JPH08220161A - Detecting device of capacitance and sensor using the device - Google Patents

Abstract

PURPOSE: To obtain a detecting device of capacitance to execute a stable measurement even when a high frequency is used and enabling highly-accurate detection of a change in a very small amount of capacitance, such as a floating capacity, and also a sensor to which the detecting device of capacitance is applied, by using a simple circuit structure. CONSTITUTION: This device is equipped with an oscillating means 102 for oscillating a rectangular wave of a prescribed frequency, a two-input logical operation means 105 and first and second resistors 103 and 104 connected in series between an output end of the oscillating means 102 and one and the other inputs of the two-input logical operation means 105 respectively and having the same characteristics. A terminal 111 to be measured is connected to one or the other input of the two-input logical operation means 105 and a change in capacitance 115 (Cp) in the terminal 111 to be measured is detected on the basis of a change in an output voltage of the two-input logical operation means 105.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance detecting device and a sensor using the same, and in particular, a simple circuit structure enables stable measurement even when a high frequency is used. By applying a capacitance detecting device capable of detecting a change in capacitance with high accuracy, and applying the capacitance detecting device to, for example, a liquid level sensor, a small amount of stray capacitance can be stably obtained even when a high frequency is used. The present invention relates to a sensor capable of detecting a change in capacitance such as, and reliably recognizing the position of a terminal to be measured.

[0002]

2. Description of the Related Art Conventionally, in the clinical field, human serum, urine, etc. have been used as measurement targets (hereinafter referred to as "samples") to react with various reagents to chemically analyze the reaction state and measure various items. An automatic chemical analyzer used for diagnosis is known.
This automatic chemical analyzer is equipped with, for example, a biosensor, an ion sensor, etc., and measures various items.

In such an automatic chemical analyzer, there are various techniques indispensable for automating the measuring operation.
One of them is that the probe (suction needle) is inserted into the test tube containing the sample, the liquid level of the sample is detected, and the probe does not move too much to damage the test tube or the device. In order to prevent carry-over due to dirt on the tip, there is a technique to set the probe at a fixed position in the test tube from the liquid level. At this time, the detection of the probe touching the liquid surface is performed by the liquid surface sensor.

Conventionally, in the automatic chemical analyzer, for example, a capacitance type liquid level sensor has been used as the liquid level sensor. The principle of liquid level detection in this capacitance type liquid level sensor is to provide a capacitance detection unit (capacitance detection device) at the tip of the probe to recognize changes in the detected capacitance. That is, when the liquid level sensor's capacitance detector (the tip of a metal probe, etc.) touches the liquid level of the sample from the air,
It recognizes that the capacitance detected by the stray capacitance of the liquid changes significantly and recognizes that the probe has touched the liquid surface.

Some liquid level sensors have two probes and detect the current between the two probes to recognize that the probes have touched the liquid level. Since the capacitance type liquid level sensor can be constituted by one probe, it has an advantage that the volume of the detecting portion is smaller than that of the two probe type sensor and detection in a narrower space is possible. . Especially, in recent automatic chemical analyzers, many of the test tubes provided inside have a small diameter, and a capacitance type liquid level sensor having a small detection unit volume is effective.

In a capacitance type liquid level sensor, as a capacitance detecting device for recognizing a change in the detected capacitance, there is a conventional one using an operational amplifier, for example, a capacitance multiplier system or a bridge. A circuit configuration is widely used. In addition to this, there are known methods such as capturing a change in oscillation frequency or phase and detecting a change in capacitance by an oscillation circuit using capacitance.

The basic circuit configuration of a device using an operational amplifier is to measure the capacitance change of the electrostatic capacitance (corresponding to the electrostatic capacitance at the probe tip) connected to one input of the operational amplifier.
Recognize by the voltage change amplified by the operational amplifier,
Alternatively, it is recognized by a change in the oscillation frequency.

Normally, the capacitance type liquid level sensor used in an automatic chemical analyzer or the like targets a stray capacitance generated in a probe, which is a very small capacitance value.
Generally, in the capacity detection, the smaller the capacity, the more accurate the measurement using a high frequency is in order to obtain a certain accuracy or more.

On the other hand, many operational amplifiers handle frequencies of about several tens [kHz] or less, and the operation of this ordinary operational amplifier becomes unstable at high frequencies due to its own frequency characteristic restriction. A high-speed operational amplifier that operates stably even at a high frequency can be used, but it is expensive and has a large effect on the product cost.

