JP4842789B2 - Gas concentration measuring device - Google Patents

Description

  The present invention relates to an apparatus for measuring a target gas concentration in an ambient atmosphere by an electrochemical gas sensor using a proton conductor film.

  2. Description of the Related Art Conventionally, devices that incorporate an electrochemical CO sensor have been known as devices for measuring the CO concentration in the surrounding atmosphere, such as a CO alarm device that detects and alarms CO gas due to incomplete combustion or the like of combustion equipment. .

  As shown in a cross-sectional view in FIG. 5, this electrochemical CO sensor 1 has a proton conductor film 3 installed in an upper opening 4 of a metal can 2 in which water 5 is accommodated, and a counter electrode 32 is provided as a metal can. The metal cap 8 having the gas adsorption filter 8 c built in is overlapped with the detection electrode 31 on the opposite side and is caulked and fixed to the upper opening 4 of the metal can 2.

  In the electrochemical CO sensor 1 having the above-described configuration, CO in the ambient atmosphere is introduced into the inside through the introduction hole 8a of the metal cap 8, and the gas adsorption filter 8c and the discharge hole 8b made of activated carbon, silica gel, zeolite, and the like, and Then, it passes through the diffusion control hole 7a of the metal diffusion prevention plate 7 interposed between the metal cap 8 and the proton conductor film 3, and reaches the detection electrode 31, where the proton conductor from the counter electrode 32 side. An oxidation reaction using the water of the water 5 in the metal can 2 supplied to the membrane 3 is caused to generate protons (2H +) and electrons (2e-) at the detection electrode 31.

  Electrons (2e−) generated in the sensing electrode 31 cannot pass through the proton conductor film 3 and therefore stay in the sensing electrode 31, while protons (2H +) pass through the proton conductor film 3. It moves to the counter electrode 32, where it causes a reduction reaction with oxygen in the container 2 to generate water (H 2 O) at the counter electrode 32.

  Therefore, between the metal cap 8 that is electrically connected to the detection electrode 31 and functions as its terminal, and the metal can 2 that is electrically connected to the counter electrode 32 via the diffusion prevention plate 7 and functions as its terminal. When a load (not shown) is connected, a flow of electrons (2e−) staying at the detection electrode 31 toward the counter electrode 32 is generated in the load, whereby a short-circuit current flows from the counter electrode 32 to the detection electrode 31 through the load. Therefore, a CO concentration signal having a voltage value corresponding to the CO concentration in the ambient atmosphere can be obtained by current-voltage conversion of the short-circuit current flowing through the load (for example, Patent Documents 1 and 2).

  The electrochemical CO sensor 1 having such a detection principle configuration itself does not require an external power supply to generate a CO concentration signal having a voltage value corresponding to the CO concentration in the surrounding atmosphere. It is suitable for use in a CO alarm device that needs to be driven for a long time by a battery.

  By the way, in the electrochemical CO sensor 1 described above, the number of electrons (2e−) generated at the detection electrode 31 is small, and the CO concentration signal corresponding to the CO concentration in the surrounding atmosphere is very weak. The CO concentration signal from the electrochemical CO sensor 1 is amplified and used for measuring the CO concentration.

FIG. 6 is a circuit diagram showing details of a signal processing circuit used for amplifying the CO concentration signal from the electrochemical CO sensor 1. The signal processing circuit indicated by reference numeral 20A in FIG. 6 is for amplifying the CO concentration signal. It has an operational amplifier AMP and a gain setting resistor Rg connected between the output terminal and the negative phase input terminal of the operational amplifier AMP.

  The positive phase input terminal of the operational amplifier AMP is connected to the metal cap 8 to the detection pole 31 of the electrochemical CO sensor 1 and is connected to a constant voltage circuit (not shown). The negative phase input terminal of the operational amplifier AMP is connected to the negative phase input terminal. An operational amplifier AMP connected to the metal can 2 to the counter electrode 32 of the electrochemical CO sensor 1 and operated by a constant voltage supplied from a constant voltage circuit (not shown) from the electrochemical CO sensor 1 with a gain corresponding to the resistance Rg. The CO concentration signal is amplified.

