JPH10246647A - Capacitive sensor - Google Patents

Abstract

(57) Abstract: Provided is a small-sized capacitive sensor having excellent characteristics including a variable capacitance whose capacitance value changes according to a change in a physical quantity to be detected and a fixed capacitance serving as a reference. The oscillation frequency f ₂ of the A variable capacitance oscillator circuit connected to the oscillation frequency f ₁ and the variable capacitance of the connected fixed capacitor oscillator circuit to a fixed capacity, of the detected physical quantity (in FIG. 1 pressure) The oscillation frequencies of the two oscillation circuits are set so as not to have the same value in the detection range. (A) shows that f ₁ > f
₂ and (b) is a case where f ₁ <f ₂ . 2
By making the oscillation frequencies of the two oscillation circuits different, abnormalities in linearity due to the interference operation of the two oscillation circuits can be avoided. In addition,
Reducing the parasitic capacitance between the respective input electrodes to the two oscillation circuits is also effective in reducing abnormalities in linearity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in, for example, an FC oscillation type flow meter, a gas meter, and a pressure sensor of a water meter, and has a static capacitance whose capacitance changes in accordance with a change in a physical quantity to be detected such as pressure or displacement. The present invention relates to a capacitance type sensor.

[0002]

2. Description of the Related Art A sensor configured to displace a diaphragm in response to a change in a physical quantity such as pressure and to detect the displacement as a change in capacitance value is a capacitance type sensor. As means for detecting the change in the capacitance value, the capacitance to be detected and the reference capacitance are incorporated as circuit constants of respective oscillation circuits, and the change in the capacitance value of the detection target capacitance is oscillated. In general, a method of converting the frequency into a change in frequency, performing an arithmetic process on a count value obtained by counting a change in the oscillation frequency with a counter based on the oscillation frequency due to the reference capacitance, and outputting the result as a digital value is generally used.

The structure of a conventional capacitance type sensor and how to connect it to a detection circuit will be described with reference to FIG. The capacitance type sensor is a diaphragm 3 that is displaced by receiving a physical quantity to be detected such as pressure (represented by pressure in the following description).
And the movable electrode 13 linked to the displacement of the diaphragm 3
And a common fixed electrode 12 facing the movable electrode 13 to form the variable capacitor 2; and a fixed capacitor 1 facing the common fixed electrode 12.
Electrode 11, movable electrode 13 and diaphragm 3
And a shield plate 14 for electrically shielding the two capacitances 1 and 2 from the outside.
The variable electrode 13 and the shield plate 14 are separated so as to have an interval that does not affect the capacitance value C ₂ of the variable capacitor 2. The fixed capacity 1 is for giving a reference value. In addition, at least between the three electrodes forming both capacitors,
In order to eliminate the influence of factors other than the electrode spacing, the same gas or dielectric is interposed.

In order to convert the variable capacitance 2 and the fixed capacitance 1 into an oscillation frequency, an oscillation circuit using a CMOS inverter is used. In this oscillation circuit, one of the two electrodes constituting the capacitance is connected to a common ground, and the other electrode is connected to the oscillation circuit as a circuit signal. In FIG. 8, the common fixed electrode 12 and the shield plate 14 are connected to a common ground of the oscillation circuit, the fixed electrode 11 is connected to the fixed capacitance oscillation circuit 10, and the movable electrode 13 is connected to the variable capacitance oscillation circuit 20. I have. The output frequencies of the two oscillation circuits 10 and 20 are as shown in FIG. That is, the output frequency f ₂ of the variable capacitance oscillation circuit 20 decreases because the movable electrode 13 approaches the common fixed electrode 12 and the capacitance value C ₂ increases with an increase in the pressure applied to the diaphragm 3. . On the other hand, the output frequency f ₁ of the fixed capacitance oscillator circuit 10, the capacitance value C ₁ of the fixed capacitance is constant is constant irrespective of the pressure.

It is to be noted that a fixed electrode of the variable capacitance 2 is separately provided on the seal diaphragm side, or
When using 14 as the fixed electrode, the tendency of change in the oscillation frequency f ₂ of the variable capacitance oscillator circuit 20 with changed and therewith the capacitance value of the variable capacitor 2 described above becomes a reverse, f in Fig ₂ Is a characteristic that rises to the right. A detection circuit that detects the position of the movable electrode 13 of the variable capacitor 2 of such a capacitance type sensor, in other words, the capacitance value C ₂ of the variable capacitor 2 includes:
For example, a circuit system as shown in FIG. 10 is used. This circuit system is disclosed in Japanese Patent Application No. 8-90 filed by the inventor of the present invention.
The circuit configuration is the same as that described in 760. In this circuit, for example, a pressure based on the atmospheric pressure as a reference pressure is converted into a pulse number and output.

The detection operation of this circuit system will be described with reference to FIGS. FIG. 11 is a time chart showing the output or input of each unit shown in FIG. This circuit system includes a fixed capacitance oscillation circuit 10 to which the fixed capacitance 1 is connected, a variable capacitance oscillation circuit 20 to which the variable capacitance 2 is connected, a gain setting oscillation circuit 30, an output oscillation circuit 40, A first Up counter 50 to which the oscillation output of the fixed capacitance oscillation circuit 10 is input; a data switching circuit 80 for switching between the oscillation output of the variable capacitance oscillation circuit 20 and the oscillation output of the gain setting oscillation circuit 30; A second Up counter 60 to which the output of the switching circuit 80 is input, and two Up counters 50
And a timing circuit 70 for outputting a signal to each oscillating circuit or the like in accordance with the signals S _A and S _B output when the count of 60 and 60 has expired.
And the pulse output P _out by the signal of the timing circuit 70
, And a gate 90 for outputting the same.

The count-up (count-up) time T ₁ of the first Up counter 50 is set when the capacitance value C ₂ of the variable capacitor ₂ is minimum (for example, when the measurement pressure is zero), that is, the oscillation for the variable capacitor. It is set to be equal to the count expiration time of the second Up counter when the oscillation frequency f ₂ of the circuit 20 is the maximum value f ₂ (0) [FIGS. 11 (a) and 11 (b)]. This setting is adjusted by an oscillation time constant adjusting resistor (not shown) of the fixed capacity oscillation circuit 10. The first Up at this time
The set count of the counter 50 is N ₁ , the set count of the second Up counter 60 is N ₂ (0),
When the oscillation frequency is f _1, the relationship between these values is as follows.

