JPH0431326B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a capacitive displacement converter that converts displacement into an electrical signal via capacitance, and particularly relates to a capacitive displacement converter that converts displacement into an electrical signal via capacitance, and in particular, This invention relates to a displacement conversion device.

<Prior Art> FIG. 6 is a block diagram showing an example of a conventional capacitive displacement converter.

Common electrode that moves in response to the displacement to be measured
Fixed electrodes ED ₁ and ED ₂ are provided opposite to ED ₃ , and a sealing liquid is filled between them to form capacitances C ₁ and C _2, respectively. These capacitances C ₁ and C ₂ are transformers having a primary winding n ₁ and secondary windings n ₂ and n ₃ .
The oscillation output of the oscillator OSC is given through _T1 . The common electrode ED ₃ is connected to the ground, and a fixed capacitor C ₀ is inserted between the ground and the common potential point COM to maintain insulation in terms of direct current but short circuit in terms of alternating current.

CON ₁ and CON ₂ are current/voltage converters, respectively.
CON ₁ consists of an operational amplifier OP ₁ and a resistor R ₀ connected to its feedback circuit, with a diode connected to its input.
The average current I ₀ corresponding to the difference between capacitances C ₁ and C ₂ given via D ₂ and D ₃ is converted into an output voltage E ₀ (=−I ₀ R ₀ ). CON ₂ consists of an operational amplifier OP ₂ and a resistor R ₁ connected to its feedback circuit, with an average current I ₂ and I ₂ R ₁ depending on the capacitance C ₂ applied to its input via a diode D ₄ Convert to voltage E ₁ .
INT is an integrator, consisting of an operational amplifier OP ₃ and a capacitance C _I connected to its feedback circuit, and an average current I ₁ corresponding to the capacitance C _I is applied to its input via a diode D ₁ . The output E ₁ of CON ₂ is applied through the resistor R ₂ and the negative reference voltage −
E _r is provided through resistor R ₃ . Further, the output of the integrator INT is given to the oscillator OSC, and the power supply voltage of the oscillator OSC, for example, is controlled depending on the magnitude thereof.

The integrator INT calculates the average current I ₁ depending on the capacitance C ₁
and E ₁ / according to the output E ₁ of the voltage/current converter CON _{2
E r / _}
The reference current _Ir of _R3 is added and integrated. and resistance
If the values of R ₁ and R ₂ are chosen equal, the current I ₃ is the capacitance
The current is an inversion of the average current I ₂ corresponding to C ₂ , and has the same polarity as I ₁ and the opposite polarity to the reference current I _r as shown in the figure. That is, the integrator INT has a capacitance C ₁ ,
Integrate the difference between the average current (I ₁ + I ₂ ) corresponding to the sum of the capacitances of C ₂ and the reference current I _r , and control the oscillator OSC so that (I ₁ + I ₂ ) becomes equal to I _r . capacitance C ₁ ,
The average current I ₀ corresponding to the difference in C ₂ is made to correspond to the displacement of the common electrode ED ₃ . Average current I ₀ is operational amplifier
Output voltage with current/voltage converter CON ₁ using OP ₁
It is detected by converting it to E ₀ . In addition, each operational amplifier
Capacitance inserted at the input end of OP ₁ to OP ₃
C _f0 , C _f1 , and C _f2 are for removing harmonic voltages.

<Problems to be Solved by the Invention> However, such conventional capacitive displacement converters do not take into account the fact that the sensor section is deformed due to static pressure or temperature applied to the sealing liquid, causing an output error. First, since the calculations are performed in an analog manner, there is a problem in that high precision cannot be achieved.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a method in which a first electrode and a second electrode are provided facing a grounded common electrode, and a seal is placed between them. An AC voltage is applied to the first and second electrodes via a transformer and a sensor section that is filled with liquid and forms first and second capacitances that differentially change according to the displacement to be detected. A capacitance conversion means that connects a common potential point and a common electrode with a fixed capacitance and rectifies a flowing current and converts it into first and second signals corresponding to the first and second capacitances, and a sensor embedded in the sensor section. temperature converting means for converting the temperature of the part into a corresponding temperature signal;
a displacement calculation means for calculating the difference between the sums of the first and second capacitances to obtain a displacement signal corresponding to the displacement;
and a dielectric constant calculation means for calculating the dielectric constant of the sealing liquid by calculating the product of the sum of the second capacitances, a static pressure calculation means for obtaining a static pressure signal using this dielectric constant and a temperature signal, and a displacement signal. The present invention is configured to include a correction means for performing a correction calculation using a temperature signal and a static pressure signal to obtain a corrected displacement signal, and a digital calculation means formed by a microprocessor.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention.

