JPS62140039A - Differential pressure converting apparatus - Google Patents

Abstract

PURPOSE:To obtain a highly accurate converting apparatus, constituted so as to perform slight correction by digital operation using a differential pressure capacity sensor and a temp. sensor reduced in mutual dependence. CONSTITUTION:An apparatus consists of a differential capacity sensor 29 forming first and second electrostatic capacitors C1, C2, a temp. sensor 13 detrecting the temp. of a seal liquid, a microprocessor unit 30 and a D/A converter means 44 converting the operation result in the unit 30 to an analogue signal. The unit 30 operates the difference of the sum of the electrostatic capacitors C1, C2 to output a first differential pressure signal corresponding to differential pressure and calculates the product of the sum thereof to output a dielectric constant signal corresponding to the dielectric con..stant of the seal liquid. Then, static pressure applied to the seal liquid calculated using the temp. signal T from the sensor 13 and the dielectric constant signal thereof and the effect of the first differential pressure signal due to static pressure and temp. is corrected using the static signal corresponding to the static pressure and the signal T to output a second differential pressure signal which is, in turn, outputted as an analogue signal by the converter means 44.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a differential pressure converting device that converts differential pressure into an electric signal button via capacitance, and particularly relates to a differential pressure converting device that converts differential pressure into an electric signal button via capacitance, and in particular, This invention relates to a pressure converter.

<Prior Art> FIG. 4 is a configuration diagram for explaining the concept of compensating for zero point fluctuation and span fluctuation due to fluctuations in temperature and static pressure in a conventional differential pressure converter. 1 shows a cross section of the main body of a differential pressure converter having a one-chamber structure, and a diaphragm 2.3 that receives the pressure PHn PL to be measured is placed on both end faces with its peripheral edge welded to this main body. A sealing liquid 5 such as silicone oil is contained in the hollow chamber surrounded by the through hole 4 and these diaphragms.
is fulfilled. An enlarged electrode chamber is formed in the center of the hollow chamber, and an insulating material 6 fitted to the main body is placed inside this electrode chamber.
A movable electrode 7 supported on one side and fixed electrodes 8 and 9 for forming an electrostatic capacitance CxpCz are arranged opposite to the movable electrode 7 . 10 connects both diaphragms 2 through a hollow chamber,
The rod connects the central part of 3, and the central part is fixed to the movable electrode 7 in the electrode chamber, transmits the displacement of the diaphragm in response to the differential pressure to the movable electrode, and increases the capacitance Ctt.
Differentially change Cz. The capacitance Cx*C2 is led to the arithmetic circuit 11 and is expressed as (C2-CI)/'(C2+C
The extraction calculation is performed, and the DC output signal e. is converted to This signal e. is led to the output circuit 12 to output the remote load RL
, an output current of 4 to 20 mA span for the series circuit of power supply EB. It can be converted to . 13 is the main body 1 or sealing liquid 5
14 is a pressure sensor that measures the pressure of the sealing liquid 5, that is, the static pressure Ps, and the outputs of these sensors are sent to the compensation voltage generating circuit 15. , 16, temperature signal eT for zero point compensation, static pressure signal e for zero point compensation
The output signal e of the arithmetic circuit 11 at addition points 17 and 18 is converted into p. By adding or subtracting from , zero point fluctuations due to temperature fluctuations or static pressure fluctuations are compensated for. If span fluctuations caused by changes in the spring constants of diaphragms 2 and 3 due to temperature or static pressure fluctuations become a problem, compensate voltage generation circuit 1
From 5.16, the temperature signal for span fluctuation compensation shown by the dotted line,
Static pressure signal eT1. e and l are generated and the voltage-to-current conversion gain of the output circuit 12 is varied to compensate for span fluctuations.

