JP3390193B2 - Potential measurement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION The present invention relates to a taste sensor, for example.
For measuring liquid horse mackerel and pH sensor
Using a sensor, such as a device that measures pH using a
Information about the liquid being measured
The present invention relates to a potential measuring circuit used for a measuring device to be obtained. [0002] 2. Description of the Related Art Here, an electric potential obtained by a taste sensor is used.
Using a mackerel measuring device that measures the mackerel of liquid
Explain the technology. FIGS. 5 (a) and 5 (b) show the results of using
Multichannel taste sensor using lipid membrane
It is sa. In this figure, the multi-channel array electrode
Three sensitive parts are shown. In the illustrated example, the substrate 25
Through the hole of 0.5mmφ and insert the silver bar into it
The electrode 26 was used. The lipid membrane 27 contacts the electrode 26 via the buffer layer 28.
It is attached to the base material 25 so as to touch it. FIG. 1 shows a horse mackerel measuring device using this taste sensor.
6 is shown. Make an aqueous solution of the taste substance and add it to the solution to be measured.
11 and put in a container 12 like a beaker. Solution to be measured
Inside, the lipid on the acrylic plate (substrate) as described earlier
Put the taste sensor array 13 made by arranging the membrane and the electrodes
Was. Before use, electrode with potassium chloride 1m mole / l aqueous solution
The potential was stabilized. In the figure, 14-1,.
The lipid membrane is indicated by black dots. As an electrode for generating a potential which is a reference for measurement,
To prepare a reference electrode 15 and put it in the solution to be measured. taste
Sensor array 13 and reference electrode 15 are separated by a predetermined distance.
Install. On the surface of the reference electrode 15, as a buffer layer 16, a salt
100m mole / l of potassium iodide covered with solidified agar
In the end, the electrode system is silver 26 | silver chloride 28 | lipid membrane 27
(14) ｜ Measurement solution 12 ｜ Buffer layer (potassium chloride 100m mole
/ L) 16 | silver chloride 28 | silver 26. [0005] The electrical signal from the lipid membrane is 8 channels in the figure.
, And leads 17-1,..., 17-8.
Lead to the buffer amplifiers 19-1,..., 19-8, respectively.
I will Each output of the buffer amplifier 19 is connected to an analog switch.
(8 channels) 20 and is added to the A / D converter 21.
available. The electric signal from the reference electrode 15 also passes through the lead wire 18.
And applied to the A / D converter 21 to determine the difference from the potential from the membrane.
Convert to digital signal. This digital signal is
Appropriately processed by a computer 22 and an XY record
Is displayed in the order 23. [0006] The electric potential used in the conventional horse mackerel measuring device
The measurement circuit will be described. Fig. 4 shows a conventional potential measurement circuit.
You. The reference electrode 1 for obtaining a reference potential is used for potential difference detection.
Connected to the reference potential input terminal 61 of the output means 6 and the ground.
Have been. What is connected to ground is the reference potential
By setting the voltage to 0 volt, the potential difference detecting means 6 is used.
To effectively use parts with good linearity such as operational amplifier 65
It is. The other input terminal 62 of the potential difference detecting means 6 measures the potential.
It is also the input terminal of the circuit, and each channel of the taste sensor 5
Electrodes are connected. FIG. 4 shows one channel for simplicity of explanation.
In the case of In this example, the potential difference detecting means 6
Is one operational amplifier 65, two input terminals 61 and 62 and two
Output terminals 63 and 64, and the two input terminals
One of the terminals is a measurement potential input terminal 62,
It is connected to the input terminal of the amplifier 65. The other one is criteria
A potential input terminal 61, one of the two output terminals;
Connected to one output terminal 64. The other output terminal 63 is before
It is connected to the output terminal of the operational amplifier 65. The potential difference
The output terminal of the detecting means 6 may be the output terminal of the potential measuring circuit.
You. The operation of this circuit will be described. Taste sensor 5
From the measuring potential input terminal 62 of the potential difference detecting means 6
The potential signal is input, and the potential difference
A reference potential signal is input to the reference potential input terminal 61. Electric
The reference potential is measured between the two output terminals of the potential difference detecting means 6.
The potential difference from the potential is output. [0009] SUMMARY OF THE INVENTION As described above,
In the conventional potential measurement circuit, the reference electrode 1 is dropped to the ground.
