Optical gas sensor device, control method, and program

Abstract

The present invention prevents an inaccurate determination using gas concentration in the event of a rapid change in temperature.　In this optical gas sensor device, a conversion unit converts an analogue detection signal, outputted from a light reception unit, into a digital detection signal. When the digital detection signal is not an upper limit value (65535) or a lower limit value (0) for the output of the conversion unit, and the temperature change rate of the detected temperature is less than a predetermined first threshold value, the control unit performs a determination based on the gas concentration of a gas to be detected, as calculated from the digital detection signal. When the digital detection signal is the upper limit value or the lower limit value for the output of the conversion unit, or when the temperature change rate is greater than or equal to the predetermined first threshold value, the control unit does not perform a determination based on the gas concentration of the gas to be detected.

Description

Optical gas sensor device, control method, and program

[0001] This invention relates to an optical gas sensor device, a control method, and a program.

[0002] Traditionally, continuous monitoring of gas concentrations has been conducted in homes, factories, and businesses from the perspective of managing chemical substances and ensuring worker safety. ２ Non-dispersive infrared absorption (NDIR) gas sensors are known for detecting the concentration of gases such as [list of gases]. NDIR gas sensors utilize the property that many gases absorb specific infrared wavelengths. When infrared light is emitted to the target gas, the sensor detects which wavelengths are absorbed and to what extent, thereby measuring the concentration of the target gas. For example, a gas sensor equipped with an infrared light source and a light receiver detects the concentration of the target gas in the optical path of the light source and light receiver.

[0003] Furthermore, a gas sensor module is known that includes a gas sensor equipped with a volume-changing element whose volume changes according to the amount of the object being measured to detect gas (see Patent Document 1). This gas sensor module amplifies the analog signal corresponding to the amount of gas measured and performs an A / D (Analog to Digital) conversion.

[0004] Japanese Patent Publication No. 2023-130161

[0005] Similar to the conventional gas sensor module described above, we consider a configuration in an NDIR gas sensor device in which the analog detection signal output from the light receiving unit is converted to AD by an AD converter. In this gas sensor device configuration, the analog detection signal output from the light receiving unit and amplified is within the operating temperature range and within the range in which the AD converter can perform AD conversion normally.

[0006] However, in the event of a rapid change in ambient temperature, the light-receiving unit may output an analog detection signal of an extremely large or small value. In this case, the output value of the amplified analog detection signal (analog detection value) exceeds the input range that the AD converter can handle. As a result, the output value of the digital detection signal from the AD converter (digital detection value) becomes the lower or upper limit of the AD converter's output. When the digital detection value is at the upper or lower limit, the gas concentration calculated from that digital detection value also becomes inaccurate, and judgments such as alarms using that gas concentration also become inaccurate. Furthermore, if the amplification factor of the amplifier is determined by considering the rapid temperature change in relation to the upper and lower limits of the AD converter, the amplification factor becomes small, and sufficient resolution of the AD converter cannot be obtained, leading to a deterioration in the accuracy of the detection value.

[0007] The object of this invention is to prevent inaccurate determinations using gas concentration during rapid temperature changes.

[0008] To solve the above problems, the optical gas sensor device of the present invention comprises: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; a conversion unit that converts the analog detection signal output from the light receiving unit into a digital detection signal; and a control unit that, when the digital detection signal is not at the upper or lower limit of the output of the conversion unit, makes a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal, and does not make a determination based on the gas concentration of the gas to be detected when the digital detection signal is at the upper or lower limit of the output of the conversion unit.

[0009] Furthermore, the optical gas sensor device of the present invention comprises: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; a conversion unit that converts the analog detection signal output from the light receiving unit into a digital detection signal; a temperature detection unit that detects the temperature corresponding to the light receiving unit; and a control unit that calculates the rate of change of the detected temperature, and if the rate of change of the temperature is less than a predetermined first threshold, makes a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal, and does not make a determination based on the gas concentration of the gas to be detected if the rate of change of the temperature is equal to or greater than the predetermined first threshold.

[0010] Furthermore, the present invention relates to a control method for an optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; and a conversion unit that converts an analog detection signal output from the light receiving unit into a digital detection signal, the control method comprising a control step in which, when the digital detection signal is not the upper or lower limit of the output of the conversion unit, a determination is made based on the gas concentration of the gas to be detected calculated from the digital detection signal, and when the digital detection signal is the upper or lower limit of the output of the conversion unit, no determination is made based on the gas concentration of the gas to be detected.

[0011] Furthermore, the present invention relates to a control method for an optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; a conversion unit that converts an analog detection signal output from the light receiving unit into a digital detection signal; and a temperature detection unit that detects the temperature corresponding to the light receiving unit, the control method comprising: calculating the rate of temperature change of the detected temperature; making a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal if the rate of temperature change is less than a predetermined first threshold; and not making a determination based on the gas concentration of the gas to be detected if the rate of temperature change is equal to or greater than a predetermined first threshold.

[0012] Furthermore, the program of the present invention causes a computer for an optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; and a conversion unit that converts an analog detection signal output from the light receiving unit into a digital detection signal, to function as a control unit that, when the digital detection signal is not the upper or lower limit of the output of the conversion unit, makes a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal, and does not make a determination based on the gas concentration of the gas to be detected when the digital detection signal is the upper or lower limit of the output of the conversion unit.

[0013] Furthermore, the program of the present invention causes a computer for an optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; a conversion unit that converts an analog detection signal output from the light receiving unit into a digital detection signal; and a temperature detection unit that detects the temperature corresponding to the light receiving unit, to function as a control unit that includes a control step of calculating the rate of temperature change of the detected temperature, making a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal if the rate of temperature change is less than a predetermined first threshold, and not making a determination based on the gas concentration of the gas to be detected if the rate of temperature change is equal to or greater than the predetermined first threshold.

[0014] According to the present invention, it is possible to prevent inaccurate determinations using gas concentration during rapid temperature changes.

[0015] This is a schematic diagram of an optical gas sensor device according to an embodiment of the present invention. This is a perspective view of the optical gas sensor device. This is a partially transmitted perspective view of the optical gas sensor device. This is a perspective view showing the sealing device. This is a perspective view of the light source. This is a diagram showing the circuit configuration of the optical gas sensor device and equipment. This is a flowchart showing the state setting process. This is a flowchart showing the intermittent light source drive process. This is a diagram showing an example of the time characteristics of the detected value when the light is on and when it is off. This is a diagram showing an example of the detected value when the light is on, the detected value when it is off, the difference detected value and the substrate temperature with respect to elapsed time. This is a diagram showing an example of the difference detected value and gas concentration with respect to elapsed time.

[0016] Embodiments of the present invention will be described in detail below with reference to the attached drawings. However, the scope of the invention is not limited to the illustrated examples.

[0017] First, the schematic configuration of the optical gas sensor device 100 of this embodiment will be described with reference to Figure 1. Figure 1 is a schematic diagram of the optical gas sensor device 100 of this embodiment.

[0018] As shown in Figure 1, the optical gas sensor device 100 of this embodiment is an NDIR type gas sensor. The optical gas sensor device 100 comprises an optical cover 1, a light source 2, an optical filter 3, a light receiving unit 4, a signal processing unit 5, and a switch 81. The optical filter 3 is an optical filter. In the optical gas sensor device 100, the light source 2 emits (emits, emits) infrared light. The emitted infrared light is emitted through the optical path (path) inside the optical cover 1 to the gas G of the detection target (measurement target) inside the optical cover 1. An AR (Anti Reflection) filter 31 (Figure 4), which will be described later, is placed between the light source 2 and the optical filter 3. The AR filter 31 is a filter that prevents reflection of infrared light and allows it to pass through. The AR filter 31 is placed, for example, in the optical path downstream of the light source 2, near the light source 2.

