JP4453872B2 - Electrochemical measuring device - Google Patents

Description

  The present invention relates to an electrochemical measurement device that electrochemically measures a specific component in an environment such as liquid or gas.

  Conventionally, as a type of electrochemical measurement device that electrochemically measures a specific component in an environment such as liquid or gas, for example, a working electrode made of a noble metal such as platinum (Pt) or gold (Au), and sodium chloride ( A reference electrode formed by immersing a metal part made of silver (Ag) and silver chloride (AgCl) in a gel-like or liquid internal solution made of NaCl) or potassium chloride (KCl) is immersed in sample water. Discloses an oxidation-reduction potentiometer that measures a voltage between a working electrode and a reference electrode generated by an oxidation-reduction reaction (see, for example, Patent Document 1 or Patent Document 2).

  Such an oxidation-reduction potentiometer has a problem that the non-linearity of the measured value is not good (the degree of non-linearity is large) because it depends on the instability of the reaction between the electrode and the sample water. In order to solve this problem, the present inventors have proposed that a resistor for reducing the impedance generated between the working electrode and the reference electrode is provided. According to this idea, since a current flows between the working electrode and the reference electrode via this resistance, the electrode and the sample water react stably, so that non-linearity is improved.

JP-A-11-64275 Japanese Patent Laid-Open No. 11-9566

  However, the resolution method based on the above idea has the following problems. When the resistance value between the working electrode and the reference electrode is small, the non-linearity of the output (voltage) generated between the working electrode and the reference electrode is particularly improved (the degree of non-linearity is particularly small) (see FIG. 8), while the output (voltage) generated between the working electrode and the reference electrode is small (see FIG. 8), and the reaction between the electrode and the sample water becomes dull. ) (See FIG. 9A). When the resistance value between the working electrode and the reference electrode is large, the output (voltage) generated between the working electrode and the reference electrode is large (see FIG. 8), and the reaction between the electrode and the sample water does not occur. While having the advantage that it is quick and is not easily affected by the stirring speed (the number of rotations of stirring) (see FIG. 9B), the nonlinearity of the output (voltage) generated between the working electrode and the reference electrode is very good. (The degree of non-linearity is relatively large. However, at a relatively low concentration (from 0 to about 0.4 mg / L), the degree of non-linearity is particularly small) (see FIG. 8).

  Therefore, in view of such a problem, an object of the present invention is to provide an electrochemical measurement apparatus that can easily measure a wide range with high accuracy.

  In order to achieve the above object, an electrochemical measurement apparatus of the present invention includes a working electrode that electrochemically reacts with a specific component in the environment, and a reference electrode that serves as a reference in the environment, and the working electrode An electrode group for outputting a detection value related to a specific component in the environment based on an electrochemical reaction by the reference and a reference by the reference electrode, and an impedance generated between the working electrode and the reference electrode in the environment In accordance with the impedance reduction means for reducing in stages, the amplification means for amplifying the detection value output by the electrode group in stages in response to the impedance reduction to each stage by the impedance reduction means, and the amplification means Normal value calculating means for obtaining a normal value of a specific component in the environment based on the amplified detection value.

  The impedance reduction means includes an impedance reduction circuit that connects a plurality of resistors in stages between the working electrode and the reference electrode, and a reduction circuit switching unit that switches a connection stage of the plurality of resistors in the impedance reduction circuit. The amplification means includes an amplification circuit that amplifies the detection value output from the electrode group in stages, and the amplification circuit according to switching to a connection stage of a plurality of resistors by the reduction circuit switching unit. And an amplification degree switching section for switching the amplification stage.

  The impedance reduction means is connected between a multi-stage voltage generation circuit that generates voltage stepwise, a potentiostat connected to the multi-stage voltage generation circuit, and the potentiostat and the working electrode. The amplifier comprises an impedance reduction circuit having an output resistance and a reduction circuit switching unit that switches a voltage generation stage in the multi-stage voltage generation circuit, and the amplification means amplifies the detection value output from the electrode group in a stepwise manner. And an amplification degree switching section that switches an amplification stage in the amplification circuit in accordance with switching to a voltage generation stage by the reduction circuit switching section.

  The electrochemical measurement apparatus according to the present invention reduces the impedance generated between the working electrode and the reference electrode in the environment step by step in the impedance reduction means (impedance reduction circuit and reduction circuit switching unit), thereby amplifying means (amplification circuit). And the amplification degree switching unit) amplify the reduced detection value output from the electrode group to a predetermined output level according to the reduced stage, and based on the amplified detection value in the normal value calculation means Find the normal value of a specific component in the environment. This makes it possible to appropriately reduce the impedance and amplify the detection value by the electrode group in accordance with the value of the specific component in the target environment. Therefore, there is an advantage that a wide range can be easily measured with high accuracy.

