TGS2442 Datasheet, PDF (6/25 Pages) List of Unclassifed Manufacturers – Detection of Carbon Monoxide

TECHNICAL INFORMATION FOR TGS2442
2. Operation Principle
The optimum conditions of sensitivity and selectivity
to CO of the TGS2442 occurs at sensor temperatures
less than 100˚C. However, at these lower temp-
eratures, the sensing element may be influenced by
humidity and other contaminants, so the sensing
element requires periodic heat cleaning at more than
300˚C. As a result, the TGS2442 is pulse heated to
achieve optimal sensing characteristics at low
temperatures.
400
350
300
250
200
150
100
50
0
0
5
10
15
20
VH pulse width (msec)
Figure 5 - Relationship of sensor temperature and
VH pulse width (VH=4.8V, RH=17Ω)
Figure 6a shows the pattern of resistance change ratio
(Rs/Ro) for various CO concentrations which occurs
during the 1 second heater pulse cycle, starting with
application of the 14ms VH pulse. During the VH
pulse, initially sensor resistance drops quickly and
then returns to a higher value. After the VH pulse
concludes and the sensing element’s surface
temperature begins to decrease (Fig. 6b), sensor
resistance reaches to its maximum value and then
begins to decline. Note that the shape of the response
pattern varies according to the concentration of CO-
-higher CO concentrations result in a minimum Rs/
Ro value which occurs more quickly and has a lower
value. In addition, shortly after the VH pulse, the
Rs/Ro value also trends downwards at a greater rate
for higher CO concentrations after reaching its
maximum value.
A signal detection point of 997.5ms into the VH pulse
cycle (ref. timing chart in Fig. 3) is used to obtain the
optimum combination of gas sensitivity performance
and minimized ambient humidity effect.
14ms VH pulse
Air
100
10
CO 30ppm
CO 100ppm
Detection point
(997.5 msec)
1
CO 300ppm
0.1
0
200
400
600
800
1000
Time (msec)
Figure 6a - Sensitivity characteristics during the VH pulse cycle
(Ro = Rs in 100ppm CO at 997.5ms of VH cycle)
1000
14ms VH pulse
Detection point
(997.5 msec.)
100
Revised 03/00
10
0
200
400
600
800
Time (msec)
Figure 6b - Surface temperature of sensing element
during VH pulse cycle
(0msec = start of VH pulse cycle)
1000
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