JPH10111274A - Residual chlorine meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve miniaturization and cost reduction and to enable highly accurate measurement by applying pulse voltage across an indicating electrode and an opposed electrode. SOLUTION: One terminal of a pulse generator 18 is connected to an opposed electrode 12 and the other terminal thereof is connected to an indicating electrode 13 through a current/voltage converter 21 and the pulse generator 18 applies pulse voltage across the opposed electrode 12 and the indicating electrode 13 on the basis of the command from an operation means CPU 19. Since the voltage applied across both electrodes is pulsative, an electrolytic time is short and no effect is exerted on the thickness of a diffusion layer. An A/D converter 20 inputs the current signal from the indicating electrode 13 outputted through the current/voltage converter 21 to perform analogue/digital conversion. The output of the A/D converter 20 is processed by an operation means 19 to be subjcted to digital/analogue conversion by a D/A converter 22 to be sent to a display means 25 to perform the display related to the concn. of free effective chlorine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a residual chlorine analyzer, and more particularly, to a method for removing the effects of other components that interfere with the measurement of chlorine concentration and removing the components electrolytically formed on the electrodes by reverse electrolysis. To a reagent-free residual chlorine analyzer.

[0002]

2. Description of the Related Art A residual chlorine meter has an indicator electrode and a counter electrode arranged opposite to each other and measures free available chlorine present in a solution in accordance with a polarographic method. In order to eliminate the influence of interfering components, pH is adjusted using a reagent. There is a type to perform and a non-reagent type. In the former, the effect of interfering components does not appear in the measurement results, but a reagent must be used.

FIG. 6 is a block diagram of a conventional reagentless residual chlorine meter. In the figure, reference numeral 1 denotes an electrode tank. The measurement liquid S introduced into the tank from the inlet 1a is guided to the measurement tank 1b, and the overflowing measurement liquid is discharged from the outlets 1c and 1e. Measurement tank 1b
Is provided with a rotation indicator pole 2 into which a spot electrode 2a at the tip is inserted, and a counter electrode 3 is provided opposite to this electrode.

Reference numeral 4 denotes an ammeter for detecting a diffusion current flowing between these electrodes, 5 denotes a power supply, and 6 denotes a DC voltage applying unit for giving an electrode potential causing an electrolytic reaction, and includes a volume and a voltmeter. In such a configuration, the water chlorine gas was blown HCLO or CLOs ^- free available chlorine is present as. When these are collectively referred to as CL ₂ , the following reduction reaction occurs at the indicator electrode 2, and Cl ₂ + 2e ⁻ → 2Cl ⁻ (1) The following electrolytic oxidation occurs at the counter electrode 3. AgCl ⁻ ← → AgCl + e ⁻ … (2)

The applied voltage level at which the electrolysis starts is known, and the volume of the DC applied voltage unit 6 is adjusted so that the applied voltage is applied between the indicator electrode 2 and the counter electrode 3. The diffusion current i ₄ flowing at this time indicates a value related to the concentration C of the liquid to be measured as follows: i ₄ = KC (where K is a constant) The current is measured to determine the concentration of free available chlorine. .

The potential in a region where the diffusion current does not increase even when the applied voltage is increased is called a plateau potential. The potential at which this plateau occurs increases as the diffusion current increases, and the voltage effect based on Ohm's law between the electrodes increases. Misplaced. Therefore, the applied voltage is changed according to the diffusion current so that the applied voltage does not deviate from the plateau potential. However, in such a residual chlorine analyzer that does not use a reagent, an interfering component remains in the measurement solution, and the interfering component affects the diffusion current to be measured.

FIG. 7 shows a polarogram of a measuring solution containing an interfering component. Pc is a plateau by free available chlorine, P
a represents a plateau caused by the first interference component, and Pb represents a plateau caused by the second interference component. ia, ib, and ic represent respective diffusion currents, and Ea, Eb, and Ec represent applied voltages that cause these plateaus.

When the measurement is performed with the applied voltage set to Ec, the first disturbing component is electrolyzed (reduced) by Ea, and the first and second disturbing components are electrolyzed (reduced) by Eb, resulting in a diffusion current. Flow, which add to the diffusion current of the free available chlorine to be measured, and ic no longer corresponds to the true free available chlorine concentration to be measured.

