JP6382561B2 - Electrochemical measuring device - Google Patents

Description

  The present invention relates to an electrochemical measurement apparatus capable of detecting connection failure, disconnection abnormality, sensitivity deterioration degree, and the like of an electrochemical sensor.

  Patent Document 1 describes a function inspection device that detects a connection failure or disconnection abnormality of an internal / external lead wire of a constant potential electrolytic gas sensor as one of electrochemical sensors. As shown in FIG. 4, this functional inspection device includes a number generated by a pulse generator 80 for a constant potential electrolytic gas sensor 10 in which a working electrode 11, a counter electrode 12, and a reference electrode 13 are immersed in an electrolyte stored in a container. A voltage pulse of mV to several tens of mV is applied to the counter electrode 12 of the gas sensor 10 by the potentiostat circuit 70, and the current flowing at that time is generated by the ammeter 60 between the working electrode 11 and the counter electrode 12. Are respectively measured by the voltmeter 50, and the presence or absence of a connection failure or disconnection abnormality is determined based on the measurement results.

For example, when the pulse generator 80 generates a pulse voltage with an amplitude of 2 mV and a pulse width of 0.1 seconds and applies it to the gas sensor 10,
(1) Normal if the measured current value is 15 μA and the measured voltage is 0 V. (2) If the measured current value is 0 A and the measured voltage is 0 V, the working electrode 11 is broken. (3) The measured voltage is 15 μA and the measured voltage. Is 300 mV, it is determined that the counter electrode 12 is broken. Moreover, if the measurement result by the pulse voltage described above is compared between the initial use of the gas sensor 10 and the present time, the degree of sensitivity deterioration of the gas sensor 10 can be determined.

  The pulse generator 80 uses a D / A converter to apply a reference voltage (bias voltage) or a pulse voltage of several mV to several tens of mV to the potentiostat circuit 70, or FIG. As shown, a resistor divider circuit is used that divides the constant voltage generated by the constant voltage diode ZD by a resistor ladder including resistors R80, R81a, R81b, R82a, R82b, R83a, R83b, R84a, and R84b. SW81 is a switch for selecting a reference voltage or a pulse voltage.

  In FIG. 5, for example, resistors R81a and R81b are for the first reference voltage Vref1, resistors R82a and R82b are for the second reference voltage Vref2, resistors R83a and R83b are for the third reference voltage Vref3, and resistors R84a and R84b are It is set for the fourth reference voltage Vref4. The resistance values are set to R81b <R81a, R82b <R82a, R83b <R83a, and R84b <R84a.

  When used as a normal gas sensor, one of the reference voltages Vref1 to Vref4 is selected and set by switching the switch SW81 according to the gas sensor 10, and the normal rotation input terminal of the potentiostat circuit 70 Apply to.

  Also, when checking connection failure, disconnection abnormality, sensitivity deterioration degree, or the like, when the reference voltage Vref1 is set by the switch SW81 according to the type of the gas sensor 10, the switch SW81 is temporarily set to the reference voltage. By switching to Vref1 + α, a pulse voltage having a magnitude α (= several mV to several tens mV) corresponding to the resistance of the resistor R81b is generated. When the reference voltage Vref2 is set, the pulse voltage having a magnitude β (= several mV to several tens mV) corresponding to the resistance of the resistor R82b is temporarily switched by switching the switch SW81 to the reference voltage Vref2 + β. Is generated. Similarly, when the reference voltages Vref3 and Vref4 are set, by temporarily switching the switch SW81 to the reference voltages Vref3 + γ and Vref4 + δ, the magnitudes γ and δ (= several mV) corresponding to the resistances of the resistors R83b and R84b. A pulse voltage of about tens of mV).

Japanese Patent No. 2613316

  However, when the D / A converter described above is used, there is a problem that the circuit scale and current consumption increase. In addition, when the resistance dividing circuit described in FIG. 5 is used, a plurality of types of reference voltages are required when corresponding to various types of gas sensors, and therefore each reference voltage is about several mV to several tens of mV. Resistors (resistors R81b, R82b, R83b, R84b in FIG. 5) for generating a changing pulse voltage are required. Also, when generating a pulse voltage that varies from several mV to several tens of mV from a constant voltage diode ZD of about 1.25 V, the required resistance ratio (resistance weighting, for example, the resistance ratio of R81a and R81b) increases. It becomes difficult to ensure accuracy.

  An object of the present invention is to generate an offset voltage with an operational amplifier constituting a potentiostat circuit so as to generate a pulse voltage for detecting an electrochemical sensor connection failure, disconnection abnormality, sensitivity deterioration degree, etc. It is an object of the present invention to provide an electrochemical measuring apparatus that solves the problems of current, the large-scaled resistance dividing circuit, and the problem of reduced detection accuracy.

In order to achieve the above object, an invention according to claim 1 includes an electrochemical sensor in which at least a working electrode and a counter electrode are immersed in a stored electrolyte, and a potentiostat circuit that applies a predetermined voltage to the counter electrode. An electrochemical measuring device for measuring an output current of the electrochemical sensor or an output voltage obtained by converting the output current into a voltage, wherein the potentiostat circuit is configured by an operational amplifier , and the normal output side load resistance and the inverted output of the operational amplifier Set a side load resistance to the same resistance value, and provide a switch that switches the resistance value of the normal output side load resistance or the inverted output side load resistance to another resistance value, and the switch is turned on to off. The offset pulse generated in step 1 is applied to the electrochemical sensor .

