JP2007285849A - Gas concentration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and space-saving gas concentration detector capable of detecting accurately a gas concentration without being affected by a gas temperature of measured gas. <P>SOLUTION: A resistance/voltage conversion circuit 20 supplies a current to a temperature measuring resistor Rs arranged in a supply passage of the measured gas and having a resistance value varied depending on a temperature, to generate a voltage in response to the resistance value of the temperature measuring resistor Rs. A CPU 25a switches a current supplied to the temperature measuring resistor Rs by an FETQ, between a current Is1 with a level of making a temperature of the temperature measuring resistor Rs higher than a peripheral temperature, and a current Is2 with a level of making the temperature of the temperature measuring resistor Rs equal to the peripheral temperature. The CPU 25a detects a voltage in response to the resistance value of the temperature measuring resistor Rs generated by the resistance/voltage conversion circuit 20, and the gas concentration is detected based on the voltage in response to the resistance value of the detected temperature measuring resistor Rs. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gas concentration detection device, and more particularly to a gas concentration detection device that detects the concentration of a gas to be measured such as hydrogen gas.

  As the above-described gas concentration detection device, one using a resistance temperature detector that generates heat and changes its resistance value depending on temperature is known. First, the principle of the gas concentration detector using this resistance temperature detector will be described. The resistance temperature detector is disposed in the supply path of the gas to be measured. As the concentration of the measured gas supplied increases, the thermal conductivity of the measured gas increases, and the measured gas takes more heat from the resistance temperature detector. As a result, the resistance value of the resistance temperature detector decreases. That is, the resistance value of the resistance temperature detector becomes a value corresponding to the concentration of the gas to be measured, and the gas concentration can be detected based on the resistance value of the resistance temperature detector.

  A humidity sensor shown in FIG. 10 has been proposed as an example of the above-described gas concentration detection device (Patent Document 1). This humidity sensor is a sensor that detects the concentration of water vapor (measuring gas) in the atmosphere. In the figure, R is a resistance temperature detector. A resistance R1H and a resistance R1L are connected in series to the resistance temperature detector R via a switch S. The resistor R1H and the resistor R1L are connected in parallel to each other.

  A series circuit composed of the resistor R2 and the resistor R3 is connected in parallel to the series circuit composed of the resistance temperature detector R and the resistor R1H or the resistor R1L. That is, a bridge circuit is formed by the resistance temperature detector R, the resistor R1H or the resistor R1L, the resistor R2, and the resistor R3. The power supply device 3 applies a voltage to the resistance temperature detector R via the switch S and causes a current to flow to generate Joule heat to bring the resistance temperature detector R to a predetermined temperature. Further, the temperature detector 5 gives information on the temperature of the measurement atmosphere to the correction device 4.

  The operation of the switch S described above is controlled by the switching control device SC. When the switching signal S1 output from the switching control device SC is H (see FIG. 11A), the contact of the switch S is connected to the resistor R1H side. Thereby, only resistance R1H among resistance R1H and resistance R1L is connected in series with resistance temperature detector R. When the resistor R1H is connected to the resistance temperature detector R, the current I supplied to the resistance temperature detector R is IH (see FIG. 11B), and the heating temperature of the resistance temperature detector R is 300 °. C or higher.

  On the other hand, when the switching signal S1 output from the switching control device SC is L (see FIG. 11A), the contact of the switch S is connected to the resistor R1L side. Thereby, only resistance R1L is connected in series with resistance temperature detector R among resistance R1H and resistance R1L. When the resistor R1L is connected to the resistance temperature detector R, the current I supplied to the resistance temperature detector R becomes IL (see FIG. 11B), and the heating temperature of the resistance temperature detector R is 100 °. C to 150 ° C.

  When the resistance thermometer R generates heat at 300 ° C. or more, the resistance value of the resistance thermometer R varies depending on the amount of water vapor contained in the atmosphere. That is, the output voltage VH of the bridge circuit when the resistance temperature detector R generates heat at 300 ° C. or more is a voltage corresponding to the amount of water vapor contained in the atmosphere, that is, the humidity (see FIG. 11C). ).

