© Isothermal Technology
Page 42 of 102
923 milliK manual - issue: 1.10
Use the
↑
↑
↑
↑
↓
↓
↓
↓
keys to select each parameter in turn and press the
↵
↵
↵
↵
key to open a soft numeric
keypad and enter the value from the calibration certificate. If no coefficient is supplied (not
all coefficients are required), set the value to zero. Select ‘Eqn Form’ and press the
↵
↵
↵
↵
key to
toggle between the a,b,c and
α
,
β
,
δ
versions of the equation. The milliK will automatically
convert the coefficients as you change the equation form selected.
3.9.4 Using a PRT with ITS90 Conversion
In 1990, the International Temperature Scale was revised and a new set of equations were
defined for converting the resistance of a PRT to temperature. These equations (commonly
referred to as ITS90) comprise a nominal conversion that represent the average conversion
characteristic and deviation functions that provide the adjustment for the characteristics of the
individual thermometer. They are intended for use with high purity platinum and provide a
better fit than can be achieved with the older Callendar Van Dusen equation. The ITS90
equations are sometimes also used with industrial PRTs, made using the lower sensitivity
0.00385K
-1
wire and can provide a small improvement in uncertainty compared with the
Callendar Van Dusen equation.
If your thermometer calibration is presented using ITS90 coefficients, use the
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keys in the
‘Thermometer’ Window to select ‘Conversion’ and then use the
←
←
←
←
→
→
→
→
keys to select
“ITS90”. Use the
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↓
keys to select ‘Coefficients’ and then press the
↵
↵
↵
↵
key to open the
‘ITS90 Coefficients’ Window:
