JP2596034Y2 - Residual chlorine meter - Google Patents

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 provided with a circuit for detecting a liquid shortage.

[0002]

2. Description of the Related Art As a conventional technique of this kind, there is known a residual chlorine meter as shown in the block diagram of a conventional residual chlorine meter shown in FIG. 2-98661 and JP-A-2-154142.
Reference).

In this type of residual chlorine meter, an indicator electrode (rotation indicator electrode) 1 and a reference electrode (counter electrode) 2 are immersed in a liquid S to be measured introduced into a liquid tank 4, and a measuring circuit is provided between these electrodes. An applied voltage is applied from 3 and the concentration of free available chlorine in the liquid S to be measured is measured based on the current flowing between the electrodes at this time.

Although the circuit means 3 is shown in FIG. 4 as being constituted by an analog circuit, there is a case where the circuit means 3 is constituted by a CPU. D indicates a drain.

[0005]

However, such a conventional technique has the following problems.

(A) In the case of the configuration shown in FIG. 4, the liquid S to be measured is measured without interruption by using the detector of the residual chlorine meter.
Cannot be identified.

(B) When a CPU (not shown) is used in the measuring circuit portion, it is theoretically possible to detect a change in the measured current by changing the applied voltage, and to determine that the liquid has run out when there is no current change. It is possible. However, it is not yet a concretely established technique to adopt a configuration of a technical content that allows continuous water cut detection.

The present invention has been made in view of the above-mentioned problems in the prior art.

It is an object of the present invention to provide a residual chlorine meter which can detect that the liquid to be measured does not come to the liquid tank without interrupting the measurement with a simple circuit configuration.

Another object of the present invention is to add a simple circuit, measure the conductivity at the same time, find out an appropriate applied voltage, and measure or display the residual chlorine stably. It provides a chlorine meter.

[0011]

In order to achieve the above object, the present invention immerses the indicator electrode and the reference electrode in the liquid to be measured introduced into the liquid tank, and applies a voltage between these electrodes. (A ) applying a DC voltage and a square wave AC voltage (V _K ) to the comparison electrode (2) in a residual chlorine meter for measuring the free available chlorine concentration in the liquid to be measured based on the current flowing between the electrodes. A voltage application means (5), a current-voltage conversion circuit (6) connected to the indicator electrode (1) for converting a measured value of the indicator electrode into a voltage, and an AC component from a voltage output of the current-voltage converter circuit. It detects the V _H calculating the conductivity from the ratio of the V _H and V _K
An identification circuit for identifying the presence or absence of the liquid to be measured and a residual chlorine detection circuit for detecting a DC component from the voltage output of the current-voltage conversion circuit (6) to detect free available chlorine in the liquid to be measured, The output of the residual chlorine detection circuit is corrected based on the conductivity from the identification circuit, and the presence / absence of the liquid to be measured is identified while performing continuous measurement of the constant liquid to be measured (claim 1). (b) display means (14) for displaying a signal proportional to the conductivity after filtering and rectifying the output from the current-to-voltage conversion circuit, and displaying the signal after filtering the output from the current-to-voltage conversion circuit. A resistance value switching means (SS1) configured to switch and select a plurality of resistance values which are guided and output to the voltage application means 5 as a feedback compensation value, based on a display of the display means. A serial that the feedback compensation value of the resistance value switching means is a selectable (claim 2).

[0012]

[Action] In a residual chlorine meter using a rotating platinum electrode,
By applying a slight AC voltage to the applied voltage (DC), the conductivity between the indicator electrode and the comparison electrode can be measured to detect the presence or absence of the liquid to be measured.

According to the present invention, the presence or absence of the liquid to be measured can be identified while the measurement of residual chlorine is continued.

That is, on the comparison electrode side, a circuit for applying a polarographic DC voltage and a rectangular wave AC voltage to the comparison electrode is provided. On the indicator electrode side, a current-voltage converter for converting a measured value (current) from the indicator electrode into a voltage is provided, and the output of the current-voltage converter is separated into a DC component and an AC component for processing. Circuit is further provided, and in this circuit,
It is possible to identify the presence or absence of a liquid to be measured while performing continuous measurement on the liquid to be measured.

