Patent Publication Number: US-2018045642-A1

Title: Gas detection device and method for detecting gas concentration

Description:
BACKGROUND 
     1. Technical Field 
     The instant disclosure relates to a gas detection device and method for detecting gas concentration, in particular, to a gas detection device and method for detecting gas concentration capable of measuring concentrations of different gases. 
     2. Description of Related Art 
     The carbon dioxide detection devices or carbon dioxide analyzing instruments in the market generally employ non-dispersive infrared (NDIR) absorption to detect the concentration of the gas. NDIR mainly utilizes calculation based on the Beer-Lambert law. The principle of such analysis is to detect the concentration of a specific gas by utilizing the absorption property of the gas toward infrared light having specific wavelength and the fact that the gas concentration is proportional to the absorption quantity. For example, carbon monoxide has a strongest absorption of a wavelength of 4.7 micron (μm) and carbon dioxide has a strongest absorption of a wavelength of 4.3 micron (μm). 
     However, the accuracy of the gas concentration detecting devices are limited to the structure of the gas sampling chamber and can only detect a specific concentration of the gas. Regarding the gas detection process employing NDIR, the absorption intensity of gas toward infrared is in positive correlation with the length and concentration. However, the gas sampling chamber of the existing gas concentration detecting devices is fixed and hence, when the length of the gas sampling chamber is too long and the concentration of the gas to be detected is too high, the gas having high concentration would absorb excessive infrared energy produced by the light emitting unit, and the light sensor unit cannot receive signals and is unable to detect the concentration of the gas. When the length of the gas sampling chamber is too short and the concentration of the gas to be detected is too low, the gas would absorb too little infrared energy, and the infrared energy generated by the light emitting unit would project onto the light sensor unit and would almost not be absorbed by the gas due to the short length of the gas sampling chamber. Moreover, when the infrared energy received by the light sensor unit is too low, the accuracy is reduced due to the noise. 
     Furthermore, the gas concentration detecting devices on the market can only detect one gas, i.e., they cannot detect a plurality of gases at the same time. 
     Therefore, there is a need for a device for detecting a plurality of gases or for detecting gases that have concentration with large differences, thereby overcoming the above disadvantages. 
     SUMMARY 
     In view of the disadvantages of the existing art, the object of the instant disclosure is to provide a gas detection device and method for detecting gas concentration. The gas detection device and method for detecting gas concentration provided by the instant disclosure employ a single light emitting module to correspond to a plurality of light sensor units, thereby detecting a plurality of gases at the same time. The gas detection device and method for detecting gas concentration provided by the instant disclosure are also adapted to an environment having gases with different concentration having large differences. 
     An embodiment of the instant disclosure provides a gas detection device comprising a chamber module, a light emitting module, and optical sensing module and a light splitting module. The chamber module comprises a light guiding chamber, a first sampling chamber connected to the light guiding chamber and a second sampling chamber connected to the light guiding chamber. The light emitting module is disposed in the light guiding chamber, and the light emitting module is configured to generate a projection light beam. The optical sensing module comprises a first optical sensing unit disposed in the first sampling chamber, and a second optical sensing unit disposed in the second sampling chamber. The light splitting module is disposed in the chamber module. The projection light beam generated by the light emitting module is split by the light splitting module for forming a first split light beam projected onto the first optical sensing unit, and a second split light beam projected onto the second optical sensing unit. 
     Another embodiment of the instant disclosure provides a method for detecting gas concentration, comprising: providing a light emitting module, the light emitting module generates a first split light beam passing a first sampling chamber and projected onto a first optical sensing unit, the light emitting module generates a second split light beam passing a second sampling chamber and projected onto a second optical sensing unit, in which the size of the first sampling chamber is larger than the size of the second sampling chamber, the first sampling chamber has a first gas therein, and the second sampling chamber has a second gas therein; calculating a first tangent slope of a first curve equation based on a first split light beam energy received by the first optical sensing unit, and calculating a second tangent slope of a second curve equation based on a second split light beam energy received by the second optical sensing unit; and judging whether the absolute value of the first tangent slope is larger than the absolute value of the second tangent slope. When the absolute value of the first tangent slope is larger than or equal to the absolute value of the second tangent slope, outputting a concentration of the first gas. When absolute value of the first tangent slope is less than the absolute value of the second tangent slope, outputting a concentration of the second gas. 
     Yet another embodiment of the instant disclosure provides a method for detecting gas concentration, comprising: providing a light emitting module, the light emitting module generates a first split light beam passing a first sampling chamber and projected onto a first optical sensing unit, the light emitting module generates a second split light beam passing a second sampling chamber and projected onto a second optical sensing unit, wherein the size of the first sampling chamber is larger than the size of the second sampling chamber; calculating a concentration of a first gas in the first sampling chamber according to a first split light beam energy received by the first optical sensing unit, and calculating a concentration of a second gas in the second sampling chamber according to a second split light beam energy received by the first optical sensing unit; and judging whether the concentration of the first gas and the concentration of the second gas are larger than a predetermined threshold. When the concentration of the first gas and the concentration of the second gas are larger than a predetermined threshold, outputting the concentration of the second gas. When the concentration of the first gas and the concentration of the second gas are less than or equal to a predetermined threshold, outputting the concentration of the first gas. 
