JPH06308080A - Ph detection device - Google Patents

Abstract

PURPOSE:To facilitate mounting and achieve miniaturization by installing a pH detection device in a liquid and then detecting the potential difference generated between two types of electrodes with different sensitive characteristics for H<+> ion. CONSTITUTION:When a first electrode 20 and a second electrode 22 are first dipped into a liquid, a potential difference is generated between the reference electrode 21 and the electrode 20. Since a certain voltage is applied between the source and drain electrodes of a first field effect transistor 24 where the electrode 20 is connected, a drain current I1 flows to the transistor 24 according to the potential difference between the electrodes 21 and 20 corresponding to the pH value of liquid and a voltage V1 is output to a point (a) of a first current voltage converter 28. A voltage which is the same as that applied between the source and drain electrodes of the transistor 24 is applied between the source and drain electrodes of a second field effect transistor 26 where the electrode 22 is connected, a drain current I2 flows to the transistor 26, and a voltage V2 is output to a point (b). A differential amplifier 32 compares voltages V1 and V2 to determine pH.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pH detecting device which detects the pH value of a liquid in response to the concentration of H ⁺ ions in the liquid.

[0002]

2. Description of the Related Art Conventionally, as a pH detecting device of this type,
Some use a glass electrode that utilizes the characteristics of a relatively thin glass film. The glass membrane has a property of selectively passing only hydrogen ions, so that the glass electrode acts reversibly on hydrogen ions, and this property can be used to measure pH. As another pH detecting device, an IS having a field effect transistor as a basic configuration.
FETs (ion sensitive field effect transistors) have been proposed. This is a structure in which the gate electrode of a normal field effect transistor is not provided, and an ion sensitive film such as an oxide film or a nitride film contacts the liquid. At this time, an electric field corresponding to the H ⁺ ion concentration in the liquid is applied to the channel of the field effect transistor, and a drain current flows. This allows
It is possible to obtain an output corresponding to the pH value of the liquid.

[0003]

However, in any of the above-mentioned pH detecting devices, in order to obtain an accurate pH value of a liquid, Ag / dip immersed in a 3.3N KCl solution is used.
It is necessary to use the AgCl electrode as the reference electrode. This Ag / AgCl reference electrode is made of a glass container,
Careful handling was required. Also, since the KCl solution in the container may flow out or dry,
It was not suitable for continuous use, and it was difficult to miniaturize it.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a pH detecting device which can be easily handled and can be miniaturized without causing any trouble in continuous use. There is.

[0005]

In order to achieve this object, the pH detecting device of the present invention comprises two types of electrodes which are installed in a liquid and have different H ⁺ ion sensitive characteristics.
And a control means for detecting the potential difference generated between the electrodes of different types and obtaining the pH value of the liquid based on the detected potential difference.

[0006]

The control means in the pH detecting apparatus of the present invention having the above structure detects the potential difference generated between the two types of electrodes, and determines the pH value of the liquid based on it.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the electrical configuration of the pH detection device of this embodiment.

The pH detecting device comprises a first electrode 20 made of a conductor sensitive to H ⁺ ions, and a first field effect transistor 24 having the electrode 20 as a part of a gate electrode.
A current-voltage converter 28 for converting the drain current of the first field-effect transistor 24 into a voltage, and a second conductor made of a conductor less sensitive to H ⁺ ions than the first electrode 20.
Electrode 22, a second field effect transistor 26 having the second electrode 22 as a part of a gate electrode, and a gate electrode of each of the first field effect transistor 24 and the second field effect transistor 26. A reference electrode 21 serving as a reference for a gate voltage corresponding to the pH value of the liquid applied to the first electrode 20 and the second electrode 22 connected to each other;
The second current-voltage converter 30 for converting the drain current of the field-effect transistor 26 into a voltage, and the differential amplifier 32 for comparing the outputs from the two current-voltage converters 28, 30. .

