ISOTECH ISOTower ITS-90 Fixed-Point Cell Furnace

Overview

The ISOTECH ISOTower is a high-stability, integrated fixed-point furnace system engineered for primary temperature calibration in national metrology institutes, accredited calibration laboratories, and high-end industrial standards labs. It operates on the fundamental principle of phase-change thermometry—leveraging the invariant equilibrium temperatures of highly purified metal–carbon eutectics or pure metals during solid–liquid transition—as defined by the International Temperature Scale of 1990 (ITS-90). Unlike conventional immersion furnaces, the ISOTower employs a monoblock design where the graphite crucible and furnace housing are structurally unified, eliminating thermal interface resistance and minimizing axial temperature gradients. This architecture, combined with patented thermal siphon technology, ensures exceptional radial and axial homogeneity across the entire 290 mm immersion zone—critical for realizing reproducible, low-uncertainty fixed-point plateaus compliant with ISO/IEC 17025 and BIPM CCT-K guidelines.

Key Features

• Patented thermal siphon circulation system enabling uniform heat distribution and suppressing convection-induced instability during plateau maintenance
• 290 mm certified immersion depth—optimized for full insertion of standard SPRTs (Standard Platinum Resistance Thermometers) and capsule-type reference sensors per ITS-90 Annex C requirements
• Monoblock crucible-furnace construction eliminates mechanical misalignment and thermal lag between heating element and cell cavity
• 6N (99.9999%) purity metal cells supplied with traceable CoA (Certificate of Analysis) and residual impurity profiling per ASTM E2302
• Programmable ramp profiles with closed-loop PID control and dual-stage overtemperature protection meeting IEC 61000-6-2 EMC immunity standards
• Robust stainless-steel enclosure rated IP54 for operation in controlled laboratory environments with ambient temperature stability ±1 °C

Sample Compatibility & Compliance

The ISOTower supports all five defining ITS-90 fixed points: Indium (156.5985 °C), Tin (231.928 °C), Zinc (419.527 °C), Aluminum (660.323 °C), and Silver (961.78 °C). Each cell is pre-assembled with high-purity metal ingots sealed under inert atmosphere in fused-silica or graphite capsules conforming to ISO 21709:2021 specifications. The furnace’s thermal profile has been validated against NPL and PTB reference data for plateau flatness (≤±0.1 mK over central 100 mm), repeatability (k = 2 uncertainty < 0.25 mK after three cycles), and long-term drift (<0.05 mK/year). It satisfies essential requirements for GLP-compliant calibration workflows and supports audit-ready documentation per FDA 21 CFR Part 11 when paired with ISOTECH’s optional TraceLink software suite.

Software & Data Management

The ISOTower is compatible with ISOTECH’s TraceLink Calibration Suite—a Windows-based application designed for automated plateau detection, multi-sensor synchronization, and uncertainty budgeting per GUM (JCGM 100:2008). TraceLink records time-stamped resistance, voltage, and temperature data at user-defined intervals (100 ms to 10 s), applies automatic baseline correction using Savitzky–Golay filtering, and generates plateau duration reports aligned with CCT/2019-02 evaluation criteria. All raw datasets are stored in HDF5 format with embedded metadata (cell ID, operator, date/time, ambient conditions), supporting version-controlled archiving and third-party validation via Python or MATLAB interfaces. Audit trails include electronic signatures, change logs, and role-based access controls compliant with ISO/IEC 17025:2017 clause 7.11.

Applications

• Primary calibration of Standard Platinum Resistance Thermometers (SPRTs) and transfer standards in NMIs and DAkkS-accredited labs
• Validation and verification of industrial blackbody cavities and radiation thermometers per ASTM E2758
• Uncertainty reduction in high-accuracy thermocouple calibration (Types R, S, B) using fixed-point interpolation
• Interlaboratory comparison studies coordinated by BIPM, EURAMET, or APMP under CIPM MRA framework
• Development and characterization of next-generation thermometric sensors requiring sub-mK stability benchmarks

FAQ

What fixed-point metals are supported by the ISOTower?
Indium, Tin, Zinc, Aluminum, and Silver—each supplied as 6N purity cells with documented impurity spectra and sealed encapsulation.
Does the ISOTower require external cooling or water circulation?
No—it operates as a self-contained air-cooled system; thermal siphon technology eliminates need for forced-air or liquid cooling during plateau hold.
Can the ISOTower be used for both freezing and melting point realization?
Yes—its symmetric thermal design and precise power modulation support both freezing-point plateau stabilization and high-reproducibility melting-point measurements per ITS-90 definitions.
Is the ISOTower compatible with non-ISOTECH SPRTs?
Yes—standard 25-mm-diameter, 300-mm-length SPRT probes from Hart, Fluke, or ASL are fully accommodated within the 290-mm immersion zone.
How is traceability maintained across calibration cycles?
Each ISOTower shipset includes a UKAS-accredited factory calibration report referencing NPL primary standards, with annual recalibration services available through ISOTECH’s UK service center under ISO/IEC 17025 scope.