Produce an equation for determining y from values of x

[carlaz]

Need some maths help with a calibration curve we have produced at work. Following the instructions we are to plot log CO2 against mV. We tried to get excel to produce an equation of the graph but it spits out natural log which when rearrange come out as zero.

We resorted to printing the graph and drawing a straight line to form an equation but that also produces nonsensical numbers.

Does anyone have the time and skill to help use produce a formula we can use to determine CO2 concentration from a mV reading? Really appreciated if you could help

Data

CO2 0.5 = 20850mV
1.0 = 19037
2.5 = 15371
4.0 = 13957

 

[tkhunny]

One would have to be a little cautious with that. What is the expected behavior?

In other words,

1) As \(\displaystyle CO_{2}\) increases, does mV decrease to zero or does it level off above zero?

2) As \(\displaystyle CO_{2}\) decreases toward zero, does mV increase without bound (maybe a transient massive value?), or does it have limits?

Have you tried \(\displaystyle mV = 21510\cdot e^{-0.115\cdot CO_{2}}\)?

 

[DrPhil]

Need some maths help with a calibration curve we have produced at work. Following the instructions we are to plot log CO2 against mV. We tried to get excel to produce an equation of the graph but it spits out natural log which when rearrange come out as zero.

We resorted to printing the graph and drawing a straight line to form an equation but that also produces nonsensical numbers.

Does anyone have the time and skill to help use produce a formula we can use to determine CO2 concentration from a mV reading? Really appreciated if you could help

Data

CO2 0.5 = 20850mV
1.0 = 19037
2.5 = 15371
4.0 = 13957

colA=CO2, colB=mV, col(C) = "=log(A2)"
Used the "LINEST" function in cell range F2:G2
=LINEST(C2:C5,B2:B5) --> Ctrl-Shift-Enter
Then formula in colD is "=G$2 + F$2*B2"
.........................colE is "=10^D2"

Linear Regression: log(CO2) = 2.3587 - 0.00012621 * (mV)