According to a second aspect of the present invention, in the electrochemical measurement device according to the first aspect, the switch has a plurality of resistance values different from each other in resistance values of the normal output side load resistance or the inverted output side load resistance. An offset pulse generated by switching one of the plurality of switches from on to off is applied to the electrochemical sensor. characterized in that it was.

  According to the present invention, since the offset voltage generating means is provided in the operational amplifier constituting the potentiostat circuit, a pulse voltage can be generated by the offset voltage generating means, and the connection failure of the electrochemical sensor, the disconnection abnormality, or the sensitivity deterioration. When detecting the degree or the like, it is not necessary to provide an additional circuit or a small current consumption as in the case of using a D / A converter, and it is not necessary to provide a resistance ladder in which a large resistance ratio is set. For this reason, problems such as an increase in circuit scale and a decrease in detection accuracy are not caused. If the offset voltage generating means is composed of switches and a plurality of switches are used, the amplitude of the generated pulse voltage can be set more finely, and more types of electrochemical sensors can be connected poorly or broken, and the degree of sensitivity deterioration. It can apply to the detection of etc.

It is a block diagram of the electrochemical measuring device of one Example of this invention. It is a circuit diagram of the modification of the potentiostat circuit of the electrochemical measuring device of FIG. It is a circuit diagram of another modification of the potentiostat circuit of the electrochemical measuring device of FIG. It is a block diagram of the conventional electrochemical measuring device which uses a constant potential electrolytic gas sensor. It is a specific circuit diagram of the pulse voltage generation circuit of the electrochemical measuring device of FIG.

  FIG. 1 shows an electrochemical measurement apparatus according to one embodiment of the present invention. Reference numeral 10 denotes a constant potential electrolytic gas sensor in which an electrolytic solution is accommodated in a container, and a working electrode 11, a counter electrode 12, and a reference electrode 13 are immersed in the electrolytic solution.

  Reference numeral 20 denotes an operational amplifier constituting a potentiostat circuit, which has a normal rotation input terminal 21, an inverting input terminal 22, and an output terminal 23, and further includes differentially connected PMOS transistors MP1 and MP2, a current source 24, and a current mirror connection. NMOS transistors MN1 and MN2 as active loads, normal output side load resistors R11 and R12, inverted output side load resistors R21 and R22, an inverting amplifier 25, and a switch SW11 for short-circuiting the resistor R12. The inverting input terminal 22 is connected to the verification electrode 13 of the gas sensor 10, and the output terminal 23 is connected to the counter electrode 12 of the gas sensor 10. The resistance values of the resistors R11, R12, R21, and R22 are set to R11 = R21 and R12 = R22. That is, the total resistance value of the normal output side load resistors R11 and R12 and the total resistance value of the inverted output side load resistors R21 and R22 are the same.

  Reference numeral 30 denotes an operational amplifier constituting a current / voltage conversion circuit, which includes an oscillation preventing resistor R31 and a feedback resistor R32, and converts the current signal Iout output from the gas sensor 10 into a voltage signal Vout and outputs the voltage signal Vout. 31 is a normal rotation input terminal, 32 is an inverting input terminal, and 33 is an output terminal.

  Reference numeral 40 denotes a reference voltage generation circuit, which selects one voltage from four reference voltages Vref1 to Vref4 obtained by dividing the power supply voltage Vdd by five resistors R41 to R45 by the switch SW41, and inputs the normal rotation of the operational amplifier 20 The signal is supplied to the terminal 21, selected by the switch SW 42, and supplied to the normal input terminal 31 of the operational amplifier 30.

  50 is a voltmeter that measures the voltage applied between the working electrode 11 and the counter electrode 12 of the gas sensor, and 60 is an ammeter that measures the output current of the gas sensor 10.

  Now, in the normal usage mode of the gas sensor 10, the voltmeter 50 and the ammeter 60 are removed, and the switch SW11 of the operational amplifier 20 is set to OFF. Further, a reference voltage corresponding to the standard of the gas sensor 10 is selected by the switch SW41 of the reference voltage generation circuit 40 and input to the normal input terminal 21 of the operational amplifier 20, and the reference voltage selected by the switch SW42 is the positive voltage of the operational amplifier 30. Input to the rotation input terminal 31. In this set state, gas detection is performed by the gas sensor 10, and an output voltage Vout corresponding to the detection result is output from the output terminal 33 of the operational amplifier 30.

  Next, when detecting a connection failure, disconnection abnormality, sensitivity deterioration degree, etc. of the gas sensor 10, the voltmeter 50 and the ammeter 60 are attached, and the switching state of the switches SW41 and SW42 of the reference voltage generation circuit 40 is left as it is. In the state, the switch SW11 of the operational amplifier 20 is instantaneously turned on / off. As a result, an offset voltage of several mV to several tens of mV is generated as a pulse voltage from the operational amplifier 10 and appears at the output terminal 23.

