JPH08271556A - Capacitive sensor - Google Patents

Abstract

PURPOSE: To determine surely that a terminal to be measured has touched a liquid level by determining the variation rate of capacitance being applied to a measuring terminal to be detected from a capacitance detector using a differentiation circuit and then making a decision based on the determination results from the differentiation circuit using a comparator. CONSTITUTION: When a stray capacity 114 (Cp) of a probe 121 is detected, the probe 323 is floated electrically and the voltage being fed to a two-input exclusive OR gate 115 has a waveform integrated through a resistor 112 (R) and the stray capacity 114 (Cp). An integration circuit 116 integrates the output waveform having pulse width corresponding to the phase difference between two inputs obtained from the gate 115 through exclusive OR operation and transforms the phase difference into a voltage value. Subsequently, a variable gain amplifier 102 amplifies the output from the circuit 116 with a gain being set variably and programmably and the integrated voltage waveform is differentiated by a differentiation circuit 103. Finally, a comparator 104 decides whether the differentiated voltage exceeds a predetermined reference voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type sensor, and more particularly, to a capacitance type sensor which is installed when a terminal to be measured is brought close to a liquid surface of a liquid or a surface of an article. The present invention relates to a capacitance type sensor capable of surely recognizing an object to be measured from a change in capacitance applied to a terminal to be measured, regardless of the structure of a device to be used and without being affected by an operator's human body or hand. .

[0002]

2. Description of the Related Art Conventionally, in the clinical field, human blood serum, urine, etc. have been used as a measurement target (hereinafter referred to as a sample), reacted with various reagents to analyze the reaction state, and various items have been measured for diagnostic use. Automatic analyzers are known. This automatic analyzer is equipped with, for example, a biosensor, an ion sensor, an absorbance measuring sensor, etc., and measures various items.

In such an automatic analyzer, there are various techniques indispensable for automating the measurement operation. One of them is to insert a probe (suction needle) into a test tube containing a sample. Detecting the liquid level, without moving the probe too much and damaging the test tube or equipment,
In addition, there is a technique to set the probe at a fixed position in the test tube from the liquid level in order to prevent carryover due to dirt on the probe tip. At this time, the detection of the probe touching the liquid surface is performed by the liquid surface sensor.

Conventionally, a liquid level sensor having, for example, two probes is known as a liquid level sensor in an automatic analyzer. The two-probe liquid level sensor detects a minute current flowing between the two probes and recognizes that the probe has reached the liquid level. However, since this liquid level sensor requires two probes, some test tubes cannot be inserted depending on the diameter of the test tube, and there is a problem that it cannot be applied to a test tube having such a small diameter. there were.

Especially, in the automatic analyzer, the amount of the sample to be handled is small because the sample in the test tube is redistributed and analyzed.
In addition, test tubes with smaller diameters are often used due to demands for downsizing of the device. In such an automatic analyzer, in addition to the external two-probe liquid level sensor, one internal A probe type liquid level sensor is required, and there is a problem that the cost of the design and the device increases.

As the liquid level sensor of the one-probe type, for example, a capacitance type liquid level sensor or the like is used. The principle of liquid level detection in this capacitance type liquid level sensor is to recognize a change in the detected capacitance by providing a capacitance detection unit for detecting the capacitance applied to the tip of the probe. 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.

However, in this capacitance type sensor, depending on the automatic analyzer in which the sensor is installed,
There is also a structure in which an object made of metal (for example, a lid or a wall) is provided around the path along which the probe of the capacitance type liquid level sensor moves. It was misrecognized by a metal object.

Even if the automatic analyzer does not have a structure including a metal object such as a lid or a wall as described above,
The capacitance type sensor applied to the test tube installed outside the automatic analyzer is easily affected by the human body or hand of the operator, and may be erroneously recognized.

[0009]

As described above, in the conventional two-probe liquid level sensor, there is a test tube in which the probe cannot be inserted depending on the diameter of the test tube. In particular, a test tube with a smaller diameter is often used inside the automatic analyzer. In such an automatic analyzer, in addition to the external two-probe liquid level sensor, However, there is a problem that a liquid level sensor of one probe type is required, the structure of the device becomes complicated, and the cost of the device increases.

Further, in the conventional capacitance type sensor, in the automatic analyzer in which the capacitance type sensor is installed,
There is a problem in that the capacitance type liquid level sensor has a structure in which a metal object is provided around the path along which the probe moves, and is erroneously recognized by the metal object.

Further, even if the automatic analyzer does not have the above-mentioned structure, in particular, in the case of the capacitance type sensor for the test tube provided outside the automatic analyzer, it is affected by the human body or hand of the operator. It was easy and there was a problem that it was erroneously recognized.

