need help

need help - Messages

#1 Posted: 2026/5/9 08:35:16
Andreas Beldowski

Andreas Beldowski

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Hello,

unfortunately, I can't find the error myself. Why VS(t) and VRG58(t) work well, but V1(t):=VS(t)-VRG58(t) not?

Regards Andreas

Auszug.pdf (114.69 KiB) downloaded 118 time(s).
Auszug.sm (16.52 KiB) downloaded 131 time(s).
#2 Posted: 2026/5/9 09:14:00
sergio

sergio

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It seems that the two quantities have different units of measurement.
Solver_FXLZ2iLlqC.png
sergio
#3 Posted: 2026/5/9 12:44:41
Andreas Beldowski

Andreas Beldowski

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Thanks Sergio,

wrong was VRG58(t):=Ig(t)*(1/ZLRG58+1/RRG58)

right is VRG58(t):=Ig(t)*(ZLRG58+RRG58)

Regards Andreas
#4 Posted: 2026/5/10 05:52:13
Andreas Beldowski

Andreas Beldowski

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Hello,

and here’s another problem. Why does the differential of V1(t) work, but not that of V2(t)?

Both are sine functions; later, I’d like to try using square-wave functions as input as well.

For V1 and V2, I need the peak-to-peak amplitude and the phase difference between the two. I want to see if I can get better approximations for determining C1 by taking RG58 and the probe tip’s internal resistance into account in the measurement results.

Regards Andreas

Translation of “Der Wert ist oberhalb der maximalen Grenze für positive Zahlen” = “The value is above the maximum limit for positive numbers”

Versuch mit R und C mit Oszi.pdf (982.36 KiB) downloaded 97 time(s). The value is above the maximum limit for positive numbers.gif Versuch mit R und C mit Oszi.sm (131.13 KiB) downloaded 132 time(s).
Edited 2026/5/10 06:01:03
#5 Posted: 2026/5/10 08:15:12
StvMath

StvMath

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"Why does the differential of V1(t) work, but not that of V2(t)?"

It's a combination of the size of the numbers and the order in which SMath does its calculations. Try:

dV2dt.png
#6 Posted: 2026/5/10 10:41:34
Andreas Beldowski

Andreas Beldowski

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Yeah, that's how it works for me, too.
#7 Posted: 2026/5/12 13:09:32
Andreas Beldowski

Andreas Beldowski

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It's me again, with a new problem.

Why doesn't the last line work, when the four lines above it do?

Versuch mit R und C mit Oszi Auszug.gif Versuch mit R und C mit Oszi Auszug.pdf (910.43 KiB) downloaded 80 time(s). Versuch mit R und C mit Oszi Auszug.sm (130.35 KiB) downloaded 110 time(s).
#8 Posted: 2026/5/13 02:13:04
Alvaro

Alvaro

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Hi. I have no idea why it fails, however this may be a workaround, consisting of directly applying the Newton-Raphson method.

image.png

Versuch mit R und C mit Oszi Auszug.sm (121.16 KiB) downloaded 97 time(s).

Best regards.
Alvaro.
#9 Posted: 2026/5/13 05:47:01
Andreas Beldowski

Andreas Beldowski

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And why can I only use the values for LV1 and LV2 once, but the values for LdV1dt and LdV2dt multiple times?
I had already deleted the `clear()` statements, but that wasn't the problem.

Versuch mit R und C mit Oszi 3.gif
Edited 2026/5/13 05:48:52
#10 Posted: 2026/5/13 09:41:38
Alvaro

Alvaro

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Hi. Use eval:

image.png

Best regards.
Alvaro.
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