JPH0278912A - Variable capacity type sensor and system using such sensor - Google Patents

Abstract

PURPOSE:To obtain high measurement accuracy and reliability by eliminating the discharging of the variable capacity type capacitor consisting of floating electrostatic capacity formed with the ground which is affected by an external electric field. CONSTITUTION:The integration output V0 of an integrating circuit 12 has potential distributions to series-connected capacitors CA and CB through a buffer amplifier 13 as shown by equations I and II. When the terminal voltage VB across the capacitor CB does not reach the threshold voltage VR of a DC power source, the series-connected capacitors CA and CB are provided with the polarity for raising the output voltage V0, i.e. negative feedback, so that the V0 is stabilized on condition that VB = VR. For the purpose, one capacitor CB is used as a transducer with variable electrostatic capacity and the other capacitor CA is used as a reference capacitor with constant electrostatic capacity to obtain the output voltage which is in direct proportion to variation in the capacity of the transducer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a variable capacitance sensor system that is used in pressure sensors and the like and detects changes in the electrical capacitance of a variable capacitor that operates as a transducer.

(Prior Art) For example, when controlling a refrigeration system installed in an automobile, a device such as a pressure sensor that detects the refrigerant pressure, converts it into an electrical signal, and outputs it to the control system is effective.

By the way, there are some pressure sensors that use a silicon semiconductor for the diaphragm, but such pressure sensors must be installed under harsh environmental conditions, such as equipment installed in automobiles, and are subject to severe fluctuations. has problems in terms of durability and reliability.

Therefore, a variable capacity transducer is a pressure sensor that is considered to be most suitable for such environmental conditions. This variable capacitance transducer derives the amount of change as a capacitance change when the distance between the two electrode plates forming the capacitor changes due to pressure etc.
An electrical signal is obtained by comparing this with a reference capacitor.

Therefore, when such a variable capacity transducer is used as a pressure detection terminal for the above-mentioned automobile refrigeration cycle, the detection pressure range is 100kpa to 5M.
Moreover, since the operating environment conditions are severe, it is necessary to perform signal processing on changes in the capacitance of the transducer in an electric circuit system provided at a position away from the pressure detection terminal.

However, if the capacitance change is processed as a signal in an electric circuit system located away from the pressure detection terminal, there is a problem that the S/N ratio is extremely low and an effective signal cannot be obtained.

Therefore, in order to overcome these problems, conventionally, as shown in Japanese Utility Model Application Publication No. 62-267636, a signal processing system was installed near the pressure detection terminal of the transducer to effectively convert capacitance changes into voltage signals. A configuration has been adopted in which it is provided. In other words, the sensor shown in this publication has a variable capacitance capacitor placed on the bottom surface of a ceramic substrate inside the sensor, and a signal processing circuit that converts a capacitance change signal into voltage and an electric circuit for sensor calibration on the top surface of the substrate. When a variable capacitor generates an electrical signal in response to a physical quantity to be measured such as pressure, this electrical signal is converted into a voltage signal by a signal processing circuit. The voltage signals required for control are obtained by calibrating each other using a calibration electric circuit.

FIG. 11 is a block diagram of the signal processing circuit disclosed in the above publication, and its outline will be explained below. In FIG. 11, a reference capacitor Cp and a variable capacitor Cv are connected in series, and the two terminals on the opposite side of the common node are connected to two sets of potential sources, that is, the terminals on the opposite side to the common node of the basic capacitor Cp. are connected to the potential sources E1 and E2, and the terminal opposite to the common node of the variable capacitor Cv is connected to the feedback potential source E3 and the potential source E4, which will be described later, respectively.
The capacitance change signal of the variable capacitor Cv with respect to the reference capacitor Cp derived from the common node is taken into the memory M in synchronization with the clock signal via the cascade-connected three-stage inverter IN. , the output of this memory M is integrated by an integrator ■ and converted into a voltage signal, and this voltage signal is sent to a voltage dividing circuit T.
A control signal is obtained through an integrating amplifier A and a configuration in which the voltage can be divided and fed back to a series circuit of both capantors via a switch SW2. In this case, selector switch S
The first stage inverter on the common node side of WI, SW2 and the capacitor series circuit! A bypass switch SW3 connected in parallel with N receives a timing signal A as shown in FIG.