The present invention has been made in view of the above-mentioned conventional problems, and when the measured terminal is brought close to the liquid surface of the liquid or the surface of the article, the electrostatic capacitance type sensor Regardless of the structure of the device to be installed and without being affected by the human body or hand of the operator, it is possible to confirm that the measured terminal has touched the liquid surface or surface from the change in the capacitance applied to the measured terminal. It is an object of the present invention to provide a capacitance type sensor that can be surely recognized.

Another object of the present invention is to reduce the influence of the device structure in which the electrostatic capacitance type sensor is installed and to reliably recognize the object to be measured, and therefore, the design flexibility of the applied device or An object of the present invention is to provide a capacitive sensor capable of increasing the degree of freedom in combination of systems.

[0014]

In order to solve the above problems, an electrostatic capacitance type sensor according to claim 1 of the present invention comprises a capacitance detecting means for detecting a change in electrostatic capacitance applied to a terminal to be measured, A changing speed identifying means for identifying the changing speed of the electrostatic capacitance detected by the capacitance detecting means, and the changing speed identifying means for bringing the measured terminal close to the liquid surface of the liquid or the surface of the article. The determination means determines whether the measured terminal has touched the liquid surface or the surface based on the identification result.

The capacitance type sensor according to a second aspect is the capacitance type sensor according to the first aspect, wherein the capacitance type sensor has a gain with which the output of the capacitance detecting means can be variably set. It is equipped with a variable gain amplifier for amplification.

According to a third aspect of the present invention, there is provided the capacitance type sensor according to the first or second aspect, wherein the determining means is the liquid surface of the liquid or the surface of the article to be measured. When the terminals are brought close to each other, it is determined that the measured terminal has touched the liquid surface or the surface based on the identification result of the changing speed identification means and the output of the capacitance detection means or the variable gain amplifier. It is a thing.

The capacitance type sensor according to a fourth aspect is the capacitance type sensor according to the first, second or third aspect, wherein the capacitance detecting means is an oscillator that oscillates a rectangular wave of a constant frequency, A first logic operation circuit having a hysteresis characteristic, and a first logic operation circuit which is connected in series between an output end of the oscillator and one input and another input of the first logic operation circuit, and has the same characteristic as each other. And a second resistor, an integrating circuit that integrates the output of the first logical operation circuit, and a terminal to be measured that is connected to one or another input of the first logical operation circuit. Is equipped with a differentiating circuit.

The capacitance type sensor according to a fifth aspect is the capacitance type sensor according to the fourth aspect, wherein the determination means compares the output of the change speed identification means with a first reference voltage. It is provided with a first comparator.

Further, the capacitance type sensor according to a sixth aspect is the capacitance type sensor according to the fourth aspect, wherein the judging means compares the output of the changing speed identifying means with a first reference voltage. Logic of a first comparator, a second comparator for comparing the output of the capacitance detecting means or the variable gain amplifier with a second reference voltage, and an output of the first comparator and an output of the second comparator And a second logical operation circuit for performing an operation.

[0020]

In the capacitance type sensor according to the first aspect of the present invention, the rate of change of the capacitance applied to the measured terminal detected by the capacitance detection means is identified by the change rate identification means, and the determination means is provided. When the terminal to be measured is brought close to the liquid surface of the liquid or the surface of the article, it is determined whether the terminal to be measured touches the liquid surface or the surface based on the identification result of the changing speed identification means. ing.

The structure of the device in which the capacitance type sensor is installed, for example, the change in capacitance due to a metal object (eg, lid or wall) formed around the path along which the terminal to be measured moves, and the device. The change in the capacitance due to the human body or hand of the operator depends on the moving speed of the terminal to be measured or the operating speed of the person, and is generally a gentle change. The change in capacitance when the terminal comes into contact with the liquid surface or surface is sharp. Therefore, regarding the rate of change of the capacitance, whether the change in the capacitance is due to a metal object or the like formed around it, or due to contact with the liquid surface or the surface of the measured terminal, etc. If the determination means is provided with a reference for determination in advance, it is possible to determine by which factor the capacitance has changed.

As a result, when the terminal to be measured is brought closer to the liquid surface of the liquid or the surface of the article, the structure of the device in which the capacitance type sensor is installed, and the human body or hand of the operator, etc. Without being affected, it is possible to reliably recognize that the measured terminal has touched the liquid surface or the surface from the change in the capacitance applied to the measured terminal.

Further, in the electrostatic capacitance type sensor according to the second aspect, the output of the capacitance detecting means is amplified by a variable gain amplifier, for example, with a gain variably set programmable,
It is supplied to the determination means.

