JP2021089156A - Gas sensor - Google Patents

Abstract

To correctly calculate an output signal indicating a concentration of a detection target gas even when a power supply voltage fluctuates.SOLUTION: A gas sensor 10 comprises: a gas sensor unit S1 connected to a power supply Vcc1 and including a thermistor Rd1 whose resistance value varies according to a concentration of a measurement target gas; and a signal processing circuit 20 that calculates an output signal Vout indicating a concentration of a detection target gas, based on a detection voltage VCO2 output from the gas sensor unit S1. The signal processing circuit 20 corrects the output signal Vout according to a voltage of the power supply Vcc1. Thus, even when the voltage of the power supply Vcc1 fluctuates, it is possible to correctly calculate the output signal Vout indicating the concentration of the detection target gas.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gas sensor that detects a gas contained in an atmosphere, and more particularly to a gas sensor that calculates an output signal indicating the concentration of a gas to be detected based on a detection voltage.

The gas sensor detects the concentration of the gas to be measured contained in the atmosphere. Among them, the gas sensor of the type that heats a temperature measuring body such as a thermistor by a heater resistance is excellent in miniaturization. For example, the gas sensor described in Patent Document 1 includes an exhaust gas side electrode, a reference gas side electrode, and a heater, and improves the controllability of heater energization by changing the control duty ratio according to a change in the power supply voltage. I'm letting you.

Japanese Unexamined Patent Publication No. 2003-50226

However, when the power supply voltage changes, the detection voltage output from the sensor element also changes. Therefore, if the output signal indicating the concentration of the detection target gas is calculated as it is based on the detection voltage, an error due to the fluctuation of the power supply voltage will occur. There was a problem that it occurred.

Therefore, according to the present invention, in a gas sensor of a type that calculates an output signal indicating the concentration of the detection target gas based on the detection voltage, the output signal indicating the concentration of the detection target gas can be correctly obtained even when the power supply voltage fluctuates. The purpose is to calculate.

The gas sensor according to the present invention is output from a first gas sensor unit including a first thermometer, which is connected to a first power source and whose resistance value changes according to the concentration of the gas to be measured, and a first gas sensor unit. The signal processing circuit includes a signal processing circuit that calculates an output signal indicating the concentration of the gas to be detected based on the detected voltage, and the signal processing circuit corrects the output signal according to the voltage of the first power source. ..

According to the present invention, since the output signal is corrected according to the voltage of the first power source, the output signal indicating the concentration of the gas to be detected can be obtained even when the voltage of the first power source fluctuates. It becomes possible to calculate correctly.

In the present invention, the signal processing circuit includes a voltage dividing circuit that divides the voltage of the first power supply, and the signal processing circuit may correct the output signal according to the voltage dividing voltage output from the voltage dividing circuit. .. According to this, even when the voltage of the first power supply is high, it is possible to correctly grasp the current voltage value.

In the present invention, the signal processing circuit may correct the output signal according to the difference or ratio between the voltage dividing voltage acquired during the calibration operation and the voltage dividing voltage acquired during the measurement operation. According to this, it is possible to perform correction according to the voltage at the time of measurement operation.

In the present invention, the signal processing circuit may adjust the correction amount of the output signal according to the difference or ratio between the detection voltage and the voltage dividing voltage acquired during the calibration operation. According to this, more accurate correction becomes possible.

The gas sensor according to the present invention further includes a temperature sensor unit including a second temperature measuring body which is connected to a first power source and whose resistance value changes according to the environmental temperature, and the first gas sensor unit is a first measuring unit. Further including a first heater resistance for heating the warm body, the signal processing circuit sets a first control voltage to be applied to the first heater resistance according to the output voltage of the temperature sensor unit and the voltage of the first power supply. You may calculate it. According to this, it is possible to apply an appropriate control voltage according to the power supply voltage to the first heater resistor.

