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post #1 of 2 (permalink) Old 02-22-2003, 10:33 PM Thread Starter
Rock's Avatar
Join Date: Mar 2000
Posts: 1,725
Question I need some MS Excel help!!

I have 9 points (x,y) that I need to expand to 30 points total.

Does anyone know how to get the 30 expanded points from the initial 9 points?

Can anyone possibly walk me through this?

Background info: I have a Tweecer RT and I'm trying to retune my MAF Transfer function. I have a Pro-M meter on the car and I have the flow sheet that gives the voltage and the kg/hr. Each axis has 9 points total. The Tweecer needs a total of 30 points for each axis. So I need to get the "extra" number to input into the tweecer.

Here are the values that I'm dealing with:

X Axis:

Y Axis:

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post #2 of 2 (permalink) Old 02-23-2003, 04:50 AM
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Join Date: May 2000
Location: Portland, OR
Posts: 8,316
If that's flow over time, I'm guessing you can calculate the seperation between each point, to find the linear curve, and be able to do a best guess input of the in-between values.

You'll need the time intervals between each value you have. Given a known time interval, you should be able to simply take a calculator, and subtract one value (b) from the previous value (a), then divide the resulting value (c) by the time lapsed between the two values (d), to get the placement of the inbetween values on the graph (e). Then you add (e) to (a) to get (e1). Then (e) to (e1) to get (e2). And so on.

b - a = c
c / d = e

For example (I just assumed a 3 second interval for this):

0.6710 - 0.3221 = 0.3489
0.3489 / 3 = 0.1163

a: 0.3221
e1: 0.4384
e2: 0.5547
b: 0.6710

And obviously e3: 0.6710

From there, just input the (e) values between the (a) and (b) values, and do that for each data pair. Once you've gotten all of the inbetween values, then you can trim down to the 20 that you need on each axis.

Just thought of this, but you might could make it easier on yourself, by subtracting the first value from the last value. Divide the resulting number by 20 (or 18, since we only need 18 in-between numbers).

a: 0.3221
e01: 0.5399
e02: 0.7577
e03: 0.9755
e04: 1.1933
e05: 1.4111
e06: 1.6289
e07: 1.8467
e08: 2.0645
e09: 2.2823
e10: 2.5001
e11: 2.7179
e12: 2.9357
e13: 3.1535
e14: 3.3713
e15: 3.5891
e16: 3.8069
e17: 4.0247
b: 4.2430

(e = 0.2178 (0.21782777777777777777777777777778, actually), which will put (e18 or b) at 4.2425 since (e) was truncated to only 4 decimal places. But should still work for the X Axis's 20 points)

Obviously, going through each data pair individually, using the actual time intervals will net more acurate results.

edit: DOH! Just re-read that you needed 30 points, not 20. Hehe. Oh well, same concept, but instead of dividing (e) by 18, divide it by 28. Hmmm... actually 29. I just recounted, and noticed my division by 18 resulted in only 19 total values, not 20. I always hated math

I guess, if you go with the time interval / data pair method above, depending on what the time intervals are, if there's not enough time interval iterations to make 30 points, you can go to half seconds, or even 1/10th or 1/100th seconds, to boost the number of time intervals between each data pair.

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Last edited by DarkWolf; 02-23-2003 at 04:59 AM.
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