Gas sensor and device having said gas sensor

Abstract

Provided is a gas sensor capable of accurate measurement. This gas sensor (100) comprises: a DC power supply (110); a bridge circuit (BC) which includes a temperature-sensitive detection element (120) and a temperature-sensitive compensation element (130); a power limiting device (150) which is connected in series to the bridge circuit (BC) between a positive electrode and a negative electrode of the DC power supply (110) and supplies power to the bridge circuit (BC); and a first voltage detection unit (140) which detects a differential voltage between output terminals of the bridge circuit (BC).

Description

Gas sensor and device having the gas sensor

[0001] The present invention relates to a gas sensor and a device having the gas sensor.

[0002] For detecting the gas concentration, a thermal conductivity type gas sensor is used (for example, Patent Documents 1 and 2). The gas thermal conductivity type gas sensor utilizes the fact that the thermal conductivity varies depending on the type of gas, and detects the gas concentration based on the change in the thermal conductivity of the gas. The gas thermal conductivity gas sensor has a temperature-sensitive element (for example, a thermistor) whose resistance value changes with temperature, and detects the change in the thermal conductivity of the gas as a temperature change of the gas by this temperature-sensitive element. Examples of devices equipped with a thermal conductivity type gas sensor include air-conditioning equipment, refrigeration and freezing equipment, vehicles (for example, automobiles), and alarm systems (for example, alarm systems for hydrogen stations).

[0003] International Publication No. 2021 / 085182, Japanese Patent Application Laid-Open No. 2018-194409

[0004] Conventional thermal conductivity type gas sensors have a limiting resistor in order to limit the power input to the temperature-sensitive element, like the sensor disclosed in Patent Document 1. However, with such a configuration, fluctuations in the power supply voltage greatly affect the measurement. Also, since the measurement by a thermal conductivity type gas sensor is affected by humidity, some thermal conductivity type gas sensors include a humidity sensor, like the sensor disclosed in Patent Document 2, in order to compensate for the influence of humidity.

[0005] An object of the present invention is to provide a gas sensor capable of accurate measurement.

[0006] To solve the above problems, a gas sensor according to an embodiment of the present invention includes a DC power supply, a bridge circuit including a detection temperature-sensitive element and a compensation temperature-sensitive element, a power limiting device connected in series with the bridge circuit between the positive and negative electrodes of the DC power supply for supplying power to the bridge circuit, and a first voltage detection unit for detecting the differential voltage between the output terminals of the bridge circuit.

[0007] The output power value of the power limiting device may be set based on the heating temperatures of the detection temperature-sensitive element and the compensation temperature-sensitive element.

[0008] The output power value of the power limiting device may be set so that the heating temperature of the sensing temperature element and the compensating temperature element is 100 degrees or less, 80 degrees or less, 60 degrees or less, or 20 degrees or less.

[0009] The DC power supply may be a constant voltage power supply, and the power limiting device may be a constant current device.

[0010] The constant current device may be a constant current diode.

[0011] In the bridge circuit, the series circuit of the temperature sensing element and the compensation temperature sensing element, and the series circuit of the first resistor and the second resistor may be connected in parallel between the input terminals of the bridge circuit.

[0012] In the bridge circuit, the series circuit of the temperature sensing element and the third resistor, and the series circuit of the compensation temperature sensing element and the fourth resistor may be connected in parallel between the input terminals of the bridge circuit.

[0013] The temperature sensing element for detection may include a first temperature sensing element and a second temperature sensing element, the temperature compensating element may include a first temperature compensating element and a second temperature compensating element, and the bridge circuit may be a full bridge circuit composed of the first temperature sensing element, the second temperature sensing element, the first temperature compensating element, and the second temperature compensating element.

[0014] The system may further include a second voltage detection unit that detects the voltage value applied to the bridge circuit.

[0015] The gas sensor may further include a control unit that controls the power output by the DC power supply based on the voltage value detected by the second voltage detection unit.

[0016] The temperature sensing element for detection may be placed in a breathable container, while the temperature sensing element for compensation may be placed in a sealed container.

[0017] The permeable container and the sealed container should preferably be made of a material (e.g., metal) that has thermal conductivity and electromagnetic shielding properties, and should be integrated and thermally bonded together.

[0018] The aforementioned breathable container may have an opening in which a gas filter is placed.

[0019] The gas filter may also be provided with waterproofing capabilities.

[0020] The gas filter may be made of a porous fluororesin.

[0021] The resistance values ​​of the temperature sensing element and the compensation temperature sensing element may be set to 5 kΩ or less when the ambient temperature is 25°C.

[0022] The temperature sensing element and the compensation temperature sensing element may be a thermistor, a resistance thermometer, or a thermopile.

[0023] The thermistor may be a thin-film thermistor.

[0024] The thickness of the substrate for the thin-film thermistor may be 150 μm or less.

[0025] The thin-film thermistor may be trimmed so that the variation in the resistance value of the thin-film thermistor is ±1 percent or less.