Depending on the position in the device where the capacitance sensor is installed, the structure of the device and the degree of influence of the human body or hand of the operator on the capacitance vary, and the liquid level of the measured terminal or The change in capacitance due to contact with the surface is also different. By variably setting the gain of the variable gain amplifier, for example, irrespective of the installation location of the capacitance sensor in the device, in other words, regardless of the metal object or the like installed near the moving path of the measured terminal. In addition, accurate sensing can be performed without malfunction, and as a result, the degree of freedom in device design can be increased.

Further, in the capacitance type sensor according to the third aspect, when the determination means brings the measured terminal close to the liquid surface of the liquid or the surface of the article, the identification result of the change speed identification means. Also, it is determined based on the output of the capacitance detecting means or the variable gain amplifier that the measured terminal has touched the liquid surface or the surface.

For example, when noise such as a hazard is present on the output of the capacitance detecting means or the variable gain amplifier, the noise is identified by the changing speed identifying means, and based on only the identification result of the changing speed identifying means. When making a determination, an erroneous determination will be made. By making a determination based on the output of the capacitance detecting means or the variable gain amplifier in addition to the identification result of the change speed identifying means, it is possible to eliminate such an erroneous determination due to noise, etc. It is possible to surely recognize.

Further, in the capacitance type sensor according to the fourth aspect, in the capacitance detecting means, the oscillator oscillates a rectangular wave of a constant frequency, and the first and second electrodes have the same characteristics.
And is supplied to one input and the other input of the first logical operation circuit having the hysteresis characteristic through the resistance of. One or the other input of the first logical operation circuit is connected to the terminal to be measured, and the input is delayed by a delay time determined by the first or second resistance and the capacitance applied to the terminal to be measured. A phase voltage will be applied. Further, the output of the first logical operation circuit is supplied to an integrating circuit for integration, and the result of the integration is supplied to a differentiating circuit in the change speed identifying means via the variable gain amplifier to be differentiated.

By the logical operation of the first logical operation circuit, an output waveform having a pulse width corresponding to the phase difference between the two inputs is obtained, and the output voltage of the first logical operation circuit is integrated to obtain a predetermined gain. By further differentiating the amplified voltage, it is possible to detect a change in electrostatic capacitance such as stray capacitance applied to the measured terminal. In other words, the change in capacitance due to the device structure or the human body or hand of the operator and the change in capacitance due to contact with the liquid surface or surface of the measured terminal are different, and this difference is the integrated voltage waveform. Of the differential voltage waveform, and by differentiating the integrated voltage waveform, the rate of change in capacitance appears as the peak value of the differential voltage waveform. Therefore, the determining means determines the peak value of the differential voltage waveform based on the peak value. ， It becomes possible to surely recognize the object to be measured.

By using the first and second resistors having the same characteristics as each other, the output voltage of the first logical operation circuit can be changed only by the change in the capacitance applied to the terminal to be measured. This makes it possible to detect with higher accuracy.

Further, in the capacitance type sensor according to claim 5, in the judging means, the output of the changing speed discriminating means is compared with the first reference voltage by the first comparator, and the judgment is made based on the comparison result. I am trying to do it.

For example, when the first comparator is added to the capacitance type sensor according to the fourth aspect, as described above, the capacitance change due to the influence of the device structure and the human body or hand of the operator. Is expressed as the peak value of the differential voltage waveform, and the peak value is different from the peak value based on the speed of capacitance change due to contact with the liquid surface or surface of the measured terminal. By setting the first reference voltage according to the characteristics based on and comparing the two, it is possible to surely recognize the object to be measured.

Further, in the capacitance type sensor according to claim 6, in the judging means, the output of the changing speed identifying means is compared with the first reference voltage by the first comparator, and by the second comparator, The output of the capacitance detecting means or the variable gain amplifier is compared with the second reference voltage, and the logical operation of the output of the first comparator and the output of the second comparator is performed by the second logical operation circuit to obtain the determination result. I am trying.

For example, when a first comparator and a second comparator are added to the capacitance type sensor according to claim 4, the first comparator is the same as in the capacitance type sensor according to claim 5. In addition, the first reference voltage is set according to the characteristics based on the device structure, etc., and due to the difference in the crest value, the part where the capacitance changes due to the influence of the device structure or the human body or hand of the operator (for example, differential voltage). In the waveform, the portion of the peak value that does not reach the first reference voltage) is canceled, and in the second comparator, noise such as hazard on the integrated voltage waveform is canceled based on the predetermined second reference voltage. By doing so, it becomes possible to more reliably recognize the change in capacitance due to contact with the liquid surface or surface of the terminal to be measured, that is, the object to be measured.

[0034]

[Embodiments] The capacitance type sensor of the present invention will be described below.
[First Embodiment] and [Second Embodiment] will be described in detail with reference to the drawings.

[Embodiment 1] FIG. 1 is a configuration diagram of an electrostatic capacitance sensor according to Embodiment 1 of the present invention.