[0019] The amount of light reaching the light-receiving unit 4 decreases as molecules of the target gas G present in the optical path absorb infrared radiation. The optical gas sensor device 100 detects the infrared radiation partially absorbed by the target gas G via the optical filter 3 to the light-receiving unit 4. The optical filter 3 is a filter that transmits infrared radiation at the absorption wavelength of gas G from the incident infrared radiation. With this configuration, the light-receiving unit 4 does not receive unfiltered infrared radiation emitted from sources other than the light source 2, improving the signal-to-noise ratio (SNR) of the sensor.

[0020] The optical gas sensor device 100 processes the detection signal detected by the light receiving unit 4 using the signal processing unit 5 to detect (measure) the concentration of the target gas G and output it. The switch 81 is a switch that turns the light emission of the light source 2 on and off, and is included in the circuit element unit 8, which will be described later. When gas detection is performed, the signal processing unit 5 turns the light source 2 on and off via the switch 81.

[0021] The optical cover 1 has a gas introduction port 11, which serves as a gas inlet and outlet for the gas G to be detected. A contamination filter 12 is attached to the gas introduction port 11. The contamination filter 12 is, for example, a metal mesh filter or a porous resin film, and prevents foreign matter from entering from the outside.

[0022] In this manner, the optical gas sensor device 100 filters the infrared light emitted from the light source 2 to the gas G to be detected by the optical filter 3 and receives it with the light receiving unit 4. The optical filter 3 is positioned near the light receiving unit 4 on the optical path upstream of the light receiving unit 4.

[0023] In this embodiment, the optical path is designed so that the infrared light received by the light-receiving unit 4 arrives after reflecting off the inner surface of the optical cover 1 from the light source 2. A higher reflectivity on the inner surface of the optical cover 1 is desirable as it increases the efficiency of light (infrared light) utilization. The optical path of the infrared light received by the light-receiving unit 4 may include not only the optical path that arrives after reflecting off the inner surface of the optical cover 1, but also an optical path that arrives directly from the light source 2.

[0024] The optical gas sensor device 100 is designed to detect alternative fluorocarbon refrigerants, which are used as refrigerants in air conditioners, as the target gas G. Alternative fluorocarbons are synthetic compound (gas) refrigerants used industrially as substitutes for specific chlorofluorocarbons (CFCs). Because CFC refrigerants have a high ozone depletion potential and contribute to the depletion of the Earth's ozone layer, replacement with hydrochlorofluorocarbon (HCFC) refrigerants, which have a lower ozone depletion potential, has begun. Furthermore, in developed countries, there is a shift from HCFC refrigerants to HFC refrigerants (R410A), which have an ozone depletion potential of 0.

[0025] CFC refrigerants, HCFC refrigerants, and HFC refrigerants are known to have high global warming potentials and to be greenhouse gases that cause global warming. For this reason, the replacement of HFC refrigerants (R410A) with HFC refrigerants (R32) with lower global warming potentials is being considered. In this embodiment, for example, R32 as a fluorocarbon refrigerant is detected as the gas G to be detected.

[0026] However, the gas G to be detected is not limited to R32. Other fluorocarbon refrigerants may also be detected, such as R-454C, which has an extremely low Global Warming Potential (GWP). Examples of other fluorocarbon refrigerants include R143a, R152a, R1132, R142b, R1234yf, R1234ze(E), R-444A, R-444B, R-445A, R-446A, R-447A, R-447B, R-451A, R-451B, R-452B, R-454A, R-454B, R-454C, R-455A, R-457A, R-459A, R-459B, R-462A, and R-465A. Furthermore, the gas G to be detected is not limited to fluorocarbon refrigerants, but may also include carbon dioxide, carbon monoxide, propane, methane, butane, ammonia, oxygen disulfide, nitrogen dioxide, nitric oxide, ozone, sulfur hexafluoride, difluoromethane, hydrochlorofluorocarbons (HCFCs), other hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), ethylene, and the like.

[0027] The optical gas sensor device 100 outputs various status signals based on the gas concentration of the detected gas G to an information processing unit of a device that performs processing based on the status of the optical gas sensor device 100. The information processing unit is, for example, the MCU (Micro Controller Unit) 300 shown in Figure 6, which will be described later. The status signals are, for example, fault signals, alarm signals, and monitoring signals (normal signals). A fault signal indicates a fault in the optical gas sensor device 100. An alarm signal indicates an abnormal state (alarm state) where the concentration of the detected gas G exceeds a threshold concentration that indicates a gas leak. A monitoring signal indicates that the concentration of the detected gas G is in a normal state. If the device is an alarm device, it will notify various alarms (for example, an alarm for a fault in the optical gas sensor device 100 based on a fault signal, or an alarm for an abnormal concentration of the detected gas G based on an alarm signal) in response to the various signals received from the optical gas sensor device 100. The device may be a device including an optical gas sensor device 100 and an MCU 300, or it may be a separate device from the optical gas sensor device 100 (an external device including the MCU 300 (for example, device 330 in Figure 6)). Examples of such devices include room air conditioners, air conditioners for shops and offices, and multi-split air conditioners for buildings.

[0028] Next, the specific configuration of the optical gas sensor device 100 will be described with reference to Figures 2 to 5. Figure 2 is a perspective view of the optical gas sensor device 100. Figure 3 is a partially transmitted perspective view of the optical gas sensor device 100. Figure 4 is a perspective view of the sealing device 20. Figure 5 is a perspective view of the light source 2.

[0029] As shown in Figures 2 and 3, the optical gas sensor device 100 comprises an optical cover 1, sealants 20 and 40, a signal processing unit 5, a substrate 6, and a circuit element unit 8. The sealant 20 has a light source 2 and an AR filter 31. The sealant 40 has an optical filter 3 and a light receiving unit 4. In Figure 2, the x, y, and z axes are shown. These three axes are the same in the other figures. Note that the contamination filter 12 is not shown in Figures 2 and 3.

[0030] The optical cover 1 is mounted on the surface of the substrate 6 in the +z direction and is a cover that covers (encompasses) the sealants 20 and 40. The optical cover 1 has a cavity (space) inside that can accommodate the gas G to be detected, and the gas G to be detected is introduced into and out of the cavity via the gas introduction port 11. The base material of the optical cover 1 is, for example, made of resin.

[0031] As shown in Figure 2, the optical cover 1 has cover portions 110A and 110B. Cover portion 110A is the upper (+z direction) part and is integrated with cover portion 110B by methods such as bonding or heat crimping. Cover portion 110B is the lower (-z direction) part and is integrated with cover portion 110A by methods such as bonding or heat crimping.

[0032] Furthermore, as shown in Figure 3, the optical cover 1 has a light guide section 13, which is a cavity into which the gas G to be detected is introduced. The light guide section 13 is a pipe-shaped optical path, with a circular cross-section perpendicular to the axial direction. Cover section 110A has a half-pipe section. Cover section 110B also has a half-pipe section. The light guide section 13 is formed by the joining of the half-pipe sections of cover sections 110A and 110B. Thus, the optical cover 1 has cover sections 110A and 110B, which are divided by the axial cross-section of the light guide section 13. As shown in Figure 3, the light guide section 13 has a roughly U-shape in three dimensions when viewed from the +z direction (in an xy-plane view).

[0033] The inner surface of the light guide section 13 is covered with an infrared reflective film. In this embodiment, gold is used as the infrared reflective film, but it is not limited to this. Silver or aluminum may also be used as the infrared reflective film. Furthermore, if necessary, a protective film such as silicon oxide or silicon nitride may be formed on the infrared reflective film to prevent corrosion of the metal film of the infrared reflective film. Methods for forming the infrared reflective film and protective film include plating, sputtering, and vacuum deposition. For example, the optical cover 1 may be integrally fabricated from a metal such as aluminum using a metal 3D printer. In any case, it is preferable to have a mirror finish on the inner surface of the light guide section 13 in order to efficiently reflect infrared rays.