Switching is controlled by B and C, and data is also taken into memory M in synchronization with the timing signal.

Therefore, by placing a signal processing circuit that can be integrated into an IC and an electrical circuit for sensor calibration in the vicinity of the detection terminal of a pressure sensor, etc., it is possible to obtain a high-quality electrical signal as a sensor output, that is, a practical one. Can be converted to a high range of voltages.

(Problem to be Solved by the Invention) However, when trying to use a configuration in which such a signal processing circuit and a calibration electric circuit are arranged near the detection terminal of a pressure sensor in an actual sensor system, the following problems occur which are undesirable in practice. New problems arise, such as:

That is, since the transducer is originally placed close to its 411 target, it is easily influenced by the electromagnetic field of the environment to be measured. Therefore, in order to obtain reliable signals, the structure must be designed to be less susceptible to electromagnetic influences from the measurement environment.

However, in the sensor system configured as described above, the reference capacitor and the variable capacitor form a double-current calculation system in which the reference capacitor and the variable capacitor are switched to one of two sets of different power supply potentials by the changeover switches SWI and SW2. Since it is operated at an intermediate potential, the pair of opposing electrodes of the traducer must be insulated from the part that is at ground potential, creating a stray capacitance between it and the object to be measured. It is easily affected by external electric field fluctuations, and a discharge circuit is formed through the floating capacitance formed between the variable capacitor and the ground, so the variable capacitor is discharged through this discharge circuit, which causes 71- There is a problem in that it leads to a constant error.

The present invention eliminates the discharge of the variable capacitor due to the influence of an external electric field or the stray capacitance formed between it and the ground, thereby providing a highly reliable variable capacitance sensor system with all constant accuracy. The primary purpose is to achieve an output voltage that is approximately proportional or inversely proportional to changes in capacitance even when using a plate-pole capacitor as a variable capacitor whose output voltage is not proportional or inversely proportional to changes in capacitance. A second object is to provide a variable capacitance type sensor that can obtain the following.

(Means for Solving the Problems) In order to achieve the first object, the present invention includes a fixed capacitance capacitor, a variable capacitor connected in series to the fixed capacitance capacitor and operating as a transducer, and a series connection of both capacitors. a comparator that detects the terminal voltage of one of the capacitors that is input from between the terminals, a memory that captures the output of this comparator in synchronization with a clock signal, and a memory that integrates the output of this memory and uses the output voltage to detect the voltage between the two terminals connected in series. The configuration includes an integrator that charges the capacitor and converts the capacitance of the variable capacitor into a voltage.

Further, in the variable capacitance type sensor system, a charging circuit is formed in which the series-connected capacitors are connected to the integrator and charged by the output voltage of the integrator, and a discharging circuit is formed while being separated from the integrator to charge the capacitors.

The configuration is such that a switching means for periodically switching control is added to the discharge circuit.

Furthermore, as another configuration of the variable capacitance type sensor system according to the present invention, a first capacitor capacitor and a second capacitor capacitor each having one end connected to a ground terminal of a power supply,
A charging circuit that is connected to the other ends of the first capacitor and the second capacitor and charges the first capacitor.

A parallel circuit that commutates the electric charge of the first capacitive capacitor to the second capacitive capacitor, and a discharge circuit that discharges the charge of the first capacitive capacitor and the second capacitive capacitor are sequentially and periodically formed. a comparator for detecting a voltage generated in both capacitors when a parallel circuit of the first capacitance capacitor and the second capacitance capacitor is formed by the switching means; a memory that captures the output of the memory in synchronization with a clock signal; and a memory that integrates the output of this memory and detects it as a voltage proportional to the first capacitance capacitor or inversely proportional to the second capacitance capacitor, and detects the output voltage. and an integrator that provides an integrator when a charging circuit for the first capacitance capacitor is formed by the switching means.

Further, in order to achieve the second object, the present invention has a fixed electrode and a movable electrode whose respective electrode surfaces face each other, and has a variable capacitance according to the displacement in the direction of the facing distance between these two electrodes. In the variable capacitance type sensor comprising a plate capacitor, a fixed capacitor is connected in series with the plate capacitor, and the combined capacitance thereof is used as a detection capacitance.