In the present invention, the temperature sensor unit includes a second temperature measuring element and a first resistor connected in series between the first power supply and the ground potential, and the voltage dividing circuit includes the first power supply and the ground potential. The output voltage output from the temperature sensor unit, including the second and third resistors connected in series between, is output from the connection point between the second thermometer and the second resistor, and is a voltage divider circuit. The voltage divider voltage output from is output from the connection point of the second resistor and the third resistor, and the difference between the resistance values of the first to third resistors may be 1% or less. According to this, it is possible to reduce the error caused by the variation in the resistance value.

The gas sensor according to the present invention further includes a second gas sensor unit including a third temperature measuring body and a second heater resistor for heating the third temperature measuring body, and further includes a first temperature measuring body and a third temperature measuring body. The body is connected in series between the first power supply and the ground potential, the detected voltage is output from the connection point between the first thermometer and the third thermometer, and the signal processing circuit is the temperature sensor unit. The second control voltage applied to the second heater resistor is calculated according to the output voltage and the voltage of the first power supply, and the first control voltage and the second control voltage are different values from each other. Therefore, the first thermometer and the third thermometer may be heated to different temperatures. According to this, it is possible to obtain a detection signal according to the concentration of the gas to be measured from the connection point between the first temperature measuring body and the third temperature measuring body.

In the present invention, the signal processing circuit operates by a second power source different from the first power source, and the voltage of the first power source may be higher than the voltage of the second power source. According to this, high detection sensitivity can be obtained and power consumption can be reduced.

As described above, according to the gas sensor according to the present invention, it is possible to correctly calculate the output signal indicating the concentration of the detection target gas even when the power supply voltage fluctuates.

FIG. 1 is a circuit diagram showing a configuration of a gas sensor 10 according to an embodiment of the present invention. FIG. 2 is a top view for explaining the configuration of the sensor unit S. FIG. 3 is a cross-sectional view taken along the line AA shown in FIG. FIG. 4 is a flowchart for explaining the operation of the gas sensor 10. FIG. 5 is a graph showing the relationship between the environmental temperature and the control voltages Vmh1 and Vmh2. FIG. 6 is a graph showing the relationship between the fluctuation of the power supply potential Vcc1 and _{the detection error of CO 2 gas.}

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing a configuration of a gas sensor 10 according to an embodiment of the present invention.

As shown in FIG. 1, the gas sensor 10 according to the present embodiment includes a sensor unit S and a signal processing circuit 20. Although not particularly limited, the gas sensor 10 according to the present embodiment detects the concentration _{of CO 2 gas in the atmosphere.}

The sensor unit S is _{a heat conduction type gas sensor for detecting the concentration of CO 2} gas, which is a gas to be detected, and has a first gas sensor unit S1, a second gas sensor unit S2, and a temperature sensor unit S3. There is. The first gas sensor unit S1 includes a thermistor Rd1 which is a first temperature measuring body and a heater resistor MH1 for heating the thermistor Rd1. Similarly, the second gas sensor unit S2 includes a thermistor Rd2 which is a third temperature measuring body and a heater resistor MH2 which heats the thermistor Rd2. On the other hand, the temperature sensor unit S3 includes a thermistor Rd3 which is a second temperature measuring body.

As shown in FIG. 1, the thermistors Rd1 and Rd2 are connected in series between the wiring to which the power supply potential Vcc1 is supplied and the wiring to which the ground potential GND is supplied. On the other hand, the thermistor Rd3 and the resistor R1 are connected in series between the wiring to which the power supply potential Vcc1 is supplied and the wiring to which the ground potential GND is supplied. Thermistors Rd1 to Rd3 are made of materials having a negative temperature coefficient of resistance, such as composite metal oxides, amorphous silicon, polysilicon, and germanium. Of these, the thermistors Rd1 and Rd2 both _{detect the concentration of CO 2} gas, but their operating temperatures are different from each other as described later.

