JPH0519098B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultra-compact gas sensor with a built-in battery for optically detecting gas concentration and the like.

(Prior Art) Conventionally, as a gas sensor for measuring the concentration of gas, for example, a voltage is applied between electrodes provided in an electrolytic solution, the gas is anodized, and the current flowing at this time is measured. Therefore, when a reducing gas is adsorbed on an electrochemical reaction type gas sensor that detects the concentration of gas, or on a metal oxide semiconductor,
There have been semiconductor-based gas sensors that take advantage of this phenomenon of increased electrical conductivity.

(Problems to be Solved by the Invention) However, among the above-mentioned conventional gas sensors, the electrochemical reaction type gas sensor uses an electrolytic solution, so it has short lifespan, large external dimensions, and is expensive. In addition, in the case of semiconductor-based gas sensors, sintered bodies of metal oxide semiconductors,
A sensitive body part made of a sintered film or a thin film,
Since it consists of a heater to heat it and an explosion-proof net, there is a limit to how small the external dimensions can be made. Therefore, there were problems in that it was extremely difficult to directly install the gas sensor in a narrow space, and that when the gas sensor was installed on the ceiling indoors, it was too conspicuous and lost its interior design.

Furthermore, since conventional gas sensors generally require 100V AC as a power source, it is necessary to install the gas sensor in a place where 100V AC power can be easily supplied.If the gas sensor is installed in a place without 100V AC power, However, since power had to be constantly supplied, the battery ran out quickly, making it impractical. Furthermore, there was a problem in that malfunctions could occur due to miscellaneous gases such as alcohol.

Therefore, in the present invention, in order to solve the above-mentioned conventional problems, an optical waveguide having the characteristics of an optical fiber is formed in an ultra-small size by using photographic technology for microfabrication such as LSI (large scale integrated circuit). Furthermore, by integrating the photoelectric section, arithmetic section, power supply section, etc. connected to the optical waveguide into a single chip, the entire gas sensor can be made ultra-compact, and the light of a wavelength that is absorbed only by a specific gas can be emitted. By using the wavelength of light that is not absorbed by the same gas as the reference light, the concentration, etc. can be detected without being affected by other gases.Also, by using a battery as the power source, the above measurement light and the reference light can be used as the measurement light. In light emission, the technical problem is to reduce the consumption of the battery and extend the life of the battery by using pulsed light with separated time intervals.

(Means for solving the problem) The technical means for solving the above problem is to install an ultra-small gas sensor for optically detecting the concentration of gas, etc. into a thin plate-shaped sensor with characteristics compatible with the cladding of an optical fiber. an optical waveguide consisting of a small base and a waveguide formed in a spiral shape on the base with characteristics corresponding to the core of the optical fiber; and a measurement light emitting device that emits measurement light at a wavelength that is absorbed by the gas. a reference light emitting means for emitting reference light having a wavelength that is not absorbed by the gas; and pulses of the measuring light and the reference light to each of the measuring light emitting means and the reference light emitting means, respectively;
and a light emission control means for outputting a light emission signal for causing light emission intermittently at regular intervals; and a light emission control means for outputting a light emission signal for causing light emission intermittently at fixed time intervals; an optical multiplexing means for transmitting the multiplexed light to the optical waveguide; and an optical multiplexing means for transmitting the multiplexed light to the optical waveguide; and after the multiplexed light from the optical multiplexing means propagates through the waveguide, it is emitted from the waveguide. a light receiving means that receives the measurement light and the reference light and outputs an electric signal corresponding to the amount of the measurement light received and the amount of the reference light received, respectively; The method is to integrally form a calculation means for calculating the concentration of the gas by inputting an electric signal and an electric signal corresponding to the received amount of the reference light.

(Function) According to the ultra-compact gas sensor configured as described above, the light emission control means pulses the measurement light and the reference light to the measurement light emission means and the reference light emission means at fixed time intervals, respectively. It also outputs a light emission signal for emitting light at a constant output. The pulsed measurement light emitted from the measurement light emitting means and the pulsed reference light emitted from the reference light emitting means are combined by the optical multiplexing means to form serial light into a spiral waveguide. propagate. During the process of the measurement light propagating through the waveguide, the evanescent wave of the measurement light generated outside the waveguide is absorbed by the gas to be detected, while the reference light is not absorbed by the gas to be detected and is emitted from the waveguide. The measuring light and the reference light are received by the light receiving means, and the light receiving means outputs electrical signals corresponding to the received amounts of the measuring light and the reference light to the calculating means. The calculation means calculates the gas concentration P based on the following equation, with V representing the electric signal corresponding to the amount of received measurement light and Vo representing the electric signal corresponding to the amount of received reference light.