  At this time, if radio waves are present in the vicinity, a high-frequency induced current flows in a superimposed manner on a line that guides the CO concentration signal to the operational amplifier. Then, the electrochemical CO sensor 1 has a kind of large capacity (several numbers). Since it functions as a capacitor, the high-frequency signal superimposed on the CO concentration signal is differentiated by the differential circuit composed of the gain setting resistor Rg of the operational amplifier AMP and the electrochemical CO sensor 1 functioning as a capacitor. The induced current is amplified by the operational amplifier AMP.

  Therefore, although the CO concentration is actually 0 ppm, the amplified CO concentration signal rises to a level of, for example, 100 ppm, which adversely affects the accuracy of the CO concentration measurement and the CO concentration alarm operation. It will end up.

  Therefore, a resistor Rs for reducing high-frequency gain characteristics is inserted between the metal can 2 which is the terminal on the counter electrode 32 side of the electrochemical CO sensor 1 and the negative phase input terminal of the operational amplifier AMP, and for setting the gain of the operational amplifier AMP. It is conceivable that a capacitor Cf as a low-pass filter is connected in parallel with the resistor Rg to lower the gain characteristic at a high frequency and lower the upper limit of the gain itself.

This prevents the high-frequency component of the induced current superimposed on the CO concentration signal from being amplified with a large gain by the operational amplifier AMP so that the accuracy of the CO concentration measurement and the CO concentration alarm operation is not adversely affected. Should be able to.
JP 2004-170101 A JP 2004-279293 A

  However, even if the above-described measures are taken, if radio waves are present around the electrochemical CO sensor 1, there is a problem that the level of the amplified CO concentration signal increases or decreases to a level different from the actual CO concentration. It was.

  Such a fluctuation in the level of the amplified CO concentration signal causes a decrease in the measurement accuracy of the CO gas concentration, similarly to a decrease in the level of the amplified CO concentration signal which is to be prevented by the resistor Rs for reducing the high frequency gain characteristics. Therefore, as described above, simply filtering the high-frequency component of the induced current that flows while being superimposed on the line that guides the CO concentration signal to the operational amplifier AMP due to the influence of nearby radio waves by the resistor Rs for reducing the high-frequency gain characteristic. It was insufficient.

  The problems described above can not only occur in the CO alarm, but the gas concentration signal from the electrochemical gas sensor is amplified by an operational amplifier, and the target gas concentration in the surrounding atmosphere is determined by the amplified gas concentration signal. When measuring, a resistance for high-frequency noise countermeasures can occur widely when interposed between an electrochemical gas sensor and an operational amplifier.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas concentration measuring apparatus capable of accurately measuring a target gas concentration in an ambient atmosphere using an electrochemical gas sensor even when radio waves exist in the vicinity. Is to provide.

  The applicant has eagerly investigated the cause of the level fluctuation of the above-described amplified CO concentration signal. As a result, a high-frequency induced current caused by radio waves existing around the electrochemical CO sensor 1 leads the CO concentration signal to the operational amplifier AMP. Not only due to the superimposed flow in the line, but in the operational amplifier AMP, the constant voltage for operation supplied from a constant voltage circuit (not shown) is moved up and down by the high frequency component of the induced current superimposed on the CO concentration signal. The present inventors have found that it is believed to be caused by fluctuations and have completed the present invention.

