JPH1082761A - Method and apparatus for measuring residual chlorine, and probe for detecting residual chlorine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus by which even an extremely small amount of residual chlorine can be correctly measured without need for a complicated operation such as calibration using a calibration liquid and without a danger of an error caused by residual current or the like. SOLUTION: Two, first and second indicator electrodes 12, 13 are provided as indicator electrodes whose oxidation-reduction potential varies depending on a residual chlorine amount contained in sample water 24a when in contact with the sample water 24a. In this case, different voltage from one another is applied respectively to each of the first and second indicator electrodes 12, 13 and a circuit including a reference electrode 11, and polaro-current in each circuit is sensed, and the difference is taken thereby offsetting residual current or the like. Thus a complicated calibration operation or the like using calibration liquid is eliminated, so that correct measurement is immediately possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a residual chlorine measuring apparatus for measuring residual chlorine remaining in a tap water or other liquid which is injected into a liquid for disinfection or the like.

[0002]

2. Description of the Related Art For example, in a water purification plant, chlorine is injected into treated water for disinfection. In addition, for example, in industries such as thermal power and nuclear power generation, chemical plants, steelmaking and oceangoing fishing boats, seawater used as a large amount of cooling water and washing water can be used to prevent adverse effects due to propagation of organisms on waterways and the like. For this reason, chlorine is injected. In such a case, it is natural that excessive chlorine should not remain in the treated tap water or the waste water after cooling or washing. For example, it is considered that the residual chlorine concentration in the wastewater returned to the sea after being used for cooling water is preferably 0.02 mg / l or less so as not to affect fish and shellfish. For this reason, it is necessary to accurately measure the residual chlorine in these waters and constantly monitor them.

[0003] By the way, as a method of measuring the residual chlorine concentration in water, conventionally, when a platinum electrode or a gold electrode is used as an indicator electrode and a silver / silver chloride electrode, a ginger electrode or a copper electrode is used as a reference electrode, an indicator is used. Utilizing the phenomenon that the current associated with the oxidation-reduction reaction occurring on the electrode surface corresponds to the amount of residual chlorine, the current has been converted into a voltage by a resistor inserted into this electrically closed circuit. The most common residual chlorine detection device is an electric circuit in which a relatively small resistor for voltage conversion is simply inserted into a connection circuit between an indicator electrode and a reference electrode. In such a method, for example, the reduction current is 20
In the case of about μA or less, the potential difference between the two electrodes is only 20 mV or less even if a 1 kΩ resistor is used, which means that the reduction current value when no voltage is applied is measured. The current in such a battery configuration is commonly called "galvanic (battery) current".

In addition, conventionally, a polaro system in which a voltage of about 1 V or higher, which is higher than the potential of the reference electrode, is applied to the indicator electrode in order to limit the substance to be measured is also known. That is, a reduction current is generated even when a voltage is positively applied from the outside between the electrodes. The current generated in this case is called a reduced polaro current. In this case, the current value when the applied voltage is changed naturally changes even if the residual chlorine has the same concentration. However, if the applied voltage is fixed, the polaro current is proportional to the residual chlorine concentration.
By measuring the polaro current, the amount of residual chlorine can be determined. Here, as substances dissolved in water, monochloramine (NH2 Cl), dissolved oxygen, and the like, which are listed in the same row as those affecting the reduction current, are considered in addition to residual chlorine. However, the reduced polaro currents based on these dissolved substances have different ranges of regions that occur unless the voltage applied to the electrodes is set in a certain region. Therefore, by setting this applied voltage to a specific range, the substance to be measured is limited, for example,
Even in a sample in which monochloramine (NH2 Cl), dissolved oxygen and the like coexist, the content of only residual chlorine can be measured.

[0005]

By the way, in the above-mentioned conventional residual chlorine detector, even if there is no residual chlorine, it is inevitable that an oxidation-reduction current of unknown substance called "residual current" occurs. It cannot be avoided.
In addition, since a considerably complicated electric circuit is inevitably interposed in the measurement system, the generation of "dark current" of a semiconductor or the like caused by the electric circuit cannot be avoided. For this reason, in order to offset this residual current and the "dark current" of a semiconductor or the like caused by adopting a complicated electric circuit,
A complicated operation such as contacting a calibration solution containing a residual chlorine decomposition reagent such as sodium thiosulfate with the indicator electrode to perform electrical zero calibration has been required. Moreover, the nature of the water sample is
It is more complicated to include factors other than the ideal conditions as described above. Therefore, there is no assurance that the residual current value at the time through the artificially prepared calibration solution having a residual chlorine concentration of zero becomes the same as the residual current value in the test of seawater or the like, so that an error may occur. That is, it is ideal that the residual current to be offset as a blank value is a value obtained by a water sample having the same composition except for residual chlorine, but it cannot be realized by a conventional apparatus using a constituent liquid.

