JP6330492B2 - Gas sensor element - Google Patents

Description

  The present invention relates to a gas sensor element that detects a target gas using a temperature-sensitive resistance element and a heater (heating resistance element).

  As one of means for detecting the target gas, one using a difference between the thermal conductivity in the atmosphere and the thermal conductivity of the target gas is known. The temperature sensing resistor element is heated by a heater, and the resistance value of the temperature sensing resistor element changes depending on the difference in thermal conductivity between the atmosphere and the target gas, and the target gas is detected from the amount of change in the resistance value. It is.

  7 and 8 show a cross-sectional structure of a conventional gas sensor element 101. FIG. In FIG. 7, a detection sensor 102 that detects a target gas and an environmental sensor 103 that detects an environmental temperature are formed on a substrate 104. The detection sensor 102 includes a temperature sensitive resistance element 105 and a heater 106. The environmental sensor 103 includes a temperature sensitive resistance element 107. Although not shown, the temperature-sensitive resistance elements 105 and 107 are composed of a temperature-sensitive resistance layer and electrodes for inputting / outputting signals, and the heater 106 is composed of a heating unit and electrodes for inputting / outputting signals, An insulating layer for electrical isolation is formed between the heaters 106.

  In FIG. 8, the heat capacity of the sensor portion is reduced by removing the substrate 104 of the detection sensor 102 and the environmental sensor 103. That is, the cavity 108 for making the sensor part into a hollow structure is formed, and it has a membrane structure. This improves the sensitivity and response speed of the sensor.

  Patent Document 1 discloses an absolute humidity sensor in which the target gas is humidity and an indirectly heated temperature sensitive resistance element is used. In this sensor element, a temperature sensitive resistance element and a heating resistance element are formed on a membrane structure. The resistance value of the temperature-sensitive resistance element changes depending on the difference in thermal conductivity due to the difference in humidity when the temperature-sensitive resistance element is heated by the heating resistance element. It is disclosed that humidity is detected by converting the change in the resistance value. The humidity detection uses two sensor elements, one is hermetically sealed in the case, and the other is structured to take in the outside air in the case with a through hole. A hermetically sealed one is used as an environmental (reference) sensor, a one having a through hole is used as a detection sensor, and a humidity change is obtained from the difference.

JP 2009-168649 A

  In the humidity sensor disclosed in Patent Document 1, a temperature-sensitive resistance element and a heating resistance element are formed in a membrane structure, thereby providing a sensor with high response speed and high accuracy and excellent mechanical strength. . However, the resistance value change (time-dependent change) of the temperature-sensitive resistance element over time is not described. The temperature-sensitive resistance element is heated by the heating resistance element, whereby the change with time is accelerated. Changing the resistance value means changing the output of the sensor, which becomes a sensor error.

  The present invention has been made in consideration of the above points, and it is possible to reduce a sensor error caused by the resistance value of the temperature-sensitive resistance element fluctuating with the lapse of time due to heating by the heating resistance element. A gas sensor element is provided.

  The present invention includes a first sensor having a function of detecting a target gas and a second temperature sensitive resistor element, including a first temperature sensitive resistor element and a first heater, and a second sensor for detecting an environmental temperature. And a third sensor for correcting the first sensor, wherein different pulse voltages are applied to the first heater and the second heater. A gas sensor element that is applied.

  According to the present invention, in addition to the detection sensor and the environment sensor, a correction sensor is prepared, thereby making it possible to reduce sensor errors due to changes over time. Here, the detection sensor is a first sensor, which is a sensor having a function of detecting a target gas. The environmental sensor is a second sensor, which is a sensor that detects the temperature of the surrounding environment. The correction sensor is a third sensor, which is a sensor for correcting resistance variation due to a change with time of the detection sensor.

  The on-time of the pulse voltage applied to the second heater in the present invention may be a gas sensor element shorter than the on-time of the pulse voltage applied to the first heater.

  In the present invention, the pulse voltage cycle applied to the second heater may be a gas sensor element longer than the pulse voltage cycle applied to the first heater.

  In the present invention, the first sensor and the third sensor may be gas sensor elements formed on a membrane structure.

  In the present invention, the target gas may be a gas sensor element that is humidity.

  According to the present invention, it is possible to reduce a sensor error caused by a change in the resistance value of the temperature-sensitive resistance element due to a change with time due to heating by the heating resistance element.

It is sectional drawing of the gas sensor element in embodiment. It is sectional drawing of the gas sensor element in embodiment. It is detail drawing of the cross-sectional structure of the gas sensor element in embodiment. It is explanatory drawing which shows schematic structure of a gas sensor element and a detection apparatus. It is a flowchart which shows the procedure of gas detection. It is a timing chart of pulse voltage in an embodiment. It is sectional drawing of the gas sensor element in a prior art example. It is sectional drawing of the gas sensor element in a prior art example.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined. In addition, various omissions, substitutions, or changes of components can be made without departing from the scope of the present invention.

