Isotech 471 Simple Argon Apparatus

The Isotech 471 Simple Argon Triple Point Apparatus is a redesigned and modernised system for realising the argon triple point (–189.3442 °C), one of the defining fixed points of the ITS‑90. Traditional argon systems were often expensive, complex and difficult to operate. The updated 471 model changes that by offering a more accessible, automated and efficient solution. Many laboratories still rely on liquid‑nitrogen comparators. Although inexpensive, LN₂ is not an ITS‑90 fixed point and lies below the argon triple point. This creates pressure‑related issues inside SPRTs, increasing self‑heating effects and calibration uncertainty. The 471 apparatus eliminates these limitations by providing a true realisation of the argon triple point with stable, controlled pressure regulation.

A new generation of argon apparatus

The upgraded 471 introduces several improvements that enhance usability and performance:

• > Automated electronic pressure control replaces the manual weight system.
• > Additional pre‑cooling pocket improves efficiency and speeds stabilisation.
• > Faster time to plateau reduces waiting time before calibration.
• > LN₂ can be replenished during operation, extending calibration sessions.
• > Faster filling time shortens setup and preparation.

Inside the system, 6N‑pure argon is sealed in a pressure vessel. Liquid nitrogen cools the chamber to approximately –195 °C, after which an electronic pressure controller raises the nitrogen boiling temperature to just above the argon point. The argon then settles into its triple‑point plateau for around four hours, providing a stable reference for SPRT calibration.

Why choose the Isotech 471 Simple Argon Apparatus?

The 471 offers a practical, safe and cost‑effective alternative to traditional systems:

• > no high‑pressure gas handling
• > no complex vacuum equipment
• > no reliance on LN₂ comparators
• > automated pressure control
• > repeatable, traceable ITS‑90 realisation

It is a self‑contained, laboratory‑friendly system that delivers reliable triple‑point performance without the cost or complexity of older designs.

What is the argon triple point?

The argon triple point (–189.3442 °C) is a defining ITS‑90 fixed point where argon exists simultaneously as a solid, liquid and gas in equilibrium. It is primarily used for calibrating Standard Platinum Resistance Thermometers (SPRTs) and is essential for national metrology institutes and accredited calibration centres requiring the lowest uncertainties.

The Isotech 471 Simple Argon Triple Point Apparatus brings true argon triple‑point realisation within reach for more laboratories than ever. With automated pressure control, faster stabilisation and a simplified operating concept, it provides a reliable, efficient and fully traceable solution for SPRT calibration at the lowest ITS‑90 fixed point.