JP2008107202A - Device for measuring oxidation/reduction material concentration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an device for measuring oxidation/reduction material concentration that dispenses with a means for controlling the flow rate of liquid to be measured, or a movable part, such as a motor for making an electrode rotate or vibrate itself. <P>SOLUTION: This device is equipped with a measuring tube 1, through which the liquid to be measured, containing an oxidation or reduction material, flows; a detection electrode 2 and a counter electrode 3 provided in contact with the liquid to be measured in the facing state on the inner wall surface of the measuring tube 1; a power supply circuit 4 for applying a voltage, set beforehand in between the detection electrode 2 and the counter electrode 3; a diffusion current detection circuit 5 for detecting the diffusion current, flowing between the detection electrode 2 and the counter electrode 3; an oxidizing/reducing material content calculating circuit 6 for calculating the content concentration of the oxidizing or reducing material, based on the diffusion current detected by the diffusion current detection circuit 5; and a restriction mechanism 7, provided in the circumscribed state to the inner circumferential wall surface of the measuring tube 1, on the upstream side of the detection electrode 2 and the counter electrode 3, for making the pressure loss of the flow of the liquid to be measured generated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an oxidation / reduction substance concentration measuring device for obtaining the concentration of oxidation or reduction substance such as residual chlorine contained in tap water by measuring diffusion current due to oxidation or reduction reaction generated near two electrodes.

  In general, an oxidation / reduction substance concentration measuring device immerses two electrodes in a liquid to be measured and applies a voltage between the electrodes, thereby generating a diffusion current due to an oxidation or reduction reaction generated near the electrodes. Measure.

  It is known that the value of the diffusion current and the concentration of oxidation or reduction substances in the measured liquid have a certain relationship as shown in the following formula. Based on the value of the diffusion current, the measured liquid The concentration of oxidized or reduced substances is calculated.

Diffusion current = K × concentration Here, K is a constant determined by the valence of the reactant, the Faraday constant, the diffusion coefficient, the area of the electrode to be detected, and the thickness of the diffusion layer.

  In order to stably measure the diffusion current from a continuously flowing aqueous solution such as tap water, it is necessary to keep the electrode surface area and the thickness of the diffusion layer constant. The thickness of this diffusion layer is measured. Influenced by changes in liquid flow rate.

  For this reason, the conventional concentration measuring devices for oxidation / reduction substances need to keep the flow rate of the liquid to be measured constant. Therefore, if there is a change in the flow rate, the flow rate sensor measures the flow rate and the diffusion current due to the flow rate change. A means for correcting the increase / decrease in the amount is taken.

  A technique for adjusting the amount of water and using a constant flow valve is disclosed in an oxidation / reduction substance concentration measuring device that maintains a constant flow rate (see, for example, Patent Document 1).

  In addition, an oxidation / reduction substance concentration measuring device that measures and corrects a flow rate is disclosed in which a vortex generator is provided in a flow path, the flow rate is calculated from the frequency of Karman vortices, and the flow rate is corrected. (For example, refer to Patent Document 2).

If the flow rate is small, a constant forced convection is applied to the tip of the electrode by rotating or vibrating the electrode itself at a constant speed or stirring the liquid to be measured at a constant speed in order to reduce the effects of flow rate changes. And a technique for making the thickness of the diffusion layer constant is disclosed (for example, see Patent Document 3).
JP 2000-46795 (2nd page, FIG. 1) JP2000-171432 (first page, FIG. 1) Japanese Patent Laid-Open No. 9-288083 (first page, FIG. 1)

  In various conventional oxidation / reduction substance concentration measuring devices as described above, the flow rate is affected, so the flow rate is constant, the electrode itself is rotated or vibrated at a constant speed, or the liquid to be measured is It was necessary to stir at a constant speed.

  When correcting the change in flow rate, it is necessary to attach a flow rate sensor different from the oxidation / reduction substance concentration measuring device, which causes a problem that the device becomes large.