[0034] The light guiding part 13 reflects, by the infrared reflective film on its inner surface, the infrared light emitted from the light source 2 of the sealing member 20 and incident through the AR filter 31. The light guiding part 13 emits the reflected infrared light to the light receiving part 4 through the optical filter 3 of the sealing member 40. In this way, by reflecting the infrared light emitted from the light source 2 with the infrared reflective film, the optical cover 1 serves as an optical path to efficiently guide the infrared light from the light source 2 to the light receiving part 4 such that at least a part of the reflected light reaches the light receiving part 4 through the optical filter 3.

[0035] In the present embodiment, the optical path inside the optical cover 1 is formed as the light guiding part 13 having a circular pipe shape with a cross-section perpendicular to the axial direction. This allows the reflection angle of infrared light to be kept constant in any direction of the three dimensions (x-axis, y-axis, z-axis) regardless of the diameter and path of the cross-section of the light guiding part 13, so that the infrared light emitted from the light source 2 is reflected inside the light guiding part 13 and can enter the light receiving part 4 efficiently. Note that the cross-section perpendicular to the axial direction of the optical path of the light guiding part 13 of the optical cover 1 may be elliptical or have a shape combining a curved line and a straight line.

[0036] In addition, the optical path length of infrared light from the light source 2 to the light receiving part 4 can be changed relatively easily by changing the diameter of the cross-section of the light guiding part 13.

[0037] In addition, for the cross-sectional area of the cross-section perpendicular to the axial direction of the light guiding part 13, the main part (the part other than the inlet part 131 and the outlet part 132 described later) is constant in the axial direction. Since the cross-sectional area is constant, the gas concentration per unit volume of the detection target gas G entering the light guiding part 13 is easily homogenized, and infrared light passes randomly without passing through a specific path, so it is easy to respond to changes in the gas concentration of the gas G. FIG. 3 shows an optical path propagation state in which a plurality of infrared optical paths in the light guiding part 13 are represented by solid arrows. As described above, the infrared optical paths are random within the light guiding part 13.

[0038] Further, infrared light emitted from the light source 2 of the sealing member 20 is incident on the light guide section 13 on the -x direction side via the AR filter 31. The axial direction of the light guide section 13 on the -x direction side extends from the -z direction side to the +z direction side, then bends in an R-shape, and extends linearly from the -y direction side to the +y direction side. An end portion of the light guide section 13 on the incident side of the infrared light is defined as an inlet portion 131. The light guide section 13 extending toward the +y direction side bends in an R-shape, has its axial direction extending from the -x direction side to the +x direction side, and bends in an R-shape again.

[0039] Then, the axial direction of the light guide section 13 on the +x direction side extends linearly from the +y direction side to the -y direction side, then bends in an R-shape and extends toward the -z direction side. The infrared light that has passed through the light guide section 13 is emitted to the light receiving section 4 via the optical filter 3 of the sealing member 40. An end portion of the light guide section 13 on the emission side of the infrared light is defined as an outlet portion 132.

[0040] The outlet portion 132 has a tapered shape whose cross-sectional area becomes smaller as the axial direction of the light guide section 13 goes from the +z direction side to the -z direction side. Similarly, the inlet portion 131 has a tapered shape whose cross-sectional area becomes smaller as the axial direction of the light guide section 13 goes from the +z direction side to the -z direction side. For this reason, the condensing degree of the infrared light emitted to the light receiving section 4 through the light guide section 13 can be increased.

[0041] Further, the cover portions 110A and 110B have hollow portions (not shown) as spaces for lightening (material reduction). These hollow portions can achieve weight reduction of the optical cover 1 (optical gas sensor device 100).

[0042] Further, the cover portion 110B has fixing pins 121 and 122. The fixing pins 121 and 122 are convex portions extending in the +z direction, and are integrated by a method such as adhesion or thermal caulking after being butted against recesses (female holes) (not shown) of the cover portion 110A. Through the integration achieved by a method such as adhesion or thermal caulking performed by butting the fixing pins against the recesses of the cover portion 110A, the cover portions 110A and 110B are positioned, fixed, and formed into an integrated component.

[0043] Furthermore, as shown in Figure 2, the cover portion 110A has gas inlet ports 111 and 112 as gas introduction ports 11. The gas inlet ports 111 and 112 are holes drilled in the -z direction from the upper surface of the cover portion 110A. The space around the sealing device 20 is electrically connected to the light guide portion 13. The space around the sealing device 40 is electrically connected to the light guide portion 13.

[0044] The gas inlets 111 and 112 are connected to the light guide section 13 via the gas inlets 133 and 134. The gas taken in from the gas inlets 111 and 112 enters the inner space of the optical cover 1 and is then introduced into the light guide section 13 through the gas inlets 133 and 134. Here, the gas inlets 133 and 134 are positioned such that, when viewed from above, the line connecting the centers of the gas inlets 111 and 112 and the centers of the gas inlets 133 and 134 forms a 45-degree angle with respect to the x-axis. Note that the shape, size, and position of the gas introduction port 11 (gas inlets 111 and 112) of the optical cover 1 in Figure 2 are examples only and are not limited thereto.

[0045] As shown in Figure 4, the sealing device 20 is mounted on the substrate 6 and seals the light source 2 inside the sealing device 20. The sealing device 20 protects the light source 2 from external environmental factors such as humidity and environmentally harmful gases inside and outside the sealing device 20, i.e., the space enclosed by the cover portions 110A and 110B. Inside the sealing device 20, the light source 2 is mounted by bonding it to the bottom (bottom surface 213) of the space enclosed by the protective cover, for example, the ceramic substrate 21 in this embodiment, using an adhesive portion (not shown), and the AR filter 31 is bonded and sealed to the upper surface of the ceramic substrate 21 with adhesive 33. The sealing device 20 may also have a configuration that includes other optical filters instead of the AR filter 31.

[0046] The ceramic substrate 21 is made of, for example, aluminum oxide (alumina) and protects the light source 2 from the sides and bottom. The ceramic substrate 21 is mounted on the bottom of the seal 20 or directly on the substrate 6. The ceramic substrate 21 also has no ventilation holes and the AR filter 31 is mounted on it.

[0047] The ceramic substrate 21 has recesses 211 and 212. Recess 211 is a recess located on the upper surface (+z direction) side, and the planar shape of its opening is approximately rectangular. Recess 212 is a recess located on the lower surface (-z direction) side of recess 211, and the planar shape of its opening is approximately rectangular and smaller than that of recess 211. Recess 212 has a bottom surface 213, and the light source 2 is bonded and mounted on the bottom surface 213. The ceramic substrate 21 electrically connects the terminals of the light source 2 and wire-bonded terminals to the terminals of the substrate 6, for example, by through holes.

[0048] The AR filter 31 is positioned across the entire upper surface of the ceramic substrate 21 so as to cover the opening on the upper surface, and is attached to the ceramic substrate 21 with adhesive 33. The adhesive 33 is an epoxy resin or silicone resin for hermetically sealing the light source 2. The adhesive 33 may also be a glass frit material for sealing the light source 2, or a preform or paste of a metallic material such as AuSn or solder. In the case of a metallic material, it is desirable to apply metallization such as Cr / Pt / Au, Cr / Ni / Au, or Ti / Ni / Au to the bonding area between the ceramic substrate 21 and the AR filter 31 to ensure adhesion.

[0049] As shown in Figure 5, the light source 2 is a MEMS (Micro Electro Mechanical Systems) type light source mounted on the upper surface (the surface in the +z direction) of the bottom surface 213. The light source 2 has a membrane structure M formed on a Si support layer 201. The membrane M is formed such that a planar heater layer 202 covers the membrane M.