The present invention does not require complicated operations such as a calibration operation using a calibration solution, does not cause an error due to residual current and the like, and can accurately measure a trace amount of residual chlorine. It is an object of the present invention to provide a method and an apparatus for measuring chlorine.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the method for measuring residual chlorine according to the present invention comprises: (Constitution 1) The amount of residual chlorine contained in a liquid to be measured when the liquid is brought into contact with the liquid to be measured; An indicator electrode that changes depending on the oxidation-reduction potential, and a reference electrode that shows a constant potential without depending on the amount of residual chlorine contained in the liquid, and in an electric circuit including the indicator electrode and the reference electrode, In the residual chlorine measurement method for determining the amount of residual chlorine contained in the liquid to be measured by measuring an electric quantity that changes depending on the amount of residual chlorine contained in the liquid to be measured, a first and second indicator electrodes are used as the indicator electrodes. And an electric quantity corresponding to a current flowing through each circuit by applying a different voltage from the outside between each of the first and second indicator electrodes and the comparison electrode. Measurement, and the magnitude of the applied voltage of the one circuit is selected as a value of a region where the current flowing through the one circuit mainly changes depending on the residual chlorine amount contained in the liquid to be measured. And, as a magnitude of an applied voltage of the other circuit, a value of a region where a current flowing through the other circuit is a residual current mainly depending on a residual substance other than residual chlorine contained in the liquid to be measured. The configuration is characterized in that the residual chlorine amount contained in the liquid to be measured is determined by selecting and determining the value of the difference between the electric amounts corresponding to the currents flowing through the two circuits. (Structure 2) The voltage applied to the two circuits is periodically changed to remove the oxide film and the like generated on the surfaces of the two indicator electrodes while maintaining the voltage in the measurement state. Suitable be provided a period for maintaining the voltage is obtained by a structure which is characterized in that so as to prevent deterioration of detection capability of the indicator electrode.

The apparatus for measuring residual chlorine according to the present invention may further comprise: (Constitution 3) an indicator electrode whose oxidation-reduction potential changes depending on the amount of residual chlorine contained in the liquid to be measured when the indicator electrode is contacted with the liquid. A reference electrode that exhibits a constant potential without depending on the amount of residual chlorine contained in the liquid, and changes depending on the amount of residual chlorine contained in the liquid to be measured in an electric circuit including the indicator electrode and the comparative electrode. In a residual chlorine measuring device for determining the amount of residual chlorine contained in the liquid to be measured by measuring an electric quantity to be measured, first and second two indicator electrodes are provided as the indicator electrodes, and the first and second indicator electrodes are provided. Voltage applying means for externally applying different voltages between each of the indicator electrodes and the comparison electrode, and two circuits each including the first and second indicator electrodes and the comparison electrode A difference measuring means for measuring an electric quantity corresponding to the flowing current; and a difference measuring means for calculating a difference between the electric quantities corresponding to the currents flowing through the two circuits. As a third embodiment, (Configuration 4) a variable voltage application unit is used as the voltage application unit, and the voltage applied by the voltage application unit is the voltage in the measurement state and the oxide film generated on the surface of the two indicator electrodes. And an applied voltage control means for controlling the voltage application means so as to alternately have two voltages with a voltage suitable for removing the voltage. When the applied voltage of the voltage applying means changes from the voltage in the measurement state to a voltage suitable for removing an oxide film generated on the surface of the two indicator electrodes, the voltage in the measurement state before the change is applied. A holding means for holding a signal from the difference measuring means when the voltage is applied and maintaining the holding state while the applied voltage maintains a voltage suitable for removing an oxide film formed on the surface of the two indicator electrodes. The configuration is characterized in that:

Further, the probe for detecting residual chlorine according to the present invention comprises: (Constitution 6) an indicator electrode whose oxidation-reduction potential changes depending on the amount of residual chlorine contained in the liquid to be measured when the probe is brought into contact with the liquid. In a residual chlorine detection probe having a reference electrode showing a constant potential without depending on the residual chlorine content contained in the liquid, a first and a second indicator electrode are provided as the indicator electrodes. It is configured.