(Function) Therefore, in a variable capacitance type sensor system having such a configuration, in a series circuit composed of a fixed capacitance capacitor and a variable capacitance capacitor, when the terminal voltage of one capacitor is detected by the comparator, the detection By integrating the voltage data when the value does not exceed the reference voltage using an integrating circuit and giving negative feedback to the series circuit of both capacitors, the terminal voltage of one capacitor is made equal to the reference voltage and stabilized. 1. It can be detected as a voltage signal proportional to the capacitance change of the variable capacitor without configuring a calculation system; : ) Yes It is possible to achieve stable operation and miniaturization at the same time.In addition, a switching means is introduced to control switching so that charging and discharging circuits are alternately formed for the fixed capacitance capacitor and variable capacitance capacitor connected in series. By doing so, it becomes possible to detect the potential distribution while constantly refreshing, and it is possible to obtain an output voltage that is directly proportional to the capacitance change of the variable capacitor without being affected by leakage resistance between the capacitor terminals.

Furthermore, in another configuration, the first capacitor is charged by controlling the other ends of the first capacitor and the second capacitor, each of which has one end connected to the ground terminal of the power source. charging circuit.

By sequentially and periodically forming a parallel circuit that commutates the electric charge of the first capacitive capacitor to the second capacitive capacitor, and a discharge circuit that discharges the charge of the first capacitive capacitor and the second capacitive capacitor, When the parallel circuit of the first capacitor and the second capacitor is formed, the voltage between the terminals of the first capacitor or the second capacitor is detected by the comparator, and the detection signal is stored in the memory and output. By integrating , it is possible to obtain an output voltage proportional to the change in capacitance of the first capacitor or inversely proportional to the change in the capacitance of the second capacitor while refreshing.

In addition, in variable capacitance type sensors, by connecting a fixed capacitor in series with a plate capacitor consisting of fixed and movable electrodes and using the combined capacitance as the detection capacitance, the displacement in the direction of the opposing distance between the plate capacitors is It becomes possible to obtain a nearly proportional variable capacitance.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

First, the basic structure of the variable capacitance type sensor system according to the present invention will be described with reference to FIG. 1. In FIG. CA and CB are connected in series, and the terminal of the capacitor CB on the opposite side from the CA connection side is connected to the ground potential of the power supply.1° is a voltage comparator into which the voltage VB between both terminals of the capacitor CB is input. (Comparator) 10, this comparator 10 compares the voltage VB across the terminals of the capacitor CB with a predetermined threshold voltage Vl?, and outputs a predetermined high potential Vll when VI3 exceeds VI3. , when VB is less than Vl?, a low potential VL is output. 11 is a memory for recording the output VC of the comparator 1o in synchronization with the clock pulse signal SP, and 13 is an integrator for integrating the output VD of this memory 11. The circuit 13 is a buffer amplifier for lowering the signal source impedance of the output voltage of the integrating circuit 12, and the output voltage VO obtained through this buffer amplifier 13 is fed back to the terminal of the capacitor CA on the opposite side from the CB connection side. 14 is a clock signal generator that provides a timing signal when reading data into the memory 11. For example, as shown in the figure, this clock signal generator 14 has a feedback resistor R11 input to a hysteresis input inverter. It consists of a hysteresis type oscillator connected to a terminal holding capacitor C11.

Note that, in the above example, the threshold voltage VR is applied to the comparator 10 from the DC power supply, but a logic IC having an approximately constant threshold level may be used as the comparator.

Next, the operation of the variable capacitance type sensor system configured as described above will be described.

The output Vo is integrated by the integrating circuit 12 through the buffer amplifier 13 for the capacitors CA and CB connected in series.
is applied, the potential distribution is VA-VOfcB/(C^+CB)l.

VB-vo+CA/(CA+CB)1.

Now, the voltage VB between the terminals of capacitor C[3 is the threshold voltage VI due to the DC power supply? If it is assumed that VB has not reached VB
-V under VR conditions. becomes stable.

Here, since CA and CB are connected in series, CA VA
-CB VB, Vo-VA +VB -VA +C^-VA/C13-
VA(1+CA/CB) -VR(1+CA/CB).