T ₁ = N ₁ / f ₁ = N ₂ (0) / f ₂ (0) (1) In such a state, pressure is applied and the capacitance C _{2 of the} variable capacitor 2 is applied. Increases, the oscillation frequency f ₂ of the variable capacitance oscillation circuit 20 decreases from the maximum value f ₂ (0) as shown in FIG. Therefore, in a state where pressure is applied, the first Up counter 50 and the second U counter
When the p-up counter 60 is counted simultaneously, the second up-counter 60 has not yet completed counting when the first up-counter 50 has completed counting. That is, the second U at this time
Assuming that the count number of the p counter 60 is N ₂ , N ₂ <N
₂ (0) [FIG. 11 (c)]. The difference between f ₂ and f ₂ (0) is determined by measuring the count of the second Up counter 60 below the count, and the value of the applied pressure is obtained.

[0009] Counting Not expiration component signal corresponding to the count number of the signal S _A [Figure 11 (d)] is the timing circuit 70 receives the signal S ₉ to a first Up counter 50 is output when count expires
To drive the gate 90 and then the second Up counter 60
There until timing circuit 70 receives the signal S _B [FIG. 11 (i)] to be output when the count expires stops the gate 90,
This corresponds to the number of pulses N ₄ output from the gate 90 [FIG.
(k)]. This pulse output P _out outputs a pulse from the output oscillation circuit 40 having the frequency f ₄ in order to match the required frequency of the signal processing circuit at the subsequent stage. This output oscillation circuit
The signal 40 is driven and stopped by a signal S3 _{& 4} generated by the timing circuit 70 receiving the signals S _A and S _B [FIG.
(h)].

The timing circuit 70 drives the gate 90.
At the same time, the data switching circuit 80 is driven, and the second Up
The input to the counter 60 is the oscillation frequency of the variable capacitance oscillator 20.
Number f _TwoOutput (Fig. 11 (c)) from the gain setting oscillation circuit 30
Oscillation frequency f_ThreeTo the output [FIG. 11 (f)]. No.
2. The count number of the Up counter 60 is equal to the set count number N.
_Two(0), the second Up counter 60 outputs the signal S_B
Is output to the timing circuit 70, and the
Signal S₉Stops the output from the gate 90. Data cut
Of the second Up counter 60 after the switching of the conversion circuit 80
N_Three[Fig. 11 (f)], N_Three+ N_Four= N_Two(0). As described above, the count of the first Up counter 50 expires.
Sometimes changing the frequency of the input to the second Up counter 60
Required to count less than
You can change the time and adjust the gain. Sand
The oscillation frequency f of the gain setting oscillation circuit 30_Threechange
By (T_Two-T₁) To adjust the gain
It is.

A first Up counter 50 and a second Up cow
Set count N of the counter 60₁And N _Two(0) is the function of (1).
At the same time as satisfying the requirements
Vibration frequency f₁Is the oscillation frequency f of the variable capacitance oscillation circuit 20._Two
Are set to be approximately the center value of the variable range of This
This means that both oscillation frequencies f₁And f_TwoBy approaching
Error due to temperature fluctuations of the oscillation circuit, power supply voltage fluctuations, etc.
It is a commonly used means to reduce the difference. Sand
In the calculation method, f₁And f_TwoIf the error of
This is because no error occurs in the output.

[0012] The ratio of N ₁ and N ₂ for the above conditions are met (0), when the minimum frequency corresponding to the maximum capacitance value of the variable capacitor 2 and f ₂ (max), [f ₂ (0) + f ₂ (max)] / 2f ₂ (0). For example, if f ₂ (0) is 100 kHz and f ₂ (max) is 50 kHz, the above equation becomes 0.75, and if the set count number N ₂ (0) of the second Up counter 60 is set to 1000 counts , The set count number N ₁ of the first Up counter 50 may be set to 750 counts.

The pressure-oscillation frequency characteristic shown in FIG. 9 is an example of one satisfying such conditions. The relationship between the pressure and the number of output pulses obtained in the circuit system of FIG. 10 has the characteristic shown in FIG. In the circuit system shown in FIG. 10, the data switching circuit 80 and the gain setting oscillation circuit 30 input thereto are replaced with the output side of the fixed capacitance oscillation circuit 10, and the first Up counter 50 completes counting ( (Count-up) time T _{1 is set} to the second U when the oscillation frequency f ₂ of the variable capacitance oscillation circuit 20 is the minimum value f ₂ (max).
The pressure can also be converted into the number of output pulses and output by setting the count to be equal to the expiration time of the p-counter 60. In this case, the characteristic is such that the number of output pulses decreases to the right with respect to the pressure. The pressure-output pulse number characteristic in this case is as shown in FIG.

Further, in the circuit system shown in FIG. 10, even if the gain setting oscillation circuit 30 and the data switching circuit 80 are omitted, the pressure can be converted into the number of output pulses and output. In this case, two Up counters 50 and 60
Can be set arbitrarily at the pressure level at which the count expiration times T ₁ and T ₂ become the same. The gate 90 is stopped at the output, and the pressure can be measured based on the number of output pulses during that period and information on which Up counter has completed counting first. However, in this case, the gain cannot be set. The pressure-output pulse number characteristic in this case is as shown by the thin line in FIG.

[0015] Two Up counter can 50 and counting expiration time T ₁ and T ₂ of the 60 arbitrarily set the level of pressure to be the same, in order to allow more gain settings, in FIG. 10 The output of the fixed capacitance oscillation circuit 10 and the first U
A data switching circuit is also provided between the input of the p-counter 50 and the output of the fixed-capacitance oscillation circuit 10 and the output of the gain setting circuit. I just need. The pressure-output pulse number characteristic in this case is as shown by the thick line in FIG.

In the above-described circuit system, if the frequency of the output P _out meets the specification, it is possible to omit the output oscillation circuit 40 and to input the output of the fixed capacitance oscillation circuit 10 to the gate 90. As described above, the pressure can be detected as the number of output pulses by the circuit system shown in FIG. 10 or a circuit system in which the circuit system is partially modified. However, when the actual characteristic data is acquired in the detection circuit having the characteristic that the oscillation frequencies of the two oscillation circuits intersect as shown in FIG.
As shown in FIG. 13B, the linearity is abnormally deteriorated in the vicinity of the pressure at which the oscillation frequencies intersect, as shown in FIG. FIG. 13C shows an abnormality in linearity by an output pulse error.