In the figure, the electrostatic capacitance type sensor of this embodiment includes an electrostatic capacitance detection device (capacity detection means in the claims) 101, a variable gain amplifier 102, a differentiation circuit (change speed identification means) 103. And a first comparator 104 (determination means 105).

Further, the capacitance detecting device 101 includes a crystal oscillator 111, a first resistor 112, a second resistor 113, a 2-input exclusive OR gate circuit (first logical operation circuit) 115, an integrating circuit 116, and a probe (target device). The measuring terminal) 121 is provided. The measurement target (capacitance) of the capacitance detection device 101 is the stray capacitance 114 (Cp) applied to the probe 121, and hereinafter, the capacitance of the measurement target is described as the stray capacitance 114 (Cp). . Also in the figure,
122 is a test tube, 123 is a sample, 124 is a metal lid,
125 is a metal wall.

First, the details of each component of the electrostatic capacitance detection device 101 will be described. In the present embodiment, a crystal oscillator is used as the oscillating means from the viewpoint of device miniaturization, but the invention is not limited to this. Also, the first resistor 1
The 12 and the second resistor 113 have the same characteristics as each other.

Further, although the 2-input exclusive OR gate circuit 115 is used as the first logical operation circuit, it is not limited to this, and AND, OR, NAND, NO.
It is also possible to use a gate circuit such as R. However,
When the exclusive OR operation element is used, it is possible to recognize the rising and falling points of the signal separately, which is more efficient than other logical operation elements.

The first logical operation circuit (two-input exclusive OR gate circuit 115) is preferably a C-MOS integrated circuit and has a hysteresis characteristic.

This is because when the stray capacitance 114 (Cp) applied to the probe 121 is detected, the probe 121 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 115 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 first logical operation circuit is the second resistance 112 (R) and the stray capacitance 114 (C
This is because it is desirable to use one having a hysteresis characteristic in order to guarantee a reliable logical operation because the voltage waveform is integrated with p).

The integrator circuit 116 is obtained by the exclusive OR operation of the 2-input exclusive OR gate circuit 115.
The output waveform having a pulse width corresponding to the phase difference between the two inputs is integrated to process the phase difference into a voltage value. That is, the stray capacitance 114 having the voltage value applied to the probe 121
The physical quantity corresponds to the change of (Cp).

Next, the variable gain amplifier 102 amplifies the output of the capacitance detecting device 101 with, for example, a gain that is variably set in a programmable manner and supplies it to the differentiating circuit 103 in the subsequent stage.

When the capacitance type sensor of this embodiment is applied to an automatic analyzer, the structure of the device (for example, the lid 124 or the wall 125), the human body of the operator, or the like depending on the position in the device to be installed. The degree of influence of the hand or the like on the capacitance is different, and the change of the capacitance due to the contact of the probe 121 with the liquid surface of the sample 123 is also different.

For example, when it is installed outside the automatic analyzer, it is easily affected by the operator and the amount of the sample to be handled is large. Therefore, the relative gain is generally controlled by the programmable gain control of the internal CPU. However, when it is installed inside the device, the effect of the operator is small and the amount of sample to be handled is small.
In general, gain control is performed so that the gain is relatively high.

As a method of controlling the output level of the capacitance detecting device 101, in addition to the method of varying the gain in the latter stage, the oscillation frequency of the crystal oscillator 111 is lowered to integrate the integration circuit 1.
16 output level is lowered, or crystal oscillator 111
It is also conceivable to increase the output frequency of the integrating circuit 116 by increasing the oscillation frequency of the.

In this way, by variably setting the gain of the variable gain amplifier 102 in a programmable manner, regardless of the installation location of the capacitance type sensor in the apparatus, in other words, a metal near the capacitance type sensor is provided. Even if an object or the like is installed, accurate sensing can be performed without malfunction, and as a result, the degree of freedom in designing a device to which the capacitive sensor of this embodiment is applied can be increased. .

The differentiating circuit 103 differentiates the integrated voltage waveform amplified by the variable gain amplifier 102 by a predetermined gain. The change in capacitance caused by the influence of the device structure and the human body of the operator, and the probe 12
Unlike the transition of the capacitance change due to the contact of the specimen 123 with the liquid surface of No. 1, this difference appears as a difference in the changing speed of the integrated voltage waveform, and further, by differentiating the integrated voltage waveform, the changing speed is changed. It will appear as a peak value.

Further, the first comparator 104 includes a differentiating circuit 10
With respect to the differential voltage which is the output of No. 3, it is compared and judged whether or not it exceeds a predetermined first reference voltage Vref1.