  On the other hand, when the resistance thermometer R generates heat between 100 ° C. and 150 ° C., it becomes insensitive to the amount of water vapor, and the resistance value of the resistance thermometer R varies depending on the ambient temperature. That is, the output voltage VL of the bridge circuit when the resistance temperature detector R generates heat at 100 ° C. to 150 ° C. is a voltage corresponding to the ambient temperature (see FIG. 11C).

Therefore, the correction device 4 can detect the humidity VI from which the influence of the ambient temperature is removed by correcting the voltage VH that is humidity information with the voltage VL that is ambient temperature information (see FIG. 11E).
JP-A-8-184576

The humidity sensor as the conventional gas concentration detection device described above corrects the voltage VH that is humidity information based on the voltage VL that is ambient temperature information, and outputs the humidity VI from which the influence of the ambient temperature is removed. However, the voltage VL described above is not exactly a value according to the ambient temperature. This is because the temperature measuring resistor R is made to self-heat by setting the temperature of the resistance temperature detector R higher than the ambient temperature so as to be 100 ° C. to 150 ° C. More specifically, the resistance temperature detector R can be expressed as shown in the following formulas (7) and (8).
R = (1 + αT) K ₀ (7)
T = T ₀ + T _W (8)
R: resistance value of resistance temperature detector, K ₀ : static resistance value of resistance temperature detector, α: resistance temperature coefficient, T: temperature of resistance temperature detector, T ₀ : ambient temperature, T _W : self-heating By temperature

As shown in the equations (7) and (8) described above, the temperature T of the resistance temperature detector R is a value obtained by adding the ambient temperature T ₀ and the temperature T _W due to self-heating. The heat distribution due to self-heating of the resistance temperature detector R is not uniform, and it is not known how many degrees the temperature resistance resistor R is at ° C. Therefore, even if the resistance value of the resistance thermometer R that is self-heating is measured, the ambient temperature is not known, that is, the accurate ambient temperature cannot be obtained from the voltage VL.

  Therefore, conventionally, a temperature detector 5 is further provided, and the voltage VH, which is humidity information, is corrected based on the temperature signal output from the temperature detector 5 (see FIG. 11D), and the ambient temperature Humidity VI from which the influence has been removed is detected.

  For this reason, the part cost increases by the provision of the temperature detector 5, and the size of the humidity sensor also increases. In addition, there is a problem that a mechanism for installing a temperature detector in the humidity sensor has to be provided, which increases the cost of processing the casing of the temperature sensor and increases the size of the casing.

  Accordingly, the present invention provides a gas concentration detection apparatus that can accurately detect the gas concentration at low cost and in a space-saving manner without being affected by the gas temperature of the gas to be measured, paying attention to the above problems. The task is to do.

  The invention according to claim 1, which has been made in order to solve the above-mentioned problems, is a resistance temperature detector that is arranged in a supply path of a gas to be measured and changes its resistance value depending on temperature, and a current in the resistance temperature detector. And a resistance / voltage conversion means for generating a voltage corresponding to the resistance value of the resistance temperature detector, and a voltage corresponding to the resistance value of the resistance temperature detector generated by the resistance / voltage conversion means is detected. In the gas concentration detection device, comprising: voltage detection means; and concentration detection means for detecting the concentration of the gas to be measured based on a voltage corresponding to the resistance value of the resistance temperature detector detected by the voltage detection means. Between a first current sized such that the temperature of the resistance temperature detector is higher than the ambient temperature and a second current sized such that the temperature of the resistance temperature detector is equal to the ambient temperature, The current supplied to the resistance temperature detector by the resistance / voltage conversion means Ri Order switching unit resides in the gas concentration measuring apparatus, wherein a is provided.

  According to a second aspect of the present invention, the resistance / voltage conversion means includes an amplifier that amplifies a voltage corresponding to a resistance value of the resistance temperature detector, and the gas concentration detection device is amplified by the amplifier. Analog / digital conversion means for converting a voltage corresponding to a resistance value of the resistance temperature detector into a digital value, and a gain of the amplifier when the second current is supplied to the resistance temperature detector are measured. 2. A gain control means for controlling a gain of the amplifier so as to be higher than a gain of the amplifier when the first current is supplied to the temperature resistor. It exists in the gas concentration detection device.

