JP2001174431A - Apparatus and method for measuring residual chlorine concentration in acidic liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for measuring the residual chlorine concentration in an acidic liquid capable of easily and stably measuring the residual chlorine concentration even when a liquid to be measured is in ether of a water flow state and a static water state. SOLUTION: The apparatus for measuring residual chlorine concentration in an acidic liquid comprises a controller 11 for controlling a voltage between a working electrode 3 and a reference electrode 5 to a predetermined voltage, and an arithmetic unit 9 for calculating the residual chlorine concentration from a current value. The apparatus further comprises a flow rate sensor 10 for detecting whether the liquid to be measured is the water flow rate or the static water state. When the sensor 10 senses the water flow rate of the liquid, the controller 11 applies a predetermined voltage corresponding to the maximum value of an electrolytic reduction current to detect the mean value of the reduction current. When the sensor 10 senses a static water state, the controller 11 sweeps the voltage between the electrodes 3 and 5 to detect the maximum value of the electrolytic reduction current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for determining the concentration of residual chlorine contained in a liquid to be measured exhibiting acidity, particularly, an acidic liquid to be treated having a pH of 5.5 or less by a reduction reaction at a working electrode. The present invention also relates to an apparatus and a method for measuring the concentration of residual chlorine in an acidic liquid, which makes it possible to determine whether the liquid to be measured is in a flowing state or a still water state and to perform highly accurate detection.

[0002]

2. Description of the Related Art In recent years, components to be measured contained in a liquid to be measured are electrolytically oxidized or reduced by using a working electrode and a counter electrode provided in a pipe, and the concentration dependence of a current value flowing at that time is utilized. Various devices have been developed for continuously measuring concentrations.

[0003] Japanese Patent Application Laid-Open No. 8-278284 (hereinafter referred to as “A”) discloses a sample liquid pipe inside a cylindrical filter.
A counter electrode chamber is formed on the outside, and the working electrode is placed in contact with the filter in the sample liquid line to increase the structural strength of the device and to stabilize the positional relationship between the working electrode and the counter electrode for measurement accuracy. There is disclosed a measuring device configured so as to be able to increase the stability of the measuring device.

[0004]

However, the conventional apparatus has the following problems.

[0005] (1) The measuring device described in the Japanese Patent Publication No. A is intended to provide high durability by improving the structural strength and to stabilize the positional relationship between the electrodes. When the flow rate of the liquid to be measured in the pipe changes, the oxidation-reduction current value between the electrodes also changes.Therefore, in order to continuously and stably measure the concentration of the target substance in the liquid to be measured, the pipe is required. It was necessary to add a mechanism such as a flow control valve in order to regulate the flow rate in the chamber to a constant value.

(2) The reduction current characteristic of residual chlorine is different between the case where the liquid to be measured is flowing water and the case where the liquid is still water, and the residual chlorine concentration is measured in any case of the liquid to be treated which shows acidity. I couldn't do this.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and it is easy to measure the residual chlorine concentration easily and stably even when the liquid to be measured is in a flowing state or a still water state. An object of the present invention is to provide a chlorine concentration measuring device and a measuring method.

[0008]

In order to achieve this object, the apparatus for measuring the residual chlorine concentration in an acidic solution according to the present invention comprises a cell into which a liquid to be measured is introduced, and a working electrode provided in the cell. A reference electrode that generates a reference potential for setting the potential of the counter electrode and the working electrode to a predetermined potential, and the working electrode and the working electrode for controlling the potential of the working electrode with respect to the reference electrode to a predetermined potential. A variable power supply unit for adjusting the voltage between the counter electrodes, a current detection unit capable of detecting a current value flowing through the working electrode, and controlling the variable power supply unit so that a voltage between the working electrode and the reference electrode is a predetermined voltage. A residual chlorine concentration measuring apparatus for measuring the residual chlorine concentration in an acidic solution, comprising: a control unit for controlling the residual liquid concentration in the acidic liquid; and a calculating unit for calculating the residual chlorine concentration from the current value. Equipped with a flow rate detector capable of When the amount detection unit detects that the water is flowing, the control unit applies a predetermined voltage corresponding to the maximum value of the electrolytic reduction current to detect the average value of the electrolytic reduction current, and the flow rate detection unit When detecting a hydrostatic state, the control unit sweeps a voltage between the working electrode and the reference electrode to detect a local maximum value of the electrolytic reduction current.

Thus, the residual chlorine concentration can be easily and stably measured regardless of whether the liquid to be measured is in a flowing state or a still water state.

