Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-07-31
2001-04-17
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S341500, C250S339090
Reexamination Certificate
active
06218665
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an infrared detector using a photoconductive infrared detector, and also to a gas analyzer having the configuration of such an infrared detector.
2. Related Art
As a device which measures the concentration of carbon dioxide in a respiratory gas, known is a non-dispersive infrared analyzer. A carbon dioxide analyzer using the principle of the device is disclosed in U.S. Pat. No. 5,153,436.
The non-dispersive infrared analyzer measures a gas concentration such that an infrared radiation through the gas to measure an amount of attenuation of the infrared radiation in wavelength absorbed by the gas. In U.S. Pat. No. 5,153,436, in order to increase the measurement accuracy, there is employed two infrared radiation detectors. The light passing through an airway adapter for guiding a respiratory gas is divided in two lights by a beam splitter. A light reflected from the bean splitter is guided to a first PbSe detector via an optical filter. This filter allows to pass a light having a band of approximately 4.3 &mgr;m which is absorbed by carbon oxide gas.
A light passing through the beam splitter is guided to a second PbSe detector via an optical filter different from the optical filter located in the first PbSe detector. This filter allows to pass a light having a band of approximately 3.7 &mgr;m which is not absorbed by carbon dioxide gas.
Assuming that output signal Vs represents the amount of the infrared light guided into the first PbSe detector and output signal Vr represents the amount of the infrared light guided in to the second PbSe detector, the gas concentration can be detected without being affected by a drift due to variation of infrared radiation of the light source, by calculating a ratio of VS/VR.
Even when the ratio of VS/VR is obtained in this way, the temperature drift remains to affect the detection because the first and second PbSe detectors are different from each other in temperature coefficient of the sensitivity. In the conventional art, therefore, the temperatures of PbSe detectors are controlled by using heaters and thermistors.
In the conventional art, as described above, heaters, thermistors, and a temperature control circuit are necessary in order to maintain a photoconductive infrared detector at a constant temperature. Therefore, there arise problems in that the production cost is high, that the power consumption is increased, and that the warm-up period is prolonged.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an infrared detector unit in which means for maintaining a photoconductive infrared detector at a constant temperature is not required and the temperature drift of the detector is corrected, and a gas analyzer having the configuration of such as infrared detector unit.
According to an aspect of the present invention, there is provided the infrared detector comprising:
a light source which intermittently generates infrared radiation;
signal outputting means having a photoconductive infrared detector which is irradiated with the infrared radiation from the light source via a measurement object, and for outputting an electric signal which corresponds to a resistance of the photoconductive infrared detector;
alternating current AC (alternating current) component detecting means for detecting an AC component from the output signal of the signal outputting means;
storage means for storing data specific to the photoconductive infrared detector, the data relating to the resistance and a sensitivity; and
correcting means for correcting that AC component detected by the AC component detecting means, based on the data stored in the storage means and a DC (direct current) component of the signal output from the signal outputting means.
According to another aspect of the present invention, the measurement object is a gas body containing carbon dioxide.
According to another aspect of the present invention, the photoconductive infrared detector is a lead selenide (PbSe) detector.
In this configuration, the resistance of the photoconductive infrared detector is varied in accordance with the magnitude of the radiation impinging on it. The signal outputting means outputs an electric signal which corresponds to the resistance. The AC component of the output signal of the signal outputting means is detected by the AC component detecting means. The AC component corresponds to the magnitude of the radiation which intermittently impinges on the detector via the measurement object. The correcting means corrects the AC component, based on the data stored in the storage means and the DC component of the signal output from the signal outputting means.
According to another aspect of the present invention, gas concentration calculation means for calculating a concentration of the designated gas, based on the AC component corrected by the correcting means.
REFERENCES:
patent: 4596931 (1986-06-01), Ehnholm et al.
patent: 5070244 (1991-12-01), Simpson
patent: 5153436 (1992-10-01), Apperson et al.
patent: 5341214 (1994-08-01), Wong
patent: 5693945 (1997-12-01), Akiyama et al.
patent: 0 385 256 (1990-09-01), None
patent: 0 733 341 (1996-09-01), None
patent: WO 88/02889 (1988-04-01), None
Patent Abstracts of Japan vol. 096 No. 009, Sep. 30, 1996 & JP 08 122254 A (Horiba LTD) May 17, 1996 *Abstract.
Dainobu Hidetoshi
Yamamori Shinji
Gagliaroi Albert
Hannaher Constantine
Nihon Kohden Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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