[0017]

SUMMARY OF THE INVENTION The present invention solves the problem of linearity in a capacitance type sensor for detecting a physical quantity to be detected by using the two oscillation circuits as described above, and provides a small-sized capacitor having excellent characteristics. It is an object of the present invention to provide a capacitance type sensor.

[0018]

[Means for Solving the Problems] To solve the problems,
First, as a result of analyzing and examining the abnormality of the linearity, it was found that the abnormality of the linearity was caused by an interference operation due to a parasitic capacitance existing between the two oscillation circuits. Below, Figure 14, Figure 15
The interference operation will be described with reference to FIG. FIG. 14 shows FIG.
And a parasitic capacitance C _e1 between the fixed electrode 11 of the fixed capacitance 1 having the capacitance value C ₁ and the movable electrode 13 of the variable capacitance 2 having the capacitance value C _2. And a parasitic capacitance _Ce2 exists between the movable electrode 13 and the ground. The parasitic capacitance _Ce1 is a capacitance between the fixed electrode 11 and the movable electrode 13 formed outside the common fixed electrode 12.

FIG. 15 is a circuit diagram of the two oscillation circuits in this state, and FIG. 16 is a diagram showing potentials at points A ₁ and B _{2 in} the circuit diagram. As is clear from FIG. 15, the parasitic capacitance _Ce1 between the fixed electrode 11 and the movable electrode 13 is connected in a state where the coupling points of the two oscillation circuits to the respective capacitances are capacitively coupled. When the two oscillation circuits are simultaneously oscillated in this state, a waveform obtained by differentiating the oscillation output waveform of each other is superimposed on the original oscillation waveform as noise, as shown in FIG. This noise _peak value increases as the capacitance value of the parasitic capacitance _Ce1 increases.

The oscillator circuit operation in the absence noise, 1/2 the threshold voltage of the power supply voltage V _cc potential at point B is changed with a time constant determined by the capacitance value and the resistance value, L
From H to L or from H to L, and the two oscillation circuits operate independently of each other. However, the parasitic capacitance C
_If both oscillation circuits are coupled by _e1 , the noise voltage is superimposed, so that switching occurs at a timing that should not be switched yet. This timing is, specifically, the timing indicated by the arrow in FIG. 16. When the potential at point B is rising, positive noise is superimposed, or when the potential at point B falls. This occurs when negative noise is superimposed when
Therefore, the potential at point B at that timing is _Vcc
If there is some distance from / 2, there is no switching. FIG. 16A shows a case where the oscillation frequency of the fixed capacitance oscillation circuit 10 is lower than the oscillation frequency of the variable capacitance oscillation circuit 20, and the oscillation circuit having the higher oscillation frequency satisfies the above conditions. This indicates that interference will occur only when the condition is satisfied. On the other hand, FIG. 16B shows the case where the oscillation frequency of the fixed capacitance oscillation circuit 10 is higher than the oscillation frequency of the variable capacitance oscillation circuit 20, and the oscillation circuit with the lower oscillation frequency is completely It is the same as the higher frequency. That is, interference is continuously received.

FIG. 16 shows the relationship between A ₁ and B ₂ , but a completely similar relationship also occurs between A ₂ and B ₁ . In other words, when the oscillating frequencies of the two oscillating circuits approach, the oscillating frequency of the lower oscillating circuit is set to the same oscillating frequency of the higher oscillating circuit. That is, a dead zone exists near the detected physical quantity at which the individual oscillation frequencies of the two oscillation circuits intersect. This state was shown
FIG. 17 (b).

As is clear from this description, even when the individual oscillation frequencies of the two oscillation circuits are not close to each other, the interference operation occurs, but in this case, the individual oscillation frequencies of the two oscillation circuits intersect. The frequency of the two oscillation circuits does not coincide with the higher frequency as in the case near the physical quantity to be detected. As is apparent from the above description, there are two types of interference operation between the two oscillation circuits, the interference only at that time and the interference in which the oscillation frequencies of the two oscillation circuits coincide with the higher one. The linearity abnormality shown in FIG. 17B is caused by the latter interference,
This is interference that must be avoided in practical use.

In order to solve the linearity abnormality caused by the interference operation, two means are conceivable. The first means is that the oscillation frequencies of the two oscillation circuits 10 and 20 are not brought close to a problem in the detection range of the physical quantity to be detected, which is a measure against the latter interference.

The second means is to make the parasitic capacitance _Ce1 sufficiently small, which is a measure against both interferences. It is clear from the above analysis that if the parasitic capacitance C _e1 can be made sufficiently small, the interference operation between the two oscillation circuits will not be a problem. The variable capacitance and the fixed capacitance are arranged on a plane as the capacitance type sensor body. If possible, it is possible to make the parasitic capacitance _Ce1 sufficiently small. However, such a configuration of the capacitance-type sensor main body increases the size of the capacitance-type sensor. SUMMARY OF THE INVENTION It is an object of the present invention to solve this problem by effective means in a capacitance type sensor body having a structure in which a variable capacitance and a fixed capacitance are superimposed.

The first to third aspects of the present invention are inventions based on the first means, and the fourth to seventh aspects of the present invention.
Is an invention according to the second means. In the first invention, a variable capacitance formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode disposed opposite to the movable electrode, and two fixed electrodes arranged in the same atmosphere as the variable capacitance The capacitance sensor body in which the fixed capacitors formed by the above are overlapped, the output of the fixed-capacitor oscillation circuit connected to the fixed capacitor, and the output of the fixed-capacitor oscillation circuit are counted to a first set count number. A first Up counter that outputs a first control signal when the output has reached, an oscillation circuit for a variable capacitor connected to the variable capacitor, and an output of the oscillation circuit for the variable capacitor. A second Up counter for outputting a second control signal; and an output of the first control signal or the control signal output earlier of the second control signal. Stop output In the capacitance type sensor and an output circuit which has a outside of the frequency of the oscillation frequency band of the variable capacitance oscillation circuit the oscillation frequency of the fixed capacitance oscillator circuit.