That is, the gas concentration measuring device of the present invention described in claim 1 includes a water container for containing water, a proton conductor film installed in the water container, provided on the proton conductor film , A detection electrode where electrons are generated by the reaction between water vapor from the container and the target gas, and a position facing the detection electrode on the proton conductor film , and the electrons generated at the detection electrode are moved. An electrochemical gas sensor having a counter electrode for flowing a short-circuit current according to the target gas concentration, a reverse-phase input terminal to which the counter electrode is connected and the short-circuit current is input, and a detection electrode is connected to be fixed from a constant voltage source. An operational amplifier having a positive-phase input terminal to which a voltage is input, and an output terminal from which a gas concentration signal, which is a voltage value corresponding to the target gas concentration obtained by converting the short-circuit current into a voltage, is amplified and output. , The gas concentration measuring apparatus having, characterized in that it has a capacitor provided between a ground and a connection point between the counter electrode and the negative phase input terminal.

  According to a second aspect of the present invention, there is provided the gas concentration measuring device according to the first aspect of the present invention, wherein the gas concentration measuring device according to the first aspect has an inductor provided between the detection electrode and the positive phase input terminal. .

Further, the gas concentration measuring device according to the third aspect of the present invention includes a water container for containing water, a proton conductor film installed in the water container, provided on the proton conductor film , A detection electrode where electrons are generated by the reaction between water vapor from the container and the target gas, and a position facing the detection electrode on the proton conductor film , and the electrons generated at the detection electrode are moved. An electrochemical gas sensor having a counter electrode for flowing a short-circuit current according to the target gas concentration, a reverse-phase input terminal to which the detection electrode is connected and the short-circuit current is input, and a counter electrode to which a constant electrode is connected An operational amplifier having a positive-phase input terminal to which a voltage is input, and an output terminal from which a gas concentration signal, which is a voltage value corresponding to the target gas concentration obtained by converting the short-circuit current into a voltage, is amplified and output. , The gas concentration measuring apparatus having, characterized in that it has a capacitor provided between a ground and a connection point between said sensing electrode and said negative-phase input terminal.

  According to a fourth aspect of the present invention, there is provided the gas concentration measuring device according to the third aspect of the present invention, wherein the gas concentration measuring device includes an inductor provided between the counter electrode and the positive phase input terminal.

  According to the gas concentration measuring apparatus of the present invention described in claim 1, the magnitude according to the concentration of the target gas in the ambient atmosphere in which the high-frequency induced voltage generated by the surrounding radio waves flows from the counter electrode to the detection electrode. The constant voltage supplied from the constant voltage source to the positive phase input terminal periodically fluctuates up and down periodically according to the frequency of the induced current. As a result, the level of the gas concentration signal amplified by the operational amplifier should periodically fluctuate up and down according to the frequency of the induced current.

  However, the high-frequency induced voltage superimposed on the flow of the short-circuit current actually flows exclusively through the capacitor to the ground side, and hardly flows to the negative-phase input terminal side of the operational amplifier. The constant voltage supplied from the constant voltage source is maintained at a constant voltage without fluctuating due to the high frequency component of the induced current.

  For this reason, high-frequency induced current generated by the influence of devices that output high-frequency radio waves, such as mobile phones nearby, flows superimposed on the line where the short-circuit current flows between the counter electrode and the negative-phase input terminal of the operational amplifier. In this case, the constant voltage supplied from the constant voltage source to the operational amplifier due to the high frequency component of the induced current, and thus the level of the gas concentration signal amplified by the operational amplifier is prevented from fluctuating up and down. The level of the gas concentration signal after amplification can be set to a constant level according to the gas concentration in the surrounding atmosphere.

  In the gas concentration measuring apparatus according to the first aspect of the present invention, the capacitor itself has a resonance frequency, and a high-frequency component of the induced current flowing through the capacitor is superimposed on the resonance frequency in the flow of the short-circuit current. If the frequencies match, resonance occurs in the capacitor, and a high-frequency current having a magnitude exceeding the withstand voltage may flow through the capacitor and cause damage to the capacitor.

