Applying function to graph, help please..!

Question

Hey Guys, 
I am very new to LabView and do not even know how do I construct the question but I´ll explain it here.
I am using LabView 8.5 combined with UV-Vis spectrometer to take the readings of absorption against time of a reaction mixture. The reaction continues for 48 hours. What I want to do is, 'at the completion of the reaction, the absorbance graph will become constant. As the absorbance becomes constant, I want the program to swtich on a pump which will push a reagent into the reaction pot containg the reaction mixture and then continue taking reading of absorbance´.. Is it clear ? Is there a way to do so ? I mean how to tell the LabView that as the absorbance becomes constant, switch on the pump while continuing measuring absorbance?
I shall highly appreciate any help.
Thank you.
 

Answer 1

What you need to do is to define how much variation in absorbance readings over some period of time is considered "constant." There will always be some noise and possibly drift in the measurements, so you cannot reasonably expect to have, say, ten consecutive identical readings.
One way to do this is to take the last group of readings (where you decide how many are in the group), do a linear regression on the readings, and define "constant" as the absolute value of the slope less than some threshold. This tends to take the noise out and may be fairly sensitive to small changes in the slope.
Lynn