By the way, the AC component passes through a filter circuit and a rectifier circuit to identify the presence or absence of the liquid to be measured from the rectified voltage. For example, a comparator or a function corresponding to this comparator (software processing by a microprocessor [μP]). And performs predetermined processing to identify the presence or absence of the liquid to be measured.

On the other hand, the direct current component is led to a residual salt signal separation circuit to obtain a residual salt signal by a predetermined process.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings showing specific embodiments. In the following drawings, the same parts as those in FIG.

FIG. 1 is a diagram showing an outline of the residual chlorine meter of the present invention. FIG. 2 is a diagram showing a specific embodiment of the residual chlorine meter of the present invention (a circuit diagram as an example in which the configuration of FIG. 1 is more specifically developed). FIG. 3 is a diagram for explaining another embodiment of the present invention. FIG. 4 is a configuration diagram of a conventional residual chlorine meter. FIG. 5 is a diagram for explaining FIG. 3 with reference to FIG.

In FIG. 1 and FIG. 2, the residual chlorine meter has a circuit means 5 for applying a DC voltage and a square wave AC voltage to the indicator electrode (rotating electrode) 1, the comparison electrode (counter electrode) 2, and the comparison electrode (2). 2, it is represented by 5 _{A. The same} applies to the following description), a current-voltage conversion circuit 6, a rectifier circuit 7, an identification circuit 8, a residual salt signal separation circuit (low-pass filter) 9, a filter F (see FIG. Represents a configuration in which a temperature compensation circuit 10, an A / D “analog / digital conversion circuit” 11, a display unit 12, and a current output circuit 13 are added).

Such a residual chlorine meter measures the conductivity between the indicator electrode 1 and the reference electrode (counter electrode) 2 by applying a slight AC voltage to the applied voltage (DC), and The presence or absence of the liquid S can be detected.

R _c represents the interelectrode resistance generated between the indicator electrode and the comparison electrode.

The circuit means 5 (5 _A), a connection terminal R to the comparison electrode 2, via a resistor R ₁ port - applying a DC voltage and an AC voltage of a small square wave for Rarogurafu the (rectangular wave portion applied voltage And a DC voltage circuit 52, for example.

The rectangular wave AC signal generating circuit 51
It may be configured to generate a rectangular wave AC voltage Vs made of a peak value V _k.

The DC voltage circuit 52 can be configured to output a polarographic DC voltage from the rectangular wave AC voltage from the rectangular wave AC signal generating circuit 51 (see the output waveform in FIG. 2).

[0025] In FIG. 2, for adding and outputting the rectangular wave signal input and the applied voltage for residual chlorine concentration measurement, as a feedback voltage applied output amplifier 52U _1, instead of the feedback resistor of FIG. 1 shows the case where the buffer amplifier 52 _a is incorporated.

From the above results, the indicator electrode 1 and the comparison electrode (counter electrode)
2, a diffusion current I proportional to the residual chlorine concentration and a current i proportional to the conductivity of the measurement liquid flow.

The current-voltage conversion circuit 6 includes a gain resistor R _f
And an inverting terminal of the input amplifier is connected to a connection terminal P to which the indicator electrode 1 is connected, and a measured value (I + i) is derived.

The current-voltage conversion circuit 6 converts the DC component and the AC component of the conductivity, that is, the voltage V _I (DC signal) obtained by converting the diffusion current I and the voltage V _i (applied rectangle) proportional to the conductivity. (AC signal with the same frequency as the wave).

After the current-voltage conversion circuit 6, there are provided, via a filter F, circuits for respectively processing the DC component and the AC component which are circuit outputs. FIG. 2 shows a case in which a high-pass filter is provided for separating the water cutoff detection signal from the input signal, or a low-pass filter is provided for separating the residual chlorine concentration signal.

The AC component is guided to the rectifier circuit 7 / identification circuit 8.