[0050] The light source 2, when viewed from the +z direction (in an xy-plane view), has a light source region 230 and electrode pads P1 and P2. The light source region 230 is a region that functions as a light source in a substantially rectangular shape and has electrodes 231 and 232. Electrode 231 extends in the y-axis direction and is located on the +x direction side of the light source region 230. Electrode 231 is electrically connected to electrode pad P1 via wiring. Electrode 232 extends in the y-axis direction and is located at the -x direction end of the light source region 230. Electrode 232 is electrically connected to electrode pad P2 via wiring.

[0051] The light source 2 has a cross-sectional configuration in which, for example, a Si support layer 201, a heater layer support layer, a heater layer 202, electrodes 231, 232, an electrode support layer, and a protective layer (those without a sign are not shown) are stacked in order from the -z direction to the +z direction. The heater layer support layer, electrode support layer, and protective layer are insulating layers that sandwich the heater layer 202 above and below in the z-axis direction.

[0052] The Si support layer 201 is a substrate made of Si and serves as a support layer for the membrane M of the light source 2. The Si support layer 201 has a circular space (cylindrical shape) when viewed from the -z direction. The space is surrounded on all four sides by the outer frame of the Si support layer 201. Therefore, the light source 2 has a circular membrane M on the xy plane perpendicular to the film thickness direction (z-axis direction). The membrane M covers the space from the upper surface (+z direction side) of the outer frame.

[0053] The heater layer support layer has, for example, a silicon oxide film, a silicon nitride film, and a silicon oxide film from the -z direction to the +z direction. The silicon oxide film is silicon dioxide (SiO₂) as an insulator (dielectric). ２ It is a thin film made of ). Alternatively, the membrane M may have no silicon oxide film on the -z direction side. The silicon nitride film is silicon nitride (Si) as an insulator (dielectric). ３ N ４ It is a thin film made of SiO. ２which is a thin film. The heater layer 202 is a thin-film heater serving as a light source (metal) layer, which generates heat when energized and heats the membrane M. The heated membrane M emits infrared rays having intensity and wavelength dependency dependent on the surface temperature and surface emissivity. The heater layer 202 is made of, for example, molybdenum disilicide (MoSi ２ ). However, the heater layer 202 is not limited thereto, and may be made of molybdenum (Mo), a compound composed of Mo and Si having a different composition ratio from MoSi ２ , tungsten (W), tungsten disilicide (WSi ２ ), a compound composed of W and Si having a different composition ratio from WSi ２ , or other materials such as platinum (Pt), titanium (Ti), gold (Au), silver (Ag), nickel chromium (NiCr), nickel (Ni), aluminum (Al), copper (Cu), titanium nitride (TiN), and polycrystalline silicon. The heater layer 202 is formed in a rectangular shape wider than the outer shape of the circular space portion on the xy plane, so as to equalize the tensile stress in the membrane M region.

[0054] Electrodes 231 and 232 are made of a metal such as an aluminum-silicon alloy (Al-Si) and are arranged so as to be electrically connected to the heater layer 202. The electrode support layer is made of SiO ２ and supports the electrodes 231 and 232. The protective layer is made of Si ３ N ４ and protects the lower layers including the electrode support layer from external disturbances. The electrodes 231 and 232 are exposed to the +z direction side from the upper surface of the protective layer.

[0055] The membrane M is a film-like portion composed of each layer excluding the Si support layer 201 among the plurality of layers of the light source 2 on the xy plane. That is, the membrane M sequentially includes, for example, a silicon oxide film, a silicon nitride film, a silicon oxide film, the heater layer 202, the electrode support layer, and the protective layer from the -z direction side to the +z direction side.

[0056] The heater layer 202 is electrically connected to electrodes 231 and 232. Electrode pads P1 and P2 are electrode pads for wire bonding, with electrode pad P1 electrically connected to electrode 231 and electrode pad P2 electrically connected to electrode 232. Electrode pads P1 and P2 are wire-bonded to the terminals of the wiring pattern on the substrate 6, and the heater layer 202 is energized by the application of voltage.

[0057] Light source 2, as a MEMS-type light source, is small and low-profile, enabling miniaturization of the sensor module. Furthermore, light source 2, as a MEMS-type light source, has features such as long lifespan, low power consumption, and short response time, contributing to low overall power consumption of the sensor module. The short response time of the MEMS-type light source allows for reduced standby time after power-on when performing intermittent operation, thereby lowering average power consumption.

[0058] Furthermore, since light source 2, as a MEMS-type light source, can directly utilize synchrotron radiation from the high-temperature surface, it can also be applied to the detection of gases with absorption bands at high wavelengths. In addition, the infrared radiation-emitting region of light source 2 is precisely patterned as a membrane M on the plane of the Si support layer 201, resulting in very small individual variations in the radiation direction. Therefore, variations in the amount of light received when light source 2 is used to construct a sensor module are reduced, contributing to improved product yield. Moreover, since light source 2 is mass-producible because it is produced in bulk using MEMS technology based on a silicon wafer, it offers excellent mass-production capabilities.

[0059] Furthermore, because the membrane M of the light source 2 is circular in shape on the xy plane and located within the region of the heater layer 202, the thermal stress generated during heating becomes uniform, improving mechanical strength. As a result, damage to the membrane M due to thermal stress during operation is suppressed in the light source 2, contributing to an extended product life.

[0060] The light source 2 is mounted on the bottom surface 213 of the sealant 20 and wire-bonded. The electrode pads P1 and P2 are electrically connected to the terminals of the sealant 20 via wires.

[0061] The AR filter 31 is a filter that prevents reflection of infrared rays and transmits them. The AR filter 31 has, for example, a silicon substrate as a base material and a multilayer film. The multilayer film is formed on the silicon substrate by coating or the like and uses materials such as ZnS or Ge as a dielectric with a refractive index lower than silicon. The spectral characteristics of the AR filter 31 are θ = 0 [°], T (AVE) 8.5 to 10.0 [μm] ≥ 80 [%], T (ABS) 8.0 to 12 [μm] ≥ 50 [%], T (ABS) 1.0 to 6.8 [μm] ≤ 1.0 [%], and T 7.5 ± 0.4 [μm] = 5 [%].

[0062] The sealing device 40 has the same structure as the sealing device 20. In other words, the sealing device 40 has a configuration in which the AR filter 31 and light source 2 of the sealing device 20 are replaced with an optical filter 3 and a light receiving unit 4. For this reason, the explanation of the ceramic substrate 21 and other components that serve as a protective cover for the sealing device 40 will be omitted, and the optical filter 3 and light receiving unit 4 will be explained.

[0063] The light-receiving unit 4 is a surface-mount component mounted on the +z side of the bottom surface of the ceramic substrate of the sealing device 40, and detects the amount of incident infrared light and outputs a detection signal as an analog electrical signal. The light-receiving unit 4 is, for example, a MEMS element of a thermopile type optical sensor (infrared sensor) having multiple thermocouples. However, the light-receiving unit 4 is not limited to a thermopile type infrared sensor, and may be a quantum type (cooled type) phototube, photoconductive type, photovoltaic type infrared sensor, or a thermal type (uncooled type) pyroelectric element type, thermocouple type, bolometer type infrared sensor, etc.

[0064] The optical filter 3 is a λ-selective filter that transmits light (infrared) of wavelength λ, which corresponds to the absorption wavelength unique to the gas G being detected, and is provided to cover the light-receiving surface of the light-receiving unit 4. In this way, the transmission wavelength of the optical filter 3 is designed to match the unique absorption wavelength of the gas G being detected. As a result, changes in light intensity caused by gases other than the gas G being detected are suppressed, and the signal-to-noise ratio of the detection signal of the light-receiving unit 4 is improved.

