LumaSense Technologies INNOVA 1412i - Manual (Page 166)

Chapter 12
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BE6025-15 1412i Photoacoustic Gas Monitor LumaSense Technologies A/S
Page 166 of 202
If the desired measurement range is mainly within the linear
range then the low concentration should be between 1000 and 10
000 times the detection limit.
If the desired measurement range is mainly above the linear
range then the low concentration should be more than 10 000
times the detection limit.
· The High Concentration should be 75% to 100% of the highest
concentration you expect to measure, but no higher than this.
Simple Test to Determine the Linearity
Let us assume that you wish to measure a gas over a dynamic range
from 100 ppm and 3000 ppm of a gas that has a detection limit of
0.3 ppm.
In this case, the range in which you want to measure is from 333
times to 10 000 times the detection limit. With our general
guidelines, you’re not able to decide whether you have to perform a
single- or two-point calibration. Therefore, we advise you to perform
the following test:
1. Perform a single-point calibration with a low concentration of the
gas. Use 10% of the highest expected concentration level. In this
case, use 300 ppm (1000 times the detection limit).
2. Perform a measurement with a high concentration of the gas.
Use, for example, 90% of the highest expected concentration
level. In this case, use 2700 ppm.
If the measured gas concentration differs by more than 5% from the
real concentration, then a two-point calibration with 2 gas
concentrations is recommended.
In the example in Fig.12.15b , we have measured 2400 ppm with
2700 ppm gas. This gives an error of 11% and an even greater error
at the highest concentration level.