Since the oscillation frequency of the fixed capacitance oscillation circuit is outside the oscillation frequency band of the variable capacitance oscillation circuit, no dead zone is generated due to the intersection of the two frequencies. In the second invention, a variable capacitor formed by a movable electrode displaced by the physical quantity to be detected and a fixed electrode disposed opposite to the movable electrode, and two fixed electrodes arranged in the same atmosphere as the variable capacitor The capacitance type sensor body in which the fixed capacitances formed in the above are superimposed, the oscillation circuit for the fixed capacitance, and the output of the oscillation circuit for the fixed capacitance are counted, and when the count reaches the first set count, the first count is reached. 1st output control signal
And the switching means for switching between the output of the variable capacitance oscillation circuit, the gain adjustment oscillation circuit, and the output of the variable capacitance oscillation circuit and the output of the gain adjustment oscillation circuit which are connected to the variable capacitance, and counting the output of the switching means. And outputs a second control signal when the second set count number is reached.
A counter, and an output circuit for starting output with the first control signal and stopping output with the second control signal, wherein the time required for the first Up counter to count the first set count is: At the maximum frequency of the variable capacitance oscillation circuit, the second Up
In the capacitance type sensor in which the counter is set to the same time as the time required for counting the second set count, the oscillation frequency of the oscillation circuit for the fixed capacitance is set outside the oscillation frequency band of the oscillation circuit for the variable capacitance. Frequency.

As in the first embodiment, no dead zone is generated due to the intersection of the two frequencies. Further, according to the present invention, gain adjustment is possible. In the third invention, a variable capacitor formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode arranged opposite to the movable electrode, and two fixed electrodes arranged in the same atmosphere as the variable capacitor. The capacitance type sensor body in which the fixed capacitances formed in the above are arranged in an overlapping manner, and the outputs of the fixed capacitance oscillation circuit, the gain adjustment oscillation circuit, the fixed capacitance oscillation circuit and the gain adjustment oscillation circuit The switching means for switching and the output of the switching means are counted, and when the count reaches a first set count number, the first
A first Up counter that outputs a control signal of the second type, a variable capacity oscillation circuit connected to the variable capacity, and a second control signal when the output of the variable capacity oscillation circuit reaches a second set count. And an output circuit for starting output with a second control signal and stopping output with a first control signal, wherein the first Up counter counts a first set count number In the capacitance type sensor in which the time required to perform the operation is set to be the same as the time required for the second Up counter to count the second set count at the minimum frequency of the variable capacitance oscillation circuit, The oscillation frequency of the capacitor oscillation circuit is set to a frequency outside the oscillation frequency band of the variable capacitor oscillation circuit.

As in the first aspect, no dead zone is generated due to the intersection of the two frequencies. Also, gain adjustment is possible. The relationship between the detected physical quantity and the number of output pulses is opposite to that in the second invention. In the fourth invention, a variable capacitance formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode disposed opposite to the movable electrode, and two fixed electrodes arranged in the same atmosphere as the variable capacitance A capacitance type sensor body in which the fixed capacitances formed by superimposing are arranged, a fixed capacitance oscillation circuit connected to the fixed capacitance, a variable capacitance oscillation circuit connected to the variable capacitance, and a fixed capacitance In a capacitance-type sensor including an arithmetic output circuit that performs arithmetic processing on an output of an oscillation circuit and an output of an oscillation circuit for a variable capacitance and outputs a signal corresponding to a detected physical quantity, a variable capacitance and a fixed capacitance are adjacent to each other. At least one of the electrodes is connected to the common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the interval between the variable capacitance and the fixed capacitance is made sufficiently larger than the electrode interval of each capacitance. There.

Since the interval between the variable capacitor and the fixed capacitor is sufficiently larger than the interval between the electrodes of each capacitor, the parasitic capacitance between the two capacitors is sufficiently reduced, and the interference operation between the two oscillation circuits is greatly improved. Is done. In the fifth invention, a variable capacitance formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode arranged opposite to the movable electrode, and two fixed electrodes arranged in the same atmosphere as the variable capacitance. A capacitance type sensor body in which the fixed capacitances formed by superimposing are arranged, a fixed capacitance oscillation circuit connected to the fixed capacitance, a variable capacitance oscillation circuit connected to the variable capacitance, and a fixed capacitance In a capacitance-type sensor including an arithmetic output circuit that performs arithmetic processing on an output of an oscillation circuit and an output of an oscillation circuit for a variable capacitance and outputs a signal corresponding to a detected physical quantity, a variable capacitance and a fixed capacitance are adjacent to each other. At least one of the electrodes is connected to the common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the electrode connected to the common ground is larger than the counter electrode forming the capacitance. It is Ku formation.

Since the electrode connected to the common ground is formed to be larger than the counter electrode forming the capacitance, this electrode cuts off between the variable capacitance and the fixed capacitance, and generates a parasitic capacitance between the variable capacitance and the fixed capacitance. The capacity becomes smaller. In the sixth invention, a variable electrode formed by a movable electrode displaced by a physical quantity to be detected and two fixed electrodes disposed opposite to the movable electrode, and the fixed electrode disposed in the same atmosphere as the variable capacitance. A capacitance type sensor body in which the fixed capacitances formed by superimposing are arranged, a fixed capacitance oscillation circuit connected to the fixed capacitance, a variable capacitance oscillation circuit connected to the variable capacitance, and a fixed capacitance In a capacitance-type sensor including an arithmetic output circuit that performs arithmetic processing on an output of an oscillation circuit and an output of an oscillation circuit for a variable capacitance and outputs a signal corresponding to a detected physical quantity, a variable capacitance and a fixed capacitance are adjacent to each other. At least one of the electrodes is connected to a common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the electrode connected to the common ground forms an outer periphery of a counter electrode forming a capacitance. It is shaped to surround the. Since the electrode connected to the common ground is formed so as to surround the outer periphery of the opposing electrode forming the capacitance, this electrode cuts off between the variable capacitance and the fixed capacitance, and between the variable capacitance and the fixed capacitance. Parasitic capacitance becomes smaller.

In the seventh invention, the fixed electrodes adjacent to the variable capacitor and the fixed capacitor are one common fixed electrode. Since adjacent electrodes are used as one common electrode, the number of components is reduced.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described in the section of the means for solving the above-mentioned problems, the present invention is roughly classified into two inventions. The first is that the oscillation frequencies of the two oscillation circuits 10 and 20 are not brought close to a problem in the detection range of the physical quantity to be detected, and the second is that the parasitic capacitance _Ce1 is sufficiently reduced.

Each embodiment of the invention will be described with reference to examples. The first embodiment and the second embodiment are embodiments related to the first embodiment, and the third and subsequent embodiments are embodiments related to the second embodiment. Note that the circuit configuration of the invention relating to the first is exactly the same as that described in the section of the prior art with reference to FIG. 10 as an example, and the detection operation is also exactly the same as that described with reference to FIG. Detailed description of the circuit system and the detection operation is omitted. The same reference numerals are used for the parts having the same functions as those of the prior art.

