JP3100477B2 - High input impedance voltage measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage measuring apparatus for measuring a voltage of a signal source having a high internal impedance.

[0002]

2. Description of the Related Art Conventionally, the following apparatus has been used for measuring the voltage of a signal source having a high internal impedance, such as an ion-sensitive electrode.

1) Voltage measuring device using negative feedback amplification An emitter or a source follower circuit using a transistor or a field effect transistor or a voltage follower circuit using an operational amplifier is provided at the first stage of an input circuit of a voltage amplifier. Voltage measuring device with high input resistance.

This is because a low-frequency filtering circuit is provided in the input circuit of the voltmeter in order to separate the voltage of the signal source from the noise voltage due to the external electric field, so that the input resistance becomes high but the impedance is very low. Output response speed is slow.

[0005] 2) A high input impedance voltage measuring circuit for eliminating current caused by stray capacitance and leakage resistance of a conductor connecting a signal source to an input terminal of the voltage measuring circuit. This is Volte
The conductor connecting the input terminal of the operational amplifier and the signal source forming the follower circuit is double covered with a conductor tube or conductor network,
The inner conductor tube or conductor network is connected to the output of the operational amplifier, the outer conductor tube or conductor network is grounded,
Even if there is stray capacitance or leakage resistance in the conductor connecting the signal source and the input end, the conductor tube or conductor network covering it has the same potential as the conductor, so there is no leakage current and the high input impedance It becomes possible to measure the voltage of the dance.

However, when the impedance of the signal source becomes high, the operating point of the input circuit flows to the positive or negative power supply voltage, and it becomes impossible to measure the voltage.

3) An emitter or source-follower circuit using a transistor or a field-effect transistor or a voltage follower circuit using an operational amplifier is provided at the first stage of a voltage amplifier, and a mechanically oscillating electrode plate is connected to the input terminal of the circuit. And a signal source connected to an electrode plate facing the electrode plate.

[0008] This is because a high voltage is induced when the vibrating electrode approaches the signal electrode, and a low voltage is induced at the input terminal of the voltage amplifying circuit when the vibrating electrode moves away from the signal electrode. It is possible to manufacture a high voltage measuring device.

However, since the stray capacitance and leakage current of the conductor from the signal source to the voltage measuring circuit cannot be removed, there is a disadvantage that the response speed is slow.

[0010]

When the ion concentration in an aqueous solution is measured by the voltage generated between the interface between the ion selective membrane immersed in the aqueous solution and the solution, for example, in the case of a pH meter, the ion concentration between the glass and the aqueous solution is measured. A voltage measuring instrument having an input resistance sufficiently higher than the resistance of the glass is required to measure the voltage generated in the glass through the resistance of the glass. Therefore, under the present circumstances, the resistance value of the glass is reduced by reducing the thickness of the glass as much as possible and expanding the area thereof so as to match the input resistance of the voltage measuring device that can be manufactured.

That is, when the ion selective membrane is an insulator, the size of the ion sensitive portion cannot be reduced because it is limited by the input resistance of the amplifier used for voltage detection.

An object of the present invention is to increase the input impedance of a voltage measuring circuit required for miniaturizing an ion sensitive section.

[0013]

Means for Solving the Problems Two voltage detection circuits which are electrically equivalent to each other are arranged, and one of the detection circuits has an electrode 60 to be measured and an input terminal of the detection circuit connected by a conductor 56, and the conductor 56 Is double covered with a conductor tube or conductor, the outer conductor tube or conductor 58 is grounded, the inner conductor tube or conductor 57 near the conductor 56 is connected to the input terminal of the other voltage detection circuit, and the input terminal Constitutes a circuit connected to the output terminal of the differential amplifier 55 that amplifies the difference between the output voltages of the two detection circuits, thereby achieving high input impedance.

[0014]

According to the present invention, even if the input impedance of the voltage measuring device becomes a high value inherent to the circuit, the response speed is fast, and the impedance of the signal source to be measured is high, The operating point of the voltage measurement circuit can be measured stably without flowing.

[0015]

【Example】

Embodiment 1 FIG. 1 shows the detection of the voltage of a conventional ion-sensitive electrode in which an ion-sensitive section (ion-sensitive electrode) and a voltage measuring section are separated, the determination of a live line in electric work and the activity in a crane work. An embodiment used for detecting an electric field such as a warning of approaching a line and detecting static electricity will be described.

