JP2684769B2 - pH converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a pH converter for measuring the pH value of the measurement liquid from a DC electromotive force generated between a glass electrode and a reference electrode, and more particularly to this The present invention relates to a pH converter capable of detecting abnormality such as breakage of a glass electrode such as a reference electrode and a reference electrode.

<Prior Art> FIG. 3 is a block diagram showing the outline of the configuration of a conventional pH converter of this type, and FIG. 4 is a schematic diagram showing the specific configuration of the glass electrode and the reference electrode shown in FIG. It is a figure. The outline of the conventional pH converter will be described below with reference to FIGS. 4 and 3.

The container 10 is, for example, grounded E, in which the measurement liquid LQ
Is satisfied.

Reference numeral 11 denotes a glass electrode, the periphery of which is surrounded by a potassium chloride solution KCL (7) having a pH of 7, in which silver chloride AgCl and silver Ag are arranged, through which a lead wire lw ₁ changes its potential. Terminal G
A thin glass film GS is placed between the potassium chloride solution KCL (7) and the measurement liquid LQ, which is pulled out to T.

Reference numeral 12 is a reference electrode, which is surrounded by a saturated potassium chloride solution KCL (S), in which silver chloride AgCl and silver Ag are arranged, and the potential thereof is connected to the lead wire lw ₂ to make a terminal. Potassium chloride solution KCL at the bottom and pulled down to RT
For example, porous ceramics is disposed as the liquid passage portion LS between (S) and the measurement liquid LQ.

Furthermore, a liquid electrode 13 for applying a voltage to this measurement liquid LQ is inserted in the measurement liquid LQ, and this is connected to the terminal LT.

By the way, the glass electrode 11 is a series circuit of the unipolar potential Vg of the glass electrode and its impedance Rg, similarly, the comparison electrode 12 is a series circuit of the unipolar potential Vr of the comparison electrode and its impedance Rr, and the liquid electrode 13 is the liquid potential Vs. As a series circuit with the impedance Rs, it can be simply expressed equivalently as shown in FIG.

Terminal GT and GT ^-, LT and LT ^- are connected by respectively between the cable _{l 1, l 2, l 3} -, RT and RT.

The terminal GT ^- is connected to the non-inverting input terminal (+) of the operational amplifier Q ₁ functioning as a voltage follower, and its output terminal is connected to one end of the input of the subtractor 14 having a smoothing function for smoothing an AC component. There is. Also, terminal GT ^- and common potential point COM
A series circuit of a contact S ₁ of a relay RL ₁ and a resistor R ₁ is connected between the and. Further, the voltage across the resistor R ₁ is output to the rectifying / smoothing circuit 15 via the capacitor C ₁ , and the output thereof outputs the abnormal signal V _A1 to the output end T ₂ .

The terminal RT ⁻ is connected to the non-inverting input terminal (+) of the operational amplifier Q ₂ functioning as a voltage follower, and the output terminal thereof is connected to the other end of the input of the subtractor 14. The terminal RT ^- the series circuit of the contacts S ₂ of the relay RL ₂ and the resistor R ₁ is connected between the common potential point COM. In addition, the resistance R ₂
The voltage across both ends of is output to the rectifying / smoothing circuit 16 via the capacitor C ₂ , and the output outputs the abnormal signal V _A2 to the output end T ₃ .

The subtractor 14 subtracts the outputs of these operational amplifiers Q ₁ and Q ₂ and outputs the pH signal V _pH to the output terminal T ₁ .

The contacts S ₁ and S ₂ of the relays RL ₁ and RL ₂ are opened / closed by a control signal from the relay drive circuit 17 to which the operation signal S _A is manually or automatically given.

In addition, the rectangular wave voltage from the rectangular wave generation circuit 18 is applied to the liquid electrode 13.
V _K is being applied.

Next, the operation of the pH converter configured as above will be described.

Under normal pH measurement conditions, relays RL ₁ and RL ₂ contacts S ₁ and S ₂
Is open and therefore the terminal T ₁ has a glass electrode.
Voltage corresponding to the difference between the electromotive force generated in 11 and the reference electrode 12,
That is, the VpH signal _pH corresponding to the pH value of the measurement liquid LQ is obtained.

