JPH06174691A - Voltage-measuring circuit - Google Patents

Abstract

PURPOSE:To provide a voltage-measuring circuit wherein even when a leakage of current occurs between a solution to be measured and the ground, a reference electrode is hardly influenced by the leakage. CONSTITUTION:A voltage difference operation means 4 having a reference voltage input terminal 41 and a measured voltage input terminal 42 receives a measured voltage signal from a sensor 5 and a reference signal from a reference electrode 1 and operates a difference voltage between the measured voltage and the reference voltage. In the voltage reference operation means 4, the reference electrode 1 connected to the reference voltage input terminal 41 is not connected to the ground but a dummy electrode 2 is provided to be connected to the ground.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object to be measured from a potential obtained by a sensor, such as a device for measuring a liquid aji using a taste sensor or a device for measuring pH using a pH sensor (glass electrode). The present invention relates to a potential measuring circuit used in a measuring device that obtains various information about a liquid.

[0002]

2. Description of the Related Art Here, a conventional technique will be described by taking an azimuth measuring device for measuring the azimuth of a liquid from an electric potential obtained by a taste sensor as an example. 5 (a) and 5 (b) show a multi-channel taste sensor using a lipid membrane, which is used in the horse mackerel measuring apparatus. In this figure, three sensitive parts of the multi-channel array electrode are shown. In the illustrated example, the substrate 25
A 0.5 mmφ hole was penetrated through and a silver round bar was inserted therein to form an electrode 26. The lipid membrane 27 is attached to the base material 25 so as to contact the electrode 26 via the buffer layer 28.

FIG. 6 shows a horse mackerel measuring apparatus using this taste sensor. Make an aqueous solution of the taste substance and use it as the solution to be measured.
11 and place in a beaker-like container 12. The taste sensor array 13 prepared by arranging the lipid film and the electrode on the acrylic plate (base material) as described above was put in the solution to be measured. Prior to use, the electrode potential was stabilized with an aqueous solution of 1m mole / l potassium chloride. In the figure, 14-1, ..., 14-8 are the lipid membranes shown by black dots.

A reference electrode 15 is prepared as an electrode for generating an electric potential serving as a standard for measurement, and the reference electrode 15 is put in a solution to be measured. The taste sensor array 13 and the reference electrode 15 are installed at a predetermined distance. The surface of the reference electrode 15 is covered with 100 m mole / l of potassium chloride solidified with agar as the buffer layer 16, so that the electrode system is eventually silver 26 | silver chloride 28 | lipid film 27.
(14) ｜ Measured solution 12 ｜ Buffer layer (potassium chloride 100m mole
/ L) 16 | silver chloride 28 | silver 26.

The electric signal from the lipid membrane becomes an 8-channel signal in the figure and is led to the buffer amplifiers 19-1, ..., 19-8 by the lead wires 17-1 ,. Each output of the buffer amplifier 19 is selected by the analog switch (8 channels) 20 and added to the A / D converter 21. The electric signal from the reference electrode 15 is also applied to the A / D converter 21 via the lead wire 18, and the difference from the potential from the membrane is converted into a digital signal. This digital signal is appropriately processed by the microcomputer 22 and displayed by the XY recorder 23.

A potential measuring circuit used in a conventional horse mackerel measuring apparatus will be described. FIG. 4 shows a conventional potential measuring circuit. The reference electrode 1 for obtaining the reference potential is connected to the reference potential input terminal 61 of the potential difference detection means 6 and the ground. It is connected to the ground in order to effectively use a portion having good linearity such as the operational amplifier 65 used in the potential difference detecting means 6 by setting the reference potential to 0 volt. The other input terminal 62 of the potential difference detecting means 6 is also an input terminal of the potential measuring circuit, and the electrode of each channel of the taste sensor 5 is connected to it.

FIG. 4 shows the case of one channel in order to simplify the explanation. In this example, the potential difference detecting means 6
Is composed of one operational amplifier 65, two input terminals 61 and 62 and two output terminals 63 and 64, one of the two input terminals being the measurement potential input terminal 62 and the operational amplifier 65. Is connected to the input terminal of. The other one is a reference potential input terminal 61, which is one of the two output terminals.
Connected to one output terminal 64. The other output terminal 63 is connected to the output terminal of the operational amplifier 65. The output terminal of the potential difference detecting means 6 is also the output terminal of the potential measuring circuit.

The operation of this circuit will be described. Taste sensor 5
The measurement potential signal is input to the measurement potential input terminal 62 of the potential difference detection means 6 from the reference electrode 1, and the reference potential signal is input from the reference electrode 1 to the reference potential input terminal 61 of the potential difference detection means 6. The potential difference between the reference potential and the measured potential is output between the two output terminals of the potential difference detection means 6.