  However, as in the gas concentration measuring apparatus according to the second aspect of the present invention, an inductor is interposed between the detection electrode and the positive-phase input terminal of the operational amplifier so that the induced current superimposed on the short-circuit current flow is reduced. If the phase of the high frequency component is shifted, the frequency of the high frequency component of the induced current is shifted with respect to the resonance frequency of the capacitor so that resonance does not occur in the capacitor, or the breakdown voltage is not exceeded even if resonance occurs in the capacitor. Therefore, the amplitude of the component having the same frequency as the resonance frequency of the capacitor included in the induced current can be reduced so that the current has a magnitude of only.

  According to the gas concentration measuring apparatus of the present invention as set forth in claim 3, the magnitude according to the concentration of the target gas in the ambient atmosphere in which the high-frequency induced voltage generated by the surrounding radio waves flows from the counter electrode to the detection electrode. The constant voltage supplied from the constant voltage source to the positive phase input terminal periodically fluctuates up and down periodically according to the frequency of the induced current. As a result, the level of the gas concentration signal amplified by the operational amplifier should periodically fluctuate up and down according to the frequency of the induced current.

  However, the high-frequency induced voltage superimposed on the flow of the short-circuit current actually flows exclusively through the capacitor to the ground side, and hardly flows to the negative-phase input terminal side of the operational amplifier. The constant voltage supplied from the constant voltage source is maintained at a constant voltage without fluctuating due to the high frequency component of the induced current.

  For this reason, high-frequency induced current generated by the influence of devices that output high-frequency radio waves such as mobile phones nearby is superimposed on the short-circuit current line connecting the detection pole and the negative-phase input terminal of the operational amplifier. Even if it flows, the constant voltage supplied from the constant voltage source to the operational amplifier due to the high frequency component of the induced current, and thus the level of the gas concentration signal amplified by the operational amplifier, is prevented from fluctuating up and down. The level of the amplified gas concentration signal can be set to a constant level according to the gas concentration in the surrounding atmosphere.

  In addition, in the gas concentration measuring apparatus according to the third aspect of the present invention, the capacitor itself has a resonance frequency, and a high frequency component of the induced current flowing through the capacitor is superimposed on the resonance frequency in the short circuit current flow. If the frequencies match, resonance occurs in the capacitor, and a high-frequency current having a magnitude exceeding the withstand voltage may flow through the capacitor and cause damage to the capacitor.

  However, as in the gas concentration measuring apparatus according to the present invention as set forth in claim 4, an inductor is interposed between the counter electrode and the positive-phase input terminal of the operational amplifier, and the high frequency of the induced current superimposed on the flow of the short-circuit current. If the phase of the component is shifted, the frequency of the high frequency component of the induced current is shifted with respect to the resonance frequency of the capacitor so that resonance in the capacitor does not occur, or the breakdown voltage is not exceeded even if resonance occurs in the capacitor. The amplitude of the component having the same frequency as the resonance frequency of the capacitor included in the induced current can be reduced so that only a large current can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view of an electrochemical CO sensor built-in CO alarm device employing a gas concentration measuring apparatus according to an embodiment of the present invention. The electrochemical CO sensor built-in CO of the present embodiment indicated by reference numeral 100 in FIG. An alarm device (hereinafter abbreviated as “CO alarm device”) is used by suspending a resin case 110 on a hook 210 of a mounting member 200 that is attached to a wall surface (not shown) of an installation destination in advance. The

  Inside the case 110 are the electrochemical CO sensor 1 of FIG. 5 (corresponding to the electrochemical gas sensor in the claims) described in the section of the prior art, and the battery B shown in the circuit diagram of the electrical configuration in FIG. Constant voltage circuit 10, signal processing circuit 20, base voltage generation circuit 30 (corresponding to a constant voltage source in claims), switch circuit IC1, power switch SW, microcomputer (hereinafter abbreviated as “μCOM”) 40, An audio IC 50, an indicator 60, and a speaker 70 are incorporated.

