Isotech is pleased to announce the availability of TRU², a new thermocouple reference unit designed to provide a stable, traceable 0 °C cold junction reference for thermocouple measurement and calibration.
Why the reference junction matters
TRU² has been developed to address a common and often overlooked limitation in thermocouple systems: the reference junction. While attention is typically focused on sensors and measuring instruments, overall accuracy is frequently constrained by how the reference junction temperature is realised, controlled, and verified.
Thermocouples do not measure absolute temperature. They measure temperature difference. Every thermocouple measurement therefore depends directly on the reference junction temperature, and any error at the reference junction adds directly to the measurement result.
In many instruments, cold junction compensation is performed internally, with the reference temperature inferred from terminal or enclosure sensors. This reference condition is often affected by ambient changes, enclosure heating, and poor thermal uniformity, and its uncertainty is rarely well defined or traceable. In practice, internal cold junction compensation is frequently the dominant contributor to thermocouple measurement uncertainty.
A physically defined reference
TRU² removes reliance on internal cold junction compensation by providing a physically defined, external reference junction, held at a controlled and stable 0 °C. By relocating the reference junction out of the measuring instrument and into a controlled reference block, cold junction compensation can be disabled and the thermocouple EMF measured directly using a precision digital voltmeter or temperature indicator.
The reference temperature is independently verifiable and supplied with calibration traceable in accordance with ISO/IEC 17025, allowing the reference contribution to be clearly included in the uncertainty budget.
Designed for modern calibration environments
Building on Isotech’s established TRU reference units, TRU² introduces greater immersion depth, higher capacity, and increased configuration flexibility to meet the needs of modern calibration laboratories and production test systems.
Key features include:
- Stable 0 °C reference temperature with typical stability of ±0.03 °C
- Solid-state Peltier control, eliminating ice baths, water handling, and consumables
- Greater immersion depth than earlier TRU models, supporting laboratory-standard thermocouples and probes
- Configurable capacity, supporting up to 100 double thermocouple junctions in a single unit
- Interchangeable well inserts, with custom drilling options available
- Flexible termination options for laboratory use or system integration
- Designed for use with precision DVMs or indicators with cold junction compensation disabled
A proven approach, extended
Ice baths have traditionally been used to realise the 0 °C reference for thermocouples, but require preparation and careful control to achieve consistent results. Isotech’s original TRU reference units replaced ice baths with solid-state, isothermal reference blocks that have been used successfully in laboratories worldwide for many years.
TRU² builds on this proven principle, extending capacity and flexibility while maintaining a stable physical reference that is independent of ambient conditions and internal instrument assumptions.
Further information
TRU² is available to order now, with multiple configurations to suit different applications and channel requirements. Datasheets and configuration guidance are available, and Isotech’s technical team would be pleased to discuss suitable options for your thermocouple measurement or calibration work.
For a full technical background on reference junctions, cold junction compensation, and best practice in thermocouple measurement, see the Isotech white paper on double junction thermocouples.
TRU² Thermocouple Reference Unit Model 992
Technical overview and performance data
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