Measuring and testing – Gas analysis – Gas of combustion
Reexamination Certificate
2001-11-15
2003-09-23
Kwok, Helen (Department: 2856)
Measuring and testing
Gas analysis
Gas of combustion
C073S025050, C073S204240, C073S025010, C422S095000, C204S258000, C204S228300
Reexamination Certificate
active
06622543
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to improvements in a detection sensor for flammable gases and oxygen gas in flammable gases. More particularly, the present invention relates to the sensor for such uses as in securing and ensuring the safety of a variety of production equipment and facilities and detection of hydrogen gas in pure water for manufacturing semiconductors and hydrogen gas in gases for manufacturing semiconductors.
BACKGROUND OF THE INVENTION
Among the detection sensors for flammable gases that have been used widely are the contact catalytic reaction type (or the contact combustion type) gas detection sensor, semiconductor type gas detection sensor and thermal conductivity type gas detection sensor. Of those types, the contact catalytic reaction type gas detection sensor has found wide uses for detection of such gases as hydrogen gas because of its long service life and reliability.
FIG. 10
shows a partially broken way view of an example of the sensor element A of the prior art contact catalytic reaction type gas detection sensor. This sensor element A includes a coil B of platinum wire some 20 &mgr;m in diameter with which a mixture of a binder and alumina or silica alumina to be a catalyst support C is sintered, with a catalyst D like platinum supported therein.
The aforesaid sensor element A is incorporated in a bridge circuit for detection of gas concentration. That is, a bridge circuit is formed, as shown in
FIG. 11
, with the sensor element A and a temperature compensation element Ao made by sintering an inert substance. A specific voltage is applied to the sensor element A to raise before hand the temperature to not lower than some 250° C. If a flammable gas like hydrogen gas comes in contact with the preheated sensor element A, the gas will undergo a contact catalytic reaction by the catalytic action of catalyst D and the sensor element A will be heated. That increases the electrical resistance of the sensor element A to break the equilibrium in the bridge circuit and to cause an electric potential difference. As a result, an indicator E turns. The extent of the turn of the indicator shows the heating value of the sensor element A, that is, the concentration of the flammable gas within the detection gas or subject gas under test.
The sensor element A as shown in
FIG. 10
has such advantages as (a) high selectivity for flammable gases, (b) hardly influenced by the co-existing H
2
O and (c) suitable for measurement of gas concentration close to the lower limit of explosion (in the case of hydrogen gas, 1 to 4%).
However, the problem with the sensor element A as shown in
FIG. 10
is that the temperature of the sensor element A has to be maintained at not lower than 250° C. and that the working temperature further rises in detection of the flammable gas concentration. That could ignite the flammable gas. To ensure the safety, the sensor element A has to be made explosion-free by covering the sensor element A with such as a wire netting with a mesh of some 200 or sintered metal. In other words, the sensor element A as shown in
FIG. 10
has a serious safety problem.
It is also noted that this type of sensor element A is so formed that catalyst D is supported within the catalyst support C as mentioned, and has a basic problem about the stability of catalytic activity. Especially, the effects on the catalyst in the sinter material by the burning of the flammable gas and the effects on the catalytic activity of carbon coming from incomplete combustion of the flammable gas haven not been elucidated well yet. Few studies are reported in which this type of the sensor element A is used for detection of a flammable gas which is present in small quantities in highly concentrated H
2
O or O
2
.
Another problem is that it is difficult to clean the inside of the catalyst support C of this kind of the sensor element A. For this reason, the sensor element A can not be used in the semiconductor manufacturing process where a high degree of cleanliness is required.
As set forth above, the application of the contact catalytic reaction type flammable gas detection sensor A for detection of a flammable gas present in small amounts in highly concentrated H
2
O or O
2
presents problems with regard to reliability and the like. It is also the case with the use of the semiconductor type flammable gas detection sensor and the thermal conductivity type flammable gas detection sensor. Furthermore, while it is possible to use this kind of the sensor element A as sensor for detection of oxygen in the flammable gases in principle, it has not been put to practical use because of the aforesaid problems like reliability, and few application studies have been reported.
In other words, the prior art flammable gas detection sensor A of the contact catalytic reaction type drops substantially with lapse of time in catalytic activity, that is, H
2
gas detection sensitivity. For reasons of poor reliability, the sensor element A can hardly be applied for such uses as detection of the concentration of unreacted hydrogen gas in the moisture take-out line of the moisture generating reactor for semiconductor manufacturing facilities. The same is the case with the aforesaid semiconductor type sensor for detection of hydrogen gas and the thermal conductivity type sensor for detection of hydrogen gas, which has been confirmed in experiments.
In the moisture generating reactor for semiconductor manufacturing facilities, it can happen that moisture is generated with excessive supply of hydrogen gas. In such a case, it is necessary to detect the concentration of unreacted oxygen gas in the generated moisture containing hydrogen in the moisture take-out line. The prior art sensor element A can not be used in such cases.
Meanwhile, the applicants of the present application developed a flammable gas detector as shown in
FIG. 12
that solved the problems with the prior art contact catalytic reaction type sensor element A for detection of flammable gases and disclosed the same in unexamined Japanese patent application No. 9-186383.
This flammable gas detector is composed of a flammable gas detection sensor
20
and a detector unit
30
. The flammable gas detection sensor
20
is formed of a first detection sensor
21
provided with a platinum coating catalyst, a second detection sensor
22
to detect the temperature of the detection gas (the gas to be detected) or subject gas under test and a sensor holder
23
.
The detector unit
30
includes a first temperature detector
31
to detect the temperature signal from the first detection sensor
21
, a second temperature detector
32
to detect the temperature signal from the second detection sensor
22
, a first temperature display
33
and second temperature display
34
to display the temperatures detected by the aforesaid two temperature detectors respectively, a temperature difference detector
35
to detect the difference between the detected temperatures and a temperature difference display
36
to display the temperature difference from the temperature difference detector
35
.
The flammable gas detection sensor
20
is placed in a T-shaped branch pipe
39
with the sensor holder
23
fitted in air-tight and with the two sensor elements
21
,
22
held in a gas feeder pipe
37
as shown in FIG.
13
. The T-shaped branch pipe
39
is provided with explosion proof metal meshes
38
in gas feeder pipe
37
.
The flammable gas detector shown in FIG.
12
and
FIG. 13
is excellent in responsiveness and gas concentration detection accuracy, and can correct the detected value without difficulty when the flow rate of the detection gas changes. Another practical advantage is that the change with lapse of years in detection sensitivity is relatively small.
But this flammable gas detector has a number of problems yet to be solved. Among the problems requiring urgent solution are contamination of the high-purity gas flowing through the pipe, the reliability of detection precision and safety.
To be specific, the first detection sensor
21
and the s
Honiden Teruo
Ikeda Nobukazu
Kawada Kouji
Komehana Katunori
Minami Yukio
Fujikin Incorporated
Griffin & Szipl, P.C.
Kwok Helen
Wiggins David J.
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