[0010]

An apparatus for measuring the concentration of residual chlorine in an acidic liquid according to the present invention comprises a cell into which a liquid to be measured is introduced, a working electrode provided in the cell, a counter electrode, and the working electrode. A reference electrode for generating a reference potential for setting the potential to a predetermined potential; and adjusting a voltage between the working electrode and the counter electrode to control the potential of the working electrode with respect to the reference electrode to a predetermined potential. A variable power supply unit, a current detection unit that can detect a current value flowing through the working electrode, a control unit that controls the variable power supply unit, and controls a voltage between the working electrode and the reference electrode to a predetermined voltage, A residual chlorine concentration measurement device in an acidic liquid, comprising a calculation unit for calculating a residual chlorine concentration from the current value, comprising a flow rate detection unit capable of detecting whether the liquid to be measured is in a flowing state or a still water state, The flow rate detector is in a water-passing state. When the control unit detects the average value of the electrolytic reduction current by applying a predetermined voltage corresponding to the maximum value of the electrolytic reduction current, and when the flow rate detection unit detects a hydrostatic state, the control unit The voltage between the working electrode and the reference electrode is swept to detect a maximum value of the electrolytic reduction current.

As a result, the following effects can be obtained.

(A) Since the control unit includes a flow rate detection unit for detecting the flow rate of the liquid to be measured and a control unit for a variable power supply unit for setting the potential between the working electrode and the reference electrode to a predetermined value, the control unit is provided inside the cell. It is possible to determine whether the liquid to be treated is in a hydrostatic state or a flowing state, and to perform optimal measurement in each state.

(B) When the flow rate signal of the liquid to be measured is substantially equal to zero, since the liquid to be measured is in a hydrostatic state, the potential of the working electrode with respect to the reference electrode is swept at a constant speed and obtained by a change in potential. Since the maximum value of the current is detected from the change in the current value, the potential giving this maximum value can be used as the optimal potential for detecting the residual chlorine concentration in the liquid to be measured.

Here, as the liquid to be measured, a liquid in an acidic region whose hydrogen ion concentration index (pH) is 5.5 or less is used. In this region coexist Cl ₂ and HClO against pH, ClO ^- is no longer present. Therefore, C in the liquid
If the reduction current of l ₂ is measured, the total residual concentration can be measured from the abundance ratio. In addition, when the pH is lower than 2, strong acidity requires acid resistance of the device, which increases the production cost, which is not preferable. Conversely, when a liquid to be measured whose pH exceeds 5.5 is used, for example, when the potential between the working electrode and the reference electrode is increased at a constant rate, the current value between the working electrode and the counter electrode becomes a maximum value. Is less likely to appear, making detection difficult.

(C) When the flow rate signal of the liquid to be measured exceeds zero, the liquid to be measured is in a flowing state, so that the potential of the working electrode with respect to the reference electrode is controlled to a predetermined potential, and the time of the electrolytic reduction current is reduced. Since the residual chlorine concentration is converted based on the average, highly accurate concentration measurement can be performed even when water is passed.

The working electrode comprises a solid electrode of platinum, gold, carbon, or the like. The counter electrode is formed of a solid electrode of the same material as that of the working electrode.
It is desirable to have a sufficiently large surface area of about 0 to 100 times. This allows the reduction reaction at the working electrode to occur smoothly and efficiently. The distance between the counter electrode and the working electrode disposed opposite thereto is preferably 5 to 20 mm.

The reference electrode is disposed, for example, in a cell, and comprises, for example, an internal solution containing potassium chloride as a supporting salt, a calomel electrode having a high electric stability which generates a constant potential regardless of the hydrogen ion concentration of the solution to be measured, Pt electrode, Ag / AgCl
A reference electrode composed of electrodes and the like, a container for accommodating the internal liquid and the reference electrode, and a porous polyethylene, a porous polyester, and a porous material that are in contact with the liquid to be measured and the internal liquid and have water absorbency for imparting conductivity. It is composed of a porous polymer such as acryl and a liquid junction made of a porous ceramic such as alumina, silica or zirconia having water absorbency. Although it is desirable to use a reference electrode made of the above material, any other configuration or material may be used as long as substitution is possible. The material and combination of the working electrode, the counter electrode, and the reference electrode are not particularly limited as long as they are materials having a configuration for obtaining a reduction current.

The flow rate detecting unit is, for example, a throttle flow meter that measures a pressure difference due to a change in flow velocity, an electromagnetic flow meter that uses an electromagnetic induction phenomenon, a vortex flow meter that uses a vibration phenomenon of a fluid, and a force that acts on the fluid. A flow rate signal obtained by converting the output into an electric signal can be obtained by the control unit.

Here, the difference between the measurement principle and the measurement method in the flowing state and the still water state will be described. Performing concentration measurement electrochemically is a common means of concentration measurement. Of this, regarding the measurement of residual chlorine concentration, in either has any value pH is to measure the residual chlorine concentration, chlorine gas Cl ₂ and HClO in the liquid, ClO ^- and HClO are either each pH And their equilibrium at their pH, and the residual chlorine concentration can be calculated in terms of conversion by measuring the electrolytic reduction current. However, this HCl
O does not contribute to the electrode reaction. And Cl ₂ and HClO
Is present at a pH of 5.5 or less, and the combination of ClO 2 ^- and HClO is present at a pH of 5.5 or more.
Therefore, the apparatus for measuring the residual chlorine concentration of an acidic solution having a pH of 5.5 or less, and thus almost all acidic solutions, can measure the concentration of the entire residual chlorine by measuring Cl ₂ .

When measuring chlorine gas (Cl ₂ ) in a liquid, the conversion method is different between the measurement in a flowing state and the measurement in a still water state as follows.