V/Vo=e×p(−αpl) (1) p=−1/αllogV/Vo (2) where α is the optical absorption rate and l is the waveguide length.
As is clear from the above equation (1), the longer the waveguide length l, the smaller V/Vo becomes, which increases the so-called gas concentration detection sensitivity.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the entire system of the ultra-small gas sensor, and FIG. 2 is a sectional view of the optical waveguide. As shown in the cross-sectional view of FIG. 2, the optical waveguide 1 shown in FIG. The waveguide 3, which corresponds to the core of the optical fiber, is formed into a spiral shape by using processing technology. For example, the waveguide substrate 2 with a diameter of 1 cm has a diameter of, for example,
When forming the 50 μm waveguide 3 in a spiral shape,
The length of each turn of the waveguide 3 is approximately 3.14 cm, so when forming a spiral waveguide 3 with a total length of 100 cm, the number of turns is 100 cm/3.14 cm = 31.8, so approximately 32 turns. It would be a good idea to make a spiral.

One open end of the waveguide 3 formed in the optical waveguide 1 is a light entrance 3 that is joined to the laser emitting part 4.
A, while the other open end of the waveguide 3 becomes a light exit 3B that is connected to a photodiode 5 that receives measurement light and reference light, which will be described later.

The laser emitting unit 4 converts the gas to be detected into, for example, methane.
CH4 includes a laser diode 4A that emits a measurement light with a wavelength that is absorbed by methane, a laser diode 4B that emits a reference light with a wavelength that is not absorbed by methane, and a laser diode 4B that combines the measurement light and the reference light and then generates both lights. into the light input port 3 as a series light.
It has a built-in optical multiplexer 4C that allows light to enter A.

The laser emitting section 4 is connected to a microcomputer 6, and the microcomputer 6 outputs a light emission signal to the laser diodes 4A and 4B. The light emission signal output from the microcomputer 6 is, as shown in Fig. 4, for example, by emitting the measurement light for 10 milliseconds and the reference light for 10 milliseconds at the same light emission level, and then emitting it again at an interval of 10 seconds. This is for intermittent light emission in which the measurement light and reference light are emitted for 10 milliseconds each. On the other hand, the photodiode 5 is connected to the microcomputer 6, and outputs to the microcomputer 6 an electric signal corresponding to the amount of received measurement light and reference light emitted from the light exit 3B of the waveguide 3. microcomputer 6
inputs the electric signal outputted from the photodiode 5 and calculates the concentration of methane by the action described later. A battery 7 is provided as a power source for the ultra-small gas sensor of this embodiment, and after the output voltage of the battery 7 is stabilized to a predetermined voltage by a stabilizing power source 8, the output voltage of the battery 7 is stabilized to a predetermined voltage by a stabilizing power source 8, and then the output voltage of the battery 7 is stabilized to a predetermined voltage by a stabilizing power source 8. is supplied to The battery 7 and the stabilized power source 8 are formed into a chip shape and incorporated into the device, such as in an IC card, so that the overall shape is made extremely small.

Next, the operation of the embodiment with the above configuration will be explained. With the ultra-compact gas sensor installed at a methane generation location, the microcomputer
outputs a light emitting signal for emitting measurement light to the laser diode 4A, causes the laser diode 4A to emit measurement light at a predetermined light intensity for 10 milliseconds at a wavelength that is absorbed by methane, for example, in the 1.3 μm band, and then A reference light having a wavelength that is not absorbed is emitted from the laser diode 4B for 10 milliseconds at the same light intensity as the measurement light. The measurement light emitted from the laser diode 4A and the reference light emitted from the laser diode 4B are multiplexed by an optical multiplexer 4C and made into series light, which is transmitted from the light entrance 3A of the optical waveguide 1 to the waveguide 3.
The light enters and propagates through the waveguide 3 formed in a spiral shape. As the measurement light propagates through the waveguide 3, an evanescent wave 10 of the measurement light is generated outside the waveguide substrate 2 as shown in FIG. 3, and when it comes into contact with methane, the evanescent wave 10 is absorbed by the methane. Ru. Therefore, the measurement light is attenuated while propagating through the waveguide 3, and the measurement light at the time it is emitted from the light exit 3B of the waveguide 3 and received by the photodiode 5 is absorbed in accordance with the concentration of methane gas. This will be the amount of light.