[0010]

As described above, in the electrostatic capacitance detecting device using the conventional operational amplifier, it is necessary to detect a minute capacitance by using high frequency, and stable operation at high frequency is required. Due to the request for guarantee, there is a problem that a high-speed operational amplifier is used to increase the product cost, or a correction circuit and the like are required to complicate the circuit configuration of the product. Further, even if a sensor such as a liquid level sensor using this capacitance detecting device is reached, the same problem occurs.

The present invention has been made in view of the above problems of the prior art. With a simple circuit structure, stable measurement is possible even when a high frequency is used, and static electricity such as a small amount of stray capacitance is generated. It is an object of the present invention to provide a capacitance detection device capable of detecting a change in capacitance with high accuracy.

Another object of the present invention is to apply the electrostatic capacity detection device proposed in the present invention to a liquid level sensor or the like so that even if a high frequency is used, a small amount of stray capacitance or the like can be stably obtained. It is an object of the present invention to provide a sensor capable of detecting a change in electrostatic capacitance and reliably recognizing a position of a terminal to be measured.

[0013]

In order to solve the above-mentioned problems, an electrostatic capacitance detection device according to claim 1 of the present invention comprises an oscillating means for oscillating a rectangular wave of a constant frequency, and a 2-input logical operation means. A first resistor and a second resistor, which are connected in series between the output end of the oscillating means and one input and the other input of the two-input logical operation means, and have the same characteristics as each other, A terminal to be measured is connected to one or other inputs of the two-input logical operation means, and a change in capacitance at the terminal to be measured is detected based on a change in output voltage of the two-input logical operation means. is there.

According to a second aspect of the present invention, there is provided the electrostatic capacitance detecting device according to the first aspect, wherein:
First and second inverter circuits having the same characteristics as each other are provided between one and the other inputs of the input logic operation means and the first and second resistors, respectively.

According to a third aspect of the present invention, there is provided the electrostatic capacitance detection device according to the first or second aspect, wherein the two-input logical operation means or the first and second inverter circuits is C. -It is composed of a MOS integrated circuit and has a hysteresis characteristic.

According to a fourth aspect of the present invention, there is provided the capacitance detecting device according to the first, second or third aspect, wherein the first and second inverter circuits are formed on the same chip. It is a thing.

A sensor according to a fifth aspect comprises the capacitance detecting device according to the first, second, third or fourth aspect,
When the terminal to be measured is brought close to the liquid surface of the liquid or the surface of the article, the terminal to be measured is set to the liquid surface or the surface of the article based on a change in capacitance obtained by the capacitance detection device. It is to detect that the surface has come close to a predetermined distance or that the liquid surface or the surface is touched.

[0018]

In the electrostatic capacitance detecting device according to the first aspect of the present invention, the oscillating means oscillates a rectangular wave having a constant frequency,
And the second input and the second input, and is supplied between one input of the two-input logical operation means and the other input, respectively. One or the other input of the 2-input logical operation means is connected to the terminal to be measured,
A voltage having a phase delayed by a delay time determined by the first or second resistance and the capacitance applied to the terminal to be measured is applied to one of the two-input logical operation means.

By the logical operation of the 2-input logical operation means, 2
An output waveform having a pulse width corresponding to the phase difference between the two inputs is obtained, and based on the change in the output voltage of the 2-input logical operation means, for example, the integrated value of the output voltage, the stray capacitance or the like applied to the measured terminal is measured. It is possible to detect a change in capacitance. By using the first and second resistors having the same characteristics as each other, the output voltage of the two-input logical operation means can be changed only by the change in the capacitance applied to the measured terminal, Higher precision detection is possible.

Further, in the electrostatic capacity detecting device according to the second or third aspect, it is preferable that the two-input logical operation means is composed of a C-MOS integrated circuit and has a hysteresis characteristic. That is, when detecting the electrostatic capacitance such as the stray capacitance applied to the terminal to be measured, the terminal to be measured is in an electrically floating state, and is high in order to detect minute changes in the input with high accuracy. C-MOS with input impedance
It is desirable to use integrated circuit devices. Moreover, since the input voltage waveform is a voltage waveform integrated by the first or second resistance and the electrostatic capacitance, it is desirable to use one having a hysteresis characteristic.

Further, in the electrostatic capacitance detecting device according to the second or third aspect, one input and the other input of the two-input logical operation means and the first and second resistors have the same characteristics, respectively. It is also possible to adopt a configuration including the first and second inverter circuits including the above, the first and the second inverter circuits including C-MOS integrated circuits, and the one including the hysteresis characteristic.

