Problem about temperature unit for SGL, LabVIEW 7.0 and 7.1

[Xu]

A question about temperature unit for SGL and DBL, LabVIEW 7.0 and 7.1.

The attachment is a test VI.

From running the test.vi it shows that the temperature units Cdeg and degC are different (why?), and Cdeg and K seem to be same.

For a SGL control in degC unit (i.e. "temperature 3" in frontpanel of test.vi), the default value can not set to zero. When set the default value to 0, it shows -6.10352E-6.

The similar problem exists for the units Fdeg and degF.

Could anyone please give me an explanation?

Thank you,

Xu

[Bob_Y.]

Cdeg is another way of saying "In degrees defined by the Celsuis scale starting from absolute zero". So it is the same as Kelvin.

degC is another way of saying "In degrees defined by the Celsius scale starting from the freezing point of pure water at sea level".

As for missing zero by a about six microdegrees, it is because when units are used, the values are always converted to base units. The base unit for tempurature is Kelvin. 0 degC just happens to be a bit off from what a computer can give for that many degrees Kelvin. I am not sure why it is changing your input, however.

[JeanPierre]

Cdeg and Fdeg are used for temperature differences, e.g. a difference of 5 Celsius (Cdeg) is equivalent to 9 Fahrenheit (Fdeg) (and to 5 Kelvin of course).

About the display, 0°C is stored internally in K (-273.15). In single precision, the closest number that can represent this is about -273,14999390 so that's why 0°C isn't exactly 0. Just change the format and precision (2 digits floating point) to display 0.00.