JP2022113472A - Hardness measuring method and hardness measuring device - Google Patents

Abstract

To provide a hardness measuring method and hardness measuring device which can accurately measure hardness to high hardness.SOLUTION: A hardness measuring method measures hardness of test water. The hardness measuring method includes the steps of: repeating injection of a predetermined amount of chelate type reagent to the test water and measurement of absorbance of the test water in measurement light having two wavelengths a plurality of times; calculating a complex absorbance component that is a component of absorbance by a chelate complex obtained by combining the reagent and a hardness component on the basis of the absorbance of the measurement light having the two wavelengths; and calculating the hardness of the test water on the basis of a change in the complex absorbance component accompanying the injection of the reagent.SELECTED DRAWING: Figure 3

Description

The present invention relates to a hardness measuring method and a hardness measuring device.

Using a reagent that exhibits a color reaction that develops or changes color by binding with the solute of the target to be measured in the sample water, the concentration of the target to be measured in the sample water is measured by measuring the change in absorbance of the sample water that accompanies the coloring of the reagent. A concentration measurement method that Furthermore, densitometers that automatically measure densities using such color reactions are also available on the market. A general concentration measuring device automatically measures the absorbance by injecting a reagent into a measurement cell having a capacity of several mL into which a sample is injected and by projecting measurement light.

A reagent is selected according to the object to be measured. When measuring hardness, a chelate-type reagent that forms a chelate complex by binding to a hardness component may be used, as described in Patent Document 1, for example.

Japanese Patent No. 4168557

In particular, when a chelate-type reagent is used, unreacted reagents can also absorb measurement light, so excessive injection of reagents may increase measurement errors. In addition, depending on the hardness and the concentration of interfering components, the chelate-type reagent does not allow the chelate-type generation reaction to proceed quantitatively, and the absorbance can be measured at the stage where unreacted reagent remains. In particular, when the sample water to be measured has a high hardness, measurement errors due to these factors tend to increase.

In view of such circumstances, an object of the present invention is to provide a hardness measuring method and a hardness measuring apparatus capable of measuring hardness up to high hardness with high accuracy.

A hardness measurement method according to an aspect of the present invention is a hardness measurement method for measuring the hardness of sample water, wherein a predetermined amount of a chelate-type reagent is injected into the sample water and measurement light of two wavelengths of the sample water is used. a step of repeating the absorbance measurement a plurality of times; a step of calculating a complex absorbance component, which is a component of absorbance due to a chelate complex in which the reagent and the hardness component are combined, based on the absorbance of the measurement light of the two wavelengths; and calculating the hardness of the test water based on the change in the absorbance component of the complex due to the injection of the reagent.

In the hardness measurement method described above, the change in the complex absorbance component accompanying the injection of the reagent is the amount of change in the complex absorbance component and the uncomplexed absorbance component, which is the absorbance component of the reagent that is not bound to the hardness component. It may be determined from the relationship with the amount of change.

In the hardness measurement method described above, the step of calculating the hardness is based on a preset approximation formula, and from a plurality of data of the complex absorbance component, the complex absorbance component when the number of injections of the reagent is increased. A step of estimating a convergence value may be included.

In the hardness measurement method described above, the plurality of data may exclude data with a small number of injections of the reagent.

In the hardness measurement method described above, the steps of injecting the reagent and measuring the absorbance, calculating the complex absorbance component, and estimating the convergence value are repeated, and the latest estimated value of the convergence value and The hardness may be calculated from the latest estimated value of the convergence value when the difference from the previous estimated value becomes equal to or less than a preset convergence threshold.

In the hardness measurement method described above, when the most recent rate of change in the complex absorbance component due to the injection of the reagent is equal to or lower than a preset saturation threshold, the latest value of the complex absorbance component is directly converted into the hardness, A step of estimating a convergence value of the complex absorbance component may be performed when the most recent rate of change of the complex absorbance component due to the injection of the reagent exceeds the saturation threshold.