  According to a third aspect of the present invention, the amplifier amplifies a difference between a voltage corresponding to a resistance value of the resistance temperature detector and a reference voltage, and the gas concentration detection device applies the reference voltage to the amplifier. A reference voltage supply means for supplying, and supplying the first current to the RTD rather than a reference voltage supplied to the amplifier when the second current is supplied to the RTD. 3. The gas concentration detection according to claim 2, further comprising reference voltage control means for controlling the reference voltage supply means so that a reference voltage supplied to the amplifier is higher when the power is supplied. Exists in the device.

  According to a fourth aspect of the present invention, the resistance / voltage conversion unit includes an amplifier that amplifies a difference between a voltage corresponding to a resistance value of the resistance temperature detector and a reference voltage, and the gas concentration detection device. Analog / digital conversion means for converting a voltage corresponding to the resistance value of the resistance temperature detector amplified by the amplifier into a digital value, reference voltage supply means for supplying the reference voltage to the amplifier, and the temperature measurement A reference supplied to the amplifier when the first current is supplied to the resistance temperature detector rather than a reference voltage supplied to the amplifier when the second current is supplied to the resistor. 2. The gas concentration detection apparatus according to claim 1, further comprising reference voltage control means for controlling the reference voltage supply means so that the voltage becomes higher.

  As described above, according to the first aspect of the present invention, it is possible to accurately detect the gas temperature without being affected by the gas concentration by using the resistance temperature detector for detecting the gas concentration. When the concentration detecting means is supplied with the resistance value of the resistance temperature detector detected by the voltage detecting means when the first current is supplied, that is, the voltage corresponding to the gas concentration and the second current. In addition, it is possible to detect the accurate concentration of the gas to be measured with temperature correction based on the resistance value of the resistance temperature detector detected by the voltage detecting means, that is, the voltage corresponding to the gas temperature. The gas concentration can be accurately detected without being affected by the gas temperature of the gas to be measured in the space.

  According to the invention described in claim 2, the second current is smaller than the first current. For this reason, compared with the fluctuation range of the voltage according to the resistance value of the resistance temperature detector when the first current is supplied, the voltage according to the resistance value of the resistance temperature detector when the second current is supplied. The fluctuation range of becomes smaller. By increasing the gain when the second current is supplied by the gain control means, the fluctuation range of the voltage according to the resistance value of the resistance temperature detector when the second current is supplied is changed to the first It is possible to approach the fluctuation range of the voltage according to the resistance value of the resistance temperature detector when the current is supplied. As a result, the voltage fluctuation region according to the resistance value of the resistance temperature detector when the first current and the second current are supplied can be matched with the voltage conversion region of the analog / digital conversion means. The gas concentration can be detected with high accuracy by improving the conversion accuracy of the analog / digital conversion means.

  According to invention of Claim 3 and 4, 2nd electric current is smaller than 1st electric current. For this reason, the voltage according to the resistance value of the resistance temperature detector when the first current is supplied, compared to the voltage fluctuation region according to the resistance value of the resistance temperature detector when the second current is supplied. The fluctuation region becomes high. When the first current is supplied by the reference voltage control means, the reference voltage supplied to the amplifier is increased to change the voltage according to the resistance value of the resistance temperature detector when the first current is supplied. The region can be brought close to a voltage fluctuation region according to the resistance value of the resistance temperature detector when the second current is supplied. As a result, the voltage fluctuation region according to the resistance value of the resistance temperature detector when the first current and the second current are supplied can be matched with the voltage conversion region of the analog / digital conversion means. The gas concentration can be detected with high accuracy by improving the conversion accuracy of the analog / digital conversion means.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a gas concentration detection apparatus of the present invention. As shown in the figure, the gas concentration detection device includes a resistance temperature detector Rs which is arranged in a supply path of hydrogen (H ₂ ) gas as a gas to be measured and whose resistance value changes depending on temperature, A resistance / voltage conversion circuit 20 (resistance / voltage conversion means) that supplies a current to the resistor Rs and generates a voltage ΔV corresponding to the resistance value of the resistance temperature detector Rs is provided.