As described above, the rate of change in capacitance due to the influence of the device structure and the human body of the operator appears as the peak value of the differential voltage waveform, and the peak value is the liquid level of the sample 123 of the probe 121. Since the peak value is different from the peak value based on the rate of change in capacitance due to contact with the touch panel, if the first reference voltage Vref1 is set according to the characteristics based on these device structures, the differential voltage will be the first reference voltage Vref1. When the probe 121 comes into contact with the liquid surface of the specimen 123, the output signal Out becomes the active level. The output signal Out is a signal indicating that the capacitance type sensor has detected the object to be measured.

Next, the operation of the capacitance type liquid level sensor of this embodiment will be described in detail with reference to the timing chart shown in FIG. The second reference Vref2 in FIGS. 3A and 3C is not related to this embodiment.

First, FIGS. 3A and 3B show the probe 1
The case where the electrostatic capacity type liquid level sensor of this embodiment is installed in an apparatus having a structure in which the lid 124 is provided around the path along which the 21 moves is described. FIG. 3A shows a variable gain amplifier 102.
Of the integrated voltage waveform amplified by a predetermined gain. In the figure, the portion B is an integrated voltage waveform corresponding to the capacitance change due to the lid 124, and shows a gentle change. Further, the portion C is a capacitance 114 (C when the probe 121 reaches the liquid surface of the specimen 123 to be originally detected.
It is an integrated voltage waveform according to the change of p), and shows a sharp change.

FIG. 3B shows the output of the differentiating circuit 103, which is a differential voltage waveform. This figure shows the same time transition as that of FIG. 3A, and A, B and C in the figure correspond to those of FIG. 3A. The figure shows the differential voltage waveform for the rising portion of the integrated voltage waveform, and the falling portion has a similar waveform in the negative direction, so it is omitted.

As described above, since the change in the capacitance due to the lid 124 is gradual, the peak value of the differential voltage waveform at the portion B is low and shows a gentle change. Further, since the capacitance 114 (Cp) changes sharply when the probe 121 reaches the liquid surface of the sample 123, the peak value of the differential voltage waveform in the C portion is high and shows a sharp change. .

In the first comparator 104, it is determined whether or not such a differential voltage exceeds the first reference voltage Vref1. The first reference voltage Vref1
Is higher than the differential voltage peak value due to the surrounding metal object in advance,
It is empirically set to a value equal to or lower than the differential voltage peak value on the liquid surface of the specimen 123.

Therefore, at C, which is the time when the probe 121 to be originally detected reaches the liquid surface of the sample 123, the differential signal exceeds the first reference voltage Vref1, and the output signal Out is activated. As described above, in the capacitance type liquid surface sensor of the present embodiment, even when the metal object (lid 124) formed around the path along which the probe 121 moves is provided as the device structure, The change in capacitance can be canceled, and the target to be detected can be reliably recognized.

Next, FIGS. 3C and 3D show the probe 1
The case where the electrostatic capacity type liquid level sensor of the present embodiment is installed in an apparatus having a wall 125 around the path along which 21 moves is described. FIG. 3C shows the variable gain amplifier 102.
Is the output of and is the integrated voltage waveform. In the figure, the portion D is an integrated voltage waveform corresponding to the change in the capacitance due to the wall 124, and shows a smooth rise change. The portion E is the sample 12 which the probe 121 should originally detect.
It is an integral voltage waveform according to the change of the electrostatic capacity 114 (Cp) when reaching the liquid level of No. 3, and has a shape in which the steep change is added to the electrostatic capacity by the wall 125.

FIG. 3D shows the output of the differentiating circuit 103, which is the differential voltage waveform. This figure shows the same time transition as in FIG. 3C, and D and E in FIG.
It corresponds to that of (c). The figure shows the differential voltage waveform for the rising portion of the integrated voltage waveform, and the falling portion has a similar waveform in the negative direction, so it is omitted.

As described above, since the rising change of the electrostatic capacity by the wall 125 is gradual, the peak value of the differential voltage waveform of the portion D is low and shows a gentle change. Further, since the capacitance 114 (Cp) changes sharply when the probe 121 reaches the liquid surface of the sample 123, the peak value of the differential voltage waveform in the E portion is high and shows a sharp change. .

In the first comparator 104, it is determined whether or not such a differential voltage exceeds the first reference voltage Vref1. Therefore, the probe 1 that should be detected originally
At E, which is the time point when 21 reaches the liquid surface of the specimen 123, the output signal Out is activated because the differential voltage exceeds the first reference voltage Vref1.

As described above, in the capacitance type liquid surface sensor of this embodiment, even if the metal object (wall 125) formed around the path along which the probe 121 moves is provided as the device structure, The change in capacitance due to a metal object can be canceled and the target to be detected can be reliably recognized.

