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Mathcad 14 get confused using units

Newbie

Mathcad 14 get confused using units

Hi,

I have made some calculation in Mathcad 14, and it seems that there is a bug....

Udklip.JPG

On the right I got the result with units, and to the left without...?

Can some buddy explain this.

Best regards

Jesper

25 REPLIES 25

Re: Mathcad 14 get confused using units

Attach please the Mathcad-sheet

Re: Mathcad 14 get confused using units

Hi,

I have now attaced the document.

Hope there is some help.

Best regards

Jesper

Re: Mathcad 14 get confused using units

Sorry but

bar.png

Re: Mathcad 14 get confused using units

Yes

Re: Mathcad 14 get confused using units

Hello Jesper,

you have two issues here: one is that you obveride a MC built in unit; i.e. S which is defined as the inverse of electrical resistance. The second issue is that you're using MCs unit conversion on an empirical equation. I happen to know this equation because I need to use it quite often (shell thickness for a cylindrical pressure vessel - right?).

You can't use the unit conversion for such an equation because there are some fudge factors hidden within the "20". If you use dimensionless variables for this kind of calculation it will work just fine.

Raiko

Re: Mathcad 14 get confused using units

Hi Raiko,

Yes your are correct it is pressure vessel. Ok, I then just change the safety factor S to S1, and sadly,

get rid of the units , unless somebody else can't help.

and thanks for the quick response

Jesper

Re: Mathcad 14 get confused using units

get rid of the units , unless somebody else can't help.

Look at the attched if it would help

Re: Mathcad 14 get confused using units

Hi Werner,

Thanks for your answer, I think I will go with this.

Jesper

Re: Mathcad 14 get confused using units

You may want to read Harveys remarks concerning empirical formulas and units here http://communities.ptc.com/message/196366#196366

and esp here http://communities.ptc.com/message/196433#196433

BTW, you don't have to rename your variable S if you don't want to do so. It does no harm as long as you don't need unit Siemens later in your sheet.

I think Raiko just wanted to explain what caused the green undeline, its just a warning as of the redefinition and you can turn off warning in Preferences.

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