  1 and 2 show a cross-sectional structure of the gas sensor element 20 according to the present embodiment. In FIG. 1, a detection sensor 9 that detects a target gas, an environmental sensor 10 that detects an environmental temperature, and a correction sensor 11 that corrects a detection output are formed on a substrate 21. The detection sensor 9 includes the first temperature-sensitive resistance element 1 and the first heater 7. The environmental sensor 10 is composed of the second temperature sensitive resistance element 2. The correction sensor 11 includes the third temperature sensitive resistance element 3 and the second heater 8.

  In FIG. 2, the heat capacity of the sensor portion is reduced by removing the substrate 21 of the detection sensor 9, the environmental sensor 10, and the correction sensor 11. That is, a hollow portion 22 for forming the sensor portion with a hollow structure is formed, and a membrane structure is formed. This improves the sensitivity and response speed of the sensor. In FIG. 2, all the sensor portions of the detection sensor 9, the environmental sensor 10, and the correction sensor 11 have a hollow structure, but only the detection sensor 9 and the correction sensor 11 have a hollow structure, and the substrate 21 of the environmental sensor 10 remains. It doesn't matter.

  A detailed view of the cross-sectional structure of FIG. 2 is shown in FIG. A lower protective film 23 is formed on the substrate 21 and the cavity 22. A heater electrode 25 constituting the first heater 7 on the lower protective film 23 and the second heater 8 on the portion serving as the correction sensor 11 is formed. The heater electrode 25 has a meander shape. An intermediate protective film 24 is formed on the heater electrode 25. The intermediate protective film 24 has a function for electrically separating the first temperature-sensitive resistance element 1 and the first heater 7, and the third temperature-sensitive resistance element 3 and the second heater 8. The first temperature-sensitive resistance element 1 is provided on the intermediate protective film 24 as the detection sensor 9, the second temperature-sensitive resistance element 2 is provided on the environment sensor 10, and the third temperature-sensitive resistance element is provided on the correction sensor 11. 3 is formed. The temperature-sensitive resistance electrode 26 has a comb-teeth shape and is an electrode pair. A temperature sensitive resistance film 27 is formed on the comb-shaped electrode pair. An upper protective film 28 is formed on the temperature sensitive resistance film 27. The upper protective film 28 where the signal of the temperature sensitive resistance electrode 26 is taken out is removed, and a pad electrode 29 is formed in the removed portion.

  FIG. 4 is an explanatory diagram showing a schematic configuration of the gas sensor element and the detection device 19 according to the present embodiment. As shown in FIG. 4, the gas sensor element and detection device 19 includes a detection sensor 9, an environment sensor 10, and a correction sensor 11. The detection sensor 9 includes a first heater 7 connected to the pulse voltage source 17 controlled by the MPU 16 and the first temperature sensitive resistance element 1. The first temperature sensitive resistance element 1 is connected in series with a first reference resistor 4 connected to a constant voltage power source 18. The environmental sensor 10 includes a second reference resistor 5 connected to the constant voltage power supply 18 and a second temperature-sensitive resistor element 2 connected in series to the second reference resistor 5. The correction sensor 11 is connected in series to the second heater 8 connected to the pulse voltage source 17 controlled by the MPU 16, the third reference resistor 6 connected to the constant voltage power supply 18, and the third reference resistor 6. And a third temperature-sensitive resistance element 3.

  The detection output (Vd) is a voltage output from the connection point between the first reference resistor 4 and the first temperature-sensitive resistance element 1 of the detection sensor 9, and the voltage output is A / D via the first impedance converter 12. The conversion unit 15 converts the analog signal into a digital signal, and the MPU 16 performs arithmetic processing. The environmental output (Vc) is a voltage output from the connection point between the second reference resistor 5 and the second temperature-sensitive resistance element 2 of the environmental sensor 10, and the voltage output is A / D via the second impedance converter 13. The conversion unit 15 converts the analog signal into a digital signal, and the MPU 16 performs arithmetic processing. The correction output (Vr) is a voltage output from the connection point of the third reference resistor 6 and the third temperature-sensitive resistance element 3 of the correction sensor 11, and the voltage output is A / D via the third impedance converter 14. The conversion unit 15 converts the analog signal into a digital signal, and the MPU 16 performs arithmetic processing. As the gas sensor element and the detection device, an output interface and the like are also required. However, the configuration of the present invention is omitted because it is not a main configuration.

  FIG. 5 is a flowchart showing a gas detection procedure according to this embodiment. The procedure for reducing the sensor error from the detection output (Vd), environmental output (Vc), and correction output (Vr) is shown.