FIG. 1 shows a physical quantity to be detected such as pressure (hereinafter, represented by pressure) and an oscillation frequency f of a fixed capacitance oscillation circuit 10 for explaining an embodiment relating to the first aspect of the present invention. ₁ and pressure shows the relationship between the oscillation frequency f ₂ of the variable capacitance oscillator circuit 20 - an oscillation frequency characteristic diagram. (A) shows a case f ₂ is f ₁ is smaller than in the entire range of the detected pressure, (b) is f ₂ in the entire pressure range
Is greater than f ₁ . In either case, it does not have the same value as f ₂ and f ₁ over the entire pressure range. That is, there is no intersection.

[First Embodiment] This embodiment is similar to FIG.
This corresponds to the case where the circuit constant is adjusted so as to have the pressure-oscillation frequency characteristic shown in FIG. As the capacitance-type sensor main body, the same one as the capacitance-type sensor main body described in the section of the related art is used, and as the circuit system, the same circuit system as that shown in FIG. 10 is employed, and the oscillation circuit for the fixed capacitance is used. The oscillation frequency f _{1 of} 10 is adjusted to 105 kHz, the maximum oscillation frequency f ₂ (0) corresponding to the reference pressure of the oscillation circuit 20 for variable capacitance is adjusted to 100 kHz, and the resistance value of a time constant adjusting resistor (not shown) is adjusted. Is set, the set value of the first Up counter 50 is set to 1050, and the second U counter is set to 1050.
The set value of the p counter 60 was set to 1000. In this case, the minimum oscillation frequency f ₂ (max) corresponding to the maximum pressure was 50 kHz.

FIG. 2 shows the linearity characteristic measurement results measured in this embodiment side by side for comparison with the case of the prior art. (A) is the case of the prior art,
(B) shows the case of this embodiment. In this embodiment, it is gone dead band observed in the vicinity of the intersection of the f ₂ and f ₁ in the case of the prior art. However, the output pulse error seen in other regions has not changed much.

[Second Embodiment] This embodiment is shown in FIG.
Corresponding to an embodiment, the oscillation frequency f ₁ of the fixed capacitance oscillator circuit 10 in the first embodiment to 45 kHz, a first U
Everything else is the same as the first embodiment except that the set value of the p counter 50 is set to 450. Even in this case,
As in FIG. 2B, a result having no dead zone was obtained.

[0038] Thus, by setting such that the oscillation frequency f ₂ of the oscillation frequency f ₁ and the variable capacitance oscillator circuit 20 of fixed capacitance oscillation circuit 10 does not match the entire detection pressure range, is both oscillation frequency crossing It is possible to avoid an abnormal phenomenon of the oscillation frequency appearing in the vicinity of the oscillating frequency, and to solve the problem of the dead zone caused by the abnormal phenomenon of the oscillation frequency.

This effect is not limited to the case of the circuit system shown in FIG. 10 (corresponding to claim 2).
30 (corresponding to claim 1), when the gain setting oscillation circuit 30 is provided on the fixed capacitance oscillation circuit 10 side (corresponding to claim 3), or when data switching is performed. It will be apparent that the present invention is also effective when the circuit 80 is provided not only on the output side of the variable capacitance oscillation circuit 20 but also on the fixed capacitance oscillation circuit 10 side. Third Embodiment FIG. 3 is an electrode configuration diagram showing a third embodiment of the capacitance type sensor according to the present invention. Unlike the case of the prior art shown in FIG. 8, the movable electrode 13 is arranged at a position close to the diaphragm 3, and the fixed electrode 16 of the variable capacitor 2 is arranged opposite to the movable electrode 13 on the opposite side to the diaphragm 3. The fixed electrode 11 for the fixed capacitance 1 and the fixed electrode 15 are arranged at a distance of about five times the capacitance gap from the fixed electrode 16. The fixed electrode 15 is arranged on the variable capacitor 2 side, and is connected to the common ground of the oscillation circuit together with the movable electrode 13.

With such an arrangement and connection, the movable electrode 13 connected to the common ground is connected to the variable capacitance oscillation circuit 20.
The fixed electrode 16 connected to the fixed electrode 16 is shielded from the diaphragm 3 to reduce the parasitic capacitance between the fixed electrode 16 and the diaphragm 3. Also, the fixed electrode 15 connected to the common ground
The fixed electrode 16 connected to the variable capacitance oscillation circuit 20 and the fixed electrode 11 connected to the fixed capacitance oscillation circuit 10 are shielded, and the fixed electrode 16 serving as an input electrode to the two oscillation circuits 10 and 20 is shielded. The distance between the fixed electrode 16 and the fixed electrode 11 is larger than that of the related art.
_e1 becomes smaller. If the distance between the shield plate 14 and the movable electrode 13 in FIG. 8 is replaced with the distance between the fixed electrode 16 and the fixed electrode 15, it is not necessary to increase the overall thickness. Thus, according to this embodiment, the parasitic capacitance C _e1 can be reduced without increasing the size of the capacitance type sensor.

FIGS. 7A and 7B show the linearity characteristics obtained by the capacitance type sensor according to the third embodiment. FIG. 7A shows the case where the circuit system according to the prior art is used, and FIG. 7B shows the first embodiment. This is a case where the circuit method shown in the example is used. In the case of (a), the width and error of the dead zone are reduced to about 1/2, and the errors in other pressure regions are also reduced by half due to the effect that the parasitic capacitance C _e1 between the input electrodes to the oscillation circuit is reduced. . In the case of (b), no dead zone occurs, and the error is reduced by half.

If the distance between two capacitances is further increased
If the parasitic capacitance C_e1And this effect is
Will be noticeable. The width of the dead zone and the reduction ratio of the error are parasitic
Quantity C _e1Is considered to be almost proportional to the decrease ratio of [Fourth Embodiment] FIG. 4 shows a capacitance type sensor according to the present invention.
FIG. 10 is an electrode configuration diagram showing a fourth embodiment of the present invention. This example
Corresponds to the common electrode 12 in the prior art shown in FIG.
Larger than the fixed electrodes 11 and the movable electrodes 13
Also has a cylindrical part surrounding its counter electrode on its outer periphery
12a.

