JP2520000B2 - Variable capacitance type sensor system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable capacitance type sensor system which is used for a pressure sensor or the like and detects an electric capacitance change of a variable capacitance capacitor which operates as a transducer.

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

By the way, there is a pressure sensor that uses a silicon semiconductor for the diaphragm, but it is not possible to use such a pressure sensor under severe environmental conditions such as equipment mounted in automobiles where the mounting conditions are severe. There is a problem in durability and reliability.

Therefore, as a pressure sensor that is considered to be most suitable under such an environmental condition, there is a variable capacitance type transducer. In this variable capacitance type transducer, when the distance between two electrode plates forming a capacitance changes due to pressure, etc., the amount of change is derived as a capacitance change, and an electric signal is obtained by comparing this with a reference capacitance. It is a thing.

Therefore, when such a variable capacitance type transducer is used as the pressure detection means of the automobile refrigeration system described above, the detected pressure range is 100 kpa to 5 MPa, and since the operating environment conditions are severe, the capacitance change of the transducer is changed. It is necessary to perform signal processing by an electric circuit system provided at a position apart from the pressure detection terminal. However, when the capacitance change is processed by an electric circuit system located away from the pressure detection terminal, the S / N ratio is extremely low, and there is a problem that an effective signal cannot be taken out.

Therefore, in order to overcome these problems, a signal processing system for effectively converting a capacitance change into a voltage signal in the vicinity of a pressure detection terminal of a transducer has been provided in the past, as disclosed in JP-A-62-267636. The configuration provided is adopted. That is, in the sensor disclosed in this publication, a variable capacitor is arranged on the lower surface of a ceramic substrate in the sensor, and a signal processing circuit for converting a capacitance change signal into a voltage on the upper surface of the substrate and an electric circuit for sensor calibration. Are arranged so that they can be integrated together compactly.When the variable capacitor temporarily generates an electric signal in response to a physical quantity to be measured such as pressure, this electric signal is converted into a voltage signal by the signal processing circuit. In addition, the voltage signal necessary for the control is obtained by performing the mutual calibration by the calibration electric circuit while being converted into.

FIG. 6 is a block diagram of the signal processing circuit disclosed in the above publication, and its outline will be described below. In FIG.
The reference capacitor Cp and the variable capacitance type capacitor Cv are connected in series, and the two terminals on the side opposite to the common node are two sets of potential sources, that is, the terminals on the side opposite to the common node of the reference capacitor Cp are the potential sources E1 and E2. The terminals on the side opposite to the common node of the variable capacitance type capacitor Cv are the feedback potential source E3 and the potential source E4 which will be described later.
, And the capacitance change signal of the variable capacitance type capacitor Cv with respect to the reference capacitor Cp derived from the common node is taken into the memory M via the cascaded three-stage inverter IN in synchronization with the clock signal, The output of the memory M is integrated by the integrator I to be converted into a voltage signal, and this voltage signal is divided by the voltage dividing circuit T and can be fed back to the series circuit of both capacitors via the switch SW2. The control signal is obtained through the amplifier A. In this case, the bias switch SW3 connected in parallel to the first-stage inverter IN on the common node side of the capacitor series circuit of the changeover switches SW1 and SW2 is the clock signal generator CL composed of the oscillator O and the frequency divider DIV.
And the clock distribution circuit CV, the switching signals are controlled by the timing signals A, B, and C as shown in FIG. 7, and the memory M also receives data in synchronization with the timing signal D. It has become.

Therefore, by arranging the signal processing circuit that can be integrated into an IC and the electric circuit for sensor calibration in this configuration in the immediate vicinity of the detection terminals such as the pressure sensor, a high-quality electric signal as a sensor output, that is, practicality Can be converted to a high range voltage.

However, when it is attempted to use such a configuration in which the signal processing circuit and the calibration electric circuit are arranged in the vicinity of the detection terminal of the pressure sensor in an actual sensor system,
The following new problems, which are not practically desirable, occur.

That is, since the transducer is placed close to the measurement target of the main body, it is easily affected by the electromagnetic field of the environment to be measured. Therefore, in order to obtain a reliable signal, it is necessary to make the configuration less susceptible to the influence of the measurement environment.

