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An ionization chamber-type CO sensor
Sensors
and Achmtors B, 13-14
(1993)
539-540
An
ionization chamber-type CO sensor
539
I. Takahashi, T. Matsuzawa and M. Sakaguchi RCGD Center, NEMOTO & Co., Ltd., 4-l&9 Takaido-higashi Suginami-ky
To@
168 (Japan)
Results and discussion
IlltrodllCtiOD
Most of conventional gas sensors are equipped with heating devices to heat the sensor elements, which make it difficult to operate with batteries, because of their high power consumption. Whereas power consumption of ionization chambers which have been applied to smoke detectors are low enough to be operated by batteries. From this point of view, in this study, an ionization chamber intended to detect CG gas was newly developed.
For the fabrication, Pt-plated electrode with a surface area of 1200 mm’ was applied to an anode and an Au-plated electrode, with the same surface area as the anode, was applied to a cathode. The gap between the electrodes of the sensor was 10 mm. The small alpharay source of Am-241, about 37 kRq, was placed in the gap to ionize the gas in the chamber. Gas-sensitivity characteristics were investigated in various gases by measuring the change of ionic current between the two electrodes with an electrometer supplying 2.0 V d.c. at room temperature in an ambient atmospheric pressure, as shown in Fig. 1.
Figure 2 shows the response characteristics of the fabricated sensor in 1000 ppm of CO gas. From the results it was found that the ionic current decreased rapidly as the gas was injected, and 90%-response time was N 10 s. Figure 3 shows effects of Orgas concentration on the sensor current and CO-gas sensitivity. Although the sensor current and the sensitivity were almost constant from 10 to 21% of 0, concentration, the sensor current went down extremely, and the sensor became insensitive in 100% of O2 gas, which implied that active points on Pt surface were previously totally occupied by O1 and few active points were left for CO gas adsorption. Studies on the adsorption of CO gas on Pt surface were reported [l, 21 and it is well known that the CO adsorption enables to change the surface
P
-air
level
L
_a*0 2 t $30 .i H2
t
CO(lOOOppm) 01
2
3
4
Time (min. )
Fig. 2. Response characteristics
Fig. 1. Scheme of the measurement
0925-4005193/$6.00
circuit.
Fii. 3. O*-gas dcpcndcncc sensitivity.
of the fabricated CO sensor.
on the sensor current and CO-gas
0 1993 - Elsevier Sequoia. All rights reserved
540
20 z
Figure 4 shows the gas-sensitivitycharacteristics of the sensor. The sensor was only sensitive to CO gas and showed excellent linearity up to 1000 ppm.
L!zizf3
,a >I .z .2 ‘0 2 t d
a co AQH5OH n a2 0 WlO
Condusion
ACH4
OO
1000
Gasconcentration
2000
(ppml
Fig. 4. Gas-sensitivity characteristics of the CO sensor.
potential. Therefore, it was suggestedthat the sensing mechanismof the fabricated sensor was not due to the difference of ionic yield between CO free air and CO gas but due to the change of surface potential of electrode caused by CO adsorption on the surface.
The fundamental characteristics obtained were: (i) the fabricated sensor was sensitive enough to detect 50 ppm of CO gas and showed good linearity up to 1000ppm, and (ii) the sensorwasinsensitiveto C&H,OH, H,, CdHI, and CH,+.
References 1 J. E. &well, E. L Gartimkel and G. A. Somorjai, Su$ Sci., 121 (1982) 303-320. 2 R. J. Behm, P. A. Thiel, P. R. Norton and G. Ertl, 1. Chk Phys., 78 (1983) 7437-7441.
and Achmtors B, 13-14
(1993)
539-540
An
ionization chamber-type CO sensor
539
I. Takahashi, T. Matsuzawa and M. Sakaguchi RCGD Center, NEMOTO & Co., Ltd., 4-l&9 Takaido-higashi Suginami-ky
To@
168 (Japan)
Results and discussion
IlltrodllCtiOD
Most of conventional gas sensors are equipped with heating devices to heat the sensor elements, which make it difficult to operate with batteries, because of their high power consumption. Whereas power consumption of ionization chambers which have been applied to smoke detectors are low enough to be operated by batteries. From this point of view, in this study, an ionization chamber intended to detect CG gas was newly developed.
For the fabrication, Pt-plated electrode with a surface area of 1200 mm’ was applied to an anode and an Au-plated electrode, with the same surface area as the anode, was applied to a cathode. The gap between the electrodes of the sensor was 10 mm. The small alpharay source of Am-241, about 37 kRq, was placed in the gap to ionize the gas in the chamber. Gas-sensitivity characteristics were investigated in various gases by measuring the change of ionic current between the two electrodes with an electrometer supplying 2.0 V d.c. at room temperature in an ambient atmospheric pressure, as shown in Fig. 1.
Figure 2 shows the response characteristics of the fabricated sensor in 1000 ppm of CO gas. From the results it was found that the ionic current decreased rapidly as the gas was injected, and 90%-response time was N 10 s. Figure 3 shows effects of Orgas concentration on the sensor current and CO-gas sensitivity. Although the sensor current and the sensitivity were almost constant from 10 to 21% of 0, concentration, the sensor current went down extremely, and the sensor became insensitive in 100% of O2 gas, which implied that active points on Pt surface were previously totally occupied by O1 and few active points were left for CO gas adsorption. Studies on the adsorption of CO gas on Pt surface were reported [l, 21 and it is well known that the CO adsorption enables to change the surface
P
-air
level
L
_a*0 2 t $30 .i H2
t
CO(lOOOppm) 01
2
3
4
Time (min. )
Fig. 2. Response characteristics
Fig. 1. Scheme of the measurement
0925-4005193/$6.00
circuit.
Fii. 3. O*-gas dcpcndcncc sensitivity.
of the fabricated CO sensor.
on the sensor current and CO-gas
0 1993 - Elsevier Sequoia. All rights reserved
540
20 z
Figure 4 shows the gas-sensitivitycharacteristics of the sensor. The sensor was only sensitive to CO gas and showed excellent linearity up to 1000 ppm.
L!zizf3
,a >I .z .2 ‘0 2 t d
a co AQH5OH n a2 0 WlO
Condusion
ACH4
OO
1000
Gasconcentration
2000
(ppml
Fig. 4. Gas-sensitivity characteristics of the CO sensor.
potential. Therefore, it was suggestedthat the sensing mechanismof the fabricated sensor was not due to the difference of ionic yield between CO free air and CO gas but due to the change of surface potential of electrode caused by CO adsorption on the surface.
The fundamental characteristics obtained were: (i) the fabricated sensor was sensitive enough to detect 50 ppm of CO gas and showed good linearity up to 1000ppm, and (ii) the sensorwasinsensitiveto C&H,OH, H,, CdHI, and CH,+.
References 1 J. E. &well, E. L Gartimkel and G. A. Somorjai, Su$ Sci., 121 (1982) 303-320. 2 R. J. Behm, P. A. Thiel, P. R. Norton and G. Ertl, 1. Chk Phys., 78 (1983) 7437-7441.