     The advantages of the instant disclosure reside in that by employing the light splitting module, the projection light beam generated by the light emitting module is split and forms a first split light beam projected onto the first optical sensing unit and a second split light beam projected onto the second optical sensing unit. The first optical sensing unit detects the property of a first gas and the second optical sensing unit detects the property of a second gas. In addition, the combination of the first optical sensing unit and the second optical sensing unit, and the first split light beam and the second split light beam generated by the projection light beam, the device and method of the instant disclosure can be adapted to environments in which the concentrations of different gases have large differences. In other words, the projection light beam generated by the light emitting module forms at least two split light beams for corresponding to at least two optical sensing units. 
     In order to further understand the techniques, means and effects of the instant disclosure, the following detailed descriptions and appended drawings are hereby referred to, such that, and through which, the purposes, features and aspects of the instant disclosure can be thoroughly and concretely appreciated; however, the appended drawings are merely provided for reference and illustration, without any intention to be used for limiting the instant disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the instant disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the instant disclosure and, together with the description, serve to explain the principles of the instant disclosure. 
         FIG. 1  is one of the three-dimensional assembled views of the gas detection device of the first embodiment of the instant disclosure. 
         FIG. 2  is one of the three-dimensional exploded views of the gas detection device of the first embodiment of the instant disclosure. 
         FIG. 3  is a module block diagram of the gas detection device of the first embodiment of the instant disclosure. 
         FIG. 4  is a sectional schematic view taken along line IV-IV of  FIG. 1 . 
         FIG. 5  is one of the light beam projection schematic views of the gas detection device of the first embodiment of the instant disclosure. 
         FIG. 6  is another light beam projection schematic view of the gas detection device of the first embodiment of the instant disclosure. 
         FIG. 7  is sectional schematic view taken from line VII-VII in  FIG. 1 . 
         FIG. 8  is a sectional schematic view of another implementation of the gas detection device of the first embodiment of the instant disclosure. 
         FIG. 9  is a three-dimensional assembled schematic view of the gas detection device of the second embodiment of the instant disclosure. 
         FIG. 10  is the sectional schematic view taken along line X-X of  FIG. 9 . 
         FIG. 11  is one of the flow charts of the method for detecting gas concentration of the third embodiment of the instant disclosure. 
         FIG. 12  is one of the curve equation of the third embodiment of the instant disclosure. 
         FIG. 13  is another curve equation of the third embodiment of the instant disclosure. 
         FIG. 14  is another flow chart of the method for detecting gas concentration of the third embodiment of the instant disclosure. 
         FIG. 15  is a flow chart of the method for detecting gas concentration of the fourth embodiment of the instant disclosure. 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Reference will now be made in detail to the exemplary embodiments of the instant disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     First Embodiment 
     Please refer to  FIG. 1  to  FIG. 4 . The first embodiment of the instant disclosure provides a gas detection device Q for detecting a concentration of a gas. The gas detection device Q comprises a chamber module  1 , a light emitting module  2 , an optical sensing module  3 , a light splitting module  4 , and a substrate module  5 . The light emitting module  2  and the optical sensing module  3  are electrically connected on the substrate module  5 . In addition, in  FIG. 3 , the substrate module  5  comprises a display unit  52  for displaying the concentration value of the gas and an operation unit  51  for calculating the concentration of the gas. The operation unit  51  is electrically connected to the display unit  52 , the light emitting module  2  and the optical sensing module  3 . In addition, for example, the light emitting module  2  can be an infrared light emitter for generating infrared light, the optical sensing module  3  is an infrared sensor such as a single-channel (single-beam) infrared sensor, or a double-channel infrared sensor (one of the infrared collecting windows is for detecting the gas concentration and another is for detecting the aging of the infrared light source, and both of which can calibrate each other). However, the instant disclosure is not limited thereto. 
     The gas detection device Q of the embodiments of the instant disclosure can detect the concentration or other properties of the gas to be measured. The gas to be measured can be carbon dioxide, carbon monoxide or the combination thereof. The instant disclosure is not limited thereto. In other words, by using a different light emitting module  2  and optical sensing module  3 , it would be able to detect different types of gases. For example, the detection of the concentrations of different gases can be achieved by changing the wavelength filter on the optical sensing module  3 . 