[0026] The electrode portion of the thin-film thermistor is connected by a lead portion to a conductive terminal portion inserted into the permeable container or to a conductive terminal portion inserted into the sealed container, and the lead portion may be joined to the electrode portion of the thin-film thermistor by welding.

[0027] The lead portion may be joined to the conductive terminal portion by welding.

[0028] The lead portion may be a lead frame with a thickness of 50 μm or less.

[0029] The thermal conductivity of the lead portion may be set to 80 W / m·K or less.

[0030] An apparatus according to one embodiment of the present invention has the gas sensor.

[0031] This invention makes it possible to provide a gas sensor capable of accurate measurement.

[0032] This is a diagram showing a gas sensor 100 according to one embodiment of the present invention. an example of a temperature sensing element 120 housed in a breathable container 200. This is a diagram showing an example of a temperature sensing element 130 housed in a sealed container 300. This is a diagram showing an example of a breathable container 200 and a sealed container 300 being integrated. This is a diagram showing an example of the change in output voltage value when a constant current is supplied to a full-bridge circuit FB. This is a diagram showing an example of the relationship between the output current value of the power limiting device 150 and the output voltage value of the temperature sensing element 120 when the power limiting device 150 is a constant current device. This is a diagram showing an example of the output characteristics for each humidity when the ambient temperature is 40 degrees when the power limiting device 150 is a constant current device. This is a diagram showing an example of a cross-section of a thin-film thermistor 400. This is a diagram showing an example of a temperature sensing element 120 housed in a breathable container 200. This is a diagram showing an example of a temperature sensing element 130 housed in a sealed container 300. This is a diagram showing an example of a cross-section of a thermopile 800. This figure shows a gas sensor 100 according to one embodiment of the present invention. This figure shows the change in temperature of the detection temperature sensing element 120 and the compensation temperature sensing element 130 when the ambient temperature is changed. This figure shows the change in the value of the voltage input to the first voltage detection unit 140 (the differential voltage between the first output terminal OT1 and the second output terminal OT2) when the ambient temperature is changed.

[0033] <Gas Sensor 100> Figure 1-3 shows a gas sensor 100 according to one embodiment of the present invention. The gas sensor 100 includes a DC power supply 110, a temperature sensing element 120 for detection, a temperature sensing element 130 for compensation, a first voltage detection unit 140, and a power limiting device 150. The gas sensor 100 is a thermal conduction type gas sensor.

[0034] The DC power supply 110 supplies DC power. The DC power supply 110 is, for example, a constant voltage power supply.

[0035] The temperature sensing element 120 and the compensation temperature sensing element 130 are temperature sensing elements whose resistance value changes with temperature, such as thermistors. In particular, the temperature sensing element 120 and the compensation temperature sensing element 130 are thin-film thermistors 400. The temperature sensing element 120 and the compensation temperature sensing element 130 may also be resistance thermometers or thermopiles with a membrane structure manufactured using microfabrication technology. The temperature sensing element 120 and the compensation temperature sensing element 130 are elements with the same structure, differing in whether or not they are positioned to come into contact with the gas being measured. The temperature sensing element 120 and the compensation temperature sensing element 130 should preferably have a resistance value of 5 kΩ or less or 2.5 kΩ or less when the ambient temperature is 25 degrees Celsius. This makes it possible to drive them with a voltage of 5 V or less. When the temperature sensing element 120 and the compensation temperature sensing element 130 are thin-film thermistors 400, it is preferable that the thin-film thermistors 400 be trimmed so that the variation in the resistance value of the thin-film thermistors 400 is ±1 percent or less.

[0036] The temperature sensing element 120 is positioned so as to be in contact with the gas to be measured. The temperature sensing element 120 is placed inside a breathable container 200, for example, as shown in Figure 4. Figure 4 shows an example of a temperature sensing element 120 housed inside a breathable container 200. In the example shown in Figure 4, the container 200 has an opening 210, through which the gas to be measured flows into the container 200. A waterproof gas filter 220 may be placed at the opening 210 of the container 200, as shown in Figure 4. The gas filter 220 may be made of, for example, a porous fluororesin. This makes it possible to reduce the effects of wind.

[0037] On the other hand, the compensating temperature sensor 130 is positioned so as not to come into contact with the gas being measured. The compensating temperature sensor 130 is placed inside a sealed container 300, for example, as shown in Figure 5. Figure 5 shows an example of a compensating temperature sensor 130 housed inside a sealed container 300.

[0038] The permeable container 200 and the sealed container 300 may be integrated and thermally coupled, as shown in Figure 6. In the example shown in Figure 6, the internal region IA1 of the container 200 housing the sensing temperature element 120 and the internal region IA2 of the sealed container 300 housing the compensating temperature element 130 are separated by an inner wall IW. In this way, the internal region IA1 of the container 200 housing the sensing temperature element 120 (i.e., the external environment of the sensing temperature element 120) and the internal region IA2 of the sealed container 300 housing the compensating temperature element 130 (i.e., the external environment of the compensating temperature element 130) can be made almost the same, and as a result, it becomes possible to detect the gas concentration with high accuracy without being affected by the external environment.