Therefore, the pulse voltage of the offset voltage generated by switching the switch SW11 from on to off is 2 mV and the pulse width is 0.1 second as in the case described with reference to FIG. 4, and the gas sensor 10 has been described with reference to FIG. If it is the same as the gas sensor 10,
(1) Normal if the measured current value is 15 μA and the measured voltage is 0 V. (2) If the measured current value is 0 A and the measured voltage is 0 V, the working electrode 11 is broken. (3) The measured voltage is 15 μA and the measured voltage. Is 300 mV, it can be determined that the counter electrode 12 is broken. Moreover, if the measurement result by the pulse voltage described above is compared between the initial use of the gas sensor 10 and the present time, the degree of sensitivity deterioration of the gas sensor 10 can be determined.

  FIG. 2 is a circuit showing an operational amplifier 20A which is a modification of the operational amplifier 20 described with reference to FIG. 1. The forward load resistance is composed of four resistors R13, R14, R15, and R16, and four inverting load resistors are included. Are provided with a switch SW12 that short-circuits the resistors R14 to R16, a switch SW13 that short-circuits the resistors R15 and R16, and a switch SW14 that short-circuits the resistor R16. The resistance values are set to R13 = R23, R14 = R24, R15 = R25, and R16 = R26.

  In the operational amplifier 20A, when the gas sensor 10 is normally operated, the switches SW12 to SW14 are turned off. Further, when detecting a connection failure, disconnection abnormality, sensitivity deterioration degree, or the like of the gas sensor 10, any one of the switches SW12 to SW14 is turned on / off. When the switch SW12 is turned on → off, the offset voltage is maximized, so that a pulse voltage with the maximum amplitude is generated. When the switch SW13 is turned on → off, the offset voltage becomes middle, so the pulse voltage with the middle amplitude is generated. When the switch SW14 is switched from on to off, the offset voltage is minimized, and a pulse voltage with the minimum amplitude is generated. As a result, a plurality of pulse voltages of several mV to several tens of mV can be generated, so that it is possible to detect a connection failure, disconnection abnormality, sensitivity deterioration degree, and the like of a plurality of types of gas sensors 10.

  FIG. 3 is a circuit showing an operational amplifier 20B as another modification of the operational amplifier 20 described in FIG. 1. In addition to the switches SW12 to SW14 described in FIG. 2, a switch SW22 that short-circuits resistors R24 to R26, a resistor R25, A switch SW23 for short-circuiting R26 and a switch SW24 for short-circuiting the resistor R26 are further added.

  In the operational amplifier 20B, when the gas sensor 10 is normally operated, the switches SW12 to SW14 and SW22 to SW24 are turned off. Further, when the switch SW12 to SW14 is turned on / off when detecting a connection failure, disconnection abnormality, sensitivity deterioration degree, or the like of the gas sensor 10, large, medium, and small pulses are performed as in the case of the circuit of FIG. A voltage is generated, but when the switches SW22 to SW24 are turned on / off, large, medium and small negative pulse voltages are generated, unlike the case of the circuit of FIG. As described above, the operational amplifier 20B of FIG. 3 can generate a plurality of positive and negative pulse voltages (± several mV to ± several tens of mV).

  In the embodiment described above, the case of detecting the connection failure, disconnection abnormality, sensitivity deterioration degree, etc. of the constant potential electrolytic gas sensor 10 has been described. However, the present invention is not limited to the constant potential electrolytic gas sensor. For all types of electrochemical sensors including those having no poles, it is possible to detect connection failures, disconnection abnormalities, sensitivity deterioration degrees, and the like.

10: constant potential electrolytic gas sensor, 11: working electrode, 12: counter electrode, 13: reference electrode, 20: operational amplifier, 21: forward input terminal, 22: inverting input terminal, 23: output terminal, 24: current source, 25: Inverting amplifier 30: operational amplifier, 31: normal input terminal, 32: inverted input terminal, 33: output terminal 40: reference voltage generation circuit 50: voltmeter 60: ammeter 70: operational amplifier 80: pulse voltage generation circuit

Claims (2)

An electrochemical sensor having at least a working electrode and a counter electrode immersed in a stored electrolyte, and a potentiostat circuit for applying a predetermined voltage to the counter electrode, and converting the output current of the electrochemical sensor or the output current into a voltage In an electrochemical measurement device that measures the output voltage
The potentiostat circuit is composed of an operational amplifier, the normal output side load resistance and the inverted output side load resistance of the operational amplifier are set to the same resistance value, and the normal output side load resistance or the resistance of the inverted output side load resistance An electrochemical measurement apparatus comprising a switch for switching a value to another resistance value, and an offset pulse generated when the switch is turned on to off is applied to the electrochemical sensor . In the electrochemical measuring device according to claim 1,
The switch comprises a plurality of switches for setting the resistance value of the normal output side load resistor or the inverted output side load resistor to one resistance value selected from a plurality of different resistance values.
An electrochemical measurement apparatus, wherein an offset pulse generated when one of the plurality of switches is turned on → off is applied to the electrochemical sensor .