[0009]

By the way, in the conventional example shown in FIG. 6, there is no diffusion control (when the applied voltage is large, there is no unreacted chlorine on the electrode surface. It is not affected and is limited by the supply rate of chlorine, which is the reactant. The reaction current at this time is called diffusion current.) Constant. Further, when the flow rate of the measurement liquid changes greatly, the thickness of the diffusion layer changes, so that the fluctuation of the flow rate must be suppressed by using a dedicated measurement tank. As a result, there is a problem that the number of operating parts increases, which causes a failure factor or a drift factor, resulting in a large size and high cost.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In the present invention, the free available chlorine in the liquid to be measured flowing between the indicator electrode and the counter electrode is described. 3. A residual chlorine meter for measuring the concentration of free available chlorine based on a diffusion current required to reduce the amount of free available chlorine, wherein a voltage applied between the indicator electrode and the counter electrode is a pulse voltage. In the configuration, a plurality of indicator electrodes are provided and the voltage applied to the plurality of indicator electrodes is a pulse voltage, and the pulse voltage application to the indicator electrodes is sequentially switched at predetermined time intervals,

According to a third aspect of the present invention, the pulse voltage is obtained by applying, as a base voltage, a voltage that generates a diffusion current due to a previously measured interference component. The method according to claim 5, wherein a current value immediately before the pulse is applied is sampled, and a difference between the sampled current values is used as a measured current (residual chlorine concentration). It is characterized in that a positive or negative pulse voltage is used as a boundary.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a main part configuration diagram showing an example of an embodiment of the present invention. In the figure, reference numeral 10 denotes a cylindrical probe. A cap-shaped counter electrode 12 is hermetically fixed to the bottom of the probe 10, and an indicator electrode 13 is hermetically sealed on a side surface of the probe at a predetermined distance from the counter electrode 2. Fixed.

A pulse generator 18 has one terminal connected to the counter electrode 12 and the other terminal connected to the indicator 13 via a current / voltage converter 21.
Is a counter electrode 1 based on a command from a calculating means (CPU) 19.
A pulse voltage is applied between 2 and the indicator electrode 13. Reference numeral 20 denotes an A for inputting a current signal from the indicator electrode 13 output via the current / voltage converter 21 and performing analog / digital conversion.
/ D converter. The output of the A / D converter 20 is processed by the arithmetic means 19, and the digital / analog conversion is performed by the D / A converter 22. The output is sent to the display means 25, and the display relating to the free available chlorine concentration is performed. .

FIG. 2 shows the pulse voltage (a) generated by the pulse generator 18 and the pulse voltage applied to the counter electrode 12.
3 shows the magnitude (b) of the current generated in the indicator electrode 13 when applied between the indicator electrode 13 and. Here, it is assumed that the types and concentrations of the interfering components other than the free available chlorine contained in the measurement solution are known and do not change.
Therefore, for example, when it is desired to measure the free available chlorine of the liquid to be measured having the output characteristics as shown in FIG. 7 described above, the initial voltage V ₀ of the base pulse is determined by the pulse applied voltage shown in FIG. 7, and the voltage Va is a voltage corresponding to Ec.

As a result, as shown in FIG.
3, a large current flows first and then gradually stabilizes.
Next, when the pulse applied voltage is turned off and becomes the initial voltage V ₀ , a large current flows in the opposite direction, and the voltage is stabilized as described above. The large current flowing in the initial stage is composed of a charging current flowing to fill the capacity of the electrode interface and an electrolytic field current flowing due to the electrolysis of residual chlorine. In the initial stage of the applied voltage change, the charging current mainly flows and changes greatly. .

In the present invention, the measurement of the current value is sampled at a point A shown immediately before the pulse application and at a point B shown in FIG.
(See FIG. 1). This difference current becomes a value related to free available chlorine. According to the above configuration, since the voltage applied between the electrodes is pulse-shaped, the electrolysis time is short, so that the thickness of the diffusion layer is not affected.