  In step 30, a pulse voltage is applied to the first heater 7. By applying a pulse voltage to the first heater 7, the first temperature-sensitive resistance element 1 is heated. The resistance value of the first temperature-sensitive resistance element 1 in the heated state changes under the influence of the thermal conductivity of the target gas. The voltage output from the connection point between the changed resistance value and the first reference resistor 4 is processed by the MPU 16 as a detection output (Vd).

  In step 31, the MPU 16 counts and stores that the pulse voltage is applied to the first heater 7. By memorizing the number of times of application of the pulse voltage, it is grasped how many times the first temperature-sensitive resistance element 1 has been heated.

  In step 32, a correction detection output (Vd ') is obtained from the detection output (Vd) and the correction value. The initial value of the correction value is 0, and the correction detection output (Vd ′) when the correction value is 0 is the same as the detection output (Vd).

  In step 33, the target gas is detected from the correction detection output (Vd ′) and the value of the environmental output (Vc) calculated by the MPU 16. The environmental output (Vc) is obtained simultaneously with the timing at which the pulse voltage is applied to the first heater 7 and the detection output (Vd) is output. The environmental temperature is calculated from the environmental output (Vc). The concentration of the target gas can be obtained by calculating the influence of the thermal conductivity of the target gas from the value of the corrected detection output (Vd ′) with the ambient temperature as a reference.

  In step 34, it is determined whether the measurement is finished or continued. When continuing, it moves to step 35. In the case of end, the measurement ends.

  In step 35, it is determined whether or not the number of times the pulse voltage is applied to the first heater is a specified number. The specified number of times is set in the MPU 16 before the measurement is started. If the specified number has not been reached, the process proceeds to step 31. If the specified number has been reached, the process proceeds to step 36.

  In step 36, a pulse voltage is applied to the first heater 7 and the second heater 8. By applying a pulse voltage to the first heater 7, the first temperature-sensitive resistance element 1 is heated. The resistance value of the first temperature-sensitive resistance element 1 in the heated state changes under the influence of the thermal conductivity of the target gas. A voltage output from the connection point between the changed resistance value and the first reference resistor 4 is output as a detection output (Vd). By applying a pulse voltage to the second heater 8, the third temperature-sensitive resistance element 3 is heated. The resistance value of the third temperature-sensitive resistance element 3 in the heated state changes under the influence of the thermal conductivity of the target gas. A voltage output from the connection point of the changed resistance value and the third reference resistor 6 is output as a correction output (Vr).

  In step 37, the MPU 16 compares the detection output (Vd) and the correction output (Vr) to obtain the difference between the detection output (Vd) and the correction output (Vr). If there is no change in the resistance value of the first temperature-sensitive resistance element 1 due to heating by the first heater 7, the detection output (Vd) and the correction output (Vr) are set to have the same value. When the resistance value of the first thermosensitive resistance element 1 is changed by the heating by the first heater 7, the detection output (Vd) and the correction output (Vr) show different values, and the difference therebetween. The amount of change in the resistance value of the first temperature-sensitive resistance element 1 due to the heating by the first heater 7 is indicated. The correction value obtained by this comparison operation is used in step 32.

  In step 38, the number of times the pulse voltage is applied to the first heater 7 stored in the MPU 16 is reset, and the process proceeds to step 32.

  According to the above procedure, it is possible to reduce the sensor error due to the resistance change of the first temperature-sensitive resistance element 1 by obtaining the correction value according to the specified number of times that the pulse voltage is applied to the first heater 7. It becomes.

  FIG. 6 is a pulse voltage timing chart according to the present embodiment. This pulse voltage is a pulse voltage applied in the flowchart of FIG. The voltage pulse 50 applied to the first heater 7 has a certain period, and the first heater 7 is heated at the on time of the pulse voltage, that is, at the rising portion (52, 53, 54, 55, 56). The detection output (Vd) and the environmental output (Vc) are read at this rising portion. The voltage pulse 51 applied to the second heater 8 has a constant cycle, and the second heater 8 is heated at the rising portions (57, 58). At this rising portion, the correction output (Vr) is read.

A specific configuration of the gas sensor element 20 will be described. The gas sensor element 20 includes a detection sensor 9, an environment sensor 10, and a correction sensor 11. The first temperature-sensitive resistance element 1 of the detection sensor 9, the second temperature-sensitive resistance element 1 of the environmental sensor 10, and the third temperature-sensitive resistance element 1 of the correction sensor 11 are NTC (Negative Temperature Coefficient) thermistors, and the temperature It has the characteristic that the resistance value decreases as the value rises. The resistance value with respect to the temperature of the NTC thermistor can be approximately expressed by the following formula (Formula 1).
In the equation, R _TH is the thermistor resistance value at temperature T, R ₀ is the thermistor resistance value at temperature T ₀ , and B is the relationship between temperature T and thermistor resistance values R _{TH and} R ₀ at T _0. Is a constant representing The first temperature-sensitive resistance element 1 and the third temperature-sensitive resistance element 3 show 2000 kΩ at 25 ° C., 30 kΩ at 200 ° C., and the B constant is 3400. The second temperature sensitive resistance element shows 100 kΩ at 25 ° C., 1.5 kΩ at 200 ° C., and the B constant is 3400.