[0065] The optical filter 3 includes, for example, a silicon substrate as a base material and a dielectric multilayer film, or a multilayer film made of an infrared-transmitting material such as Si, Ge, sulfide, and fluoride. The silicon substrate is a planar silicon substrate. However, the material of the substrate is not limited to silicon, but can also be germanium (Ge), quartz (SiO2). ２ ), alumina (Al ２ O ３ ), barium fluoride (BaF ２ ), calcium fluoride (CaF ２ ) and the like can be used. A multilayer film is a plurality of layered films provided on both sides of a silicon substrate.

[0066] The optical filter 3 is a bandpass filter that transmits light in the wavelength band including the absorption wavelength of gas G. Alternatively, the optical filter 3 may be configured to use a longpass filter that cuts out light on the shorter wavelength side than an arbitrary cutoff wavelength and transmits light including the absorption wavelength of gas G on the longer wavelength side.

[0067] The signal processing unit 5 is mounted on a planar area of ​​the substrate 6 on the +z side surface other than the optical cover 1, and is an AFE (Analog Front End)-IC (Integrated Circuit) that performs signal processing related to the detection signal of the light receiving unit 4. The signal processing unit 5 amplifies the analog detection signal of the light receiving unit 4 and performs AD conversion, and when the light source 2 is driven intermittently, it generates a difference value between the detection value when the light source 2 is ON and the detection value when the light source 2 is OFF. The signal processing unit 5 corrects the difference value of the detection values ​​for temperature and individual variations of the optical gas sensor device 100, and generates various status signals from the said digital difference value of the detection values. The signal processing unit 5 outputs the digital difference value of the detection values ​​and the status signals.

[0068] The substrate 6 is an FR-4 (Flame Retardant type-4) PCB (Printed Circuit Board) with conductive wiring printed on a board made of glass epoxy resin or the like. The optical cover 1, sealing devices 20 and 40, signal processing unit 5, and circuit element unit 8 are mounted on the +z side of the substrate 6. The +z side of the substrate 6 is approximately parallel to the light-emitting surface of the light source 2, the optical filter 3, and the light-receiving surface of the light-receiving unit 4.

[0069] Furthermore, a connector (not shown) may be mounted on the circuit board 6. The connector is mounted on a planar area on the +z side surface of the circuit board 6 other than the optical cover 1 and the signal processing unit 5, and is a connector for outputting various digital signals output from the signal processing unit 5 to the information processing unit of a subsequent device (for example, device 330). The connector is connected to the information processing unit of the device via a cable with a plug.

[0070] The circuit element section 8 consists of circuit elements such as switches 81, amplifiers 84 and 85 (described later), chip resistors 83, chip capacitors, and an LDO (Low Drop Out) 82.

[0071] Next, the circuit configuration of the optical gas sensor device 100 will be explained with reference to Figure 6. Figure 6 is a diagram showing the circuit configuration of the optical gas sensor device 100 and the equipment 330.

[0072] As shown in Figure 6, the optical gas sensor device 100 has a circuit configuration consisting of a light source 2, a light receiving unit 4, a signal processing unit 5, and a circuit element unit 8. The signal processing unit 5 includes a clock generation unit 512, a multiplexer 52, an AD converter 53 as a conversion unit, an NVM (Non-Volatile Memory) 54, a data processor 55 as a control unit, a communication unit 56, and a status output terminal 57. The circuit element unit 8 includes a switch 81, an LDO 82, a resistor 83, amplifiers 84 and 85, and a temperature sensor 86 as a temperature detection unit. The optical gas sensor device 100 is also connected to the MCU 300 of the device 330. The device 330 includes the MCU 300, resistors 311 and 312, a capacitor 313, and a notification unit 314.

[0073] The MCU 300 is a control unit that controls various parts of the device 330 and has a communication unit 301. The communication units 56 and 301 are serial communication units using the I2C communication method. The communication unit 56 of the optical gas sensor device 100 and the communication unit 301 are connected by a connector via a clock line SCL and a data line SDA. The communication unit 301 generates a clock signal and outputs it to the communication unit 56, and transmits and receives data signals to and from the communication unit 56. Note that the communication method of the communication units 56 and 301 is not limited to IC2, and other serial communication methods such as UART (Universal Asynchronous Receiver / Transmitter) and CSI (Clocked Serial Interface) can also be used. In addition, the MCU 300 is connected to a status output terminal 57 via a signal line 320 and receives status signals from the optical gas sensor device 100, which will be described later. The MCU 300 controls the notification unit 314 based on the status signal of the optical gas sensor device 100. The notification unit 314, in accordance with the control of the MCU 300, notifies the status of the optical gas sensor device 100 based on the status signal through display, sound output, etc.

[0074] Furthermore, the power supply section for the power supply voltage VDD is connected to the clock line SCL (serial clock) via resistor 311, to the data line SDA (serial data) via resistor 312, and to ground via capacitor 313. Resistors 311 and 312 are pull-up resistors. Noise is removed from the power supply voltage VDD by capacitor 313.

[0075] The LDO 82, resistor 83, light source 2, and switch 81 are connected in series between the power supply unit and ground, respectively, for the power supply voltage VDD. The LDO 82 is a linear regulator that can operate even with a small input / output voltage difference, and it converts and stabilizes the power supply voltage VDD before applying it to the resistor 83. The resistor 83 drops the output voltage of the LDO 82 and applies it to the light source 2. The resistor 83 is also connected to the input terminal for voltage detection of the signal processing unit 5. The voltage applied to the light source 2 is called the light source voltage.

[0076] Switch 81 is a switch for turning the light source 2 on (emitting light) / off (turning off). Switch 81 is made up of an NMOSFET (N-channel Metal-Oxide-Semiconductor Field Effect Transistor), and its gate, which serves as a control terminal, is connected to the signal processing unit 5. Switch 81 may also be made up of a CMOS (Complementary Metal-Oxide-Semiconductor) or the like. The light receiving unit 4 detects infrared IR emitted from the light source 2 and input via gas G, optical filter 3, etc., and outputs an analog detection signal from its output terminal. The output terminal of the light receiving unit 4 has two systems: a first output terminal through which the output signal when the light source 2 is on flows, and a second output terminal through which the output signal when the light source 2 is off flows.

[0077] Amplifier 84 amplifies the analog detection signal input from the first output terminal of the light receiving unit 4 and outputs it to the input terminal of the signal processing unit 5. Amplifier 85 amplifies the analog detection signal input from the second output terminal of the light receiving unit 4 and outputs it to the input terminal of the signal processing unit 5. The temperature sensor 86 is located near the light receiving unit 4 and detects the temperature of the substrate 6 in the vicinity (substrate temperature) and outputs an analog temperature signal to the input terminal of the signal processing unit 5. The output terminals of the temperature sensor 86 and amplifiers 84 and 85 are connected to multiple input terminals of the multiplexer 52. Also, for example, the light source voltage output from the light source 2 and resistor 83 is divided, for example, and input to the input terminal of the multiplexer 52. The temperature sensor may also be provided within the signal processing unit 5. Alternatively, both the temperature sensor 86 and the temperature sensor within the signal processing unit 5 may be provided, and the substrate temperature signal may be calculated from the two temperature signals by appropriately coordinating the two temperature sensors.

[0078] The clock generation unit 512 is a clock generation circuit that generates a digital clock signal and outputs it to the data processor 55. The clock generation unit 512 may also be connected to the AD converter 53 and configured to generate an analog clock signal and output it to the AD converter 53.

[0079] The multiplexer 52, for example in response to the selection control of signals from the data processor 55, multiplexes the amplified analog detection signal input from the light receiving unit 4, the analog temperature signal input from the temperature sensor 86, and the divided light source voltage into a single analog multiplexed signal and outputs it to the input terminal of the AD converter 53. The AD converter 53 converts the input multiplexed signal into a multiplexed signal of the digital detection signal from the light receiving unit 4, the digital temperature signal, and the digital divided power supply voltage, and outputs it to the data processor 55.