[0039] As shown in Figure 1-3, the temperature sensing element 120 and the compensation temperature sensing element 130 form a bridge circuit BC. The bridge circuit BC has two input terminals to which power is supplied (positive terminal PT1, negative terminal PT2) and two output terminals to which the measured voltage is output (first output terminal OT1, second output terminal OT2).

[0040] In the example shown in Figure 1, the temperature sensing element 120 and the compensation temperature sensing element 130 are connected in series between the positive terminal PT1 and the negative terminal PT2. The circuit in which the temperature sensing element 120 and the compensation temperature sensing element 130 are connected in series (first connection circuit SC1) is connected in parallel with the circuit in which the first resistor 160A and the second resistor 160B are connected in series (second connection circuit SC2) between the positive terminal PT1 and the negative terminal PT2. In the example shown in Figure 1, the temperature sensing element 120 is located on the positive terminal PT1 side, but it may also be located on the negative terminal PT2 side.

[0041] In the example shown in Figure 1, the first output terminal OT1 of the bridge circuit BC is connected to the line connecting the temperature sensing element 120 and the compensation temperature sensing element 130, and the second output terminal OT2 of the bridge circuit BC is connected to the line connecting the first resistor 160A and the second resistor 160B. At least one of the first resistor 160A and the second resistor 160B may be a variable resistor. In the example shown in Figure 1, the second resistor 160B is a variable resistor. In this way, even if there is a variation in the resistance value of the temperature sensing element 120 and the resistance value of the compensation temperature sensing element 130, it is possible to compensate for the variation by adjusting the resistance value of the second resistor 160B.

[0042] In the example shown in Figure 2, the temperature sensing element 120 is connected in series with the third resistor 160C, forming a third connection circuit SC3 with the third resistor 160C, and the temperature compensating element 130 is connected in series with the fourth resistor 160D, forming a fourth connection circuit SC4 with the fourth resistor 160D. As shown in Figure 2, the third connection circuit SC3 and the fourth connection circuit SC4 are connected in parallel between the positive terminal PT1 and the negative terminal PT2 of the bridge circuit BC. In the example shown in Figure 2, the temperature sensing element 120 and the temperature compensating element 130 are both located on the positive terminal PT1 side in the third connection circuit SC3 and the fourth connection circuit SC4, but they may also be located on the negative terminal PT2 side.

[0043] In the example shown in Figure 2, the first output terminal OT1 of the bridge circuit BC is connected to the line connecting the temperature sensing element 120 and the third resistor 160C, and the second output terminal OT2 of the bridge circuit BC is connected to the line connecting the compensation temperature sensing element 130 and the fourth resistor 160D. At least one of the third resistor 160C and the fourth resistor 160D may be a variable resistor. In the example shown in Figure 2, the fourth resistor 160D is a variable resistor. In this way, even if there is a variation in the resistance value of the temperature sensing element 120 and the resistance value of the compensation temperature sensing element 130, it is possible to compensate for the variation by adjusting the resistance value of the fourth resistor 160D.

[0044] In the example shown in FIG. 3, the temperature sensing element 120 for detection has a first temperature sensing element 120A for detection and a second temperature sensing element 120B for detection, and the temperature sensing element 130 for compensation has a first temperature sensing element 130A for compensation and a second temperature sensing element 130B for compensation. The first temperature sensing element 120A for detection, the second temperature sensing element 120B for detection, the first temperature sensing element 130A for compensation, and the second temperature sensing element 130B for compensation constitute a full bridge circuit. In the example shown in FIG. 3, a circuit (fifth connection circuit SC5) in which the first temperature sensing element 120A for detection and the first temperature sensing element 130A for compensation are connected in series, and a circuit (sixth connection circuit SC6) in which the second temperature sensing element 120B for detection and the second temperature sensing element 130B for compensation are connected in series are connected in parallel between the positive electrode side terminal PT1 and the negative electrode side terminal PT2. In the example shown in FIG. 3, the first temperature sensing element 120A for detection is arranged on the positive electrode side terminal PT1 side, but the first temperature sensing element 120A for detection may be arranged on the negative electrode side terminal PT2 side. Also, in the example shown in FIG. 3, the second temperature sensing element 120B for detection is arranged on the negative electrode side terminal PT2 side, but the second temperature sensing element 120B for detection may be arranged on the positive electrode side terminal PT1 side.

[0045] In the example shown in FIG. 3, the first output terminal OT1 of the bridge circuit BC is connected to the line connecting the first temperature sensing element 120A for detection and the first temperature sensing element 130A for compensation, and the second output terminal OT2 of the bridge circuit BC is connected to the line connecting the second temperature sensing element 120B for detection and the second temperature sensing element 130B for compensation. By making the bridge circuit BC a full bridge circuit as shown in FIG. 3, it is possible to double the detection sensitivity of the gas.

[0046] The first voltage detection unit 140 is connected to the first output terminal OT1 and the second output terminal OT2, and detects the differential voltage between the first output terminal OT1 and the second output terminal OT2. The gas concentration is calculated based on the differential voltage detected by the first voltage detection unit 140.