In the water flow state, the conversion formula changes when the water flow rate changes. That is, a predetermined reduction potential (a potential giving a maximum value among the reduction currents, +0.4 V in the case of Cl ₂ (when the reference electrode is Ag / AgCl)) is applied to flow the electrolytic reduction current (change in water flow rate) The change with time of each reduction current corresponding to (1) varies linearly and almost constant, although there is a slight variation. Therefore, the average value during this period is adopted as the measured value.)
Can be used to calculate the residual chlorine concentration. In the flowing state, new liquid is replenished around the electrode, and the chlorine gas to be measured is always sufficient around the electrode, which is the reason that there is almost no change with time. The average value of the electrolytic reduction current has a maximum value as compared with the electrolytic reduction current of another potential.

In the hydrostatic state, the voltage between the working electrode and the reference electrode is swept to detect a local maximum value, and the concentration is converted from the current value giving the local maximum value (the change in the reduction current with respect to the sweep potential has a local maximum value). Since it is in a hydrostatic state, ions around the electrode diffuse first, then chlorine gas Cl ₂ in the liquid diffuses, receives electrons at the electrode, causes a reduction reaction, and forms a maximum value. The reaction ends. Note that C
lO ^- When measuring tend to maximum value that can be used when measuring the Cl ₂ in reduction current is less likely to appear.

According to a second aspect of the present invention, there is provided an apparatus for measuring the concentration of residual chlorine in an acidic liquid, wherein a cell into which the liquid to be measured is introduced, and a potential of a working electrode, a counter electrode, and the working electrode provided in the cell are set to predetermined values. A reference electrode that generates a reference potential for setting a potential, and a variable power supply unit that adjusts a voltage between the working electrode and the counter electrode to control a potential of the working electrode with respect to the reference electrode to a predetermined potential. A current detection unit that can detect a current value flowing through the working electrode, a control unit that controls the variable power supply unit to control a voltage between the working electrode and the reference electrode to a predetermined voltage, and A residual chlorine concentration measuring apparatus for measuring the residual chlorine concentration in an acidic liquid, comprising: a calculating unit for calculating the residual chlorine concentration, wherein the flow rate detecting unit includes a flow rate detecting unit capable of detecting whether the measured liquid is in a flowing state or a still water state. Check that Then, the control unit is configured to detect an average value of a predetermined said electrolytic reduction current voltage is applied to corresponding to the maximum value of the electrolytic reduction current.

As a result, the following effects can be obtained.

A flow rate detector for detecting the flow rate of the liquid to be measured;
Since the control unit of the variable power supply unit that sets the potential between the working electrode and the reference electrode to a predetermined value is provided, the control unit determines whether the liquid to be treated in the cell is in a hydrostatic state or not. Since optimal measurement is performed when water is passed in the state, optimal control is not performed when water is passed in the still water state.

According to a third aspect of the present invention, in the apparatus for measuring a residual chlorine concentration in an acidic liquid according to the first or second aspect, the arithmetic unit corrects the average value based on the flow rate detection signal detected by the flow rate detection unit, and the residual value is determined. It is configured to calculate the chlorine concentration.

Thus, the following operation is obtained in addition to the operation of the first or second aspect.

At the time of passing water, even if the flow rate of the liquid to be measured changes,
The residual chlorine concentration can be corrected according to the change in the flow rate.

According to a fourth aspect of the present invention, there is provided an apparatus for measuring the concentration of residual chlorine in an acidic solution, wherein a cell into which the liquid to be measured is introduced, and a potential of a working electrode, a counter electrode, and the working electrode provided in the cell are set to predetermined values. A reference electrode that generates a reference potential for setting a potential, and a variable power supply unit that adjusts a voltage between the working electrode and the counter electrode to control a potential of the working electrode with respect to the reference electrode to a predetermined potential. A current detection unit that can detect a current value flowing through the working electrode, a control unit that controls the variable power supply unit to control a voltage between the working electrode and the reference electrode to a predetermined voltage, and A residual chlorine concentration measuring apparatus for measuring the residual chlorine concentration in an acidic liquid, comprising: a calculating unit for calculating the residual chlorine concentration, wherein the flow rate detecting unit includes a flow rate detecting unit capable of detecting whether the measured liquid is in a flowing state or a still water state. Before detecting a still water condition Controller by sweeping the voltage between the reference electrode and the working electrode is configured to detect a maximum value of the electrolytic reduction current.

As a result, the following effects can be obtained.

A flow rate detector for detecting the flow rate of the liquid to be measured;
Since the control unit of the variable power supply unit that sets the potential between the working electrode and the reference electrode to a predetermined value is provided, the control unit determines whether the liquid to be treated in the cell is in a hydrostatic state or not, and In this case, the optimum measurement is performed when the water is still.

According to a fifth aspect of the present invention, there is provided an apparatus for measuring the concentration of residual chlorine in an acidic liquid according to any one of the first to fourth aspects.
A conversion table for converting the current value to the residual chlorine concentration is provided for each of the flowing state and the still water state, and the calculation unit selects one conversion table based on a flow signal from the flow detection unit. To calculate the residual chlorine concentration.