  In order to make the flow rate constant, a method of controlling the flow rate using a constant flow valve or a water receiving tank at the top of the measurement tank immersed in the electrode, keeping the water surface of the water receiving tank and the measuring tank constant, the pressure difference Even in the case of the method of controlling the flow rate by means of the above, there is a concern that the apparatus becomes large, and when a constant flow valve is used, there is a concern that the flow rate may change due to clogging, so periodic maintenance is required. There's a problem.

  When the electrode itself rotates or vibrates at a constant speed, or when driving by a motor for stirring the liquid to be measured at a constant speed is required, rotation, vibration or stirring of the liquid to be measured due to a failure of the drive motor Is a problem that requires regular maintenance.

  The present invention has been made to solve the above problems, and is an oxidation / reduction substance having no moving parts such as means for controlling the flow rate of the liquid to be measured and a motor for rotating or vibrating the electrode itself. An object is to provide a concentration measuring device.

  In order to achieve the above object, an oxidation / reduction substance concentration measurement apparatus according to claim 1 of the present invention is opposed to a measurement tube in which a liquid to be measured containing an oxidation or reduction substance flows, on the inner wall surface of the measurement tube, A detection electrode and a counter electrode provided in contact with the liquid to be measured, a power supply circuit that applies a preset voltage between the detection electrode and the counter electrode, and a diffusion current that flows between the detection electrode and the counter electrode A diffusion current detection circuit for detecting the concentration, an oxidation / reduction substance concentration calculation circuit for calculating the concentration of the oxidized or reduced substance based on the diffusion current, and an upstream side of the detection electrode and the counter electrode, And a throttle mechanism that is provided so as to circumscribe the peripheral wall surface and generates a pressure loss in the flow of the liquid to be measured.

  In order to achieve the above object, an oxidation / reduction substance concentration measuring apparatus according to claim 2 of the present invention comprises a measuring tube through which a liquid to be measured containing an oxidizing or reducing substance flows, and an outer peripheral wall of the measuring tube. A throttling mechanism for generating a pressure loss of the flow of the liquid to be measured, and a symmetrical position on the upstream side and the downstream side of the liquid to be measured on the inner wall surface of the measuring pipe from the attachment position of the throttling mechanism Two sets of counter electrodes that are opposed to each other and are provided in contact with the liquid to be measured, a pressure detector that measures the pressure on the upstream side and the downstream side of the throttle mechanism, and the pressure detector A counter electrode switching control circuit for comparing the pressure on the upstream side and the lower side detected in step, determining the direction in which the liquid to be measured flows, and selecting a set of the counter electrodes on the side determined to be the downstream side; Between the counter electrodes selected by the electrode switching circuit A power supply circuit for applying a preset voltage; a diffusion current detection circuit for detecting a diffusion current flowing between the counter electrodes selected by the electrode switching circuit; and a concentration of an oxidizing or reducing substance based on the diffusion current And an oxidizing / reducing substance concentration calculation circuit for calculating

  In order to achieve the above object, an oxidation / reduction substance concentration measuring device according to claim 3 of the present invention is opposed to a measurement tube through which a liquid to be measured containing an oxidation or reduction substance flows, and the inner wall surface of the measurement tube, A plurality of counter electrodes each having a detection electrode and a counter electrode provided in contact with the liquid to be measured; and provided on the upstream side of the plurality of counter electrodes and in contact with an inner peripheral wall surface of the measurement tube. A throttling mechanism that generates a pressure loss of the flow of the gas, a power supply circuit that generates a preset measurement voltage, adhesion determination voltage, and cleaning voltage applied between the counter electrodes, and a plurality of the counter electrodes A diffusion current detection circuit that measures a diffusion current flowing through each of the currents, an oxidation / reduction substance concentration calculation circuit that calculates a content concentration of an oxidation or reduction substance based on the diffusion current when the measurement voltage is applied, Between the counter electrodes A switch for switching the measurement voltage, the adhesion determination voltage, and the cleaning voltage independently, and an applied voltage switching control circuit that selectively controls the switch by the diffusion current. .