     Next, please refer to  FIG. 2  to  FIG. 4 . The chamber module  1  comprises a light guiding chamber  11 , a first sampling chamber  12  connected to the light guiding chamber  11  and a second sampling chamber  13  connected to the light guiding chamber  11 . The light guiding chamber  11  is disposed between the first sampling chamber  12  and the second sampling chamber  13 . However, the instant disclosure is not limited thereto. In order to detect an environment in which the same gas has different concentrations with large differences, the size of the first sampling chamber  12  and the size of the second sampling chamber  13  are different. In the embodiments of the instant disclosure, the size of the first sampling chamber  12  is larger than the size of the second sampling chamber  13 , i.e., the length of the first sampling chamber  12  is larger than the length of the second sampling chamber  13 . However, the instant disclosure is not limited thereto. In other embodiments, the relationship between the sizes of the first sampling chamber  12  and the second sampling chamber  13  is not limited, as long as the first optical sensing unit  31  and the second optical sensing unit  32  can be used to detect a first gas and a second gas different from the first gas. In other words, the first optical sensing unit  31  is adapted to detect the properties of a first gas, and the second optical sensing unit  32  is adapted to detect the properties of a second gas different from the first gas. Therefore, an environment in which a same gas has very large different concentrations can be measured, or the properties of different gases can be detected, by employing a single light emitting module  2  corresponding to at least two optical sensing units. 
     For example, in the embodiments of the instant disclosure, the length direction of the first sampling chamber  12  (X direction) and the length direction of the light guiding chamber  11  (Y direction) are substantially perpendicular to each other. However, the instant disclosure is not limited thereto. In other words, in other embodiments, the length direction of the first sampling chamber  12  and the length direction of the second sampling chamber  13  can locate along the Z direction (for example, the length direction of the third sampling chamber  14  and the fourth sampling chamber  15  are both located along the Z direction as shown in the second embodiment). Moreover, in other embodiments, the length direction of the first sampling chamber  12  and the length direction of the second sampling chamber  13  are substantially parallel to the length direction of the light guiding chamber  11  (not shown), i.e., the length direction of the light guiding chamber  11 , the length direction of the first sampling chamber  12  and the length direction of the second sampling chamber  13  are arranged along the Y direction. 
     Next, as shown in  FIG. 4 , the light guiding chamber  11  has a light guiding space  111  and a reflective surface  112 , the first sampling chamber  12  has a first sampling space  121  and a first receiving space  122 , the second sampling chamber  13  has a second sampling space  131  and a second receiving space  132 . The light guiding space  111 , the first sampling space  121  and the second sampling space  131  are interconnected with each other. In addition, the light emitting module  2  is disposed in the light guiding chamber  11 , the light emitting module  2  comprises a light emitting unit  21  and a connecting wire  22  electrically connected to the substrate module  5  (the connection between the connecting wire  22  and the substrate module  5  is not shown in the figure) for providing electrical energy to enable the light emitting unit  21  to generate a projection light beam T (please refer to  FIG. 5  and  FIG. 6 ) such as infrared light. In addition, the optical sensing module  3  comprises a first optical sensing unit  31  and a second optical sensing unit  32 , the first optical sensing unit  31  is disposed in the first receiving space  122  and the second optical sensing unit  32  is disposed in the second receiving space  132  for receiving the projection light beam T generated by the light emitting unit  21 . The connecting wire  35  of the optical sensing module  3  (the connecting wire  35  of the first optical sensing unit  31  and the connecting wire  35  of the second optical sensing unit  32 ) can be electrically connected with the substrate module  5  (the connection between the connecting wire  35  and the substrate module  5  is not shown in the figure). The instant disclosure does not limit how the light guiding space  111 , the first sampling space  121  and the second sampling space  131  are intercommunicated with each other. 
     The first sampling space  121  of the first sampling chamber  12  and the second sampling space  131  of the second sampling chamber  13  are rectangular. However, the instant disclosure is not limited thereto. Each inner surface of the first sampling chamber  12  and the second sampling chamber  13  has a reflective layer (not shown) formed by metal plating or plastic plating. The reflective layer can be formed of gold-containing metal materials, nickel or the combination thereof. Therefore, the projection light beam T generated by the light emitting module  2  is repeatedly reflected in the first sampling space  121  and the second sampling space  131 , thereby integrating the intensity of the projection light beam T generated by the light emitting module  2  and increasing the uniformity of the integrated light. The reflective surface of the light guiding chamber  11  can have a reflective layer for increasing the reflectance and increasing the amount of light projected onto the light splitting module  4 . 
     Please refer to  FIG. 4  to  FIG. 6 . The light splitting module  4  is disposed between the first sampling chamber  12  and the second sampling chamber  13 , and the projection light beam T generated by the light emitting module  2  is split by the light splitting module  4  to form a first split light beam T 1  projected onto the first optical sensing unit  31  and a second split light beam T 2  projected onto the second optical sensing unit  32 . For example, the light splitting module  4  comprises a first light splitting surface  41  and a second light splitting surface  42 . Therefore, the projection light beam T generated by the light emitting unit  21  forms the first split light beam T 1  projected onto the first optical sensing unit  31  and the second split light beam T 2  projected onto the second optical sensing unit  32  by the first light splitting surface  41  and the second light splitting surface  42  respectively. The light splitting module  4  is not limited to the prism shown in the figures. In other embodiments, the light splitting module  4  utilizes a plurality of light splitters to form the first split light beam T 1  and the second split light beam T 2  from the projection light beam T generated by the light emitting unit  21 . 