Thus, in addition to the function of any one of claims 1 to 4, the following function is obtained. That is, since the conversion table is provided corresponding to the still water state and the water flow state, the conversion table of the still water state and the water flow state can be immediately selected according to the flow rate signal. The flow rate can be grasped and the correction corresponding to the flow rate can be performed on the conversion table.

According to a sixth aspect of the present invention, there is provided a method for measuring a residual chlorine concentration in an acidic liquid according to any one of the first to fifth aspects, further comprising a voltage detecting unit for detecting a potential of the working electrode with respect to the reference electrode. The control unit is configured to control the voltage of the variable power supply unit to a potential detected by the voltage detection unit.

Thus, in addition to the function of any one of the first to fifth aspects, the following function can be obtained. That is, since the voltage detecting unit for detecting the potential of the working electrode with respect to the reference electrode is provided, the applied voltage state can be grasped, so that a measurement abnormality can be easily found.

The method for measuring the residual chlorine concentration in an acidic liquid according to the present invention detects whether the cell in which the liquid to be measured is put is in a flowing state or a still water state, and operates when the cell is in a flowing state. An average value of the electrolytic reduction current is detected by applying a predetermined voltage corresponding to the maximum value of the electrolytic reduction current between the electrode and the reference electrode, and when in a hydrostatic state, the voltage between the working electrode and the reference electrode is determined. The maximum value of the electrolytic reduction current is detected by sweeping, and the residual chlorine concentration is converted from the average value or the maximum value.

As a result, the following effects can be obtained.

Detecting whether the inside of the cell is in a water passing state or a still water state,
It is possible to calculate the residual chlorine concentration with high accuracy by adopting an optimal and unique measurement method in each state.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

(Embodiment 1) FIG. 1 is a configuration diagram showing a residual chlorine concentration measuring apparatus according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 1 denotes the passage of the liquid to be measured,
A cell for measuring the residual chlorine concentration in the liquid to be measured, a pipe 2 for introducing and discharging the liquid to be measured containing residual chlorine and the like into the cell 1, and a cell 3 for measuring by the electrode reaction of the liquid to be measured. A working electrode 4 for detecting residual chlorine contained in the liquid, a counter electrode 4 is fixed in the cell 1 and is electrically connected to the working electrode 3, and a reference electrode 5 is a reference of the potential of the working electrode 3. ,
Reference numeral 6 denotes a voltmeter serving as a voltage detecting unit that indicates a potential difference between the working electrode 3 and the reference electrode 5 with reference to the reference electrode 5; 7, a variable power supply unit that variably controls a voltage between the working electrode 3 and the counter electrode 4;
Is a current detector for measuring an electrolytic reduction current generated by an electrode reaction on the working electrode 3; 9 is a calculator for calculating the residual chlorine concentration based on the electrolytic reduction current measured by the current detector 8; Inside the cell 1 or pipe 2 through which the liquid to be measured flows
And a flow detecting unit which detects whether the liquid to be measured in the cell 1 is in a hydrostatic state or a flowing state, and can output a flow signal corresponding to the flow rate in the flowing state. Power supply unit 7 based on the flow signal output from
And a controller for controlling the potential difference between the working electrode 3 and the reference electrode 5.

The operation and the like of the apparatus for measuring the concentration of residual chlorine in an acidic liquid thus constructed will be described with reference to FIGS.

FIG. 2 is a graph showing the relationship between the reduction current value A and the potential V when the potential V of the working electrode with respect to the reference electrode is swept at a constant sweep rate in a hydrostatic state. FIG. 4 is a graph showing a relationship between a current value A and a residual chlorine concentration C. FIG. 4 shows the reduction current value A and the time T when the potential V of the working electrode with respect to the reference electrode is kept constant in the flowing state.
FIG. 5 is a graph showing the relationship between the reduction current value A and the residual chlorine concentration C at this time.

As shown in FIG. 1, a liquid to be measured containing residual chlorine and located in an acidic region is introduced into a cell 1 through a pipe 2.
In the cell 1, a working electrode 3 for detecting the concentration of residual chlorine by an electrode reaction of the liquid to be measured, a counter electrode 4 disposed opposite to the working electrode 3, and a reference for the potential of the working electrode 3. The reference electrode 5 is immersed in the arrangement.

The working electrode 3 and the counter electrode 4 are electrically connected, and a predetermined potential V is applied to the working electrode 3 with respect to the reference electrode 5. As a result, an electrolytic reduction current flows between the working electrode 3 and the counter electrode 4 in accordance with the flow state of the liquid to be measured or the residual chlorine concentration, and the concentration of the liquid to be measured is determined by utilizing the concentration dependency of the reduction current value generated at that time. The concentration of residual chlorine contained therein can be calculated.