  The constant voltage circuit 10 converts the voltage of the battery B to a constant voltage, and the signal processing circuit 20 is connected between the metal cap 8 and the metal can 2 of the electrochemical CO sensor 1 so as to be electrochemical. A CO concentration signal (corresponding to a gas concentration signal in the claims) having a voltage value corresponding to a short circuit current from the counter electrode 32 of the CO sensor 1 to the metal cap 8 to the detection electrode 31 through the metal can 2 and the signal processing circuit 20 is amplified. And output as a CO concentration signal after amplification.

  The base voltage generation circuit 30 generates a base voltage that determines a gain when the CO concentration signal is amplified in the signal processing circuit 20, and a metal cap 8 that is a terminal on the detection electrode 31 side of the electrochemical CO sensor 1 and a signal processing circuit. 20 to be supplied.

  The signal processing circuit 20 and the base voltage generation circuit 30 apply the constant voltage from the constant voltage circuit 10 while the power switch SW that is turned on when measuring the CO concentration in the ambient atmosphere of the CO alarm device 100 is turned on. The power source operates as a power source, and the base voltage generation circuit 30 outputs the signal to the metal cap 8 and the signal processing circuit 20 of the electrochemical CO sensor 1. The base voltage (reference voltage) that determines the gain of the operational amplifier AMP (see FIG. 3) in the signal processing circuit 20 is a constant voltage supplied from the constant voltage circuit 10 when measuring the CO concentration when the power switch SW is ON. For example, when the CO concentration is not measured when the power switch SW is OFF, the constant voltage power is not supplied from the constant voltage circuit 10 and is 0 V.

  The switch circuit IC1 operates with the constant voltage supplied from the constant voltage circuit 10 as the power source when the power switch SW is turned on, and is forcibly turned off when the CO concentration is not measured when the power switch SW is OFF. In this OFF state, the counter electrode 32 of the proton conductor film 3 is disconnected from the signal processing circuit 20 and the power switch SW is turned on to measure the CO concentration by the control of the μCOM 40 described later. When turned on, the signal processing circuit 20 is connected to the counter electrode 32 of the proton conductor film 3.

The μCOM 40 is always connected to the constant voltage circuit 1 regardless of whether the power switch SW is ON or OFF.
Operates in response to the supply of constant voltage power from 0, controls the ON / OFF of the power switch SW and the switch circuit IC1, and based on the CO concentration signal input from the signal processing circuit 20, a CO alarm device It is determined whether or not the CO concentration in the ambient atmosphere of 100 has reached the alarm level, and when it is reached, the indicator 60 is turned on and “Pippo-Pippo is dangerous because the air is dirty. Open the window and ventilate. Read out the voice message from the voice IC 50 and cause the speaker 70 to ring (voice output).

  Incidentally, the negative side of the battery B, the constant voltage circuit 10, the signal processing circuit 20, the base voltage generation circuit 30, the switch circuit IC1, and the μCOM 40 are all grounded (0 V).

  In the CO alarm device 100 having such a configuration, when the timing for intermittently measuring the CO concentration in the ambient atmosphere of the electrochemical CO sensor 1 is reached, the power switch SW is turned on by the control of the μCOM 40, whereby the switch The circuit IC1 is turned on so that the signal processing circuit 20 is connected to the counter electrode 32 of the proton conductor film 3 and supplied from the base voltage generation circuit 30 to the metal cap 8 which is a terminal on the detection electrode 31 side of the proton conductor film 3. The base voltage is changed from 0V to 2.7V.

  Then, electrons (2e−) generated at the detection electrode 31 of the proton conductor film 3 according to the CO concentration in the ambient atmosphere of the electrochemical CO sensor 1 are turned on by the switch circuit IC1 to turn on the metal can 2 and the signal processing circuit. 20, moves to the counter electrode 32 through the metal cap 8.