The thermistor Rd1 is heated by the heater resistor MH1. The heating temperature of the thermistor Rd1 by the heater resistor MH1 is, for example, 150 ° C. _{If CO 2} gas is present in the measurement atmosphere while the thermistor Rd1 is heated, the heat dissipation characteristics of the thermistor Rd1 change according to its concentration. Such a change appears as a change in the resistance value of the thermistor Rd1. When the heating temperature of the thermistor Rd1 is 150 ° C., the resistance value of the thermistor Rd1 changes with the first sensitivity according to the concentration of _{CO 2 gas.} The first sensitivity has a sensitivity capable of sufficiently changing the _{detection voltage V CO2} appearing at the connection point between the thermistor Rd1 and the thermistor Rd2. Further, when water vapor is present in the measurement atmosphere, the heat dissipation characteristics of the thermistor Rd1 change according to the concentration thereof.

The thermistor Rd2 is heated by the heater resistor MH2. The heating temperature of the thermistor Rd2 by the heater resistor MH2 is, for example, 300 ° C. _{Even if CO 2} gas is present in the measurement atmosphere while the thermistor Rd2 is heated, the resistance value of the thermistor Rd2 hardly changes. This is because when the heating temperature of the thermistor Rd2 is 300 ° C., the resistance value of the thermistor Rd2 _{changes with the second sensitivity according to the concentration of CO 2} gas, but the second sensitivity is higher than the first sensitivity. This is because it is significantly lower, preferably 1/10 or less of the first sensitivity, and more preferably almost zero. Therefore, _{even if the concentration of CO 2} gas changes, the resistance value of the thermistor Rd2 hardly changes. On the other hand, when water vapor is present in the measurement atmosphere, the heat dissipation characteristics of the thermistor Rd2 change according to its concentration.

As described above, the thermistor Rd1 and the thermistor Rd2 are connected in series, and the detection voltage V _CO2 is output from the connection point. On the other hand, the output voltage Va of the temperature sensor unit S3 is output from the connection point between the thermistor Rd3 and the resistor R1. The detection voltage V _CO2 and the output voltage Va are input to the signal processing circuit 20.

The signal processing circuit 20 includes a voltage dividing circuit 21, a buffer 22, a differential amplifier 23, an AD converter (ADC) 24, a DA converter (DAC) 25, and a control unit 26. The voltage dividing circuit 21 is composed of resistors R2 and R3 connected in series between the wiring to which the power supply potential Vcc1 is supplied and the wiring to which the ground potential GND is supplied, and the voltage is divided from the connection point between the resistors R2 and R3. The voltage 1 / 2Vcc_in is output. A power supply potential Vcc2 different from the power supply potential Vcc1 is supplied to the other circuits constituting the signal processing circuit 20, and operates by a voltage between the power supply potential Vcc2 and the ground potential GND. Although not particularly limited, the power supply potential Vcc1 is higher than the power supply potential Vcc2. As an example, the power potential Vcc1 is 3V and the power potential Vcc2 is 1.8V. As described above, if Vcc1> Vcc2, the detection sensitivity of the sensor unit S can be increased and the power consumption of the signal processing circuit 20 can be suppressed. When the power supply potential Vcc1 is high, voltage fluctuations are likely to occur, but as will be described later, in the present embodiment, the measurement error caused by the voltage fluctuations of the power supply potential Vcc1 is cancelled.

The buffer 22 generates a temperature signal Vtemp by buffering the output voltage Va. Further, the differential amplifier 23 _{compares the detected voltage V CO2} with the reference voltage Vref and amplifies the difference. The temperature signal Vtemp output from the buffer 22 and the gas detection signal Vamp output from the differential amplifier 23 are input to the AD converter 24.

The AD converter 24 digitally converts the value of the voltage dividing voltage 1 / 2Vcc_in, the temperature signal Vtemp, and the gas detection signal Vamp, and supplies the values to the control unit 26. On the other hand, the DA converter 25 generates the reference voltage Vref and the control voltages Vmh1 and Vmh2 by analog-converting the reference signal supplied from the control unit 26. The control unit 26 calculates an output signal Vout indicating the _{current concentration of CO 2} gas based on the digitally converted gas detection signal Vamp. Although the details will be described later, in the calculation of the output signal Vout, the correction is performed according to the current voltage dividing voltage 1 / 2Vcc_in. Further, the levels of the control voltages Vmh1 and Vmh2 are calculated by using the temperature signal Vtemp.