A potential necessary for reducing residual chlorine contained in the liquid to be measured is applied to the working electrode 3 by the variable power supply unit 7, and the residual chlorine Cl ₂ in the liquid to be measured is applied to the working electrode 3. Electrolytic reduction is performed above, the reduction current value A generated at this time is detected by the current detection unit 8, and the calculation unit 9 can calculate the concentration of residual chlorine based on the reduction current value A. In order to set the applied potential to the working electrode 3,
The reference electrode 5 serving as a reference for the potential is used.
Of the working electrode 3 can be detected by the voltmeter 6. Further, depending on whether the liquid to be measured in the cell 1 is in a hydrostatic state or a flowing state, the control unit 11 allows the output of the voltmeter 6 to be swept at a predetermined sweeping speed or to maintain the potential at which a reduction reaction occurs. The power supply unit 7 is provided.

A flow detecting unit 10 for detecting the flow state of the liquid to be measured is disposed in either the cell 1 or the pipe line 2. A control unit 11 that determines whether the state is in the water state and controls the variable power supply unit 7 that applies a potential to be applied to the working electrode 3 includes a microcomputer or the like.

The potential of the working electrode 3 can be detected by a voltmeter 6 provided between the working electrode 3 and the reference electrode 5. Control unit 11
Can control the potential applied to the working electrode 3 by adjusting the output of the variable power supply unit 7 and change the potential V indicated by the voltmeter 6 according to the flow rate state.

Here, when the flow signal from the flow detecting unit 10 is substantially equal to zero, the following operation can be performed using the control unit 11. That is, the working electrode 3
In order to detect residual chlorine existing near the electrode surface of
The control unit 11 controls the voltage between the working electrode 3 and the counter electrode 4 using the variable power supply unit 7 so that the potential of the working electrode 3 can be swept at a constant sweep speed based on the potential of the reference electrode 5. In this way, the potential applied to the working electrode 3 set with respect to the reference electrode 5 is swept at a constant speed, so that residual chlorine is reduced on the working electrode 3. The current generated by the electrode reaction on the working electrode 3 is detected by the current detection unit 8 and converted into the residual chlorine concentration by the calculation unit 9.

When the liquid to be measured introduced into the cell 1 is in a flowing state, the following operation is performed. That is, in order to detect residual chlorine that comes into contact with the electrode surface of the working electrode 3, the potential of the working electrode 3 is applied to a constant value with reference to the potential of the reference electrode 5. In the case of Cl ₂ , it is +0.4 V (when the reference electrode is Ag / AgCl). When the control section 11 controls the variable power supply section 7 so that the voltmeter 6 indicating the applied potential to the working electrode 3 with respect to the reference electrode 5 maintains a constant potential, the reduction current can be detected by the current detection section 8. . The applied potential here is a potential at which the average value of the electrolytic reduction current becomes maximum with respect to the applied potential, and is a potential at which the concentration of residual chlorine contained in the liquid to be measured can be detected most accurately.

Further, the reduction current A detected by the working electrode 3 changes depending on whether the liquid to be measured in the cell 1 is in a hydrostatic state or a flowing state, and in accordance with an increase or decrease in the flow rate. With respect to the increase and decrease of the flow rate, when the residual chlorine as the substance to be measured is reduced on the working electrode 3, the applied potential and the reduction current value at that time change, and the liquid to be measured flowing through the cell 1 And a current gradient proportional to the residual chlorine concentration.

The calculating section 9 is provided with a conversion table for calculating the concentration of the target substance contained in the liquid to be measured from the current value A according to the flow signal.

In FIG. 2, when the flow rate signal from the flow rate detection unit 10 provided in the cell 1 or the pipe line 2 is substantially zero and in a hydrostatic state, the potential of the working electrode 3 with respect to the reference electrode is changed at a constant sweep speed. 4 shows the relationship between the reduction current value A and the potential V when sweeping.

As shown in FIG. 2, the current value A at which the residual chlorine contained in the liquid to be measured is reduced changes as the output of the potential of the working electrode 3 changes due to the sweeping of the potential of the working electrode 3, and the potential specific to Cl _2. (Approximately +0.8 V) indicates a limit current value Ac at which the reduction current value A is maximized. The potential Vc giving this limit current value Ac is equal to the working electrode 3 of Cl ₂ contained in the liquid to be measured.
And the concentration dependence of the obtained current value Ac and the residual chlorine concentration C can be used to calculate the concentration of residual chlorine contained in the liquid to be measured.

In FIG. 2, the curves show the residual chlorine concentrations of 0 mg / L, 12 mg / L, and 24 mg / L, respectively.
L, 40 mg / L and 50 mg / L are shown.

Therefore, as shown in FIG. 2, the relationship between the reduction current value A and the potential V obtained when the control section 11 sweeps the potential of the working electrode 3 with respect to the reference electrode 5 at a constant sweep speed. The arithmetic unit 9 detects the limiting current Ac, and as shown in FIG. 3, always obtains a stable value by using a conversion table which gives a relationship between the limiting current value Ac and the concentration C of the residual chlorine contained in the liquid to be measured. Thus, the residual chlorine concentration can be accurately obtained. In FIG. 3, the reference electrode 5 is A
g / AgCl electrode, and the potential of the working electrode 3 is +
The current value that gives the maximum value when 0.8 V is applied is the limit current Ac.