In the hardness measurement method described above, the two wavelengths may be a wavelength shorter than the isosbestic point and a wavelength longer than the isosbestic point for the reaction between the reagent and the hardness component.

A hardness measuring device according to an aspect of the present invention is a hardness measuring device that measures the hardness of sample water, and comprises a reagent injection unit that injects a predetermined amount of a reagent into a measurement cell that stores the sample water; an absorbance measuring unit that measures the absorbance at each of the wavelengths of the test water by projecting measurement light of two wavelengths to the absorbance measurement unit, and based on the absorbance at the two wavelengths, the absorbance of the chelate complex of the reagent and the hardness component. An absorbance component calculation unit that calculates a complex absorbance component, which is a component, and a hardness calculation unit that calculates the hardness based on a change in the complex absorbance component that accompanies injection of the reagent.

ADVANTAGE OF THE INVENTION According to this invention, the hardness measuring method and hardness measuring device which can measure hardness to high hardness with sufficient accuracy can be provided.

1 is a schematic diagram showing the configuration of a hardness measuring device according to an embodiment of the present invention; FIG. It is a figure which shows the relationship between the absorbance of 2 wavelengths, a complex absorbance component, and an uncomplex absorbance component. 4 is a flow chart showing the procedure of a hardness measuring method according to an embodiment of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a hardness measuring device 1 according to one embodiment of the present invention. The shape of each component of the illustrated hardness measuring apparatus 1 is simplified, and the dimensions of each component are adjusted so as to be easy to see.

The hardness measuring device 1 measures the hardness of sample water by executing the hardness measuring method according to one embodiment of the present invention. The hardness measurement device 1 includes a measurement cell 2, a reagent injection section 3, an absorbance measurement section 4, an absorbance component calculation section 5, a hardness calculation section 6, a water supply section 7, a stirring section 8, and an adjustment section 9. , provided.

The measurement cell 2 is a container that stores test water. The measuring cell 2 is formed so as to be at least partially transparent to the measuring light of the absorbance measuring section 4 . It is preferable that the capacity of the measurement cell 2 be as small as possible within a range in which accuracy can be ensured in order to suppress consumption of the reagent. A specific capacity of the measurement cell 2 can be, for example, 2 mL or more and 10 mL or less.

The reagent injection unit 3 is configured to inject a predetermined amount of reagent into the measurement cell 2 . As a specific example, the reagent injection unit 3 includes a reagent tank 31 that stores the reagent, a chemical injection pump 32 that delivers the reagent, and a chemical injection control unit 33 that controls the chemical injection pump according to commands from the adjustment unit 9. .

As the reagent injected by the reagent injection unit 3, a chelate-type reagent that develops or changes color by forming a chelate complex by forming a chelate bond with the hardness component in the test water is used. Examples of such chelate-type reagents include solutions containing calmagite, eriochrome black T, HSNN, and the like. Also, the reagent may further include, for example, a sensitizer, a desensitizer, and the like.

The absorbance measurement unit 4 projects measurement light of two wavelengths onto the measurement cell 2 to measure the absorbance of the test water at each wavelength. The absorbance measuring unit 4 includes a first light emitting element 41 that emits a first measurement light of a first wavelength, a second light emitting element 42 that emits a second measurement light of a second wavelength, and the measurement cell 2. A first light receiving element 43 for detecting the light intensity of the first measurement light, a second light receiving element 44 for detecting the light intensity of the second measuring light transmitted through the measurement cell 2, and the first light receiving element 43 and the second light receiving element 44. and an absorbance calculator 45 for calculating the absorbance at the first wavelength and the absorbance at the second wavelength of the test water in the measurement cell 2 from the measured values.