Therefore, as is clear from the above equation, by using one capacitor CB as a transducer with variable capacitance and using the other capacitor CA as a basic capacitor with constant capacitance, one end of the transducer can be It becomes possible to obtain an output voltage that can be set to the same potential as one end of the power supply voltage and that is directly proportional to the change in capacitance of the transducer.

The above is the basic configuration of the sensor system, but in actual use, it is actually difficult to obtain a capacitor structure in which the influence of leakage resistance between terminals can be completely ignored. For this reason, when the voltage applied to the capacitors connected in series does not change or changes slowly, the potential distribution of the series capacitors ends up being controlled by the distribution ratio of leakage resistance between the terminals. Therefore, it is practical to detect the potential distribution of the series capacitor while refreshing it at a fast cycle.

FIG. 2 is a circuit configuration diagram showing an embodiment of a sensor system according to the present invention that takes this point into consideration.

In FIG. 2, parts that are the same as those in FIG. 1 are given the same reference numerals and their explanations are omitted. Here, a circuit for refreshing the series-connected capacitors C3 and CY at a fast cycle is shown. I will mainly discuss this. That is, in this embodiment, the clock oscillation output signal SP output from the clock pulse oscillator 14 is given to the clock pulse distributor 16,
The electronic switch circuit 15 is switched and controlled by the pulse signal distributed by the clock pulse distributor 16, and a charging circuit that charges the series capacitors C8 and CY with the output voltage of the buffer amplifier 13 and a discharging circuit that discharges the same are alternately formed. The potential distribution is detected while refreshing the series capacitor C8°CY. Here, as shown in FIG. 3, the clock pulse distributor 16 provides the clock pulse signal SP outputted from the clock pulse oscillator 14 to the inverter through a delay circuit to obtain an inverted delayed signal 16b and also outputs the clock pulse signal SP. and an inverted delayed signal 16b are passed through a NAND circuit to obtain a signal 16c and its inverted signal 16d. The electronic switch circuit 15 includes four electronic switches Sl whose opening and closing are controlled by pulses output from the pulse distributor 16.

S2. S3. S4 are connected in series, one end of the electronic switch S1 is connected to the output end of the buffer amplifier 13, and one end of the electronic switch S4 is connected to the input end of the comparator 10. One end of the series circuit of capacitors C3 and CY is connected between electronic switches S2 and 83, and the other end is connected between electronic switches S3 and 84, and between capacitors C8 and CY. One end of an electronic switch S4 is connected to.

Next, the operation of the sensor system configured as described above will be described.

Now, the terminal voltage of the capacitor CY detected by the comparator 10 is applied to the memory 1 in synchronization with the rising edge of the clock pulse signal 16c output from the pulse distributor 16.
1, the voltage data is integrated by the integrating circuit 12, and further, the output voltage vo is derived from the output terminal to by the buffer 7 amplifier 13 and is applied to the electronic switch circuit 15. First, when the electronic switches S1 and 82 are simultaneously closed and the electronic switches S3 and 84 are opened, the capacitors C8 and CY are charged by the output voltage vo obtained through the buffer 7 amplifier 13. Further, when one of the electronic switches Sl and S2 is opened and the electronic switches S3 and 84 are closed, a discharge circuit of the capacitors C8 and CY is formed, and the capacitors cs and cv are simultaneously discharged.

Therefore, the electronic switch circuit 15 is connected to the capacitor cs,
By pulse driving so that the repetition period of charging and discharging cy becomes sufficiently fast, the potential distribution can be detected while ignoring the leakage resistance that exists between the terminals of the capacitors C3 and CY.

Hence the transducer with variable capacitance.

By using capacitor Cv as a reference capacitor and using capacitor C8 as a reference capacitor having a constant capacitance, it is possible to obtain an output voltage that is directly proportional to the change in capacitance of the transducer without being affected by leakage resistance between the capacitor terminals. In this case, the output voltage vo is given by Vo = (,1+cy/C3).

The above has described the case of obtaining an output voltage proportional to the change in capacitance of the transducer using a variable capacitor that operates as a transducer and a fixed capacitor as the base. There are cases where you want to obtain the output voltage.