However, in the sensor system having the above-mentioned configuration, the reference capacitor and the variable capacitor constitute a complicated arithmetic system in which two sets of different power supply potentials are switched by the changeover switches SW1 and SE2.
Since the pair of counter electrodes of the transducer must be insulated from the part at the ground potential because they are operated at the intermediate potential state, stray capacitance is generated between them and the measured object, and the external electric field is generated. It is easily affected by fluctuations, and since a discharge circuit is formed through the floating electrostatic capacitance formed between the variable capacitor and the ground, the variable capacitor is discharged through this discharge circuit, which causes a measurement error. is there.

Therefore, the present inventor solves such a problem by
The inventor has invented a variable capacitance type sensor system having a structure as shown in the previously filed Japanese Patent Application No. 63-230983 (Japanese Patent Publication No. 6-78913). FIG. 8 shows a variable capacitance type sensor system in the case of obtaining an output voltage proportional or inversely proportional to the capacitance change of the transducer by using a variable capacitance capacitor which operates as a transducer and a fixed capacitance capacitor as a reference in the prior application. It shows a configuration example. That is, as shown in FIG. 8, the clock oscillation output signal SP output from the clock pulse oscillator 14 is applied to the clock pulse distributor 18, and the electronic switch circuit 17 is switched by the pulse signal distributed by the clock pulse distributor 18. Two capacitors that are controlled and have one end commonly connected to one end of the power supply
The other ends of Ca and Cb are switched and connected in the following form. That is, the output voltage V ₀ of the buffer amplifier 13
The charging circuit that charges one of the capacitors Ca by this, the parallel connection circuit that disconnects the charged capacitor Ca from the output end side of the buffer amplifier 13 and moves the charge from the capacitor Ca to Cb, and discharges the charged charge of the capacitor Cb. The discharge circuit can be switched to any one. Here, the clock pulse distributor 18 gives the clock pulse signal SP output from the clock pulse oscillator 14 to the flip-flop circuit FF to obtain the output signal 18a and the inverted output of the flip-flop circuit FF as shown in FIG. And a clock pulse signal SP through an AND circuit AND, and a signal 18c obtained by further delaying this signal 18b by a delay circuit TD. The electronic switch circuit 17 is formed by connecting three electronic switches S5, S6, S7 in series. One end of the electronic switch S5 is connected to the output end of the buffer amplifier 13, and one end of the electronic switch S7 is connected to the capacitors Ca, C.
It is connected to one end of each of b and to one end of a power source, and the input end of the comparator 10 is connected between the electronic switches S6 and S7.

In the variable capacitance type sensor system having such a configuration, the electronic signals S5 and S7 of the electronic switch circuit 17 are closed by the pulse signal 18a output from the pulse distributor 18, and S
When 6 opens, one capacitor Ca turns into a buffer amplifier 13
While being charged by the output voltage V ₀ of the capacitor Cb, a discharge circuit is formed in the other capacitor Cb to discharge the charge. Next, when the electronic switch S6 is closed and S5 and S7 are opened, one capacitor Ca is disconnected from the output end of the buffer amplifier 13, and at the same time, both capacitors Ca and Cb are connected in parallel and one capacitor Ca is connected to the other. Electric charges move to the capacitor Cb, and the voltage VS generated at both capacitors Ca and Cb at that time is detected by the comparator 10. Then, after the voltages of the capacitors Ca and Cb are detected by the comparator 10, the capacitors Ca and Cb are discharged to prepare for the next circulation cycle. In this case, the stable state obtained by the above operation is represented by the following equation.

V ₀ Ca = Vs (Ca + Cb) = VR (Ca + Cb) Therefore, V ₀ = (1 + Cb / Ca) VR. However, VR is a threshold voltage by the DC power supply of the comparator 10.

Therefore, if the capacitor Cb has a fixed capacitance and Ca has a variable capacitance, the output voltage V ₀ inversely proportional to the variable capacitance of Ca can be obtained while refreshing by periodically performing the switching control as described above. Similarly, the capacitor Ca
Let C be a fixed capacitance and Cb be a variable capacitance, Cb
It is possible to obtain an output voltage V ₀ proportional to the variable capacitance of
Also, since both ends of the capacitors Ca and Cb can be commonly connected to one end of the power supply, one end of the transducer has the same potential as one end of the power supply. This is equivalent to configuring a shield for, and enables accurate and highly reliable measurement without being affected by external noise.