As the first wavelength and the second wavelength, it is preferable to select wavelengths that increase the difference in the rate of change in absorbance due to the reaction between the reagent and the hardness component. More preferably, the first wavelength and the second wavelength are wavelengths shorter and longer than the isosbestic point for the reaction between the reagent and the hardness component, that is, the reaction between the reagent and the hardness component progresses. A wavelength at which the absorbance decreases and a wavelength at which the absorbance increases as the reaction between the reagent and the hardness component progresses are used. By using measurement light having such a wavelength, the complex absorbance component and the uncomplexed absorbance component can be calculated more accurately by the absorbance component calculator 5, which will be described later. Specifically, when a reagent containing Calmagite is used as a coloring component (a dye component responsible for a coloring reaction), for example, red light with a wavelength of 645 nm or more and 665 nm or less is used as the first measurement light, and wavelength of 410 nm or more and 430 nm is used as the second measurement light. The following violet lights can be used.

Based on the absorbance at the two wavelengths measured by the absorbance measurement unit 4, the absorbance component calculation unit 5 calculates the complex absorbance component, which is the component of the absorbance due to the chelate complex of the reagent and the hardness component, and the reagent that is not bound to the hardness component (present The uncomplexed absorbance component, which is the component of the absorbance due to the color component), is calculated.

The values of the complex absorbance component and the uncomplexed absorbance component in the test water are proportional to the concentration of the chelate complex and the concentration of the uncomplexed, respectively, and the constant of proportionality is determined by the type of reagent. Moreover, the measured value of the absorbance measuring unit 4 can be considered as a simple sum of the complex absorbance component and the uncomplexed absorbance component.

Let Xs be the absorbance of the test water under the first measurement light, Xc be the absorbance of the chelate complex, Xb be the absorbance of the uncomplexed, Xc ₀ be the absorbance of the unit concentration of the chelate complex, Xb ₀ be the absorbance of the uncomplexed, 2 Ys is the absorbance of the test water under the measurement light, Yc is the absorbance of the chelate complex, Yb is the absorbance of the uncomplexed, Yc ₀ is the absorbance of the chelate complex at a unit concentration, Yb ₀ is the absorbance of the uncomplexed complex, and the complex absorbance Assuming that the component is C and the uncomplexed absorbance component is B, Xs=Xc+Xb=C·Xc ₀ +B·Xb ₀ and Ys=Yc+Yb=C·Yc ₀ +B·Yb ₀ . By solving these simultaneous equations, the complex absorbance component C and the uncomplexed absorbance component B can be calculated.

FIG. 2 shows the relationship between the absorbance at two wavelengths, the complex absorbance component and the uncomplex absorbance component. In the figure, the absorbance at the first wavelength (red) is shown on the horizontal axis, and the absorbance at the second wavelength (purple) is shown on the vertical axis. The figure shows the absorbance (Xs, Ys) of the test water of a certain sample, the absorbance (Xc ₀ , Yc ₀ ) when only the chelate complex is contained at a unit concentration, and the absorbance ( Xb ₀ , Yb ₀ ) and . The absorbance (Xc, Yc) due to the chelate complex and the absorbance (Xb, Yb) due to the uncomplexed sample water are the chelate of unit concentration of the vector of the measured absorbance (Xs, Ys) of the sample water in the coordinate plane shown. It can be grasped as a vector component in the direction of absorbance (Xc ₀ , Yc ₀ ) when only the complex is included and a vector component in the direction of absorbance (Xb ₀ , Yb ₀ ) when only the uncomplexed unit concentration is included.

The hardness calculator 6 calculates the hardness based on the change in the complex absorbance component that accompanies the injection of the reagent. By calculating the hardness based on the change in the absorbance component of the complex, it is possible to prevent excessive injection of the reagent and measure the hardness with high accuracy. Further, by calculating the hardness from the change in the absorbance component of the complex, the hardness can be calculated relatively accurately without reacting the entire amount of the hardness component with the reagent, so the number of injections of the reagent can be reduced. Therefore, overflow of the measurement cell 2 (outflow of the reagent and dilution of the hardness component in the test water) is unlikely to occur, so that the hardness of the test water can be measured with high accuracy up to a high hardness.