FIG. 5 is a configuration diagram showing another conventional configuration of a differential pressure converter. This differential pressure converter has a detection section 19 that is connected to a sensor and a
/' Consists of a D conversion section. As shown in FIG. 5(A), a thin circular diaphragm 20 is formed in the center of the detection part 19, and a pressure PH29 is applied to both sides of the diaphragm 20.

The peripheral edge of the diaphragm 20 has a differential pressure (ΔP=PH−PL
) is formed.A static pressure sensor 22 is formed on the fixed part outside the diaphragm 20 to detect the static pressure P8, and a static pressure sensor 22 is formed to detect the temperature T of the silicon single crystal. A temperature sensor 23 is formed for this purpose.

An analog-to-digital converter (referred to as an A/'D converter) 24 that converts analog signals from these sensors into digital signals is mounted in the detector.

Each output from these composite sensors is inputted to a microprocessor 25 as shown in FIG. 5(b).

By the way, since each of the sensors 21, 22, and 23 are all made of semiconductor, they are affected by the temperature T1 and the static pressure Ps.

For example, the differential pressure sensor 21 is not only sensitive to the differential pressure ΔP, but merely has a high sensitivity to the differential pressure ΔP. Therefore, if the output of the differential pressure sensor 21 is Xds, the output of static pressure sensor 22 is Xps, and the output of temperature sensor 23 is xl, it can be expressed as follows.If the functions of f, g, and h are known for each sensor, (1 ) by solving the simultaneous equations of (
The solution to equation (1) is found as shown in equation (2).

ΔP =F(X, Iy Xpp x,) j
Identification of these functions r, g, h and functions F, G
, H (quantification) can be carried out for each individual sensor. The characteristic data of these sensors is obtained by the manufacturing calculator 26, and is stored in the FROM memo 1J.
27 as data unique to the detection unit 19, and the microprocessor 25 performs a correction calculation using this unique data. The result is converted into an analog voltage by a digital-to-analog converter (referred to as a D/A converter) 28, and further transmitted as a direct current of 4 to 20 mA.

<Problems to be Solved by the Invention> However, in the conventional differential pressure converter shown in FIG. 4, the signal e corresponding to the differential pressure ΔPK. Since the zero point or span is corrected in an analog manner, there is a problem that highly accurate correction cannot be performed.In the conventional differential pressure converter shown in FIG. , temperature sensor 23 are both made of semiconductor, so the differential pressure ΔP
, the static pressure Ps, and the temperature T are significantly dependent on each other and 1
) has a complicated relationship as shown in the equation. Solving the simultaneous equations of equation (1) so as to obtain the functional relationship shown by equation (2) requires complicated calculations, which causes a problem of decreased accuracy or yield.

<Means for solving the problem> The present invention uses a differential capacitance sensor and a temperature sensor.
It is designed to obtain a high-precision differential pressure converter that does not have the above-mentioned problems by performing simple digital correction calculations on the differential pressure output while using sensors with little dependence between static pressures. Its structure is such that a first electrode and a second electrode are provided facing the moving electrode, and the sealed liquid is swirled between them to differentially adjust the pressure according to the differential pressure to be detected. and the second
A differential capacitance sensor that forms capacitance, a temperature sensor that detects the temperature of the sealed liquid, and a capacitance signal that corresponds to the first and second capacitances and a temperature signal that corresponds to the temperature are converted into digital signals. A differential pressure converter has a microcomputer unit that performs arithmetic processing, and a digital-to-analog converter that converts the arithmetic results of the microcomputer unit into an analog signal, the microcomputer unit converting the first and second electrostatic charges. differential pressure calculating means for calculating the difference in the sum of the capacitances and outputting a first differential pressure signal corresponding to the differential pressure; a dielectric constant calculation means that outputs a dielectric constant signal corresponding to the dielectric constant; a static pressure calculation means that uses the temperature signal and the dielectric constant signal to calculate the static pressure applied to the filled liquid; a correction calculating means for correcting the influence of static pressure and temperature on the first differential pressure signal using the pressure signal and the temperature signal and outputting the second differential pressure signal; It is designed to be output as a signal.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. Note that the same reference numerals are given to the parts having the same functions as in the prior art, and the explanation will be omitted as appropriate.