Then, the potential is measured with reference to the ground. Also,
In many cases, a high impedance
It can respond to the sensor of the sensor. Conventional potential
If a configuration like a measurement circuit is used, the solution to be measured
Between the solution to be measured 11 in the container and the ground
If there is a current leak, current will flow through the reference electrode 1
I will. [0010] In the measurement while maintaining the solution to be measured at a constant temperature
Is used to place the container containing the solution to be measured in circulating water.
The circulating water may be grounded.
In many cases, especially the risk of leaks is high.
No. Also, do not take the solution to be measured in a container.
There is also a danger of leaks when measuring the solution
high. In addition, generally, the solution to be measured was stored.
The container is a conductor dropped to ground for stable measurement.
To avoid leaks.
It is. When a current flows through the reference electrode 1, the reference electrode 1
Causes a redox chemical reaction (depending on the direction of current flow).
It determines whether oxidation occurs or reduction occurs. ), Reference
The potential fluctuates at pole 1 (the grounded output of reference electrode 1)
The potential difference between the force side and the side in contact with the solution to be measured fluctuates
I do. ). Also, even if the leak disappears, the original
Does not return to potential. Because the reference potential becomes unstable,
A large error occurs in the measurement result. An object of the present invention is to solve the aforementioned problems,
Leakage of current between the solution to be measured in the container and the ground
The effect on the reference electrode is small (i.e.,
(The constant error is small.) [0013] [MEANS FOR SOLVING THE PROBLEMS]
In addition, the potential measurement circuit according to the first aspect of the present invention
Instead of dropping it on the dummy electrode 2
Drop the dummy electrode 2 immersed in the solution to ground
And the potential of the solution to be measured is set to 0 volt.
You. That is, the reference electrode 1 immersed in the solution to be measured,
A reference potential input for inputting a reference potential signal from the reference electrode 1
Measurement from force terminal 41 and sensor immersed in solution to be measured
A potential difference having a measured potential input terminal 42 for inputting a potential signal
The arithmetic means 4 is immersed in the solution to be measured and grounded.
Dummy electrode 2. The potential measuring circuit according to the second invention is described in
Rather than drop electrode 1 directly to ground,
And drop it. That is, immersion in the solution to be measured
The immersed reference electrode 1 and the reference potential signal from the reference electrode 1
Input, reference potential input grounded via resistor 3
The measurement voltage from the terminal 41 and the sensor immersed in the solution to be measured
Potential difference input terminal 42 for inputting the potential signal
Calculation means 4. [0015] The potential measuring circuit according to the first aspect of the present invention includes a dummy electrode.
Then, the dummy electrode immersed in the solution to be measured is grounded.
The solution to be measured and the ground
Current flows through the dummy electrode
It does not flow to the reference electrode. If a leak occurs,
Means that a current flows, a chemical change occurs, and the liquid potential and ground
The potential difference between and fluctuates. However, this potential difference
Included in both the measured potential from the sensor and the reference potential from the reference electrode.
Be taken by taking the difference between the measured potential and the reference potential.
Is erased. Further, for a potential measurement circuit according to a second aspect of the invention, refer to
Rather than drop the electrode directly to ground,
Since the solution is to be dropped,
Current flowing through the reference electrode
Therefore, it is limited. [0017] DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the first invention and the second invention will be described below.
Each will be described with reference to the drawings. FIG. 1 shows the first invention.
Schematic configuration showing an embodiment (hereinafter, referred to as a first embodiment)
FIG. The potential measuring circuit according to the first embodiment includes a dummy electrode
2. Reference electrode 1 and potential difference for obtaining reference potential
It is composed of arithmetic means 4. The reference electrode 1 has a potential
Connected to the reference potential input terminal 41 of the difference calculation means 4
The dummy electrode 2 is connected to the ground. Another input terminal 42 of the potential difference calculating means 4 is a potential
It is also the input terminal of the measurement circuit and detects the potential of the solution to be measured
, For example, a taste sensor or the like is connected. FIG.
Shows the case of one channel for simplicity.
I have. In this example, the potential difference calculating means 4 comprises three operational amplifiers.
Input terminals of the potential difference calculating means 4
The operational amplifiers are connected to first and second operational amplifiers 45 and 46, respectively.
The output terminals of the operational amplifiers 45 and 46 are the input terminals of the third operational amplifier 47.
Each is connected to a terminal. The third operational amplifier 47
Is the output terminal of the potential difference calculating means 4, and
It is also the output terminal of the potential measurement circuit. The operation of this circuit will be described. A taste sensor?