[0047] The power limiting device 150 is connected in series with the bridge circuit BC between the positive and negative terminals of the DC power supply 110 and supplies power to the bridge circuit BC. The power limiting device 150 supplies constant power to the bridge circuit BC, for example. If the DC power supply 110 is a constant voltage power supply, the power limiting device 150 is a constant current device and supplies a constant current to the bridge circuit BC. In this case, the constant current device may be a constant current circuit using an operational amplifier, but it is preferable to use a constant current diode. By using a constant current diode as the constant current device, it is possible to reduce the number of components. A boost circuit may be provided between the DC power supply 110 and the power limiting device 150 in order to stably heat the temperature sensing element 120 and the compensation temperature sensing element 130.

[0048] In this embodiment, the power limiting device 150 supplies power to the bridge circuit BC. Therefore, when the power limiting device 150 supplies constant power to the sensing temperature element 120 and the compensating temperature element 130, constant power is supplied to the sensing temperature element 120 and the compensating temperature element 130 even if there is a fluctuation in the voltage of the DC power supply 110. As a result, in this embodiment, when the power limiting device 150 supplies constant power to the sensing temperature element 120 and the compensating temperature element 130, fluctuations in the output voltage values ​​of the sensing temperature element 120 and the compensating temperature element 130 due to fluctuations in the voltage of the DC power supply 110 are suppressed. As a result, in this embodiment, it is possible to provide a gas sensor capable of accurate measurement.

[0049] Figure 7 shows an example of the change in output voltage value when a constant current is supplied to the bridge circuit BC. In the example shown in Figure 7, the change in output voltage value is shown when the concentration of R32 refrigerant gas is 3.6 percent, and three trials were performed. In the example shown in Figure 7, even if the power supply voltage value (voltage value of DC power supply 110) fluctuates by ±10 percent, the fluctuation in the output voltage value is kept to approximately ±3 percent.

[0050] Furthermore, in this embodiment, it becomes possible to expand the voltage range of the DC power supply 110. In conventional thermal conduction gas sensors (i.e., thermal conduction gas sensors that use a limiting resistor to limit the power input to the temperature sensing element), the voltage value of the power supply is 5V ± 10%, but in this embodiment, for example, if the power limiting device 150 is a constant current diode, even if the voltage value of the DC power supply 110 changes significantly (for example, even if the output voltage value of the DC power supply 110 is changed from 5V to 26V), the current flowing into the bridge circuit BC remains almost constant.

[0051] Figure 15 shows the temperature changes of the sensing temperature element 120 and the compensating temperature element 130 when the ambient temperature is changed. In this embodiment, as shown in Figure 15, even if the ambient temperature rises by 100 degrees from -40 degrees to 60 degrees, the temperature of the sensing temperature element 120 and the compensating temperature element 130 rises by only 44 degrees, from 22 degrees to 66 degrees. The temperature change of the sensing temperature element 120 and the compensating temperature element 130 is small compared to the change in ambient temperature. This is because the power limiting device 150 (for example, a constant current diode) limits the value of the current flowing into the bridge circuit BC, thereby suppressing the temperature rise of the sensing temperature element 120 and the compensating temperature element 130. Therefore, in this embodiment, when the sensing temperature element 120 and the compensating temperature element 130 are thermistors, the influence of variations in the B constant of the sensing temperature element 120 and the compensating temperature element 130 on the measured value of the gas sensor 100 is reduced, and the accuracy of measurement can be improved. Furthermore, since the lifespan of a thermistor follows the Arrhenius law, in this embodiment, when the sensing temperature element 120 and the compensating temperature element 130 are thermistors, it is possible to extend the lifespan of the sensing temperature element 120 and the compensating temperature element 130.

[0052] Figure 16 shows the change in the value of the voltage input to the first voltage detection unit 140 (the differential voltage between the first output terminal OT1 and the second output terminal OT2) when the ambient temperature is changed. In conventional thermal conduction gas sensors (i.e., thermal conduction gas sensors that use a limiting resistor to limit the power input to the temperature sensing element), the linearity of the voltage input to the voltage detection device is maintained only within an ambient temperature range of approximately 50 degrees. On the other hand, in this embodiment, as shown in Figure 16, the voltage input to the first voltage detection unit 140 changes linearly over a wide range of 80 degrees from -40 degrees to 40 degrees of ambient temperature, exhibiting characteristics suitable for temperature measurement. Therefore, in this embodiment, it is possible to more accurately capture temperature changes according to the thermal conductivity of the gas, and as a result, this embodiment makes it possible to provide a gas sensor that can perform accurate measurements.

[0053] The gas sensor 100 may further include a second voltage detection unit 170, as shown in Figure 1-3. The second voltage detection unit 170 detects the voltage value applied to the bridge circuit BC. In the example shown in Figure 1-3, the second voltage detection unit 170 is connected to the positive terminal PT1 of the bridge circuit BC, and the negative terminal PT2 of the bridge circuit BC is grounded.

[0054] Since the voltage applied to the bridge circuit BC changes with ambient temperature, information about the ambient temperature can be obtained by detecting the voltage applied to the bridge circuit BC. By obtaining this information about the ambient temperature, it becomes possible to change the alarm level voltage setting of the gas sensor 100 according to the ambient temperature.