FIG. 2 is a top view for explaining the configuration of the sensor unit S. Further, FIG. 3 is a cross-sectional view taken along the line AA shown in FIG. The drawings are schematic, and for convenience of explanation, the relationship between the thickness and the plane dimension, the ratio of the thickness between the devices, and the like are different from the actual structure within the range where the effect of the present embodiment can be obtained. It doesn't matter if you do.

The sensor unit S is a heat conduction type gas sensor that detects the gas concentration based on the change in heat dissipation characteristics according to the concentration of _{CO 2 gas, and as shown in FIGS. 2 and 3, the two gas sensor units S1 and S2} A temperature sensor unit S3 arranged between the gas sensor unit S1 and the gas sensor unit S2, and a ceramic package 51 accommodating these sensor units S1 to S3 are provided.

The ceramic package 51 is a box-shaped case having an open upper portion, and a lid 52 is provided on the upper portion. The lid 52 has a plurality of vents 53, which allows CO ₂ gas in the atmosphere to flow into the ceramic package 51. The lid 52 is omitted in FIG. 2 in consideration of the legibility of the drawing.

Although not particularly limited, in the present embodiment, three sensor units S1 to S3 are integrated on a single substrate 61. Three cavities 61a to 61c corresponding to the three sensor units S1 to S3 are formed on the substrate 61.

The substrate 61 protects the insulating films 62 and 63, the heater resistors MH1 and MH2 provided on the insulating films 63, the heater protective films 64 covering the heater resistors MH1 and MH2, and the heater protection films 64 at positions overlapping the cavities 61a to 61c, respectively. The thermistors Rd1 to Rd3 and thermistor electrodes 35, 45, 65 provided on the film 64, and a thermistor protective film 66 covering the thermistors Rd1 to Rd3 and the thermistor electrodes 35, 45, 65 are provided.

The substrate 61 is not particularly limited as long as it has an appropriate mechanical strength and is a material suitable for fine processing such as etching, and is not particularly limited, and is a silicon single crystal substrate, a sapphire single crystal substrate, a ceramic substrate, or a quartz substrate. , Glass substrate and the like can be used. The insulating films 62 and 63 are made of an insulating material such as silicon oxide or silicon nitride. The heater resistors MH1 and MH2 are metal materials made of materials having a relatively high melting point, for example, molybdenum (Mo), platinum (Pt), gold (Au), tungsten (W), tantalum (Ta), palladium (Pd), and the like. Iridium (Ir) or an alloy containing any two or more of these is suitable. Thermistors Rd1 to Rd3 are made of materials having a negative temperature coefficient of resistance, such as composite metal oxides, amorphous silicon, polysilicon, and germanium. Here, the thermistor is used as the resistance temperature detector because the resistance temperature coefficient is larger than that of the platinum resistance temperature detector and the like, so that a large detection sensitivity can be obtained. As the material of the heater protective film 64, the same material as that of the insulating film 63 can be used.

Thermistor electrodes 35, 45, 65 are a pair of electrodes having a predetermined interval, the thermistor Rd1 is provided between the pair of thermistor electrodes 35, the thermistor Rd2 is provided between the pair of thermistor electrodes 45, and the pair of thermistors. A thermistor Rd3 is provided between the electrodes 65. As a result, the resistance value between the pair of thermistor electrodes 35, 45, 65 is determined by the resistance value of the thermistors Rd1 to Rd3, respectively. The materials of the thermista electrodes 35, 45, 65 include molybdenum (Mo), platinum (Pt), gold (Au), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or any of these. An alloy containing two or more kinds is suitable.

As shown in FIG. 2, both ends of the heater resistor MH1 are connected to the electrode pads 37a and 37b, respectively, and both ends of the heater resistor MH2 are connected to the electrode pads 47a and 47b, respectively. Further, both ends of the thermistor electrode 35 are connected to electrode pads 37c and 37d, respectively, both ends of the thermistor electrode 45 are connected to electrode pads 47c and 47d, respectively, and both ends of the thermistor electrode 65 are connected to electrode pads 67a and 67b, respectively. .. These electrode pads are connected to the package electrode 54 provided on the ceramic package 51 via the bonding wire 55. The package electrode 54 is connected to the signal processing circuit 20 shown in FIG. 1 via an external terminal 56 provided on the back surface of the ceramic package 51.