     As shown in  FIG. 5 , preferably, the reflective surface  112  of the light guiding chamber  11  is a paraboloid having a focus point F, and the light emitting unit  21  is disposed corresponding to the focus point F, i.e., the light emitting unit  21  is disposed on the focus point F and overlaps the focus point F. Therefore, a first projection light beam T 11  and a second projection light beam T 21  projected onto the light guiding chamber  11  can be uniformly reflected by the paraboloid and projected onto the light splitting module  4 . In addition, in order to increase the reflectance of the paraboloid, a reflective layer described above can be disposed thereon. 
     Specifically, the projection light beam T comprises the first projection light beam T 11  and the second projection light beam T 21  projected onto the light guiding chamber  11 , the first projection light beam T 11  is reflected by the paraboloid of the light guiding chamber  11  and forms a first reflection light beam T 12  projected onto the first light splitting surface  41  of the light splitting module  4 , the first reflection light beam T 12  is reflected by the first light splitting surface  41  and forms a first split light beam T 1  projected onto the first optical sensing unit  31 . The second projection light beam T 21  is reflected by the light guiding chamber  11  and forms a second reflection light beam T 22  projected onto the second light splitting surface  42  of the light splitting module  4 , and the second reflection light beam T 22  is reflected by the second light splitting surface  42  and forms a second split light beam T 2  projected onto the second optical sensing unit  32 . 
     In addition, as shown in  FIG. 6 , the projection light beam T generated by the light emitting unit  21  further comprises a first incident light beam T 13  directly projected onto the first light splitting surface  41  of the light splitting module  4 , and a second incident light beam T 23  directly projected onto the second light splitting surface  42  of the light splitting module  4 . The first incident light beam T 13  is reflected by the first light splitting surface  41  and forms a first split light beam T 1  projected onto the first optical sensing unit  31 , and the second incident light beam T 23  is reflected by the second light splitting surface  42  and forms a second split light beam T 2  projected onto the second optical sensing unit  32 . 
     In other words, the projection light beam T generated by the light emitting unit  21  comprises the first split light beam T 1  projected onto the first optical sensing unit  31  and the second split light beam T 2  projected onto the second optical sensing unit  32 . The first split light beam T 1  projected onto the first optical sensing unit  31  can be formed of the first projection light beam T 11 , the first reflection light beam T 12  and the first incident light beam T 13 . The second split light beam T 2  projected onto the second optical sensing unit  32  can be formed of the second projection light beam T 21 , the second reflection light beam T 22  and the second incident light beam T 23 . When the light guiding chamber  11  is without the reflective surface  112 , the first split light beam T 1  projected onto the first optical sensing unit  31  can be directly formed by the first incident light beam T 13 , and the second split light beam T 2  projected onto the second optical sensing unit  32  can be directly formed by the second incident light beam T 23 . 
     In addition, the first sampling chamber  12  further comprises a first gas diffusion tank  123  disposed thereon, and the second sampling chamber  13  further comprises a second gas diffusion tank  133  disposed thereon. The first gas diffusion tank  123  and the second gas diffusion tank  133  can be rectangular. The cross-section of the first gas diffusion tank  123  and the second gas diffusion tank  133  can be in a V-shape as shown in  FIG. 5  to  FIG. 7  and hence, the gas to be measured is subjected to Bernoulli&#39;s principle. Therefore, when the gas flows through the first gas diffusion tank  123  and the second gas diffusion tank  133  having a V-shape cross-section, the flow speed would increase since the diameter of the flow path changes, thereby increasing the diffusion of the gas and reducing the detecting time. A gas filtering membrane (not shown) can be further disposed on the first gas diffusion tank  123  and the second gas diffusion tank  133  to avoid the suspended particles in the gas to be measured from entering the first sampling space  121  and the second sampling space  131 , causing internal pollution and affecting the detection accuracy. 
     In the embodiments of the instant disclosure, in order to detect environments in which the gases to be measured have concentrations with large differences, the first sampling chamber  12  has a first predetermined length L 1 , the second sampling chamber  13  has a second predetermined length L 2 , and the first predetermined length L 1  of the first sampling chamber  12  is larger than the second predetermined length L 2  of the second sampling chamber  13  Therefore, the first sampling chamber  12  is more suitable for detecting gases with low concentration, and the second sampling chamber  13  is more suitable for detecting gases with high concentration. In addition, since the first split light beam T 1  and the second split light beam T 2  received by the first optical sensing unit  31  and the second optical sensing unit  32  respectively are generated by the same light emitting unit  21 , the detecting error is reduced. 