SNS is the sensor section, CCV is the capacitance conversion section, DAD is the digital calculation section, and OPC is the output section.

In the sensor section SNS, capacitances C _H and C _L are formed by fixed current electrodes ED ₁ and ED ₂ B facing the grounded common electrode ED ₃ , and a sealing liquid is filled between them. . In addition, the temperature sensor T _H that measures the temperature of the body or sealing liquid of the sensor unit SNS is
is inserted into. The temperature sensor T _H measures the temperature by utilizing, for example, the fact that the voltage V _be between the base and emitter of a transistor has temperature dependence.

The capacitance conversion unit CCV is a capacitance conversion circuit CAV that converts the capacitances C _H and C _L into analog voltages, and an analog/digital conversion circuit that converts these voltages and the voltage from the temperature sensor T _H into digital signals, respectively.
It has ADC ₁ and ADC ₂ .

The digital calculation unit DAD has random access memory RAM and read-only memory ROM.
These addressing are done from the processor CPU via the bus BUS ₁ latch decoder LAD. BUS ₂ is a data bus. Output data from the analog/digital conversion circuits ADC ₁ and ADC ₂ is stored in random access memory RAM. A predetermined calculation program is stored in the read-only memory ROM, and the results calculated according to the calculation procedures stored in the read-only memory ROM under the control of the processor CPU are stored in the random access memory RAM. Ru. Note that the illustration of the control bus is omitted.

The final calculation result is converted to a duty signal by the counter CTR, and the duty signal is sent to the output circuit.
The OPC converts the current into a current of 4 to 20 mA, for example, and supplies it to the load.

FIG. 2 is a block diagram specifically showing the configuration of the capacitance conversion circuit CAV in FIG. 1. Components having the same functions as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. The transformer T ₂ has a secondary winding n ₂ ,
n ₃ and n ₄ , one end of which is connected to the fixed electrodes ED ₁ and ED ₂ and the reference capacitor _CR . The reference capacitance _CR used is one that is stable with respect to temperature. The other ends of the secondary windings n ₂ , n ₃ , n ₄ are connected to the anodes of the diodes D ₁ , D ₃ , D ₅ , and their cathodes are connected to the common potential point COM, respectively. Also,
A diode _D4 is connected to the other end of the secondary winding _n3 with a polarity opposite to that of the diode _D3 . The current/voltage converter CON ₄ is connected to the operational amplifier OP ₄ and its feedback resistor R _4
The output voltage E _{CL (} =k _{CL ,}
k is a constant). Furthermore, a diode D _{2 is connected to the other end of the secondary winding n 2 with} a polarity opposite to that of the diode D ₁ . The current/voltage converter CON ₅ consists of an operational amplifier OP ₅ and its feedback resistor R ₅ , which is a diode
The average current I ₅ corresponding to the capacitance C _H given via D ₂ is converted into an output voltage E _CH (=kC _L ). Furthermore,
A diode _D6 is connected to the other end of the secondary winding _n4 with a polarity opposite to that of the diode _D5 . The current/voltage converter CON ₆ is connected to the operational amplifier OP ₆ and its feedback resistor R ₆
The average current I depending on the capacitance C _R given through the diode D _{6 and} the output voltage E _CR (=kC _R )
Convert to In addition, each operational amplifier OP ₄ , OP ₅ ,
Capacitances C _f4 , C _f5 inserted between the input ends of OP ₆ ,
C _f6 is used for high frequency noise removal. Among these, the circuit that generates the output voltage E _CR is not necessarily necessary, but is also described for convenience of explanation.

In this way, output voltages E _CL and E _CH corresponding to the capacitances C _H and _CL are obtained. Obtained output voltage
E _CL , ECH are converted to digital values by analog/digital converter ADC ₁ , and temperature sensor T _H
The voltage from is converted into a digital value by an analog/digital converter ADC ₂ .

Next, the flowchart shown in Fig. 3 describes the procedure for executing calculations by the processor CPU shown in Fig. 1 using the digital signals obtained from the capacitances C _H and _CL and the temperature sensor T _H as described above. This will be explained using figures.