  As described above, according to the present invention, there is provided a throttling mechanism for the liquid to be measured flowing in the measurement tube on the upstream side of the detection electrode and the counter electrode provided in contact with the liquid to be measured and in contact with the liquid to be measured. Since the pressure loss is generated and the turbulent flow is generated downstream of the throttling mechanism so that the thickness of the diffusion layer of the liquid to be measured is made constant, the means for controlling the flow rate of the liquid to be measured and the measurement It is possible to provide an oxidation / reduction substance concentration measuring apparatus that does not have a movable part that stirs a liquid to be measured in a tube.

  Embodiments of the present invention will be described below with reference to the drawings.

  Example 1 of an oxidation / reduction substance concentration measuring apparatus according to the present invention will be described with reference to the drawings. FIG. 1 (a) is a block diagram showing an embodiment of the oxidation / reduction substance concentration measuring apparatus of the present invention, and FIG. 1 (b) is a view from the tube axis direction indicated by the xx arrow in FIG. 1 (a). FIG.

  The oxidation / reduction substance concentration measuring apparatus according to the present invention will be described in the case where, for example, the residual chlorine concentration of tap water is measured, in which the liquid to be measured contains an oxidation or reduction substance.

  A measurement tube 1 for flowing the liquid to be measured, a detection electrode 2 and a counter electrode 3 provided to face the tube wall of the measurement tube 1, and a measurement voltage set in advance between the detection electrode 2 and the counter electrode 3 are applied. A power source circuit 4, a diffusion current detection circuit 5 that detects a diffusion current flowing between the detection electrode 2 and the counter electrode 3, and an oxidation or reduction substance such as residual chlorine contained in the liquid to be measured from the output of the diffusion current detection circuit 5 An oxidizing / reducing substance concentration calculating circuit 6 for obtaining the concentration of concentration; and a throttle mechanism 7 provided on the upstream side of the detection electrode 2 and the counter electrode 3 so as to circumscribe the inner peripheral wall surface of the measuring tube 1 and having a preset opening inner diameter; Consists of.

  Next, the detail of each part is demonstrated. The measuring tube 1 is made of an insulator such as vinyl chloride, and the detection electrode 2 and the counter electrode 3 are opposed to the inner wall surface of the measuring tube 1 while being in close contact with or protruding from the inner wall surface, as shown in FIG. Each of them is wetted and fixed.

  When measuring the residual chlorine concentration contained in tap water, it is desirable that the electrode is made of gold for the detection electrode 2 and silver or silver chloride for the counter electrode 3.

  The power supply circuit 4 is a stabilized power supply that generates a DC voltage of about ± 500 mV, and a voltage in a range in which the diffusion current and the concentration are proportional is preset. The diffusion current detection circuit 5 that measures the diffusion current flowing between the detection electrode 2 and the counter electrode 3 when this voltage is applied has a circuit configuration that can detect a current of several μA level.

  The oxidation / reduction substance concentration calculation circuit 6 is composed of a microcomputer having a storage and calculation function, stores the relationship between the concentration of the liquid to be measured and the diffusion current in a table, and stores the detected diffusion current. The corresponding density is determined with reference to this table.

  The throttle mechanism 7 is an insulating plate made of polyvinyl chloride or the like made of the same material as the measurement tube 1, and a donut plate having a throttle hole concentric with the measurement tube 1 is formed on the inner peripheral wall surface of the measurement tube 1 in a direction perpendicular to the tube axis. The outer periphery of the disk is joined and fixed.

  The material of the measuring tube 1 and the diaphragm mechanism 7 may be any structure that does not affect the mechanical strength required for these and the measurement of diffusion current. A structure in which an insulating material is lined on the liquid contact portion may be employed.

  The diameter d1 of the throttle hole of the throttle mechanism 7 is between the throttle mechanism 7 and the detection electrode 2 and the counter electrode 3 downstream thereof so that the diffusion current does not change within the change range of the flow velocity of the liquid to be measured which is predicted in advance. A diameter d1 at which a constant turbulent state occurs on the liquid contact surface of the detection electrode 2 and the counter electrode 3 and the distance d2 are selected in advance within a predetermined distance d2.