  The resistance / voltage conversion circuit 20 described above includes resistors R11 and R12 that form a half-bridge circuit together with the resistance temperature detector Rs, a constant voltage source 22, a differential amplifier OP (amplifier), and a field effect transistor (FET) Q. It is composed of The resistor R12 and the FETQ are connected in series. The series circuit composed of the resistor R12 and the FET Q and the resistor R11 are connected in parallel to each other. The constant voltage source 22 supplies a constant voltage Va to a parallel circuit composed of a resistance temperature detector Rs and resistors R11 and R12.

The above-described FETQ is controlled to be turned on / off by a CPU 25a in the μCOM 25 described later. When the FET Q is turned on, the parallel resistance of the resistor R11 and the resistor R12 is connected to the resistance temperature detector Rs. At this time, the current Is1 flowing through the resistance temperature detector Rs is expressed by the following equation (1).
Is1 = Va / (Rs + R11 // R12) (1)

  When the current Is1 is passed through the resistance temperature detector Rs, Joule heat is generated in the resistance temperature detector Rs. The magnitude of the current Is1 is set so that the temperature of the resistance temperature detector Rs becomes higher than the ambient temperature due to Joule heat generated in the resistance temperature detector Rs. That is, the magnitude of the current Is1 is set so that the resistance temperature detector Rs self-heats. More specifically, when the amount of heat generated in the resistance temperature detector Rs by flowing the current Is1 is larger than the amount of heat radiated to the surroundings, the temperature of the resistance temperature detector Rs becomes higher than the ambient temperature.

On the other hand, when the FET Q is turned off, only the resistor R11 of the resistors R11 and R12 is connected to the resistance temperature detector Rs. At this time, the current Is2 flowing through the resistance temperature detector Rs is expressed by the following equation (2).
Is2 = Va / (Rs + R11) (2)

  When the current Is2 is passed through the resistance temperature detector Rs, Joule heat is generated in the resistance temperature detector Rs. The magnitude of the current Is2 is set so that the temperature of the resistance temperature detector Rs does not become higher than the ambient temperature but equal to the ambient temperature even when Joule heat is generated in the resistance temperature detector Rs. That is, the magnitude of the current Is2 is set so that the resistance temperature detector Rs does not self-heat. More specifically, when the amount of heat generated in the resistance temperature detector Rs by flowing the current Is2 is smaller than the amount of heat radiated to the surroundings, the temperature of the resistance temperature detector Rs remains equal to the ambient temperature.

  A voltage generated at a connection point between the resistance temperature detector Rs and the resistors R11 and R12 is supplied as an output voltage V to the inverting input of the differential amplifier OP. A reference voltage Vref supplied from a digital / analog (D / A) converter 23 (reference voltage supply means) to be described later is supplied to the inverted input of the differential amplifier OP. The differential amplifier OP outputs a value obtained by amplifying the difference between the output voltage V and the reference voltage Vref with a gain α as an output voltage ΔV (= α × (V−Vref)).

When the FET Q is turned on and the parallel resistances of the resistors R11 and R12 are connected to the resistance temperature detector Rs, the output voltage V described above becomes a value represented by the following equation (3).
V = {(R11 // R12) / (Rs + R11 // R12)} × Va (3)
Therefore, the output voltage ΔV of the differential amplifier OP becomes a value represented by the following equation (4).
ΔV = α × [{(R11 // R12) / (Rs + R11 // R12)} × Va−Vref] (4)

On the other hand, when the FET Q is turned off and only the resistor R11 of the resistors R11 and R12 is connected in series to the resistance temperature detector Rs, the output voltage V described above is a value represented by the following equation (5). .
V = {R11 / (Rs + R11)} × Va (5)
Therefore, the output voltage ΔV of the differential amplifier OP becomes a value represented by the following equation (6).
ΔV = α × [{R11 / (Rs + R11)} × Va−Vref] (6)

  The resistance values of the resistors R11 and R12 described above do not change depending on the temperature, and the resistance values are always fixed. Therefore, as apparent from the above formulas (3) to (6), the output voltages V and ΔV are voltages according to the resistance value of the resistance temperature detector Rs. As is clear from the equations (4) and (6), the differential amplifier OP corresponds to an amplifier that amplifies the difference between the voltage V corresponding to the resistance value of the resistance temperature detector Rs and the reference voltage Vref.