The gain of the variable gain amplifier 102 is the same as the wall 1
The integrated voltage is variably set, for example, to a value such that the integrated voltage does not saturate the circuit even when the capacitance is detected by 25.

[Embodiment 2] FIG. 2 is a block diagram of an electrostatic capacity sensor according to Embodiment 2 of the present invention.

In the figure, the electrostatic capacitance type sensor of this embodiment includes an electrostatic capacitance detecting device (capacitance detecting means) 101, a variable gain amplifier 102, and a differentiating circuit (change speed identifying means) 10.
3, first comparator 104, second comparators 206 and 2
The determination unit 205 includes an input logical product gate circuit (second logical operation circuit) 207.

Since the capacitance detecting device 101, the variable gain amplifier 102, and the differentiating circuit 103 are the same as those in the first embodiment, the judging means 205, particularly the constituent elements added to the first embodiment, The 2 comparator 206 and the second logical operation circuit 207 will be described in detail.

The first comparator 104, like the first embodiment,
The differential voltage output from the differentiating circuit 103 is compared to determine whether it exceeds a predetermined first reference voltage Vref1. That is, the rate of change in capacitance appears as the peak value of the differential voltage waveform. Therefore, if the first reference voltage Vref1 is set according to the characteristics based on the device structure, the probe 121 contacts the liquid surface of the sample 123. At that time, the differential voltage exceeds the first reference voltage Vref1 and the output becomes active.

The second comparator 206 compares the output of the variable gain amplifier 102, which is an integrated voltage amplified by a predetermined gain, with a predetermined second reference voltage Vref2.

In the configuration of the capacitance type sensor of the first embodiment,
Since the judgment is made only based on the differential voltage waveform, for example,
When noise such as a hazard is on the output (integrated voltage) of the variable gain amplifier 102, the noise is differentiated.
3 is identified, and an erroneous determination is made. The configuration of the present embodiment eliminates erroneous determination due to such noise by performing determination based on this differential voltage waveform as well as the integrated voltage waveform output from the variable gain amplifier 102.

That is, in the first comparator 104, the first reference voltage Vref1 is set according to the characteristics based on the device structure and the like, and due to the difference in the crest value, it is based on the influence of the device structure and the human body or hand of the operator. The changing portion of the electrostatic capacitance (the portion of the peak value that does not reach the first reference voltage Vref1 in the differential voltage waveform) is canceled, and the second comparator 206 determines the integrated voltage waveform based on the second reference voltage Vref2. It is supposed to cancel the noise such as existing hazards.

As a result, the probe 121 becomes the specimen 123.
The output of the first comparator 104 and the second comparator 206 becomes active only when the liquid surface of the first comparator 104 and the second comparator 206 come into contact, and the output signal Out becomes active by ANDing the two outputs with the two-input AND gate circuit 207. It becomes a level. As a result, it becomes possible to more reliably recognize the object to be measured.

Next, the operation of the capacitance type liquid level sensor of this embodiment will be described in detail with reference to the timing chart shown in FIG. When the capacitance type liquid level sensor of the present embodiment is installed in an apparatus having a wall 125 around the path along which the probe 121 moves (see FIG. 3).
Since (c) and (d) are the same as those in the first embodiment, the description thereof will be omitted.

Referring to FIGS. 3 (a) and 3 (b), the case where the capacitance type liquid level sensor of this embodiment is installed in an apparatus having a lid 124 around the path along which the probe 121 moves is referred to. And explain. Variable gain amplifier 1 shown in FIG.
In the output of 02 (integrated voltage waveform), B and C portions are the same as those in the first embodiment. A part A shows a state in which noise due to hazards or the like is on the integrated voltage waveform.

The B and C portions in the output (differential voltage waveform) of the differentiating circuit 103 shown in FIG. 3B are also the same as those in the first embodiment. In part A, noise due to hazards and the like is shown on this integrated voltage waveform. Since the change in the integrated voltage due to this noise is steep, the peak value of the differential voltage waveform in the portion A is high and shows a sharp change.

The second comparator 206 compares and determines whether or not the integrated voltage waveform exceeds the second reference voltage Vref2, and the first comparator 104 determines whether or not the differential voltage is the first.
It is judged whether or not it exceeds the reference voltage Vref1,
An output signal Out is generated by taking a logical product of two comparison results by the 2-input AND gate circuit 207.

Therefore, in the portion A, the first comparator 104
Output becomes active but the output of the second comparator 206 does not become active, and in the part B, the output of the second comparator 206 becomes active but the output of the first comparator 104 becomes
Since the output of is not active, the output signal Out that is the determination result is not active. However, in the portion C where the probe 121 to be originally detected reaches the liquid surface of the sample 123, the first comparator 1
Since the outputs of both 04 and the second comparator 206 are active, the output signal Out is active.