Further, in the electrostatic capacitance detection device according to the fourth aspect, it is desirable that the first and second inverter circuits are formed on the same chip. By this,
Since the manufacturing process is the same, it is possible to further reduce characteristic variations such as input characteristics and temperature drift.
Higher precision detection is possible. For example, the first and second
Since the input capacitances of the inverter circuits are almost the same since they are in the same process, the influences of these input capacitances are canceled out, and the output voltage of the 2-input logical operation means is changed only by the change in the capacitance applied to the measured terminal. Therefore, it is possible to perform detection with higher accuracy.

Further, a sensor according to a fifth aspect is configured by including the capacitance detecting device according to the first, second, third or fourth aspect, and a measured terminal is provided for a liquid surface of a liquid or a surface of an article. When approaching, it is detected that the measured terminal is close to the liquid surface or surface for a predetermined distance or touches the liquid surface or surface based on the change in the electrostatic capacity obtained by the electrostatic capacity detection device. I am trying to do it. With this, the liquid level or the distance to the surface can be sequentially detected along with the movement of the terminal to be measured.
By using the electrostatic capacitance detection device described in 3 or 4, it is possible to stably detect a small change in electrostatic capacitance such as a stray capacitance even when a high frequency is used, and to reliably recognize the position of the measured terminal. The sensor to obtain can be realized.

[0024]

Embodiments of the electrostatic capacitance detection device of the present invention and a sensor using the same will be described below in detail with reference to the drawings.

[Embodiment 1] FIG. 1 is a configuration diagram of an electrostatic capacitance detection device according to Embodiment 1 of the present invention and an electrostatic capacitance type liquid level sensor using the same.

In the figure, a capacitance detecting device 101 of this embodiment is a crystal oscillator (oscillating means in claims).
102, a first resistor 103, a second resistor 104, a 2-input exclusive OR gate circuit (2-input logical operation means) 105, a processing unit 106, and a probe (terminal to be measured) 111. The measurement target (capacitance) of the capacitance detection device 101 is the stray capacitance 115 (Cp) applied to the probe 111, and hereinafter, the capacitance of the measurement target is described as the stray capacitance 115 (Cp). .

FIG. 1 also shows the configuration of a capacitance type liquid level sensor using the capacitance detecting device 101. The capacitance type liquid level sensor includes a capacitance detecting device 101 and a judging section. And 121.

In the present embodiment, a crystal oscillator is used as the oscillating means from the viewpoint of miniaturization of the device, but it is not limited to this. The first resistor 103 and the second resistor 104 have the same characteristics.

Further, although the 2-input exclusive OR gate circuit 105 is used as the 2-input logical operation means, it is not limited to this, and AND, OR, NAND, N.
It is also possible to use a gate circuit such as an OR. However, when using the exclusive OR operation element, it is possible to recognize the rising and falling points of the signal separately, which is more efficient than other logical operation elements.

It is desirable that the 2-input logical operation means (2-input exclusive OR gate circuit 105) is composed of a C-MOS integrated circuit and has a hysteresis characteristic.

This is because when the stray capacitance 115 (Cp) applied to the probe 111 is detected, the probe 111 is
Is in an electrically floating state, and in order to detect a minute change in the input voltage of the two-input exclusive OR gate circuit 105 with high accuracy, CM having a high input impedance is used.
This is because it is desirable to use the elements of the OS integrated circuit.

The voltage waveform input to the 2-input logical operation means is the second resistor 104 (R) and the stray capacitance 115.
This is because a voltage waveform integrated with (Cp) is obtained, and therefore it is desirable to use one having a hysteresis characteristic in order to guarantee a reliable logical operation.

The processing unit 106 is, for example, an integrating circuit,
The output waveform having a pulse width corresponding to the phase difference between the two inputs obtained by the exclusive OR operation of the two-input exclusive OR gate circuit 105 is integrated, and the phase difference is processed into a voltage value. is there. That is, the voltage value becomes a physical quantity corresponding to the change in the stray capacitance 115 (Cp) applied to the probe 111.

Further, the electrostatic capacitance detection device 101 of this embodiment
Can be used to configure a capacitance type liquid level sensor. The capacitance type liquid level sensor changes the capacitance obtained by the capacitance detection device 101 when the probe 111 is brought close to the liquid level of the sample (serum, urine, etc.) 113 in the container 112. Based on the above, it is detected that the probe 111 has approached the liquid surface to a predetermined distance or has touched the liquid surface. That is, the determination unit 121 is
Probe 11 based on the integrated value and the like obtained by
The change in the stray capacitance 115 (Cp) associated with 1 is determined.