  For example, FIG. 2 illustrates the relationship between the diffusion current (μA) and the flow rate (L / min) when tap water containing residual chlorine, which can be regarded as the same concentration according to the present invention, is passed through the measuring tube 1 having the diameter D. The broken line indicates the characteristic when the diaphragm mechanism 7 is not provided, the solid line indicates the characteristic when the diaphragm mechanism 7 according to the present invention is provided, and the one-dot broken line indicates the characteristic of the conventional method in which the electrode itself is rotated.

  In the experiment according to the present invention, the aperture ratio α (= d1 / D) of the aperture mechanism 7 is set to 0.2 to 0.75, and the distance d2 between the detection electrode 2 and the counter electrode 3 is set to a range of 0.5D to 2D. As shown by the solid line, even if the flow rate of the liquid to be measured having the same concentration changes in the range of 2 (L / min) to 10 (L / min), the value of the diffusion current is 0.55 to 0.00. It was confirmed that the level value was almost the same as 65 (μA).

  As shown in FIG. 2, when the detection electrode 2 and the counter electrode 3 are provided in the straight measuring tube 1 not provided with the throttle mechanism 7, the diffusion current is approximately proportional to the increase in the flow rate as shown by the broken line. However, in the case where the diaphragm mechanism 7 is provided, the diffusion current value has the same level of stability as the conventional method shown by the one-dot broken line as shown by the solid line.

  That is, the oxidation / reduction substance concentration measuring apparatus including the throttle mechanism 7 configured as described above is a liquid to be measured such as a polarographic method as disclosed in Patent Document 3 due to turbulent flow generated on the downstream side of the throttle mechanism 7. The same effect as that obtained by stirring can be obtained, and measurement that is not easily affected by changes in flow rate can be performed.

  A second embodiment of the oxidation / reduction substance concentration measurement apparatus of the present invention will be described with reference to FIGS.

  FIG. 3 is a block diagram of Embodiment 2 of the oxidation / reduction substance concentration measuring apparatus of the present invention, and FIG. 4 is a flowchart for explaining the operation thereof. About each part of Example 2, the same part as the oxidation / reduction substance density | concentration measuring apparatus of Example 1 shown in FIG. 1 attaches | subjects the same symbol, and abbreviate | omits the description.

  The difference between the second embodiment and the first embodiment is that in the first embodiment, the counter electrode composed of the detection electrode 2 and the counter electrode 3 is attached to the inner peripheral wall surface of the measurement tube 1 in the direction perpendicular to the tube axis. In the downstream direction of the concentric disc diaphragm mechanism 7, it is provided within a predetermined distance from the diaphragm mechanism 7. However, in the second embodiment, a pair of counter electrodes symmetrically on the tube axis with respect to the mounting position of the diaphragm mechanism 7. Are further measured, and the pressure in the two measurement tubes 1 on the left and right sides of the throttle mechanism 7 is measured to determine the direction in which the liquid to be measured flows, and the counter electrode on the downstream side of the liquid to be measured is automatically selected. Thus, the concentration of the liquid to be measured is measured.

  In FIG. 3, the detection electrode 2 </ b> A and the counter electrode 3 </ b> A, and the detection electrode 2 </ b> B and the counter electrode 3 </ b> B are provided on the left and right sides of the diaphragm mechanism 7 within a predetermined distance d <b> 2.

  Further, semiconductor pressure sensors 8A and 8B for measuring the left and right pressures of the throttle mechanism 7, a pressure detector 8 for obtaining a left and right pressure difference from the outputs of the semiconductor pressure sensors 8A and 8B, and a lower pressure on the downstream side A counter electrode switching circuit 9 that determines and selects the counter electrode on the side determined to be the downstream side, and a switch SW1 are provided.

  The semiconductor pressure sensors 8A and 8B are embedded in the inner wall of the measuring tube 1 and provided so as to be in contact with the liquid. In addition, a pressure guiding tube is provided on the tube wall of the measuring tube 1, and two internal pressures are guided to the differential pressure transmitter for measurement. You may make it do.

  Next, the operation of the second embodiment configured as described above will be described with reference to FIG.

  First, a pressure difference ΔP between the semiconductor pressure sensor 8A and the semiconductor pressure sensor 8B is obtained (s1). Next, the polarity of the pressure difference ΔP is determined (s2).