The rectifier circuit 7 has a half-wave rectifier circuit configuration as shown in FIG. 2, and rectifies the AC component V _i , that is, a rectangular wave signal proportional to the electrical conductivity, to obtain a rectified voltage (a water cutoff detection signal). and it outputs the V _2.

The discriminating circuit 8 comprises, for example, a comparator for identifying when there is a water cutoff detection signal in FIG. 2 by comparing the signal with a reference value D which is a comparison voltage for water cutoff detection (or a comparator for this). A necessary identification process for identifying the presence or absence of the liquid S to be measured is performed.

This identification circuit 8 outputs a signal K when there is the above-mentioned outage detection signal. And this signal K is
It can be used for relay signals or voltage signals for contact output.

The rectified voltage V ₂ to be input to the identification circuit 8 in this case, the protection resistor _{R 1, R 2 R 1 <<} R C, R 2 <
<R _C , V ₂ = V _k · {R _f / (R ₁ + R _c + R ₂ )} (1) (this is approximately V _k · (R _f / R _c )) . When the liquid S to be measured is lost in the measuring tank, the rectified voltage V
_{Since 2} is substantially "0", the identification circuit 8 can easily detect the presence or absence of the liquid to be measured.

However, since the inter-electrode resistance R _c has a capacity (for example, C ₁ ) when the electrode comes into contact with the liquid to be measured,
Equivalent circuit at that time, the capacity of C in series with the resistor R _c
1 is connected in series. Therefore, the frequency of the rectangular wave AC signal Vs at this time, the interelectrode resistance (liquid resistance) of capacity of C ₁ with respect to R _c Inpi - it is necessary to set the dance becomes sufficiently small.

On the other hand, the DC component is a signal obtained by converting the diffusion current I proportional to the residual chlorine into a current-voltage signal. In order to obtain the residual salt concentration signal V ₁ , a residual salt signal separating circuit (low-pass) Filter) 9.

The residual salt concentration signal V ₁ is output to the DC voltage circuit 52 or processed as it is by the output circuit means, that is, for example, via the A / D (analog / digital conversion circuit) 11 to the display unit 12. Or display the current output circuit 1
Current output I _out of 4 to 20 mA through circuit means such as 3
Or the display / output processing may be performed by arranging both circuits in parallel.

Although not necessarily required, in FIG. 2, a platinum resistance element or a temperature measuring element having good positive characteristics / linearity (shown as a platinum resistance temperature measuring element in the figure) is provided before the output circuit means. 3) shows a case where a temperature compensation circuit 10 using Pt is provided. The temperature compensation referred to here is a reference temperature ( _tr ).
Is compensated using the measured temperature t and the temperature coefficient α [% / ° C.].

The feature of the temperature compensating circuit 10 shown here is that it is composed of one amplifier, whereby the variable input value can always be temperature compensated.

[0040] As a structure, the inverting terminal of the amplifier U, fixed resistors R _E which Yutakatai Pt and the other measuring platinum resistor is connected to the output terminal is connected to the non-inverting terminal, is disposed between the output terminal and the ground The divided voltage obtained from the connection between the resistors R _L and R _R is fed back.

Here, for example, when Pt1000 is used, R _E = 300Ω ± 1%, R _L = 1KΩ ± 1%, and R
And _R = the variable resistor (20 ° C), V _F feedback voltage, type V _1, in the case where the output V _10, can be adjusted so as to satisfy the following equation.

{(V ₁₀ −V _F ) / _RE } + {(V ₁ −V _F ) / Pt} = 0 (2) and V ₁₀ {R _R / (R _R + R _L )} = V _F ... from _{(3), V 10 = {} (- (R L + R R) · R E / (R L · Pt-R R · R E)} to obtain a · V ₁ ... (4).

The temperature condition is 0 ° C. (the temperature compensation rate is 0.50
4 "The temperature compensation rate is [1- {2.48 / 100 (t ₀ -t ₂₀ )}}, but 2.
48 is a temperature coefficient% / ° C], Pt = 1000Ω), 20
° C (temperature compensation rate is 1, Pt = 1077.9Ω), 40 ° C
(Temperature compensation rate is 1.496, Pt = 1155.4Ω), the resistance value between 0 ° C / 20 ° C is _RR・ R _E = 920.8435 ・_RL The resistance value between 20 ° C / 40 ° C is , R _R · R _E = 921.65 · R _L , and taking this average value, the resistance values (921.
247Ω).