  Therefore, a short-circuit current flows through the signal processing circuit 20 on the movement path of the electrons (2e−), current-voltage conversion of the short-circuit current into a CO concentration signal in the signal processing circuit 20 and signal amplification are performed. In the μCOM 40 to which the CO concentration signal is input, it is determined whether or not the CO concentration indicated by the amplified CO concentration signal has reached the alarm level, and an alarm using the indicator 60 or the speaker 70 when the alarm level is reached. The operation is appropriately performed.

  Here, if radio waves exist around the CO alarm 100, a high-frequency induced current flows through the metal can 2 of the electrochemical CO sensor 1, and the metal can is measured when measuring the CO concentration when the power switch SW is ON. A high-frequency induced current is superimposed on the short-circuit current flow corresponding to the CO concentration in the ambient atmosphere, which flows from 2 through the signal processing circuit 20 to the metal cap 8.

  This state will be described with reference to the circuit diagram of FIG. 3 showing details of the signal processing circuit 20. The signal processing circuit 20 is an operational amplifier that operates by a constant voltage supplied from the constant voltage circuit 10 when the power switch SW is turned on. AMP and a parallel circuit of a resistor Rg for gain setting and a capacitor Cf as a low-pass filter connected between the output terminal and the negative phase input terminal of the operational amplifier AMP.

  The positive phase input terminal of the operational amplifier AMP is connected to the metal cap 8 to the detection pole 31 of the electrochemical CO sensor 1 via serial choke coils L3 and L4, and the electrochemical CO sensor is connected to the negative phase input terminal of the operational amplifier AMP. 1 is a capacitor C as a high-pass filter having one end grounded (0V) between the metal can 2 and the negative phase input terminal of the operational amplifier AMP. ) Is connected to the other end.

  In the CO alarm device having such a configuration, a high-frequency induced current generated by radio waves around the electrochemical CO sensor 1 flows from the metal can 2 toward the metal cap 8 according to the CO concentration in the ambient atmosphere. When the current is superposed on the flow of the short-circuit current, the base voltage of 2.7 V supplied from the base voltage generation circuit 30 to the positive-phase input terminal to which the metal cap 8 is connected in the operational amplifier AMP is induced. As a result, the level of the CO concentration signal amplified by the operational amplifier AMP should periodically fluctuate up and down according to the frequency of the induced current.

  However, the high-frequency induced current superimposed on the flow of the short-circuit current actually flows exclusively through the capacitor C to the ground side and hardly flows to the negative-phase input terminal side of the operational amplifier AMP. The base voltage supplied from the base voltage generation circuit 30 to the phase input terminal is not changed by the high frequency component of the induced current, and is kept constant at 2.7V.

  Therefore, the high frequency induction current that flows into the metal can 2 of the electrochemical CO sensor 1 due to the influence of a device that outputs a high frequency radio wave such as a mobile phone near the CO alarm device causes the metal can 2 and the operational amplifier AMP to Even when the current flows superimposed on a line through which a short-circuit current is connected to the negative-phase input terminal, the base voltage supplied to the operational amplifier AMP from the base voltage generation circuit 30 and thus the amplification are affected by the high frequency component of the induced current. The level of the subsequent CO concentration signal can be prevented from fluctuating up and down, and the level of the amplified CO concentration signal can be made constant according to the CO concentration in the surrounding atmosphere.

  Thereby, without disturbing the waveform of the CO concentration signal amplified by the operational amplifier AMP, the CO concentration is accurately detected, and an alarm by the indicator 60 or the speaker 70 indicating that the CO concentration in the ambient atmosphere has reached the alarm level. Can be displayed and sounded accurately.

  The capacitor C itself has a resonance frequency. When the frequency of the high frequency component of the induced current generated in the metal can 2 of the electrochemical CO sensor 1 and flowing through the capacitor C matches this resonance frequency, the capacitor C There is a possibility that resonance occurs at C, and a high-frequency current having a magnitude exceeding the breakdown voltage flows through the capacitor C, causing damage to the capacitor C.