  The first heater 7 of the detection sensor 9 and the second heater 8 of the correction sensor 11 are platinum resistors, and generate heat due to Joule heat when a pulse voltage is applied. The first heater 7 and the second heater 8 have a resistance of 140Ω, and the first temperature sensing resistor element 1 and the third temperature sensing resistor element are applied by applying a voltage of 1.5 V at the rising edge of the pulse voltage. 3 are each heated to 200 ° C. A table summarizing the above relationships is shown in Table 1.

  As the temperature sensitive resistance element is heated to 200 ° C., the temperature sensitive resistance element changes with time. When the time during which the pulse voltage is applied is 100 h, the resistance value of the temperature-sensitive resistance element is increased by 0.4%. When the time is 500 h, the resistance value of the temperature-sensitive resistance element is increased by 2.0% and when it is 1000 h, The resistance value of the temperature sensitive resistance element increases by 3.0%. When converted to a resistance value of 30 kΩ, it becomes 30.15 kΩ at 100 h, 30.60 kΩ at 500 h, and 30.90 kΩ at 1000 h.

  The voltage of the constant voltage power supply 18 is 3 V, the first reference resistor 4 is 30 kΩ, the second reference resistor is 100 kΩ, and the third reference resistor is 30 kΩ. The detection output (Vd) and the environmental output (Vc) in the initial state ), The correction output (Vr) is 1.5V.

  When the measurement using the gas sensor element is performed, the first temperature-sensitive resistance element 1 is heated to 200 ° C. by the pulse voltage applied to the first heater 7 and is heated by performing the measurement for a long time. Time is accumulated. As a result, a change with time occurs in the first temperature-sensitive resistance element 1, and an error occurs in the detection output (Vd). If the error at 0 h is 0.0%, an error of 0.2% at 100 h, 0.99% at 500 h, and 1.48% at 1000 h will occur. Table 2 summarizes the above relationships.

  The period in which the pulse voltage is applied to the second heater 8 is set to 10 times the period in which the pulse voltage is applied to the first heater 7. The application count in step 31 is set to 10. Under this condition, measurement is performed according to the flowchart of FIG. 5, so that when the integration time due to heating reaches 1000 h, the error of the detection output (Vd) is 1.48%, and the correction output (Vr ) Is within 0.2%, and the sensor error can be reduced by obtaining the correction value from this correction output (Vr). Thus, it has been shown that a gas sensor element with reduced sensor error is provided.

  The present invention is mounted on industrial equipment and environmental monitoring devices, and is used for the purpose of detecting a target gas.

DESCRIPTION OF SYMBOLS 1 1st temperature sensitive resistance element 2 2nd temperature sensitive resistance element 3 3rd temperature sensitive resistance element 4 1st reference resistance 5 2nd reference resistance 6 3rd reference resistance 7 1st heater 8 2nd Heater 9 detection sensor 10 environmental sensor 11 correction sensor 12 first impedance conversion unit 13 second impedance conversion unit 14 third impedance conversion unit 15 A / D conversion unit 16 MPU
DESCRIPTION OF SYMBOLS 17 Pulse voltage source 18 Constant voltage power supply 19 Gas sensor element and detection apparatus 20 Gas sensor element 21 Substrate 22 Cavity part 101 Gas sensor element 102 Detection sensor 103 Environmental sensor 104 Substrate 105, 107 Temperature sensitive resistance element 106 Heater 108 Cavity part

Claims (4)

A first sensor including a first temperature-sensitive resistance element and a first heater and having a function of detecting a target gas; a second sensor including a second temperature-sensitive resistance element and detecting an environmental temperature; A third sensor that includes a third temperature-sensitive resistance element and a second heater and that corrects the first sensor , wherein the first sensor and the third sensor are formed on a membrane structure; cage, wherein the first heater and different pulse voltages to the second heater is applied, the said third sensor and the first sensor is a gas sensor element characterized Rukoto is heated to the same temperature. 2. The gas sensor element according to claim 1, wherein an ON time of a pulse voltage applied to the second heater is shorter than an ON time of a pulse voltage applied to the first heater. 3. The gas sensor element according to claim 2, wherein a pulse voltage cycle applied to the second heater is longer than a pulse voltage cycle applied to the first heater. The gas sensor element according to any one of claims 1-3, wherein the target gas is moisture.

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