Next, the electrostatic capacitance detection device 101 of this embodiment
The operation will be described in detail with reference to the timing chart shown in FIG.

FIG. 2A shows a connection node A between the first resistor 103 and one input of the 2-input exclusive OR gate circuit 105.
Is also the waveform of the reference signal input from the crystal oscillator 102. 2B shows a voltage waveform of the connection node B between the second resistor 104 and the other input of the 2-input exclusive OR gate circuit 105, and the connection node B is a stray capacitance 115 applied to the probe 111. It is also the connection node of.

Therefore, the voltage waveform at the connection node B in FIG. 2B has a phase delayed from the voltage waveform at the connection node A in FIG. 2A by the delay time td. That is, the signal at the connection node B becomes a voltage waveform integrated by the integrating circuit formed by the second resistor 104 (R) and the stray capacitance 115 (Cp), and the 2-input exclusive OR gate circuit 105
The threshold value (switching from "L" level to "H" level) at the input of is delayed by the time td. Here, the delay time td is determined by the resistance value R of the second resistor 104 and the capacitance value Cp of the stray capacitance 115.

Further, FIG. 2C shows a voltage waveform of the output node C of the 2-input exclusive OR gate circuit 105, which is obtained by performing an exclusive OR with the above two signals as inputs. In this way, at the output of the 2-input exclusive OR gate circuit 105, a rectangular wave signal having a pulse width corresponding to the phase difference between the two inputs, that is, the delay time td is obtained.

As described above, in the electrostatic capacitance detection device 101 of this embodiment, the crystal oscillator 102, the first resistor 103, the second resistor 104, and the two-input exclusive OR gate circuit 105.
This embodiment is realized by a simple circuit structure provided with, and a capacitance detecting device using a conventional operational amplifier becomes unstable in operation at high frequencies, whereas this embodiment uses an element with low frequency dependence. With this, stable measurement is possible even when a high frequency is used, and it is possible to detect changes in electrostatic capacitance such as a small amount of stray capacitance with high accuracy.

Further, by applying the electrostatic capacitance detection device 101 to a liquid level sensor, even when a high frequency is used, it is possible to stably detect a slight change in electrostatic capacitance such as a stray capacitance, and to reliably detect the capacitance. A sensor that can recognize the position of the measurement terminal can be realized.

[Embodiment 2] FIG. 3 is a block diagram of a capacitance detecting device according to Embodiment 2 of the present invention.

The electrostatic capacitance detection device of this embodiment is different from that of the first embodiment in that one input and the other input of the two-input exclusive OR gate circuit 305, the first resistor 103 and the second resistor 10 are provided.
4, a first inverter circuit 307 and a second inverter circuit 308 having the same characteristics as each other are provided, and the first inverter circuit 307 and the second inverter circuit 308 are configured by a C-MOS integrated circuit, The point is that one having a hysteresis characteristic is used, and that the two-input exclusive-OR gate circuit 305 is composed of a C-MOS integrated circuit and there is no restriction to have a hysteresis characteristic.

When the first inverter circuit 307 and the second inverter circuit 308 are realized by an integrated circuit, it is desirable to use those formed on the same chip. This is because the manufacturing process is the same, it is possible to further reduce characteristic variations such as input characteristics and temperature drift, and it is possible to perform detection with higher accuracy.

The other components, the operation and effect of the capacitance detecting device of this embodiment are the same as those of the first embodiment.

[0045]

As described above, claim 1 of the present invention
According to the electrostatic capacitance detection device of the present invention, the oscillating means oscillates a rectangular wave having a constant frequency, and the rectifying wave is generated between the one input and the other input of the two-input logical operation means via the first and second resistors. A voltage having a phase delayed by a delay time determined by the first or second resistance and the electrostatic capacitance such as the stray capacitance applied to the terminal to be measured is applied to one of the two-input logical operation means, Since the output waveform having the pulse width corresponding to the phase difference between the two inputs is obtained by the logical operation of the 2-input logical operation means, the change of the output voltage of the 2-input logical operation means, for example, the integrated value of the output voltage It is possible to detect the change of electrostatic capacitance such as stray capacitance applied to the terminal to be measured based on the above. Also, by using the first and second resistors of the same characteristics, two inputs The output voltage of the logic operation means It can only be changed by the change in the electrostatic capacitance, such as mowing the stray capacitance, thereby enabling more accurate detection.

Generally, in order to obtain a certain degree of accuracy,
The smaller the capacitance of the object to be measured is, the more advantageous the measurement using the high frequency is. However, according to the capacitance detection device according to claim 1 of the present invention, the measurement is stable even when the high frequency is used. Therefore, it is possible to provide an electrostatic capacitance detection device having a simple circuit structure, which can detect a change in electrostatic capacitance such as a small amount of stray capacitance with high accuracy.

