JP4766697B2 - Small gas detector - Google Patents

Description

The present invention is used when detecting gas leakage due to deterioration of piping of city gas or chemical plant, for example, and is a portable small gas detector that optically detects gas using infrared absorption characteristics of gas. Relates to the device.

  For example, it is already known that gases such as methane, carbon dioxide, acetylene, and ammonia have an absorption band that absorbs light of a specific wavelength in accordance with molecular rotation, vibration between constituent atoms, and the like. In a gas detection device using this absorption band, a light source part and a light receiving part are arranged at a predetermined distance (the measurement optical path length is determined by this distance), and laser light frequency-modulated by a semiconductor laser of the light source part is used. It passes through the atmosphere containing the measurement target gas, and the transmitted light is received by the photodetector of the light receiving unit to detect the gas, and the gas concentration of the measurement target gas is measured from the output signal at this time. Further, as disclosed in Patent Document 1 below, there is also known a gas detection device configured such that the light source unit and the light receiving unit described above are accommodated in a common casing and can be carried. Even if the light source unit and the light receiving unit are arranged at the same position, the measurement optical path length is secured if the measurement light can be received as reflected light.

  Here, a large offset due to intensity modulation occurs in a fundamental phase sensitive detection signal (hereinafter referred to as “1f signal”) having a modulation frequency detected from the output signal of the light receiving unit. For this reason, in order to measure a particularly minute gas concentration with high sensitivity, a second harmonic phase sensitive detection signal (hereinafter abbreviated as 2f signal) having a considerably smaller offset than the 1f signal is used.

When actually measuring the gas concentration, when the measurement light with the wavelength matched to the measurement gas absorption line passes through the measurement gas atmosphere, the measurement light is absorbed by the gas to be measured, and the intensity according to the gas concentration optical path length product. A 2f signal is generated by an intensity change (2f signal component I _2f ) at a frequency twice the modulation frequency. The value of the ratio I _2f / I _1f between the intensity change of the 2f signal and the intensity change of the 1f signal (1f signal component I _1f ) which is the original modulation frequency is proportional to the gas concentration optical path length product. Multiplying the coefficient to get the gas concentration.

  By the way, as a conventional gas detection device of this type, Japanese Patent Application Laid-Open No. 2004-228561 discloses a portable gas concentration measurement device capable of detecting a gas in a measurement atmosphere while confirming the emission position of measurement light. FIG. 5 is a perspective view showing an external appearance of a conventional gas detection device having a configuration equivalent to that of the gas concentration measurement device disclosed in Patent Document 1, and FIG. 6 is a partial cross-sectional view of the housing taken along line BB in FIG. .

A gas concentration measuring device (hereinafter referred to as a conventional device) 51 shown in FIGS. 5 and 6 is formed as a whole with a gun-like shape and has a bottomed cylindrical housing 53 having an opening 52 on one surface, and a housing. 53, and a grip portion 54 that grips the casing 53. A semiconductor laser unit 55 is incorporated in the housing 53, and a light receiver 56 is disposed at the back of the housing 53 on the central axis. The semiconductor laser unit 55 includes a semiconductor laser module 57 including a semiconductor laser that emits measurement light for detecting a gas in a measurement atmosphere, a laser pointer 58, and a multiplexing means 59. A condensing lens 60 for condensing the reflected measurement light from the measurement atmosphere accompanying the emission of the measurement light onto the light receiver 56 is fixed in the opening hole 52 of the housing 53. The laser pointer 58 is fixed to the rear of the condenser lens 60 of the housing 53 by an inverted V-shaped support member 61, and emits visible light as guide light for confirming the emission position of the measurement light. The multiplexing means 59 is disposed on the optical axis LL of the light receiver 56 behind the condenser lens 60 of the housing 53, and combines the measurement light and the guide light on the optical axis LL of the light receiver 56. Then, the light is emitted from the central glass window 62 of the condenser lens 60.
JP-A-2005-106521

  However, in the conventional apparatus 51 shown in FIGS. 5 and 6 described above, the measurement light and the guide light are emitted substantially on the same axis, so that the measurement light and the guide light are within the light collection area of the condenser lens 60. A laser pointer 58 is arranged so as to be multiplexed on 56 optical axes LL. For this reason, the reflected measurement light from the measurement atmosphere accompanying the emission of the measurement light is blocked by the support member 61 of the laser pointer 58, and the reflected measurement light having a sufficient amount of light cannot be guided to the light receiver 56.

