JP4962796B2 - Redox current measuring device - Google Patents

Description

The present invention relates to a redox current measuring device, and more particularly to a rotary or vibration type redox current measuring device capable of continuously and accurately measuring a redox current.

Conventionally, measurement of redox current of polarographic method or galvanic cell method for the purpose of measuring residual chlorine, chlorine demand, chlorine dioxide, chlorous acid, dissolved ozone, hydrogen peroxide, etc. in tap water, sewage, pool water, etc. The device is used.
For example, in a polarographic redox current measuring device, a working electrode (detection electrode) made of platinum or gold and a counter electrode made of silver or lead are immersed in sample water, and a predetermined voltage is applied between both electrodes. Thus, the concentration of the measurement target component can be determined by measuring the current that flows when electrolytic reduction (or oxidation) of the measurement target component occurs in the vicinity of the working electrode.

The oxidation-reduction current measured in such an oxidation-reduction current measuring device is called a diffusion current, which is in contact with the electrode during the electrolysis process, and is a thin solution with a concentration gradient due to the mass transfer due to diffusion. In the layer (diffusion layer), this is a current that flows when the component to be measured carried to the working electrode surface is oxidized and reduced. Therefore, in order to obtain a diffusion current (oxidation reduction current) corresponding to the concentration of the component to be measured, it is necessary to constantly replace the diffusion layer. For this reason, the sample water is caused to flow relative to the working electrode surface. In order to cause the sample water to flow relative to the surface of the working electrode, there is a method of rotating or vibrating (precessing) a working electrode support provided with the working electrode with a motor.

In such a system, the working electrode support (working electrode) rotates or vibrates at a linear velocity much higher than the normal flow rate of the sample water. For this reason, a stable diffusion layer can be obtained regardless of the flow rate of the sample water, and the measurement value due to fluctuations in the flow rate of the sample water is not easily affected.
However, the surface of the working electrode is likely to be contaminated with electrolytes generated at the counter electrode and contaminants in the sample water. When these stains are attached, the value of the current flowing between the working electrode and the counter electrode decreases. This causes a decrease in the concentration instruction value of the measurement target component.
For this reason, conventionally, a cap containing abrasive beads is attached so as to cover the working electrode support, and the working electrode support (working electrode) is rotated or vibrated by a motor in the abrasive beads. In addition, the working electrode is polished to prevent the adhesion of dirt, so that stable measurement can be performed (see Patent Document 1, Patent Document 2, and Patent Document 3).

Japanese Utility Model Publication No. 6-30764 JP 2002-90339 A JP 2004-340762 A

In these conventional techniques, if the abrasive beads are sandwiched between the cap and the working electrode support, the working electrode support may not be able to rotate or vibrate with the normal driving force of the motor (so-called foreign object engagement). (Hereinafter referred to as “bead bite state”). In this case, not only the working electrode cannot be polished with the abrasive beads, but also a stable and new diffusion layer cannot be obtained, the measured value of the oxidation-reduction current decreases, and the concentration of the component to be measured can be accurately obtained. There was a problem that I could not.
On the other hand, when the measured value of the oxidation-reduction current (measured concentration value of the component to be measured) becomes a predetermined value or less, an alarm is issued so that an operator can check. However, since the decrease in the measured value naturally occurs due to a decrease in the concentration of the measurement target component in the sample water, it is not possible to quickly determine which cause caused the decrease in the measured value. For this reason, for example, in a monitoring system for residual chlorine concentration in tap water, sewage, pool water, etc., when it is designed to inject a disinfectant when the residual chlorine concentration decreases, There was a problem of excessive input.

Further, in the case of a motor that does not have an overcurrent protection circuit, the motor itself does not stop even if it becomes a bead bite state. However, since the rotation or vibration of the working electrode support stops, there is a problem that the measured value of the oxidation-reduction current is lowered, and an excessive current flows through the motor to heat and burn the motor.
On the other hand, in the case of a motor having an overcurrent protection circuit, the motor stops when overload operation occurs, so that heating or burning of the motor can be avoided. However, in order to restore the stopped motor, the operator must turn off the power supply of the redox current measuring device once and then turn it back on. There was a problem that continuous measurement was interrupted.
Furthermore, in order to automatically return the stopped motor without turning off the redox current measuring device, the current value of the motor is monitored and it is determined that the protection circuit has been activated when almost no current flows. It is also conceivable to design such that the power supply circuit to the motor is temporarily cut off and then the power supply is resumed. However, in this case, it is necessary to add a circuit for monitoring the current value of the motor, which causes an increase in cost.

  Therefore, the problem to be solved by the present invention is that the rotation or vibration of the working electrode support does not stop, and even if the rotation or vibration of the working electrode support stops, rotation or vibration does not occur without human intervention. An object of the present invention is to provide a redox current measuring device capable of continuously and accurately measuring the redox current corresponding to the concentration of the component to be measured by being restored.

