance.
Content and uncertainties of calibration tests and certificates
Calibration testing evaluates the measured resistance value, its corresponding temperature, and its "uncertainty." Uncertainty is a new measure used to express the reliability of measurement results, quantitatively indicating the degree of variation in the measured values. Calibration certificates include not only the measured values of the calibration results but also the uncertainty value. Standards such as ISO/IEC 17025 require the evaluation of uncertainty, and its calculation takes into account various factors (calibration uncertainty, aging, resolution, noise, etc.). As an example of uncertainty calculation, an uncertainty budget table is created, and the expanded uncertainty is obtained by combining the standard uncertainties of each factor.
Traceability System Flow
A traceability system is chart illustrating the seamless chain of calibration, from national metrology standards to measuring instruments used in the field.
- National Metrology Standards: These are the highest high-order standards development and maintained by the National Institute of Advanced Industrial Science and Technology (NMIJ).
- Designated standards and designated sub-standards: These are standards that are directly traceable to national metrological standards.
- registration and Accredited Businesses (JCSS Calibration Laboratories): Businesses accredited by NITE (National Institute of Technology and Evaluation) perform calibrations using specified standards and issue JCSS calibration certificates.
- Users (testing laboratories, factories, etc.): Ensure the traceability of your measurements by using standards and measuring instruments calibrated by JCSS calibration laboratories.
This diagram allows you to see at a glance the path taken by measuring instruments to calibration and how they reach national standards.
Case study: Flow and key points in calibration work
JCSS-accredited businesses like Chino are recognized by NITE (National Institute of Technology and Evaluation) as temperature and humidity calibration laboratories under the Measurement Law, and issue calibration certificates bearing symbol mark. Chino handles the calibration of a wide range of temperature and humidity sensors, including thermocouples, radiation thermometer resistance thermometer radiation thermometers, glass thermometers, electronic hygrometers, and dew point meters. In particular, for standard platinum resistance thermometer, calibration at defined fixed points such as the triple point of water and the freezing point of metals, as well as precise comparative calibration, are provided to support traceability. Calibration can be performed on a single sensor, contributing to the maintenance of quality systems such as ISO9000 and IATF16949.
Related products and services
R800
JCSS Calibration Service
Date created: 2026.06.17
