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Dec 21, 2020
03:28 PM

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Dec 21, 2020
03:28 PM

MathCAD exponential functions

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!

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2 REPLIES 2

Dec 21, 2020
04:16 PM

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Dec 21, 2020
04:16 PM

Does this make sense?

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:

is reduced by me to

because the two surrounding expressions are not assigning anything.

Success!

Luc

Dec 21, 2020
04:56 PM

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Dec 21, 2020
04:56 PM

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!