  In order to solve the above problems, a redox current measuring apparatus to which the present invention is applied includes a working electrode, a counter electrode, a working electrode support including the working electrode, and a motor that rotates or vibrates the working electrode support. And a redox current measuring device that measures a redox current flowing between the working electrode and the counter electrode while rotating or vibrating the working electrode support, and temporarily supplying power to the motor. A power shut-off means capable of shutting off automatically, and a control means for controlling the power shut-off means. The control means controls the power shut-off means during measurement of the oxidation-reduction current. Features.

  In the present invention, the control means may control the power shut-off means at one or more cycles.

  According to the present invention, since the power supply to the motor can be temporarily interrupted during the measurement of the oxidation-reduction current (that is, the operation of the motor can be turned on / off), the bead biting state is prevented. Moreover, even if it becomes a bead bite state, it can be eliminated. For this reason, the rotation or vibration of the working electrode support does not stop, or even if it stops, it can be automatically and quickly restored, and the oxidation-reduction current corresponding to the concentration of the component to be measured is continuously measured with high accuracy. It is possible to provide an oxidation-reduction current measuring apparatus that can perform the above-described process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 is a schematic diagram of the overall configuration of the oxidation-reduction current measuring apparatus 1 according to this embodiment.
The oxidation-reduction current measuring apparatus 1 shown in FIG. 1 includes a detector 2 including a working electrode support 20 having a working electrode 21 and a counter electrode 22, a motor 12, and the like, an applied voltage mechanism 51, a switch mechanism 52, and an arithmetic control unit. 61, a measurement unit 62, a display unit 63, and an output unit 64.

In FIG. 1, the switch mechanism 52 provided in the circuit connected to the motor 12 is normally closed. When the power of the oxidation-reduction current measuring device 1 is turned on and the measurement operation is possible, the switch 12 is turned on. Is supplied with electric power through the applied voltage mechanism 51. Inside the detector 2, the working electrode support 20 is connected to the motor 12 as will be described in detail later, and vibrates (precesses) as the motor 12 rotates.
Further, the measuring unit 62 applies a voltage between the working electrode 21 and the counter electrode 22 according to a control signal from the arithmetic control unit 61 to measure an oxidation-reduction current (diffusion current) flowing in both electrodes, and the measured value is obtained. This is sent to the calculation control unit 61.
The arithmetic control unit 61 obtains the concentration of the measurement target component from the measured value of the oxidation-reduction current, displays it on the display unit 63, and outputs it from the output unit 64 to the outside. Further, the arithmetic control unit 61 controls the switch mechanism 52 to open and close at a predetermined timing during the measurement of the redox current. Thereby, the power supply to the motor 12 is temporarily interrupted.

Next, FIG. 2 is a sectional view of the detection unit 2 of the oxidation-reduction current measuring apparatus 1 according to this embodiment.
The detection unit 2 of the oxidation-reduction current measuring apparatus 1 shown in FIG. 2 is provided with a substantially cylindrical case 10, and a holder 30 having a through-hole formed in the center of the shaft is provided at the lower end opening of the case 10. Is retained. In addition, a connector 11 is provided at the upper end opening of the case 10, and a working electrode 21, a counter electrode 22, a motor 12 and the like are electrically connected to the connector 11 (not shown), via a cable. It is connected to the measuring unit 62 and the calculation control unit 61 of the oxidation-reduction current measuring device 1.

A motor 12 is attached to the upper part of the holder 30 (inside the case 10), and an eccentric coupling 14 is fixed to the rotating shaft 13 of the motor 12, and a connecting shaft 15 is connected to the eccentric coupling 14. Has been. And the site | part connected with the eccentric coupling 14 of the connection shaft 15 carries out a circular motion. The connecting shaft 15 is formed in a substantially rod shape, and a circular flange 16 is held at a position about 1/3 from the lower end of the connecting shaft 15 so as to be in contact with the inner peripheral surface of the holder 30, and further acts on the lower surface of the flange 16. The pole support 20 is connected, and the working electrode support 20 is configured to vibrate (precession) with the flange 16 as a fulcrum.

A working electrode 21 made of gold (Au) is provided at the lower end of the working electrode support 20 and is connected to the measuring unit 62 of the oxidation-reduction current measuring apparatus 1 via the connector 11 as described above.
In addition, a pair of upper and lower circular windows 31 are formed in a substantially central portion in the axial direction of the holder 30. A recess 32 is formed in the circumferential direction near the lower end of the holder 30, and a counter electrode 22 made of silver chloride wire (AgCl) is wound around the entire periphery of the recess 32. A platinum resistance thermometer (not shown) is provided, and the counter electrode 22 and the platinum resistance thermometer are connected to the measuring unit 62 of the oxidation-reduction current measuring apparatus 1 via the connector 11.
A cap 33 is held at the lower end of the holder 30, and a large number of beads 34 for polishing (cleaning) the working electrode 21 are accommodated in the cap 33.