(Problems to be solved by the invention) By the way, in the variable capacitance type sensor system having such a configuration, as the variable capacitance type sensor, as shown in FIG. 10, a disk-shaped fixed electrode 1a and a movable electrode made of a thin metal plate are provided. 1b
In some cases, a plate electrode capacitance type sensing structure, that is, a plate electrode capacitor in which the respective electrode surfaces are arranged to face each other and the end portion of the movable electrode 1b is fixed by the fixing member 2, that is, a plate electrode capacitor is used. This plate capacitor is
The movable electrode 1b is used in such a manner that the movable electrode 1b moves in the direction of the facing distance d with respect to the fixed electrode 1a, and its electrostatic capacitance CW is CW.
= K · S / d (the facing area is S, the facing distance is d, and the constant is K), and is inversely proportional to the facing distance d. Therefore, if it is used as it is, the electrostatic capacitance is not directly proportional to the moving amount of the movable electrode 1b, and the change of the output voltage thereof largely deviates from the proportional relationship. Moreover,
In the plate capacitor having such a structure, the movable electrode 1b
When an evenly distributed load P acts on the movable electrode 1b, the distance d facing the fixed electrode 1a differs between the central portion and the peripheral portion due to the deflection, and an error occurs in the relationship between the electrostatic capacitance Cw and the facing distance d. I will end up. For this reason, it is difficult to realize it, even though it is possible to design to obtain an output proportional to the load P on the assumption that it is completely inversely proportional to the facing distance d.

Therefore, if the variable facing distance type capacitor CW having such a configuration is connected in series with the fixed capacitance capacitor CF as shown in FIG. 11 to form the detection capacitor CY, the movable electrode 1b
The capacitance between the fixed electrode 1a and the fixed electrode 1a is as shown by the curve CW in FIG. Therefore, as is clear from the curve CW, since the linear change amount with respect to the change of the distance d is larger than that of the characteristic CW ′ when the fixed capacitance capacitor CF is not connected, the change with respect to the distance change of the capacitance of the opposed distance variable type is large. It can be obtained as an almost proportional output voltage.

However, even with such a configuration, it is still difficult to secure sufficient linearity with respect to a wide range of pressure fluctuations.

According to the present invention, even when a plate electrode type capacitor whose output voltage is not proportional to a change in capacitance is used as a variable capacitance type sensor, it is possible to obtain an output voltage almost proportional to a change in capacitance over a wide range of pressure fluctuations. It is an object to provide a variable capacitance type sensor system.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a first capacitor and a second capacitor, one ends of which are connected to a common terminal of a power supply.
Has a capacitor of, and is charged from the other end of the first capacitor with an output voltage to be measured by the first signal output from the pulse distributor, and is charged by the second signal output from the pulse distributor. A first and a second capacitor are connected in parallel to charge the first capacitor with the second charge.
In the variable capacitance type sensor system in which the terminal voltage of the second capacitor is input to the comparator and the output signal thereof is integrated into the output signal to be measured, the first capacitor is the first capacitor. A parallel circuit of a fixed capacitor and a first variable capacitor formed by a first electrode among electrodes forming a plurality of regions and a movable electrode of a transducer, wherein the second capacitor is an electrode forming the plurality of regions. It is composed of a series circuit of a second variable capacitor and a fixed capacitor formed by a second electrode therein and a movable electrode of the transducer.

(Operation) In the variable capacitance type sensor system having such a configuration, a plate having a movable electrode and a fixed electrode whose end is fixed as the variable capacitance type sensor and which is flexibly deformed by receiving an evenly distributed load on one surface Even in the case of a polar capacitor, a variable capacitor formed by a first electrode and a second electrode among a plurality of electrodes that are components of the first capacitor and the second capacitor, and a movable electrode of the transducer, respectively. Changes with the displacement of the distance between the opposing electrodes, and the effect of the capacitance change is compensated so that an output voltage almost proportional to the pressure change is obtained, so the linearity of the response output voltage with respect to pressure is improved. In addition, it is possible to secure sufficient linearity even when the pressure varies over a wide range.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a structural example of a sensor used in the variable capacitance type sensor system according to the present invention. In the present embodiment, as shown in FIG. 1, a fixed electrode 32 is disposed opposite to a thin metallic movable electrode 31 whose edges are fixed, and a part of the whole area is cut out in an arc shape on an insulating substrate 33. A plurality of divided electrode regions 34, 35 are provided, and the electrode region 35 is
As shown in FIG. 2, the first variable electrode Cc is connected in parallel with the fixed capacitor Ca to form the first capacitor CA, and the electrode region 34 is used as the second variable electrode Cb in series with the fixed capacitance capacitor CF. The second capacitor CB is connected and the combined capacitance thereof is used as a detection capacitor.