  The electrochemical measurement device of the present invention is configured by including an electrode group, impedance reduction means, amplification means, and normal value calculation means.

  The electrode group includes a working electrode that electrochemically reacts with a specific component in the environment (liquid, gas, etc.), and a reference electrode that serves as a reference in this environment. Then, a detection value related to a specific component (residual chlorine or the like) in the environment based on the electrochemical reaction by the working electrode and the reference by the reference electrode is output (voltage between electrodes).

  The impedance reducing means reduces the impedance generated between the working electrode and the reference electrode in the environment in a stepwise manner. More specifically, the impedance reduction is small when the value (concentration, etc.) of the specific component in the environment is small, and the impedance reduction is large when the value of the specific component in the environment is large.

  The amplifying means amplifies the detection value output from the electrode group in a stepwise manner in response to the impedance reduction to each stage by the impedance reducing means. In other words, the reduced detection value output from the electrode group in accordance with the stage where the impedance is reduced by the impedance reduction means, the predetermined output level (the normal value calculation means requires the normal value of the specific component in the environment) Amplified to the output level necessary for calculation with resolution).

  The normal value calculating means obtains a normal value of a specific component in the environment based on the detection value amplified by the amplifying means.

  The electrochemical measurement apparatus configured in this manner reduces the impedance generated between the working electrode and the reference electrode in the environment stepwise in the impedance reduction means, and the amplification means in the electrode group according to the reduced step. The reduced detection value output from is amplified to a predetermined output level, and the normal value calculation means can determine the normal value of the specific component in the environment based on the amplified detection value. According to this, according to the value of a specific component in the target environment, it is possible to appropriately reduce impedance and amplify the detected value by the electrode group, so that it is possible to easily measure a wide range with high accuracy. It will have.

  Hereinafter, the embodiment described above will be specifically described with reference to an example of an in-liquid residual chlorine concentration meter which is a kind of electrochemical measurement device.

  First, a specific configuration of the in-liquid residual chlorine concentration apparatus according to the present invention will be described with reference to an external view shown in FIG. 1 and a block diagram shown in FIG.

  The apparatus for concentration of residual chlorine in liquid according to the present invention includes a main body 1 having an input unit 4 and a display 5 on the front surface, a sensor body 2 having an electrode group 6 (working electrode 6a and reference electrode (reference electrode) 6b), A cable 3 for connecting the main body 1 and the sensor body 2 is provided in appearance, and includes an amplifier circuit 7, an A / D converter 8, an impedance reduction circuit 9, a reduction circuit switching unit 13, an amplification degree switching unit 14, an EEPROM 10, and a micro. The electronic board on which the computer 11 is arranged and the power supply unit 12 are provided inside the main body, so that the whole is roughly configured.

The input unit 4 includes an ON key 4 a , a start key 4 b, a mode key 4 c, a + key 4 d, and a − key 4 e, and inputs for power supply, measurement start, switching, and the like. ON key 4 a is used to start supplying electric power from the power supply unit 12 to the electrical system units. Start key 4b is intended to start the measurement. The mode key 4c is for switching to the calibration mode or the measurement mode. The + key 4d and the-key 4e are used for setting the calibration value of the sample water and selecting display items and numerical values.

  The display 5 displays the input status, measurement results, various modes, and the like.

  The sensor body 2 includes a working electrode 6a and a reference electrode 6b at the tip of a rod-shaped housing 2a, detects residual chlorine in the liquid, and generates an interelectrode voltage (detected value). The working electrode 6a is made of platinum (Pt), and generates a potential indicating the degree of reaction with residual chlorine when immersed in the liquid. The reference electrode 6b is formed by coating silver (Ag) with a silver chloride film (AgCl), and generates a reference potential when immersed in a liquid.

  The cable 3 is connected to the working electrode 6a and the reference electrode 6b of the sensor body 2 with one end of the conducting wire connected to the sensor body 2, and the other end of the conducting wire is an electronic board inside the main body 1. A connector 3a is provided so that the wiring connection is possible.

  The power supply unit 12 supplies power to each part of the electrical system.

  The amplifier circuit 7 is composed of a non-inverting amplifier circuit using feedback resistors R6 and R7 (R6 <R7) in the operational amplifier A1, and stepwise generates an inter-electrode voltage (analog signal) generated between the working electrode 6a and the reference electrode 6b. Amplify to.

  The A / D converter 8 converts the amplified interelectrode voltage into a digital signal.

