JPH10339698A - Infrared-type gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared-type gas detector that can improve the response property and reliability of gas detection and at the same time can expand the life of a light source by improving the linearity of sensor sensitivity for gas concentration. SOLUTION: An infrared-type gas detector device consists of a light source 1 for generating infrared rays, a cylindrical cell 2 for measurement for taking in a measurement gas, and an infrared detection sensor 3 that is provided at one side of the cell 2 for measurement and detects that the infrared rays being radiated from the other side of the cell 2 for measurement into an internal part are absorbed by the measurement gas. The device has a light source driving circuit K for gradually lighting up and driving the light source 1 and at the same time uses a current amplification-type infrared detection sensor 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various gases utilizing infrared rays, for example, gases generated in a smoldering fire, specifically, hydrocarbons, carbon dioxide gas classified as a toxic gas, and carbon monoxide. , Nitric oxide, hydrogen cyanide, acrolerin (CH
₂ = CHCHO), hydrochloric acid, ammonia, etc., to detect a fire at an early stage, and thereby to use an infrared gas detection device to enable blame and early fire fighting from that location. .

[0002]

2. Description of the Related Art The above-mentioned infrared type gas detector comprises a light source for generating infrared light, a cylindrical measuring cell for taking in a measuring gas, and infrared light radiated inside from one end of the measuring cell by the light source. In general, an infrared detection sensor is provided at the other end of the measuring cell in order to detect absorption by the measuring gas. Therefore, when a gas enters the measuring cell, the gas is irradiated with infrared rays, and the gas absorbs the infrared rays. This is detected by an infrared detection sensor to determine the type and concentration of the gas, thereby determining whether or not a fire has occurred.

The infrared gas detection device having the above-described structure is always in operation so that it can be detected for 24 hours. Therefore, a voltage amplification type pyroelectric sensor is changed to an infrared detection sensor so as to be advantageous in power consumption. Was composed.

As described above, the voltage amplification type pyroelectric sensor is
Although it is advantageous for power consumption, not only does the responsiveness decrease accordingly, but the chopping frequency can be up to 10 Hz.
(Measured 10 times per second)
Rapid changes cannot be detected immediately,
Large variations occurred in the detection results, and the reliability was lacking. In addition, since the light source for irradiating the measuring cell with infrared light is also driven in synchronization with the frequency (10 Hz), a single driving (lighting) of the light source is performed, for example, as compared with the case of driving at 60 Hz. The time and the drive stop (light-out) time increase. For this reason, the filament of the light source heated during the driving (lighting) time is stopped (lights off).
In a long time, the filament is greatly cooled down, and the filament is heated to a high temperature again at the next driving (lighting), so that the filament is cut off early.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, the present invention aims to solve the problem by improving the linearity of the sensor sensitivity with respect to the gas concentration, thereby improving the responsiveness and reliability of gas detection. An object of the present invention is to provide an infrared gas detection device that can improve the light source and can prolong the life of the light source.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a light source for generating infrared light, a cylindrical measuring cell for taking in a measuring gas, and one end of the measuring cell by the light source. An infrared gas detection device comprising an infrared detection sensor provided at the other end of the measurement cell to detect that the infrared light applied to the inside is absorbed by the measurement gas. An infrared gas detection device comprising a light source driving circuit for driving and lighting, and a current amplification type infrared detection sensor. Therefore, by using a current amplification type infrared sensor, it is possible to improve the high-speed response and improve the measurement accuracy. Moreover,
Since the driving frequency of the sensor can be increased to about 60 Hz, the linearity is improved, and the accuracy can be further improved. Also, by driving the light source at a higher frequency than before, the cooling time of the filament of the light source can be drastically shortened as compared with the case where the conventional light source is driven at 10 Hz. In addition, since the light source is gradually turned on and driven by the light source driving circuit, a shock at the time of lighting can be reduced, so that the life of the light source can be extended.
Further, by driving the light source at a high frequency, it is possible to achieve the same or substantially the same stability as continuous lighting.