Reference numeral 29 denotes a differential capacitance sensor, which is substantially the same as the part mechanically connected to the main body 1 in FIG. 4. 30 is a microcombination unit. 31 is a capacitance c1. A capacitance/time converter converts c2 into a corresponding time signal, and 32 is a timer counter that converts the time signal into a digital value, and these constitute an analog/digital converter 33. The temperature signal T from the temperature sensor 13 in the differential capacitance sensor 29 is converted into a digital value by an analog/digital converter 34. 35 is RAM (random access memory), 36
is a ROM (read only memory), and these addresses are specified from the CPU (processor) 37 to the bus 38.
, through the latch decoder 39. 4o is a data bus. Output data from the timer counter 32 and analog/digital converter 34 are stored in the RAM 35.

The ROM 36 stores predetermined calculation programs and initial data, and is stored in the ROM 3 under the control of the CPU 37.
The result calculated according to the calculation procedure stored in 6 is RA.
M35(+?: Stored. Note that the control bus is not shown.

The final calculation result is converted into a side signal by a timer/counter 41, and the data signal is converted into an analog signal by a duty/analog converter 42 and outputted to an output terminal 43. The timer/counter 41 and the duty/analog converter 42 constitute a digital/analog converter 44.

FIG. 2 is a block diagram showing the configuration of the capacitance/time converter in FIG. 1.

There is a stray capacitance C8 between the moving electrode 7 and the common potential point COM.
is formed, and the moving electrode 7 is connected to the input end of the inverter G1. The output end of the inverter G1 is connected to the input end CLK of the counter CT via the inverter G2. One end of the input of Nant gate G3 is counter CT
One end of the input of the Nandt gate G4 is connected to the n-bit output terminal Qn of the counter CT via an inverter G5. Nando Day) G3. G4
The other input ends of the inverter G1 are connected to the output ends of the inverter G1, and the output ends thereof are connected to the fixed electrodes 9 and 8, respectively.

Well, 1! Nando Day) G3. Each input terminal of a gate G6 is connected between the output terminals of G4, and the output terminal thereof is connected to the input terminal of an inverter G1 via a bidirectional constant current circuit OO. Note that each element is formed of, for example, 0MO8.

During the period when the output terminal Qn of the counter OT is held negative (low level), a positive feedback loop is formed by the tenant gate G4, the capacitance 01, and the inverter G1.

Therefore, when the potential at the output end of the Nant gate G4 is a positive power supply voltage E (high level), the capacitance 01 is charged, the input voltage of the inverter G1 rises, and when it reaches the threshold voltage vTH, the output of the inverter G1 The potential at the end falls vertically to a negative power supply voltage -K (low level). Therefore, the output terminal of Nant gate G4 becomes high level,
The output terminal of the Nant gate G3 is the output terminal Qn of the counter OT.
As long as is held at a low level, it remains at a high level, so the output terminal of the Nant gate G6 becomes a low level, and the bidirectional constant current circuit C○ discharges the charge of the capacitance 01 with a constant current value of 1. Begin to. Therefore, the potential at the input terminal of inverter G1 decreases at a constant rate, reaching the threshold voltage v
When T■( is reached, the potential at the output end of inverter G1 is inverted to high level. The time t1 from the fall of the input voltage of inverter G1 until reaching the threshold voltage vTH due to discharge of bidirectional constant current circuit C0 is It is proportional to the capacitance [01.

Next, when the potential at the output end of the inverter G1 becomes high level, the potential at the output end of the Nandt gate G4 becomes low level, and the capacitance C1 is charged in the opposite direction.