FIG. 4 shows another embodiment of the present invention when applied to such a purpose, and the same parts as in FIG.

I will only mention the points that are true.

In this embodiment, as shown in FIG. 4, the clock oscillation output signal SP output from the clock pulse oscillator 14 is applied to the clock pulse distributor 18, and the pulse signal distributed by the clock pulse distributor 18 is used to control the electronic switch circuit 1.
7, one end of each of which is commonly connected to one end of a power supply, and the other ends of two capacitors are connected in the following manner. That is, buff 7
A charging circuit that charges one capacitor Ca with the output voltage of the amplifier 13, a parallel connection circuit that disconnects the charged capacitor Ca from the output end of the buffer amplifier 3 and moves the charge from the capacitor Ca to cb, and these circuits. The circuit is configured to be switched to either one of the discharge circuits for discharging the charges in the capacitors Ca and Cb. Here, the clock pulse distributor 18 supplies the clock pulse signal SP outputted from the clock pulse oscillator 14 to the flip-flop circuit as shown in FIG.
8a, a signal 18b obtained by passing the inverted output of this flip-flop circuit and a signal obtained by delaying the clock pulse signal SP by a delay circuit through an AND circuit, and a signal 18c obtained by further delaying this signal 18b by a delay circuit.
This is what you get. The electronic switch circuit 17 includes three electronic switches S5. S6. S7 are connected in series, one end of the electronic switch S5 is connected to the output end of the buffer amplifier 13, one end of the electronic switch S7 is connected to one end of each of the capacitors Ca and Cb, and one end of the power supply. , the input terminal of the comparator 10 is connected between the connections of the electronic switches S6 and 87.

Next, the operation of the sensor system having such a configuration will be described.

Now, when the capacitor Ca is in the discharged state t, the pulse signal 18a output from the pulse distributor 18 causes the electronic switch S5. S7 is closed,
When S6 is opened, one capacitor Ca is charged by the output voltage vo of the buffer amplifier 13, and a discharge circuit is formed in the other capacitor cb, so that the charged charges are discharged. Next, electronic switch S6 is closed and S5. When S7 is opened, one capacitor Ca is connected to the buffer amplifier 13.
At the same time, both capacitors Ca and c
b are connected in parallel, and charge moves from one capacitor Ca to the other capacitor cb, and at that time both capacitors C
The voltage VS generated at a and Cb is detected by the comparator 10. After the voltages of these capacitors Ca and Cb are detected by the comparator 10, each is discharged to prepare for the next circulation cycle. In this case, the stable state obtained by the above operation is expressed by the following equation.

Vo Ca = VS (Ca + Cb) = VR (Ca +
Cb) Therefore, Vo-(1+Cb/Ca) VR.

Therefore, by periodically performing switching control as described above with capacitor cb as a fixed capacitor and Ca as a variable capacitor, an output voltage vo inversely proportional to the variable capacitance of Ca can be obtained while being refreshed. Also, since both capacitors Ca and C1+ can have one end connected directly to one end of the power supply, one end of the transducer is at the same potential as one end of the power supply, which means that one side of the plate is sensitive to the external electric field of the internal circuit. This is equivalent to configuring a shield, and enables accurate and reliable measurements without being affected by external noise. Furthermore, since Cb/Ca is a factor that determines sensitivity, if Ca or cb can be easily adjusted from the outside, there is a great advantage that sensitivity can be changed as appropriate.

This configuration has the great advantage that, with the same circuit configuration, outputs that are proportional or inversely proportional to capacitance changes can be arbitrarily selected as required while ensuring exactly the same stability.

Next, the capacitor used in the variable capacitance sensor system will be described.

There are various types of proximity sensors, but a generally simple and inexpensive one has a fixed electrode 1a and a movable electrode 1b, as shown in FIG. 6, and the respective electrode surfaces are arranged facing each other. A flat plate capacitor 1, which is a plate capacitance type sensing structure, is known. In this plate capacitor 1, its capacitance ffi
Cv is expressed as -S/d in Cw=, where S is the opposing area, d is the opposing distance, and K is a constant, and is inversely proportional to the opposing pressure #ld. Therefore, if the movable electrode 1b is displaced parallel to the fixed electrode 1a, that is, if the opposing area changes, the capacitance will change proportionally to the amount of movement of the movable electrode 1b. It will be done. However, the movable electrode 1a
When the movable electrode 1b is opposed to the fixed electrode 1b and moved in the direction of tld, the capacitance changes inversely as the movable electrode 1b moves. Therefore, if used as is, the capacitance will not be directly proportional to the amount of movement of the movable electrode 1b, and the change in output voltage will deviate greatly from the proportional relationship.

