Kiwis help change world-wide measurement standard

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Release from Industrial Research
28 November 2006

Wellington scientists have been instrumental in changing the world-wide standard practice for the precise calibration of thermometers.

Standards laboratories around the world use the “triple point” of water as the most accurate way to check thermometers, using what is known as a triple point “cell” to do so.

It has been years in the making, but by comparison, almost over night, two of the world’s largest manufacturers of triple point cells changed their business operations to accommodate the New Zealander’s refinements to the process.

The triple point is the temperature at which a substance coexists as a solid, liquid and vapour - in equilibrium. By internationally agreed definition, this happens for water at an exact temperature of 0.01 degrees C.

Industrial Research’s measurement standard scientist Rod White says getting that measurement right is especially important for research organisations that require high precision accuracy – like laboratories involved with oil testing or researchers needing to measure ocean currents.

“For example, by measuring ocean temperatures to a thousandth of a degree or so, you can identify a body of water then track submarine currents. This in turn can track what food-life is available and that has a very direct impact on the fishing industry.”

Over the years though, the Industrial Research scientists began to wonder whether the triple point of water measurement was really as reliable as everyone thought it was.

So when the international bureau of weights and measures (BIPM) decided to carry out an international comparison of triple point of water cells, scientists at Industrial Research were keen to participate.

They had long had an inkling that the isotopic composition of the water (the atomic structure that determines light or heavy water) had an influence on the water’s triple point temperature.

Test samples with water from the Antarctic and water from New Zealand proved they were onto something. Further testing concluded that the source of water used in a triple point of water cell indeed had a much larger influence than anyone had realised.

“That’s why scientists living closer to the equator were getting much higher readings on their cells than people like us in New Zealand,” Dr White says.

Several published papers later, the findings began to sink in with the rest of the science world, and as of October last year, the international standard for triple point of water cell measurements changed to take into account the isotopic structure of the water.

Now it is the legal measurement system that most industry world-wide refer to and it’s given the New Zealand Measurement Standards Laboratory (part of Industrial Research) the credibility that many laboratories strive to achieve.

“We’d never have dreamt that we’d make such an impact at an international level – but it’s been a very satisfying experience for a very small group of New Zealanders.”

ENDS

Background
The New Zealand Measurement Standards Laboratory is the national metrology institute, responsible for the provision of physical measurement standards in New Zealand. It is based at Industrial Research’s head office in Lower Hutt, Wellington region. www.msl.cri.nz

Industrial Research Ltd is a technology company based on world-class science and engineering capability. It is also one of New Zealand’s crown research institutes. www.irl.cri.nz

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