As described above, in the capacitance type liquid surface sensor of this embodiment, the metal object (lid 124) formed around the path along which the probe 121 moves is provided as a device structure, or the integration is performed. Even if noise is added to the voltage waveform, the change in capacitance due to the metal object can be canceled, and the noise on the integrated voltage waveform can also be canceled, so that the target to be detected can be recognized more reliably.

[Modification of Second Embodiment] Next, a modification of the capacitance type sensor according to the second embodiment will be described. First,
In the first modification, a D-type flip-flop is added to the output Out of the 2-input AND gate circuit 207 to output the output Out.
This is a configuration for latching t. In this case, the D-type flip
The data input terminal D of the flop is fixed to the power supply Vcc level, and the output Out is input to the clock terminal CK. As a result, the active level "1" is latched at the rise of the output Out which is the detection result. For example, if the reset timing of the reset terminal RES is reset except when the detection is performed, unnecessary output It is possible to obtain the effect of not having to issue.

In the second modification, the 2-input AND gate circuit 207 is replaced with a D-type flip-flop,
The output of the flip-flop is set to the output Out. In this case, the output of the second comparator 206 is supplied to the data input terminal D of the D-type flip-flop, and the output of the first comparator 104 is supplied to the clock terminal CK. As a result, when the output of the second comparator 206 is active and the output of the first comparator 104 rises to the active level, the active level "1" is latched, and for example, the reset timing of the reset terminal RES will be detected. If all are reset except when, the effect that unnecessary output is not output is obtained.

[0080]

As described above, claim 1 of the present invention
According to the capacitance type sensor of the present invention, the change speed identifying means identifies the speed of change of the capacitance applied to the measured terminal detected by the capacitance detecting means, and the determining means
Since the determination is made based on the identification result of the change speed identification means, when the terminal to be measured is brought close to the liquid surface of the liquid or the surface of the article, the capacitance sensor is installed in the device. Capacitance capable of reliably recognizing that the measured terminal has touched the liquid surface or surface from the change in the capacitance applied to the measured terminal without being affected by the structure or the human body or hand of the operator. A sensor can be provided.

According to the capacitance type sensor of the second aspect, the output of the capacitance detecting means is amplified by the variable gain amplifier, for example, by the gain which is variably set programmable, and is supplied to the judging means. Therefore, regardless of the installation location of the capacitance sensor in the device, in other words, regardless of the metal object or the like installed near the moving path of the terminal under test, accurate sensing can be performed without malfunction. As a result, it is possible to provide a capacitance type sensor that can increase the degree of freedom in device design.

Further, according to the capacitance type sensor of the third aspect, when the determination means brings the measured terminal close to the liquid surface of the liquid or the surface of the article, the change speed identification means Since it is determined that the terminal to be measured has touched the liquid surface or the surface based on the identification result and the output of the capacitance detection means or the variable gain amplifier, for example, noise such as a hazard causes the capacitance detection means or the variable noise to change. It is possible to eliminate an erroneous determination due to the noise or the like when the output is on the gain amplifier, and it is possible to provide a capacitance type sensor that can more reliably recognize an object to be measured.

Further, according to the capacitance type sensor of the fourth aspect, in the capacitance detecting means, the oscillator oscillates a rectangular wave having a constant frequency, and the first and second resistors having the same characteristics are mutually provided. Supply to one input and the other input of the first logical operation circuit having hysteresis characteristics,
One or the other input of the first logical operation circuit is connected to the terminal to be measured, and the input is delayed by a delay time determined by the first or second resistance and the capacitance applied to the terminal to be measured. The voltage of the phase is applied, the output of the first logical operation circuit is supplied to the integrating circuit for integration, and the integrated result is supplied to the differentiating circuit in the changing speed identifying means via the variable gain amplifier to differentiate. By the logical operation of the first logical operation circuit, 2
An output waveform having a pulse width corresponding to the phase difference between two inputs is obtained, the output voltage of the first logical operation circuit is integrated, and the voltage amplified by a predetermined gain is further differentiated to apply to the measured terminal. Since it is possible to detect changes in capacitance such as stray capacitance, changes in capacitance due to device structure, operator's human body, hands, etc., and contact with the liquid surface or surface of the measured terminal, etc. The difference with the transition of the capacitance change due to is expressed as the difference of the integrated voltage waveform, and by further differentiating the integrated voltage waveform, the speed of the capacitance change can be expressed as the peak value of the differentiated voltage waveform. As a result, the determination means can surely recognize the object to be measured based on the peak value in the differential voltage waveform.

Further, by using the first and second resistors having the same characteristics as each other, the output voltage of the first logical operation circuit can be changed only by the change in the capacitance applied to the measured terminal. This makes it possible to detect with higher accuracy.