  The impedance reduction circuit 9 is composed of a resistor R1 (for example, 10 MΩ) and a resistor R2 (for example, 200 kΩ) connected between the working electrode 6a and the reference electrode 6b, and the working electrode 6a and the reference electrode when immersed in liquid. Impedance generated between 6b and 6b is reduced.

  The EEPROM 10 stores a conversion coefficient value calculated by the microcomputer 11 and other various data in a rewritable manner.

  The microcomputer 11 includes a CPU, a calculation control program (switching control between the resistors R1 and R2 of the impedance reduction circuit 9, switching control between the resistors R6 and R7 of the amplifier circuit 7, calculation of a conversion coefficient, residual sample water Chlorine concentration calculation and other calculation control)-ROM for storing calculation formulas for calculating conversion factors, calculation formulas for calculating residual chlorine concentration in sample water, calculation result data, input data, etc. temporarily RAM, timer, I / O port, etc. stored in memory, switching control between resistors R1 and R2, switching control between resistors R6 and R7, calculation of conversion coefficient, calculation of residual chlorine concentration of sample water, and other various information Performs arithmetic control and the like.

  In addition, the reduction circuit switching unit 13 is configured by Sw1, Sw2, and the microcomputer 11. Further, Sw6, Sw7, and the microcomputer 11 constitute an amplification degree switching unit 14. The impedance reduction circuit 9 and the reduction circuit switching unit 13 constitute an impedance reduction unit. The amplification circuit 7 and the amplification degree switching unit 14 constitute amplification means. Further, the microcomputer 11 constitutes a normal value calculation means.

  Next, using the main flowchart shown in FIG. 3, specific operations and operations mainly in the measurement mode of the in-liquid residual chlorine concentration apparatus according to the present invention will be described.

When the ON key 4a is pressed, power is supplied from the power supply unit 12 to each part of the electric system (step S1), and the microcomputer 11 determines whether measurement or calibration is selected (step S2). When the mode key 4c is pressed (mode key is turned on in step S2), the calibration mode is entered (step S4). This calibration mode will be described in detail later.

  On the other hand, when the tip portion where the electrode group 6 of the sensor body 2 is placed is immersed in the sample water and the start key 4b is pressed (the start key is turned on in step S2), the OFF control from the ports P2 and P7 of the microcomputer 11 is performed. The switches Sw2 and Sw7 are turned off based on the signal, the resistors R2 and R7 are disconnected, and the switches Sw1 and Sw6 are turned on based on the ON control signal from the ports P1 and P6 of the microcomputer 11. R1 and R6 are connected (step S3).

  Subsequently, when an inter-electrode voltage (analog signal) is generated between the working electrode 6a and the reference electrode 6b, the generated inter-electrode voltage (analog signal) is amplified in the amplifier circuit 7, and the A / D converter 8 It converts into a digital signal and takes in in the microcomputer 11 (step S5).

  Subsequently, the microcomputer 11 calculates the interelectrode voltage generated between the working electrode 6a and the reference electrode 6b by dividing the interelectrode voltage taken in from the A / D converter 8 by the amplification degree in the amplifier circuit 7. Then, it is determined whether or not the calculated interelectrode voltage is 200 mV or more (step S6).

  Here, when the calculated interelectrode voltage is 200 mV or more (YES in step S6), the changeover switches Sw1 and Sw6 are turned off based on the OFF control signals from the ports P1 and P6 of the microcomputer 11, and the resistor R1 , R6 is disconnected, and the changeover switches Sw2, Sw7 are turned on based on the ON control signals from the ports P2, P7 of the microcomputer 11, and the resistors R2, R7 are connected (step S7).

  Subsequently, when an inter-electrode voltage (analog signal) is generated between the working electrode 6a and the reference electrode 6b, the generated inter-electrode voltage (analog signal) is amplified in the amplifier circuit 7, and the A / D converter 8 It converts into a digital signal and takes in in the microcomputer 11 (step S8).

  Subsequently, when the interelectrode voltage calculated in step S6 is not 200 mV or higher (NO in step S6), or after step S8, the microcomputer 11 converts the interelectrode voltage acquired from the A / D converter 8 into the EEPROM 10. By multiplying the stored conversion coefficient value, the residual chlorine concentration of the sample water is calculated (step S9), and the calculated residual chlorine concentration of the sample water (measured concentration value of the sample water) is displayed on the display 5. (Step S10).

  Thereafter, the process can be repeated by returning to step S2.

  Next, specific operations and operations mainly in the calibration mode of the in-liquid residual chlorine concentration apparatus according to the present invention will be described using a subroutine flowchart shown in FIG.