The fixed electrode 11 and the movable electrode 13 are common electrodes 12a.
, The parasitic capacitance C between the fixed electrode 11 and the movable electrode 13 which are input electrodes to the two oscillation circuits.
_e1 is significantly reduced and the output pulse error is correspondingly reduced. The error in the linearity characteristics obtained by the capacitance type sensor according to this embodiment is further reduced than in FIG.

In this embodiment, the common electrode 12
a has a cylindrical portion surrounding both the fixed electrode 11 and the movable electrode 13 on the outer peripheral portion.
A large effect can be obtained even with a cylindrical portion surrounding any of the above. In addition, a considerable effect can be obtained only by eliminating the cylindrical portion and expanding the size to a size equivalent to the electrostatic cap. [Fifth Embodiment] FIG. 5 is an electrode configuration diagram showing a fifth embodiment of the capacitance type sensor according to the present invention. In this embodiment, the fixed electrode 15 in the third embodiment shown in FIG. 3 is enlarged to form a fixed electrode 15a having a tubular portion surrounding the fixed electrode 11 which is a counter electrode on the outer periphery thereof.

By surrounding the fixed electrode 11 with a fixed electrode 15a, a fixed electrode, which is an input electrode to two oscillation circuits, is formed.
The parasitic capacitance C _e1 between 11 and the fixed electrode 16 is greatly reduced,
The output pulse error is correspondingly reduced. In FIG. 5, the distance between the fixed electrode 16 and the fixed electrode 15a is several times the electrostatic gap. However, in the case of the configuration of this embodiment, the fixed electrode 16 and the fixed electrode 15a are brought close to each other. However, the parasitic capacitance _Ce1 can be sufficiently reduced.

[Sixth Embodiment] FIG. 6 is an electrode configuration diagram showing a sixth embodiment of the capacitance type sensor according to the present invention. In this embodiment, the common fixed electrode 12a in the fourth embodiment shown in FIG. 4 is replaced with a common fixed electrode 12b formed by alternately bending the outer peripheral portion of the plate up and down.
Since the common fixed electrode 12b can be formed by simply bending the peripheral portion of the flat plate up and down, the cost is reduced.

[0047]

According to the first aspect of the present invention, the variable capacitance formed by the movable electrode displaced by the physical quantity to be detected and the fixed electrode arranged opposite to the movable electrode and the same atmosphere as the variable capacitance are formed. The capacitance type sensor body in which the fixed capacitances formed by the two fixed electrodes arranged in a superposed manner are superposed, the oscillation circuit for the fixed capacitance connected to the fixed capacitance, and the output of the oscillation circuit for the fixed capacitance. A first Up counter that outputs a first control signal when counting reaches a first set count number, an oscillator circuit for a variable capacitor connected to the variable capacitor, and an output of the oscillator circuit for the variable capacitor. The second Up counter that outputs the second control signal when the set count number reaches 2, and the output is started with the first control signal or the control signal that is output earlier of the second control signal. Output after In the capacitance-type sensor that has an output circuit that stops the output with the control signal, the oscillation frequency of the oscillation circuit for the fixed capacitance is set to a frequency outside the oscillation frequency band of the oscillation circuit for the variable capacitance. Even if there is an interference operation due to the above, a dead zone due to the approach of both frequencies does not occur, and a small-capacitance sensor with good linearity and excellent characteristics can be provided.

In the second aspect, the variable capacitance formed by the movable electrode displaced by the physical quantity to be detected and the fixed electrode disposed opposite to the movable electrode is disposed in the same atmosphere as the variable capacitance. The capacitance sensor body in which the fixed capacitors formed by the two fixed electrodes are superposed, the oscillation circuit for the fixed capacitor, and the output of the oscillation circuit for the fixed capacitor are counted, and when the first set count number is reached. A first Up counter for outputting a first control signal; and an output of a variable capacitance oscillation circuit, a gain adjustment oscillation circuit, a variable capacitance oscillation circuit, and a gain adjustment oscillation circuit connected to the variable capacitance. A switching means for switching, and a second Up counter for outputting the second control signal when the output of the switching means is counted and reaching the second set count number, and the output is started by the first control signal and the second Up counter is started. An output circuit for stopping the output with a control signal, wherein the time required for the first Up counter to count the first set count number is equal to or less than the second Up counter when the maximum frequency of the variable capacitance oscillation circuit is reached. In the capacitance type sensor set to be the same as the time required to count the set count number of 2, the oscillation frequency of the fixed capacitance oscillation circuit is set to a frequency outside the oscillation frequency band of the variable capacitance oscillation circuit. Therefore, even if there is interference operation due to parasitic capacitance, a dead zone due to the approach of both frequencies does not occur, and a small-capacitance sensor with good linearity and excellent characteristics and capable of gain adjustment can be provided. it can.

In the third invention, the variable capacitance formed by the movable electrode displaced by the physical quantity to be detected and the fixed electrode disposed opposite to the movable electrode is disposed in the same atmosphere as the variable capacitance. A capacitance sensor body in which fixed capacitances formed by two fixed electrodes are arranged in an overlapping manner; an oscillation circuit for fixed capacitance, an oscillation circuit for gain adjustment, and an output of the oscillation circuit for fixed capacitance and an oscillation circuit for gain adjustment. Switching means for switching between output and output, a first Up counter for counting the output of the switching means and outputting a first control signal when a first set count is reached, and a variable capacitance oscillation circuit connected to the variable capacitance A second Up counter that counts the output of the variable capacitance oscillation circuit and outputs a second control signal when the count reaches a second set count number, and starts outputting with the second control signal and outputs the first control signal. An output circuit for stopping the output with a control signal, wherein the time required for the first Up counter to count the first set count is equal to or less than the second Up counter when the minimum frequency of the variable capacitance oscillation circuit is reached. In the capacitance type sensor set to be the same as the time required to count the set count number of 2, the oscillation frequency of the fixed capacitance oscillation circuit is set to a frequency outside the oscillation frequency band of the variable capacitance oscillation circuit. Therefore, even if there is interference operation due to parasitic capacitance, a dead zone due to the approach of both frequencies does not occur, and a small-capacitance sensor with good linearity and excellent characteristics and capable of gain adjustment can be provided. it can.