  The above-described output voltage ΔV of the differential amplifier OP is supplied to an analog / digital (A / D) converter 24 (analog / digital conversion means). The A / D converter 24 converts the analog output voltage ΔV into a digital value and supplies it to the μCOM 25.

  The μCOM 25 is used in various processing steps in the CPU 25a, an arithmetic processing unit (hereinafter referred to as CPU) 25a that performs various processes according to a processing program, a ROM 25b that is a read-only memory that stores a program for processing performed by the CPU 25a, and the like. A RAM 25c that is a readable / writable memory having a work area, a data storage area for storing various data, and the like is provided.

  The temperature measuring resistor Rs described above is provided on a diaphragm 27 supported by the Si substrate 26 as shown in FIG.

  Next, as described above, the resistance value change of the resistance temperature detector Rs when the current Is1 flows through the resistance temperature detector Rs, and the resistance value of the resistance temperature detector Rs when the current Is2 flows through the resistance temperature detector Rs. The resistance value change will be described below with reference to FIGS. Generally, heat is generated when a current is passed through a resistor. This amount of heat depends on the amount of current flowing through the resistor. As the current flowing through the resistor increases, a large amount of heat is generated in the resistor. As the current flowing through the resistor decreases, a small amount of heat is generated in the resistor.

If the current Is2 that does not self-heat from the resistance temperature detector Rs is supplied to the resistance temperature detector Rs and H ₂ gas is supplied, the resistance value of the resistance temperature detector Rs is equal to that of the H ₂ gas as shown in FIG. The value depends on the temperature. When the resistance thermometer Rs does not self-heat and its temperature is equal to the ambient temperature, that is, the gas temperature, there is no amount of heat taken away by the H ₂ gas. For this reason, as shown in FIG. 6, the resistance value of the resistance temperature detector Rs is completely insensitive to the gas concentration of the H ₂ gas.

The temperature of the resistance temperature detector Rs increases as the ambient temperature, that is, the gas temperature increases, and decreases as the gas temperature decreases. For this reason, the resistance value of the resistance temperature detector Rs is a value corresponding to the gas temperature of the H ₂ gas while the FET Is turned off and the current Is2 having a magnitude that does not self-heat is supplied.

On the other hand, when a current Is1 having a magnitude that causes the temperature measuring resistor Rs to self-heat is passed through the temperature measuring resistor Rs, the temperature measuring resistor Rs self-heats and the temperature becomes higher than the ambient temperature, that is, the gas temperature. In this case supplying a H ₂ gas in RTD Rs, H ₂ gas rob heat corresponding to the concentration of RTD Rs. Therefore, as shown in FIG. 4, the temperature of the resistance temperature detector Rs becomes a value corresponding to the gas concentration of the H ₂ gas. Since the resistance temperature detector Rs is a resistance whose resistance value changes according to the temperature, the resistance value of the resistance temperature detector Rs is a value corresponding to the gas concentration of the H ₂ gas as shown in FIG.

  The operation of the gas concentration detection apparatus having the above-described configuration will be described below with reference to FIGS. 7A shows the on / off state of the FET Q, FIG. 7B shows the current Is, FIG. 7C shows the output voltage V, FIG. 7D shows the gain of the differential amplifier OP, FIG. 7E shows the reference voltage Vref, and FIG. 4 is a time chart of an output voltage ΔV of the dynamic amplifier OP. FIG. 8 is a flowchart showing the processing procedure of the CPU 25a in the gas concentration detection processing.