The flow rate detector 1 provided in the cell 1 or the pipe 2
A flow signal was output from 0, and when the liquid to be measured introduced into the cell 1 was in a flowing state, the potential was obtained when the potential of the working electrode 3 was kept constant with respect to the potential of the reference electrode 5 and was continuously applied. FIG. 4 shows the relationship between the reduction current value A and the time T.
In FIG. 4, the curves each show a residual chlorine concentration of 0 mg.
/ L, 5 mg / L, 13 mg / L, 42 mg / L, 50
The data in the cases of mg / L and 73 mg / L are shown.

In FIG. 4, by controlling the output potential of the variable power supply section 7 provided between the working electrode 3 and the counter electrode 4, the indication of the voltmeter 6 provided between the reference electrode 5 and the working electrode 3 is obtained. The change with time of the current value obtained by the current detection unit 8 that controls the voltage to be constant and detects the reduction current of the working electrode 3 is shown. Each data shows that the reduction current slightly varies with time, but basically has a constant value. Therefore, in the present invention, in the water-flowing state, the average value of the electrolytic reduction current is obtained and used for conversion of residual chlorine.

Accordingly, as shown in FIG. 5, the relationship between the average value of the reduction current and the residual chlorine concentration when the potential of the working electrode 3 with respect to the reference electrode 5 is constant is obtained at a constant voltage. The concentration of residual chlorine contained in the liquid to be measured can be constantly and accurately calculated by the reduced current.

The three straight lines in FIG. 5 indicate that the flow rate of the liquid to be measured flowing through the cell is 0.2 L / min and 0.5 L / min, respectively.
The data for L / min and 1.0 L / min are shown, from which it can be seen that the residual chlorine concentration is expressed in a proportional relationship to the reduction current.

As described above, the applied potential to the working electrode 3 is a potential that gives a limit current value Ac at which the average value of the reduction current becomes a maximum value with respect to the applied potential. Since the reference electrode 5 is used as an Ag / AgCl electrode, the potential of the working electrode 3 with respect to the reference electrode 5 is +
The values when a voltage near 0.4 V is applied are shown.

Further, as shown in FIG. 5, in response to the flow rate signal from the flow rate detecting section 10, the average flow rate of the reducing current detected by the current detecting section 8 is determined based on the flow rate. When the current value detected by the calculation unit 9 is calculated from the conversion table to the density using the conversion table,
If the correction is performed in consideration of the flow rate, the residual chlorine concentration can always be stably and accurately measured in response to the flow rate change during the passage of water.

As described above, according to the first embodiment, the optimum measurement can be performed in each state depending on whether the liquid to be measured is in a still water state or in a flowing state. The reduction current can be easily and stably detected without being affected by the still water, and the residual chlorine concentration can be accurately calculated.

(Embodiment 2) FIG. 6 is a block diagram showing a residual chlorine concentration measuring apparatus according to Embodiment 2 of the present invention.

In FIG. 6, 12 is a D / A converter for converting a digital signal into an analog signal, 13 is an A / D converter for converting an analog signal from the flow rate detecting section 10 to a control section 11 and outputting the digital signal, Reference numeral 14 denotes an A / D converter for converting an analog signal of the current detection unit 8 into a digital signal, and reference numeral 15 denotes a voltage amplification circuit incorporated in the current detection unit 8. In the following description, components having the same functions as in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the first embodiment, the potential of the working electrode with respect to the reference electrode is detected by the voltmeter 6, and the voltage of the variable power supply 7 is controlled by the control unit 11 so that the detected potential becomes a predetermined potential. did. However, in the second embodiment, the potential of the working electrode with respect to the reference electrode is controlled to a predetermined potential output from the control unit 11 without specially providing a voltmeter.

The variable power supply unit 7 according to the second embodiment includes a counter electrode side operational amplifier 16 and a working electrode side operational amplifier 17. The opposite-side operational amplifier 16 is supplied with a voltage to the + input terminal so as to have a predetermined sweep potential in order to sweep the potential of the working electrode 3. The D / A converter 12 converts the voltage into a sweeping voltage. The reference electrode 5 is connected to the negative input terminal. At this time, the voltage of the counter electrode 4 is adjusted due to the imaginary short of the operational amplifier, and the sweep potential input to the + input terminal and the reference electrode 5 become the same potential.

Next, the output of the operational electrode side operational amplifier 17 is fed back to the negative input terminal, thereby forming a follower.

This + input terminal is connected to the control section 11 via the D / A converter 12, and outputs a predetermined potential to the working electrode 3 during sweeping. In this way, the working electrode 3 is swept relative to the reference electrode 5.

In order to detect the reduction current flowing between the working electrode 3 and the counter electrode 4, the output of the working electrode side operational amplifier 17 is detected as a voltage by the resistor R. This is sent to the calculation unit 9 via the voltage amplification circuit 15 and the A / D converter 14, and the calculation unit 9 temporarily stores the relationship between the reduction current and the sweep potential in the memory. It should be noted that such a sweep is performed when the control unit 11 detects that the liquid to be measured is not flowing through the cell 1 (that is, detects that it is in a still water state) by the flow rate detection unit 10. Command. The calculation unit 9 detects a maximum value of the reduction current from the relationship between the sweep potential and the reduction current, and converts the maximum value into a residual chlorine concentration.