First, the relationship between the capacitances C _H and _CL and the displacement x of the common electrode ED ₃ before correction will be explained. displacement x
Common electrode ED ₃ and fixed electrode ED ₁ when is zero,
If the distance from ED ₂ is d, the electrode area of fixed electrodes ED ₁ and ED ₂ is A, and the dielectric constant of the sealing liquid is ε, then the capacitance is
C _H and _CL are as follows: C _H =Aε/d+x (1) C _L =Aε/d−x (2). Determining the displacement x from equations (1) and (2) yields x=dC _L −C _H /C _L +C _H (3). Here, C _L , C _H are current/voltage converters
By CON ₄ and CON ₅ , E _CL =kC _L , E _CH
= _kCH , so equation (3) can be expressed as x=dE _CL −E _CH /E _CL +E _CH (4).

Next, the relationship between the dielectric constant ε of the sealing liquid and the static pressure P _s will be explained. Using equations (1) and (2), the dielectric constant ε of the sealing liquid becomes as follows.

ε=2d/A・C _L C _H /C _H +C _L =2d/A・E _CL・E _CH /E _CL +E
_CH (5) As the temperature T increases, the dielectric constant ε of the sealing liquid decreases,
Since the dielectric constant ε decreases as the static pressure P _s increases, a _T is the temperature coefficient, a _P is the pressure coefficient, T ₀ , P ₀
If the dielectric constant at the reference temperature, reference pressure, and reference temperature is ε ₀ , the dielectric constant ε can be expressed by the following equation.

ε=ε ₀ {1−a _T (T−T ₀ )}{1+a _P (P _s −P ₀ )} Therefore, the static pressure P _s is P _s =1/a _p [1−(ε/ε ₀ )/1−a _T (T−T ₀ )}
+P ₀ (6). However, the voltage between the pace emitter of temperature sensor T _H is V _be , and the temperature sensor when T = 0
When the output voltage of T _H is V _g0 and a is a constant, V _be =V _g0 −aT, and T is obtained as T=V _g0 −V _be /a (7).

Furthermore, a case will be described in which the static pressure P _s and temperature are corrected with respect to the displacement x. The temperature correction coefficient for displacement x is b _T , the static pressure correction coefficient is b _p , and even at displacement x, the sensor section is affected by temperature or static pressure.
Since the SNS deforms, the true displacement X can be expressed by the following equation, assuming that the correction coefficients are C _T and C _p .

X={1+b _T (T-T ₀ )}{1+b _p (P _s −P ₀
)}x+C _T (T-T ₀ )+C _p (P _s -P ₀ ) (8) The digital calculation unit DAD performs calculations in consideration of the above points. Prior to the calculation, the read-only memory ROM stores calculation procedures for equations (4), (5), (6), (7), and (8). In the steps of FIG. 3, the random access memory RAM has coefficients a _p ,
a _T , b _p , b _T , C _p , C _T , a, etc. are set, and physical property values such as d, A, ε ₀ , V _g0 , T ₀ , P ₀ are also set.

In the above state, under the control of the processor CPU, the voltages E _CL and E _CH corresponding to the capacitances C _L and C _H are read from the sensor section SNS through the capacitance conversion section CCV by steps and stored in the random access memory.
Stored in RAM. Using the stored data, the calculation program stored in the read-only memory ROM executes the calculation of the displacement x before correction shown in equation (4) and stores it in the random access memory RAM (step).

After the above calculations, the process moves to the step and uses E _CL and E _CH read in the step to calculate the dielectric constant ε shown in equation (5), and then stores the random access memory.
Store in RAM.

Next, the process moves to step, where the base-emitter voltage V _be is read from the temperature sensor T _H , and the calculation shown in equation (7) is executed to calculate the temperature T (step). In the step, the static pressure P _s shown in equation (6) is calculated using the dielectric constant ε obtained in the step and the temperature T obtained in the step, and the true displacement X shown in equation (8) is calculated using these. calculate. The results of these calculations are stored in the random access memory RAM and the process returns to step. Repeat the same process below.

FIG. 4 is a block diagram showing another embodiment of the capacitance conversion circuit according to the present invention. In the embodiment shown in FIG. 2, when the distance between the sensor section SNS and the capacitance conversion section CCV increases, the capacitance of the cable between the fixed electrodes ED ₁ and ED ₂ and the ground increases, and the capacitance of the cable between the fixed electrodes ED 1 and ED ₂ and the
Stray capacitance between the next windings n ₂ and n ₃ is inserted in parallel.
As a result, a fixed capacitor is inserted in parallel with the capacitances C _L and C _H , which tends to cause errors, but this effect is alleviated in the capacitance converter CCV shown in FIG. 4.