     Next, please refer to  FIG. 5 ,  FIG. 6  and  FIG. 8 . By comparing  FIG. 8  to  FIG. 5 , one can realize that in other embodiments, the location of the light splitting module  4  can be adjusted to adjust the light energy received by the first optical sensing unit  31  and the second optical sensing unit  32 . Specifically, as shown in  FIG. 5  and  FIG. 6 , the light guiding chamber  11  comprises a reflective surface  112  and a light axis P passing through a focus point F of the second light splitting surface  42 , the light splitting module  4  has a center axis I between the first light splitting surface  41  and the second light splitting surface  42 , and the center axis I passes through the light guiding space  111  and the light axis P overlaps with the center axis I. Alternatively, as shown in  FIG. 8 , the light axis P of the light guiding chamber  11  and the center axis I do not overlap with each other. In addition, in the present embodiment, since the projection light beam T and the first split light beam T 1  are perpendicular to each other and the projection light beam T and the second split light beam T 2  are perpendicular to each other, the first light splitting surface  41  and the center axis I has an included angle of 45 degrees, and the second light splitting surface  42  and the center axis I has an included angle of 45 degrees. However, the instant disclosure is not limited thereto. 
     Second Embodiment 
     Please refer to  FIG. 9  and  FIG. 10 . The second embodiment of the instant disclosure provides a gas detection device Q′. As shown in  FIG. 9 , the difference between the second embodiment and the first embodiment is that the chamber module  1 ′ provided by the second embodiment further comprises a third sampling chamber  14  connected to the light guiding chamber  11  and a fourth sampling chamber  15  connected to the light guiding chamber  11 . The third sampling chamber  14  has a third sampling space  141  and a third receiving space  142 , the fourth sampling chamber  15  has a fourth sampling space  151  and a fourth receiving space  152 . The light guiding space  111 , the third sampling space  141  and the fourth sampling space  151  are intercommunicated with each other. In other words, the third sampling space  141  and the fourth sampling space  151  are interconnected with the first sampling space  121  and the second sampling space  131 . However, as long as the projection light beam T forms a plurality of split light beams (such as the first split light beam T 1  and the first split light beam T 1 ) projected onto a plurality of optical sensing units (such as the first optical sensing unit  31  and the second optical sensing unit  32 ), the sampling spaces are not limited to the structure described above. In other words, the sampling spaces can be interconnected with each other or do not interconnect with each other. In addition, the third sampling chamber  14  and the fourth sampling chamber  15  can further comprise a third gas diffusion tank  143  and a fourth gas diffusion tank  153  disposed thereon to facilitate the diffusion of the gas and reducing the detection time. 
     The light splitting module  4  further comprises a third light splitting surface  43  and a fourth light splitting surface  44 , the optical sensing module  3  further comprises a third optical sensing unit  33  and a fourth sensing unit  34 , the third optical sensing unit  33  is disposed in the third receiving space  142 , the fourth sensing unit  34  is disposed in the fourth receiving space  152 . Therefore, the projection light beam is split by the light splitting module  4  and forms a third split light beam projected onto the third optical sensing unit (not shown), and a fourth split light beam projected onto the fourth optical sensing unit. 
     The projection light beam comprises a third projection light beam and a fourth projection light beam (not shown) projected onto the light guiding chamber  11 , the third projection light beam is reflected by the paraboloid of the light guiding chamber  11  and forms a third reflecting light beam (not shown) projected onto the third light splitting surface  43  of the light splitting module  4 , the third reflecting light beam is reflected by the first light splitting surface  41  and forms a third split light beam projected onto the third optical sensing unit  33 . In addition, the fourth projection light beam is reflected by the light guiding chamber  11  and forms a fourth reflecting light beam (not shown) projected onto the fourth light splitting surface  44  of the light splitting module  4 , and the fourth reflecting light beam is reflected by the fourth light splitting surface  44  and forms a fourth split light beam projected onto the fourth sensing unit  34 . 
     In addition, the projection light beam T further comprises a third incident light beam (not shown) directly projected onto the third light splitting surface  43  of the light splitting module  4 , and a fourth incident light beam (not shown) directly projected onto the fourth light splitting surface  44  of the light splitting module  4 . The third incident light beam is reflected by the third light splitting surface  43  and forms a third split light beam projected onto the third optical sensing unit  33 , the fourth incident light beam is reflected by the fourth light splitting surface  44  and forms a fourth split light beam projected onto the fourth sensing unit  34 . 
     The other structure features (such as the light guiding chamber  11 , the first sampling chamber  12 , the second sampling chamber  13 , the light emitting module  2 , the light splitting module  4  and the projection light beam T) of the second embodiment of the instant disclosure are similar to that of the previous embodiment and hence, are not described again herein. Therefore, by the addition of the third sampling chamber  14  and the fourth sampling chamber  15 , the detecting range of the concentration of the gases can be increased, or the property of different gases can be detected (such as the concentrations of different gases). 