If the flow rate detecting section 10 detects that the liquid to be measured is flowing through the cell 1, the control section 11 is in the water-passing state, and the control section 11 determines the + input terminal of the working electrode side operational amplifier 17 and the counter electrode side operational amplifier 16. A known reduction potential (a potential giving a maximum value among reduction currents, a Cl ₂ gas in a liquid (a reference electrode is an Ag / AgCl electrode)), and +0.4
A potential which gives a difference near V is input.

As described for the sweep potential,
The potential of the working electrode 3 with respect to the reference electrode 5 is adjusted to this predetermined reduction potential. At this time, the reduction current flowing between the working electrode 3 and the counter electrode 4 is almost constant although there is a slight temporal variation, and the current value detected by the current detection unit 8 is averaged by the calculation unit 9, and the calculation unit 9 calculates the average value Can be used to convert the concentration of residual chlorine.

[0073]

According to the apparatus for measuring the concentration of residual chlorine in an acidic liquid according to the present invention, the following effects can be obtained.

(A) Since there is provided a flow rate detecting section for detecting the flow rate of the liquid to be measured and a control section for a variable power supply section for setting the potential between the working electrode and the reference electrode to a predetermined value, the control section is provided inside the cell. It is possible to determine whether the liquid to be treated is in a hydrostatic state or a flowing state, and to perform optimal measurement in each state.

(B) When the flow rate signal of the liquid to be measured is substantially equal to zero, since the liquid to be measured is in a hydrostatic state, the potential of the working electrode with respect to the reference electrode is swept at a constant speed, and is obtained by a change in potential. Since the maximum value of the current is detected from the change in the current value, the potential giving this maximum value can be used as the optimal potential for detecting the residual chlorine concentration in the liquid to be measured.

(C) When the flow rate signal of the liquid to be measured exceeds zero, since the liquid to be measured is in a flowing state, the potential of the working electrode with respect to the reference electrode is controlled to a predetermined potential, and the time of the electrolytic reduction current is reduced. Since the residual chlorine concentration is converted based on the average, highly accurate concentration measurement can be performed even when water is passed.

According to the apparatus for measuring the residual chlorine concentration in an acidic liquid according to the second aspect, the following effects can be obtained.

A flow rate detector for detecting the flow rate of the liquid to be measured,
Since the control unit of the variable power supply unit that sets the potential between the working electrode and the reference electrode to a predetermined value is provided, the control unit determines whether the liquid to be treated in the cell is in a hydrostatic state or not. Since optimal measurement is performed when water is passed in the state, optimal control is not performed when water is passed in the still water state.

According to the apparatus for measuring the residual chlorine concentration in an acidic liquid according to the third aspect, the following effects can be obtained in addition to the effects of the first or second aspect.

At the time of passing water, even if the flow rate of the liquid to be measured changes,
The residual chlorine concentration can be corrected according to the change in the flow rate.

According to the apparatus for measuring the residual chlorine concentration in an acidic liquid according to the fourth aspect, the following effects can be obtained.

A flow rate detector for detecting the flow rate of the liquid to be measured,
Since the control unit of the variable power supply unit that sets the potential between the working electrode and the reference electrode to a predetermined value is provided, the control unit determines whether the liquid to be treated in the cell is in a hydrostatic state or not, and In this case, the optimum measurement is performed when the water is still, so that there is no case where the optimal control is performed when the water is still flowing while the water is flowing.

According to the apparatus for measuring the concentration of residual chlorine in an acidic liquid according to the fifth aspect, the following effects can be obtained in addition to the effects of any of the first to fourth aspects.

Since the conversion tables are provided in correspondence with the still water state and the water passing state, the conversion table for the still water state and the water passing state can be immediately selected according to the flow rate signal. Thus, the flow rate can be grasped, and the correction corresponding to the flow rate can be performed on the conversion table.

According to the apparatus for measuring the residual chlorine concentration in an acidic liquid according to the sixth aspect, the following effects can be obtained in addition to the effects of the first to fifth aspects.

Since the voltage detecting section for detecting the potential of the working electrode with respect to the reference electrode is provided, the state of the applied voltage can be grasped, so that a measurement abnormality can be easily found.

According to the method for measuring the residual chlorine concentration in an acidic liquid according to the seventh aspect, the following effects can be obtained.

Detecting whether the inside of the cell is in a water passing state or a still water state,
It is possible to calculate the residual chlorine concentration with high accuracy by adopting an optimal and unique measurement method in each state.

[Brief description of the drawings]

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

FIG. 2 shows a potential V of a working electrode with respect to a reference electrode in a hydrostatic state.
Graph showing the relationship between the reduction current value A and the potential V when sweeping is performed at a constant sweep speed.

FIG. 3 is a graph showing a relationship between a reduction current value A and a residual chlorine concentration C;

FIG. 4 shows a potential V of a working electrode with respect to a reference electrode in a flowing state.
Graph showing the relationship between the reduction current value A and the time T when the temperature is kept constant.