The configuration shown in FIG. 4 differs from the configuration shown in FIG. 2 in that diodes D ₁ to D ₄ are arranged close to the fixed electrodes ED ₁ and ED ₂ and inside the sensor section SNS.
With this configuration, the secondary winding of transformer _T2
Since half-wave rectified average currents I ₅ ' and I ₄ ' flow through n 2 and n ₃ , the influence of stray capacitance between the secondary windings n ₂ and n _{3 and} the ground can be reduced. In addition, since the charges charged in the capacitances C _L and C _H are discharged through the diodes D ₃ and D ₁ , the fixed electrodes ED ₂ and ED ₁ and the diodes
Although an alternating current flows between D ₃ , E ₄ , D ₁ , and D ₁ , the distance therebetween is small because it is within the sensor section SNS, and the influence of the stray capacitance can be ignored.

Note that the circuit portion of the current/voltage converter CON ₆ is provided corresponding to FIG. 2, and is not necessarily required.

FIG. 5 is a block diagram showing still another embodiment of the capacitance conversion circuit according to the present invention. In the embodiment shown in Fig. 4, the sum of the currents flowing through the capacitances C _L and C _H is converted into a voltage via an integrator INT to control the power supply voltage of the oscillator OSC. . Therefore, even if, for example, there is a large change in the capacitance C _L , the range of the voltage E C _L is regulated, so that the analog/digital converter ADC ₁ can be used within a highly accurate range.

Note that to know the capacitance C _L , E _CL = kC _L , for example, the output of the current/voltage converter CON ₄ shown in Figure 2 may be used, but the reference capacitance in Figure 2
It may also be determined by using the output E _CR of C _R to perform the calculation C _L =C _R E _CL /E _CR in the digital arithmetic unit DAD. According to this calculation, the oscillator OSC included in k
effects such as frequency changes can be removed. For _CH , it can be obtained from the relationship: _CH = C _R E _CH /E _CR .

Also, since E _CH = (1-E _CL ), find E _CL ,
E _CH may also be determined by calculation. Furthermore, the temperature sensor T _H can generate a large temperature signal by connecting a plurality of transistors in series. Two analog/digital conversion circuits, ADC ₁ and ADC ₂ , are provided, but
This can be switched and used to form one analog/digital conversion circuit.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, even if the sensor section is deformed due to static pressure or temperature applied to the sealing liquid, correction calculations based on static pressure and temperature can be performed digitally. Since this is carried out, a highly accurate capacitive displacement converter can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Fig. 2 is a block diagram showing the configuration of the capacitance conversion circuit in Fig. 1, Fig. 3 is a flow diagram showing the calculation procedure in Fig. 1, and Fig. 4 shows another configuration of the capacitance conversion circuit in Fig. 1. FIG. 5 is a block diagram showing still another configuration of the capacitive conversion circuit in FIG. 1, and FIG. 6 is a block diagram showing the configuration of a conventional capacitive displacement converting device. SNS...sensor section, CCV...capacitance conversion section,
DAD...Digital calculation unit, CAV...Capacity conversion circuit, ADC ₁ , ADC ₂ ...Analog/digital conversion circuit, CTR...Counter, OPC...Output circuit,
CON ₁ ~ CON ₆ ...Current/voltage converter, ED ₁ ,
ED ₂ ...Fixed electrode, ED ₃ ...Common electrode, INT...Integrator, _T1 , _T2 ...Transformer.

Claims (1)

[Claims] 1 The first and second electrodes are connected to a grounded common electrode.
A sensor section in which electrodes are provided facing each other and a sealing liquid is filled between the electrodes to form first and second capacitances that differentially change according to the displacement to be detected, and a sensor section through a transformer. An AC voltage is applied to the first and second electrodes, a common potential point and the common electrode are connected with a fixed capacitance, and the flowing current is rectified to form the first and second capacitances corresponding to the first and second capacitances. a capacitance conversion means for converting the temperature into a signal; a temperature conversion means embedded in the sensor section and converting the temperature of the sensor section into a corresponding temperature signal; a displacement calculation means for obtaining a displacement signal corresponding to the displacement; and
A dielectric constant calculating means for calculating the dielectric constant of the sealing liquid by calculating the product of the sum of capacitances, a static pressure calculating means for calculating the static pressure signal using the dielectric constant and the temperature signal, and a static pressure calculating means for calculating the static pressure signal using the dielectric constant and the temperature signal. 1. A capacitive conversion device comprising: a correction means for performing a correction calculation using the temperature signal and the static pressure signal to obtain a correction displacement signal; and digital calculation means formed by a microprocessor.