In FIG. 2, the same components as those in FIG. 6 are designated by the same reference numerals, and the description thereof will be omitted here.

In this case, the variable capacitance type sensor used in the present embodiment has a structure in which a diaphragm electrode having a fixed edge as shown in FIG. Unlike the one in which the surfaces move in parallel and the facing distance changes, the response of the pressurizing pressure and capacity is determined for each specific diaphragm according to factors such as the diameter, thickness and Young's modulus of the diaphragm. is there. Here, in FIG. 3, 41 is a metal diaphragm electrode provided in the upper opening, that is, a movable electrode.
In a case in which the end edge portion of 31 is fixed, a fixed electrode 32 formed by providing a plurality of divided electrode regions 34, 35 on the insulating substrate 33 facing the movable electrode 31 in the case 41 is a C-shaped washer. 42
Is fixed through. In addition, the fixed electrode in the case 41
32 Electronic components such as amplifiers 43 and power supply and output terminals 44 below
A circuit board 45 to which is attached is disposed, and an insulating board that constitutes the fixed electrode 32 at a predetermined terminal on the circuit board 45.
Electrode lead-out terminals 34a, 3 drawn out from the electrode regions 34, 35 on 33
5a is connected.

Therefore, using a sensor such as that shown in FIG.
With the configuration shown in the figure, the output voltage V ₀ can be expressed by the following equation.

V ₀ = (1 + CB / CA) VR However, CB = Cb · CF / (Cb + CF), CA = Ca + Cc In the above formula, paying attention to the denominator term CA,
In CA, the capacitance component of the variable capacitor Cc that changes according to the change in pressure is added to the fixed capacitor Ca, so that the output voltage V ₀ tends to be suppressed as the capacitance of the entire sensor increases.

Here, when the fixed capacitor Ca is used as the first capacitor CA and the variable capacitor Cb is used as the second capacitor CB, that is, when the configuration as shown in FIG. What was the curve K ₀ shown in the figure,
If a variable capacitor Cb in which a fixed capacitor CF is connected in series is used as the second capacitor CB,
As shown by the curve K ₁ , the ratio of deviation from the straight line decreases, resulting in good linearity. However, since the rate of increase of the curve K ₀ tends to become steeper as the pressure P increases, it is necessary to use the fixed capacitance capacitor CF having a large value in order to maintain good linearity over a wide range of pressure changes. As the fixed capacitance CF becomes larger, the rate of change of CA / CB becomes smaller, so that the sensitivity becomes larger.

On the other hand, in the present embodiment, the capacitance component of the variable capacitance capacitor Cc, which is variable according to the change in pressure, is added to the fixed capacitance capacitor Ca as the first capacitor CA, that is, the change in CA is positively used. Therefore, the increase in CA / CB in the region where the pressure P is large as shown by the dotted line K _{3 in} FIG. 4 is effectively suppressed, and the overall decrease in sensitivity can be prevented.

Further, it is possible to positively realize the saturation characteristic K _{2 in} which the expansion of the output is relaxed for the pressure equal to or higher than the constant pressure value Pm.