Next, a case where the offset is considered will be described. The voltage at the non-inverting input terminal at this time and V _F + V _off (offset voltage).

[0045] [{V ₁₀ over _{(V F + V off)}} / R E] + [{V 1 over _{(V F + V off)}} / Pt] = 0 ... from _{(5), V 10 · Pt} = -V ₁ · R _E + (Pt + R _E ) V _off + V ₁₀ (Pt + R _E ) (6)

[0046] From equation (3) and _{(6), V 10 = {(R L} + R R) / (R L · Pt-R R · R E)} · (-V 1 · R E) + obtain _{{(R L + R R)} / (R L · Pt-R R · R E)} · {(Pt + R E) V off} ... (7).

[0047] As a result, the gain of the circuit _{is, {- (R L + R} R) · R E)} / (R L · Pt-R R · R E)} ... (8) , and the positive feedback (denominator Is subtracted), it is possible to have a coefficient larger than the temperature coefficient of the temperature measuring element Pt.

The gain for the offset is larger than the gain of the input signal and is {(Pt + R _E ) / R _E } times. However, by using an amplifier having a small offset voltage V _off or adjusting the offset,
This effect can be reduced.

By the way, in the above apparatus, usually,
There is no particular concept of measuring conductivity.

However, in a reagent-free residual chlorine meter, as will be described in detail below, the plateau characteristic in the residual chlorine characteristic changes depending on the conductivity of the measurement liquid. Therefore, when the conductivity of the measurement liquid changes, it is necessary to correct (change) the applied voltage according to the change in the plateau characteristic.

However, since the electrical conductivity of _ cannot be measured with the configuration of the apparatus described above, the correction is performed by using _ experience up to that time, using past data, or measuring After the liquid is brought back, it is necessary to use the measured value of the conductivity of the measurement liquid.

Here, a technique related to the conductivity and the plateau characteristic, which is a premise of the description of FIG. 3, which will be described later, will be described with reference to FIG.

When a voltage is applied between the indicator electrode 1 and the counter electrode 2, residual chlorine concentration characteristics A, B, and C as shown in FIG. 5 are obtained. At this time, the polarogram of the signal current with respect to the applied voltage changes under the influence of the conductivity K [S / cm] of the measurement liquid (Va in FIG. 5 represents the start voltage of the applied voltage).

[0054] This is because there is the influence of the voltage drop due to the resistance component R _c of the liquid. In order to correct the influence of the voltage drop of a signal current due to the resistance component R _c are relative to applied voltage Va when the signal current is zero, will apply to apply a voltage signal current proportional to the increase in There is a need. Thus, an appropriate applied voltage can be applied even if the conductivity of the measurement liquid changes.

As described above, if the conductivity can be measured at the same time, an appropriate applied voltage can be known, and the residual chlorine can be measured more stably and reliably.

Therefore, specifically, as shown below, the conductivity of the liquid to be measured is measured at the same time so that the optimum applied voltage can be selected at the site, or the optimum applied voltage can be automatically selected more than that. It is also possible to do so. This achieves a configuration that enables highly reliable measurement of residual chlorine. A specific example is shown in FIG.
And will be described.

[0057] In FIG. 3, portions different from the Figure 2, the first, was placed a means SS ₁ switching resistance of the resistance value can be switched respectively selected between the low pass filter 9 and the buffer amplifier 52 _A That is.

Second, the display unit 14 is provided, and the rectifier circuit 7 is provided.
Is to display the rectified voltage value of the rectangular wave signal proportional to the conductivity of the signal. Also, this voltage can be adjusted and displayed as conductivity.

[0059] Then, in this case, by determining the display of the display unit 14, also as it is possible to select the feedback compensation value to the buffer amplifier 52 _A by switching means SS ₁ switching the resistance value it can.