Here, for example, gold is preferably used as the material of the first electrode 20. Further, as the material of the second electrode 22, for example, silver is preferably used.
Furthermore, platinum is preferably used as the reference electrode 21, and is connected to the ground here. With the above-described configuration, it is not necessary to use an electrode that has poor maintainability and cannot be downsized, such as the Ag / AgCl electrode that has been conventionally required for pH measurement.
That is, the entire device can be downsized. Also,
Continuous use for a long period is also possible. At the same time, due to the potential difference between the two electrodes corresponding to the pH value of the liquid to be inspected, the output from the pH detection device can be finally obtained stably.

Next, the operation of the pH detecting apparatus of the present embodiment constructed as described above will be explained. First, when each electrode is immersed in a liquid, a potential difference is generated between the reference electrode 21 and the first electrode 20. Since a certain constant voltage is applied between the source electrode and the drain electrode of the first field effect transistor 24 to which the first electrode 20 is connected, the reference electrode 21 corresponding to the pH value of the liquid is applied. First
The drain current I1 flows through the first field effect transistor 24 due to the potential difference between the electrodes 20 of the two. At this time, the first
The voltage V1 represented by I1R is output to the point a in the subsequent stage of the current-voltage converter 28. On the other hand, the reference electrode 21 and the second
Another potential difference is generated between the electrodes 22 of. Second electrode 2
2 is connected between the source electrode and the drain electrode of the second field effect transistor 26 to which the first electrode 20 is connected, and applied between the source electrode and the drain electrode of the first field effect transistor 24 to which the first electrode 20 is connected. The same voltage as the voltage applied is applied. As a result, the drain current I2 flows through the field effect transistor 26.

At this time, the voltage V2 represented by I2R is output to the point b in the subsequent stage of the second current-voltage converter 30. First current-voltage converter 28 and second current-voltage converter 3
The differential amplifier 32 connected to the subsequent stage of 0 functions to compare the voltages V1 and V2 generated at the points a and b in FIG. As shown in the figure, if the resistance values R1 connected to the front and rear stages of the differential amplifier 32 are the same, the voltage V0 output to the rear stage of the differential amplifier 32 is V1-V2 = (I1-I2) R. Is equal to In this way, the voltage V0 corresponding to the pH value of the liquid is output from the pH detecting device.

As mentioned above, the detection of the pH value of the liquid is
Since it is performed by differentially detecting the potential difference between two types of electrodes having different sensitivity characteristics to H ⁺ ions, even if the actual potential of the platinum electrode that functions as the reference electrode fluctuates, the pH value of the obtained liquid will not change. Corresponding output is stable. That is, the accurate pH value of the liquid can be continuously detected without using a reference electrode that generates a certain potential such as an Ag / AgCl electrode.

The second electrode 22 need not be made of a conductor insensitive to H ⁺ ions, but may be made of a conductor sensitive to H ⁺ ions which causes a potential difference of the opposite polarity to the first electrode 20. It may be an electrode.

[0014]

As is clear from the above description, according to the pH detecting device of the present invention, it is easy to handle without causing any trouble in continuous use, and Ag / A
It is possible to detect the accurate pH value of a liquid without using a reference electrode such as a gCl electrode that generates a predetermined potential. Furthermore, it is possible to reduce the size because it is based on a field effect transistor that applies semiconductor technology. Thus, a high speed response to a change in pH can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing an electrical configuration of a pH detection device of the present invention.

[Explanation of symbols]

 20 1st electrode 21 Reference electrode 22 2nd electrode 24 1st field effect transistor 26 2nd field effect transistor 28 1st current voltage converter 30 2nd current voltage converter 32 Differential amplifier

Claims (1)

[Claims] 1. A pH detection device for detecting the pH value of a liquid by sensing the concentration of H ⁺ ions in the liquid, comprising two types of electrodes installed in the liquid and having different sensitivity characteristics to H ⁺ ions. And a control unit that detects a potential difference generated between the two types of electrodes and determines the pH value of the liquid based on the detected potential difference.