In the variable capacitance type sensor used in the above embodiment, since the central portion of the metal diaphragm as the movable electrode 11 has a large deflection, a large capacitance change can be obtained, while its peripheral portion is fixed. There is little change because it exists. Therefore, the electrode region 35 forming the variable capacitance capacitor Cc of the fixed electrode 32 connected in parallel to the fixed capacitance capacitor Ca.
As shown in FIG. 1, it is not always necessary to cut out a part of the entire region in an arc shape in proportion to the other regions, and to form the variable capacitance capacitor Cc as shown in FIG. The electrode region 35 may be provided so as to correspond to the peripheral portion of the metal diaphragm where the deflection is small, and this portion may be used as the fixed capacitance capacitor Ca of the first capacitor CA. In this case, even if it is used as the fixed capacitance capacitor Ca, the function as the variable capacitance capacitor CC is substantially included. If such a sensor is configured, it is not necessary to separately use the fixed capacitance capacitor Ca, and therefore the size and simplification of the entire system can be achieved. Also, by changing the shape and arrangement of the electrode region facing the diaphragm surface, the first capacitor CA is made a variable capacitor Cc, and the second capacitor CB is also made a variable capacitor Cb, and fixed to the variable capacitor Cc. Capacitor Ca
It is also possible to provide the variable capacitance capacitor Cb with the function as the fixed capacitance capacitor CF. By doing so, the fixed capacitance capacitors Ca and CF can be substantially omitted, so that the overall size and simplification of the system can be further reduced.

[Effects of the Invention] As described above, according to the present invention, even when a plate electrode type capacitor whose capacitance change is not perfectly proportional or inversely proportional to pressurization is used as a variable capacitance type sensor, a wide range of pressure fluctuation can be obtained. It is possible to provide a variable capacitance type sensor system that can obtain an output voltage that is approximately proportional to the output voltage.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration example of a transducer used in a variable capacitance type sensor system according to the present invention, FIG. 2 is a circuit configuration diagram showing an embodiment of the present invention, and FIG. 3 is a transducer shown in FIG. 4 is a sectional view showing a detailed configuration example of
FIG. 5 is a characteristic diagram for explaining the function and effect of the same embodiment, fifth.
FIG. 6 is a plan view of a fixed electrode different from the transducer of FIG. 1, FIG. 6 is a circuit diagram showing the configuration of a conventional variable capacitance type sensor system, and FIG. 7 is a time chart for explaining the operation of the system. FIG. 8 is a circuit configuration diagram showing an example of the invention previously applied, FIG. 9 is a time chart showing switching timing of the electronic switch circuit, and FIG. 10 is a plate electrode capacitor in which an edge of a movable electrode is fixed. FIG. 11 is a circuit diagram showing a configuration example when a plate capacitor is used as a variable capacitance sensor according to the present invention, and FIG. 12 is a characteristic diagram of the variable capacitance sensor according to the configuration example. 10 …… Comparator, 11 …… Memory, 12 …… Integrator circuit,
13 …… Buffer amplifier, 14 …… Clock signal generator, 17
...... Electronic switch, 18 …… Clock pulse distributor, 1…
… Plate electrode capacitor, 31 …… Movable electrode, 32 …… Fixed electrode,
33 ... Insulating substrate, 34, 35 ... Electrode area, CA ... First capacitor, CB ... Second capacitor.

Claims (3)

(57) [Claims] 1. A first signal having a first capacitor and a second capacitor each having one end connected to a common terminal of a power supply, and having the other end of the first capacitor output from a pulse distributor. Is charged by the output voltage to be measured by the second capacitor, and the first and second capacitors are connected in parallel by the second signal output from the pulse distributor to charge the first capacitor with the second capacitor. In the variable capacitance type sensor system in which the terminal voltage of the second capacitor is input to the comparator and the output signal thereof is integrated into the output signal to be measured, the first capacitor is the first fixed capacitor. And a parallel circuit of a first variable capacitor formed by a first electrode among electrodes forming a plurality of regions and a movable electrode of a transducer,
The second capacitor comprises a series circuit of a second capacitor and a fixed capacitor formed by a second electrode of the electrodes forming the plurality of regions and a movable electrode of the transducer, and a variable capacitor. Capacitive sensor system. 2. A first capacitor is a variable capacitor formed by a first electrode among electrodes forming the plurality of regions and a movable electrode of a transducer, and a second capacitor is an electrode forming a plurality of regions. The variable capacitance type sensor system according to claim 1, wherein the variable capacitance type sensor system is a second variable capacitor formed by a second electrode therein and a movable electrode of the transducer. 3. A first capacitor is a variable capacitor formed by a first electrode among electrodes forming a plurality of regions and a movable electrode of a transducer, and a second capacitor is an electrode forming the plurality of regions. The variable capacitance sensor system according to claim 1, wherein the variable capacitance sensor system is configured as a series circuit of a second variable capacitor and a fixed capacitor formed by a second electrode therein and a movable electrode of the transducer.