(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Hi, I'm asking the usual "what formula gives me these results" question, but with a twist; I'm attempting to make a "virtual" analogue multimeter that replicates a physical piece of equipment, for training purposes. The idea is that a random MegaOhm value will be generated, and displayed by the needle; the user must then determine whether it falls within the pass or fail mark for a piece of equipment being tested.

The problem is that the scale is non-linear. It's exponential of some sort. But after a day of intensive online searching, and resorting to throwing numbers at various equations, I can't come up with a formula that gives a reasonable approximation, or even anything remotely close!

NB: ANY formula that fits the points is fine by me; I've severely over-engineered this problem, but I'm determined to get it working!

2. Relevant equations

Essentially the multimeter needle range is 90degrees of motion, going from zero MOhms to Infinite MOhms in an exponential manner. The following are data points relating MOhms to degrees, very roughly measured from a photo of the multimeter:

value, angle (degrees)

0, 0

0.1, 5.5

0.2, 11.25

0.5, 28

1, 39.7

2, 46.5

5, 61.8

10, 68.65

20, 79.2

50, 86

100, 88.35

200, 89.4

infinity, 90

[EDIT] Here's an example multimeter to show the exponential scale (different from mine, but you get the idea)

http://www.opamp-electronics.com/tutorials/images/dc/50035.jpg

3. The attempt at a solution

I've tried plotting these in Excel and using a trendline, but nothing comes remotely close.

Tried creating dynamic formula that I could change various key values of and see the results for all input values, but could never get a curve that came close; always curved too sharply too late, and I just don't know what terminology I should be searching for to fix it!

I can SEE a definite trend in the plotted points, but Excel doesn't seem to see what I see.

This is intended just as a "cool" factor for some training material, and I've spent way too much time on it, so it's highly frustrating that something that should be so simple has had me (and several of my colleagues) climbing up the walls! Any help would be greatly appreciated!

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# Homework Help: Multimeter Ohms exponential scale; formula?

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