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RV_102433071-Visitor
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August 22, 2022
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Units reverting into base units

  • August 22, 2022
  • 2 replies
  • 2973 views

Hi,

 

I want Mathcad to display me units in °C/W but it keeps reverting into base units.

So after that I thought to myself to create a unit named CpW but it does not matter it will keep switching into base units. I've seen this post on the forum.

 

https://community.ptc.com/t5/Mathcad/Mathcad-Prime-5-0-automatically-converts-my-defined-units-to/m-p/618572

 

But it does not seems like I can change the base unit inside the matrix TTIsmaj when I display the result, Any idea on how can I do this ?

 

 Thanks

 

RV_10243307_1-1661176455763.png

 

 

RV_10243307_0-1661176375821.png

 

    Best answer by LucMeekes

    In your text you write °C/W (that is: degrees Celsius per Watt),

    in your Prime definition of CpW you define it .as C/W (that is: Coulomb per Watt). You'll probably want to correct that.

    The temperature unit °C is a strange one, because it doesn't relate to the base unit K with just a multiplication factor. The unit °C in Prime is implemented using a function, and that results in the fact that you cannot simply apply it to a vector:

    LucMeekes_0-1661179030666.png

    But you can do:

    LucMeekes_3-1661179422111.png

    I bet in your case those temperatures are temperature differences, in which case you could replace °C with K (because a temperature difference of one degree Celsius is the same as one Kelvin). Alternatively you could use the unit Delta °C:

    LucMeekes_2-1661179220497.png

    All that said: Prime does NOT allow to change the units of individual elements of a result array (vector or matrix).

     

    Success!
    Luc

     

     

     

    2 replies

    L
    LucMeekes23-Emerald IVAnswer
    23-Emerald IV
    August 22, 2022

    In your text you write °C/W (that is: degrees Celsius per Watt),

    in your Prime definition of CpW you define it .as C/W (that is: Coulomb per Watt). You'll probably want to correct that.

    The temperature unit °C is a strange one, because it doesn't relate to the base unit K with just a multiplication factor. The unit °C in Prime is implemented using a function, and that results in the fact that you cannot simply apply it to a vector:

    LucMeekes_0-1661179030666.png

    But you can do:

    LucMeekes_3-1661179422111.png

    I bet in your case those temperatures are temperature differences, in which case you could replace °C with K (because a temperature difference of one degree Celsius is the same as one Kelvin). Alternatively you could use the unit Delta °C:

    LucMeekes_2-1661179220497.png

    All that said: Prime does NOT allow to change the units of individual elements of a result array (vector or matrix).

     

    Success!
    Luc

     

     

     

      W
      Werner_E25-Diamond I
      25-Diamond I
      August 22, 2022

      Unfortunately there is no solution for your problem. Its a great drawback that we cannot manually change the units for single elements in a matrix.

      You could edit the placehoder after the matrix to read C/W. So your second column would show the values you want to see but your first column (time values) will look quite strange 😉

      Only workaround I can think of is to display the two columns singly and change the unit for the second one to C/W.

      T
      TR_97819639-Granite
      9-Granite
      August 22, 2022

      How to determine in what equation when to use deltaC or C? Is there any base requirement when to use which or when the equation is multiplication or addition subtraction or complicated or simple equation?

      W
      Werner_E25-Diamond I
      25-Diamond I
      August 22, 2022

      As Luc already wrote, working with temperature other than Kelvin can be tricky and confusing. Units in Prime usually are implemented as constant multiplication factors. But this is not possible with temperatures because he conversion also requires a shift. So these units are implemented as functions.
      When it comes to a rise of temperatures you should use Delta°C and not °C. Any value given in °C is converted to Kelvin but a value in Delta°C is equivalent to the same value in K

      Werner_E_0-1661186140762.png

      This should explain the examples below

      Werner_E_1-1661186169305.png

      You may also note the examples in the help, especially #5

      https://support.ptc.com/help/mathcad/r8.0/en/index.html#page/PTC_Mathcad_Help%2Fexample_working_with_temperatures.html%23wwID0EK5ZDB

       

       

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