FIG. 3 is a block diagram showing an example of the second embodiment of the present invention. In the figure, the same elements as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. In the figure, A to D are indicator poles, and in this example, four indicator poles are counter electrodes 1
2 are equidistant from each other. A switching means 30 transmits a current signal generated at each indicator electrode to the current / voltage converter 21 based on a switching signal instructed by the arithmetic means 19.

FIG. 4 shows an example of the pulse applied voltage and the switching timing of the switching means 30. The pulse of the indicator pole B is emitted in synchronization with the falling timing of the pulse a of the indicator pole A. An electric signal generated at each indicator electrode is transmitted to the current / voltage converter 21 until a pulse is emitted from the indicator electrode D and a pulse b next to the indicator electrode A is emitted. Also in this case, the base voltage of the pulse voltage applied to one electrode and the timing of sampling are performed under the same conditions as those described with reference to FIG.

According to the configuration of FIG. 4, the pulse interval applied to one indicator electrode can be lengthened, so that the diffusion layer on the indicator electrode surface during non-measurement can be restored to a steady state more reliably. Accurate free available chlorine measurement.

[0020] FIG. 5 (a) relative to the base voltage V ₀ pulse applied voltage V _a (e.g. -500 mV) applied to a predetermined time (pulse width) after reverse voltage (V _b ... for example 200 mV)
Is applied, and as a result, the state of the diffusion current generated in the indicator electrode is shown. By applying a pulse that changes positively and negatively from zero as described above, the metal film adhered to the indicator electrode by electrolysis while the positive voltage is applied can be removed.

[0021]

As described above in detail, according to the present invention, based on the diffusion current required for reducing free available chlorine in the liquid to be measured flowing between the indicator electrode and the counter electrode, the free In a residual chlorine meter for measuring the concentration of available chlorine, the voltage applied to the indicator electrode was a pulse voltage. Therefore, the influence on the diffusion layer can be essentially eliminated, and a rotating mechanism and a measuring tank of the indicator electrode, which were conventionally required for applying a DC voltage constantly, become unnecessary. Could be reduced. As a result, a small-sized, low-cost residual chlorine analyzer was realized. In addition, since a plurality of indicator electrodes were provided, the diffusion layer on the indicator electrode surface could be more reliably restored to a steady state, and accurate measurement of free available chlorine became possible. Further, since positive and negative pulses were applied, the metal film adhering to the indicator electrode was removed by electrolysis, and a highly accurate residual chlorine meter could be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a pulse applied voltage and a measured current.

FIG. 3 is a configuration diagram showing an example of an embodiment when a plurality of indicator electrodes are provided.

FIG. 4 is a diagram showing an example of a pulse applied voltage and a switching timing.

FIG. 5 is a diagram showing a state of a diffusion current flowing when positive and negative pulses are applied.

FIG. 6 is a configuration diagram showing an example of a conventional residual chlorine meter.

FIG. 7 is a diagram showing a polarogram of a measurement solution containing an interfering component.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Probe 12 Counter electrode 13 Indicator electrode 18 Pulse generator 19 Computing means 20 A / D converter 21 Current / voltage converter 22 D / A converter 25 Display means

Claims (5)

[Claims] 1. A residual chlorine meter for measuring the concentration of free available chlorine based on a diffusion current required to reduce free available chlorine in a liquid to be measured flowing between an indicator electrode and a counter electrode, A residual chlorine meter, wherein the voltage applied between the indicator electrode and the counter electrode is a pulse voltage. 2. The method according to claim 1, wherein a plurality of said indicator poles are provided, and a voltage applied to said plurality of indicator poles is a pulse voltage, and application of the pulse voltage to said indicator poles is sequentially switched at predetermined time intervals. The residual chlorine meter according to claim 1, wherein 3. The residual chlorine meter according to claim 1, wherein the pulse voltage is applied as a base voltage that generates a diffusion current due to a previously measured interference component. 4. The method according to claim 1, wherein a current value immediately before application of a pulse is sampled from a current flowing by applying the pulse voltage, and a difference between the sampled current values is used as a measured current (residual chlorine concentration). 3. The residual chlorine meter according to 1 or 2. 5. The residual chlorine meter according to claim 1, wherein the pulse voltage is a pulse voltage that changes positively and negatively with zero as a boundary.