Therefore, in the present invention, the plate capacitor 1 is used as a sensor, and the movable electrode 1b is placed opposite the fixed electrode 1a! f
Even when the distance d is changed in the direction of the lid, an output voltage that is approximately proportional to the change in the distance d can be obtained.

FIG. 7 shows an example of the configuration of such a variable capacitance sensor, in which a fixed capacitance capacitor CP and a variable facing distance capacitor Cv are connected in series, and the combined capacitance of these two capacitors is used to form a detection capacitor CY. This is how it is configured.

The characteristics of this detection capacitor CY are shown in Fig. 8, as follows: CY -CP +1-CP / (CF +0w)
). As is clear from comparing this characteristic with the graph showing the capacitance change with respect to the opposing Md in the lower part of Fig. 8,
The capacitance change of the variable capacitance type capacitor Cw with respect to the displacement that shortens the distance from the constant distance d, to dl is complemented in the direction of linearizing the output voltage, that is, so that an output voltage approximately proportional to the opposing ad is obtained.

Therefore, if the detection capacitor CY has such a configuration, it becomes possible to use a plate-pole capacitor that is used to change the distance between opposing electrodes as a proximity sensor.

On the other hand, as shown in FIG. 9, in the case where the plate capacitor 2 is composed of a circular thin plate and the edge portion of the movable electrode 2b provided opposite to the fixed electrode 2a is fixed, , when a uniformly distributed load P acts on the movable electrode 2b,
The facing distance d between the movable electrode 2b and the fixed electrode 2a changes depending on the deflection. Therefore, if a variable facing distance capacitor having such a configuration is connected in series with a fixed capacitance capacitor to form the detection capacitor CY as shown in FIG. 7, the electrostatic charge between the movable electrode 2b and the fixed electrode 2a can be reduced. The capacitance is represented by a curve Cv' shown by a dashed line in FIG. Therefore, as is clear from this curve Cw', the linear change becomes thicker with respect to the change in distance d (because it becomes thicker), it is possible to obtain an output voltage that is more proportional to the change in the facing distance of the variable facing distance type capacitor. can.

Furthermore, when the above-mentioned plate capacitor is used as a variable capacitance type sensor under harsh environmental conditions, the plate structure changes its unique dimensions depending on the surrounding thermal environment, so it becomes static as the ambient temperature changes. Capacity tends to increase or decrease.

Therefore, in such a case, a dielectric film 4 having a reasonable dielectric constant temperature coefficient is inserted between the fixed electrode 3a and the movable electrode 3b, as shown in FIG. 10, to increase the capacitance against temperature changes. The plate-pole capacitor 3 may be configured to compensate for the fluctuations in . In this case, the temperature coefficient of the dielectric film 4, for example, a polyethylene film is -150.
0PPm/'C, and the temperature coefficient of polyethylene terephthalate film is +400PPm/'
It is already known that by inserting these films as dielectric films between fixed and movable electrodes, it is possible not only to compensate for fluctuations in ambient temperature, but also to compensate for the short circuit between the fixed and movable electrodes. This is also preferable in terms of avoiding obstacles.

