Kiwi scientists help change world-wide measurement standard
Click to enlarge
Click to enlarge
Release from Industrial Research
28 November 2006
Wellington scientists have been instrumental in changing the world-wide standard practice for the precise calibration of
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
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
“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.”
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