In the fourth invention, the variable capacitance formed by the movable electrode displaced by the physical quantity to be detected and the fixed electrode disposed opposite to the movable electrode is disposed in the same atmosphere as the variable capacitance. A capacitance-type sensor body in which fixed capacitances formed by two fixed electrodes are arranged in an overlapping manner, an oscillation circuit for the fixed capacitance connected to the fixed capacitance,
An oscillation circuit for the variable capacitance connected to the variable capacitance, and an arithmetic output circuit for arithmetically processing the output of the oscillation circuit for the fixed capacitance and the output of the oscillation circuit for the variable capacitance and outputting a signal corresponding to the detected physical quantity. In a capacitance type sensor, at least one of the electrodes adjacent to the variable capacitance and the fixed capacitance is connected to a common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the distance between the variable capacitance and the fixed capacitance is Since the capacitance is sufficiently larger than the electrode interval, the parasitic capacitance between the two capacitances becomes sufficiently small. As a result, the interference operation between the two oscillation circuits is greatly improved.

In the fifth aspect, the variable capacitance formed by the movable electrode displaced by the physical quantity to be detected and the fixed electrode disposed opposite to the movable electrode is disposed in the same atmosphere as the variable capacitance. A capacitance-type sensor body in which fixed capacitances formed by two fixed electrodes are arranged in an overlapping manner, an oscillation circuit for the fixed capacitance connected to the fixed capacitance,
An oscillation circuit for the variable capacitance connected to the variable capacitance, and an arithmetic output circuit for arithmetically processing the output of the oscillation circuit for the fixed capacitance and the output of the oscillation circuit for the variable capacitance and outputting a signal corresponding to the detected physical quantity. In a capacitance type sensor, at least one of the electrodes adjacent to the variable capacitance and the fixed capacitance is connected to a common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the electrode connected to the common ground is connected to the common ground. Since the electrode is formed larger than the counter electrode forming the capacitance, this electrode shields between the variable capacitance and the fixed capacitance. As a result, the parasitic capacitance between the variable capacitance and the fixed capacitance is reduced, and the interference operation between the two oscillation circuits can be significantly improved.

In the sixth invention, the variable capacitance formed by the movable electrode displaced by the physical quantity to be detected and the two fixed electrodes disposed opposite to the movable electrode is disposed in the same atmosphere as the variable capacitance. A capacitance type sensor body in which fixed capacitances formed by fixed electrodes are overlapped and arranged, an oscillation circuit for fixed capacitance connected to the fixed capacitance,
An oscillation circuit for the variable capacitance connected to the variable capacitance, and an arithmetic output circuit for arithmetically processing the output of the oscillation circuit for the fixed capacitance and the output of the oscillation circuit for the variable capacitance and outputting a signal corresponding to the detected physical quantity. In a capacitance type sensor, at least one of the electrodes adjacent to the variable capacitance and the fixed capacitance is connected to a common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the electrode connected to the common ground is connected to the common ground. Since the electrode is formed so as to surround the outer periphery of the counter electrode forming the capacitance, this electrode shields between the variable capacitance and the fixed capacitance. As a result, the parasitic capacitance between the variable capacitance and the fixed capacitance is reduced, and the interference operation between the two oscillation circuits can be significantly improved without increasing the volume of the capacitance type sensor.

In the seventh aspect, since the fixed electrodes adjacent to the variable capacitor and the fixed capacitor are one common fixed electrode, the number of components can be reduced.

[Brief description of the drawings]

FIGS. 1A and 1B show first and second embodiments of a capacitance type sensor according to the present invention, wherein FIG. 1A is a pressure-oscillation frequency characteristic diagram in the first embodiment, and FIG. 1B is a first embodiment. Pressure-oscillation frequency characteristic diagram

FIG. 2 shows the characteristics of a conventional capacitance sensor (conventional sensor) and the first or second embodiment (invention sensor) of the capacitance sensor according to the present invention; Linearity characteristic diagram, (b) is a linearity characteristic diagram of the inventive sensor

FIG. 3 is an electrode configuration diagram showing a third embodiment of the capacitance type sensor according to the present invention;

FIG. 4 is an electrode configuration diagram showing a fourth embodiment of the capacitance type sensor according to the present invention;

FIG. 5 is an electrode configuration diagram showing a fifth embodiment of the capacitance type sensor according to the present invention;

FIG. 6 is an electrode configuration diagram showing a sixth embodiment of the capacitance type sensor according to the present invention;

7A and 7B show characteristics of a third embodiment of the capacitance type sensor according to the present invention, wherein FIG. 7A is a linearity characteristic diagram according to a conventional circuit system, and FIG. 7B is a circuit according to the first or second invention; Of linearity characteristics by method

FIG. 8 is an electrode configuration diagram of a conventional sensor.

FIG. 9 is a pressure-oscillation frequency characteristic diagram of an oscillation circuit in a conventional sensor.

FIG. 10 is a block circuit diagram of a detection circuit;

FIG. 11 is a time chart for explaining the operation of the detection circuit;

12A and 12B show pressure-output pulse number characteristics according to the circuit system of the detection circuit. FIG. 12A shows the case of the circuit configuration shown in FIG.
In the circuit configuration of FIG.
(C) is a pressure-output pulse number characteristic diagram when the data switching circuit in FIG. 10 is omitted and when the data switching circuit is arranged before each of the two Up counters.

13A and 13B show characteristics of a detection circuit, wherein FIG. 13A is an ideal pressure-oscillation frequency characteristic diagram, FIG. 13B is a pressure-oscillation frequency characteristic diagram of a conventional detection circuit, and FIG. Linearity characteristic diagram

FIG. 14 is a diagram showing a parasitic capacitance in an electrode configuration of a conventional sensor.

FIG. 15 is a circuit diagram including a parasitic capacitance in an oscillation circuit of a detection circuit.

[Figure 16] shows the voltage waveform of _one point and B ₂ points A in FIG. 15, (a) shows the voltage waveform diagram when higher than the frequency of the fixed capacitor oscillator circuit toward the frequency of the variable capacitance oscillator circuit,
(B) is a voltage waveform diagram when the frequency of the variable capacitance oscillation circuit is lower than the frequency of the fixed capacitance oscillation circuit.

17A and 17B show pressure-oscillation frequency characteristics of a detection circuit according to the related art, where FIG. 17A is a characteristic diagram in an ideal state, and FIG.