In order to measure the oxidation-reduction current with the oxidation-reduction current measuring apparatus 1 as described above, first, a flow cell (not shown) in which the sample water flows continuously by introducing and discharging the sample water. The detector 2 is soaked in to make the oxidation-reduction current measuring device 1 ready for the measurement operation. Then, the motor 12 operates and the rotating shaft 13 rotates. At this time, the portion of the connecting shaft 15 connected to the eccentric coupling 14 performs a circular motion, and the working electrode support 20 vibrates (precesses) using the flange 16 as a fulcrum. Then, a voltage is applied between the working electrode 21 and the counter electrode 22 to measure the oxidation-reduction current (diffusion current) flowing in both electrodes by the measuring unit 62, and the calculation control unit 61 obtains the concentration of the component to be measured, and the output unit The measured value is output or displayed on the display unit 53 or the display unit 54.
Note that the measurement of the oxidation-reduction current is continuously performed during the operation of the oxidation-reduction current measuring apparatus 1.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 3 is a timing chart showing an open / closed state (off / on) of the switch mechanism 52 during the measurement operation of the oxidation-reduction current measuring apparatus 1.
The switch mechanism 52 is closed (hereinafter also referred to as “on”) at the same time when the measurement operation of the oxidation-reduction current measuring apparatus 1 is started. Then, electric power is supplied to the motor 12, the rotating shaft 13 rotates, and the working electrode support 20 vibrates.
When the on-time T1 elapses from the start of the measurement operation, the switch mechanism 52 is opened (hereinafter also referred to as “off”) by the control unit, and is turned on again by the control unit when the off-time T2 elapses. Thereafter, after the on-time T1 has elapsed, the switch mechanism 52 is turned off, and when the off-time T2 has elapsed, the switch mechanism 52 is turned on. Thereafter, the same operation is repeated.
That is, while the oxidation-reduction current measuring apparatus 1 is continuously operating, the measurement of the oxidation-reduction current is continuously performed, but the power supply to the motor 12 is controlled to be temporarily interrupted.
The control means for controlling the opening / closing operation of the switch mechanism 52 can be realized by providing a known means such as a timer mechanism or control by a microcomputer in the arithmetic control unit 61.

Thus, by temporarily shutting off the power supply to the motor 12 (opening / closing operation of the switch mechanism 52), the gap between the working electrode support 20 and the bead is caused by vibration or the like when the operation of the motor 12 is resumed. Since it slightly changes, even if the vibration of the working electrode support 20 is stopped by the bead bite, the vibration can be restored.
That is, in the case where the motor 12 does not have an overcurrent protection circuit, the motor itself does not stop even if it becomes a bead bite state, but the vibration of the working electrode support 20 may stop. . Even in such a case, it is possible to prevent the bead biting state from being eliminated, the vibration of the working electrode support 20 to be restored, and the measured value of the oxidation-reduction current from being lowered.
Further, by forcibly opening (turning off) the switch mechanism 52, it is possible to prevent the motor from being heated or burned due to an excessive current flowing through the motor.
On the other hand, when the motor 12 is a motor having an overcurrent protection circuit, the motor 12 is stopped if the overload operation is caused by the bead biting state, but the switch mechanism 52 is forcibly opened (turned off) and further closed ( By turning it on), the operation of the motor 12 is restarted, the vibration of the working electrode support 20 is restored, and the measured value of the oxidation-reduction current can be prevented from decreasing.
Further, in any case, the bead biting state may be prevented by vibration or the like when the operation of the motor 12 is resumed. As a result, the oxidation-reduction current can be measured continuously and accurately.

Here, the ON time T1 of the switch mechanism 52 is preferably several seconds to several minutes, and more preferably about several tens of seconds. This is because if the on-time T1 is too short, the measurement is affected, and if it is too long, the bead biting state may last for a long time.
On the other hand, the off time T2 is preferably about 0.001 to 1 second, and more preferably about 0.01 to 0.1 second. This is because if it is too short, the overcurrent protection circuit of the motor 12 cannot be reset, and if it is too long, the measurement is affected.

Next, the operation of another embodiment will be described with reference to FIG. FIG. 4 is a timing chart showing an open / closed state (off / on) of the switch mechanism 52 during the measurement operation of the oxidation-reduction current measuring apparatus 1 according to another embodiment.
In this embodiment, the switch mechanism 52 includes an on time T1 (first period) and an on time T1 ′ with an off time T2 interposed therebetween.
It is opened and closed in two cycles (second cycle). That is, when the on-time T1 elapses from the start of the measurement operation, the switch mechanism 52 is turned off, and when the off-time T2 elapses, it is turned on for the on-time T1 ′. Then, after repeating the off time T2, the on time T1 ′, and the off time T2, the same operation is repeated by returning to the on time T1.