[0010]

FIG. 1 is a block diagram showing a configuration of a residual chlorine measuring apparatus according to one embodiment of the present invention, and FIG. 2 is a residual chlorine detecting probe according to one embodiment of the present invention. Hereinafter, a method and an apparatus for measuring residual chlorine and a probe for detecting residual chlorine according to an embodiment will be described with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral 1 denotes a residual chlorine detection probe. The residual chlorine detection probe 1 has a comparison electrode 11, a first indicator electrode 12, and a second indicator electrode 13.

An outline of the residual chlorine measuring apparatus of one embodiment is as follows. A residual chlorine detection probe 1 is brought into contact with a test water through a water test flow path 2, and a probe is provided between a comparative electrode 11 and a first indicator electrode 12, as well as a comparative electrode. A different voltage is applied between the first electrode 11 and the second indicator electrode 13 through the DC voltage generating circuit 6 and the applied voltage control circuit 5, and the current flowing in each circuit is converted into a voltage through the detection resistors 3a and 3b. The difference between the voltages is obtained by the differential voltage amplifier circuit 3, and the output is sent to the outside through the display signal output circuit.

The comparative electrode 11 is a silver / silver chloride electrode.
This electrode is an electrode that exhibits a constant potential without depending on the amount of residual chlorine contained in the liquid to be contacted. The first indicator electrode 12 and the second indicator electrode 13 are platinum electrodes. These indicator electrodes are electrodes whose oxidation-reduction potential changes depending on the amount of residual chlorine contained in the liquid to be measured when the indicator electrode is brought into contact with the liquid.

The DC voltage generation circuit 6 generates a necessary DC power supply from a commercial power supply and supplies it to the applied voltage control circuit 5.
The applied voltage generation circuit 5 includes a comparison electrode and a first indicator electrode 1.
2 and between the comparison electrode 11 and the second indicator electrode 13, and a voltage having a polarity opposite to the applied voltage is periodically applied for a predetermined time. The application of the reverse voltage dissolves and removes the oxide film formed on the surface of each indicator electrode, thereby preventing a decrease in sensitivity. That is, when a reverse voltage is applied, a current flowing between the electrodes is increased by dissolved substances other than residual chlorine, and an oxide film, which is said to be formed on the indicator electrode surface by about one atomic layer, is instantaneously reduced and dissolved and removed. When the applied voltage is returned to the normal state, an oxidizing current is generated for several seconds, and the reducing current decreases. In that case, depending on the residual chlorine concentration, an oxidation current having the opposite polarity may be exhibited. About one minute after the voltage switching, the reduction current increases, reaches an equilibrium state, and stabilizes.

The applied voltage control circuit 5 sends a command signal to the display signal output circuit 4 when switching the applied voltage. When switching to the reverse voltage, control is performed so that the signal sent from the differential voltage amplifier circuit 3 to the display signal output circuit 4 at that time is held and sent to the outside. After the switching from the reverse voltage to the normal applied voltage, the hold is released after a certain period of time (after the reduction current is stabilized). Therefore, during the application of the reverse voltage, the measured value immediately before the start of the application of the reverse voltage is held and sent to the outside. Note that the voltage switching cycle can be about 2 minutes.

When a normal voltage is applied, the first indicator electrode 12
Is applied with a voltage of 200 to 400 mV (comparative electrode 1).
1), and a voltage higher by about 200 to 800 mV is applied to the second indicator electrode 13. In this case, according to the first indicator electrode 12 to which a voltage of 200 to 400 mV is applied, the reduced polaro current changes depending on the content of the free residual chlorine, but the monochromator having a different reduction characteristic from the free residual chlorine. A reduced polaro current based on other dissolved substances such as lamin (NH2 Cl) and dissolved oxygen does not occur. That is, the current generated via the first indicator electrode 12 may be a plate containing other dissolved substances such as monochloramine and dissolved oxygen in addition to free residual chlorine in the test water,
A value corresponding to the amount of residual chlorine is shown without being influenced by these components. However, this current includes an oxidation-reduction current of an unknown target substance called “residual current” and a “dark current” of an electric circuit.

On the other hand, according to the second indicator electrode 13 to which a voltage of 400 to 1200 mV is applied, it is needless to say that a reduced polar current based on free residual chlorine does not occur (when the residual chlorine is as high as 20 mg / l). Does not occur), and almost no reduced polarocurrent based on other dissolved substances such as monochloramine (NH2 Cl) or dissolved oxygen having a different reduction characteristic from free residual chlorine. That is, the second
The current generated through the indicator electrode 13 is substantially “residual current”.
And "dark current" alone.

