It's a long time since I learned about quadratic functions like ax^2+bx+c, so I need some help finding the correct way to express the following points.

x=0, y=0
x=630, y=500
x=1000, y=900

It's for the calibration of my fill level, using an mps pressure 40. I know when the tank is empty (0mbar, 0ml), when it's half full, which it is at the moment (630mbar, 500ml) and I know when it's full (1000mbar, 900ml). I assume that the max for the mps is 1000mbar, correct me if my assumption is incorrect.

Zitat von »rapapa«

You can easiliy use Wolfram Alpha for this. Use this input. This gives you a = 67/233100 (approx. 0,000287) and b = 14279/23310 (approx 0,613). c should be zero because y=0 at x=0.
Good luck!

Not sure if I get that one.

I need the x values for y=100, 200, 300 etc. up to 900. How do I get them from your solution? A formula I can plug into Excel would be great.

Zitat von »rapapa«

I was just using the formula you mentioned. So you would be using a quadratic interpolation, which I asume would be a good approximation. The formula would then be :Level = 0,000287*pressure²+0,613*pressure.

I had to adjust the numbers a little and tried this formula, which gave a curve that goes negative for the start of the graph and since I can't have less than 0ml in the reservoir I'm not sure where I failed.

The pressure with 500ml in the tank is 800mbar, with 900ml in the tank it's 1023mbar (the maximum the meter allows for).

500=a*800*800+b*800, 900=a*1023*1023+b*1023

X Y
--------------
0 0
68 -14
136 -18
205 -11
273 6
341 34
409 73
477 122
546 182
614 253
800 500
682 334
750 426
818 529
887 642
955 766
1023 900

I've topped the tank now to check the maximum pressure, but it will take some time before the value is steady.

And I forgot that it has to be corrected for the actually atmospheric pressure.

Zitat von »rapapa«

Are you sure you´ve connected the tubes the right way to the sensor? I actually would expect a near lineair curve.

I'm redoing the whole stuff now, measuring every 10% of the tank. The max value of 1023 isn't correct anyway. Hoping a number of values will get me to understand how this pressure sensor works, as a level meter.