  Therefore, the frequency of the high frequency component of the induced current is largely shifted with respect to the resonance frequency of the capacitor C so that resonance does not occur, or the amplitude of the component having the same frequency as the resonance frequency of the capacitor C included in the induced current is set. In order to ensure that the current does not exceed the withstand voltage of the capacitor C even when resonance occurs in the capacitor C, the metal cap 8 of the electrochemical CO sensor 1 and the positive phase input terminal of the operational amplifier AMP The phase of the high-frequency component of the induced current superimposed on the short-circuit current flow may be shifted by the series choke coils L3 and L4 interposed therebetween.

  However, the choke coils L3 and L4 may be omitted when the withstand voltage of the capacitor C has a sufficient margin. When the choke coils L3 and L4 are used, a single inductor is used for convenience of setting the inductor. Or a series circuit of three or more inductors.

  In this embodiment, the CO alarm device that measures the CO concentration and performs an alarm operation using the electrochemical CO sensor 1 has been described as an example. However, the present invention is not limited to CO, and the target gas is an electrochemical gas sensor. Needless to say, the present invention is widely applicable to the measurement of gas concentrations.

  In the embodiment described above, the counter electrode 32 is connected to the negative phase input terminal of the operational amplifier AMP and the detection electrode 31 is connected to the positive phase input terminal of the operational amplifier AMP. However, the present invention is not limited to this. . For example, as shown in FIG. 4, the detection electrode 31 may be connected to the negative phase input terminal of the operational amplifier AMP, and the counter electrode 32 may be connected to the positive phase input terminal of the operational amplifier AMP. In this case, the capacitor C is provided between the connection point between the detection electrode 31 and the negative phase input terminal and the ground. The inductors L3 and L4 are provided between the counter electrode 32 and the positive electrode input terminal.

  In the CO alarm device having such a configuration, a high-frequency induced current generated by radio waves around the electrochemical CO sensor 1 flows from the metal can 2 toward the metal cap 8 according to the CO concentration in the ambient atmosphere. When the current is superposed on the flow of the short-circuit current, the base voltage of 2.7 V supplied from the base voltage generation circuit 30 to the positive-phase input terminal to which the metal cap 8 is connected in the operational amplifier AMP is induced. As a result, the level of the CO concentration signal amplified by the operational amplifier AMP should periodically fluctuate up and down according to the frequency of the induced current.

  However, the high-frequency induced current superimposed on the flow of the short-circuit current actually flows exclusively through the capacitor C to the ground side and hardly flows to the negative-phase input terminal side of the operational amplifier AMP. The base voltage supplied from the base voltage generation circuit 30 to the phase input terminal is not changed by the high frequency component of the induced current, and is kept constant at 2.7V.

  Therefore, the high frequency induction current that flows into the metal can 2 of the electrochemical CO sensor 1 due to the influence of a device that outputs a high frequency radio wave such as a mobile phone near the CO alarm device causes the metal can 2 and the operational amplifier AMP to Even when the current flows superimposed on a line through which a short-circuit current is connected to the negative-phase input terminal, the base voltage supplied to the operational amplifier AMP from the base voltage generation circuit 30 and thus the amplification are affected by the high frequency component of the induced current. The level of the subsequent CO concentration signal can be prevented from fluctuating up and down, and the level of the amplified CO concentration signal can be made constant according to the CO concentration in the surrounding atmosphere.

  Thereby, without disturbing the waveform of the CO concentration signal amplified by the operational amplifier AMP, the CO concentration is accurately detected, and an alarm by the indicator 60 or the speaker 70 indicating that the CO concentration in the ambient atmosphere has reached the alarm level. Can be displayed and sounded accurately.

  The capacitor C itself has a resonance frequency. When the frequency of the high frequency component of the induced current generated in the metal can 2 of the electrochemical CO sensor 1 and flowing through the capacitor C matches this resonance frequency, the capacitor C There is a possibility that resonance occurs at C, and a high-frequency current having a magnitude exceeding the breakdown voltage flows through the capacitor C, causing damage to the capacitor C.