  When the value of the pressure difference ΔP is positive, the semiconductor pressure sensor 8B side is determined to be the downstream side, and a control output for selecting the detection electrode 2B and the counter electrode 3B side is transmitted from the counter electrode switching control circuit 9 to the switch SW1. The electrodes are switched (s4).

  When the pressure difference ΔP is a negative value, the semiconductor pressure sensor 8A side is determined to be downstream, and a control output for selecting the detection electrode 2A and the counter electrode 3A side is transmitted from the counter electrode switching control circuit 9 to the switch SW1, The counter electrode is switched (s3).

  Therefore, when the flow direction is changed as in a water pipe, in the configuration in which the detection electrode 2 and the counter electrode 3 are only provided in one of the throttle mechanisms 7, measurement becomes impossible when the flow direction changes. According to the present invention in which the flow direction of the liquid to be measured is determined based on the pressure difference and the detection electrode 2 and the counter electrode 3 before and after the throttle mechanism 7 are automatically selected, the movable part can be measured even if the flow direction changes. An oxidation / reduction substance concentration measuring device that does not have can be provided.

  Embodiment 3 of the oxidation / reduction substance concentration measuring apparatus according to the present invention will be described with reference to FIGS.

  FIG. 5 is a configuration diagram of Example 3 of the oxidation / reduction substance concentration measurement apparatus. About each part of Example 3, the same part as the oxidation / reduction substance density | concentration measuring apparatus of Example 1 shown in FIG. 1 attaches | subjects the same symbol, and abbreviate | omits the description.

  The difference between the third embodiment and the first embodiment is that, in the first embodiment, a pair of counter electrodes composed of the detection electrode 2 and the counter electrode 3 is provided in the downstream direction of the aperture mechanism 7, but in the third embodiment, A plurality of pairs of counter electrodes were provided on the downstream side of the throttle mechanism 7.

  The power supply circuit 14 includes a plurality of applied voltages for determining the contamination state of the counter electrode surface, and the applied voltage switching control circuit 21 for determining the contamination of the counter electrode from a change in preset diffusion current output. And determining the contamination state of the counter electrode and switching the counter electrode to be used to measure the concentration of the liquid to be measured.

  The power supply circuit 14 is provided with a constant voltage circuit that generates a measurement voltage 14a, an adhesion determination voltage 14b, and a cleaning voltage 14c having a polarity opposite to that described later.

  A switch SW2 for independently switching voltages applied to the counter electrodes of the detection electrode 2C and the counter electrode 3C, the detection electrode 2D and the counter electrode 3D, and an applied voltage switching control circuit 21 for controlling the switch SW2 with the value of the diffusion current. Is provided.

  The diffusion current measuring circuits 5a and 5b for measuring the diffusion current flowing between the respective counter electrodes may be provided independently as shown in the figure, or may be switched to one.

  In general, when tap water containing residual chlorine is the liquid to be measured, the relationship between the applied voltage applied between the counter electrodes and the diffusion current flowing between the counter electrodes has the relationship shown by the solid line in FIG. It has been.

  When the applied voltage is changed to lower the potential of the detection electrode with respect to the counter electrode, the reaction speed increases and the value of the diffusion current increases (region 1). When the potential is further lowered, the current decreases less, and a diffusion current proportional to the concentration is obtained (region 2).

  This is because when the reaction rate becomes sufficiently high, the diffusion rate cannot catch up with the reaction rate, and the concentration is polarized in the detection electrode 2 to form each diffusion layer, and a diffusion current corresponding to the concentration is applied to the detection electrode 2. It is thought to flow.

  Further, when the applied potential is lowered, the diffusion current increases again in proportion to the applied voltage (region 3).

  Such voltage-current characteristics are measured in a concentration measurement range from high concentration to low concentration.

  Then, a measurement voltage 14a (for example, −120 mV) to be applied at the time of measurement is determined in the measurement region (region 2) proportional to the concentration, and the relationship between the concentration and the diffusion current is tabulated in advance and stored in the oxidation / reduction substance concentration calculation circuit 6. Keep it.