[0055] <Heating temperature of the sensing temperature element 120 and the compensating temperature element 130> The output power value of the power limiting device 150 (or, if the power limiting device 150 is a constant current device, the value of the constant current supplied by the constant current device to the bridge circuit BC) should be set based on the heating temperature of the sensing temperature element 120 and the compensating temperature element 130 (i.e., the temperature of the sensing temperature element 120 and the compensating temperature element 130 when heated and measuring the gas concentration). In particular, the output power value of the power limiting device 150 (or, if the power limiting device 150 is a constant current device, the value of the constant current supplied by the constant current device to the bridge circuit BC) should be set so that the heating temperature of the sensing temperature element 120 and the compensating temperature element 130 is 100 degrees or less, 80 degrees or less, 60 degrees or less, or 20 degrees or less.

[0056] Figure 8 shows an example of the relationship between the output current value of the power limiting device 150 and the output voltage value of the temperature sensing element 120 when the power limiting device 150 is a constant current device. In Figure 8, circles indicate the output voltage value when R32 refrigerant gas is present (R32 output voltage value), and squares indicate the output voltage value when R32 refrigerant gas is absent (comparative output voltage value). Here, the output voltage value when R32 refrigerant gas is absent (comparative output voltage value) is the output voltage value that is affected only by humidity when R32 refrigerant gas is absent. Therefore, the degree of humidity influence can be measured by the ratio of the comparative output voltage value to the R32 output voltage value ((comparative output voltage value) / (R32 output voltage value)).

[0057] In the example shown in Figure 8, if the output current value of the power limiting device 150 is 1 mA or less, the influence of humidity (R32 output voltage value / comparative output voltage value) is 12 percent or less. In the example shown in Figure 8, if the output current value of the power limiting device 150 is 1 mA or less, the heating temperature of the sensing temperature element 120 is 20 degrees or less. In other words, by setting the output current value of the power limiting device 150 so that the heating temperatures of the sensing temperature element 120 and the compensation temperature element 130 are 20 degrees or less, it is possible to reduce the influence of humidity to 12 percent or less, and to detect the gas concentration without compensating for the influence of humidity. As a result, by setting the output power value of the power limiting device 150 (or, if the power limiting device 150 is a constant current device, the value of the constant current supplied by the constant current device to the bridge circuit BC) so that the heating temperature of the sensing temperature element 120 and the compensating temperature element 130 is 20 degrees or less, the gas sensor 100 does not need to be equipped with a humidity sensor or a computer for calculating compensation for the effects of humidity, and the manufacturing and maintenance costs of the gas sensor 100 can be reduced.

[0058] Figure 9 shows an example of the output characteristics for different humidity levels when the ambient temperature is 40 degrees Celsius, assuming the power limiting device 150 is a constant current device. In Figure 9, the horizontal axis represents the gas concentration (%), and the vertical axis represents the output voltage value (mV) of the temperature sensing element 120. The circles represent the output characteristics at 30% humidity, the squares represent the output characteristics at 55% humidity, and the triangles represent the output characteristics at 97% humidity. As shown in Figure 9, at a detection voltage of 0.5 mV, the output characteristics for all humidity levels (30%, 55%, and 97%) are included within the range of 1.5% ± 0.72% gas concentration (the range indicated by the arrows in Figure 9), satisfying the IEC standard and the JRA 4068 standard. In the example shown in Figure 8, if the output current value of the power limiting device 150 is 2 mA or less, the heating temperature of the temperature sensing element 120 is 60 degrees Celsius or less. In other words, the output power value of the power limiting device 150 (or, if the power limiting device 150 is a constant current device, the value of the constant current supplied by the constant current device to the bridge circuit BC) can be set so that the heating temperature of the sensing temperature element 120 and the compensating temperature element 130 is 60 degrees or less, thereby satisfying the IEC standard and the JRA 4068 standard, and enabling the detection of gas concentration without compensating for the effects of humidity. Note that the output characteristics when the heating temperature of the sensing temperature element 120 is greater than 100 degrees do not satisfy the IEC standard and the JRA 4068 standard. Therefore, in order to detect gas concentration without compensating for the effects of humidity, it is preferable to set the output power value of the power limiting device 150 (or, if the power limiting device 150 is a constant current device, the value of the constant current supplied by the constant current device to the bridge circuit BC) so that the heating temperature of the sensing temperature element 120 and the compensating temperature element 130 is 100 degrees or less, or 80 degrees or less.

[0059] In the example shown in Figure 2, it is preferable to set the resistance values ​​of the third resistor 160C and the fourth resistor 160D to small values. By doing so, it becomes possible to lower the voltage required to raise the temperature of the temperature sensing element 120 and the compensation temperature sensing element 130 to the heating temperature, and as a result, it becomes possible to reduce the voltage value of the DC power supply 110. Furthermore, by doing so, it is possible to reduce the differential voltage between the first output terminal OT1 and the second output terminal OT2, and it is possible to reduce the voltage applied to the first voltage detection unit 140 without providing an attenuation circuit between the first output terminal OT1 and the second output terminal OT2 and the first voltage detection unit 140.