(Effects of the Invention) As described above, according to the present invention, the discharge of the variable capacitor due to the influence of an external electric field or the stray capacitance formed between the capacitor and the ground can be eliminated, resulting in high measurement accuracy. It is possible to provide a reliable variable capacitance sensor system, and even when using a plate capacitor whose output voltage is not proportional or inversely proportional to a change in capacitance as a variable capacitor, it is easy to use. It is possible to provide a variable capacitance type sensor that can obtain an output voltage that is approximately proportional or inversely proportional to a change in capacitance using the correction means.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the basic configuration of a variable capacitance type sensor system according to the present invention, Fig. 2 is a circuit diagram showing an embodiment of the present invention, and Fig. 3 is a switching timing of an electronic switch circuit of the same embodiment. FIG. 4 is a circuit configuration diagram showing another embodiment of the present invention. FIG. 5 is a time chart showing the switching timing of the electronic switch circuit of the same embodiment. FIG. 6 is the principle of a plate-pole capacitor. A configuration diagram to explain the
Fig. 7 is a circuit diagram showing a configuration example when a plate capacitor is used as a variable capacitance type sensor according to the present invention, Fig. 8 is a characteristic diagram of a variable capacitance type sensor according to the same configuration example, and Fig. 9 is a movable electrode A block diagram of a plate-pole capacitor with fixed edges,
Fig. 10 is a block diagram of a plate capacitor that takes into account correction means for errors caused by ambient temperature changes, Fig. 11 is a circuit diagram showing the structure of a conventional variable capacitance sensor system, and Fig. 12 explains the operation of the system. This is a time chart for 10...Comparator, 11...Memory, 12...
・Integrator circuit, 13...Buffer amplifier, 14...Clock signal generator, 15.17...Electronic switch, 1
6゜18...Clock pulse distributor, CA, CI3.
C.S. CY, Ca, Cb... Capacitor, 1-3... Plate capacitor. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 p Figure 3 t. Figure 14 Figure 5 Figure 7 Figure 8 Figure 119 Figure 10 Procedural amendment 63, 12. −? S Showa year month day

Claims (4)

[Claims] (1) A fixed capacitance capacitor, a variable capacitor that operates as a transducer with one end connected in series to the fixed capacitance capacitor and the other end connected to the ground terminal of a power supply, and input from between these two capacitors connected in series. A comparator that detects the terminal voltage of the variable capacitor, a memory that captures the output of this comparator in synchronization with a clock signal, and a memory that integrates the output of this memory and charges both capacitors connected in series with the output voltage. A variable capacitance sensor system comprising: an integrator that converts the voltage into a voltage proportional to the capacitance of the variable capacitor. (2) A fixed capacitance capacitor, a variable capacitor that operates as a transducer with one end connected in series to this fixed capacitance capacitor and the other end connected to the ground terminal of a power supply, and input from between the series connection of these two capacitors. A comparator that detects the terminal voltage of the variable capacitor, a memory that captures the output of this comparator in synchronization with a clock signal, and a memory that integrates the output of this memory and charges both capacitors connected in series with the output voltage. an integrator that converts the voltage into a voltage proportional to the capacitance of the variable capacitor; a charging circuit that connects the series-connected capacitor to the integrator and charges it with its output voltage; and a discharging circuit that disconnects the capacitor from the integrator. form,
A variable capacitance type sensor system characterized by comprising a switching means for periodically switching and controlling these charging and discharging circuits. (3) a first terminal, each one end of which is connected to the ground terminal of the power supply;
a capacitive capacitor and a second capacitive capacitor, a charging circuit connected to the other ends of the first capacitive capacitor and the second capacitive capacitor to charge the first capacitive capacitor, and a charging circuit that charges the first capacitive capacitor; a switching means for controlling switching so that a parallel circuit for commutating current to the second capacitance capacitor and a discharging circuit for discharging the charges of the first capacitance capacitor and the second capacitance capacitor are sequentially and periodically formed; When a parallel circuit of the first capacitance capacitor and the second capacitance capacitor is formed by this switching means, a comparator is provided to detect the voltage generated in both capacitors, and the output of this comparator is synchronized with a clock signal. The memory to be taken in and the output of this memory are integrated and detected as a voltage proportional to the capacitance of the first capacitor or inversely proportional to the capacitance of the second capacitor, and the output voltage is set to the first capacitor by the switching means. A variable capacitance type sensor system comprising: an integrator that provides a voltage when a charging circuit for a capacitance capacitor is formed. (4) A variable capacitance type sensor consisting of a plate capacitor that has a fixed electrode and a movable electrode with their electrode surfaces facing each other, and that obtains a variable capacitance according to the displacement in the direction of the opposing distance between these two electrodes. A variable capacitance type sensor characterized in that a fixed capacitance capacitor is connected in series to the plate capacitor and the combined capacitance is used as a detection capacitance.