Ian,
you asked on Fri, 04 Jun 2004 15:06:14 +0100:
I am writing some software to test our IRcels, these are infra red gas
detection sensors used to detect CO2 or hydrocarbons eg pentane.
For the test I have to calculate the standard fractional absorbance(X)
of the test gas from the following equation.
%CO2=(((3.10933*(X*X))+(.5602*X)))/(0.30204-X)
For a gas bottle of 2%CO2 I have been given a value of 0.19144 for X
so far so good. Plug a value of 0.19144 into the equation and you will get a solution of 1.99999
In reality the gas concentration would not be 2.00 it would probably be 2.05 for example therefore I have to use the equation in an iterative manner, modifying the value of X each time until the solution = 2.05 ...snip...
No!
Others have stated a solution for this equation to calculate a proper value of X in order to get the required result. So far so good.
I've done (respiration) gas analysis in my PhD project (years ago).
What you describe sounds more like calibration problems similar to what I had to perform.
If your equation is given 'ad hoc' and can not change ist parameters, then you should get another reading for X from your cells. It should, however, be in the range of those values as given from the equation's solution.
But those coefficients do not 'look' like 'fixed' parameters, but more like results of a calibration process, e.g. a curve fitting or such.
If you are going to somehow calibrate your cells you should consider feeding them with differrent mixed gases and perform an individual calibration on each of the cells. If you know the fractional gas concentration in fresh air and in your actual test gas, you'll need only about two or three other gas samples to do your curve fitting.
Greetings from Germany! -- Uwe Frenz
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