     Third Embodiment 
     Please refer to  FIG. 5 ,  FIG. 6  and  FIG. 11 . The third embodiment of the instant disclosure provides a method for detecting gas concentration comprising the following steps. As shown in step S 102 : providing a first split light beam T 1  passing the first sampling chamber  12  and projected onto the first optical sensing unit  31 , and providing a second split light beam T 2  passing the second sampling chamber  13  and projected onto the second optical sensing unit  32 . Specifically, a projection light beam T can be generated by a light emitting module  2 , and the projection light beam T passes through a light splitting module  4  and generates a first split light beam T 1  and a second split light beam T 2 . In order to detect an environment in which the concentrations of the gases have large differences, the size of the first sampling chamber  12  is larger than the size of the second sampling chamber  13 . For example, in the third embodiment, the first predetermined length L 1  of the first sampling chamber  12  is four times of the second predetermined length L 2  of the second sampling chamber  13 , i.e., L 1 =4L 2 , in which L 1  is the first predetermined length L 1 , L 2  is the second predetermined length L 2 . In addition, in the third embodiment, the projection light beam T is an infrared beam, the first sampling chamber  12  has a first gas therein and the second sampling chamber  13  has a second gas therein. The first gas and the second gas in the third embodiment are the same type of gas (such as carbon dioxide, CO 2 ). However, the instant disclosure is not limited thereto. 
     Next, as shown in step S 104 : calculating a first tangent slope of a first split light beam energy received by the first optical sensing unit  31  relative to a first curve equation, and calculating a second tangent slope of a second split light beam energy received by the second optical sensing unit  32  relative to a second curve equation. Generally, in order to measure the concentration of the first gas and the second gas, the calculation can be carried out by the operation unit  51  in the substrate module  5  using the Beer-Lambert Law. Assuming I 0  is the energy of the infrared incident light (the initial energy of the infrared before being absorbed by the gas); I t  is the energy of the infrared received by the infrared light sensing unit (the energy received by the infrared light sensing unit after the infrared light being absorbed by the gas); K is the absorption coefficient; L is the length of the light path of the gas for absorbing light; C is the concentration of the gas. Based on the Beer-Lambert Law, the following equation is obtained: 
         I   t   =I   0 ×exp×(−( L×K×C ))
 
     Next, please refer to  FIG. 12  and  FIG. 13 . According to the Beer-Lambert Law, f 1 (x) is defined as a first split light beam energy received by the first optical sensing unit  31  in the first sampling chamber  12 , f 2 (x) is defined as a second split light beam energy received by the second optical sensing unit  32  in the second sampling chamber  13 . x is the concentration of the first gas or the second gas. In the present embodiment, the first predetermined length L 1  of the first sampling chamber  12  is four times the second predetermined length L 2  of the second sampling chamber  13  and hence, the concentration of the first gas in the first sampling chamber  12  and the concentration of the second gas in the second sampling chamber  13  can be calculated based on the following equation: 
         f   1 ( x )= I   0 ×exp×(−(4 L×k×x ))  (first curve equation)
 
         f   2 ( x )= I   0 ×exp×(−(1 L×k×x ))  (second curve equation)
 
     Specifically, the first curve equation and the second curve equation both satisfy the Beer-Lambert Law, and the operation unit  51  can calculate the concentration of a first gas in the first sampling chamber  12  based on a first split light beam energy received by the first optical sensing unit  31  and the first curve equation, and calculate the concentration of a second gas in the second sampling chamber  13  based on a second split light beam energy received by the second optical sensing unit  32  and the second curve equation. By obtaining the slope of the first curve equation and the second curve equation, one is able to judge whether the first optical sensing unit  31  or the second optical sensing unit  32  is able to obtain a larger infrared energy change in the same concentration interval. 
     As shown in  FIG. 12 , concentration intervals are used for description. The x 1 , x 2 , x 3  and x 4  in  FIG. 12  represent different concentration values respectively. For example, the concentration value x 1  is 15,000 ppm (parts per million), the concentration value of x 2  is 20,000 ppm, the concentration value x 3  is 30,000 ppm, and the concentration value x 4  is 40,000 ppm. When the concentration of the first gas detected by the first optical sensing unit  31  and the concentration of the second gas detected by the second optical sensing unit  32  calculated by the operation unit  51  is between the concentration values x 1  and x 2 , one is able to judge whether the first optical sensing unit  31  or the second optical sensing unit  32  can obtain a detecting value with more accuracy based on the calculation of a first tangent slope of the first curve equation between the concentration values x 1  and x 2 , and a second tangent slope of the second curve equation between the concentration values x 1  and x 2 . 
     Specifically, when the concentrations of the first gas and the second gas are between the concentration values x 1  and x 2 , compared to the second curve equation, the first curve equation has more infrared energy change value for analyzing the concentration of the first gas having a concentration between the concentration values x 1  and x 2 . In other words, the concentration value is more accurate when the infrared energy change is larger. Therefore, the first sampling chamber  12  is more suitable for the detection in the range of concentration value x 1  to concentration value x 2 . 
     Alternatively, when the concentration of the first gas detected by the first optical sensing unit  31  and the concentration of the second gas detected by the second optical sensing unit  32  are between the concentration values x 3  and x 4 , one is able to judge whether the first optical sensing unit  31  or the second optical sensing unit  32  can obtain a detecting value with higher accuracy based on the calculation of a first tangent slope of the first curve equation between the concentration values x 3  and x 4 , and a second tangent slope of the second curve equation between the concentration values x 3  and x 4 . Specifically, as shown in  FIG. 12 , when the concentration of the first gas and the concentration of the second gas are between the concentration values x 3  and x 4 , compared to the first curve equation, the second curve equation has more infrared energy change value for analyzing the concentration of the first gas having a concentration between the concentration values x 3  and x 4 . In other words, the concentration value is more accurate when the infrared energy change is larger. Therefore, the second sampling chamber  13  is more suitable for the detection in the range of concentration value x 3  to concentration value x 4 . 