The hardness calculator 6 may determine the change in the complex absorbance component due to the injection of the reagent from the relationship between the amount of change in the uncomplexed absorbance component and the amount of change in the complex absorbance component. That is, by expressing the complex absorbance component as a function of the uncomplexed absorbance component, it is possible to predict the complex absorbance component at the chelate complex content when all the hardness components are combined with the reagent. In this way, by making a judgment based on the uncomplexed absorbance component whose rate of change increases due to the decrease in the unbonded hardness component, even when there is a large error in the injection amount of the reagent, the complexed absorbance component accompanying the injection of the reagent can accurately detect a decrease in the amount of change in Note that "judgment from the relationship between the amount of change in the uncomplexed absorbance component and the amount of change in the complexed absorbance component" does not require calculation of the amount of change in the uncomplexed absorbance component and the complexed absorbance component due to the injection of the reagent. do not have.

Specifically, the hardness calculation unit 6 calculates the convergence value for estimating the convergence value of the complex absorbance component when the number of injections of the reagent is increased from a plurality of data of the complex absorbance component based on a preset approximation formula. The configuration may include an estimating unit 61 and a hardness conversion unit 62 that converts the actually measured value (value calculated from the actually measured absorbance) of the complex absorbance component or the convergence value into hardness.

The convergence value estimating unit 61 performs fitting to specify coefficients of an approximation formula preset using a change in the complex absorbance component due to the injection of the reagent, that is, a plurality of data of the complex absorbance component, and derives from the fitted approximation formula. Calculate the hardness of the sample water from the convergence value of the complex absorbance component when the number of times of injection of the reagent used is increased, that is, the estimated value of the complex absorbance component at the content of the chelate complex when all the hardness components are combined with the reagent can be configured as In this way, by estimating the convergence value of the complex absorbance component based on a preset approximation formula, the injection amount of the reagent can be reliably suppressed, and the reaction between the hardness component and the reagent can be quantified. Even if it does not progress, hardness can be measured relatively quickly and accurately.

In addition, it is preferable to exclude data with a small number of injections of the reagent from the plurality of data of the absorbance component of the complex. Specifically, data in which the number of injections of the reagent is less than a predetermined number may be excluded, and data in which the change rate of the complex absorbance component due to the injection of the reagent exceeds a predetermined value may be excluded. If the sample water has a high hardness or a high concentration of interfering components, the chelate reaction does not proceed quantitatively and the color is not appropriately developed when the number of injections of the reagent is small, which tends to increase the error. Therefore, by excluding the data when the number of reagent injections is small and estimating the convergence value based on the data when the number of reagent injections is large, the hardness can be compared even when the concentration of hardness and interfering components is high. can be measured accurately.

Further, when the most recent change rate of the complex absorbance component due to the injection of the reagent is equal to or less than a preset saturation threshold, the hardness calculation unit 6 calculates the complex absorbance component from the absorbance actually measured by the hardness conversion unit 62. may be directly converted to the hardness, and when the most recent rate of change in the complex absorbance component due to the injection of the reagent exceeds the saturation threshold, the convergence value estimating unit 61 estimates the convergence value of the complex absorbance component, The estimated convergence value may be converted into hardness by the hardness conversion unit 62 . If the rate of change in the absorbance component of the complex due to the injection of the reagent is small and it is considered that substantially all the hardness components are already bound to the reagent, the value of the absorbance component of the complex at that time is directly converted to the hardness. By doing so, the calculation load can be reduced, and the hardness can be quickly derived without lowering the accuracy. On the other hand, if the change rate of the complex absorbance component has not sufficiently decreased and it is thought that the reagent and unbound hardness component remain in the test water, the convergence value of the complex absorbance component is estimated. Hardness can be accurately derived.

The water supply unit 7 supplies new test water and pushes out the measured test water to replace the test water in the measuring cell 2 . The water supply unit 7 may be configured to have a water supply valve 71 .

