Two-wavelength type respiratory gas concentration measuring apparatus

• US 4,998,018 A
• Filed: 02/22/1990
• Issued: 03/05/1991
• Est. Priority Date: 03/01/1989
• Status: Expired due to Term

• Current Assignee: Nihon Kohden Corporation
• Original Assignee: Nihon Kohden Corporation
• Inventors: Kurahashi, Muneshige, Kato, Naoki
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Glick, Edward J.
• Application Number:
  US07/483,914
• Time in Patent Office: 376 Days
• Field of Search: 250/339, 250/343, 250/341, 356/437
• US Class Current: 250/343
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: G01J 2001/161 Ratio method, i.e. Im/Ir
• CPC Class Codes: G01J 2001/1684 and selecting also a DC level from the signal
• CPC Class Codes: G01J 2001/1689 one separated signal being processed differently
• CPC Class Codes: G01J 2001/444 Compensating; Calibrating, e.g. dark current, temperature drift, noise reduction or baseline correction; Adjusting
• CPC Class Codes: G01N 2021/317 Special constructive features
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A two-wavelength type respiratory gas concentration measuring device includes a connector tube which is held in the mouth of an examinee and which has airtight windows, a light source which applies infrared rays through the windows of the connector tube, and first and second filters. The first filter allows the transmission of a light component whose wavelength is such that it is absorbed by the respiratory gas, and the second filter allows the transmission of a light component whose wavelength is such that it is not absorbed by the respiratory gas. A photodetector converts the infrared rays transmitted through the filters into an electric signal. A first detector receives the electric signal and detects the light output of the first filter. A second detector receives the electric signal and detects the light output of the second filter. A power computing circuit performs a power computation of the output of the second detector with a power exponent m. A divider circuit divides the output of the first detector by the output of the first power computing circuit. A DC level detector detects the DC level of the photodetector when no infrared rays are applied. A second power computing circuit performs a power computation of the output of the DC-level detector with a power exponent of 2(m-1). A multiplier circuit multiplies the output of the second power computing circuit by the output of the divider.

Claims

1. A two-wavelength type respiratory gas concentration measuring apparatus comprising:

a connector tube equipped with a tube end to be held in the mouth of an examinee and an opposite open end, and having airtight windows provided between both ends of said connector tube;

a light source adapted to apply infrared rays in a light path passing transversely through said connector tube by way of said windows;

a first filter which allows the transmission of a light component whose wavelength is such that it is absorbed by a particular gas of a respiratory gas breathed into the tube by the examinee;

a second filter which allows the transmission of a light component whose wavelength is such that it is not absorbed by said particular gas;

means for alternately positioning the first filter and the second filter in the light path;

photodetector means for converting the infrared rays transmitted through said filters to an electric signal, the photodetector means including a PbSe infrared-ray sensor;

first detector means for detecting the light output of said first filter from said electric signal;

second detector means for detecting the light output of said second filter from said electric signal;

first power computing means for performing the power computation of the output of said second detector means with a power exponent m;

divider means for dividing the output of said first detector means by the output of said first power computing means;

DC level detector means for detecting the DC level of said photodetector means when no infrared rays are applied thereto;

second power computing means for performing the power computation of the output of said DC-level detector means with a power exponent of 2(m-1); and

multiplier means for multiplying the output of said second power computing means by the output of said divider means;

said power component m representing the ratio of a temperature-dependent coefficient α

₁, with respect to the incident light quantity of the light component of the infrared rays whose wavelength is absorbed by the particular gas, of the variation with respect to temperature in resistance of the PbSe infrared-ray sensor to a temperature dependent coefficient α

₂, with respect to the incident light quantity of the light component of the infrared rays whose wavelength is not absorbed by the particular gas, of the variation with respect to temperature in resistance of the PbSe infrared-ray sensor, whereby said power exponent m and said temperature-dependent coefficients α

₁ and α

₂ are in the relationship;

##EQU9## said photodetector means supplying a constant voltage to said PbSe infrared-ray sensor, and detecting the current flowing through said infrared-ray sensor as an infrared-ray detection signal.

2. A two-wavelength type respiratory gas concentration measuring apparatus comprising:

a connector tube equipped with an open tube end to be held in the mouth of an examinee and an opposite open end and airtight windows provided between both ends of said connector tube;

a light source adapted to apply infrared rays in a path passing transversely through said connector tube by way of said windows;

a chopper having first and second filters situated thereon and adapted to alternately position in said light path the first filter which allows the transmission of a light component whose wavelength is such that it is absorbed by a particular gas and the second filter which allows the transmission of a light component whose wavelength is such that it is not absorbed by said particular gas;

a photodetector including a PbSe infrared-ray sensor adapted to convert the infrared rays transmitted through said filters to an electric signal by means of the PbSe infrared-ray sensor;

a first detector adapted to detect the output of said first filter from said electric signal;

a second detector adapted to detect the output of said second filter from said electric signal;

a first power computing circuit adapted to perform the power computation of the output of said second detector with a power exponent m;

a divider circuit for dividing the output of said first detector by the output of said first power computing circuit;

a DC level detector for determining the DC level of said photodetector when no infrared rays are applied;

a second power computing circuit for performing the power computation of the output of said DC-level detector with a power exponent of 2(m-1); and

a multiplier circuit for multiplying the output of said second power computing circuit by the output of said divider circuit;

said power component m representing the ratio of a temperature-dependent coefficient α

₁, with respect to the incident light quantity of the light component of the infrared rays whose wavelength is absorbed by the particular gas, of the variation in resistance, which exponentially fluctuates with respect to temperature changes, of the PbSe infrared-ray sensor to a temperature-dependent coefficient α

₂, with respect to the incident light quantity of the light component of the infrared rays whose wavelength is not absorbed by the same particular gas, of the variation in resistance, which exponentially fluctuates with respect to temperature changes, of the PbSe infrared-ray sensor, whereby said power exponent m and said temperature-dependent coefficients α

₁ and α

₂ are in the relationship;

##EQU10## said photodetector circuit supplying a constant voltage to said PbSe infrared-ray sensor, and detecting the current flowing through said infrared-ray sensor as an infrared-ray detection signal.