[0009]

As described above, the conventional potential measuring circuit drops the reference electrode 1 to the ground and measures the potential with reference to the ground. Also,
In many cases, a buffer amplifier 65 is provided so as to be compatible with a high impedance sensor. When the conventional potential measuring circuit is used, if the solution to be measured spills and there is a current leak between the solution to be measured 11 in the container and the ground, the current flows to the reference electrode 1. It will flow.

In the measurement while keeping the solution to be measured at a constant temperature, there may be used a constant temperature bath of a type in which a container containing the solution to be measured is put in circulating water, and the circulating water may be connected to a ground. Many, especially the risk of leaks. Further, there is a high risk of leakage even when the solution to be measured is measured in a factory line without storing the solution to be measured in a container. In addition to this, in general, the container containing the solution to be measured is often covered with a conductor dropped to the ground in order to perform the measurement stably, so that there is a risk of leakage.

When a current flows through the reference electrode 1, a redox chemical reaction takes place in the reference electrode (whether oxidation or reduction occurs depending on the direction of the current flow), and the potential at the reference electrode 1 fluctuates. (The potential difference between the grounded output side of the reference electrode 1 and the side in contact with the solution to be measured fluctuates.). Moreover, even if the leak disappears, it does not return to the original potential immediately. Since the reference potential becomes unstable,
This will cause a large error in the measurement result.

The object of the present invention is to solve the aforementioned problems,
An object of the present invention is to provide a potential measurement circuit that has a small influence on the reference electrode (that is, a measurement error is small) even if a current leaks between the measured solution in the container and the ground.

[0013]

In order to solve the above problems, in the potential measuring circuit of the first invention, the reference electrode 1 is not dropped to the ground, but a dummy electrode 2 is provided so that the reference electrode 1 is placed in the solution to be measured. The immersed dummy electrode 2 is dropped to the ground so that the potential of the measured solution is 0 volt. That is, the reference electrode 1 immersed in the solution to be measured,
Potential difference calculating means 4 having a reference potential input terminal 41 for inputting a reference potential signal from the reference electrode 1 and a measurement potential input terminal 42 for inputting a measurement potential signal from a sensor immersed in the solution to be measured, and a solution to be measured And a dummy electrode 2 that is grounded.

In the potential measuring circuit according to the second aspect of the invention, the reference electrode 1 is not dropped directly to the ground, but is dropped via the resistor 3. That is, from the reference electrode 1 immersed in the solution to be measured, the reference potential input terminal 41 for inputting the reference potential signal from the reference electrode 1 and grounded via the resistor 3, and the sensor immersed in the solution to be measured. And a potential difference calculating means 4 having a measurement potential input terminal 42 for inputting the measurement potential signal.

[0015]

In the potential measuring circuit according to the first aspect of the present invention, the dummy electrode is provided and the dummy electrode immersed in the solution to be measured is dropped to the ground. Therefore, a leak occurs between the solution to be measured and the ground. Also, current flows through the dummy electrode but not through the reference electrode. When a leak occurs, a current flows in the dummy electrode to cause a chemical change, and the potential difference between the liquid potential and the ground fluctuates. However, since this potential difference is included in both the measurement potential from the sensor and the reference potential from the reference electrode, it is canceled by taking the difference between the measurement potential and the reference potential.

Further, in the potential measuring circuit of the second invention, the reference electrode is not dropped directly to the ground but is dropped via a resistor. Therefore, even if a leak occurs between the solution to be measured and the ground, The current flowing through the reference electrode is limited by the resistance.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the first invention and the second invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of the first invention (hereinafter referred to as the first embodiment). The potential measuring circuit of the first embodiment is composed of a dummy electrode 2, a reference electrode 1 for obtaining a reference potential, and a potential difference calculating means 4. The reference electrode 1 is connected to the reference potential input terminal 41 of the potential difference calculating means 4, and the dummy electrode 2 is connected to the ground.

The other input terminal 42 of the potential difference calculating means 4 is also an input terminal of the potential measuring circuit, and is connected with a sensor for detecting the potential of the solution to be measured, such as a taste sensor. Figure 1
Shows the case of one channel for simplification of description. In this example, the potential difference calculating means 4 is composed of three operational amplifiers, and the input terminals of the potential difference calculating means 4 are connected to the first and second operational amplifiers 45 and 46, respectively. The output terminals of are connected to the input terminals of the third operational amplifier 47, respectively. The third operational amplifier 47
The output terminal of is the output terminal of the potential difference calculating means 4 and also the output terminal of the potential measuring circuit.