According to the capacitance type sensor of the fifth aspect, in the judging means, the output of the change speed identifying means is compared with the first reference voltage by the first comparator,
The determination is made based on the comparison result. For example, when the first comparator is added to the capacitance type sensor according to claim 4, the static sensor based on the influence of the device structure and the human body or hand of the operator. The rate of change in capacitance appears as the peak value of the differential voltage waveform, and the peak value differs from the peak value based on the rate of change in capacitance due to contact with the liquid surface or surface of the measured terminal. Since the first reference voltage is set according to the characteristics based on the device structure and the like and both are compared, it is possible to provide a capacitance type sensor that can surely recognize an object to be measured.

Further, according to the capacitance type sensor of the sixth aspect, in the judging means, the output of the change speed identifying means is compared with the first reference voltage by the first comparator,
Further, the second comparator compares the output of the capacitance detecting means or the variable gain amplifier with the second reference voltage, and the logical operation of the output of the first comparator and the output of the second comparator is performed by the second logical operation circuit. When the first comparator and the second comparator are added to the capacitance type sensor according to claim 4, the first comparator has characteristics based on the device structure and the like. The first reference voltage is set accordingly, and due to the difference in peak value, the portion where the capacitance changes due to the influence of the device structure and the human body or hand of the operator is canceled,
Since the second comparator cancels noise such as hazards on the integrated voltage waveform based on the predetermined second reference voltage, electrostatic due to contact with the liquid surface or surface of the measured terminal It is possible to provide a capacitance type sensor that can more reliably recognize a change in capacitance, that is, an object to be measured.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an electrostatic capacitance sensor according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a capacitance type sensor according to a second embodiment of the present invention.

FIG. 3 is a timing chart for explaining the operation of the electrostatic capacitance type liquid level sensor according to the first and second embodiments.
3 (a) and 3 (b) are installed in an apparatus having a structure having a lid around the path along which the probe moves, FIGS. 3 (c) and 3 (d) show a wall around the path along which the probe moves. 3 is an integrated voltage waveform and a differential voltage waveform when installed in a device having a different structure.

[Explanation of symbols]

101 Capacitance Detection Device (Capacity Detection Means) 102 Variable Gain Amplifier 103 Differentiation Circuit (Change Speed Identification Means) 104 First Comparator 105 Judgment Means 111 Crystal Oscillator 112 First Resistor 113 Second Resistor 114 Stray Capacitance (Cp) 115 2-input exclusive OR gate circuit (first logical operation circuit) 116 integrating circuit 121 probe (terminal to be measured) 122 test tube 123 sample 124 metal lid 125 metal wall Out output signal 205 determination means 206 second comparison 207 2-input AND gate circuit (second logical operation circuit) Vref1 first reference voltage Vref2 second reference voltage

Claims (6)

[Claims] 1. A capacitance detecting means for detecting a change in electrostatic capacitance applied to a terminal to be measured, a change speed identifying means for identifying a change speed of the electrostatic capacitance detected by the capacitance detecting means, and a liquid surface of the liquid. Alternatively, when the measured terminal is brought closer to the surface of the article, a judgment means for judging that the measured terminal has touched the liquid surface or the surface based on the discrimination result of the changing speed discrimination means. And a capacitive sensor having: 2. The capacitance type sensor according to claim 1, wherein the capacitance type sensor has a variable gain amplifier that amplifies the output of the capacitance detecting means with a gain that can be variably set. 3. The determination means, when bringing the measured terminal close to the liquid surface of the liquid or the surface of the article, the identification result of the change speed identification means and the capacitance detection means or the variable gain amplifier. The electrostatic capacitance sensor according to claim 1 or 2, wherein it is determined that the measured terminal has touched the liquid surface or the surface based on the output of the. 4. The capacitance detecting means comprises an oscillator for oscillating a rectangular wave having a constant frequency, and a first hysteresis characteristic.
A logical operation circuit, first and second resistors connected in series between the output end of the oscillator and one input and the other input of the first logical operation circuit, and having the same characteristics as each other; It has an integrator circuit for integrating the output of the first logical operation circuit, and a measured terminal connected to one or other inputs of the first logical operation circuit, and the changing speed identification means has a differentiating circuit. The claim 1, 2, or 3 characterized in that
The capacitance-type sensor described. 5. The capacitance type sensor according to claim 4, wherein the determination means has a first comparator that compares the output of the change speed identification means with a first reference voltage. 6. The determining means compares a first comparator for comparing an output of the changing speed identifying means with a first reference voltage, an output of the capacitance detecting means or the variable gain amplifier and a second reference voltage. The electrostatic capacitance according to claim 4, further comprising: a second comparator for comparison, and a second logical operation circuit for performing a logical operation between the output of the first comparator and the output of the second comparator. Sensor.