By controlling the voltage between the source and the drain of the field effect transistors 1 and 28 and the source current to constant values, the voltage change between the gate and the ground can be reduced.
Two circuits are provided which convert the voltage into a voltage change between the ground and the ground and output the same. One circuit has a probe for measuring the voltage or electric field, and the probe 60 and the gate of the field effect transistor 1 are connected. The conductors are connected by conductors 56, the conductors are doubly covered by a conductor tube or conductor network, the outer conductor tube or conductor network 58 is grounded, and the inner conductor tube or conductor network 57 near conductor 56 is The gate of the circuit is connected to the gate of the field effect transistor 28, and the gate is connected to the output terminal of the differential amplifier 55 for amplifying the output voltage difference between the two circuits. Since the gates of the field effect transistors 1 and 28 are controlled by the differential amplifier 55 so as to be equal to each other, a conductor 56 connecting the electrode to be measured and the gate of the field effect transistor 1 and an inner portion covering the conductor are provided. The potential of the conductor tube or the conductor 57 becomes equal, the leakage current due to the stray capacitance and the leakage resistance of the covered conductor is canceled, and the input impedance seen from the measuring probe 60 becomes the input impedance specific to the measurement circuit. -Dance and get very high. FIG. 2 shows a method of measuring the input impedance of the voltage measurement circuit of the present invention shown in FIG. 1 when the input of the voltage measurement circuit is viewed from the measurement probe 60. A coupling capacitor is connected between the measurement probe 60 and the output terminal of the low-frequency oscillator, and a ratio (voltage amplification) of the output voltage Vo1 when the capacitor is inserted and when the capacitor is not inserted.
Is obtained for the capacitance value of the capacitor, and the result is shown in FIG. In FIG. 3, when the capacitance of the capacitor coincides with the capacitance between the gate and source of the transistor 1 used, the voltage amplification becomes half at a value of 6 pF,
This shows that the input impedance of this voltage measuring circuit is determined only by the capacitance between the gate and source of the transistor 1.

Embodiment 2 FIG. 4 shows an application example to an ion sensor in which a voltage measuring probe and an ion-sensitive electrode are integrated. Only the measurement probe 60 is exposed, this is used as an ion-sensitive electrode, an ion-selective film 61 is formed on the conductor surface thereof, immersed in an aqueous solution, and the interface voltage generated between the ion-selective film and the aqueous solution is measured. In the case of measurement, sufficient measurement is possible even if the area of the probe surface for pH measurement covered with a tantalum pentoxide film having a thickness of 0.2 μm is 6 × 10 ⁻² mm ² .

[0018]

The input impedance of the voltage measuring circuit is a high impedance inherent to the circuit, and the operating point of the voltage measuring circuit is stable without flowing, and the voltage of a signal source having a high impedance can be measured. As a result, the size of the ion-sensitive electrode using the insulating ion selective membrane can be reduced.

[0019]

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a voltage measuring circuit having a high input impedance and a sectional view of a measuring probe.

FIG. 2 is a diagram illustrating a method of measuring the input impedance of a voltage measurement circuit.

FIG. 3 is a result of an experiment for estimating an input impedance of a voltage measurement circuit.

FIG. 4 is a diagram showing a structure of an ion-sensitive electrode.

[Explanation of symbols]

 1, 28 field effect transistor 2, 29 transistor 3, 30 resistor 4, 31 transistor 5, 32 operational amplifier 6, 33 operational amplifier 7, 34 operational amplifier 8, 35 resistor 9, 36 resistor 10, 37 resistor 11, 38 resistor 12 , 39 Resistance 13, 40 Transistor 14, 41 Zener Diode 15, 42 Zener Diode 16, 43 Transistor 17, 44 Resistance 18, 45 Operational Amplifier 19, 46 Operational Amplifier 20, 47 Resistance 21, 48 Resistance 22 , 49 Resistance 23, 50 Resistance 24, 51 Zener diode 25, 52 Resistance 26, 53 Resistance 27, 54 Zener diode 55 Operational amplifier 56 Coaxial core conductor for voltage measurement 57 Coaxial inner conductor 58 Coaxial outer conductor 59 Insulator 60 Probe for measurement 61 Ion selective membrane 62 Potassium chloride water Liquid 63 solution exchange opening

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiko Kojima 4-75-3, Kamiida Kitamachi, Kita-ku, Nagoya-shi, Aichi 2-411 Kamiiida 2nd complex 2-411 (72) Inventor Mitsuru Tsutohito Sanno, Nakagawa-ku, Nagoya-shi, Aichi Prefecture 1-5-5-25 (56) References Shigeyo Morinaga and four others, “Ion Sensitivity Measurement Circuit for ISFET”, Nagoya City Industrial Research Institute Research Report No. 76, p. 14-17 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 19/00-19/32 G01N 27/416

Claims (1)

(57) [Claims] An electric voltage detection circuit is provided. One of the detection circuits has an electrode to be measured (60) and an input terminal of the detection circuit connected by a conductor (56). 56) is doubly covered with a conductor tube or conductor, the outer conductor tube or conductor (58) is grounded, and the inner conductor tube or conductor (57) near the conductor (56) is the input of the other voltage detection circuit. A voltage measuring device, characterized in that it is connected to a terminal and an input terminal thereof is connected to an output terminal of a differential amplifier (55) for amplifying a difference between output voltages of the two detection circuits.