Therefore, the difference between the current flowing in the circuit including the first indicating electrode 12 and the current flowing in the circuit including the second indicating electrode 13 is the difference between the “residual current” and the “dark current”. This means that the physical quantity depends only on the “residual chlorine amount”. That is, the detection resistors 3a, 3
The output from the differential voltage amplifying circuit 3, which amplifies the voltage generated at b and takes the difference, is a value corresponding to the amount of residual chlorine in the test water accurately after error factors such as residual current are corrected. Actually, the “residual current” and the like also change according to the applied voltage. Therefore, by configuring the differential voltage amplifying circuit 3 so that the respective gains can be adjusted, the indication value indicating that there is no residual chlorine is zero. Perform the zero adjustment so that In addition, the values of the detection resistors 3a and 3b can be actually adjusted, and by adjusting these resistance values, span calibration is performed by a calibration method such as a colorimetric method.

The test water flow path 2 sends the test water 24 a introduced into the bead introduction tank 22 by the water test introduction pipe 24 to the measurement tank 21 together with a part of the fine beads 22 a staying in the bead introduction tank 22. After being brought into contact with the chlorine detection probe 1, the beads are returned to the bead introduction tank 22 together with a part of the beads 22a and discharged to the outside. In this case, the water sample 24a
At the same time, the bead 22a carried to the measuring tank 21 repeatedly collides with the surfaces of the first indicator electrode 12 and the second indicator electrode 13 to constantly polish the surfaces of these electrodes. A part of the polished beads is returned to the bead introduction tank 22 together with the sample, and only the sample is transferred to the outside through the filter 23. The polishing works synergistically with the above-described application of the reverse voltage to bring about an epoch-making effect on the cleaning of the electrode surface. An actual test confirmed that there was no change from the initial state without any sensitivity adjustment for more than three months.

The residual chlorine detection probe 1 has an indicator electrode holding portion 15 fixed to the tip of a comparative electrode holding rod 16 fitted and fixed to a substantially cylindrical probe base 17. A silver electrode whose surface is oxidized is spirally wound around the comparative electrode holding rod 16 to form the comparative electrode 11. Indicator electrode holder 1
5, a first indicator electrode 12 and a second indicator electrode 13 made of disc-shaped platinum are fixed side by side at a predetermined interval such that one main surface faces the outside. . The lead wires of these indicator electrodes are connected to an external circuit together with the lead wire of the reference electrode 11 through the inside of the reference electrode indicator rod and further through the lead wire take-out portion 18. The reference electrode holding rod 16 is housed in the support tube 14. The support tube 14 is provided with a probe base 17.
, One end is fixed, and the other end is fixed to the indicator electrode holder 15. A plurality of minute liquid passage holes 14a, 14b and the like are provided at a lower portion of the support cylinder 14, and a vent hole 14c is provided at an upper portion. The inside of the indicator electrode holding rod 16 is filled with a resin or the like to insulate the lead wires from each other and to prevent erosion and disconnection.

This residual chlorine detection probe 1 performs water detection for 2
The two contact electrodes 12 and 13 are brought into contact with each other.
The reduction current generated between the indicator electrode and the comparison electrode can be detected by bringing the electrode into contact with the comparison electrode 11 through 4a, 14b and the like.

The comparative electrode, which is relatively resistant to mechanical friction and impact and does not require polishing, is housed in the indicator tube 14 and protected, while the comparative electrode is relatively resistant to mechanical friction and impact and has a coating on its surface. Since the formation of such as affects the detection sensitivity, the structure is adopted so that the indicator electrode, whose surface needs to be constantly polished and cleaned if possible, is exposed to the outside. And so on.

According to the above-described embodiment, since the difference between the reduction currents of the two electrodes is calculated, a measurement value in which the residual current and the like are offset can be immediately obtained. This eliminates the need to perform complicated calibration operations using liquids and the like.

In addition, since a reverse voltage is periodically applied to the electrode and a fine bead is mixed into the sample to clean the electrode at all times, the detection sensitivity and the like fluctuate over a long period of time. Since there is no such a possibility, accurate measurement is always possible, and there are advantages such as remarkably easy maintenance.

[0025]

As described in detail above, the present invention provides a first electrode as an indicator electrode whose oxidation-reduction potential changes depending on the amount of residual chlorine contained in a liquid to be measured when the electrode is brought into contact with the liquid.
And two second indicator electrodes are provided, and the first and second indicator electrodes are provided.
A different voltage is applied to the circuit including each of the indicator electrodes and the reference electrode, the polar current of each circuit is detected, and the difference is taken to cancel the residual current etc. This eliminates the need for a simple calibration operation or the like so that accurate measurement can be performed immediately.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a residual chlorine measuring device according to one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a residual chlorine detection probe according to one embodiment of the present invention.

