One last question about potentiometers and graphing results SOLVED

So you all have been very helpful with the voltage divider simulation that I've been preparing for my students. Also, I understand the R.K sweep variable now. I have one last issue and it comes out in the interpretation of the graphical results.

When the results of an R.K simulation using a potentiometer are graphed, the graph has the x-axis as the R.K value from 0 to 1 and the y-axis as potential or current as requested in the graph simulation expressions. I've searched and played, but I see no way to multiply the R.K axis by the constant maximum value of the potentiometer so that a true value of the appropriate (V versus R) or (I versus R) result needed can be picked off the graph. I'm working in particular with a Wheatstone Bridge setup. ( ).

You'll notice on the graph that 0.667 times the 35k Ohm max potentiometer resistance gives the correct balance for the Bridge. However, nothing I do can change the x-axis to R4.K * 35k so the result is obvious. Yes, I can plot from Excel, but I was wondering if that is my only choice.

Thanks for all of your help, Carol Strong UAH

by strongc
August 30, 2020

2 Answers

Answer by mrobbins

Two options.

Option 1:

Use a resistor for R4 instead of a potentiometer, and then sweep over R4.R directly from 0 to 35k. Try this one:

Option 2:

Define a parameter DESIRED_RESISTANCE. The DC sweep controls this directly from 0 to 35k. We've set R4.K = DESIRED_RESISTANCE / 35k. So for every point on the DESIRED_RESISTANCE x-axis, the simulator recalculates the corresponding R4.K before solving the circuit. Try this one:

ACCEPTED +1 vote
by mrobbins
August 30, 2020

I did a quick easy adjustment on one of the circuits you have in the Textbook to help with others having my same difficulties. I've set my circuit as Public, but am including the URL here if you would like to add it to your stash. I think the steps should be clear to even a newbie like me.

Again, thanks for your help.

Carol Strong

by strongc
August 31, 2020

Answer by strongc

Fantastic!! I was pretty sure there was a way. I walked away after I posted the message to let my mind wander and I was just starting to think about defining a variable like you did in the second example. I had seen something like this in the textbook in the solving equations sections. I really want the students to have a grasp of what a potentiometer looks like and how it works, but was lost on a hint for the x-axis to relate it back to the 35k max. This makes lots of sense and the students will understand also

Thanks so much for getting back to me so quickly. I'll sleep better tonight and I'll be able to have this finished for myself and my TA by tomorrow.

If you were in town, I'd hand you some of my fresh homemade Sherried Indian Cheese Spread. If you're into skirting the edge of not-actually-cooking, let me know and I'll pass along the recipe. If you can fry bacon, you can make it!

Thanks once again, Carol Strong UAH

+1 vote
by strongc
August 30, 2020

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