It goes without saying that the above contents can be simultaneously processed as a series of operations by using a CPU.

In FIG. 3, a portion corresponding to the above-described conductivity meter is seen.

[0062] (voltage for measuring residual chlorine) buffer amplifier 52 is the output pressure voltage of _A, i.e., rectangular, which is the output of the current over-voltage conversion circuit 6 for the voltage values V _k of the square wave component for conductivity measurements The relationship between the wave component and the voltage value V _H is as follows: V _H / V _k = R _f / (R ₁ + R _c + R ₂ ) (9) (This is approximately R _f / R _c , where R ₁ << R _C , R ₂ <
<R _C ).

Assuming that the cell constant is S _k [cm ^-1 ], the conductivity K [S / cm] is as follows: K = S _k (1 / R _f ) · (V _H / V _k ) (10) Can be represented. From this, the conductivity K can be obtained by measuring the voltage value V _H.

Therefore, as described above, since the applied voltage compensation rate must be changed depending on the conductivity, if the compensation rate is selectively switched based on the conductivity obtained by the equation (10), more stable measurement of residual chlorine can be achieved. You can do it.

According to the above description, it is possible to determine the presence or absence of the liquid to be measured while continuing to measure the residual chlorine, and also to measure the conductivity, so that accuracy and reliability can be improved. In addition, it is possible to perform more excellent measurement in terms of properties.

[0066]

The present invention is configured as described above, and has the following effects.

(A) A circuit capable of discriminating the presence or absence of the liquid to be measured while performing continuous measurement can be simply configured and added.

(B) Thus, when the indication of the residual chlorine meter is zero, it is possible to determine whether the measured value of the liquid to be measured is truly zero or the liquid to be measured does not flow. Becomes

(C) As a result, the reliability of the measured values of the apparatus can be remarkably improved.

(D) If the conductivity can be measured at the same time, an appropriate applied voltage can be known, so that the residual chlorine can be more stably and reliably measured.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a residual chlorine meter of the present invention.

FIG. 2 is a diagram showing a specific embodiment of the residual chlorine meter of the present invention.

FIG. 3 is a diagram for explaining another embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional residual chlorine meter.

FIG. 5 is a diagram for explaining FIG. 3 using FIG. 4;

[Explanation of symbols]

 1 Indicator electrode (rotation indicator electrode) 2 Reference electrode 3 Measurement circuit 4 Liquid tank 6 Current-voltage conversion circuit 9 Residual salt signal separation circuit 10 Temperature compensation circuit

Claims (2)

(57) [Scope of request for utility model registration] 1. An indicator electrode and a reference electrode are immersed in a liquid to be measured introduced into a liquid tank, and a voltage is applied between the electrodes to release the electrode in the liquid to be measured based on a current flowing between the electrodes. In the residual chlorine meter for measuring chlorine concentration, the reference electrode (2)
A voltage application means (5 ) for applying a DC voltage and a rectangular wave AC voltage (V _K ) to a current-voltage conversion circuit (6) connected to the indicator electrode (1) and converting a measured value of the indicator electrode into a voltage. )
And the AC component V _H from the voltage output of the current-voltage conversion circuit.
The When detected and for calculating a conductivity from the ratio of the V _H and V _K DOO
An identification circuit for identifying the presence or absence of the liquid to be measured;
A residual chlorine detection circuit that detects a direct current component from the voltage output of the voltage conversion circuit (6) to detect free available chlorine in the liquid to be measured, and an output of the residual chlorine detection circuit based on the conductivity from the identification circuit. A residual chlorine meter for performing correction and identifying the presence or absence of the liquid to be measured while continuously measuring the constant liquid to be measured. 2. A display means for displaying a signal proportional to the conductivity after filtering the output from the current - voltage converter circuit rectifier (14), from the current first voltage converter
A resistance switching means (SS1) configured to switch and select a plurality of resistance values to be output to the voltage application means 5 as a feedback compensation value by guiding a filtered signal of the output of the display section. 2. A residual chlorine meter according to claim 1, wherein a feedback compensation value of said resistance value switching means can be selected based on the display.