  Therefore, the frequency of the high frequency component of the induced current is largely shifted with respect to the resonance frequency of the capacitor C so that resonance does not occur, or the amplitude of the component having the same frequency as the resonance frequency of the capacitor C included in the induced current is set. In order to ensure that the current does not exceed the withstand voltage of the capacitor C even when resonance occurs in the capacitor C, the metal cap 8 of the electrochemical CO sensor 1 and the positive phase input terminal of the operational amplifier AMP The phase of the high-frequency component of the induced current superimposed on the short-circuit current flow may be shifted by the series choke coils L3 and L4 interposed therebetween.

  However, the choke coils L3 and L4 may be omitted when the withstand voltage of the capacitor C has a sufficient margin. When the choke coils L3 and L4 are used, a single inductor is used for convenience of setting the inductor. Or a series circuit of three or more inductors.

  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 perspective view showing one embodiment of a CO alarm with a built-in electrochemical CO sensor to which the present invention is applied. FIG. 2 is a circuit diagram of an electrical configuration built in the electrochemical CO sensor built-in CO alarm device of FIG. 1. FIG. 3 is a circuit diagram showing details of the signal processing circuit of FIG. 2. It is a circuit diagram which shows the detail of the signal processing circuit of FIG. 2 in other embodiment. It is sectional drawing which shows the structure of a general electrochemical CO sensor. FIG. 6 is a circuit diagram showing details of a conventional signal processing circuit that amplifies a CO concentration signal output from the electrochemical CO sensor of FIG. 5.

Explanation of symbols

1 Electrochemical CO sensor (electrochemical gas sensor)
30 Base voltage generator (constant voltage source)
31 detection electrode 32 counter electrode AMP operational amplifier C capacitor (capacitor)
L3, L4 Choke coil (inductor)

Claims (4)

A water container for containing water, a proton conductor film installed in the water container, a detection electrode provided on the proton conductor film and generating electrons due to a reaction between water vapor from the water container and a target gas And a counter electrode that is provided at a position facing the detection electrode on the proton conductor film and moves the electrons generated at the detection electrode to flow a short-circuit current according to the target gas concentration. An electrochemical gas sensor, a negative-phase input terminal to which the counter electrode is connected and the short-circuit current is input, a positive-phase input terminal to which the detection electrode is connected and a constant voltage is input from a constant voltage source, and the short-circuit current is a voltage In a gas concentration measuring device having an operational amplifier having an output terminal that amplifies and outputs a gas concentration signal that is a voltage value corresponding to the target gas concentration obtained by conversion,
A gas concentration measuring apparatus comprising a capacitor provided between a connection point between the counter electrode and the negative phase input terminal and ground.   The gas concentration measuring apparatus according to claim 1, further comprising an inductor provided between the detection electrode and the positive phase input terminal. A water container for containing water, a proton conductor film installed in the water container, a detection electrode provided on the proton conductor film and generating electrons due to a reaction between water vapor from the water container and a target gas And a counter electrode that is provided at a position facing the detection electrode on the proton conductor film and moves the electrons generated at the detection electrode to flow a short-circuit current according to the target gas concentration. An electrochemical gas sensor, a negative phase input terminal to which the detection electrode is connected and the short circuit current is input, a positive phase input terminal to which the counter electrode is connected and a constant voltage is input from a constant voltage source, and the short circuit current is a voltage In a gas concentration measuring device having an operational amplifier having an output terminal that amplifies and outputs a gas concentration signal that is a voltage value corresponding to the target gas concentration obtained by conversion,
A gas concentration measuring apparatus comprising a capacitor provided between a connection point between the detection electrode and the negative phase input terminal and ground.   The gas concentration measuring apparatus according to claim 3, further comprising an inductor provided between the counter electrode and the positive phase input terminal.

Images