The above is the configuration of the gas sensor 10 according to the present embodiment. Next, the operation of the gas sensor 10 according to the present embodiment will be described.

The gas sensor 10 according to the present embodiment _{utilizes the fact that the thermal conductivity of CO 2} gas is significantly different from the thermal conductivity of air, and the gas detection voltage changes the heat dissipation characteristics of the thermistas Rd1 and Rd2 depending on the concentration of _{CO 2 gas.} Take out as _{V CO2.} However, since the thermal conductivity of the measurement atmosphere _{changes not only with the concentration of CO 2} gas but also with the humidity, that is, the concentration of water vapor, the influence of humidity causes a measurement error. Therefore, in the gas sensor 10 according to the present embodiment, the thermistor Rd1 is heated to, for example, 150 ° C. by using the heater resistor MH1, and the thermistor Rd2 is heated to, for example, 300 ° C. by using the heater resistor MH2. When the heating temperature is 150 ° C, _{the heat dissipation characteristics of the thermistor Rd1 change greatly depending on the concentration of CO 2} gas, whereas when the heating temperature is 300 ° C, the heat dissipation characteristics of the thermistor Rd2 _{change greatly according to the concentration of CO 2 gas.} The heat dissipation characteristics hardly change. On the other hand, when the heating temperature is 150 ° C. or 300 ° C., the heat dissipation characteristics of the thermistors Rd1 and Rd2 change depending on the humidity. Therefore, by connecting the thermistors Rd1 and Rd2 in series, the influence of humidity is canceled. can do. Here, when there is a difference in the sensitivities of the thermistors Rd1 and Rd2 with respect to humidity, it is possible to reduce the difference in sensitivity by connecting a correction resistor in parallel with the thermistor Rd1 or thermistor Rd2.

Further, the gas sensor 10 according to the present embodiment has a control voltage Vmh1 based on the temperature signal Vtemp and the current voltage dividing voltage 1 / 2Vcc_in so that the heating temperatures of the thermistors Rd1 and Rd2 are constant even if the environmental temperature changes. , Vmh2 level is adjusted. Further, the gas sensor 10 according to the present embodiment is corrected according to the current voltage dividing voltage 1 / 2Vcc_in so that the influence of the fluctuation of the power supply potential Vcc1 is canceled even in the calculation of the output signal Vout.

FIG. 4 is a flowchart for explaining the operation of the gas sensor 10 according to the present embodiment.

In the operation of the gas sensor 10, a calibration operation is first performed (step S10). The calibration operation is an operation in which the divided voltage 1 / 2Vcc_in and the gas detection signal Vamp are read and a predetermined calculation is performed in a state where the environmental temperature, humidity, and the concentration of the gas to be measured are stable. The calibration operation may be executed at the time of starting the gas sensor 10, or may be executed at regular intervals even after the start of the gas sensor 10. In the calibration operation, first, the voltage dividing voltage 1 / 2Vcc_in and the gas detection signal Vamp are digitally converted by the AD converter 24, the initial level of the voltage dividing voltage 1 / 2Vcc_in is saved (step S11), and the control unit 26 The voltage ratio A is calculated (step S12). The voltage ratio A is calculated by calculating the ratio of the voltage dividing voltage 1 / 2Vcc_in to the detected voltage V _CO2 (1 / 2Vcc_in ÷ V _CO2). Instead of calculating the voltage ratio A, the difference between the voltage dividing voltage 1 / 2Vcc_in and the detected voltage V _{CO2 may be calculated.} The detected voltage V _CO2 can be calculated by performing the calculation of the equation (1) by the control unit 26.
V _CO2 = (Vamp-Vref) / AMP + Vref ... (1)
Here, "AMP" is the amplification ratio of the differential amplifier 23. The calculated voltage ratio A is stored inside the control unit 26 (step S13).