[0060] <Thin-film thermistor 400> The temperature sensing element 120 and the compensation temperature sensing element 130 are, for example, thin-film thermistors 400 as shown in Figure 4-6. Figure 10 shows an example of a cross-section of the thin-film thermistor 400. As shown in Figure 10, the thin-film thermistor 400 has a substrate 410, a conductive layer 420, a thin-film element layer 430, and a protective insulating layer 440.

[0061] The substrate 410 is formed from an insulating ceramic such as alumina, aluminum nitride, or zirconia, or from a semiconductor material such as silicon or germanium. The shape of the substrate 410 is, for example, rectangular. An insulating thin film is formed on one surface of the substrate 410 by sputtering. The substrate 410 is, for example, extremely thin, with a thickness of 150 μm or less. In particular, a thickness of 50 μm to 150 μm is preferred. By making the substrate 410 of the thermistor 400 a thin film in this way, the heat capacity of the substrate 410 is reduced, making it possible to provide a gas sensor 100 that is highly sensitive and has excellent thermal response.

[0062] The conductive layer 420 is formed on the substrate 410 and constitutes the wiring pattern. The conductive layer 420 is formed, for example, by depositing a thin metal film on the substrate 410 by sputtering. The conductive layer 420 is made of, for example, precious metals such as platinum (Pt), gold (Au), silver (Ag), palladium (Pd), or alloys thereof (for example, Ag-Pd alloy).

[0063] The thin-film element layer 430 is a thermistor composition and is made of an oxide semiconductor having a negative temperature coefficient. The thin-film element layer 430 is deposited on the conductive layer 420 by a sputtering method or the like. The thin-film element layer 430 is electrically connected to the conductive layer 420. The thin-film element layer may also be made of an oxide semiconductor having a positive temperature coefficient. The thin-film element layer 430 is made of two or more elements selected from transition metal elements such as manganese (Mn), nickel (Ni), cobalt (Co), and iron (Fe).

[0064] A portion of the conductive layer 420 is exposed, as shown in Figures 4-6, 10, and this exposed portion functions as an electrode portion 421 for connecting the lead portion 700. The electrode portions 421 are arranged at both ends of the substrate 410, for example, as shown in Figures 4-6, 10.

[0065] The protective insulating layer 440 is formed on the thin-film element layer 430 and the conductive layer 420, and covers a portion of the thin-film element layer 430 and the conductive layer 420. The protective insulating layer 440 is, for example, a protective glass layer formed of borosilicate glass.

[0066] A conductive terminal portion 600 is inserted through an insulating member 500 into a container 200 that houses the temperature sensing element 120 and a sealed container 300 that houses the compensation temperature sensing element 130. The container 200 that houses the temperature sensing element 120 may be composed of an upper part 200T and a lower part 200B through which the conductive terminal portion 600 is inserted, as shown in Figure 4. The sealed container 300 that houses the compensation temperature sensing element 130 may be composed of an upper part 300T and a lower part 300B through which the conductive terminal portion 600 is inserted, as shown in Figure 5. The insulating member 310 is, for example, an insulating material such as glass or resin.

[0067] As shown in Figure 4-6, the electrode portion 421 of the thin-film thermistor 400 is connected to the conductive terminal portion 600 by a lead portion 700. The lead portion 700 is joined to the conductive terminal portion 600 by welding, soldering, or the like, and is electrically connected. For example, the lead portion 700 is joined to the conductive terminal portion 600 by laser welding.

[0068] The lead portion 700 is joined to the electrode portion 421 of the thin-film thermistor 400 by welding and electrically connected. The lead portion 700 is joined to the electrode portion 421 of the thin-film thermistor 400 by, for example, laser welding. In this way, no additional materials such as filler material (brazing material) used in soldering are present between the electrode portion 421 and the lead portion 700, reducing the heat capacity of the connection and making it possible to reduce the thermal time constant. As a result, the thermal response of the thin-film thermistor 400 can be accelerated. Furthermore, it becomes possible to ensure durability against thermal runaway caused by overpower.

[0069] The lead portion 700 should preferably be formed from a material with low thermal conductivity, such as a copper alloy or nickel alloy (e.g., constantan or phosphor bronze). The thermal conductivity of the lead portion 700 should preferably be 80 W / m·K or less. In particular, a thermal conductivity of 5 W / m·K to 25 W / m·K is preferred. Furthermore, the lead portion 700 should be a lead frame with a thickness of 50 μm or less. In particular, a thickness of 10 μm to 50 μm is preferred. The lead portion 700 may also be a thin wire, in which case a diameter of 30 μm to 100 μm is preferred. The cross-sectional area of ​​the lead portion 700 should be 0.2 mm². ２ It is preferable to have the following: In particular, the cross-sectional area of ​​the lead portion 700 should be 0.001 mm². ２ -0.03 mm ２ This is preferable. By lowering the thermal conductivity of the lead portion 700 and reducing the thickness and cross-sectional area of ​​the lead portion 700, the heat capacity of the lead portion 700 and the amount of heat dissipated in the lead portion 700 are reduced. As a result, the thin-film thermistor 400 is kept in a heated state, making it possible to provide a gas sensor 100 that is highly sensitive and has excellent thermal responsiveness.

