Voltage Divider: Solve for Missing Variable

#1 Posted: 4/8/2022 3:17:40 AM

Mark R Harris

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Hi,

I've been unable to solve this (pardon the pun):

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20220408 Voltage Divider Solve.sm (36 KiB) downloaded 56 time(s).

Any thoughts?

Thank you in advance.
Mark

#2 Posted: 4/8/2022 9:25:46 AM

overlord

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You have defined R2, maybe that's why you can't solve.
First you need to be sure calculation variable cleared.
And if you defined your function, it will also prevent the solution.

Some remembrance for smath solvers;
solve(), roots() and al_nleqsolve() won't work directly with units.
You have to trick them for units, adding into equations.
Maple solve and FindRoot() can work with units.
I also included mathblock method, which relies on FindRoot().

If your root is beyond -20,20 you have to specify it for roots() and solve().
Unless you didn't already change Root Ranges in options.
And you also have to guess a starting point for FindRoot().

Regards

20220408 Voltage Divider Solve_v2.sm (50 KiB) downloaded 53 time(s).

#3 Posted: 4/8/2022 9:32:28 AM

Jean Giraud

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I've been unable to solve this

Make it SI ...

#4 Posted: 4/8/2022 9:41:34 AM

overlord

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Wrote
Make it SI ...

That kΩ is not an SI unit you clown.
It is simply equal to 1, not (kg*m^2)/(A^2*s^3).

#5 Posted: 4/8/2022 10:08:47 AM

Jean Giraud

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That kÎ© is not an SI unit

#6 Posted: 4/8/2022 10:09:50 AM

⚜ Kenny Lemens, P.E. ᵂᴵ

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Resistive Voltage Divider Solve for R2 (or any variable)

Greetings Mark,

For your first part, you can copy and paste this formula (solved for R2):

R2:{R1*V.out}/{V.in-V.out}

For your second part, please reference the following forum topic: https://en.smath.com/forum/yaf_postst21770findunread_solving-simultaneous-equations-with-Solve.aspx
There is a healthy discussion of various methods to solve for an unknown variable.

Hope that Helps!
-Kenny Lemens, P.E.

"No matter where you go, there you are." -Buckaroo BanzaiHotkeys: https://en.smath.com/forum/resource.ashx?a=45771&b=2

#7 Posted: 4/8/2022 10:16:47 AM

overlord

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Wrote

Your kΩ is not SI unit dumbass, which has value of 1.
The one you have defined as 1, that you wrote kΩ:1.
SMath kΩ of course is a SI unit, not your goofer kΩ.

If you claim your kΩ is suitable to SI, just share us the multiplication of "your" kΩ with A^2.
A is Ampere if I could help your unitless brain. For your information, result is kW.

I will just wait your gibberish reply and answer it with a new insult.

#8 Posted: 4/8/2022 3:19:29 PM

Jean Giraud

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I've been unable to solve this

As well, maple will solve. Maple is unit-less.
Smath w/o maple is missing the best, particularly in
Process Control & Instrumentation.
Why not a new thread for your Thermodynamic/Chemical project.
Cherrs ... Jean.

#9 Posted: 4/8/2022 3:48:02 PM

Alvaro Diaz Falconi

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...
As well, maple will solve. Maple is unit-less.
...

Of course not. Maple units help page: https://www.maplesoft.com/index.html?path=units

Either Wolfram Mathematica:

My old units package, for version 5.0: https://library.wolfram.com/infocenter/MathSource/5511/

New Quantity package: https://reference.wolfram.com/language/ref/Quantity.html

Best regards.
Alvaro.

#10 Posted: 4/8/2022 4:25:15 PM

Mark R Harris

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Thank you all so much. The help is very greatly appreciated.
Mark

#11 Posted: 4/8/2022 4:42:43 PM

Mark R Harris

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Wrote

Wrote
Resistive Voltage Divider Solve for R2 (or any variable)

Greetings Mark,

For your first part, you can copy and paste this formula (solved for R2):
R2:{R1*V.out}/{V.in-V.out}
...

Hope that Helps!
-Kenny Lemens, P.E.

Thank you so much Kenny. The direct 'no solving required' approach is perfect.

Again, thank you.
Mark

#12 Posted: 4/8/2022 8:37:47 PM

Jean Giraud

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Of course not

Of course NOT !

Inst_Valve Sizing CV series.sm (6 KiB) downloaded 44 time(s).

#13 Posted: 4/8/2022 10:17:53 PM

overlord

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Of course NOT !

Of course it is, even your example can solve with SI units.
If you were not a duffer and enter units as they should be, you would witness the miracle.
Look Jean. No magic numbers, no conversion factors, only numbers and units.
Units can easily be shown in their kilo, mega, centi, mili form by using SI.
Declaring them as 1 or creating same name units is just pure stupidity.
I get it, you learn to calculate when units are not a thing for softwares back then.
But time is changed. Softwares have unit supports now, it is the correct path to use units.
You simply resist to learn new things, in every situation, and encourage your ignorance to new users.
Which means you don't have primer feature of a scientist or engineer.

#14 Posted: 4/9/2022 6:44:26 AM

Вячеслав Мезенцев

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To be completely honest, I helped Maple understand units. The plugin uses the old 6th version of the program, and support for units appeared in the 7th version.

Russia ☭ forever, Viacheslav N. Mezentsev

#15 Posted: 4/9/2022 10:38:56 AM

Jean Giraud

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About that long discussion Si and Solve,
you can get lot more solving on the canvas.
Willing difficult Titration, more convivial Pitot.
Cheers ... Jean.
By same token: thanks Viacheslav for maple/Units

Titration.sm (26 KiB) downloaded 39 time(s).

#16 Posted: 4/10/2022 12:16:13 AM

overlord

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To be completely honest, I helped Maple understand units. The plugin uses the old 6th version of the program, and support for units appeared in the 7th version.

Thanks for the unit support. So original maple has unit support since 2001.
And smath maple plugin has also unit support, that is what concerns us, which proves Jean is wrong again.

#17 Posted: 4/10/2022 4:11:22 AM

Вячеслав Мезенцев

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Thanks for the unit support.

Wrote
Updated (maple()). Fixed issue with trigonometric functions, added support for units.

A post about this can be found here.

And how it works:

In Maple units are passed as undefined variables wrapped in single quotes. Therefore, in fact, the SMath does all the work with units. This happens implicitly. But Maple can also work with them, as with symbolic variables.

Russia ☭ forever, Viacheslav N. Mezentsev

#18 Posted: 4/10/2022 9:44:02 AM

Jean Giraud

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Thanks for the unit support. So original maple has unit support since 2001.
And smath maple plugin has also unit support, that is what concerns us, which proves Jean is wrong again

Viacheslav can confirm the date maple/Units.

#19 Posted: 4/10/2022 9:49:18 AM

overlord

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