The operation of this circuit will be described. The measured potential signal is input from the taste sensor to the input terminal of the potential difference calculating means, and the reference potential signal is input from the reference electrode to the reference potential input terminal of the potential difference calculating means. The potential difference calculation means calculates the potential difference from the measured potential signal and the reference potential signal input to each input terminal, and the potential difference is output from the output terminal.

Since the potential difference calculating means only has to calculate the potential difference between the measured potential from the taste sensor and the reference potential from the reference electrode, various modifications can be considered depending on the sensor and other conditions. For example, the taste sensor has a low impedance, and the first and second operational amplifiers 45 and 46 are
The second operational amplifier 46 may be removed if the amplification factor is doubled. Further, this example is a type of potential difference calculation means for performing calculation in analog, but the outputs of the first and second operational amplifiers 45 and 46 are input to the analog-digital converter, and the measured potential and the reference potential are digitalized. Converted to CPU
Alternatively, the calculation may be performed digitally. However, no matter what the configuration is, it is necessary to keep high impedance between the input terminal to which the reference electrode is connected and the other input terminals, and between each input terminal and the ground. This is because no current is applied to the reference electrode.

Here, adding a little to the dummy electrode 2, it is better that the dummy electrode generate a potential close to that of the reference electrode 1. This is because a portion having good linearity such as an operational amplifier used in the potential difference calculating means 4 can be used for measurement. As one method, the same electrode as the reference electrode may be used. Also, platinum (Pt), gold (A
u), a silver (Ag) line or the like may be used. Platinum and gold generally have unstable potentials but do not corrode. Since silver has an oxidation-reduction reaction with chloride ions, the potential changes depending on the chloride ion concentration, but it is stable if the chloride ion concentration is constant. The potential of the dummy electrode varies by several hundred mV at most due to chemical changes, and even if the potential varies depending on the type and concentration of the solution to be measured, this potential is a common mode for the measurement potential and the reference potential, and the sensor (measurement potential ) And the reference electrode (reference potential), the measured value is not affected. However, it is necessary not to exceed the range of the common mode of the operational amplifier used in the potential difference calculation means.

FIG. 2 is a schematic configuration diagram showing an embodiment of the second invention (hereinafter referred to as the second embodiment). The potential measuring circuit of the second embodiment comprises a reference electrode 1 for obtaining a reference potential, a potential difference calculating means 4 and a resistor 3. The reference electrode is connected to the reference potential input terminal of the potential difference calculating means, and is also connected to the ground via the resistor. The other input terminal of the potential difference calculating means is also an input terminal of the potential measuring circuit, and is connected with a sensor for detecting the potential of the solution to be measured, such as a taste sensor. FIG. 2 shows the case of one channel for the sake of simplicity. In this example, the potential difference calculating means is composed of three operational amplifiers, and the respective input terminals of the potential difference calculating means are connected to the first and second operational amplifiers 45 and 46, and the outputs of the respective operational amplifiers 45 and 46. The terminals are connected to the input terminals of the third operational amplifier 47, respectively. The output terminal of the third operational amplifier is the output terminal of the potential difference calculating means and also the output terminal of the potential measuring circuit.

The operation of this circuit will be described. The measured potential is input from the taste sensor to the input terminal of the potential difference calculating means, and the reference potential is input from the reference electrode to the reference potential input terminal of the potential difference calculating means. The difference between the measured potential and the reference potential input to each input terminal is calculated by the potential difference calculation means and output from the output terminal.

Since this potential difference calculating means has only to calculate the potential difference between the measured potential from the taste sensor and the reference potential from the reference electrode, various modifications are conceivable depending on the sensor and other conditions. Even with such a structure, it is necessary to keep high impedance between the input terminals and between the input terminals and the ground, as in the case of the first embodiment.

Here, the resistance value of the resistor will be described. FIG. 3 shows an equivalent circuit in the potential measuring circuit of FIG. 2 when there is a leak between the measured solution and the ground. The internal resistance value of the reference electrode is R ₀ , the potential difference between the output side and the measured solution side is V ₀ , the internal resistance value of the taste sensor is R ₁ , the potential difference between the output side and the measured solution side is V 0. ₁ , the resistance value of the resistor 3 is R, the output voltages of the first and second operational amplifiers 45 and 46 are E ₀ and E ₁ , respectively, and the resistance value between the measured solution and the ground when a leak occurs and The potential difference is r,
The relations of the equations (1) and (2) are established, where v is the current value flowing through the reference electrode due to leakage. I = (V ₀ + v) / (R + R ₀ + r) (1) E ₁ −E ₀ = V ₁ −V ₀ −IR ₀ ……… (2) “IR” in the formula (2) ₀ ”is the shift due to leak,
It causes a measurement error. By substituting the equation (1) into "IR ₀ ", IR ₀ = (V ₀ + v) R ₀ / (R + R ₀ + r) (3)