[0070] The container 200 housing the temperature sensing element 120 and the sealed container 300 housing the temperature compensation element 130 are made of a material (for example, metal) that has thermal conductivity and electromagnetic shielding properties, such as copper, silver, aluminum, nickel, iron, or alloys of these metals. The container 200 housing the temperature sensing element 120 and the sealed container 300 housing the temperature compensation element 130 may also be made of ceramic, resin material, etc. In this case, it is preferable to apply metal plating or the like to the inner wall surfaces of the container 200 housing the temperature sensing element 120 and the sealed container 300 housing the temperature compensation element 130 so that the inner wall surfaces of the container 200 housing the temperature sensing element 120 and the sealed container 300 housing the temperature compensation element 130 have the function of reflecting infrared rays.

[0071] If the container 200 housing the temperature sensing element 120 is composed of an upper part 200T and a lower part 200B through which the conductive terminal portion 600 is inserted, as shown in Figure 4, and the sealed container 300 housing the compensation temperature sensing element 130 is composed of an upper part 300T and a lower part 300B through which the conductive terminal portion 600 is inserted, as shown in Figure 5, then the lower parts 200B and 300B may be made of insulating material. Doing so eliminates the need for an insulating member 500. The conductive terminal portion 600 may also be made of a printed circuit board or the like.

[0072] <Thermopile 800> The temperature sensing element 120 and the compensation temperature sensing element 130 may be, for example, a thermopile 800 as shown in Figures 11 and 12. Figure 13 shows an example of a cross-section of the thermopile 800. As shown in Figure 13, the thermopile 800 has a substrate 810, an insulating film 820, an n-type polycrystalline silicon layer 830, a metal thin film layer 840, and an electrode pad 850.

[0073] An insulating film 820, such as silicon dioxide or silicon nitride, is provided on the lower surface of the substrate 810, and cavities CA are formed in the substrate 810 by anisotropic etching, as shown in Figure 13. The substrate 810 is formed from a silicon material.

[0074] A membrane portion 821 made of an insulating film 820 is formed on the upper surface of the substrate 810 and on the cavity CA. On the membrane portion 821, a thermocouple's hot junction portion and cold junction portion (n-type polycrystalline silicon layer 830) are laminated via the insulating film 820. The hot junction portion of the n-type polycrystalline silicon layer 830 is sequentially connected to the cold junction portion of the adjacent n-type polycrystalline silicon layer 830 by a metal thin film layer 840, forming a thermoelectric element array. The final end of the thermoelectric element array is connected to an electrode pad 850. As shown in Figures 11 and 12, the electrode pad 850 is electrically connected to a conductive terminal portion 600 by a lead portion 700.

[0075] <Control Unit 180> As shown in Figure 14, the gas sensor 100 further includes a control unit 180, and the control unit 180 may include a first voltage detection unit 140 and a second voltage detection unit 170. The control unit 180 is, for example, a computer such as a microcontroller, and includes, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and input / output I / O (Input / Output).

[0076] In addition to the first voltage detection unit 140 and the second voltage detection unit 170, the control unit 180 may further include, for example, a gas concentration calculation unit 181 and a power supply control unit 182, as shown in Figure 14.

[0077] The gas concentration calculation unit 181 calculates the gas concentration based on the differential voltage between the first output terminal OT1 and the second output terminal OT2, which is detected by the first voltage detection unit 140.

[0078] The power control unit 182 controls the power output by the DC power supply 110. The power control unit 182 controls the power output by the DC power supply 110 based on, for example, the voltage value applied to the bridge circuit BC detected by the second voltage detection unit 170. At this time, the DC power supply 110 has a power supply that outputs DC power and a power supply circuit that controls the power output from the power supply, and the power control unit 182 controls the power output by the DC power supply 110 by controlling this power supply circuit.

[0079] As described above, according to the above embodiment, it is possible to improve gas detection sensitivity and gas selectivity (for example, excluding humidity from the gas to be detected), and to reduce power consumption. Therefore, according to the above embodiment, it is possible to provide a device equipped with a gas sensor that can improve gas detection performance. Examples of devices equipped with the gas sensor according to the above embodiment include air conditioning equipment, refrigeration equipment, vehicles (for example, automobiles), and alarm systems (for example, alarm systems for hydrogen stations).

[0080] The present invention has been described above with reference to preferred embodiments. While specific examples have been provided to illustrate the present invention, various modifications and changes can be made to these examples without departing from the spirit and scope of the invention as described in the claims. The present invention is not limited to the configuration of the above embodiments, and various modifications are possible without departing from the gist of the invention. Furthermore, the above embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made. These embodiments and their variations are included in the scope and gist of the invention, as well as in the scope of the invention and its equivalents as described in the claims.

