TGS2442 Datasheet, PDF (20/25 Pages) List of Unclassifed Manufacturers – Detection of Carbon Monoxide

CALIBRATION OF TGS2442
c. Compensation for variation within Rs grades
10
Variation in absolute Rs values among sensors within
any given grade should be normalized by adjusting
ƒ(Rref) as part of the calibration process.
1
ƒ(Rref) = ( 5 - V3 ) / V3
ƒ(Rs^) is defined as a variation compensated ƒ(Rs^x)
value:
0.1
ƒ(Rs^) = ƒ(Rs^x) / ƒ(Rref)
To calibrate the sensor correctly, ƒ(Rs^) should be
equal to 1.0 at the desired concentration. To do this,
change V3 values by adjusting VRadj. Figures 6a and
6b show the variation within Rs grades and the result
of compensating for such Rs variation.
0.01
10
d. Compensation for variation within β grades
10
Variation in sensitivity slopes (α) among sensors
within any β grade should be compensated in the
calibration process. This requires that a second ƒ(Rs^)
value (at 300ppm of CO, for example) be obtained:
1
* measure actual ƒ(Rs) at second CO␣ concentration
* calculate ƒ(Rs^) for the second concentration
* using the ƒ(Rs^) values for the two concentrations, _0.1
calculate the slope (α):
α
=
log
ƒ(Rs^)
(300ppm) - log ƒ(Rs^)
log 300 - log 100
(100ppm)
* store the α value in the microcomputer
0.01
10
e. Converting ƒ(Rs^) to CO concentration output
Using the sensitivity curve slope (α) determined
10
above, actual CO␣ concentration (C) can be calculated
for usage in conversion to COHb:
C = 100 x ƒ(Rs^)^1/α
max
center
min
100
1000
CO Concentration (ppm)
Figure 6a - Rs variation within Rs grades
(Ro = Rs at 100ppm CO, 25˚C/40%RH)
100
1000
CO Concentration (ppm)
Figure 6b - Rs variation compensation
(Ro = Rs at 100ppm CO, 25˚C/40%RH)
1
Revised 04/01
0.1
10
100
CO Concentration (ppm)
Figure 7 - α variation within β grades
(Ro = Rs at 100ppm CO, 25˚C/40%RH)
max
center
min
1000
5