  By the way, even when the liquid to be measured is tap water, ions such as calcium, magnesium, iron, and manganese are deposited on the detection electrode 2 in a long-time measurement, and the deposited material adheres to the electrode surface, thereby reducing the electrode surface area. Thus, it is known that the value of the diffusion current decreases.

  If there is deposit, the value of the diffusion current will hardly change even if the applied voltage is increased as shown by the broken line, but if there is no deposit and the concentration is low, if the applied voltage is further reduced, the diffusion current will suddenly increase. 6 is applied, a voltage 14b (for example, −500 mV) at the time of adhesion determination as shown in FIG. 6 is applied, and the presence / absence of adhesion to the electrode surface is determined by observing the fluctuation amount of the diffusion current at this time. be able to.

In order to determine the presence or absence of the adhesion, when the measurement voltage 14a is applied and the diffusion current falls below a predetermined lower limit Imin, the adhesion determination voltage is applied, and the diffusion current at this time Judgment is made based on whether or not the upper limit value Imax has been exceeded.

  Next, the operation of the third embodiment configured as described above will be described with reference to FIG. 7, FIG. 5, and FIG.

  The diffusion current I flowing between the detection electrode 2C and the counter electrode 3C being measured is detected by the diffusion current detection circuit 5a. At this time, the applied voltage switching control circuit 21 determines whether or not the diffusion current I has become the lower limit value Imin or less (s11).

  If the diffusion current I is not less than or equal to the lower limit value Imin, the switch SW2 is kept as it is, and the concentration measurement is continued (s12).

  When it is determined that the value is equal to or lower than the lower limit value Imin, the applied voltage switching control circuit 21 switches the switch SW2 so as to select the adhesion determination time voltage 14b (s13).

  Next, the applied voltage switching control circuit 21 determines whether or not the diffusion current I is less than or equal to the upper limit value Imax in the state where the adhesion determination time voltage 14b is applied (s14).

  Otherwise, it is determined that there is no adhesion, the applied voltage is switched to the measurement voltage 14a, and the concentration measurement is continued.

  In the case of the upper limit Imax or less, the detection electrode 2D and the counter electrode 3D that are determined to be attached and are on standby are selected, the measurement voltage 14a is applied (s15), and the concentration is determined from the output of the diffusion current detection circuit 5b. Measured (s12).

  The detection electrode 2C and the counter electrode 3C determined to be attached are subjected to electrochemical cleaning that can remove positive ions attached to the detection electrode 2c by applying a cleaning voltage 14c having a polarity opposite to the measurement voltage 14a. .

  According to the present embodiment, there is provided an oxidation / reduction substance concentration measurement device having no movable part that can be switched to another counter electrode and continue measurement even when the detection electrode is contaminated with a deposit of positive ions or the like. can do.

  The present invention is not limited to the embodiment described above, and the shape of the measuring tube 1 may be a rectangular tube instead of a cylindrical tube, and the hollow shape of the throttle mechanism 7 depends on the shape of the measuring tube 1. The present invention may be variously modified and can be changed as appropriate without departing from the gist of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram of the oxidation / reduction substance concentration measuring apparatus of Example 1 of this invention. An explanatory view of the state of flow of a liquid to be measured and diffusion current characteristics. The block diagram of the oxidation / reduction substance concentration measuring apparatus of Example 2 of this invention. 9 is a flowchart for explaining the operation of the second embodiment. The block diagram of the oxidation / reduction substance concentration measuring apparatus of Example 3 of this invention. Explanatory drawing with respect to the applied voltage of the oxidation / reduction substance density | concentration measuring apparatus of Example 3 of this invention with respect to the applied voltage. 10 is a flowchart for explaining the operation explained in the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measuring tube 2, 2A thru | or 2D Detection pole 3, 3A thru | or 3D Counter electrode 4 Power supply circuit 5, 5a, 5b Diffusion current detection circuit 6 Oxidation / reduction substance concentration calculation circuit 7 Throttle mechanism 8 Pressure detector 8A, 8B Semiconductor pressure sensor 9 Counter electrode switching control circuit 14 Power supply circuit 14a Measurement voltage 14b Adhesion determination voltage 14c Washing voltage 21 Applied voltage switching control circuit SW1, SW2 switch