     As shown in  FIG. 13 , under a specific concentration value (x 5 ), the first tangent slope of the first curve equation is equal to the second tangent slope of the second curve equation. In other words, the concentration value (x 5 ) would be the judging factor for determining the use of the first sampling chamber  12  or the second sampling chamber  13 . Therefore, the concentration value (x 5 ) is a predetermined threshold. Under the concentration value x 5 , the first tangent slope is equal to the second tangent slope. The predetermined threshold x 5  will be described in the following fourth embodiment. In addition, the first tangent slope of the first curve equation and the second tangent slope of the second tangent slope can be calculated by differentiation: 
     
       
         
           
             
               
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     Please refer to  FIG. 11 . As shown in step S 106 : judging whether the absolute value of the first tangent slope is larger than the absolute value of the second tangent slope. Specifically, by judging the first tangent slope of the first curve equation and the second tangent slope of the second curve equation, one is able to judge which of the sampling chambers (the first sampling chamber  12  or the second sampling chamber  13 ) is suitable for detecting the concentration of the gas to be detected. 
     Next, as shown in step S 108 : outputting a concentration of the first gas. Specifically, when the absolute value of the first tangent slope is larger than the absolute value of the second tangent slope, the concentration of the first gas is smaller than the predetermined threshold x 5 , and the operation unit  51  can output the concentration of the first gas onto the display unit  52  for displaying the current concentration of the first gas. In other words, the current gas to be detected is suitable for being detected by the first sampling chamber  12 . When the absolute value of the first tangent slope is equal to the absolute value of the second tangent slope, the concentration of the first gas can be output as well. 
     Next, as shown in step S 110 : outputting a concentration of the second gas. Specifically, when the absolute value of the first tangent slope is smaller than the absolute value of the second tangent slope, the concentration of the second gas is output. In other words, when the absolute value of the first tangent slope is smaller than the absolute value of the second tangent slope, the concentration of the second gas is larger than the predetermined threshold x 5 , and the operation unit  51  can output the concentration of the second gas onto the display unit  52  for displaying the current concentration of the second gas. In other words, the second sampling chamber  13  is suitable for detecting the current gas. 
     Next, please refer to  FIG. 14 . In another implementation, the method for detecting a gas concentration provided by the third embodiment of the instant disclosure further comprises step S 105 : calculating the concentration of the first gas in the first sampling chamber according to the first split light beam energy received by the first optical sensing unit and the first curve equation, and calculating the concentration of the second gas in the second sampling chamber. For example, the concentration of the first gas in the first sampling chamber  12  can be calculated according to the first split light beam energy received by the first optical sensing unit  31  and the first curve equation. Meanwhile, the concentration of the second gas in the second sampling chamber  13  can be calculated according to the second split light beam energy received by the second optical sensing unit  32  and the second curve equation. Therefore, the concentration of the first gas in the first sampling chamber  12  and the concentration of the second gas in the second sampling chamber  13  are optionally output onto the display unit  52 . 
     Although step S 105  is shown after step S 104  in  FIG. 14 , the performing order of step S 105  and step S 104  is not limited in the instant disclosure. In other words, step S 105  can be performed before the step of calculating the first tangent slope and the second tangent slope, during the step of calculating the first tangent slope and the second tangent slope or after the step of calculating the first tangent slope and the second tangent slope. In other words, step S 105  and S 104  can be performed independently. In addition, the first sampling chamber  12 , the second sampling chamber  13 , the light emitting module  2 , the optical sensing module  3  and the substrate module  5  provided in the third embodiment are similar to that of the previous embodiments and are not described herein. 
     Fourth Embodiment 
     Please refer to  FIG. 15 . The fourth embodiment of the instant disclosure provides a method for detecting a gas concentration. As shown in  FIG. 15 , the main difference between the fourth embodiment and the third embodiment resides in that the method for detecting a gas concentration provided by the fourth embodiment involves directly judging whether the concentration of the first gas and the concentration of the second gas is larger than a predetermined threshold for determining which of the concentration of the first gas or the concentration of the second gas to be output. 
     Please refer to  FIG. 13  and  FIG. 15 . The method for detecting the gas concentration provided by the fourth embodiment comprises the following steps. As shown in step S 202 , providing a first split light beam T 1  passing a first sampling chamber  12  and projected onto a first optical sensing unit  31 , and providing a second split light beam T 2  passing the second sampling chamber  13  and projected onto the second optical sensing unit  32 . Step S 202  is similar to step S 102  mentioned before and is not described in detail herein. 