  Therefore, the opening hole 52 of the housing 53 provided with the condenser lens 60 is formed as large as possible so that a sufficient amount of reflected measurement light is condensed from the condenser lens 60 onto the light receiver 56. In addition, the emission position of the measurement light and the guide light is on the center of the condenser lens 60 (optical axis LL), and the focal length of the condenser lens 60 with respect to the light receiver 56 (on the optical axis LL). When the distance from the center of the lens to the light receiving surface of the light receiver 56 is short, a lot of reflected measurement light is collected by the laser pointer 58 and the support member 61 when the reflected measurement light is condensed on the light receiver 56 by the condenser lens 60. It will be blocked. For this reason, the light receiver 56 is arranged in the inner part of the housing 53, and the focal length of the condenser lens 60 is set to be long so that the attenuation amount of the reflected light is reduced. As a result, in the conventional apparatus 51 shown in FIGS. 5 and 6, the outer diameter and thickness of the condenser lens 60, which is an optical part, are increased and the focal length is increased. There was a problem of increasing the size. 5 and FIG. 6, the arrangement position of the laser pointer 58 is also arranged so that the reflected measurement light condensed from the condenser lens 60 to the light receiver 56 is not blocked as much as possible. There is a problem that it is limited to the position close to the condenser lens 60.

Accordingly, the present invention has been made in view of the above problems, and provides a small gas detection device (hereinafter abbreviated as a gas detection device) capable of reducing the size of the entire device by reducing the optical portion. The purpose is to do.

In order to achieve the above object, a gas detector according to claim 1 of the present invention includes an emission unit 8 that emits laser light for measuring gas in a measurement atmosphere as measurement light,
An aspherical Fresnel lens 7 made of a single acrylic resin that condenses laser light reflected from the measurement atmosphere as reflected measurement light as the measurement light is emitted to the measurement atmosphere;
A gas detection device 1 in which a light receiving unit 9 that receives the reflected measurement light collected by the aspheric Fresnel lens is disposed in a single housing 2,
The emitting portion and the light receiving portion are disposed in the same space within the single casing, and the emitting portion is condensed by the aspheric Fresnel lens in the same space. The measuring light is arranged outside the area and emits the measuring light from outside the aspheric Fresnel lens .

The gas detection device according to claim 2 of the present invention is the gas detection device according to claim 1,
The emitting unit 8 emits visible light for confirming the emitting position of the measurement light from outside the light condensing area as the guide light together with the measurement light.
The gas detection device according to claim 3 of the present invention is the gas detection device according to claim 1 or 2,
The single casing 2 has a rectangular parallelepiped shape.

According to the gas detection device of the present invention, the emitting part and the light receiving part are arranged in a common space inside a single housing, and from outside the light condensing area by the condensing lens in the common space. Since the emission part is built into the housing to emit measurement light (measurement light and guide light), the condensing lens, which is the optical part, can be made small, the entire device can be miniaturized, and the design of the emission part is free. Also increases.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. 1 is a perspective view showing an external appearance of a gas detector according to the present invention, FIG. 2 is a partial cross-sectional view of a housing taken along line AA in FIG. 1, and FIG. 3 is provided with an emitting portion and a light receiving portion in FIG. FIG. 4 is a block diagram of the gas detector according to the present invention.

  The gas detection device according to the present invention is used in a portable manner, for example, when detecting gas leakage accompanying deterioration of gas pipes such as city gas or chemical plant, and optically utilizing absorption of laser light by gas. Gas is detected.