Next, in order to detect the presence / absence of an abnormality in the glass electrode 11, the abnormality detection signal S _A is applied, a current is passed through the relay RL ₁ , and the contact S ₁ is closed. In this state, the abnormal signal V _A1 generated at both ends of the resistor R ₁ becomes V _A1 = R _K V _K / (Rg + Rs + R ₁ ) (1). However, since Rs << Rg is generally satisfied, V _A1 ≈R _K V _K / (Rg + R ₁ ) ... (2)

Further, in order to detect the presence / absence of abnormality of the reference electrode 12, the abnormality detection signal S _A is applied and a current is applied to the relay RL ₂ to make contact S.
Close ₂ In this state, the abnormal signal V _A2 generated across the resistor R ₂ becomes V _A2 = R _K V _K / (Rr + Rs + R ₁ ) ... (3). However, since Rs << Rr is generally satisfied, V _A1 ≈R _K V _K / (Rr + R ₁ ) ... (4)

Therefore, if there is an abnormality such as damage to the glass film GS of the glass electrode 11 or the liquid junction LS of the reference electrode 12, the resistance R
Since g and Rr are significantly different from the normal case (2),
As can be seen from the relationship of the equation (4), by measuring the abnormal signals V _A1 and V _A2 , it is possible to easily know the damage from their magnitudes.

<Problems to be Solved by the Invention> However, in the conventional pH converter as described above, firstly, in order to know an abnormality such as breakage of the glass electrode 11 or the reference electrode 12, first, abnormality detection is performed. The pH value cannot be known during the operation, and secondly, the voltage is detected by the resistors R ₁ and R ₂ via a high impedance such as a glass electrode or a reference electrode, so that the relays RL ₁ and RL _{2 have} high values. There are drawbacks such as the inconvenience of using an insulated relay.

<Means for Solving the Problem> In order to solve the above problems, the present invention determines the pH value of the measurement liquid from the DC electromotive force generated between the glass electrode immersed in the measurement liquid and the reference electrode. In a pH converter for measurement, a voltage generating means for applying an alternating voltage to a measurement liquid via a liquid electrode, and a first signal detecting means for detecting a first alternating voltage component generated between a glass electrode and the liquid electrode. And a second AC voltage component for detecting a second AC voltage component generated between the reference electrode and the liquid electrode.
And a signal detecting means for detecting abnormality of the glass electrode from the first AC voltage component and abnormality of the reference electrode from the second AC voltage component.

<Operation> The AC voltage is constantly applied to the measurement liquid from the voltage generating means via the liquid electrode, and the magnitude of this AC voltage is detected from the glass electrode by detecting the first AC voltage component related to this AC voltage. The abnormality of the comparison electrode is detected from the degree of the AC voltage by detecting the abnormality of the glass electrode from the degree of the AC voltage and the second AC voltage component related to the AC voltage of the voltage generating means from the comparison electrode. At the same time as detecting, the pH signal is always obtained from the difference in DC electromotive force between the glass electrode and the reference electrode, that is, from the pH value.

<Example> Next, the Example of this invention is described using figures.
FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. The parts having the same functions as those of the embodiment shown in FIGS. 3 and 4 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

In order to express the glass electrode 11 more accurately, the equivalent capacitance Cg of the glass film GS is connected in parallel to the impedance Rg of the glass electrode 11, and the liquid resistance R _l1 between the liquid electrode 13 and the reference electrode 12 is A liquid resistance R ₁₁ between the electrode 13 and the glass electrode 11 is added.

The terminal GT ⁻ is connected to the common potential point COM via the capacitor C ₃ and the output terminal is connected to the inverting input terminal (−) and the non-inverting input terminal (+) of the operational amplifier Q ₃ is connected to the resistor R. Connected through ₃ . Further, its inverting input terminal (-) is connected to the shield of the cable l ₁ via the terminal GTS via the resistor R ₄ .

The output terminal of the operational amplifier Q ₃ is connected to the non-inverting input terminal (+) of the buffer amplifier Q ₄ via the low-pass filter LPF ₁ ,
This output is connected to the output terminal T ₁ where the pH signal V _pH
Is output.

Also, the output terminal of the operational amplifier Q ₃ is a high-pass filter HPF ₁
Is connected to one switching end of the switch SW ₁ via. The other switching end is connected to the common potential point COM via a series circuit of a resistor R ₅ and a capacitor C ₄ . The common end is connected to the output end T ₂ via the low-pass filter LPF ₂ and outputs an abnormality signal V _A3 for detecting an abnormality in the glass electrode 11.

The terminal RT ⁻ has a non-inverting input terminal (+) with a resistance R via a resistance R _6.
It is connected to the inverting input terminal (−) of the operational amplifier Q ₅ connected to the common potential point COM via ₇ .

Further, the inverting input terminal - the series circuit of the capacitor C ₆ and the resistance R ₈ is connected between the output terminal (). The connection point between the capacitor C ₆ and the resistor R ₈ is connected to the inverting input terminal (−) of the amplifier Q ₆ functioning as a voltage follower via the resistor R ₉ .