     Next, as shown in step S 204 , calculating the concentration of a first gas in the first sampling chamber  12  and calculating the concentration of a second gas in the second sampling chamber  13 . Specifically, the concentration of a first gas in the first sampling chamber  12  is calculated based on a first split light beam received by the first optical sensing unit  31 , and the concentration of a second gas in the second sampling chamber  13  is calculated based on a second split light beam received by the second optical sensing unit  32 . To be specific, as mentioned in the third embodiment, the concentration of the first gas is calculated based on the first split light beam energy and a first curve equation, and the concentration of the second gas is calculated based on the second split light beam energy and a second curve equation, and the first curve equation and the second curve equation satisfy the Beer-Lambert Law. 
     As shown in step S 206 , judging whether the concentration of the first gas and the concentration of the second gas are larger than a predetermined threshold x 5 . Specifically, the predetermined threshold x 5  can be set according to the first tangent slope and the second tangent slope mentioned in the third embodiment. In other words, the predetermined threshold x 5  satisfies the condition that the concentration of the first gas is equal to or close to (having an error that can be ignored) the concentration of the second gas, and that the first tangent slope of the concentration of the first gas relative to the first curve equation is equal or close to the second tangent slope of the concentration of the second gas relative to the second curve equation. For example, as shown in  FIG. 13 , at 23,000 ppm, the first tangent slope is equal to or close to the second tangent slope. Therefore, the predetermined threshold can be 23,000 ppm. However, the instant disclosure is not limited thereto. In other implementation, the first predetermined length L 1  can be 3 centimeters (cm) to 6 centimeters for detecting carbon dioxide having a concentration value of 0˜50,000 ppm, and the second predetermined length L 2  can be 2 centimeters to 3 centimeters for detecting carbon dioxide having a concentration value of more than 50,000 ppm. In other words, by adjusting the first predetermined length L 1  of the first sampling chamber  12  and the second predetermined length L 2  of the second sampling chamber  13 , the predetermined threshold x 5  can be changed. Therefore, one is able to detect environments with large gas concentration differences. 
     Next, as shown in step S 208 : outputting the concentration of the second gas. Specifically, when the concentration of the first gas and the concentration of the second gas are larger than the predetermined value x 5 , the concentration of the second gas is output. In other words, the absolute value of the first tangent slope is smaller than the absolute value of the second tangent slope, and the second sampling chamber  13  is suitable for detecting the current gas concentration. Therefore, operation unit  51  outputs the concentration of the second gas on the display unit  52  for displaying the concentration of the second gas. 
     Next, as shown in step S 210 : outputting the concentration of the first gas. Specifically, when the concentration of the first gas and the concentration of the second gas are smaller than or equal to the predetermined value x 5 , the concentration of the first gas is output. In other words, the absolute value of the first tangent slope is larger than the absolute value of the second tangent slope, and the first sampling chamber  12  is suitable for detecting the current gas concentration. Therefore, operation unit  51  outputs the concentration of the first gas on the display unit  52  for displaying the concentration of the first gas. 
     Effectiveness of the Embodiments 
     In sum, the advantage of the instant disclosure is that by using the light splitting module  4 , the gas detecting devices (Q, Q′) and the methods for detecting gas concentration provided by the embodiments, the instant disclosure is able to split the projection light beam T generated by the light emitting module  2  through the light splitting module  4  for forming a first split light beam T 1  projected onto the first optical sensing unit  31  and a second split light beam T 2  projected onto the second optical sensing unit  32 . Therefore, the first optical sensing unit  31  can be used to detect the property of the first gas and the second optical sensing unit  32  can be used to detect the property of the second gas. In addition, based on the combination of the first optical sensing unit  31  and the second optical sensing unit  32 , and the first split light beam T 1  and second split light beam T 2  generated by the projection light beam T, the gas detecting devices (Q, Q′) and the methods for detecting gas concentration provided by the embodiments of the instant disclosure are suitable for detecting environments having gases with large concentration differences. 
     Therefore, the projection light beam T generated by the light emitting module  2  forms at least two split light beams (the first split light beam T 1 , and the second split light beam T 2 ) corresponding to at least two optical sensing units (the first optical sensing unit  31  and the second optical sensing unit  32 ). By using a plurality of split light beams (the first split light beam T 1  and the second split light beam T 2 ) formed by the same light emitting module  2 , the accuracy of the concentration detection is increased and the cost is reduced. In addition, by setting the size of the first sampling chamber  12  larger than the size of the second sampling chamber  13 , when the gas concentration is low, the first sampling chamber  12  with longer length can be used; when the gas concentration is high, the second sampling chamber  13  with shorter length can be used; and when the concentration is equal to or close to the predetermined threshold x 5 , the first sampling chamber  12  with longer length can be used (since the infrared energy received by the sensing unit is larger). 
     The above-mentioned descriptions represent merely the exemplary embodiment of the instant disclosure, without any intention to limit the scope of the instant disclosure thereto. Various equivalent changes, alterations or modifications based on the claims of the instant disclosure are all consequently viewed as being embraced by the scope of the instant disclosure.