[0080] The NVM54 is a memory that stores information non-volatilely, and stores, for example, a second threshold, a gas concentration alarm threshold A for gas G, thresholds C1 and C2 indicating the fault range of gas concentration failures, thresholds N1, N2, N3, and N4 indicating the fault range of light source voltage values, a first threshold, a temperature change rate threshold R, and a correction coefficient. Threshold A is a threshold for determining the alarm state and normal state (non-alarm state) of the gas concentration of the optical gas sensor device 100 based on the gas concentration, and is a threshold indicating the upper limit of the gas concentration in the normal state. Threshold A is, for example, 10000 [ppm]. Thresholds C1 and C2 are thresholds for determining the fault state and normal state (non-fault state) of the optical gas sensor device 100 based on the gas concentration, and are thresholds indicating the upper and lower limits of the gas concentration in the normal state (C1 < C2). In other words, the fault range of the gas concentration is the range in which the gas concentration is less than threshold C1 or higher than threshold C2. Thresholds N1 and N2 are thresholds used to determine faulty and normal (non-faulty) states based on the light source voltage value when the light source is off, and they indicate the lower and upper limits of the light source voltage value in a normal state (N1 < N2). In other words, the faulty range of the light source voltage value when the light source is off is the range in which the light source voltage value is less than or equal to threshold N1 or greater than or equal to threshold N2. Thresholds N3 and N4 are thresholds used to determine faulty and normal (non-faulty) states based on the light source voltage value when the light source is on, and they indicate the lower and upper limits of the light source voltage value in a normal state (N3 < N4). In other words, the faulty range of the light source voltage value when the light source is on is the range in which the light source voltage value is less than or equal to threshold N3 or greater than or equal to threshold N4. The temperature change rate threshold R is a threshold used to determine abnormal and normal states based on the temperature change rate, and it indicates the upper limit of the temperature change rate in a normal state. The temperature change rate is the rate of change (slope) of temperature over a predetermined time (e.g., 6 seconds). The correction coefficient is a correction coefficient used to perform correction processing on the detected value of the light receiving unit 4, such as temperature correction and correction for individual variations in the optical gas sensor device 100.

[0081] The data processor 55 is a control unit (processor) that performs signal processing related to the detection signal of the light receiving unit 4, and for example, it has a CPU (Central Processing Unit), RAM (Random Access Memory), and a storage unit. The CPU controls the optical gas sensor device 100. The RAM is a volatile memory that temporarily stores information. The storage unit is composed of non-volatile memory such as ROM (Read Only Memory) and stores various data and programs. The storage unit may also be shared with an NVM 54, which is a non-volatile memory provided separately from the data processor 55. As for the NVM 54, mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash memory, etc., can be used. In the data processor 55, the CPU reads the program stored in the storage unit, expands it into the RAM, and performs various processing in cooperation with the expanded program. The storage unit is assumed to store a state setting program for executing the state setting processing described later.

[0082] The data processor 55 calculates the gas concentration of gas G using the digital detection signal and digital temperature signal from the light receiving unit 4 input from the multiplexer 52 and the correction coefficient stored in the NVM 54. The data processor 55 calculates the temperature change rate using the digital temperature signal for a predetermined time input from the multiplexer 52. The data processor 55 compares the calculated gas concentration, light source voltage value, and temperature change rate with each threshold value stored in the NVM 54. Based on the comparison result, the data processor 55 generates status signals (fault signal, alarm signal, monitoring signal) indicating various states of the optical gas sensor device 100. The data processor 55 transmits the gas concentration to the MCU 300 of the device 330 via the communication unit 56. The data processor 55 also transmits the status signals of the optical gas sensor device 100 to the MCU 300 via the status output terminal 57 in a predetermined format. The data processor 55 may also be configured using circuits such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit).

[0083] The communication unit 56 transmits and receives data signals (such as gas concentration) to and from the communication unit 301 via the data line SDA.

[0084] Next, the operation of the optical gas sensor device 100 will be explained with reference to Figures 7 to 11. Figure 7 is a flowchart showing the state setting process. Figure 8 is a flowchart showing the intermittent light source driving process. Figure 9 is a diagram showing an example of the time characteristics of the detected value when the light is on and the detected value when the light is off. Figure 10 is a diagram showing an example of the detected value when the light is on, the detected value when the light is off, the difference detected value, and the substrate temperature with respect to elapsed time. Figure 11 is a diagram showing an example of the difference detected value and gas concentration with respect to elapsed time.

[0085] Prior to this, the optical gas sensor device 100 is connected to the MCU 300 of the equipment 330, and the gas G to be detected is introduced into the optical cover 1 from the gas introduction port 11. The optical gas sensor device 100 is powered off. The data processor 55 of the signal processing unit 5 is triggered when the optical gas sensor device 100 is powered on by the user, and executes a state setting process according to the state setting program stored in its internal memory.

[0086] As shown in Figure 7, first, the data processor 55 performs initialization of the signal processing unit 5 and other operations to prepare the signal processing unit 5 for operation (step S10). Then, the data processor 55 performs intermittent light source drive processing (step S11). The intermittent light source drive processing will be explained with reference to Figure 8.

[0087] First, the data processor 55 starts turning off the light source 2 for a predetermined time T1 by turning off the switch 81 (step S31). In this embodiment, the light source 2 is driven intermittently for a predetermined time T1 = 750 [ms] when it is turned off and a predetermined time T2 = 250 [ms] when it is illuminated. The period of this intermittent drive is 1 [s]. However, the predetermined times T1 and T2 are not limited to these examples.

[0088] Then, during the predetermined time T1 of step S31, the data processor 55 acquires the digital temperature signal detected by the temperature sensor 86 as the substrate temperature (step S32). In step S32, the data processor 55 similarly calculates and acquires the light source voltage value when the light source is off, based on the digitally divided voltage input from the light source 2 and the resistor 83. In step S32, the data processor 55 similarly acquires the digital off detection signal input from the light receiving unit 4 as the off detection value.

[0089] Then, after the light has been off for a predetermined time T1, the data processor 55 turns on the switch 81 to start turning on (emitting light) the light source 2 for a predetermined time T2 (step S33). During the predetermined time T2 in step S33, the data processor 55 acquires the digital temperature signal detected by the temperature sensor 86 as the substrate temperature (step S34). In step S34, the data processor 55 similarly calculates and acquires the light source voltage value when the light source is turned on, based on the digitally divided voltage input from the light source 2 and the resistor 83. In step S34, the data processor 55 similarly acquires the digital light emission detection signal input from the light receiving unit 4 as the light emission detection value.

[0090] Then, the data processor 55 calculates a difference detection value by subtracting the detection value obtained in step S32 from the detection value obtained in step S34 when the light is off (step S35). In step S35, the data processor 55 calculates the average substrate temperature by adding the substrate temperature obtained in step S32 when the light is off and the substrate temperature obtained in step S34 when the light is on. The calculated average substrate temperature is stored in the NMV 54 of the data processor 55 in association with the measurement time. In step S35, the data processor 55 calculates the temperature change rate of the average substrate temperature for a predetermined time based on the past average substrate temperatures stored in the NMV 54 and the calculated current average substrate temperature. In step S35, the data processor 55 reads the correction value from the NMV 54, calculates the gas concentration from the difference detection value, and corrects the gas concentration using the current average substrate temperature and the correction coefficient. The data processor 55 transmits the calculated gas concentration to the MCU 300 via the communication unit 56.