  First, when a calibration value of the sample water (residual chlorine concentration of the sample water accurately obtained by another method) is input with the + key 4d and the -key 4e, the calibration value of the sample water is temporarily stored in the RAM of the microcomputer 11. Store (step S21).

  Subsequently, the microcomputer 11 determines whether or not the input calibration value is 0.4 mg / L or more (step S22).

  If the input calibration value is not 0.4 mg / L or more (NO in step S22), the changeover switches Sw2 and Sw7 are turned off based on the OFF control signals from the ports P2 and P7 of the microcomputer 11. Then, the resistors R2 and R7 are disconnected, and the changeover switches Sw1 and Sw6 are turned on based on the ON control signal from the ports P1 and P6 of the microcomputer 11, and the resistors R1 and R6 are connected (step S23). ).

  On the other hand, when the input calibration value is 0.4 mg / L or more (YES in step S22), the selector switches Sw1 and Sw6 are turned off based on the OFF control signal from the ports P1 and P6 of the microcomputer 11. Then, the resistors R1 and R6 are disconnected, and the changeover switches Sw2 and Sw7 are turned on based on the ON control signals from the ports P2 and P7 of the microcomputer 11, and the resistors R2 and R7 are connected (step S24). ).

  Subsequently, when an interelectrode voltage (analog signal) is generated between the working electrode 6a and the reference electrode 6b after step S23 or step S24, the amplifying circuit 7 amplifies the generated interelectrode voltage (analog signal). The A / D converter 8 converts it into a digital signal and the microcomputer 11 takes it in (step S25).

  Subsequently, the microcomputer 11 calculates the conversion coefficient by dividing the calibration value of the sample water temporarily stored in the RAM by the interelectrode voltage taken from the A / D converter 8 (step S26). The calibration mode is exited (step S27).

  The above is the description of the example of the residual chlorine concentration meter in the liquid.

  In the above-described embodiment, the determination of the interelectrode voltage generated between the working electrode 6a and the reference electrode 6b in step S6 is 200 mV or more, and the determination of the sample water calibration value in step S22 is 0. The reason for determining whether or not it is 4 mg / L or more is that the resistance R1 is connected between the working electrode 6a and the reference electrode 6b as shown in the relationship graph between the interelectrode voltage and the residual chlorine concentration in FIG. Non-linearity in the range where the interelectrode voltage generated between the working electrode 6a and the reference electrode 6b when the concentration is detected is about 0 to 200 mV (corresponding to a residual chlorine concentration of 0 to 0.4 mg / L). This is because the non-linearity is particularly low (the degree of non-linearity is particularly small), and the non-linearity is not so good in the range beyond this (the degree of non-linearity is relatively large).

  In the above-described embodiment, the impedance reduction circuit is realized only by the resistors (R6, R7). However, as shown in the block diagram of FIG. 6, voltage generation circuits (R16, R17, R18, The impedance reduction circuit 21 may include R19), a potentiostat connected to the voltage generation circuit, and an output resistor (R20) connected between the potentiostat and the working electrode 6a. In this case, the reduction circuit switching unit 13 is a reduction circuit switching unit 22 configured only by the microcomputer 11.

  In addition, the impedance reduction circuit is realized by two resistors R6 and R7, but can be similarly implemented even if it is realized by a plurality of three or more.

  In addition, the electrode group is constituted by the working electrode and the reference electrode, and the detection system is configured to detect the voltage between the electrodes. However, the electrode group is constituted by the working electrode, the reference electrode and the reference electrode, and the working electrode and the reference electrode ( The present invention can be similarly implemented as a detection system that detects a current generated between the reference electrode and the reference electrode.

  In addition, the graph showing the relationship between the interelectrode voltage and the residual chlorine concentration shown in FIG. 5 is an example of data in the case of a certain electrode shape. The value is different. For example, the point (200 mV, 0.4 mg / L location) that shifts from the linear relationship of R1 to the non-linear relationship varies depending on the electrode shape and the like.

  The specific operation and operation mainly in the measurement mode of the liquid residual chlorine concentration apparatus according to the present invention have been described with reference to the main flowchart shown in FIG. 3, but the main flowchart shown in FIG. It may be done in a flow.

  Specific operations and operations mainly in the measurement mode according to the main flowchart shown in FIG. 7 will be described in detail. Steps S41 to S45 are the same as steps S1 to S5 in the main flowchart shown in FIG.

  Subsequent to step S45, the microcomputer 11 calculates the residual chlorine concentration of the sample water by multiplying the interelectrode voltage taken from the A / D converter 8 by the conversion coefficient value stored in the EEPROM 10 (step S45). S46).