Internal resistance value R of the reference electrode₀Is generally low.
For example, in the case of AgCl (silver chloride) electrode, several hundred Ω
From several kΩ. When a leak occurs, the solution to be measured and the
The resistance value r with the land is r, which is the worst case
= 0Ω, internal resistance value R of the reference electrode₀R₀= 1kΩ
age, If the resistance value R of the resistor is R = 10 MΩ, then V₀+
v is 1 V (If the leak occurs between the liquids, the osmotic pressure difference
Potential difference is determined and maximum is about 200 mV through conductor
When leaking, the redox potential is about 1 V at maximum.
It Even if there is, the error is suppressed to 0.1 mV
It In the conventional potential measuring circuit, it corresponds to R = 0Ω,
If the other conditions are the same, the error becomes 1V.

From the experience of the inventors of the present invention in the measurement of horse mackerel using a taste sensor, the meaning of the error of 0.1 mV will be described. The Weber ratio that can be recognized to have a difference in horse mackerel is 20% for the general public and 5% for professional tasters. The difference in output of the taste sensor, which corresponds to the same 5% Weber ratio as a professional taster, is about 1.0 to 1.5 mV for sourness and saltiness, and about 0.2 for sweetness and bitterness.
~ 0.5 mV. Further, when compared from different angles, for example, in order to determine the type of beer, the error is required to be about 0.5 mV.

In the case of a pH meter, it is quite difficult to measure with an accuracy of pH = 0.05, but an error of 0.1 mV is pH =
This corresponds to 0.0015. From these things, even if there is a leak, it is significant that it is about 0.1 mV.

[0029]

In the potential measuring circuit of the first invention, the dummy electrode is provided and the dummy electrode immersed in the solution to be measured is dropped to the ground. Therefore, there is a leak between the solution to be measured and the ground. However, current flows through the dummy electrode but not through the reference electrode. When a leak occurs, a current flows in the dummy electrode to cause a chemical change, and the potential difference between the liquid potential and the ground fluctuates. However, since this potential difference is included in both the measurement potential from the sensor and the reference potential from the reference electrode, it can be canceled by taking the difference between the measurement potential and the reference potential.

In the potential measuring circuit according to the second aspect of the invention, the reference electrode is not directly dropped to the ground but is dropped via a resistor, so that the leak may occur between the solution to be measured and the ground. The current flowing through the reference electrode is small, and the damage to the reference electrode and the influence on the measured value are small. That is, both the potential measuring circuit of the first invention and the potential measuring circuit of the second invention have little influence on the reference electrode even if there is a current leak between the measured solution in the container and the ground. This is a potential measurement circuit (that is, a measurement error is small), and is useful for an apparatus for measuring potential using a liquid as an object to be measured, in which leakage easily occurs. In particular, one of the conditions is that the reference electrode has low impedance, so that the effect of the present invention is great.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing an equivalent circuit in the case where there is a leak between a solution to be measured and a ground in the potential measuring circuit according to the second embodiment of the present invention.

FIG. 4 is a diagram showing a conventional potential measuring circuit.

FIG. 5 is a view showing a taste sensor, (a) is a front view,
(b) is a sectional view.

FIG. 6 is a diagram showing an horse mackerel measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 reference electrode 2 dummy electrode 3 resistance 4 potential difference calculating means 5 sensor 6 potential difference detecting means 11 solution to be measured 12 container 13 taste sensor array 14 each lipid membrane (indicated by black dots) 15 reference electrode 16 buffer layer 17 lead wire 18 lead wire 19 Buffer amplifier 20 Analog switch 21 A / D converter 22 Microcomputer 23 XY recorder 24 Ground potential 25 Base material (substrate) 26 Electrode 27 Lipid membrane 28 Buffer layer 29 Lead wire 30 Base membrane

Claims (2)

[Claims] 1. A reference electrode (1) immersed in a solution to be measured.
And a potential difference calculating means (4) having a reference potential input terminal for inputting a reference potential signal from the reference electrode and a measurement potential input terminal for inputting a measurement potential signal from a sensor immersed in a solution to be measured, and a measured potential difference A potential measuring circuit comprising a dummy electrode (2) immersed in a solution and grounded. 2. A reference electrode (1) immersed in a solution to be measured.
And a reference potential input terminal for inputting a reference potential signal from the reference electrode, which is grounded via a resistor (3), and a measurement potential input terminal for inputting a measurement potential signal from a sensor immersed in the solution to be measured. A potential measuring circuit comprising: a potential difference calculating means (4) having