The output terminal of the amplifier Q ₆ is connected to one switching terminal of the switch SW ₂ . The other switching end is connected to the common potential point COM via the resistor R ₁₀ . Then, the common end thereof is connected to the output end T ₃ via the low-pass filter LPF ₃ and outputs an abnormality signal V _A4 for detecting an abnormality of the comparison electrode 12.

A series circuit of a resistor R ₁₁ and a Zener diode D ₁ is connected between the positive power supply V _CC and the common potential point COM, and these connecting points are connected to each other through a resistor R ₁₂ and a non-inverting input terminal (+). It is connected to the common potential point COM via the resistor R ₁₃ and is connected to the inverting input terminal (−) of the inverting amplifier Q ₇ which is connected to the resistor R ₁₄ between the output terminal and the inverting input terminal (−).

Then, a positive constant voltage + is applied across the Zener diode D _1.
The VRs respectively generate a negative constant voltage −VR at the output terminal of the inverting amplifier Q ₇ , which are applied to the respective switching terminals of the switch SW ₃ .

Common end capacitor C ₇ switches SW _3, via a resistor R ₁₅ terminal LT ^- connected to further connection point between the capacitor C ₇ and the resistance R ₁₅ is connected to the amplifier Q ₅ through a resistor R ₁₆ There is.

Reference numeral 19 denotes an oscillator that generates a clock signal CK, which is output to the switch control circuit 20, where the timing signals ST ₁ and S for opening and closing the switches SW _{1 to} SW ₃ are opened.
Outputs T ₂ and ST ₃ .

Each amplifier Q ₃ to Q ₇ is V _CC as a positive power supply, V _EE is applied respectively as a negative power supply.

Next, the operation of the embodiment configured as described above will be described with reference to the waveform chart shown in FIG.

2 (a) shows the clock signal C which is the output of the oscillator 19.
K and (b) are waveforms of voltage V ₁ at the common end of switch SW ₃ ,
(C) is the waveform of voltage V ₂ at the connection point between capacitor C ₇ and resistor R ₁₆ , (D) is the waveform of voltage V ₃ at the output end of operational amplifier Q ₃ ,
(E) is a timing signal ST that switches switches SW ₁ and SW _2.
Waveforms of ₁ and ST ₂ are shown.

First, the measurement of pH value will be described. The operational amplifier Q ₅ operates so that the two input terminals have the same potential.
RT ^- is equivalently equal to the potential of the common potential point COM. The single electrode potential Vg of the common potential point glass electrode 11 and reference electrode 12 with respect to COM potential difference Vr to each other dynamically summed with terminal GT ^- the voltage difference (Vg-Vr) is generated.

This differential voltage (Vg-Vr) corresponds to the pH value of the solution LQ to be measured, which is passed through the operational amplifier Q ₃ to the low-pass filter LPF ₁
Is output to This low pass filter LPF ₁ has a differential voltage (Vg
Terminal LT in -Vr) ^- removal of the voltage of the rectangular wave to be described later is superimposed from extracts only a DC difference voltage (Vg-Vr). The extracted DC differential voltage (Vg-Vr) is the operational amplifier Q ₄
Output as a pH signal V _pH to the output terminal T ₁ via.

In this case, since the shield of the cable l ₁ between the terminals GT and GT ⁻ of the glass electrode 11 is held at the same potential as the terminal GT ⁻ by the operational amplifier Q ₃ via the terminal GTS, the influence of the cable capacitance is exerted. I will not receive it.

Next, the impedance measurement of the comparison electrode will be described.

The clock signal CK (Fig. 2 (a)) output from the oscillator 19 is switched by the switch control circuit 20 with the timing signal ST ₃ similar to the waveform shown in Fig. 2 (b) to switch the switch SW ₃ and peak at its common end. It outputs a square wave voltage V ₁ (Fig. 2 (b)) whose value is ± VR.

On the other hand, at the output terminal of the operational amplifier Q _5, the liquid potential Vs and the unipolar potential are
Differential voltage between Vr (Vs-Vr) is generated as a voltage V ₃ of the direct current,
A voltage V ₂ that is the sum of this difference voltage and the rectangular wave voltage (FIG. 2B) is generated at the connection point between the capacitor C ₇ and the resistor R ₁₆ .

The voltage V ₄ generated at the input of the amplifier Q ₆ is given by the following equation.

_{V 4 = V 1 R 8 /} (R 15 + R 6 + Rs + Rr + R l1) ... (5) The voltage is applied to one end of the switch end switch SW _2. This switch SW ₂ is opened / closed by the timing signal ST ₂ shown in FIG. 2 (e), synchronously rectified, smoothed by the low-pass filter LPF ₃ and output to the output terminal T ₃ as an abnormal signal V _A4 .

