Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-05-28
2001-11-20
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S343000
Reexamination Certificate
active
06320192
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a detector for use in so-called “nondispersive infrared gas analyzer” (NDIR), a flow detector element for use in the detector, and a process for producing the element.
A detector for use in infrared gas analyzers is known that comprises two gas compartments that are filled with a gas showing the same absorption characteristics as the gas to be measured and that are arranged in series with or parallel to a load cell, a gas channel via which the two gas compartments communicate with each other, and a flow detector element provided in said gas channel in a position that blocks it. The flow detector element may be of a thermal type as described in Examined Published Japanese Utility Model Publication (kokoku) Nos. 59-26278/(1984) and 59-24993/(1984), as well as Unexamined Published Japanese Utility Model Application (kokai) No. 56-99462/(1981) and Unexamined Published Japanese Patent Application No. 7-140075/(1995).
As shown in
FIGS. 1 and 2
, the thermal flow detector element consists of two heaters (a) that are made of a metal (e.g. Ni) foil and that run in a serpentine path and plates (b) that are made of an insulating material such as glass and which support the two heaters (a) in a face-to-face relationship. The plates (b) have an opening (c) and the gaps (d) between adjacent branches of each heater (a) that are located within the opening (c) provide gas flow channels.
With a constant voltage being applied to the heaters (a) so that their temperature becomes higher than that of the gas in the gas compartments by a certain value, the two heaters a provide the temperature profile shown by (i) in
FIG. 2
if there is no gas flow. However, if the gas flows through the gaps d as indicated by an arrow, the heater (a) in the upstream position is cooled in accordance with the gas flow rate whereas the heater (a) in the downstream position is heated with the heat taken from the upstream heater (a); as the result, the two heaters (a) provide the temperature profile shown by (j) in FIG.
2
. This temperature change causes a change in the resistance of the heaters (a), which is measured with a Wheatstone bridge, thereby detecting the gas flow. Note that the detected gas flow corresponds to the quantity of infrared absorption by the gas of interest (hence its concentration) that is passed through the load cell (not shown) in a nondispersive infrared gas analyzer.
However, the above-described conventional detector has several limitations. First, the resistance of the metal of which the heaters are made does not have a very high temperature coefficient. Second, the heaters cannot be supplied with a very high voltage.
Thirdly, the heating temperature cannot be very high and if it approaches 500° C., the gas in the gas compartments will deteriorate or decompose. Because of these difficulties, the signal output is very small and the detection sensitivity is accordingly low and dependent on the ambient temperature.
According to Unexamined Published Japanese Patent Application (kokai) No. 60-173443/(1985), it is proposed that a pressure detector be used in place of the detector element working as a thermal flow meter. A problem with this proposal is that due to the need to detect a small pressure difference, a large enough signal output cannot be produced to achieve high detection sensitivity.
The conventional thermal flow detector element shown in
FIGS. 1 and 2
has the following additional problems. Since all gaps (d) between adjacent branches of each heater (a) that are located within the opening (c) serve as gas flow channels, the channel or flow path area is large compared to the area of the detector element and the gas flow rate is so much retarded that the change in the temperature of the heaters (a) due to the gas flow is insufficient to provide high sensitivity.
That part of the heaters a which is located within the opening (c) (i.e., which is not supported with the plates (b)) must have a sufficient strength to retain shape, so a thick enough metal foil has to be used to compose the heaters (a). However, if the thickness of the heaters (a) is increased, the heat capacity increases correspondingly to slow down the response speed.
SUMMARY OF THE INVENTION
The present invention has been accomplished under these circumstances and has as an objective providing a detector for use in infrared gas analyzers that has a markedly higher sensitivity than the prior art version and which yet is not subject to the effects of disturbances such as ambient temperature.
Another object of the invention is to increase the sensitivity and response speed of a flow detector element for use in infrared gas analyzers.
The first object of the invention can be attained by a detector for use in infrared gas analyzers that has two gas compartments to be filled with a gas showing the same absorption characteristics as the gas to be measured and which are arranged in series with a load cell, characterized in that said gas compartments communicate with each other via a gas channel in which a pyroelectric flow detector element is provided.
The two gas compartments may be arranged in parallel so that they correspond to the load cell and a reference cell, respectively. If desired, the sensing portion of the pyroelectric flow detector element may be adapted to be heatable.
The first object of the invention can also be attained by a detector for use in infrared gas analyzers that has two gas compartments to be filled with a gas showing the same absorption characteristics as the gas to be measured and which are arranged in series with a load cell, characterized in that said gas compartments communicate with each other via a gas channel in which a first pyroelectric flow detector element is provided, with a second pyroelectric flow detector element being provided as a compensating means in the neighborhood of said first pyroelectric flow detector element.
The two gas compartments may be arranged in parallel so that they correspond to the load cell and a reference cell, respectively.
The first object of the invention can also be attained by a detector for use in infrared gas analyzers that has two gas compartments to be filled with a gas showing the same absorption characteristics as the gas to be measured and which are arranged in series with a load cell, characterized in that said gas compartments communicate with each other via a gas channel in which two pyroelectric flow detector elements are provided in a superposed relationship.
The two gas compartments may be arranged in parallel so that they correspond to the load cell and a reference cell, respectively.
At least one of the pyroelectric flow detector elements may be adapted to be heatable.
The above-described detector for use in infrared gas analyzers employs one or two pyroelectric flow detector elements and, hence, is capable of positive detection of the slightest change in the gas temperature to produce a sufficiently large signal output that its sensitivity is significantly improved over that of the conventional detector for use in infrared gas analyzers.
The second object of the invention can be attained by a flow detector element in a detector for use in infrared gas analyzers that comprises two gas compartments filled with a gas showing the same absorption characteristics as the gas to be measured, a gas channel via which the two gas compartments communicate with other, and a flow detector element provided in said gas channel in a position that blocks it, characterized in that a gas passage hole whose setting of channel area is smaller than the area of the gap between adjacent segments of a heater to be supplied with a constant voltage s o that its temperature is a certain value higher than the temperature of the gas in the gas compartments is formed in the neighborhood of said heater.
The flow detector element may be of either a thermal or pyroelectric type.
Since gas passage holes of which the channel area is smaller than the area of the gap between adjacent segments of the heater to be supplied with a
Matsumoto Koichi
Takada Shuji
Tominaga Koji
Hannaher Constantine
Horiba Ltd.
Israel Andrew
Sughrue Mion Zinn Macpeak & Seas, PLLC
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