The stirring unit 8 stirs the sample water to disperse the reagent injected into the measurement cell 2 into the sample water. The stirring unit 8 may have a known structure such as a magnetic stirrer.

The adjustment unit 9 controls the reagent injection unit 3, the absorbance measurement unit 4, the absorbance component calculation unit 5, the hardness calculation unit 6, It controls the operation timing of the water supply unit 7 and the stirring unit 8 . The adjustment unit 9 can be realized by causing a computer device to execute an appropriate program, and may be integrated with the chemical injection control unit 33, the absorbance calculation unit 45, the absorbance component calculation unit 5, and the hardness calculation unit 6. .

FIG. 3 shows the procedure of the hardness measurement method executed by the adjusting section 9. As shown in FIG. This hardness measurement method includes a test water introduction step (step S01), a blank measurement step (step S02), a reagent injection step (step S03), an absorbance measurement step (step S04), an absorbance component calculation step (step S05), and a saturation confirmation step. Step (step S06), measured value hardness conversion step (step S07), data number confirmation step (step S08), convergence value estimation step (step S09), estimated value number confirmation step (step S10), convergence value confirmation step (step S11), and a convergence value hardness conversion step (step S12).

In the test water introduction process of step S01, new test water is introduced into the measurement cell 2 by the water supply unit 7. As shown in FIG.

In the blank measurement process of step S02, the absorbance measurement unit 4 measures the transmitted light intensity at two wavelengths of the measurement cell 2 before the reagent is injected into the test water. Specifically, detection of the light amount of the first measurement light received by the first light receiving element 43 when the first light emitting element 41 emits light, and second measurement light received by the second light receiving element 44 when the second light emitting element 42 emits light. Light quantity detection is performed in order. Thereby, the transmitted light intensity automatically adjusted according to the contamination of the measuring cell 2, turbidity in the test water, etc. is confirmed.

In the reagent injection step of step S<b>03 , the reagent injection unit 3 injects a predetermined amount of reagent into the measurement cell 2 .

In the absorbance measurement step of step S04, the absorbance measurement unit 4 measures the transmitted light intensity at two wavelengths of the test water after the reagent is injected, and calculates the absorbance. Specifically, detection of the light amount of the first measurement light received by the first light receiving element 43 when the first light emitting element 41 emits light, and second measurement light received by the second light receiving element 44 when the second light emitting element 42 emits light. The light quantity of light is detected in order, and the absorbance calculation unit 45 detects the transmitted light intensity at each wavelength based on the ratio of the transmitted light intensity automatically adjusted according to the dirt of the measurement cell 2 measured in the blank measurement process and the turbidity in the test water. Calculate the absorbance of

In the absorbance component calculation step of step S05, the absorbance component calculator 5 calculates the complex absorbance component C and the hardness component, which are components of the absorbance due to the chelate complex in which the reagent and the hardness component are combined, based on the absorbance of the measurement light of two wavelengths. An uncomplexed absorbance component B, which is a component of absorbance due to a reagent (coloring component) that is not bound to , is calculated.

In the saturation confirmation step of step S06, based on the most recent change rate of the complex absorbance component accompanying the injection of the reagent, whether or not the chelate reaction between the hardness component and the reagent in the test water is saturated, that is, substantially all Check if the hardness component is bound to the reagent. When it is determined that the chelate reaction is saturated, the process proceeds to step S07, and when it is determined that the chelate reaction is not saturated, the process proceeds to step S08.

Specifically, in the saturation confirmation step, the rate of change between the complex absorbance component in the latest absorbance measured after the most recent reagent injection and the complex absorbance component in the absorbance measured after the previous reagent injection is set in advance as a saturation threshold value. When the following states continue for a predetermined number of times or more, it can be determined that the chelate reaction is saturated. Therefore, the reagent injection step, the absorbance measurement step, and the absorbance component calculation step are repeated at least multiple times. Note that the number of confirmations may be one.