  As shown in FIG. 1, the gas detection device 1 of the present example has a single rectangular parallelepiped housing 2 that can be carried and operated by a user as a main body. As shown in FIGS. 1 and 2, a rectangular opening hole 3 is formed on one surface in the longitudinal direction of the housing 2 toward the upper side. A condensing lens 7 to be described later is fixed in the opening hole 3. As shown in FIGS. 1 and 2, two circular window holes 4 (4 a, 4 b) are formed side by side in the lower portion of the opening hole 3. In each of the window holes 4a and 4b, a protective plate 5 (5a and 5b) made of a glass material whose surface is subjected to antireflection treatment such as an AR coating (Anti-Reflection Coat) is fixed. Furthermore, the radiator 6 is fixedly installed in the opening portion on the bottom surface of the housing 2 near the surface where the opening hole 3 and the window hole 4 are formed, with the radiation fins 6a exposed to the outside. On the radiator 6, an emission unit 8 described later is disposed.

  As shown in FIG. 4, the housing 2 is provided with a condenser lens 7, an emitting unit 8, a light receiving unit 9, an electrical conversion unit 10, an operation input unit 11, a control unit 12, and a display unit 13. . As shown in FIG. 1 and FIG. 2, a battery as a power source for supplying driving power to each part is provided on the surface of the housing 2 opposite to the surface on which the opening hole 3 and the window hole 4 are formed. A battery box 15 containing 14 is detachably provided.

  The condenser lens 7 is fixed in the opening hole 3 of the housing 2, and reflects reflected measurement light reflected from the measurement atmosphere as the measurement light is emitted from the emission unit 8 toward the measurement atmosphere. Condensed on the light receiving surface.

  Specifically, the condenser lens 7 is composed of an aspheric Fresnel lens made of an acrylic resin, and is formed as thin as 1 mm in order to reduce transmission loss. The acrylic transmittance is about 70% and the outer shape is The focal length (distance from the center of the lens to the light receiving surface of the light receiving unit 9 on the optical axis LL) is 40 mm. In addition, in the example of FIG. 1, although the condensing lens 7 is made into the rectangular shape, it can also be made into a circular shape.

  As shown in FIGS. 2 to 4, the emission unit 8 includes a measurement light emission unit 8 a that emits measurement light to the measurement atmosphere to be detected, and guide light that emits guide light for confirming the emission position of the measurement light. It consists of the emission part 8b. In addition, the emission part 8 is good also as a structure only of the measurement light emission part 8a.

  The measurement light emitting unit 8a uses a laser beam having a wavelength (absorption line wavelength of a gas to be detected) matched with an absorption line peculiar to a predetermined gas as measurement light, and is controlled by the control unit 12 to measure the measurement atmosphere (for example, (Reflecting material such as gas piping). The measurement light emitting unit 8a is formed of a known semiconductor laser module as disclosed in, for example, the above-described Patent Document 1 (Japanese Patent Laid-Open No. 2005-106521). An example of the configuration will be described. The semiconductor laser module is based on a box-shaped butterfly case body having a plurality of pairs of electrodes, a through hole is formed on one surface of the case body, and an emission window such as glass is formed in the through hole. Is provided. The semiconductor laser module emits laser light that is frequency-modulated by controlling the oscillation wavelength to the measurement wavelength, and emits the laser light emitted from the front surface and the laser light emitted from the front surface, and is emitted from the rear surface. A semiconductor laser that uses laser light as reference light, a collimating lens that collimates measurement light into parallel light, an optical isolator that suppresses the return of reflected light to the semiconductor laser, a Peltier element (temperature control element) that controls the temperature of the semiconductor laser, A gas cell filled with a wavelength stabilizing gas, a photodiode (receiver) that receives and detects the reference light, and a thermistor (temperature measurement element) that detects the temperature of the semiconductor laser are housed in the case body. The optical axis is adjusted and hermetically sealed.