FIG. 5 is a graph showing a relationship between a reduction current value A and a residual chlorine concentration C.

FIG. 6 is a configuration diagram showing a residual chlorine concentration measuring device according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 cell 2 conduit 3 working electrode 4 counter electrode 5 reference electrode 6 voltmeter 7 variable power supply unit 8 current detection unit 9 calculation unit 10 flow detection unit 11 control unit 12 D / A converter 13 A / D converter 14 A / D converter 15 Voltage amplification circuit 16 Op amp on the opposite electrode side 17 Op amp on the working electrode side

Claims (7)

[Claims] 1. A cell into which a liquid to be measured is introduced, a working electrode provided in the cell, a counter electrode, and a reference electrode for generating a reference potential for setting the potential of the working electrode to a predetermined potential. A variable power supply unit that adjusts the voltage between the working electrode and the counter electrode to control the potential of the working electrode with respect to the reference electrode to a predetermined potential, and a current detection unit that can detect a current value flowing through the working electrode A control unit that controls the variable power supply unit to control the voltage between the working electrode and the reference electrode to a predetermined voltage; and an arithmetic unit that calculates a residual chlorine concentration from the current value. A residual chlorine concentration measuring device, comprising: a flow rate detection unit that can detect whether the liquid to be measured is in a water-flowing state or a still water state, and when the flow rate detection unit detects that the liquid is in a water-flowing state, the control unit For the maximum value of electrolytic reduction current The control unit sweeps a voltage between the working electrode and the reference electrode when the flow rate detecting unit detects a hydrostatic state by applying an appropriate predetermined voltage to detect the average value of the electrolytic reduction current, and An apparatus for measuring the concentration of residual chlorine in an acid solution, which detects a maximum value of a reduction current. 2. A cell into which a liquid to be measured is introduced, a working electrode provided in the cell, a counter electrode, and a reference electrode for generating a reference potential for setting the potential of the working electrode to a predetermined potential. A variable power supply unit that adjusts the voltage between the working electrode and the counter electrode to control the potential of the working electrode with respect to the reference electrode to a predetermined potential, and a current detection unit that can detect a current value flowing through the working electrode A control unit that controls the variable power supply unit to control the voltage between the working electrode and the reference electrode to a predetermined voltage; and an arithmetic unit that calculates a residual chlorine concentration from the current value. A residual chlorine concentration measuring device, comprising: a flow rate detection unit that can detect whether the liquid to be measured is in a water-permeating state or a still water state. For the maximum value of electrolytic reduction current An apparatus for measuring the concentration of residual chlorine in an acid solution, wherein an average value of the electrolytic reduction current is detected by applying a corresponding predetermined voltage. 3. The acidic liquid according to claim 1, wherein the calculating section corrects the average value based on the flow rate detection signal detected by the flow rate detecting section to calculate the residual chlorine concentration. Equipment for measuring residual chlorine concentration. 4. A cell into which a liquid to be measured is introduced, a working electrode provided in the cell, a counter electrode, and a reference electrode for generating a reference potential for setting the potential of the working electrode to a predetermined potential. A variable power supply unit that adjusts the voltage between the working electrode and the counter electrode to control the potential of the working electrode with respect to the reference electrode to a predetermined potential, and a current detection unit that can detect a current value flowing through the working electrode A control unit that controls the variable power supply unit to control the voltage between the working electrode and the reference electrode to a predetermined voltage; and an arithmetic unit that calculates a residual chlorine concentration from the current value. A residual chlorine concentration measuring device, comprising: a flow rate detecting unit that can detect whether the liquid to be measured is in a flowing state or in a still water state, and when the flow rate detecting unit detects a still water state, the control unit is configured to control the working electrode and the hydrostatic state. The voltage between the reference electrodes An apparatus for measuring the residual chlorine concentration in an acid solution, wherein the maximum value of the electrolytic reduction current is detected by sweeping. 5. A conversion table for converting the current value into a residual chlorine concentration is provided for each of a water passing state and a still water state, and the calculation unit is configured to perform one of the conversion based on a flow signal from the flow detection unit. The apparatus for measuring a residual chlorine concentration in an acidic liquid according to any one of claims 1 to 4, wherein a conversion table is selected to calculate the residual chlorine concentration. 6. A voltage detecting section for detecting a potential of the working electrode with respect to the reference electrode, wherein the control section controls a voltage of the variable power supply section to a potential detected by the voltage detecting section. An apparatus for measuring the concentration of residual chlorine in an acidic liquid according to any one of claims 1 to 5. 7. Detecting whether the inside of the cell into which the liquid to be measured is filled is in a flowing state or a hydrostatic state, and when the state is in the flowing state, the maximum value of the electrolytic reduction current is applied between the working electrode and the reference electrode. Applying a predetermined voltage to detect the average value of the electrolytic reduction current, and when in a hydrostatic state, sweep the voltage between the working electrode and the reference electrode to detect the maximum value of the electrolytic reduction current, A method for measuring the residual chlorine concentration in an acidic liquid, comprising converting the residual chlorine concentration from an average value or the maximum value.