[Explanation of symbols]

Reference Signs List 1 fixed capacitance 2 variable capacitance 11, 15, 15a, 16 fixed electrode 12, 12a, 12b common fixed electrode 13 movable electrode 14 shield plate 3 diaphragm 10 fixed capacitance oscillation circuit 20 variable capacitance oscillation circuit 30 gain setting oscillation circuit 40 Output oscillation circuit 50 Up counter-A 60 Up counter-B 70 Timing circuit 80 Data switching circuit 90 Gate f ₁ Oscillation frequency of fixed capacitance oscillation circuit f ₂ Oscillation frequency of variable capacitance oscillation circuit f ₃ Oscillation circuit for gain setting Oscillation frequency f ₄ Oscillation frequency of output oscillation circuit P f ₁ = f ₂ point S _A Up counter-A output S _B Up counter-B output S _{1 & 2} , S _{3 & 4} , S ₈ , S ₉ Timing circuit Output N ₁ Up counter-A count number N ₂ , N ₃ Up counter-B count number N ₄ Output pulse number C ₁ Capacitance value of fixed capacitance C ₂ Capacitance value of variable capacitance C _e1 Fixed capacitance Parasitics between variable capacitance Capacitance C _e2 Parasitic capacitance between variable capacitance and ground

Claims (7)

[Claims] 1. A variable capacitor formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode arranged opposite to the movable electrode, and formed by two fixed electrodes arranged in the same atmosphere as the variable capacitor. The output of the capacitance-type sensor main body in which the fixed capacitances overlap each other, the fixed-capacity oscillation circuit connected to the fixed capacitance, and the output of the fixed-capacity oscillation circuit are counted to reach the first set count number. A first Up counter for outputting a first control signal, a variable capacity oscillating circuit connected to the variable capacity and an output of the variable capacity oscillating circuit. A second Up counter that outputs a control signal of the first control signal or an output of the first control signal or the control signal that is output earlier of the second control signal, and outputs an output using a control signal that is output later. Output to stop In the capacitance type sensor and a road, the electrostatic capacity-type sensor, wherein the oscillation frequency of the fixed capacitance oscillation circuit is outside of the frequency of the oscillation frequency band of the variable capacitance oscillator circuit. 2. A variable capacitance formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode arranged opposite to the movable electrode, and formed by two fixed electrodes arranged in the same atmosphere as the variable capacitance. A capacitance sensor body in which the fixed capacitances overlap each other, an oscillation circuit for the fixed capacitance, and an output of the oscillation circuit for the fixed capacitance, and a first control signal when the count reaches a first set count. Output the first
And the switching means for switching between the output of the variable capacitance oscillation circuit, the gain adjustment oscillation circuit, and the output of the variable capacitance oscillation circuit and the output of the gain adjustment oscillation circuit which are connected to the variable capacitance, and counting the output of the switching means. And outputs a second control signal when the second set count number is reached.
A counter, and an output circuit for starting output with the first control signal and stopping output with the second control signal, wherein the time required for the first Up counter to count the first set count is: At the maximum frequency of the variable capacitance oscillation circuit, the second Up
In the capacitance type sensor in which the counter is set to have the same time as that required for counting the second set count, the oscillation frequency of the oscillation circuit for the fixed capacitance is out of the oscillation frequency band of the oscillation circuit for the variable capacitance. A capacitance type sensor having a frequency. 3. A variable capacitor formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode disposed opposite to the movable electrode, and formed by two fixed electrodes arranged in the same atmosphere as the variable capacitor. The capacitance type sensor body in which the fixed capacitances overlap each other, and switching between the output of the fixed capacitance oscillation circuit, the gain adjustment oscillation circuit, and the output of the fixed capacitance oscillation circuit and the output of the gain adjustment oscillation circuit A first Up counter for counting the outputs of the means and the switching means and outputting a first control signal when the output reaches a first set count, a variable capacity oscillation circuit connected to the variable capacity, and a variable capacity oscillation The second Up which outputs the second control signal when the output of the circuit is counted and reaches the second set count number
A counter, and an output circuit that starts output with the second control signal and stops output with the first control signal, and the time required for the first Up counter to count the first set count is: At the minimum frequency of the variable capacitance oscillation circuit, the second Up
In the capacitance type sensor in which the counter is set to have the same time as that required for counting the second set count, the oscillation frequency of the oscillation circuit for the fixed capacitance is out of the oscillation frequency band of the oscillation circuit for the variable capacitance. A capacitance type sensor having a frequency. 4. A variable capacitance formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode arranged opposite to the movable electrode, and formed by two fixed electrodes arranged in the same atmosphere as the variable capacitance. Capacitance sensor body in which the fixed capacitances overlap each other, an oscillation circuit for the fixed capacitance connected to the fixed capacitance, an oscillation circuit for the variable capacitance connected to the variable capacitance, and an oscillation circuit for the fixed capacitance And a calculation output circuit for calculating the output of the variable capacitance oscillation circuit and outputting a signal corresponding to the physical quantity to be detected. Is connected to the common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the interval between the variable capacitance and the fixed capacitance is sufficiently larger than the electrode interval of each capacitance. Capacitive sensor, wherein. 5. A variable capacitor formed by a movable electrode displaced by a physical quantity to be detected and a fixed electrode disposed opposite to the movable electrode, and formed by two fixed electrodes arranged in the same atmosphere as the variable capacitor. Capacitance sensor body in which the fixed capacitances overlap each other, an oscillation circuit for the fixed capacitance connected to the fixed capacitance, an oscillation circuit for the variable capacitance connected to the variable capacitance, and an oscillation circuit for the fixed capacitance And a calculation output circuit for calculating the output of the variable capacitance oscillation circuit and outputting a signal corresponding to the physical quantity to be detected. At least one of them is connected to the common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the electrode connected to the common ground is formed larger than the counter electrode forming the capacitance. Capacitive sensor, characterized in that is. 6. A variable capacitance formed by a movable electrode displaced by a physical quantity to be detected and two fixed electrodes disposed opposite to the movable electrode, and a fixed electrode formed in the same atmosphere as the variable capacitance. Capacitance sensor body in which the fixed capacitances overlap each other, an oscillation circuit for the fixed capacitance connected to the fixed capacitance, an oscillation circuit for the variable capacitance connected to the variable capacitance, and an oscillation circuit for the fixed capacitance And a calculation output circuit for calculating the output of the variable capacitance oscillation circuit and outputting a signal corresponding to the physical quantity to be detected. At least one of them is connected to the common ground of the variable capacitance oscillation circuit and the fixed capacitance oscillation circuit, and the electrode connected to the common ground surrounds the outer periphery of the counter electrode forming the capacitance. Capacitive sensor, characterized in that it has been formed into. 7. The capacitive sensor according to claim 5, wherein the fixed electrode adjacent to the variable capacitor and the fixed capacitor is one common fixed electrode.