First, the CPU 25a performs an on / off process in which the FETQ is repeatedly turned on / off (see FIG. 7A). As a result, a current Is1 that is self-heated and a current Is2 that does not self-heat flow alternately through the temperature measuring resistor Rs (see FIG. 7B). That is, the CPU 25a functions as switching means in the claims. When the current Is2 that does not generate heat is supplied to the resistance temperature detector Rs, the resistance value of the resistance temperature detector Rs is a value corresponding to the gas temperature of the H ₂ gas. On the other hand, when the current Is1 that self-heats is supplied to the resistance temperature detector Rs, the resistance value of the resistance temperature detector Rs becomes a value corresponding to the gas concentration of the H ₂ gas. Therefore, the output voltage V corresponding to the gas temperature and the output voltage V corresponding to the concentration are alternately output from the half bridge circuit (see FIG. 7C).

  Next, the CPU 25a functions as a gain control unit, and performs a gain control process for controlling the gain α of the differential amplifier OP in synchronization with the on / off process. In the gain control process, the CPU 25a uses the differential amplifier OP when the gain α of the differential amplifier OP when the current Is2 is supplied to the temperature measuring resistor Rs and the current Is1 is supplied to the temperature measuring resistor Rs. The gain of the differential amplifier OP is controlled so as to be higher than the gain (see FIG. 7D).

  Further, the CPU 25a functions as a reference voltage control supply unit, and performs a reference voltage control process for controlling the reference voltage V supplied to the differential amplifier OP in synchronization with the on / off process. In the reference voltage control process, the CPU 25a supplies the current Is1 to the temperature measuring resistor Rs rather than the reference voltage supplied to the differential amplifier OP when the current Is2 is supplied to the temperature measuring resistor Rs. A digital reference voltage is output to the D / A converter 24 so that the reference voltage supplied to the differential amplifier OP is higher (see FIG. 7E).

  In FIG. 7C, VEQ1 indicates a fluctuation region of the output voltage V when the current Is1 is supplied, and VEQ2 indicates a fluctuation region when the current Is2 is supplied. As described above, the current Is2 is smaller than the current Is1. For this reason, as shown in the figure, the width of the variable region VEQ2 is smaller than the width of the variable region VEQ1. Therefore, by increasing the gain α when the current Is2 is supplied by the gain control process described above, the fluctuation range of the output voltage ΔV of the differential amplifier OP when the current Is2 is supplied is set to the current Is1. It is possible to approach the fluctuation range of the output voltage ΔV of the differential amplifier OP during supply.

  Further, as can be seen by comparing the fluctuation ranges VEQ1 and VEQ2, the output voltage V when the current Is1 is supplied fluctuates at a relatively high level. On the other hand, the output voltage V when the current Is2 is supplied fluctuates at a relatively low level. Therefore, by increasing the reference voltage when the current Is1 is supplied by the above-described reference voltage control process, the fluctuation region of the output voltage ΔV of the differential amplifier OP when the current Is1 is supplied is changed to the current Is2. Can be brought close to the fluctuation region of the output voltage ΔV of the differential amplifier OP. When the current Is1 and the current Is2 are supplied, the fluctuation region of the output voltage ΔV of the differential amplifier OP and the conversion region VEQ3 of the A / D converter 24 can be matched, and conversion by the A / D converter 24 is performed. The gas concentration can be detected with high accuracy by improving the accuracy.

  Ideally, the gain of the differential amplifier OP is such that the fluctuation region of the output voltage ΔV of the differential amplifier OP when the currents Is1 and Is2 are supplied completely coincides with the conversion region VEQ3 of the A / D converter 24. In addition, it is desirable to control the reference voltage Vref supplied to the differential amplifier OP.

  Further, the CPU 25a performs density detection processing in parallel with the above-described on / off control processing, gain control processing, and reference voltage control processing. The processing procedure of the CPU 25a in this density detection process will be described below with reference to the flowchart of FIG.

  First, the CPU 25a turns off the FET Q and causes the current Is2 to flow through the resistance temperature detector Rs (step S1). Next, the CPU 25a functions as a voltage detection unit, and detects an output voltage ΔV corresponding to the resistance value of the resistance temperature detector Rs output from the A / D converter 24 (step S2). Next, the CPU 25a stores the output voltage ΔV detected in step S2 in the RAM 25c as a voltage corresponding to the gas temperature (step S3).

