ISOTECH Primary Fixed-Point Cell (Sealed & Open-Type)

Overview

The ISOTECH Primary Fixed-Point Cell is a metrological-grade reference standard engineered for the realization and dissemination of thermodynamic temperature scales in accordance with the International Temperature Scale of 1990 (ITS-90). Designed and manufactured in the United Kingdom, these cells serve as primary standards in national metrology institutes (NMIs), calibration laboratories accredited to ISO/IEC 17025, and high-accuracy industrial temperature validation facilities. Each cell functions as a stable, reproducible phase-change reference—utilizing highly purified elemental metals (e.g., Indium, Tin, Zinc, Aluminium, Silver, Copper) that undergo solid–liquid transition at precisely defined triple or freezing points under controlled pressure conditions. The sealed variant employs ultra-high-purity argon (6N) at 101.325 kPa to suppress oxidation and ensure long-term chemical stability of the metal charge; the open-type configuration supports in-situ insertion of high-stability thermometers (e.g., SPRTs, capsule-type PRTs) for direct immersion during fixed-point realization.

Key Features

• Ultra-high metal purity: 99.99995% (6N5) certified by independent analysis per ASTM E290 and ISO 80000-8, minimizing impurity-induced depression of freezing point.
• Optimized geometry: Minimum working length >200 mm ensures uniform axial temperature gradient and sufficient immersion depth for standard platinum resistance thermometers (SPRTs) complying with IEC 60751 Class AA tolerances.
• Hermetically sealed argon environment (for sealed cells): Eliminates oxidation, maintains stoichiometric integrity over decades, and enables traceable storage without vacuum reconditioning.
• UKAS-accredited characterization: Each unit undergoes full thermal homogeneity mapping, freezing plateau duration assessment (>15 min typical), and repeatability verification at the National Physical Laboratory (NPL)-aligned NPTL facility.
• Integrated metrological accessories: Includes stainless-steel outer canister, insulated transport case, calibrated thermal shunt, and precision-engineered radiation reflector to minimize parasitic heat loss during furnace-based realization.

Sample Compatibility & Compliance

These fixed-point cells are compatible with standard ITS-90 realization furnaces (e.g., Hart Scientific 56xx series, Fluke 914x, Isotech MTS-200), SPRTs meeting IEC 60751:2022 Class AA requirements, and automated fixed-point systems compliant with EURAMET cg-18 guidelines. All cells conform to the physical definition of ITS-90 fixed points specified in CCT/2007-19 and are traceable to the UK’s national temperature standard maintained by NPL. Documentation includes full uncertainty budgets (k=2) per GUM (JCGM 100:2008), UKAS-endorsed calibration certificates (ISO/IEC 17025:2017), and material certification aligned with ISO 17034 for reference material producers.

Software & Data Management

While the cells themselves are passive reference artifacts, their integration into automated calibration workflows is supported via compatibility with industry-standard software platforms including MET/TEAM, LabWare LIMS, and Fluke Metrology Software Suite. Data acquisition systems may log plateau onset time, slope stability (<0.1 mK/min), and plateau duration to support GLP/GMP audit trails. All supplied certificates include machine-readable QR codes linking to digital UKAS records, enabling seamless integration into electronic quality management systems (eQMS) compliant with FDA 21 CFR Part 11 requirements for electronic signatures and audit logging.

Applications

• Primary calibration of Standard Platinum Resistance Thermometers (SPRTs) in NMIs and ISO/IEC 17025 accredited labs.
• Validation and periodic verification of industrial dry-well calibrators, fluid-bath calibrators, and multi-zone furnaces.
• Inter-laboratory comparison studies coordinated by BIPM, EURAMET, or APMP under CIPM Mutual Recognition Arrangement (CIPM MRA).
• Development and verification of thermodynamic temperature measurement models for cryogenic and high-temperature applications (−38.83 °C to 1084.62 °C).
• Supporting ISO 9001, ISO 13485, and pharmaceutical temperature mapping protocols requiring documented traceability to SI units.

FAQ

What is the difference between sealed and open-type ISOTECH fixed-point cells?
Sealed cells contain pre-purified metal under inert argon atmosphere and require no user handling of the charge; open cells allow direct thermometer insertion and are typically used for high-precision SPRT calibration where immersion depth control is critical.
Are UKAS certificates provided with every cell shipment?
Yes—each unit ships with a UKAS-accredited calibration certificate (ref. number traceable to NPL) and a separate material purity certificate verified by NPTL testing.
Can these cells be used for ITS-90 realizations above 660 °C?
Yes—copper (1084.62 °C), silver (961.78 °C), and gold (1064.18 °C) cells are available with quartz or graphite crucibles rated for extended high-temperature stability and low emissivity.
How often should a fixed-point cell be recalibrated?
Recalibration is recommended every 5 years for sealed cells and annually for open cells subjected to frequent thermal cycling or mechanical handling, per EURAMET cg-18 recommendations.
Do ISOTECH cells meet FDA 21 CFR Part 11 requirements?
The cells themselves are passive artifacts; however, their associated UKAS certificates and digital traceability infrastructure fully support Part 11 compliance when integrated into validated eQMS environments.