In the measured value hardness conversion step of step S07, the hardness conversion unit 62 directly converts the latest value of the complex absorbance component calculated from the measured absorbance into hardness.

In the data number confirmation step of step S08, it is confirmed whether or not the number of data of the complex absorbance component calculated from the actually measured absorbance satisfies the number necessary for estimating the convergence value in the next convergence value estimation step. . That is, in the data number confirmation step, it is confirmed whether or not the number of execution times of the reagent injection step and the absorbance measurement step is equal to or greater than the preset convergence calculation possible number. If the number of data on the complex absorbance component is greater than or equal to the required number, the process proceeds to step S09, and if the number of data on the complex absorbance component is less than the required number, the process returns to step S03.

In the convergence value estimating step of step S09, the convergence value estimating unit 61 calculates the convergence value of the complex absorbance component when the number of injections of the reagent is increased from a plurality of data of the complex absorbance component based on a preset approximation formula. to estimate

In the step of confirming the number of estimated values in step S10, it is confirmed whether or not there are a plurality of estimated values of the convergence values of the complex absorbance components calculated in the convergence value estimation step, and the number of executions of the convergence value estimation step. Therefore, in the present embodiment, estimation of the convergence value of the complex absorbance component is performed at least twice.

In the convergence value confirmation step of step S11, it is determined whether or not the estimated value of the convergence value is a probable value. As a specific example, in the convergence value confirmation step, if the difference between the latest estimated value of the convergence value and the previous estimated value is equal to or less than a preset convergence threshold, the difference between the two is sufficiently small and the estimated value is confirmed. judge it to be true. If the difference between the latest estimated value and the previous estimated value is sufficiently small and the estimated value is considered probable, proceed to step S12, and if the difference between the latest estimated value and the previous estimated value is large , the process returns to step S03 in order to repeat the reagent injection step, absorbance measurement step, absorbance component calculation step, and convergence value estimation step.

In the convergence value hardness conversion step of step S12, the hardness conversion unit 62 converts the latest estimated value of the convergence value of the complex absorbance component into hardness.

Thus, in the hardness measuring device 1, the hardness is calculated in the measured value hardness conversion step from the complex absorbance component calculated from the actually measured absorbance, or the convergence value calculated in the converged value hardness conversion step from the estimated value of the convergence value of the complex absorbance component. The hardness of the test water shall be the hardness of the test water.

As is clear from the above description, the method for measuring hardness according to the present invention includes the steps of repeatedly injecting a predetermined amount of a chelate-type reagent into sample water and measuring the absorbance of the sample water with two wavelengths of measurement light. , calculating the complex absorbance component, which is the absorbance component of the chelate complex in which the reagent and the hardness component are combined, based on the absorbance of the measurement light of the two wavelengths; and calculating the hardness of the test water. By calculating the hardness based on the change in the absorbance component of the complex in this way, even if the hardness of the test water is high, the overflow of the measurement cell 2 can be suppressed and the hardness can be measured relatively accurately.

Although preferred embodiments of the hardness measuring method and hardness measuring apparatus of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be modified as appropriate.

For example, in the hardness measuring method and hardness measuring device according to the present invention, the specific procedure for calculating the hardness based on the change in the absorbance component of the complex is not limited to the above-described embodiment, and arbitrary modifications are possible. As an example, estimation of the convergence value of the complex absorbance component in the hardness measurement method and the hardness measurement device according to the present invention may be performed by expressing the complex absorbance component as a function of the number of injections (injection amount) of the reagent.

Further, in the above-described embodiment, the convergence value of the complex absorbance component is estimated multiple times to determine whether or not the estimated convergence value is probable. In the apparatus, the propriety of the estimated convergence value may be determined by the correlation coefficient between the approximate expression and the data of the absorbance component of the complex, and the step of judging the propriety of the estimated convergence value may be omitted. The hardness may be calculated by estimating the convergence value.