Further, according to the capacitance detecting device of the second or third aspect, since the 2-input logical operation means is composed of the C-MOS integrated circuit and the one having the hysteresis characteristic is used, Even if the input voltage waveform of the input logic operation means is a voltage waveform integrated by the first or second resistance and the capacitance to be measured, a reliable logic operation is possible and electrically floating. It is possible to provide an electrostatic capacitance detection device that can detect even a small amount of change in electrostatic capacitance with high accuracy.

Further, according to the capacitance detecting device of the second or third aspect, one input and the other input of the two-input logical operation means and the first and second resistors are mutually connected. The first and second inverter circuits having the same characteristics are provided, and the first and second inverter circuits are C-MO.
Since an S integrated circuit having hysteresis characteristics is used, the input voltage waveform of the 2-input logical operation means is integrated by the first or second resistance and the capacitance to be measured. It is possible to perform a reliable logical operation even with a different voltage waveform, and it is possible to detect even a small change in the electrostatic capacitance that has strayed electrically with high accuracy, and it is stable even when a high frequency is used. It is possible to provide a capacitance detection device that can perform measurement.

Further, according to the capacitance detecting device of the fourth aspect, since the first and second inverter circuits are formed on the same chip, the input characteristic and the temperature drift are not generated. It is possible to further reduce variations in characteristics such as, and it is possible to perform detection with higher accuracy.

According to a fifth aspect of the present invention, the sensor according to the first aspect, the second aspect, the third aspect, or the fourth aspect of the present invention is provided with the capacitance detecting device, and the liquid level of the liquid or the surface of the article is measured. When the terminals are brought close to each other, the measured terminal has come close to the liquid surface or the surface by a predetermined distance or touches the liquid surface or the surface based on the change in the electrostatic capacity obtained by the electrostatic capacity detection device. Is detected, the liquid surface or the distance to the surface can be sequentially detected along with the movement of the terminal to be measured.
By using the described capacitance detection device, a sensor that can stably detect a small change in capacitance such as a stray capacitance even when a high frequency is used and can reliably recognize the position of the terminal to be measured is provided. Can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a capacitance detection device according to a first embodiment of the present invention and a capacitance type liquid level sensor using the same.

FIG. 2 is a timing chart illustrating the operation of the electrostatic capacitance detection device according to the first exemplary embodiment.

FIG. 3 is a configuration diagram of a capacitance detection device according to a second embodiment of the present invention.

[Explanation of symbols]

101 Capacitance Detection Device 102 Crystal Oscillator (Oscillation Means) 103 First Resistor (R) 104 Second Resistance (R) 105,305 2 Input Exclusive OR Gate Circuit (2 Input Logical Operation Means) 106 Processing Unit 307 1 Interface Circuit 308 Second Interface Circuit 111 Probe (Terminal to be Measured) 112 Container 113 Sample 115 Stray Capacitance (Cp) on Probe 121 Judgment Unit

Claims (5)

[Claims] 1. An oscillating means for oscillating a rectangular wave having a constant frequency, a two-input logical operation means, and an output terminal of the oscillating means and one input and the other input of the two-input logical operation means, respectively. First connected in series and having the same characteristics as each other
And a second resistor, the measured terminal is connected to one or the other inputs of the two-input logical operation means, and the measured terminal is based on the change of the output voltage of the two-input logical operation means. An electrostatic capacitance detection device, which detects a change in electrostatic capacitance in the. 2. A first and a second inverter circuit having mutually the same characteristics are provided between one input and the other input of the two-input logical operation means and the first and second resistors, respectively. The electrostatic capacitance detection device according to claim 1, wherein: 3. The two-input logical operation means or the first
3. The electrostatic capacitance detection device according to claim 1, wherein the second inverter circuit is composed of a C-MOS integrated circuit and has a hysteresis characteristic. 4. The first and second inverter circuits,
The electrostatic capacitance detection device according to claim 1, wherein the electrostatic capacitance detection device is formed on the same chip. 5. The electrostatic capacitance detecting device according to claim 1, 2, 3 or 4, wherein the electrostatic capacitance is provided when the measured terminal is brought closer to a liquid surface of a liquid or a surface of an article. Detecting that the terminal to be measured comes close to the liquid surface or the surface to a predetermined distance, or that the liquid surface or the surface is touched, based on the change in the capacitance obtained by the capacitance detection device. Characteristic sensor.