Problem with units

Problem with units - Сообщения

#1 Опубликовано: 11.07.2011 18:43:06
jessedavis

jessedavis

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consider following entry: 715*'BTU/'hr*'ft^2*'degF = where degF stands for the deg symbol and F as found in the units popup. All the units are blue and 715 and = sign are black. This is a perfectly good constant (heat flow) which I wanted to convert to SI units; however, no matter what I do I get a units mismatch error. I check out each unit individually and found them to be correct. 0.89 build 3856---- you can not have a units mismatch in a constant no matter what units you choose - a constant is a defined entity (could be laundry#/raisins). I think it is a bug but I am not sure. I leave it to you.




Regards,
jd

p.s. This is a nicely done program; however, it needs better advertisement to increase the user base and the dollars
#2 Опубликовано: 12.07.2011 04:01:25
Radovan Omorjan

Radovan Omorjan

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Hello,

It is a known issue regarding relative and absolute temperature scales. You should not use relative temperature scales in the expression like these. Please look at the posts under Temperature scales
Here is an example as well in order to clarify a bit:
[LIVE width=394 height=308]http://smath.info/live/?file=2936[/LIVE]
As you could see, if you use the relative temperatures unit in the expression (Fahrenheit) SMath will get confused. The solution is to define new temperature units using the absolute temperature scales (Rankine. Kelvin)

I hope it makes the things more clear now.

Regards,
Radovan
When Sisyphus climbed to the top of a hill, they said: "Wrong boulder!"
#3 Опубликовано: 14.07.2011 15:57:50
maweilian

maweilian

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Just to add to what Radovan is saying, please take a look at the Examples page on the wiki, see the last entry under the Engineering section called Engine Heat Rejection Calcs. This is another example of how to perform calculations using relative temperature scales in Smath. Here is a direct link as well: Heat Rejection Calcs

Sincerely,
Will
Will Massie Mechanical Engineer Oregon, USA
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Radovan Omorjan 14.07.2011 16:03:00
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