In this case, the potential at the output end of the Nant gate G6 becomes high level, and the capacitor 01 is charged with a constant current value i by the bidirectional constant current circuit CO, and the potential at the input end of the inverter G1 increases at a constant rate. When the threshold voltage vTH is reached, the potential at the output terminal of the inverter G1 is inverted to a low level. Time t' until this inverter Gl is inverted
is also proportional to the capacitance C1. The above operation is repeated until the counter OT counts n bits. Therefore, the period T1 during which the potential of the output terminal Qn of the counter OT is held at a low level has a value proportional to the capacitance 01.

When the counter OT counts n bits, the potential at its output terminal Qn is inverted to high level, and the Nant gate G3. A positive feedback loop composed of capacitance 02 and inverter G1 is selected, and oscillates in the same manner as when the output terminal of counter OT is held at a low level. Therefore, the period T2 during which the output terminal Qn of the counter OT is held at a high level is proportional to the capacitance C2.

As described above, the capacitance/time converter 31 periodically converts the capacitances 01 and 02 into time T1-T2.

The timer counter 32 converts the converted time TI-T2 into a digital value, and the A/D converter 34 converts the temperature signal T into a digital value.

The processing of these converted digital values in FIG. 1 will now be described with reference to the flowchart shown in FIG.

First, the relationship between the capacitances 0□, 0□ and the differential pressure ΔP before correction will be explained. When the differential pressure ΔP is zero, the value of each capacitance 01.0□ is O8, and the spring constant of the moving electrode 7 is K.
Then, the capacitance 00,0□ is 01 = CO 1
It can be expressed as w(s) 02=Coding sales w(4). From these equations, the differential pressure ΔP is as follows.

Furthermore, if the dielectric constant of the sealing liquid 5 is 8 and the capacitance in vacuum is Cv, the capacitance of 0° is 0° = gov, so (3
), using equation (4).

Next, the relationship between dielectric constant ε, static pressure ps, and W degree T will be explained. As the temperature T rises, the dielectric constant a decreases, and the static pressure P
As 3 increases, the dielectric constant 6 increases. Therefore, if the dielectric constant at the reference temperature is 0' where a+b is a constant, the dielectric constant C is expressed by the following equation.

ε= a (1-aT+bPs)
(7) Modifying this, the static pressure P8 becomes. The rate of change of permittivity 8 is Δ6, α=17b, β=
-a/b, equation (8) becomes Ps=α·Δε−βT(9). α and β are correction coefficients for Δ1 and T, respectively.

On the other hand, the differential pressure ΔP is expressed by equation (5), which is expressed in the ideal case, that is, when the fixed electrodes 8 and 9 and the movable electrode 7 are parallel to each other, and the spring constant is also constant. This formula holds true in such cases. However, in reality, when the static pressure P3 or temperature T changes, the main body l deforms (
5) The differential pressure ΔP obtained by formula changes. Therefore, the differential pressure Δ
It is necessary to correct P. Assuming that the correction coefficient for static pressure PS is 1 and the correction coefficient for temperature is 2, the corrected differential pressure ΔPo becomes K as follows.

ΔP = ΔF (1+kIPs+k, 2T)
The microcomputer unit 30 is operated by taking the above points into consideration. %ROM 36 before operation
As initial data, the static pressure P is set as shown in step ■.
Temperature T, dielectric constant ε. is set, and further, in step S+ (2), the calculation procedures of each equation (5), (6), (9), and 111 are stored. RAM35, 0 as correction coefficient, k2, σ, β, spring constant, X empty capacitance C
V is set at step t.

In the above state, the static capacitances C1 and C2 are read from the differential capacitance sensor 29 under the control of the CPU 37 (step 2) and stored in the RAM 35. Using the stored data, the calculation program stored in the box 0M36 executes the differential pressure calculation shown in (5) 2 and stores it in the box AM35.

Next, using the static pressure P8, temperature T, and ΔP data obtained from the differential pressure calculation of equation (5) as initial values, the difference shown in equation 00 is calculated using the calculation program stored in 0M36. Execute pressure calculation (step ■). The calculation result is output via the digital/analog converter 44.