[0091] Returning to Figure 7, the data processor 55 reads thresholds N1 to N4 from the NMV 54 and determines whether the light source voltage value acquired in steps S32 and S34 is within the fault range (step S12). In step S12, if the light source voltage value acquired in step S32 when the light source is off is less than or equal to threshold N1 or greater than or equal to threshold N2, it is determined to be within the fault range. Similarly, if the light source voltage value acquired in step S34 when the light source is on is less than or equal to threshold N3 or greater than or equal to threshold N4, it is determined to be within the fault range. In all other cases, it is determined not to be within the fault range. If the light source voltage value is within the fault range (step S12; YES), the optical gas sensor device 100 is in a state where the light source voltage value is low or high when the light source is off or on due to a malfunction. For this reason, the data processor 55 sets the device to a fault state, generates a fault signal indicating the fault state, and transmits the fault signal to the MCU 300 via the status output terminal 57 (step S13). The fault signal is, for example, a PWM (Pulse Width Modulation) signal, and its ON pulse width is different from other status signals (alarm signals, monitoring signals). The process then proceeds to step S11.

[0092] If the light source voltage value is not within the fault range (step S12; NO), the data processor 55 determines whether the off-time detection value or the light-on-time detection value acquired in steps S32 and S34 is within the upper limit (= 65535) or lower limit (= 0) of the output of the AD converter 53 (step S14). If the light-on detection value or the off-time detection value is not within the upper limit or lower limit (step S14; NO), the light-on detection value and the off-time detection value are within the normal range. Therefore, the data processor 55 reads the threshold R from the NMV 54 and determines whether the temperature change rate calculated in step S35 is greater than or equal to the threshold R (step S15).

[0093] If the detected value for light emission or the detected value for extinction is at the upper or lower limit (step S14; YES), the detected value for light emission or the detected value for extinction is abnormal. Since the gas concentration calculated from the abnormal detected value for light emission or the detected value for extinction will also be abnormal, the data processor 55 does not determine a fault state or alarm state based on the gas concentration and maintains the determination state immediately before the start of the no-determination (step S16). The process proceeds to step S11. If the rate of temperature change is greater than or equal to the threshold R (step S15; YES), a rapid temperature change has occurred, and the process proceeds to step S16.

[0094] If the rate of temperature change is less than the threshold R (step S15; NO), a rapid temperature change has not occurred. Therefore, the data processor 55 reads the thresholds C1 and C2 from the NMV 54 and determines whether the gas concentration calculated in step S35 is less than the threshold C1 or greater than the threshold C2, which is the fault range (step S17). If the gas concentration is less than the threshold C1 or greater than the threshold C2 (step S17; YES), the process proceeds to step S13.

[0095] If the gas concentration is greater than or equal to threshold C1 and less than or equal to threshold C2 (step S17; YES), the data processor 55 reads threshold A from the NMV 54 and determines whether the gas concentration calculated in step S35 is greater than or equal to threshold A (step S18). If the gas concentration is greater than or equal to threshold A (step S18; YES), the gas concentration is at a level that requires an alarm. Therefore, the data processor 55 sets the system to an alarm state, generates an alarm signal indicating the alarm state, and transmits the alarm signal to the MCU 300 via the status output terminal 57 (step S19). The process then proceeds to step S11.

[0096] If the gas concentration is less than threshold A (step S18; NO), the gas concentration is at a normal level. Therefore, the data processor 55 sets the system to a monitoring state (normal state), generates a monitoring signal indicating this monitoring state, and transmits the monitoring signal to the MCU 300 via the state output terminal 57 (step S20). The process then proceeds to step S11.

[0097] As shown in Figure 9, an example of the detection value when the light is off, obtained in step S32 of the state setting process, and the detection value when the light is on, obtained in step S34, is depicted over time. During the period from time t1 to t2, the detection value when the light is on reaches the upper limit of the AD converter output (65535). Therefore, the result is NO in step S14, and assuming that the light source voltage value and temperature change rate are normal, the process of steps S11 → S12 → S14 → S16 → S11… is repeatedly executed. Thus, the period from time t1 to t2 is a period of no determination, during which no determination is made using the gas concentration based on the abnormal detection value when the light is on. Also, during the period from time t1 to t2, the determination state immediately before time t1 is maintained.

[0098] During the period from time t2 to t3, the light emission detection value does not reach the upper limit of the AD converter output. Therefore, if the answer in step S14 is YES, and the light source voltage value, temperature change rate, and gas concentration are normal, the process of steps S11→S12→S14→S17→S18→S20… is repeatedly executed. In this way, the period from time t2 to t3 is a normal determination period in which no determination is made using the gas concentration based on the abnormal light emission detection value. The period from time t3 to t4 is a period of no determination, similar to the period from time t1 to t2.

[0099] For example, during periods when the detected value at the time of power-off does not reach the lower limit (0) of the AD converter's output, a no-determination period is observed where no judgment is made using the gas concentration based on the abnormal detected value at the time of power-off. Also, the detected values ​​at the time of power-on and the detected values ​​at the time of power-off in Figure 9 are shown as periodic values ​​for clarity, but are not limited to these.

[0100] As shown in Figure 10, an example of each detection value [LSB (Least Significant Bit)], including the off detection value acquired in step S32 of the state setting process, the on detection value acquired in step S34, and the difference detection value calculated in step S35, along with the substrate temperature [°C] acquired in step S35, is plotted according to the elapsed time [sec]. Here, the measurement conditions are assumed to be constant, with a constant gas concentration of the gas G to be detected. Therefore, under normal circumstances where the elapsed time is less than approximately 180 [sec], the difference detection value is approximately constant.

[0101] As shown in Figure 11, corresponding to Figure 10, the difference detection value [LSB] calculated in step S35 and the gas concentration [ppm] calculated in step S35 are plotted according to the elapsed time [sec].

[0102] As shown in Figure 10, a rapid decrease in substrate temperature [°C] occurs after approximately 180 seconds. In response to the rapid decrease in substrate temperature [°C], the detected value at the time of emission increases and reaches the upper limit of the output of the AD converter 53 (65535), causing the differential detected value to decrease. As shown in Figure 11, during the abnormal period in which the differential detected value decreases, the calculated gas concentration [ppm] becomes an abnormal value of threshold A (10000 [ppm]) or higher, reaching the alarm range of threshold A or higher in step S18.

[0103] However, during the abnormal period (the period between the dashed lines in Figure 11), step S14 results in NO, and step S16 is performed instead of steps S18 and S19. Therefore, during the abnormal period, the alarm judgment value (1: alarm state, 0: normal state) does not become an alarm state. Thus, during the abnormal period, no false alarms are generated, which would occur if the actual gas concentration were constant.

[0104] As described above, according to this embodiment, the optical gas sensor device 100 comprises a light source 2, an optical filter 3, a light receiving unit 4, an AD converter 53, and a data processor 55. The light source emits infrared light to the gas to be detected. The optical filter 3 transmits infrared light emitted from the light source 2 through the gas G to be detected. The light receiving unit 4 detects the infrared light incident through the optical filter 3 and generates a detection signal. The AD converter 53 converts the analog detection signal output from the light receiving unit 4 into a digital detection signal. The data processor 55 makes a determination based on the gas concentration of the gas G to be detected calculated from the digital detection signal if the digital detection signal is not at the upper limit (65535) or lower limit (0) of the output of the AD converter 53. The data processor 55 does not make a determination based on the gas concentration of the gas G to be detected if the digital detection signal is at the upper limit or lower limit of the output of the AD converter 53. Furthermore, the optical gas sensor device 100 includes an optical cover 1 that covers the light source 2, optical filter 3, and light receiving unit 4, forming an infrared light path from the light source 2 to the light receiving unit 4. This prevents inaccurate determinations using gas concentration during rapid temperature changes.