  Next, the CPU 25a turns on the FET Q and causes the current Is1 to flow through the resistance temperature detector Rs (step S4). Next, the CPU 25a functions as a voltage detection unit, and detects an output voltage ΔV corresponding to the resistance value of the resistance temperature detector Rs output from the A / D converter 24 (step S5). Next, the CPU 25a stores the output voltage ΔV detected in step S6 in the RAM 25c as a voltage corresponding to the gas concentration (step S6).

  Next, the CPU 25a functions as a gas concentration detection means, and detects the gas concentration from which the influence of the gas temperature is removed by performing a correction operation based on the output voltage ΔV corresponding to the gas temperature and the output voltage ΔV corresponding to the gas concentration. (Step S7), the process returns to Step S1 again.

  According to the gas concentration detection device described above, the CPU 25a supplies the current supplied to the resistance temperature detector Rs by the resistance / voltage conversion circuit 20 so that the temperature of the resistance temperature detector Rs is higher than the ambient temperature. It switches between the current Is1 and the current Is2 having a magnitude such that the temperature of the resistance temperature detector Rs is equal to the ambient temperature. When the current Is1 is passed through the resistance temperature detector Rs, the resistance temperature detector Rs self-heats and its temperature becomes higher than the ambient temperature, that is, the gas temperature. At this time, the H2 gas takes away the amount of heat corresponding to the gas concentration from the resistance temperature detector Rs, and the temperature of the resistance temperature detector Rs, that is, the resistance value changes according to the gas concentration. When the current Is2 is passed through the resistance temperature detector Rs, the resistance temperature detector Rs does not self-heat and its temperature becomes equal to the ambient temperature, that is, the gas temperature. For this reason, the temperature of the resistance temperature detector Rs, that is, the resistance value is completely insensitive to the gas concentration and changes according to the gas temperature.

  Therefore, it is possible to accurately detect the gas temperature without being affected by the gas concentration by using the resistance temperature detector Rs for detecting the gas concentration. The resistance value of the resistance temperature detector Rs detected when the current Is1 is supplied, that is, the resistance value of the resistance temperature detector Rs detected when the voltage and the current Is2 according to the gas concentration are supplied. Based on the resistance value, that is, the voltage corresponding to the gas temperature, it is possible to detect an accurate concentration of the gas to be measured, which has been subjected to temperature correction. For this reason, it is possible to accurately detect the gas concentration at low cost and in a space-saving manner without being affected by the gas temperature of the H2 gas.

  In the above-described embodiment, the CPU 25a controls on / off of the FET Q, thereby changing the resistance value of the resistor connected in series with the resistance temperature detector Rs and switching the current flowing through the resistance temperature detector Rs. However, the present invention is not limited to this. That is, the resistance / voltage conversion circuit 20 may be of any configuration as long as the current flowing through the resistance temperature detector Rs can be changed. For example, the configuration shown in FIG.

  As shown in the figure, the constant voltage source 22 is configured such that the constant voltage Va can be converted, and the constant voltage Va supplied from the constant voltage source 22 is switched by the CPU 25a to switch the current flowing through the resistance temperature detector Rs. It may be.

  In the above-described embodiment, the resistance / voltage detection circuit 20 is configured by a half bridge circuit including the resistance temperature detector Rs, but the present invention is not limited to this. That is, the resistance / voltage detection circuit 20 may be any circuit that generates a voltage corresponding to the resistance value of the resistance temperature detector Rs. For example, a conventional bridge circuit may be configured.

  In the above-described embodiment, the currents Is1 and Is2 are passed through the resistance temperature detector Rs using the constant voltage source 22, but the present invention is not limited to this, and the temperature measurement is performed using the constant current source. A current may be passed through the resistor Rs.

  Further, the above-described embodiments are merely representative forms of the present invention, and the present invention is not limited to the embodiments. That is, various modifications can be made without departing from the scope of the present invention.