In the above-described embodiments, the complex absorbance component and the uncomplexed absorbance component were described as dimensionless numbers normalized by the absorbance of the chelate complex at a unit concentration and the absorbance of the uncomplexed unit at a unit concentration, respectively. The absorbance component has the dimension of absorbance, and may be a value that is normalized in the step of converting to hardness, such as a combination of absorbance at a first wavelength and absorbance at a second wavelength.

The hardness measuring device according to the present invention may have, for example, a third wavelength light-emitting element and a light-receiving element, etc., in order to realize other measuring functions. Further, the hardness measuring device may use a disposable cell filled with test water in advance without a water supply unit.

1 Hardness Measuring Device 2 Measuring Cell 3 Reagent Injecting Part 4 Absorbance Measuring Part 41 First Light Emitting Element 42 Second Light Emitting Element 43 First Light Receiving Element 44 Second Light Receiving Element 45 Absorbance Calculator 5 Absorbance Component Calculator 6 Hardness Calculator 61 Convergence Value estimation unit 62 Hardness conversion unit 7 Water supply unit 8 Stirring unit 9 Adjustment unit

Claims (8)

A hardness measurement method for measuring the hardness of sample water,
a step of repeatedly injecting a predetermined amount of a chelate-type reagent into the test water and measuring the absorbance of the test water with two wavelengths of measurement light;
a step of calculating a complex absorbance component, which is an absorbance component of a chelate complex in which the reagent and the hardness component are combined, based on the absorbance of the measurement light of the two wavelengths;
calculating the hardness of the sample water based on the change in the complex absorbance component accompanying the injection of the reagent;
A hardness measurement method comprising: The change in the complex absorbance component due to the injection of the reagent is determined from the relationship between the amount of change in the complex absorbance component and the amount of change in the uncomplexed absorbance component, which is the absorbance component due to the reagent not bound to the hardness component. The hardness measuring method according to claim 1, wherein The step of calculating the hardness includes a step of estimating a convergence value of the complex absorbance component when the number of injections of the reagent is increased from a plurality of data of the complex absorbance component based on a preset approximation formula. 3. The method of measuring hardness according to claim 1 or 2, comprising: 4. The hardness measuring method according to claim 3, wherein, as said plurality of data, data in which the number of injections of said reagent is small is excluded. The step of injecting the reagent and measuring the absorbance, the step of calculating the complex absorbance component, and the step of estimating the convergence value are repeated, and the difference between the latest estimated value of the convergence value and the previous estimated value 5. The method of measuring hardness according to claim 3, wherein the hardness is calculated from the latest estimated value of the convergence value when is equal to or less than a preset convergence threshold. when the most recent rate of change of the complex absorbance component accompanying the injection of the reagent is equal to or lower than a preset saturation threshold, directly converting the latest value of the complex absorbance component into the hardness,
6. The hardness according to any one of claims 3 to 5, wherein the step of estimating a convergence value of the complex absorbance component is performed when the most recent change rate of the complex absorbance component due to the injection of the reagent exceeds the saturation threshold. Measuring method. 7. The hardness measuring method according to claim 1, wherein a wavelength shorter than an isosbestic point and a wavelength longer than the isosbestic point for the reaction between said reagent and said hardness component are used as said two wavelengths. A hardness measuring device for measuring the hardness of sample water,
a reagent injection unit for injecting a predetermined amount of reagent into the measurement cell storing the test water;
an absorbance measuring unit that projects measurement light of two wavelengths onto the measurement cell and measures the absorbance at each of the wavelengths of the test water;
an absorbance component calculation unit that calculates a complex absorbance component, which is a component of absorbance due to a chelate complex of the reagent and the hardness component, based on the absorbance at the two wavelengths;
a hardness calculation unit that calculates the hardness based on a change in the absorbance component of the complex due to the injection of the reagent;
A hardness measuring device.

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