JPH05332933A - Portable co2 concentration measuring device - Google Patents

Abstract

PURPOSE:To obtain a portable, compact. and light CO2 concentration measuring device. CONSTITUTION:The title measuring device is provided with a specimen cell 8 where the expiration gas of a person passes, an infrared ray source 1 which emits infrared rays passing through the specimen cell 8, a lens 12 for focusing infrared rays passing through the specimen cell 8, a detection element 20 which infrared rays which are focused by the lens 12 are applied to, and a detection circuit 27 which detects the change in resistance of the detection element 20 due to application of infrared rays as a bridge output without an optical chopper and then detects CO2 concentration within the specimen cell 8, thus obtaining a compact and portable CO2 concentration detector which can detect CO2. concentration accurately and stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable CO ₂ concentration detecting device which is carried by a subject and used to detect the CO ₂ concentration in exhaled gas.

[0002]

2. Description of the Related Art By measuring the concentration of CO _{2 in} the breath of a subject, the function of the respiratory organs of the subject can be accurately grasped, and the effect of treatment or the amount of physical activity due to exercise can be determined. To obtain useful information on medicine and physiology. For this reason, a CO ₂ detection device for detecting the CO ₂ concentration in the breath of a subject has been announced and used. Since it is desirable to measure this type of CO ₂ concentration in the daily operation of the subject, the need for a portable device has increased in recent years.

By the way, CO ₂ has a strong absorption band near a wavelength of 4.2 μm. By measuring the light absorption in a narrow wavelength range, the concentration of CO ₂ can be measured without being affected by other gases. For this reason, the conventional method of measuring the concentration of CO ₂ uses an infrared absorption method.

First, referring to FIGS. 2 to 4, a conventional CO
_{A two-} concentration detection device will be described. Here, FIG. 2 shows a conventional CO
FIG. 3 is an explanatory diagram showing the overall configuration of the _two- concentration measuring device, FIG. 3 is an explanatory diagram of the chopper portion of FIG. 2, and FIG. 4 is an explanatory diagram of the detection operation of the conventional CO ₂ concentration detecting device.

As shown in FIG. 2, a comparison cell 7 and a sample cell 8 are arranged side by side, and one end side of these cells is a lens for making the infrared rays from the infrared light source 1 into parallel rays and making them enter each cell. 5, a chopper 2 rotatable by a rotary shaft 3 is provided in the vicinity of the front surface of the infrared light source 1, and an aperture 6 is provided between the chopper 2 and the lens 5.

On the other end side of the comparison cell 7 and the sample cell 8,
A lens 12 that collects infrared rays is provided on the detection element 13, and an interference filter 10 is arranged between the lens 12 and each cell. As shown in FIG. 3, the chopper 2 is formed with slits 2a and 2b and notches 2c and 2d at positions facing each other, and the light emitting diodes 15a and 15b are sandwiched by a part of the peripheral surface of the chopper 2. And photodiode 16
a and 16b are arranged to face each other.

In the conventional CO ₂ concentration detecting device having such a configuration, the reference cell is filled with the standard gas, the sample cell 8 is allowed to pass the breath of the subject, and a motor (not shown) is used. Infrared rays are emitted from the infrared ray source 1 while being driven and rotating the chopper 2. In the state of FIG. 3, the cutout 2d is located at the position of the comparison cell 7, and infrared rays from the infrared source 1 are transmitted through the comparison cell 7 and detected by the detector 13 via the interference filter 10 and the lens 12. At this time, an optical path is formed between the light emitting diode 15b and the photodiode 16b by the cutout 2c, so that a comparison cell detection signal is emitted from the photodiode 16b.

From this position, the chopper 2 moves 9 in the direction of the arrow X.
When rotated by 0 °, the slit 2a reaches the position of the sample cell 8, and infrared rays from the infrared source 1 are transmitted through the sample cell 8 and detected by the detector 13 via the interference filter 10 and the lens 12. At this time, since the slit 2b forms an optical path between the light emitting diode 15a and the photodiode 16a, a sample cell detection signal is emitted from the photodiode 16a. Also, during this period, the comparison cell 7 and the sample cell 8
There is a state in which none of the above is detected.

In this way, as shown in FIG. 4, the standard gas concentration of the comparison cell 7 and the CO ₂ concentration of the sample cell 8 are detected across the state where no detection is performed, and the standard gas is detected. The CO ₂ concentration in the sample cell 8 is accurately detected with respect to the absolute value of the concentration.

[0010]

In the above-mentioned conventional CO ₂ concentration measuring device, the chopper 2 and the motor for rotating the chopper 2 are required, and as a result, the device becomes large in size and becomes a portable device. It is inconvenient to do.

