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ML_96327091-Visitor
1-Visitor
December 21, 2020
Question

MathCAD exponential functions

  • December 21, 2020
  • 1 reply
  • 2122 views

Hi all,

 

I have a slight problem with my code.

I have highlighted and explained the flow as well as i can. Please let me know if further clarification is required. The .mcd file is also attached for your reference.

My question: When I look at the values of U_n and PTCU_n, the values seem to keep increasing indefinitely. In theory, PTCU_n should stabilize at 75% when tn_n reaches 6xRTC and not increase any further. I am not sure where I am going wrong.

 

Thoughts?

 

Any help is appreciated.

Thank you in advance!

 

 

 

ML_9632709_0-1608582117471.png

 

    1 reply

    L
    LucMeekes23-Emerald IV
    23-Emerald IV
    December 21, 2020

    Does this make sense?

    LucMeekes_0-1608585061540.png

    I reduced the scale of PTCU by a factor of 100, to make it fit on the same scale as the others.

    Note that your construct:

    LucMeekes_1-1608585152627.png

    is reduced by me to

    LucMeekes_3-1608585257472.png

    because the two surrounding expressions are not assigning anything.

    Success!

    Luc

     

      M
      ML_96327091-VisitorAuthor
      1-Visitor
      December 21, 2020

      Thanks for your response, Luc.

       

      A clarification: The square waveform generator section is designed that way because I am modelling a motor inrush. Hence the two equations surrounding a<--a+1 are to define the spike in current during a motor start.

       

      That aside, this certainly polishes my graph by a lot.

      However, the exponential function (U_n) and thereby the PTCU_n function still does not settle at 75%. I am not sure why. With my hand calculation, the model yields the desired answer. But, with my code, it never seems to settle.

      Do you think changing the exp to a log function might help?

       

      Thank you, again!

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