Since temperature T1 and static pressure P8 do not change in a short time, (5)
Compared to the calculation cycle of the differential pressure ΔP in the formula, the correction term for the differential pressure ΔPK of the differential pressure ΔPa shown in the four formulas is 175 to 1/1
The temperature T and the static pressure 8 may be read and corrected in the 0 cycle. Therefore, in step (2), this correction cycle is determined. If the predetermined correction period is not reached, the capacitance C1,
Repeat the 0° reading. When the predetermined correction period has been reached, proceed to step (2) to perform the dielectric constant calculation shown in equation 6), read the temperature T in step (2), and execute the calculation of the static pressure Ps shown in equation (9) in step (2). ), return to step ■.

The calculation in the next step (2) is executed using the temperature T read in step (2) and the static pressure PS obtained in step (2). Hereafter, repeat the process in the same manner.

In the above explanation, as shown in FIG. 2, the capacitance tC
An output signal is obtained as a time Ti, T2 corresponding to 1, C2, and the timer counter 32 inputs the data as a digital signal to the microcombiner unit 30, but this is not limited to this, and the analog signal can be converted into a digital signal. It is fine as long as it can be converted to .

Further, in equation (2), static pressure P8 and temperature TK are linearly corrected, but non-linear (quadratic or cubic) correction may be made if necessary.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, a configuration is adopted in which a slight correction is made by digital calculation using a differential pressure capacitance sensor and a temperature sensor, which are slightly interdependent. Therefore, correction calculations are simpler than in the past, and correction can be performed with high precision.

[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 specific configuration of the capacitance/time converter in Fig. 1, Fig. 3 is a flowchart showing the calculation procedure in Fig. 1, and Fig. 4 is a conventional differential pressure converter. FIG. 5 is a configuration diagram showing the configuration of another conventional differential pressure converter. l...Main body, 5...Sealing liquid, 7...Moving electrode, 8,
9... Fixed electrode, 11... Arithmetic circuit, 19... Detection unit, 20... Diaphragm, 21... Differential pressure sensor, 22... Static pressure sensor, 23... Temperature sensor, 29
... Differential capacitance sensor, 30 ... Microcomputer unit, 33.34 ... Analog/digital converter, 35 ... RAM, 36 ... OM, 37
...CPU, 44...Digital/analog converter, C1, C2...Capacitance, CO...Bidirectional constant current circuit, OT...Counter. Fig. 2 Mi1 capacitance/Usima transformer

Claims (1)

[Claims] A first electrode and a second electrode are provided to face the moving electrode, and a sealed liquid is filled between the first and second electrodes, and the first and second electrostatic charges vary differentially in accordance with the differential pressure to be detected. a differential capacitance sensor forming a capacitance, a temperature sensor detecting the temperature of the sealed liquid, and converting a capacitance signal corresponding to the first and second capacitances and a temperature signal corresponding to the temperature into digital signals. A differential pressure conversion device comprising: a microcomputer unit that performs calculation processing; and digital-to-analog conversion means that converts the calculation result of the microcomputer unit into an analog signal; differential pressure calculating means for calculating the difference between the sums of the two capacitances and outputting a first differential pressure signal corresponding to the differential pressure; and calculating the product of the sums of the first and second capacitances. a dielectric constant calculation means for outputting a dielectric constant signal corresponding to the dielectric constant of the filled liquid; and a static pressure calculation means for calculating a static pressure applied to the filled liquid using the temperature signal and the dielectric constant signal. and a correction calculation means for correcting the influence of the first differential pressure signal due to the static pressure and the temperature using the static pressure signal corresponding to the static pressure and the temperature signal and outputting a second differential pressure signal. A differential pressure conversion device that generates a second differential pressure signal and outputs the second differential pressure signal as the analog signal.