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ptc-31713101-Visitor
1-Visitor
March 31, 2010
Question

Negative Temperature Problem

  • March 31, 2010
  • 1 reply
  • 2017 views
Hi I am having an issue with negative temperature calculations. One of my worksheets has the following calculation: T1=-4°C T2=19°C T3=T1-T2 This should evaluate to T3=-23°C however MathCAD evaluates it to T3=-842.45°C Closer inspection shows the problem is with the conversion of the negative temperature value from °C to °K: T1=-4°C=-277.15K is clearly wrong, Mathcad appears to be converting the 4°C to K, then applying the - sign. +tve temp values convert to K correctly. Anyone else have problems with this? I can work around it using a refernence temperature, and deltaC units but this adds unneccesarry complication to a very simple equation! Cheers Jamie

1 reply

T
TomGutman1-Visitor
1-Visitor
March 31, 2010
It's the way you've (implicitly) parenthesized the expression. While what you wanted was (-4)°C, what you actually have is -(4°C). BTW, your stated expectation for T3 is wrong. The difference between two Celcius temperatures is not a Celsius temperature. While common usage uses °C for both temperatures and temperature differences, the two are actually quite distinct units and require different conversions. In Mathcad °C is used only for temperatures, not temperature differences.
M
mzeftel1-Visitor
1-Visitor
April 2, 2010
See this article from October 2008 issues of PTC Express on Working with Temperatures in Mathcad, http://www.imakenews.com/ptcexpress/e_article001226319.cfm?x=bdw3H0f,b3jsqcsB,w Mona
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