  Subsequently, the microcomputer 11 determines whether or not the calculated residual chlorine concentration of the sample water is 0.4 mg / L or more (step S47).

  Here, when the calculated residual chlorine concentration of the sample water is 0.4 mg / L or more (YES in step S47), the changeover switch Sw1 based on the OFF control signals from the ports P1 and P6 of the microcomputer 11 is selected. Sw6 is turned off, resistors R1 and R6 are disconnected, and switches SW2 and Sw7 are turned on based on an ON control signal from ports P2 and P7 of microcomputer 11, and resistors R2 and R7 are connected. (Step S48).

  Subsequently, when an inter-electrode voltage (analog signal) is generated between the working electrode 6a and the reference electrode 6b, the generated inter-electrode voltage (analog signal) is amplified in the amplifier circuit 7, and the A / D converter 8 It converts into a digital signal and takes in in the microcomputer 11 (step S49).

  Subsequently, the microcomputer 11 calculates the residual chlorine concentration of the sample water after switching by multiplying the interelectrode voltage taken in from the A / D converter 8 by the conversion coefficient value stored in the EEPROM 10 (step S11). S50).

  Subsequently, when the residual chlorine concentration of the sample water is not 0.4 mg / L or more in step S47 (NO in step S47), or after step S50, the calculated residual water concentration (sample water) of the sample water is displayed on the display 5. (Measured concentration value) is displayed (step S51).

  Thereafter, the process can be repeated by returning to step S2.

It is an external view of a residual chlorine concentration apparatus (electrochemical measurement apparatus) in liquid. It is a block diagram of a residual chlorine concentration device (electrochemical measurement device) in liquid. It is a liquid residual chlorine concentration apparatus (electrochemical measurement apparatus) main flowchart. It is a subroutine flowchart of a residual chlorine concentration apparatus (electrochemical measurement apparatus) in a liquid. It is a graph which shows the relationship between the voltage between electrodes and residual chlorine concentration. It is another block diagram of the residual chlorine concentration apparatus (electrochemical type measuring apparatus) in a liquid. It is another main flowchart of the residual chlorine concentration apparatus (electrochemical type measuring apparatus) in a liquid. It is a graph which shows the relationship between an output (detection value regarding the specific component in an environment) and density | concentration (value of the specific component in an environment). (Background technology) It is a graph which shows the relationship between the ratio of the output between electrodes, and the stirring rotation speed. (Background technology)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main body 2 Sensor body 2a Rod-shaped housing 3 Cable 3a Connector 4 Input part 4a ON key 4b Start key 4c Mode key 4d + key 4e-key 5 Display 6 Electrode group 6a Working electrode 6b Reference electrode (reference electrode)
7 Amplification circuit 8 A / D converter 9, 21 Impedance reduction circuit 10 EEPROM
11 Microcomputer 12 Power supply unit 13, 22 Reduction circuit switching unit 14 Amplification switching unit

Claims (3)

A working electrode that electrochemically reacts with a specific component in the environment and a reference electrode that serves as a reference in the environment, and the environment based on the electrochemical reaction by the working electrode and the reference by the reference electrode A group of electrodes that output detection values relating to specific components of
Impedance reducing means for stepwise reducing impedance generated between the working electrode and the reference electrode in the environment;
Amplifying means for stepwise amplifying the detection value output by the electrode group in response to the reduction of impedance to each stage by the impedance reducing means;
Normal value calculation means for obtaining a normal value of a specific component in the environment based on the detection value amplified by the amplification means;
An electrochemical measurement device comprising: The impedance reduction means includes: an impedance reduction circuit that connects a plurality of resistors in stages between the working electrode and the reference electrode; and a reduction circuit switching unit that switches a connection stage of the plurality of resistors in the impedance reduction circuit. Consists of
The amplifying means includes an amplifying circuit that amplifies the detection value output by the electrode group in a stepwise manner, and an amplifying stage in the amplifying circuit according to switching to a connecting stage of a plurality of resistors by the reduction circuit switching unit. 2. The electrochemical measurement device according to claim 1, further comprising an amplification degree switching unit for switching. The impedance reduction means includes a multi-stage voltage generation circuit that generates a voltage stepwise, a potentiostat connected to the multi-stage voltage generation circuit, and an output resistor connected between the potentiostat and the working electrode. And a reduction circuit switching unit that switches a voltage generation stage in the multi-stage voltage generation circuit,
The amplification means includes an amplification circuit that amplifies the detection value output from the electrode group in stages, and an amplification that switches the amplification stage in the amplification circuit according to switching to a voltage generation stage by the reduction circuit switching unit. The electrochemical measurement device according to claim 1, further comprising a degree switching unit.

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