In such an embodiment, for example, the on time T1 can be several seconds to several minutes, and the on time T1 ′ and the off time T2 can be about 0.001 second to 1 second. Since the bead bite is easily eliminated by vibration or the like during the opening / closing operation (when the operation of the motor 12 is stopped and restarted), it is particularly effective when it is difficult to eliminate the bead bite.
Note that the combination of the on-time T1 (first period), the on-time T1 ′ (second period), and the off-time T2 is not limited to the above example, and can be changed as appropriate. The number is not limited to two and may be three or more.
In any of the embodiments, the opening / closing operation of the switch mechanism 52 does not have to be repeated periodically. For example, the opening / closing operation may be performed when a measured value falls below a certain value. good.

  In the above-described embodiment, a description has been given of an oxidation-reduction current measuring device that is a polarographic method and in which the working electrode support 20 vibrates (precession). However, the present invention is also applicable to a galvanic cell method. In addition, the present invention can also be applied to a redox current measuring device 1 of a type in which the working electrode support 20 rotates.

(Test example)
Using the above-described oxidation-reduction current measuring apparatus 1, residual chlorine was measured using tap water as the sample water to be measured. In this case, the above-described on-time T1 is set to 40 seconds, and the off-time T2 is changed to 0.01 seconds, 0.05 seconds, 0.1 seconds, 0.5 seconds, and 1 second. The measurement unit 62 measured the value of the current flowing between the two electrodes.
The results are shown in FIG. From FIG. 5, when the off time T2 is 0.01 seconds, 0.05 seconds, and 0.1 seconds, the measured current value is within a certain range, but the off time T2 is 0.5 seconds and 1 seconds. It can be seen that in the case of seconds, there may be a significant deviation.

FIG. 6 shows a transmission output result from the output unit 64 of the oxidation-reduction current measuring apparatus 1. In the oxidation-reduction current measuring apparatus 1, the current value measured by the measurement unit 62 is converted into the concentration of the measurement target component by the calculation control unit 61, and this is output or displayed on the output unit 53 or the display unit 54. At this time, if the measured value is directly output or displayed, the variation in the measured value increases, and therefore smoothing is performed based on a predetermined number (time) of acquired data. From FIG. 6, the transmission output when the off-time T2 is 0.1 seconds is almost flat, whereas when the off-time T2 is 0.5 seconds and 1 second, it is waved up and down. I understand.

Conventionally, it has not been considered to stop the operation of the motor 12 during continuous measurement of the oxidation-reduction current. This is because, as described above, by operating the motor 12, the working electrode support 20 is rotated or vibrated, and a stable diffusion layer is obtained near the surface of the working electrode 21, thereby depending on the concentration of the component to be measured. This is because it was thought that the oxidation-reduction current can be measured continuously and accurately.
However, as a result of the present tests by the inventors, it has been found that if the off time T2 is, for example, 0.1 seconds or less, the measurement is hardly affected.

It is a schematic diagram of the whole structure of the oxidation reduction current measuring apparatus 1 which concerns on embodiment of this invention. It is sectional drawing of the detection part of the oxidation reduction current measuring apparatus 1 which concerns on embodiment of this invention. 5 is a timing chart showing a state of an open / close state of a switch mechanism 52 during a measurement operation of the oxidation-reduction current measuring apparatus 1 according to the embodiment of the present invention. It is the timing chart which showed the mode of the opening / closing state of the switch mechanism 52 at the time of measurement operation | movement of the oxidation-reduction current measuring apparatus 1 which concerns on other embodiment of this invention. It is a chart which shows the measured current value at the time of changing off time T2 in an example. It is a chart which shows the transmission output value at the time of changing OFF time T2 in an Example.

Explanation of symbols

1: redox current measuring device 2: detector 10: case 11: connector 12: motor 13: rotating shaft 15: connecting shaft 20: working electrode support 21: working electrode 22: counter electrode 30: holder 33: cap 34: beads 51: Applied voltage mechanism 52: Switch mechanism 61: Calculation control unit 62: Measurement unit 63: Display unit 64: Output unit

Claims (2)

A working electrode, a counter electrode, a working electrode support provided with the working electrode, and a motor for rotating or vibrating the working electrode support,
A redox current measuring device that measures a redox current flowing between the working electrode and the counter electrode while rotating or vibrating the working electrode support,
A power shut-off means capable of temporarily shutting off the power supply to the motor;
Control means for controlling the power shut-off means,
The control means controls the power cut-off means during the measurement of the oxidation-reduction current. 2. The oxidation-reduction current measuring apparatus according to claim 1, wherein the control unit controls the power shut-off unit at one or more cycles.