[Explanation of symbols]

1 ... residual chlorine detection probe, 2 ... water detection channel, 3 ... differential voltage amplifying circuit, 4 ... display signal output circuit, 5 ... applied voltage control circuit, 6 ... DC voltage generation circuit, 11 ... comparison electrode, 12 ...
1st indicator electrode, 13 ... 2nd indicator electrode, 24a ... Water sample.

Claims (6)

[Claims] 1. An indicator electrode whose oxidation-reduction potential changes depending on the amount of residual chlorine contained in a liquid to be measured when brought into contact with the liquid to be measured, and an indicator electrode which does not depend on the amount of residual chlorine contained in the liquid. A measurement electrode having a comparison electrode indicating a potential, and measuring an electric amount that changes depending on an amount of residual chlorine contained in the measurement target liquid in an electric circuit including the indicator electrode and the comparison electrode. In the residual chlorine measurement method for determining the amount of residual chlorine contained in the first and second indicator electrodes, a first and a second indicator electrode are provided as the indicator electrodes, and between each of the first and second indicator electrodes and the comparative electrode. By applying different voltages from the outside, an electric quantity corresponding to the current flowing through each circuit can be measured, and the current flowing through the one circuit is mainly used as the magnitude of the applied voltage of the one circuit. As a value of a region that changes depending on the residual chlorine amount contained in the liquid to be measured, and the current flowing through the other circuit is mainly the current as the magnitude of the applied voltage of the other circuit. By selecting a value in a region where the residual current depends on the residual substance other than the residual chlorine contained in the liquid to be measured, and determining the value of the difference between the electric quantities corresponding to the currents flowing in the two circuits, A method for measuring residual chlorine, comprising determining an amount of residual chlorine contained in the liquid to be measured. 2. The method according to claim 1, wherein the voltage applied to the two circuits is periodically changed, and a period during which the voltage in the measurement state is maintained and an oxide film formed on the surface of the two indicator electrodes are removed. 2. The method for measuring residual chlorine according to claim 1, wherein a period for maintaining the voltage is provided to prevent the detection capability of the indicator electrode from deteriorating. 3. An indicator electrode whose oxidation-reduction potential changes depending on the amount of residual chlorine contained in a liquid to be measured when brought into contact with the liquid to be measured, and a constant potential independent of the amount of residual chlorine contained in the liquid. A reference electrode having a reference electrode, and in the electric circuit including the indicator electrode and the reference electrode, by measuring an electric quantity that changes depending on an amount of residual chlorine contained in the liquid to be measured, to the liquid to be measured. In a residual chlorine measuring device for determining the amount of residual chlorine contained, first and second two indicator electrodes are provided as the indicator electrodes, and an external device is provided between each of the first and second indicator electrodes and the comparative electrode. A voltage applying means for applying different voltages to each other, and a difference for measuring an electric quantity corresponding to a current flowing through two circuits each including the first and second indicator electrodes and the comparison electrode. An apparatus for measuring residual chlorine, comprising: a measuring unit; and a difference measuring unit that obtains a difference between electrical quantities corresponding to currents flowing through the two circuits. 4. A voltage applying means having a variable applied voltage is used, and the applied voltage of said voltage applying means is
Applying voltage control means for controlling the voltage applying means so as to alternately have two of a voltage in the measurement state and a voltage suitable for removing an oxide film formed on the surfaces of the two indicator electrodes. The residual chlorine measuring device according to claim 3, characterized in that: 5. When the voltage applied by the voltage applying means changes from the voltage in the measurement state to a voltage suitable for removing an oxide film formed on the surface of the two indicator electrodes, the voltage in the measurement state before the change is changed. A signal from the difference measuring means when a voltage is applied is held, and the hold state is maintained while the applied voltage maintains a voltage suitable for removing an oxide film generated on the surface of the two indicator electrodes. 5. The residual chlorine measuring apparatus according to claim 4, further comprising a holding means for performing the operation. 6. An indicator electrode whose oxidation-reduction potential changes depending on the amount of residual chlorine contained in a liquid to be measured when brought into contact with the liquid to be measured, and an indicator electrode which does not depend on the amount of residual chlorine contained in the liquid. What is claimed is: 1. A residual chlorine detection probe, comprising: a reference electrode indicating a potential; and a first and a second indicator electrode provided as said indicator electrode.