[garyed]

This is a formula I found online that converts temperature to R22 pressures.

x = ((temp - 32) / 1.8 + 273.15);
y = (75.30265 + (- 4155.54) / x + 0.018343 * x + (- 11.3186) * log(x));
pressure= exp -1.01325;

In this formula I get the pressure from knowing the temp.
What i'm trying to do is reverse the formula where I know the pressure & want to get the temp.
Are there any math wizards out there that can do it because I sure can't ?

 

[garyed]

Yes it's called PT chart


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I've got plenty of charts but I'm looking for a formula.

 

[garyed]

Doesn't your gage have pressure and temperature on it? The link you included can calculate temperature or pressure. Are you wanting to not use the link?

Sure my gauges tell me all i need to know in the field & it's not that i'm not wanting to use the link, but the formula is for a different programming purpose. The gas pressure calculator in the link gets it's info from a database of different PT charts. When I saw this formula & saw that it gives similar results to a PT chart I thought it would be useful & a lot less memory intensive for programming if I could reverse it but I don't have the math skills to do it.

 

[garyed]

Programing is easier than algebra 1?

Reversing exponential and logarithmic equations is not so easy, assuming it can even be done.

 

[garyed]

You need a new equation. The equation can be flipped around, but it wont do any good, as pressure is derived from 3 variables.


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Not really because the first part of the equation is just converting temp from Fahrenheit to kelvin & I should have just left it out since that's not a problem. I really just need to solve the second line of the equation & the rest I can do.
y = (75.30265 + (- 4155.54) / x + 0.018343 * x + (- 11.3186) * log(x)); The equation as is works fine if you know the value of "x" which is the temperature in degrees kelvin. I just can't figure out how to find "x" if I know the value of "y". Changing the equation to : x= ........................... is the problem I can't solve.

 

[garyed]

I'll ask my kid later if he can do it.
Is it written out on all numbers and math symbols somewhere?
Im no good with word problems

Actually that is all math symbols but the "log" should be "ln" instead because its the natural logarithm so the mathematical equation is: y = 75.30265 + (- 4155.54) / x + 0.018343 * x + (- 11.3186) * ln(x)
If you do the equation on an advanced calculator & substitute 273.15 for "x" which is Kelvin for 32* F then y= 1.6020564547328
Since "x" is in so many places besides the natural log I'm lost at how to reverse engineer the equation.

 

[garyed]

None of this may be nessasary if you tell us what you're up to

I'm working on an android app & trying to keep things a little less memory intensive by using formulas instead of charts. If you look at this temporary page: http://www.oceanhvac.com/r22.php
If you enter the temperature it uses a formula instead of a pt chart to get the corresponding psi for R-22. I want to reverse the formula so you can enter the psi & get the corresponding saturated temperature.
If anyone wants to download the android app & try it feel free to do so by clicking the download button on the page. I'd like to hear any critiques or ideas. I already got the idea for a ductulator from someone on this group.
It has a Dctulator, SH calculator, CFM calculator, Delta T calculator & a Defrost sensor resistance finder. In order to install the app you have to allow apps from unknown sources. I give Hvacrmedic credit because I use his SH formula whenever conditions fall outside the manufacturers SH charts that I have. Anyways I'm just in the planning stages right now with this formula & it may be more useful in an arduino program than for android but its just a project for now.

 

[garyed]

Try this. I lifted it from refrigeration engineer forum. For R22

Temp=-8.13681513E+01+3.20065359E+00*Press-3.81813098E-02*Press^2+2.96408154E-04*Press^3-1.29284314E-06*Press^4+2.90447694E-09*Press^5-2.61193736E-12*Press^6

Just pasted it into the Excel app on my iPhone. Works pretty good. The pressure is in psia though, you'll have to convert.

Thanks,

I tried it using php & it works pretty close to the other formula in reverse. It's amazing to think that someone actually figured out these formulas from scratch. Almost as amazing as your superheat formula.