Here, the switching portion of the waveform of the voltage V ₄ shown in FIG. 2D has a differential waveform because it is caused by the cable capacitance between the terminal RT ⁻ and the other terminals. But,
As shown in FIG. 2 (e), since the switch SW ₂ is turned on at the portion where the waveform immediately before switching is stable, the abnormal signal V _A4 is not affected by this.

In the equation (5), the resistors R ₈ , R ₁₅ and R ₆ are constants,
And Rr»Rs, voltage V ₄ because it is R _l1 is governed by the resistance Rr. For this reason, for example, when the potassium chloride solution KCl (s) in the liquid junction LS of the reference electrode 12 disappears, the resistance Rr becomes extremely large, so that the voltage V ₄ becomes small and the abnormal signal V _A4
Becomes smaller, and conversely, if the liquid junction LS is cracked or dropped, the resistance Rr becomes extremely small, so that the voltage V ₄ becomes large and the abnormal signal V _A4 becomes large accordingly.

Therefore, the abnormality of the reference electrode 12 can be known by monitoring the abnormality signal V _A4 .

Next, the measurement of the impedance of the glass electrode 11 will be described. Again, since the relationship of Rg»R _l2, Rs is established, omitting the R _l2, Rs, and consider the AC component.

The AC voltage V ₅ that appears at the output of the operational amplifier Q ₃ is given by the following equation.

V ₅ = (V ₁ / jωC ₃ ) / $ where $ = [Rg / (1 + jωCgRg)] + (1 / jωC ₃ ) ... (6) Therefore, for example, when the glass film GS of the glass electrode 11 is damaged. Is Rg = 0, so V ₅ = V ₁ and the glass electrode
When the platinum wire Pt of 11 is broken, Rg / (1 + jωCgRg) =
It becomes ∞ and V ₅ = 0.

From the above, if only the AC voltage V ₅ appearing at the output terminal of the operational amplifier Q ₃ is rectified synchronously under the control of the timing signal ST _{1 by} the take-out switch SW ₁ via the high-pass filter HPF ₁ , the output terminal T ₂ It is possible to output an abnormal signal V _A3, which can be used to detect disconnection or breakage of the glass electrode 11.

<Effects of the Invention> According to the present invention as specifically described above with reference to the embodiments, the voltage generating means for applying an alternating voltage to the measurement liquid via the liquid electrode and the glass electrode and the liquid electrode. A first signal detecting means for detecting a first alternating voltage component generated and a second signal detecting means for detecting a second alternating voltage component generated between the comparison electrode and the liquid electrode are provided. Since the abnormality of the glass electrode is detected from the component and the abnormality of the comparison electrode is detected from the second AC voltage component, the glass electrode,
Alternatively, it is possible to constantly monitor for abnormalities such as breakage of the reference electrode, and even if this abnormality is constantly monitored, the pH value can be constantly output, and a highly insulated relay must be used as in the past. There is no inconvenience.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the constitution of one embodiment of the present invention, FIG. 2 is a waveform diagram explaining the operation of the embodiment shown in FIG. 1, and FIG. 3 is an outline of the constitution of a conventional pH converter. Block diagram showing,
FIG. 4 is a schematic diagram showing a specific configuration of the glass electrode and the reference electrode shown in FIG. 11 …… Glass electrode, 12 …… Comparison electrode, 13 …… Liquid electrode, 17
...... Relay drive circuit, 19 …… Oscillator, 20 …… Switch control circuit, V _pH …… pH signal, V _{A1 to} V _A4 …… Abnormal signal, GS…
… Glass film, LS… Liquid junction, LQ… Measured liquid, Vg, Vr…
Unipolar potential, ST _{1 to} ST ₃ ... Timing signal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Josef Michael Bicycle Netherlands, 3829, AA, Hoflanderveen, Fantaisturat, 1A (56) Reference JP-A-62-261950 (JP, A)

Claims (1)

(57) [Claims] 1. A pH converter for measuring the pH value of the measurement liquid from a DC electromotive force generated between a glass electrode immersed in the measurement liquid and a reference electrode, wherein the pH value of the measurement liquid is measured via the liquid electrode. Voltage generating means for applying an AC voltage, first signal detecting means for detecting a first AC voltage component generated between the glass electrode and the liquid electrode, and generated between the comparison electrode and the liquid electrode A second signal detecting means for detecting a second AC voltage component for detecting the abnormality of the glass electrode from the first AC voltage component and the abnormality of the comparison electrode from the second AC voltage component. PH converter characterized by.