On the other hand, since the reference light is not absorbed by the rotane, it is received by the photodiode 5 with almost no attenuation. The output signal corresponding to the amount of measurement light received by the photodiode 5 is V, the output signal corresponding to the amount of reference light received by the photodiode 5 is Vo, and the light absorption rate of methane is α (0.054 atm ^-1・cm ^-1 ), the length l of the waveguide 3 is (cm), and the gas concentration is p (ppm), then the absorption formula by methane is V/Vo=exp(-αpl)...(3), and the equation (3) ), formula (4) for determining the gas concentration p is derived: p=-1/αllogV/Vo (4). From the above equation (4), now the waveguide length l=
When 100 cm and α=0.054 atm ⁻¹ ·cm ⁻¹ V/Vo=0.984, the gas concentration p is 5000 ppm.

Note that when the methane gas concentration p is 5000 ppm and the length l of the waveguide 3 is 1000 cm, V/Vo = 0.85 from equation (3), so the detection sensitivity of the gas concentration can be improved. . Furthermore, by connecting a display, a piezoelectric buzzer, etc. to the microcomputer 6, the gas concentration can be displayed.

(Effects of the Invention) As described above, according to the present invention, the waveguide corresponding to the core of the optical fiber is formed in a spiral shape on the thin plate-like base corresponding to the cladding of the optical fiber. The gas sensor can be constructed in an ultra-compact size by ensuring the waveguide length and further forming the measuring light emitting means, the reference light emitting means, the light receiving means, the calculating means, the battery, etc. in an integrated and compact manner. It can be installed without limiting the setting location and without losing the interior design of the room, etc. Also, since the measurement light and reference light are emitted intermittently, the battery life is extended. The effect is that it can be done.

[Brief explanation of the drawing]

The drawings relate to embodiments, and FIG. 1 is an overall system diagram of an ultra-small gas sensor, FIG. 2 is a partial sectional view of an optical waveguide, and FIGS. 3 and 4 are explanatory views of the operation. 1... Optical waveguide, 2... Waveguide substrate, 3... Waveguide,
4... Laser emitting section, 4A... Laser diode, 4
B...Laser diode, 4C...Optical multiplexer, 5...Photodiode, 6...Microcomputer, 7
...Battery, 8...Stabilized power supply.

Claims (1)

[Claims] 1. An ultra-compact gas sensor for optically detecting gas concentration, etc. using a battery as a power source, which consists of a small thin plate-like base with characteristics compatible with optical fiber cladding and optical fiber cladding. an optical waveguide formed in a spiral shape on the substrate and having characteristics corresponding to the core; a measurement light emitting means for emitting measurement light having a wavelength that is absorbed by the gas; a reference light emitting means for emitting a reference light of a wavelength that is not detected; and the measuring light and the reference light are applied to each of the measuring light emitting means and the reference light emitting means in a pulsed manner and intermittently at regular intervals. a light emission control means for outputting a light emission signal for causing light to be emitted; and a light emission control means for combining the pulsed measurement light emitted from the measurement light emission means and the pulsed reference light emitted from the reference light emission means. , an optical multiplexer for transmitting the multiplexed light to the optical waveguide, and after the multiplexed light from the optical multiplexer propagates through the waveguide, the measurement light and the reference light output from the waveguide. a light-receiving means that receives the light and outputs an electric signal corresponding to the received amount of the measurement light and the received amount of the reference light, and an electric signal corresponding to the received amount of the measurement light output from the light-receiving means and the reference light An ultra-compact gas sensor characterized in that an electric signal corresponding to the amount of received light is input, and a calculation means for calculating the concentration of the gas and the like are integrally formed.