The measured potential signal is input to the input terminal of the potential difference
Input terminal for the reference potential of the potential difference calculating means from the reference electrode.
Is supplied with a reference potential signal. Input to each input terminal
From the measured potential signal and the reference potential signal,
Is calculated and output from the output terminal. This potential difference calculating means is provided for detecting the potential difference from the taste sensor.
Calculate the potential difference between the measured potential and the reference potential from the reference electrode
It may be various depending on the sensor and other conditions.
Can be considered. For example, if the taste sensor
And the first and second operational amplifiers 45 and 46
If the gain is doubled, the second operational amplifier 46
May be removed. Also, this example performs the operation in analog
Type of potential difference calculating means, the first and second calculating means
Input the outputs of amplifiers 45 and 46 to analog-digital converter
And converts the measured potential and the reference potential into digital data,
The calculation may be performed digitally by using. Only
However, regardless of the configuration, the reference electrode
Connect between the input terminal to be connected and other input terminals, and
It is necessary to keep high impedance between
You. This is to prevent a current from flowing to the reference electrode. Here, the dummy electrode 2 is slightly attached.
In addition, the dummy electrode has a potential close to the potential of the reference electrode 1.
It is better to generate. Because it is used by the potential difference calculating means 4
For measuring parts with good linearity such as operational amplifiers
Available. One method is to use the same electrode as the reference electrode.
May be used. In addition, platinum (Pt), gold (A
u), silver (Ag) wire or the like. One for platinum and one for gold
Generally, the potential is unstable, but does not corrode. Silver is chlorine ion
Due to oxidation-reduction reaction with chlorine
The potential changes, but the chlorine ion concentration is constant
Is stable. The potential of the dummy electrode fluctuates due to chemical change
The number is at most several hundred mV.
Even if the potential fluctuates depending on the
This is a common mode for the sub-potential, and the sensor (measurement
Value) and the difference between the reference electrode (reference potential)
Has no effect. However, it is not used in the potential difference calculation means.
Do not exceed the common mode range of operational amplifiers
is necessary. FIG. 2 shows an embodiment of the second invention (hereinafter referred to as a second embodiment).
It is called an embodiment. FIG. Second implementation
The example potential measurement circuit uses a reference to obtain a reference potential.
It comprises an electrode 1, a potential difference calculating means 4 and a resistor 3.
You. The reference electrode is a reference potential input terminal of the potential difference calculating means.
Connected to the ground and via the resistor
It is connected to the. The other input terminal of the potential difference calculation means is
It is also the input terminal of the position measurement circuit and detects the potential of the solution to be measured.
An output sensor, for example, a taste sensor or the like is connected. Figure
2 shows the case of one channel for the sake of simplicity.
ing. In this example, the potential difference calculating means comprises three operational amplifiers.
Each input terminal of the potential difference calculating means.
Is connected to the first and second operational amplifiers 45 and 46,
The output terminals of the amplifiers 45 and 46 are input terminals of the third operational amplifier 47.
Each child is connected. The output of the third operational amplifier
The force terminal is the output terminal of the potential difference calculating means, and
It is also the output terminal of the measurement circuit. The operation of this circuit will be described. A taste sensor?
The measured potential is input to the input terminal of the potential difference
Reference from input electrode to reference potential input terminal of potential difference calculation means
The potential is input. The measured potential input to each input terminal
The difference between the reference potential and the reference potential is calculated by the potential difference calculating means, and the output terminal
Output from child. This potential difference calculating means measures the potential from the taste sensor.
Calculate the potential difference between the constant potential and the reference potential from the reference electrode.
It may be various, depending on the sensor and other conditions.
Possible deformation, but of any configuration
However, even if the
Must be high impedance between
And the like are the same as in the first embodiment. Here, the resistance value of the resistor will be described. Figure
Reference numeral 3 denotes the potential measurement circuit shown in FIG.