[0081] 100 Gas sensor 110 DC power supply 120 Temperature sensing element for detection 120A First temperature sensing element for detection 120B Second temperature sensing element for detection 130 Temperature sensing element for compensation 130A First temperature sensing element for compensation 130B Second temperature sensing element for compensation 131 Container 140 First voltage detection unit 150 Power limiting device 160A First resistor 160B Second resistor 160C Third resistor 160D Fourth resistor 170 Second voltage detection unit 180 Control unit 181 Gas concentration calculation unit 182 Power control unit 200 Container 200T Top of container 200 200B Bottom of container 200 210 Opening of container 200 220 Gas filter 300 Sealed container 300T Upper part of sealed container 300 300B Lower part of sealed container 300 400 Thin film thermistor 410 Substrate 420 Conductive layer 430 Thin film element layer 440 Protective insulating layer 500 Insulating member 600 Conductive terminal part 700 Lead part 800 Thermopile 810 Substrate 820 Insulating film 821 Membrane part 830 n-type polycrystalline silicon layer 840 Metal thin film layer 850 Electrode pad

Claims

1. A gas sensor comprising: a DC power supply; a bridge circuit including a temperature sensing element for detection and a temperature sensing element for compensation; a power limiting device connected in series with the bridge circuit and supplying power to the bridge circuit between the positive and negative terminals of the DC power supply; and a first voltage detection unit for detecting the differential voltage between the output terminals of the bridge circuit.

2. The gas sensor according to claim 1, wherein the output power value of the power limiting device is set based on the heating temperature of the sensing temperature element and the compensating temperature element.

3. The gas sensor according to claim 2, wherein the output power value of the power limiting device is set such that the heating temperature of the sensing temperature element and the compensating temperature element is 100 degrees or less, 80 degrees or less, 60 degrees or less, or 20 degrees or less.

4. The gas sensor according to any one of claims 1 to 3, wherein the DC power supply is a constant voltage power supply and the power limiting device is a constant current device.

5. The gas sensor according to claim 4, wherein the constant current device is a constant current diode.

6. The gas sensor according to any one of claims 1 to 3, wherein a series circuit of the temperature sensing element and the compensation temperature sensing element and a series circuit of the first resistor and the second resistor are connected in parallel between the input terminals of the bridge circuit.

7. The gas sensor according to any one of claims 1 to 3, wherein a series circuit of the temperature sensing element and a third resistor and a series circuit of the compensation temperature sensing element and a fourth resistor are connected in parallel between the input terminals of the bridge circuit.

8. The gas sensor according to any one of claims 1 to 3, wherein the temperature sensing element for detection comprises a first temperature sensing element and a second temperature sensing element, the temperature compensating element comprises a first temperature compensating element and a second temperature compensating element, and the bridge circuit is a full bridge circuit composed of the first temperature sensing element, the second temperature sensing element, the first temperature compensating element, and the second temperature compensating element.

9. The gas sensor according to any one of claims 1 to 3, further comprising a second voltage detection unit for detecting the voltage value applied to the bridge circuit.

10. The gas sensor according to claim 9, further comprising a control unit that controls the power output by the DC power supply based on the voltage value detected by the second voltage detection unit.

11. The gas sensor according to any one of claims 1 to 3, wherein the temperature sensing element for detection is disposed in a breathable container, and the temperature sensing element for compensation is disposed in a sealed container.

12. The gas sensor according to claim 11, wherein the permeable container and the sealed container are made of a material having thermal conductivity and electromagnetic shielding properties, are integrated together, and are thermally bonded.

13. The gas sensor according to claim 11, wherein the breathable container has an opening in which a gas filter is arranged.

14. The gas sensor according to claim 13, wherein the gas filter has waterproof performance.

15. The gas sensor according to claim 13, wherein the gas filter is a porous fluororesin.

16. The gas sensor according to any one of claims 1 to 3, wherein the resistance values ​​of the temperature sensing element and the compensation temperature sensing element are 5 kΩ or less when the ambient temperature is 25°C.

17. The gas sensor according to any one of claims 1 to 3, wherein the temperature sensing element for detection and the temperature sensing element for compensation are a thermistor, a resistance thermometer, or a thermopile.

18. The gas sensor according to claim 17, wherein the thermistor is a thin-film thermistor.

19. The gas sensor according to claim 18, wherein the thickness of the substrate of the thin-film thermistor is 150 μm or less.

20. The gas sensor according to claim 18, wherein the thin film thermistor is trimmed and the variation in the resistance value of the thin film thermistor is ±1 percent or less.

21. The gas sensor according to claim 18, wherein the electrode portion of the thin film thermistor is connected by a lead portion to a conductive terminal portion inserted into the permeable container or to a conductive terminal portion inserted into the sealed container, and the lead portion is joined to the electrode portion of the thin film thermistor by welding.

22. The gas sensor according to claim 21, wherein the lead portion is joined to the conductive terminal portion by welding.

23. The gas sensor according to claim 21, wherein the lead portion is a lead frame with a thickness of 50 μm or less.

24. The gas sensor according to claim 21, wherein the thermal conductivity of the lead portion is 80 W / m·K or less.

25. An apparatus having a gas sensor according to any one of claims 1 to 3.

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