[0105] The optical gas sensor device 100 includes a temperature sensor 86 that detects the substrate temperature corresponding to the light receiving unit 4. The data processor 55 calculates the temperature change rate of the detected substrate temperature, and if the temperature change rate is less than a predetermined threshold R, it makes a determination based on the gas concentration of the target gas G calculated from the digital detection signal. The data processor 55 does not make a determination based on the gas concentration of the target gas G if the temperature change rate is greater than or equal to the predetermined threshold R. Even if the upper or lower limit of the AD converter 53 is not reached, if there is a rapid temperature change, the difference between the detected value when the light is on and the detected value when the light is off will be greater than the difference due to the gas concentration, and the accuracy of the detection difference value will deteriorate. Therefore, it is possible to further prevent inaccurate determinations using gas concentration in the event of rapid temperature changes.

[0106] The data processor 55 intermittently drives the light source 2, switching it on and off, and calculates the difference detection value between the analog detection signal when the light is on and the analog detection signal when the light is off. From this difference detection value, it calculates the gas concentration of the gas to be detected G. This suppresses fluctuations in gas concentration due to changes in the substrate temperature corresponding to the light receiving unit 4, thereby reducing power consumption.

[0107] The determination involves two steps: whether to set an alarm state based on whether the gas concentration is above a predetermined threshold A, and whether to set a fault state based on whether the gas concentration is within a predetermined fault range (below threshold C1 or above threshold C2). This prevents inaccurate alarm and fault state determinations based on gas concentration during rapid temperature changes.

[0108] The above description of the embodiment is merely an example of the optical gas sensor device, state setting method, and program according to the present invention, and is not limited thereto.

[0109] For example, in the above embodiment, the light source 2 and the light receiving unit 4 are sealed with sealing devices 20 and 40, but the configuration is not limited to this. The light source 2 and the light receiving unit 4 may also be surface mounted (COB (Chip On Board) mounted) to the substrate 6 via a plurality of adhesive parts. In this configuration as well, at least one of the light source 2 and the light receiving unit 4 may be sealed on the substrate 6 with a sealing device.

[0110] Alternatively, the light source 2 and the light receiving unit 4 may be surface-mounted onto a small substrate acting as a child substrate via multiple adhesive joints. The small substrate on which the light source 2 or the light receiving unit 4 is mounted is then mounted onto the substrate 6 acting as a parent substrate. In this configuration as well, at least one of the light source 2 and the light receiving unit 4 may be sealed on the small substrate with a sealing device.

[0111] Furthermore, the detailed configuration and operation of the optical gas sensor device 100 in the above embodiment can also be modified as appropriate without departing from the spirit of the present invention.

[0112] As described above, the optical gas sensor device, state setting method, and program according to the present invention are suitable for detecting gases such as refrigerants.

[0113] 100 Optical Gas Sensor Device G Gas 1 Optical Cover 110A, 110B Cover Section 11 Gas Inlet Port 111, 112 Gas Inlet 12 Contamination Filter 13 Light Guide Section 131 Inlet Section 132 Outlet Section 133, 134 Gas Inlet 20, 40 Sealing Membrane M Membrane P1, P2 Electrode Pads 21 Ceramic Substrate 211, 212 Recess 213 Bottom Surface 2 Light Source 201 Si Support Layer 202 Heater Layer 3 Optical Filter IR Infrared 31 AR Filter 33 Adhesive 4 Light Receiving Section 5 Signal Processing Section 512 Clock Generation Section 52 Multiplexer 53 AD Converter 54 NVM 55 Data Processor 56 Communication Section 57 Status Output Terminal SCL Clock Line SDA data line 6 board 8 circuit element section 81 switch 82 LDO 83 resistor 84, 85 amplifier 86 temperature sensor 330 equipment 300 MCU 301 communication section 311, 312 resistor 313 capacitor 314 notification section 320 signal line

Claims

1. An optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; a conversion unit that converts the analog detection signal output from the light receiving unit into a digital detection signal; and a control unit that, when the digital detection signal is not at the upper or lower limit of the output of the conversion unit, makes a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal, and does not make a determination based on the gas concentration of the gas to be detected when the digital detection signal is at the upper or lower limit of the output of the conversion unit.

2. The optical gas sensor device according to claim 1, further comprising a temperature detection unit that detects the temperature corresponding to the light receiving unit, wherein the control unit calculates the rate of change of the detected temperature, makes a determination based on the gas concentration of the gas to be detected if the rate of change of the temperature is less than a predetermined first threshold, and does not make a determination based on the gas concentration of the gas to be detected if the rate of change of the temperature is equal to or greater than the predetermined first threshold.

3. An optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects the infrared rays incident through the optical filter and generates a detection signal; a conversion unit that converts the analog detection signal output from the light receiving unit into a digital detection signal; a temperature detection unit that detects the temperature corresponding to the light receiving unit; and a control unit that calculates the rate of change of the detected temperature, and if the rate of change of the temperature is less than a predetermined first threshold, makes a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal, and if the rate of change of the temperature is equal to or greater than a predetermined first threshold, does not make a determination based on the gas concentration of the gas to be detected.

4. The optical gas sensor device according to any one of claims 1 to 3, wherein the control unit intermittently drives the light source to emit light and extinguish light, calculates a difference detection value between the analog detection signal when the light is emitted and the analog detection signal when the light is extinguished, and calculates the gas concentration of the gas to be detected from the difference detection value.

5. The optical gas sensor device according to any one of claims 1 to 3, wherein the determination is at least one of: determining whether or not to set the device to an alarm state based on whether or not the gas concentration is above a predetermined second threshold; and determining whether or not to set the device to a fault state based on whether or not the gas concentration is within a predetermined fault range.

6. An optical gas sensor device according to any one of claims 1 to 3, comprising an optical cover that covers the light source, the optical filter, and the light receiving unit, and forms the optical path of the infrared light from the light source to the light receiving unit.

7. A control method for an optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; and a conversion unit that converts an analog detection signal output from the light receiving unit into a digital detection signal, the control method including a control step of making a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal when the digital detection signal is not the upper or lower limit of the output of the conversion unit, and not making a determination based on the gas concentration of the gas to be detected when the digital detection signal is the upper or lower limit of the output of the conversion unit.

8. A control method for an optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; a conversion unit that converts an analog detection signal output from the light receiving unit into a digital detection signal; and a temperature detection unit that detects the temperature corresponding to the light receiving unit, the control method comprising a control step of calculating the rate of change of the detected temperature, making a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal if the rate of change of the temperature is less than a predetermined first threshold, and not making a determination based on the gas concentration of the gas to be detected if the rate of change of temperature is equal to or greater than the predetermined first threshold.

9. A program to cause the computer of an optical gas sensor device, which comprises a light source that emits infrared rays to a gas to be detected, an optical filter that transmits infrared rays emitted from the light source through the gas to be detected, a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal, and a conversion unit that converts an analog detection signal output from the light receiving unit into a digital detection signal, to function as a control unit that, when the digital detection signal is not the upper or lower limit of the output of the conversion unit, makes a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal, and does not make a determination based on the gas concentration of the gas to be detected when the digital detection signal is the upper or lower limit of the output of the conversion unit.

10. A program to cause a computer for an optical gas sensor device, comprising: a light source that emits infrared rays to a gas to be detected; an optical filter that transmits infrared rays emitted from the light source through the gas to be detected; a light receiving unit that detects infrared rays incident through the optical filter and generates a detection signal; a conversion unit that converts an analog detection signal output from the light receiving unit into a digital detection signal; and a temperature detection unit that detects the temperature corresponding to the light receiving unit, to function as a control unit including a control step that calculates the rate of temperature change of the detected temperature, makes a determination based on the gas concentration of the gas to be detected calculated from the digital detection signal if the rate of temperature change is less than a predetermined first threshold, and does not make a determination based on the gas concentration of the gas to be detected if the rate of temperature change is equal to or greater than the predetermined first threshold.

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