Easy-to-use, inexpensive standard with uncertainty better than ±
0.0001 °C
Four sizes and two shells (glass and quartz) to choose from
Isotopic composition of Vienna Standard Mean Ocean Water
The triple point of water (TPW) is not only the most accurate and
fundamental temperature standard available, it’s also one of the least
expensive and simplest to use.
Triple point of water cells fill four critical purposes.
First, they provide the most reliable way to identify unacceptable
thermometer drift between calibrations including immediately after a
calibration if the thermometer has been shipped.
Iterim checks are critical for maintaining confidence in thermometer
readings between calibrations. Second, they provide a critical
calibration point with unequaled uncertainties.
Third, for users who characterize probes using ratios,
interim checks at the triple point of water allow for quick and easy
updates to the characterizations of critical thermometer standards,
which can be used to extend calibration intervals.
And lastly, the triple point of water is where the practical temperature
scale (ITS-90) and the thermodynamic temperature scale meet,
since the triple point of water is assigned the value 273.16 K (0.01
°C) by the ITS-90 and the Kelvin is defined as 1/273.16 of the
thermodynamic temperature of the triple point of water.
Good triple point of water cells contain only pure water and pure
water vapor. (There is almost no residual air left in them.)
When a portion of the water is frozen correctly and water coexists
within the cell in its three phases, the triple point of water" is realized.
Fluke Calibration water cells achieve this temperature with expanded
uncertainties of less than 0.0001 °C and reproducibilities within
0.00002 °C.