Claims (6)

A measuring tube through which a liquid to be measured containing an oxidizing or reducing substance flows;
A detection electrode and a counter electrode that are opposed to each other on the inner wall surface of the measurement tube and are in contact with the liquid to be measured
A power supply circuit for applying a preset voltage between the detection electrode and the counter electrode;
A diffusion current detection circuit for detecting a diffusion current flowing between the detection electrode and the counter electrode;
An oxidation / reduction substance concentration calculation circuit that calculates the concentration of the oxidation or reduction substance based on the diffusion current; and
Oxidation / reduction comprising a throttling mechanism that is provided on the upstream side of the detection electrode and the counter electrode so as to circumscribe the inner peripheral wall surface of the measurement tube and generates a pressure loss of the flow of the liquid to be measured Substance concentration measuring device. A measuring tube through which a liquid to be measured containing an oxidizing or reducing substance flows;
A throttle mechanism that is provided circumscribing the inner peripheral wall surface of the measurement tube and generates a pressure loss of the flow of the liquid to be measured;
Two detection electrodes and a counter electrode are provided that are opposed to each other on the inner wall surface of the measurement tube and are in contact with the liquid to be measured at symmetrical positions on the upstream and downstream sides of the liquid to be measured from the attachment position of the throttle mechanism. A pair of counter electrodes;
A pressure detector for measuring the pressure on the upstream side and the downstream side of the throttle mechanism;
Compare the upstream and lower pressures detected by the pressure detector, determine the direction in which the liquid to be measured flows, and select a pair of counter electrodes that are determined to be downstream A control circuit;
A power supply circuit for applying a preset voltage between the counter electrodes selected by the electrode switching circuit;
A diffusion current detection circuit for detecting a diffusion current flowing between the counter electrodes selected by the electrode switching circuit;
An oxidation / reduction substance concentration measuring device comprising an oxidation / reduction substance concentration calculation circuit for calculating a concentration of oxidation or reduction substance based on the diffusion current. A measuring tube through which a liquid to be measured containing an oxidizing or reducing substance flows;
A plurality of counter electrodes consisting of a detection electrode and a counter electrode facing each other at the inner wall surface of the measurement tube and in contact with the liquid to be measured;
On the upstream side of the plurality of counter electrodes, a throttle mechanism that is provided to circumscribe the inner peripheral wall surface of the measurement tube and generates a pressure loss of the flow of the liquid to be measured;
A power supply circuit that generates a preset measurement voltage, adhesion determination voltage, and cleaning voltage applied between the counter electrodes;
A diffusion current detection circuit for measuring a diffusion current flowing between each of the plurality of counter electrodes;
An oxidation / reduction substance concentration calculation circuit that calculates the concentration of the oxidation or reduction substance based on the diffusion current when the measurement voltage is applied; and
A switch for switching between the measurement voltage, the adhesion determination voltage, and the cleaning voltage independently of each counter electrode;
An oxidizing / reducing substance concentration measuring device comprising: an applied voltage switching control circuit that selectively controls the switch by the diffusion current.   The applied voltage switching control circuit applies the measurement voltage, and gives an electric potential difference larger than the measurement voltage when the output of the diffusion current detection circuit becomes smaller than a preset lower limit value. When the diffusion current flowing at this time is smaller than a preset value, the counter electrode is switched to any one of the other counter electrodes. Reducing substance concentration measuring device.   The applied voltage switching control circuit applies the measurement voltage, and gives an electric potential difference larger than the measurement voltage when the output of the diffusion current detection circuit becomes smaller than a preset lower limit value. When the diffusion current flowing at this time is smaller than a preset upper limit value, the counter electrode is switched to one of the other counter electrodes, the voltage at the time of adhesion determination is applied, and the diffusion flowing at this time The cleaning voltage having a polarity opposite to that of the measurement voltage is applied between the counter electrodes determined to have a current smaller than the preset upper limit value. Oxidation / reduction substance concentration measuring device.   The oxidation / reduction substance concentration measurement according to any one of claims 1 to 3, wherein the throttle mechanism is formed of a hollow disk having a throttle hole concentric with the measurement tube. apparatus.

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