TGS2442 Datasheet, PDF (21/25 Pages) List of Unclassifed Manufacturers – Detection of Carbon Monoxide

CALIBRATION OF TGS2442
3. Calibration Using Classified Sensors
This section describes the procedure for calibrating
at 100ppm of CO using sensors classified as shown
in Tables 4 and 5. Figure 8 illustrates the flow of the
calibration process, including the method of signal
processing which takes place in the microcomputer.
3-1. Preheating
To stabilize sensor characteristics prior to calibration,
it is recommended that sensors be preheated under
standard circuit conditions for 2 - 7 days. To shorten
preheating time and simplify this process, Figaro is
currently studying alternative methods and will issue
new recommendations shortly.
3-2. Pre-calibration (adjustment during assembly)
a. Select a load resistor (RL)
Select the load resistor (RL, same as RA in Figure 1)
based on the Rs grade shown in Table 4. For optimal
resolution, the RL used should have a value as close
as possible to the Rs grade’s center value. The sensor
output signal (V1) at the calibration concentration
should be near 2.5V which is 1/2 the value of Vc.
According to the maximum and minimum values of
Rs values for each Rs grade as shown in Table 4, V1
would fall in the following range:
1.70 v ≤ V1 (at 100ppm) ≤ 3.30 v
b. Compensation according to β grade
Each Rs grade is divided into six β grades as shown
in Table 5. Using data from this table, α values for
these grades can be determined as follows and should
be stored in the microcomputer (see Table 6):
α = log β (center) / log (300/100)
Using the α value calculated above, compensation
for β grade can be done by utilizing a circuit such as
that shown in Figure 9 and connecting the three
jumper lines as indicated in Table 6.
Grade
1
2
3
4
Rs in CO 100ppm (kΩ)
Min. Center Max.
6.81
12.1
21.5
10.0
17.8
31.6
14.7
26.1
46.4
21.5
38.3
68.1
Recommended
RL (kΩ)
12
18
27
39
Table 4 - Rs grades of TGS2442
Grade
A
B
C
D
E
F
β (Rs in 300ppm/Rs in 100ppm)
Min.
Center
Max.
0.230
0.285
0.340
0.260
0.315
0.370
0.290
0.345
0.400
0.320
0.375
0.430
0.350
0.405
0.460
0.380
0.435
0.490
Table 5 - β grades of TGS2442
β Grade
A
B
C
D
E
F
α Value
-1.14
-1.05
-0.969
-0.862
-0.823
-0.758
Jumper
Connection
001
010
011
100
101
110
Table 6 - Recommended jumper connections
for β grade compensation circuit
Figure 9 - Recommended circuit for β grade compensation
Revised 04/01
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