  The guide light emitting unit 8b is composed of a visible light laser having an oscillation wavelength in the visible light region (400 to 720 nm), and the control unit 12 controls the emission position of the measurement light emitted from the measurement light emitting unit 8a. Visible light for guiding the measurement light to the target position in the measurement atmosphere is emitted as guide light while checking.

  As shown in FIG. 2, the measurement light emission part 8a and the guide light emission part 8b are positioned behind the protective plates 5a and 5b on the bottom side in the housing 2 as positions that do not hinder the collection of the reflected measurement light. It is located on the radiator 6 in the vicinity.

  That is, the emitting unit 8 emits the measurement light and the guide light from a position outside the condensing area by the condensing lens 7 (the region in which the reflected measurement light collected by the condensing lens 7 is collected on the light receiving unit 9). May be disposed in the housing 2. In this example, as shown in FIG. 2, the condensing lens 7 and the light receiving unit are arranged between the condensing lens 7 and the light receiving unit 9 on the bottom surface side of the housing 2 outside the condensing area. 9 and anywhere in the housing 2 outside the light condensing area.

  Further, it is preferable that the measurement light emission part 8 a and the guide light emission part 8 b are inclined at a predetermined angle toward the central axis (optical axis LL) side of the condenser lens 7. Specifically, the emission angle is inclined by about 5 mrad toward the central axis (optical axis LL) side of the condenser lens 7 so as to improve the light receiving level of the light receiving unit 9 when measuring a short distance of, for example, about 50 cm to 1 m. .

  The light receiving unit 9 is composed of, for example, a photodiode, the center of the light receiving surface is located at the focal length of the condenser lens 7, and is reflected from the measurement atmosphere as the measurement light is emitted from the measurement light emitting unit 8a to the measurement atmosphere. The reflected measurement light collected by the condenser lens 7 is received, and a measurement light signal based on the received reflected measurement light is output to the electrical converter 10. In addition, the light receiving unit 9 reduces the noise level and the cost by reducing the diameter of the light receiving surface to, for example, φ1 mm.

  The electrical conversion unit 10 is configured by a preamplifier, and the amplification degree is optimal for each of the 1f signal and the 2f signal so that the 1f signal and the 2f signal detected by the light receiving unit 9 have the same detection level in the measurement target gas concentration range. Amplification is set. The electrical conversion unit 10 converts the light reception current of the measurement light signal detected and output from the light reception unit 9 into a light reception voltage, and further amplifies it with a set amplification degree and outputs it to the control unit 12.

  The operation input unit 11 includes operation keys, operation buttons, and the like that are provided on the housing 2 and are directly operated by a user. In addition to inputting a start or stop instruction for gas detection in the measurement atmosphere, An alarm level for outputting an alarm is set, and these instruction inputs and setting information are input to the control unit 12.

  The control unit 12 performs overall control of processes related to gas detection, and includes a light emission control unit 12a, a concentration calculation unit 12b, and a display control unit 12c.

Based on the instruction input from the operation input unit 11, the light emission control unit 12a controls the emission of the measurement light from the measurement light emission unit 8a and the emission of the guide light from the guide light emission unit 8b. The density calculation unit 12b performs signal processing on the measurement light signal amplified by the electrical conversion unit 10 to perform phase sensitive detection on the 1f signal and the 2f signal, and changes the intensity (2f signal component I) of the phase sensitive detection 2f signal. _2f ) and the change in intensity of the 1f signal (1f signal component _I1f ), the value of the ratio _I2f / _I1f is multiplied by a predetermined coefficient to calculate the gas concentration optical path length product.

  Based on the setting information from the operation input unit 11, the display control unit 12 c displays a display related to the gas concentration optical path length product obtained by the calculation of the concentration calculation unit 12 b, a display related to the alarm level, etc. for a cycle of several hundred milliseconds (for example, 500 milliseconds) The display on the display unit 13 is controlled so as to be sequentially rewritten at a period).