By configuring the measuring cell from a plurality of cells having different cell lengths, the wavelength band that can be measured can be expanded. In addition, by configuring the light source for irradiating the plurality of cells with infrared light from a single light source, it is possible to obtain an advantage in cost as compared with the case where a plurality of light sources are provided. Then, by arranging the light source so that the distance from the light source to the beginning of the infrared irradiation direction of each cell is substantially the same, and by arranging the infrared detection sensor close to the end of the infrared irradiation direction of each cell While it is possible to make the amount of infrared light reaching each cell from the light source substantially equal, it is possible to avoid a decrease in detection accuracy when there is a distance between the infrared irradiation direction end of each cell and the infrared detection sensor. be able to.

[0008] A plurality of band-pass filters for the infrared detection sensor are mounted on a rotatable rotatable body, and the rotatable body is driven and rotated every time a set time elapses, so that only a specific wavelength is controlled. Since it can be taken out, the detection accuracy can be improved.

[0009]

FIG. 1 shows an infrared gas detection apparatus according to the present invention. This is a light source 1 that generates infrared light.
A cylindrical measuring cell 2 for taking in a measuring gas;
An infrared detection sensor 3 provided at the other end of the measuring cell 2 to detect that the infrared light emitted from one end of the measuring cell 2 to the inside by the light source 1 is absorbed by the measuring gas. .

As the light source 1, a light source having a voltage of 6.3 V and 200 mA is used, and a specific circuit of a driving circuit K of the light source 1 is shown in FIG. This is because the two FETs are turned on and off based on a signal from a change circuit 4 for changing the duty ratio of a drive pulse for driving the light source 1.
The drive control of the light source 1 is performed by performing FF control. The light source 1 is driven by the voltage / current supply circuit 5 when the two FETs are turned on. That is, the light source drive circuit K is changed to the change circuit 4
And a voltage / current supply circuit 5. The voltage / current supply circuit 5 includes, in addition to the resistors R1 to R3, an operational amplifier 6 arranged to obtain stable characteristics, a constant voltage diode 7 for maintaining a constant voltage, and a current control circuit for performing current control. It has a capacitor 8. By the capacitor 8, as shown in FIG. 5, the current pulse can be controlled so as to have a region X that draws a gentle curve until reaching the set maximum current value. I can do it. Then, after reaching the maximum current value, by maintaining the maximum current value for the set time, the life of the light source 1 can be extended. The degree of bending of the curve and the time for maintaining the maximum current value can be freely changed.

The infrared detecting sensor 3 comprises two elements 3
FIG. 3 shows a drive circuit for the infrared detection sensor 3 which is configured as a dual element type having the A and 3A.
This drive circuit includes an operational amplifier 9 having excellent responsiveness and reliability, a low-pass filter 10 for removing high-frequency noise components, a resistor R4 for amplifying an input signal to a non-inverting input terminal, and a part of an output. Negative feedback resistor R5 for sending back to the end, resistors R6 and R7 for stabilizing the circuit
And the like, and is configured as a current amplification type.

As shown in FIG. 2, in front of the infrared detection sensor 3, an 8 μm cut-on filter B and four kinds of band-pass filters A for discriminating various gases in combination with the cut-on filter B are used. , C,
D and E are attached to a rotating body 12 that can be driven and rotated by a pulse motor 11, and the pulse motor 11 is drive-controlled so that the rotating body 12 is rotated 45 degrees every time a set time elapses. The band pass filter A includes:
This filter has a high transmittance in the 4.3 μm frequency band,
C is a filter having a high transmittance in the 4.7 μm frequency band, D is a filter having a high transmittance in the 5.3 μm frequency band, and E is a filter having a high transmittance in the 3.4 μm frequency band. . Reference numerals 14 and 15 shown in FIG. 1 are filters for preventing external light rays from entering the inside from both ends of the measuring cell 2. Incidentally, the infrared absorption wavelength of the hydrocarbon is 3.3 to 3.5 μm, which can be detected by the filter E. The infrared absorption wavelength of carbon dioxide gas is 4.3 μm, and the detection is performed by the filter A. In addition, the infrared absorption wavelength of carbon monoxide is 4.7 μm, and can be detected by the filter C. The infrared absorption wavelength of nitric oxide is 5.3 μm, and the filter D So that it can be detected. In this embodiment, the four types of gases are detected, but other types of gases may be detected. The type and number of gases are not limited to these examples. Absent. Incidentally, the infrared absorption wavelength of ammonia is 3.6 μm,
The infrared absorption wavelength of sulfur dioxide is 7.4 and the infrared absorption wavelength of hydrogen cyanide is 3.1 μm, and a filter for detecting these is prepared.