5 shows an equivalent circuit in the case where there is a leak between the input and output. reference
The internal resistance of the electrode is R₀, Between the output side and the solution to be measured side
Is the potential difference of V₀, The internal resistance of the taste sensor is R₁,output
V is the potential difference between the₁, Resistance of resistance 3
The value is R, and the output voltages of the first and second operational amplifiers 45 and 46 are
Each E₀, E₁, Solution to be measured when a leak occurs
And r, the resistance and the potential difference between
v, let I be the current value flowing through the reference electrode due to leakage
And the relations of Equations (1) and (2) hold.       I = (V₀+ V) / (R + R₀+ R) …………… (1)       E₁-E₀= V₁-V₀-IR₀              …………… (2) "IR" in equation (2)₀”Is the shift due to the leak,
A measurement error results. “IR₀Substituting equation (1) into       IR₀= (V₀+ V) R₀/ (R + R₀+ R) …………… (3) Becomes The internal resistance R of the reference electrode₀Is generally low.
For example, in the case of AgCl (silver chloride) electrode,
Several kΩ. The solution to be measured and the
The resistance value r with the land is set to r which is the worst case.
= 0Ω and the internal resistance R of the reference electrode₀To R₀= 1kΩ
age, If the resistance value R of the resistor is R = 10 MΩ, then V₀+
v is 1V (If a leak occurs between liquids,
The potential difference is determined and the maximum is about 200 mV through the conductor
In the case of leakage, the maximum oxidation-reduction potential is about 1 V.
You. ) Even if there is, the error is suppressed to 0.1mV
You. In the conventional potential measurement circuit, it is equivalent to R = 0Ω.
If the other conditions are the same, the error will be 1V. Measurement of horse mackerel using the taste sensor of the present inventors
From the experience with constants, what does an error of 0.1 mV mean?
About having Recognition that there is a difference in horse mackerel
The Weber ratio that can be cut is 20% for ordinary people, professional taste
It is 5% in tar. Same weber as professional taster
The difference in the output of the taste sensor corresponding to the sensitivity of 5% is the sourness.
・ About 1.0-1.5mV for salty taste, about 0.2 for sweetness / bitterness
０．５0.5 mV. Also try to compare from different angles
Then, for example, to determine the type of beer, the error is
It is required to be about 0.5 mV. In the case of a pH meter, measurement is performed with an accuracy of pH = 0.05.
It is quite difficult to determine, but an error of 0.1 mV
It corresponds to 0.0015. There are leaks from these things
Even if it is about 0.1 mV, the significance is large.
No. [0029] According to the first aspect of the present invention, the potential measuring circuit
Providing a pole, the dummy electrode immersed in the solution to be measured
The solution to be measured and the ground
Current flows through the dummy electrode even if leakage occurs between
Does not flow to the reference electrode. In case of leak, dummy electrode
In this case, a current flows and a chemical change occurs,
The potential difference between the gate and the gate fluctuates. However, this potential difference
Both the measured potential from the sensor and the reference potential from the reference electrode.
Since it is included, the difference between the measured potential and the reference potential
Can be turned off. The potential measuring circuit according to the second invention is described in
Rather than drop the electrode directly to ground,
Between the solution to be measured and the ground.
There is little current flowing through the reference electrode,
The damage to the electrodes and the effect on the measured values are small. Toes
The potential measurement circuit of the first invention and the potential measurement circuit of the second invention
In any of the constant circuits, the solution to be measured in the container and the ground
Current leakage between the reference electrodes
Potential measurement circuit with small (that is, small measurement error)
Liquid, which is likely to leak
It is useful for a device for measuring In particular, the reference electrode
One of the conditions is that the
Ming's effect is great.

BRIEF DESCRIPTION OF THE 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 a 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 measurement circuit. FIG. 5 is a diagram showing a taste sensor, wherein (a) is a front view,
(b) is a sectional view. FIG. 6 is a diagram showing a horse mackerel measuring device. [Description of Signs] 1 Reference electrode 2 Dummy electrode 3 Resistance 4 Potential difference calculating means 5 Sensor 6 Potential difference detecting means 11 Measured solution 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 Substrate (substrate) 26 Electrode 27 Lipid film 28 Buffer layer 29 Lead wire 30 Base film

Claims (1)

(57) [Claims] [Claim 1] Only electrodes and reference electrodes constituting a sensor
Measurement times used in a measurement device using an electrode system consisting of
Reference electrode in the road, that will be immersed in the sample solution (1)
When a potential difference calculating means (4) having a reference potential input terminal and the measurement potential input terminal for inputting a measuring potential signal from a sensor that will be immersed in the sample solution to enter the reference potential signal from the reference electrode, one end which is connected to the reference potential input terminal, and the potential measuring circuit, characterized in that a resistor whose other end is grounded (3) is connected to the reference electrode.