The present invention has been made in view of the current state of the CO ₂ concentration measuring apparatus as described above, and an object thereof is to provide a portable CO ₂ concentration measuring apparatus which is small and lightweight.

[0012]

In order to achieve the above object, the present invention provides a sample cell through which exhaled gas of a subject passes,
An infrared source that emits infrared light that passes through the sample cell, a lens that collects the infrared light that passes through the sample cell, a detection element that is irradiated with the infrared light that is collected by the lens, and the detection element that emits infrared light. And a detecting means for detecting the CO ₂ concentration in the sample cell by detecting the change in the resistance value as a bridge output without an optical chopper.

[0013]

With this structure, the infrared ray from the infrared source passes through the sample cell through which the breath of the subject passes and is attenuated by the lens in a state corresponding to the amount of CO ₂ gas in the sample cell. The light is collected and applied to the detection element. The resistance value of the detection element that has been irradiated with infrared rays changes depending on the amount of infrared light that is irradiated, so this change in resistance value is detected by the detection means, and from this change in resistance value, CO ₂ in the sample cell is detected. The concentration is detected.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Here, FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the present invention.

As shown in FIG. 1, an infrared source 1 is arranged on one end side of a sample cell 8, and an aperture 6 is arranged between the infrared source 1 and one end of the sample cell 8. A lens 12 is provided at the other end of the cell 8. On the other hand, the sensing element 20 and the variable resistor 2 on which the interference filter 27 is surface-mounted.
The series connection circuit of 2 and the comparison element 23 and the series connection circuit of the resistor 24 and the resistor 25 are connected in parallel to each other, and the connection point of the resistor 24 and the resistor 25 and the sliding of the variable resistor 22. A DC power supply 26 is connected between the terminals to form a bridge circuit 21.

In this way, the infrared light focused by the lens 12 as described above is applied to the detection element 20 which constitutes the circuit element of the bridge circuit 21. Further, the detection element 20 is formed of PbSe having a characteristic that the resistance value is changed by the irradiation of infrared rays. Then, the output terminal t of this bridge circuit 21
The detection circuit 27 is connected between 1 and t2.

Next, the operation of the embodiment having such a configuration will be described.

The exhaled breath of the subject is guided to the sample cell 8, and the infrared gas from the infrared source 1 is incident on the exhaled gas passing through the sample cell 8 through the aperture 6. in a state of being attenuated by the CO _2, the detection interference filter is incident on the lens 12 is surface-mounted element 2
It is focused and irradiated at 0.

When the infrared rays are irradiated in this way, the resistance value of the detecting element 20 changes depending on the amount of the infrared rays irradiated.
A detection signal corresponding to the change amount is output from the output terminals t1 and t2 of the bridge circuit 21, and the detection circuit 27 detects the CO ₂ concentration in the sample cell 8 corresponding to the change in the resistance value of the detection element 20.

As described above, according to the embodiment, a chopper and a motor for rotating the chopper are not required unlike the conventional device, and the whole is greatly reduced in size and weight, which is extremely convenient for portable use and infrared rays. Element 2 by irradiation
By detecting the resistance change of 0, the CO ₂ concentration in the breath of the subject can be measured with high accuracy and stability.

[0021]

As described above, in the present invention, infrared rays are transmitted through the sample cell through which the breath gas of the subject passes.
Infrared rays that have passed through the sample cell are condensed by a lens and are applied to a detection element, and the detection means detects a change in the resistance value of the detection element due to the irradiation of infrared rays, and based on this detection value, the CO ₂ concentration in the sample cell. Is detected, a portable CO ₂ concentration detector capable of detecting the CO ₂ concentration in a highly compact and stable manner is provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a conventional CO ₂ concentration detecting device.

FIG. 3 is an explanatory diagram showing a configuration of the chopper of FIG.

FIG. 4 is an explanatory diagram of an operation of a conventional CO ₂ concentration detecting device.

[Explanation of symbols]

 1 Infrared Source 6 Aperture 8 Sample Cell 12 Lens 20 Sensing Element 21 Bridge Circuit 23 Comparison Element 27 Detection Circuit

Claims (1)

[Claims] 1. A sample cell through which exhaled gas of a subject passes, an infrared source for emitting infrared rays that pass through the sample cell, a lens that collects the infrared ray that has passed through the sample cell, and a lens that collects the light. Detected as a bridge output without the optical chopper, the change in the resistance value of the detection element due to the irradiation of infrared rays, and the detection element irradiated with the infrared rays,
Portable CO ₂ concentration measuring apparatus characterized by having a detecting means for detecting a CO ₂ concentration in the sample cell.