  The display unit 13 performs various displays including a display regarding the gas concentration optical path length product and a display regarding the alarm level under the control of the display control unit 12c.

  As described above, in the gas detection device 1 of this example, the emission portion 8 is incorporated in the housing 2 so as to emit measurement light (measurement light and guide light) from outside the light collection area by the condenser lens 7. Thereby, the condensing lens 7 can be made small and size reduction of the whole apparatus can be achieved. In addition, since the emission unit 8 may be a position where the measurement light and the guide light are emitted from the outside of the condensing area of the condensing lens 7, the arrangement position is larger than that of the conventional device 51 shown in FIGS. 5 and 6. And the degree of freedom in designing the emission part 8 increases.

  Here, the gas detection apparatus of this example and the conventional apparatus 51 shown in FIGS. 5 and 6 will be compared with specific numerical examples. First, in the configuration of the conventional apparatus 51 shown in FIGS. 5 and 6, the condenser lens 60 has a thickness of 2 mm, an outer diameter of 95 mm, and a focal length of 168 mm, and the light receiving surface diameter of the light receiver 56 is φ2 mm. Thus, the external dimensions of the conventional apparatus 51 are 250 mm (corresponding to D2 in FIG. 5), 112 mm (corresponding to W2 in FIG. 5), and 248 mm (corresponding to H2 in FIG. 5).

  On the other hand, in the gas detection device 1 of this example, a thickness of 1 mm, an outer shape of 30 mm × 40 mm, and a focal length of 40 mm can be used as the condensing lens 7, and the light receiving surface diameter of the light receiving unit 9 is φ1 mm. As a result, the external dimensions of the gas detector 1 of this example are 175 mm in width (corresponding to D1 in FIG. 1), 40 mm in depth (corresponding to W1 in FIG. 1), and 70 mm in height (corresponding to H1 in FIG. 1). ing.

  As is clear from the above numerical comparison, the gas detection device 1 of this example includes the condensing lens 7 including the light receiving surface diameter of the light receiving unit 9 as compared with the conventional device 51 shown in FIGS. , Thickness, outer shape, and focal length can be reduced. As a result, the overall external dimensions of the apparatus are reduced, and downsizing can be achieved.

It is a perspective view which shows the external appearance of the gas detection apparatus which concerns on this invention. It is a fragmentary sectional view of the housing | casing in the AA line of FIG. It is a top view of the heat radiator in which the emission part and light-receiving part in FIG. 2 were arrange | positioned. It is a block block diagram of the gas detection apparatus which concerns on this invention. It is a perspective view which shows the external appearance of the conventional gas detection apparatus by the structure equivalent to the gas concentration measuring apparatus disclosed by patent document 1. FIG. It is a fragmentary sectional view of the housing | casing in the BB line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas detection apparatus 2 Case 7 Condensing lens 8 Output part 8a Measurement light output part 8b Guide light output part 9 Light receiving part 10 Electrical conversion part 12 Control part

Claims (3)

An emission section (8) for emitting laser light for detecting gas in the measurement atmosphere as measurement light;
An aspheric Fresnel lens (7) made of a single acrylic resin that condenses the laser light reflected from the measurement atmosphere as the measurement light with the emission of the measurement light to the measurement atmosphere;
A gas detector (1) in which a light receiving part (9) for receiving the reflected measurement light collected by the aspheric Fresnel lens is disposed in a single casing (2),
The emitting portion and the light receiving portion are disposed in the same space within the single casing, and the emitting portion is condensed by the aspheric Fresnel lens in the same space. A small gas detection device, which is disposed outside an area and emits the measurement light from outside the aspheric Fresnel lens . 2. The small gas detection according to claim 1, wherein the emission unit (8) emits visible light for confirming an emission position of the measurement light from outside the light collection area together with the measurement light as guide light. apparatus. The small gas detector according to claim 1 or 2, wherein the single casing (2) has a rectangular parallelepiped shape.

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