Next, the operation of detecting gas by the infrared detection sensor 3 will be described. First, the light source 1 is driven by turning on the power supply to the infrared gas detection device,
Set to the detection operation state. In this state, for example, carbon dioxide gas passes through the many holes 2A formed in the measurement
When entering the inside of the filter, the band-pass filter A
Is located opposite to the element 3A, that is, in a state where it is detected through the bandpass filter A, it is detected that carbon dioxide gas has entered, and this detection signal is output to the amplifier 1
3, and output to a control device or the like.

FIG. 6 shows the chopping frequency characteristics. Three prototypes of the infrared gas detection device having the above-described configuration were manufactured, and the chopping frequency characteristics of these three devices were measured. As can be seen from FIG.
Even when the frequency is set to 0 Hz, the output of the prototype device whose performance is inferior among the three devices is 70% or more, and it can be seen that a highly reliable detection result can be obtained even when the frequency is set to 60 Hz.

FIG. 7 is a graph showing the results of measuring the concentration of carbon dioxide and the sensitivity of the sensor for each frequency. As is apparent from the result, the higher the frequency is, the more linear the linearity becomes.

FIGS. 8A and 8B show a plurality of (four in the figure) cells 2a and 2 having different cell lengths.
b, 2c, and 2d, and the infrared detection sensor 3 is arranged close to the end of the infrared irradiation direction of each cell. Accordingly, gases having different wavelengths can be introduced into the measuring cell 2 and, for example, the position of the infrared detection sensor 3 for detecting the gas having the longest wavelength, which is located on the right side in FIG. Three infrared detection sensors 3 including the located infrared detection sensor 3
In the case where a plurality of cells are provided, a distance is generated between the end of the infrared irradiation direction of each cell and the infrared detection sensor, thereby preventing the detection accuracy of the infrared detection sensor 3 from being reduced. 16 and 16 shown in the figure are cells 2a and 2
It is a spacer for positioning b, 2c, 2d.
17 is a cover member for covering the light source 1. A reflecting member for irradiating the cells 2a, 2b, 2c and 2d with light from the light source 1 is provided on an inner surface 17A of the cover member 17. Attachment is performed, or a reflective material is coated so that the inner surface 17A itself becomes a reflective surface.
By arranging the light source 1 on the top of the inner surface 17A of the cover member 17 formed in a parabolic shape, the distance from the light source 1 to the beginning of each cell 2a, 2b, 2c, 2d in the infrared irradiation direction is the same. And from the light source 1 to each cell 2
a, 2b, 2c, and 2d, besides making it possible to equalize the amounts of infrared rays reaching the light source 1, the light source 1 may be arranged at the focal point of a parabola located inside the cover member 17, or slightly deviated from these positions. The light sources 1 may be arranged at different positions to make the light amounts substantially equal.

FIGS. 9A and 9B show the measurement cell 2 in which the mounting direction of the light source 1 and the shape of the inner surface 17A of the cover member 17 are changed. In FIG. 8A, the cross section is formed in a semicircle, but in FIG. 9A, the cross section is formed in a substantially semi-elliptical shape, and as shown in FIG. Thus, it is possible to prevent the light emitted from the light source 1 from being applied to unnecessary portions and
a, 2b, 2c, and 2d can be efficiently irradiated. As shown in FIG. 9 (a), by changing the mounting direction of the light source 1 so that the light source 1 also irradiates toward the inner surface 17A of the cover member 17, the light source 1 can be compared with the one shown in FIG. 8 (a). And four cells 2a, 2
There is an advantage that the amount of light that can be applied to b, 2c, and 2d can be increased. Cover member 17 shown in FIG.
The inner surface 17A is also configured to be able to reflect the light emitted from the light source 1 as described above.