It is a circuit diagram which shows one Embodiment of the gas concentration detection apparatus of this invention. It is a figure which shows the Si base and diaphragm with which the resistance temperature sensor Rs which comprises the gas concentration detection apparatus shown in FIG. 1 is mounted. It is a graph which shows the relationship between the resistance value of the resistance thermometer Rs, and gas temperature when the electric current Is2 which does not self-heat the resistance thermometer Rs flows. It is a graph which shows the relationship between the temperature of the resistance thermometer Rs, and gas concentration when the electric current Is1 which self-heating of the resistance thermometer Rs flows. It is a graph which shows the relationship between the resistance value of the resistance temperature detector Rs, and gas concentration when the electric current Is1 which self-heating of the resistance temperature detector Rs flows. It is a graph which shows the relationship between the resistance value of the resistance thermometer Rs, and gas concentration when the electric current Is2 which does not self-heat the resistance thermometer Rs flows. (A) is the on / off state of the FETQ, (b) is the current Is, (c) is the output voltage V, (d) is the gain of the differential amplifier OP, (e) is the reference voltage Vref, and (f) is the differential amplifier. 6 is a time chart of an OP output voltage ΔV. It is a flowchart which shows the process sequence of CPU25a in a gas concentration detection process. It is a circuit diagram which shows an example of the gas concentration detection apparatus in other embodiment. It is a circuit diagram which shows the humidity sensor as an example of the conventional gas concentration detection apparatus. It is a time chart of the signal of each part of the humidity sensor shown in FIG. 10, an electric current, and a voltage.

Explanation of symbols

Is1 current (first current)
Is2 current (second current)
OP Differential Amplifier (Amplifier)
Rs RTD 20 Resistance / voltage conversion circuit (resistance / voltage conversion means)
23 D / A converter (reference voltage supply means)
24 A / D converter (analog / digital conversion means)
25a CPU (switching means, gain control means, reference voltage control means)

Claims (4)

A resistance temperature detector whose resistance value varies depending on the temperature is arranged in the supply path of the gas to be measured, and supplies a current to the resistance temperature detector to generate a voltage corresponding to the resistance value of the resistance temperature detector. Resistance / voltage conversion means to be generated, voltage detection means for detecting a voltage corresponding to the resistance value of the resistance temperature detector generated by the resistance / voltage conversion means, and the resistance temperature detector detected by the voltage detection means In a gas concentration detection device comprising a concentration detection means for detecting the concentration of the gas to be measured based on a voltage corresponding to the resistance value of
Between the first current having a magnitude such that the temperature of the resistance temperature detector is higher than the ambient temperature and the second current having a magnitude such that the temperature of the resistance temperature detector is equal to the ambient temperature. A gas concentration detection device comprising switching means for switching a current supplied to the resistance temperature detector by the resistance / voltage conversion means. The resistance / voltage converting means includes an amplifier for amplifying a voltage corresponding to a resistance value of the resistance temperature detector; and
The gas concentration detector supplies an analog / digital conversion means for converting a voltage corresponding to a resistance value of the resistance temperature detector amplified by the amplifier into a digital value, and supplies the second current to the resistance temperature detector. Gain control means for controlling the gain of the amplifier so that the gain of the amplifier when the current is being supplied is higher than the gain of the amplifier when the first current is supplied to the resistance temperature detector. The gas concentration detection device according to claim 1, further comprising: The amplifier amplifies a difference between a voltage corresponding to a resistance value of the resistance temperature detector and a reference voltage; and
Reference voltage supply means for supplying the reference voltage to the amplifier and a reference voltage supplied to the amplifier when the gas concentration detection device supplies the second current to the resistance temperature detector. Reference voltage control means for controlling the reference voltage supply means so that the reference voltage supplied to the amplifier is higher when the first current is supplied to the resistance temperature detector. The gas concentration detection apparatus according to claim 2, wherein The resistance / voltage converting means includes an amplifier that amplifies a difference between a voltage corresponding to a resistance value of the resistance temperature detector and a reference voltage; and
The gas concentration detection device converts an analog / digital conversion means that converts a voltage corresponding to a resistance value of the resistance temperature detector amplified by the amplifier into a digital value, and a reference voltage supply means that supplies the reference voltage to the amplifier. And the amplifier when the first current is supplied to the resistance temperature detector than the reference voltage supplied to the amplifier when the second current is supplied to the resistance temperature detector. The gas concentration detection device according to claim 1, further comprising a reference voltage control unit that controls the reference voltage supply unit so that a reference voltage supplied to the reference voltage is higher.

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