After the series of calibration operations (step S10) is completed, a measurement operation for actually measuring the concentration of the gas to be measured is performed (step S20). The measurement operation may be performed intermittently at predetermined intervals. In the measurement operation, first, the voltage dividing voltage 1 / 2Vcc_in is read (step S21). The level of the voltage dividing voltage 1 / 2Vcc_in is ideally the same as the initial level acquired during the calibration operation, but when the power supply potential Vcc1 fluctuates, a potential difference occurs between the two, so that potential difference Vdiv Is calculated (step S22). Instead of the potential difference Vdiv, the ratio of the voltage dividing voltage 1 / 2Vcc_in stored in step S11 and the voltage dividing voltage 1 / 2Vcc_in read in step S21 may be used. Next, the current level of the power supply potential Vcc1 is calculated by doubling the value of the read voltage dividing voltage 1 / 2Vcc_in (step S23).

Next, the temperature signal Vtemp is read (step S24), and the temperature value Ta is calculated based on the level of the power potential Vcc1 calculated in step S23 and the level of the temperature signal Vtemp read in step S24 (step S25). The temperature value Ta is calculated by calculating the current resistance value Rref of the thermistor Rd3 by performing the calculation of the formula (2) and then performing the calculation of the formula (3).

In the formulas (2) and (3), "R" is the resistance value of the resistor R1, "B" is the temperature coefficient of the thermistor Rd3, and Rref @ 25 is the resistance value of the thermistor Rd3 when the environmental temperature is 25 ° C. Yes, all use digital values stored in advance in the control unit 26. Further, "1 / 2Vcc_in" is a digital value of the voltage dividing voltage 1 / 2Vcc_in, and "Va" is a digital value of the temperature signal Vtemp.

Next, the reference voltage Vref and the control voltages Vmh1 and Vmh2 are calculated using the temperature value Ta calculated in step S25 (step S26). The control voltages Vmh1 and Vmh2 can be calculated by performing the calculations of the equations (4) and (5), respectively.
Vmh1 = -0.00301 × Ta + 1.15 ・ ・ ・ (4)
Vmh2 = −0.00151 × Ta + 2.19 ・ ・ ・ (5)
As a result, the differential amplifier 23 is given a reference voltage Vref according to the current environmental temperature, and the thermistors Rd1 and Rd2 are heated to predetermined temperatures (for example, 150 ° C. and 300 ° C.), respectively. FIG. 5 is a graph showing the relationship between the environmental temperature and the control voltages Vmh1 and Vmh2. As shown in FIG. 5, it can be seen that the control voltages Vmh1 and Vmh2 decrease linearly as the environmental temperature rises.

Next, the gas detection signal Vamp is read (step S27), the gas detection signal Vamp is corrected using the potential difference Vdiv (step S28), and then the output signal Vout is calculated (step S29). The correction of the gas detection signal Vamp is performed by calculating the equation (4) by the control unit 26.
Vamp (after correction) = Vamp + Vdiv x AMP / A ... (4)
As a result, the offset of the gas detection signal Vamp caused by the fluctuation of the power supply potential Vcc1 is canceled, and the correct output signal Vout can be generated.

FIG. 5 is a graph showing the relationship between the fluctuation of the power supply potential Vcc1 and _{the detection error of CO 2} gas, the solid line shows the detection error in the gas sensor 10 according to the present embodiment, and the broken line shows the current voltage dividing voltage 1 / 2Vcc_in. The detection error when the correction used is not performed is shown.

As shown in FIG. 5, when the correction using the current voltage dividing voltage 1 / 2Vcc_in is not performed, a large detection error occurs due to a slight fluctuation of the power supply potential Vcc1, whereas the gas sensor 10 according to the present embodiment has a large detection error. According to this, it can be seen that even if the power supply potential Vcc1 fluctuates, almost no detection error occurs.