[0018]

According to the first aspect, by driving the light source at a higher frequency than in the prior art, the temperature change of the filament can be suppressed small, and the light source is gradually turned on by the light source driving circuit. Therefore, the life of the light source can be synergistically increased because the shock at the time of lighting can be reduced. Further, since the light source can be driven at a higher frequency than in the related art, the same or substantially the same stability as continuous lighting can be achieved. Moreover, by using a current amplification type infrared detection sensor, a highly reliable infrared gas detection device that can increase the high-speed response and measurement accuracy of the sensor can be provided.

According to the present invention, the measuring cell is constituted by a plurality of cells having different cell lengths, and the light source for irradiating the plurality of cells with infrared rays is constituted by a single light source. By setting the installation position of the infrared detection sensor rationally, the measurable wavelength band can be expanded, and the amount of infrared light reaching each cell from the light source can be made substantially equal, but cost is reduced. In addition, there is an advantage that it is possible to avoid a decrease in detection accuracy when there is a distance between the end of the infrared irradiation direction of each cell and the infrared detection sensor.

According to the third aspect, a plurality of band-pass filters for the infrared detection sensor are mounted on a rotatable rotatable body, and the rotatable body is driven and rotated every time a set time elapses. Since only a specific wavelength can be extracted, detection accuracy can be improved. In addition, in the case of a filter formed by laminating a plurality of layers, energy loss can be avoided by making the filter extremely expensive or transmitting the filter through the multilayer filter.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an infrared gas detection device.

FIG. 2 is a front view of a rotating body.

FIG. 3 is a driving circuit of an infrared detection sensor.

FIG. 4 is a light source driving circuit.

FIG. 5 shows a voltage pulse waveform and a current pulse waveform.

FIG. 6 is a graph showing chopping frequency characteristics.

FIG. 7 is a graph showing the concentration of carbon dioxide and the sensitivity of the sensor for each frequency.

8A is a cross-sectional view showing another embodiment of the measuring cell, and FIG. 8B is a cross-sectional view taken along line II in FIG.

9A is a cross-sectional view showing another embodiment of the measuring cell, and FIG. 9B is a cross-sectional view taken along the line II-II in FIG. 9A.

[Explanation of symbols]

 Reference Signs List 1 light source 2 measurement cell 2A hole 3 infrared detection sensor 3A element 4 change circuit 5 voltage / current supply device 6 operational amplifier 7 constant voltage diode 8 capacitor 9 operational amplifier 10 low-pass filter 11 pulse motor 12 rotating body 13 amplifier 14 filter 15 filter 16 spacer 17 Cover member 17A Inner surface K Light source drive circuit X area R1-R7 Resistance

Claims (3)

[Claims] 1. A light source for generating infrared light, a cylindrical measuring cell for taking in a measuring gas, and a light source for detecting that infrared light radiated inside from one end of the measuring cell by the light source is absorbed by the measuring gas. An infrared gas detection device comprising: an infrared detection sensor provided at the other end of the measuring cell for detection, wherein a light source drive circuit for gradually lighting and driving the light source is provided, and a current is supplied to the infrared detection sensor. An infrared gas detection device characterized by using an amplification type. 2. The measuring cell comprises a plurality of cells having different cell lengths, and the light source for irradiating the plurality of cells with infrared rays is constituted by a single light source. 2. The infrared light according to claim 1, wherein the light sources are arranged so that the distances to the start of the infrared irradiation direction of the cells are substantially the same, and the infrared detection sensor is arranged close to the end of the infrared irradiation direction of each cell. Gas detector. 3. The apparatus according to claim 1, wherein a plurality of band-pass filters for the infrared detection sensor are mounted on a rotatable rotatable body, and the rotatable body is driven and rotated each time a set time elapses. Infrared gas detector.