The detection error of CO ₂ gas is also caused by the variation in the resistance values of the resistors R1 to R3. In order to reduce the detection error caused by the variation in the resistance values of the resistors R1 to R3, it is necessary to design the resistance values of the resistors R1 to R3 to be the same value and suppress the variation in the resistance values to 1% or less. It is valid.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention, and these are also the present invention. Needless to say, it is included in the range.

For example, in the above embodiment _{, the case where the measurement target gas is CO 2} gas has been described as an example, but the present invention is not limited thereto. Further, it is not essential that the sensor unit used in the present invention is a heat conduction type sensor, and another type of sensor such as a contact combustion type sensor may be used.

10 Gas sensor 20 Signal processing circuit 21 Pressure division circuit 22 Buffer 23 Differential amplifier 24 AD converter 25 DA converter 26 Control unit 35, 45, 65 Thermistor electrodes 37a to 37d, 47a to 47d, 67a, 67b Electrode pad 51 Ceramic package 52 lid 53 Vent 54 Package electrode 55 Bonding wire 56 External terminal 61 Substrate 61a to 61c Cavity 62,63 Insulation film 64 Heater protection film 65 Thermistor electrode 66 Thermistor protection film MH1, MH2 Heater resistance R1 to R3 Resistance Rd1 to Rd3 Thermistor S sensor S1 First gas sensor unit S2 Second gas sensor unit

Claims (8)

A first gas sensor unit including a first temperature measuring body, which is connected to a first power source and whose resistance value changes according to the concentration of the gas to be measured,
A signal processing circuit that calculates an output signal indicating the concentration of the detection target gas based on the detection voltage output from the first gas sensor unit is provided.
The signal processing circuit is a gas sensor characterized in that the output signal is corrected according to the voltage of the first power supply. The signal processing circuit includes a voltage dividing circuit that divides the voltage of the first power supply.
The gas sensor according to claim 1, wherein the signal processing circuit corrects the output signal according to a voltage dividing voltage output from the voltage dividing circuit. 2. The signal processing circuit is characterized in that the output signal is corrected according to the difference or ratio between the voltage dividing voltage acquired during the calibration operation and the voltage dividing voltage acquired during the measurement operation. The described gas sensor. The gas sensor according to claim 3, wherein the signal processing circuit adjusts a correction amount of the output signal according to a difference or ratio between the detected voltage and the divided voltage acquired during the calibration operation. Further provided with a temperature sensor unit including a second temperature measuring body connected to the first power source and whose resistance value changes according to the environmental temperature.
The first gas sensor unit further includes a first heater resistor for heating the first resistance temperature detector.
2. The signal processing circuit is characterized in that the first control voltage applied to the first heater resistor is calculated according to the output voltage of the temperature sensor unit and the voltage of the first power supply. The gas sensor according to any one of 4 to 4. The temperature sensor unit includes the second resistance temperature detector and a first resistor connected in series between the first power supply and the ground potential.
The voltage divider circuit includes second and third resistors connected in series between the first power supply and the ground potential.
The output voltage output from the temperature sensor unit is output from the connection point between the second temperature measuring body and the second resistor.
The voltage dividing voltage output from the voltage dividing circuit is output from the connection point between the second resistor and the third resistor.
The gas sensor according to claim 5, wherein the difference between the resistance values of the first to third resistors is 1% or less. A third temperature measuring body and a second gas sensor unit including a second heater resistor for heating the third temperature measuring body are further provided.
The first resistance temperature detector and the third resistance temperature detector are connected in series between the first power supply and the ground potential, and are connected in series.
The detected voltage is output from the connection point between the first resistance temperature detector and the third resistance temperature detector.
The signal processing circuit calculates a second control voltage to be applied to the second heater resistor according to the output voltage of the temperature sensor unit and the voltage of the first power supply.
The first control voltage and the second control voltage have different values, whereby the first temperature measuring body and the third temperature measuring body are heated to different temperatures. The gas sensor according to claim 5 or 6. The signal processing circuit is operated by a second power source different from the first power source.
The gas sensor according to any one of claims 1 to 7, wherein the voltage of the first power source is higher than the voltage of the second power source.

Images