JPS62140040A - Differential pressure converting apparatus - Google Patents

Abstract

PURPOSE:To obtain a highly accurate differential pressure converting apparatus, constituted so as to perform slight correction by digital operation using a differential pressure capacity sensor, a fixed capacity sensor and a temp. sensor reduced in mutual dependence. CONSTITUTION:The title apparatus consists of a detection part 29 provided with a differential capacity sensor forming first and second electrostatic capacitors C1, C2, a fixed capacity sensor 14 detecting fixed capacity Ck and a temp. sensor 13 detecting the temp. of a seal liquid, a microprocessor unit 30 converting differential capacity corresponding to the capacitors C1, C2, a fixed capacity signal corresponding to the capacity Ck and a temp. signal T corresponding to temp. to digital signals to perform operational processing and a D/A converter means 44. The unit 30 calculates the difference of the sum of the capacitors C1, C2 to output a first differential pressure signal corresponding to differential pressure. Further, the static pressure applied to the seal liquid is calculated using the signal T and the fixed capacity signal and the effect of the first differential pressure signal due to static pressure and temp. is corrected using the static pressure signal corresponding to static pressure and the signal T to output a second differential pressure signal which is, in turn, outputted as an analogue signal.

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 via an electrostatic capacitor, and in particular corrects the effects of temperature and static pressure. The present invention relates to a differential pressure converter.

<Prior Art> FIG. 7 is a block diagram for explaining the concept of compensating for zero point fluctuations and span fluctuations due to fluctuations in temperature and static pressure in a conventional differential pressure converter. 1 indicates the cross section of the main body of a differential pressure converter having a one-chamber structure; 1 Diaphragms 2 and 3, which receive the pressure PH1PL to be measured on both end faces, are arranged with their peripheral edges trap-welded to the main body, and are formed in one main body. A hollow chamber surrounded by the through hole 4 and these diamond slams is filled with a sealing liquid 5 such as silicone oil. An enlarged electrode chamber is formed in the center of the hollow chamber, and within this electrode chamber there is a movable electrode 7 supported on one side by an insulating material 6 fitted to the main body, and a movable electrode 7 having capacitances C1 and C2 opposite thereto. Fixed electrodes 8 and 9 to be formed are arranged. 10 connects both diaphragms 2 and 3 through a hollow chamber.
The center part is fixed to the movable electrode 7 in the electrode chamber, and the displacement of the diaphragm in response to the differential pressure trap is transferred @1! Transferred to the L pole, capacitance C1
, C2 are converted to a differential Kt. This signal e. is led to the output circuit 12 and the remote load R? ! For the series circuit of source EB, L' is converted into an output current 1o with a span of 4-20 mA. 1
3 is a temperature sensor for measuring the temperature T of the main body 1 or the seal fr1.5; 14 is a pressure sensor for measuring the pressure of the sealing liquid 5, that is, the static pressure P8; the outputs of these sensors are sent to the compensation voltage generating circuit 15; .161C is derived and converted into a temperature signal for zero point compensation and a static pressure signal ep for zero point compensation.

Tl Output signal e of the arithmetic circuit 11 at addition points 17 and 18. is added to or subtracted from to compensate for zero point fluctuations due to temperature fluctuations or static pressure fluctuations. If span fluctuations caused by changes in the spring constant of the diamond slam 2.3 due to temperature or static pressure fluctuations become a problem, use the temperature signal for span fluctuation compensation indicated by the dotted line in the compensation voltage generation circuit 15.16, and the static pressure signal e',
ep and changes the voltage-to-current conversion gain of the output circuit 12 to compensate for the span variation.

FIG. 8 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.
A) It is composed of a conversion section. As shown in FIG. 8(a)K, a circular diaphragm 20 is thinly formed in the center of the detection part 19, and a pressure PH19 is applied to both sides of the diaphragm 20. There is a differential pressure (ΔP=PH−PL) at the periphery of the diaphragm 20.
A differential pressure sensor 21 for detecting strain corresponding to K is formed, and a static pressure sensor 22 . Silicon single crystal temperature T
A temperature sensor 23 is formed to detect the temperature. An analog-to-digital converter (referred to as a digital converter) that converts analog signals from these sensors into digital signals.
24 is mounted inside the detection section.

Each output from these composite sensors is input to a microprocessor 5 and 25 as shown in FIG. 8(b).

By the way, since each sensor 21, 22, 23 is all made of semiconductor, it is affected by temperature T and static pressure P8.

For example, the differential pressure sensor 21 is not sensitive only to the differential pressure ΔP, but merely has a high sensitivity to the differential pressure ΔPK. Therefore, the output of the differential pressure sensor 21 is X6.

The output of the static pressure sensor 22 is x, the output of the temperature sensor 23 is x
, then.

x f(ΔPIPS, T) x=g(Δp, Ps, T)
(1) It can be expressed as x=h(Δp, Ps, T), and if the functions of f, g, and h are known in each cell, then by solving the simultaneous equations of equation (1), equation (1) can be obtained. The solution is obtained as shown in equation (2).

ΔP ” F (Xdr Xp+ X()Ps= G
(Xd' Xp+ Xt) (2
) T = It (x x + x)
d'pt Identification of these functions f, g, h and functions F, G,
The task of determining H (quantification) is performed for each individual sensor. These characteristic data for each sensor are obtained by the manufacturing computer 26 and stored in the FROM memory 27 as data unique to the detection unit 19, and correction calculations are performed by the microprocessor 25 using this unique data. Ru. 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. 7, 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. ．． Since the temperature sensors 23 are all made of semiconductor, the differential pressure ΔP
, quiet pressure p8. significantly dependent on each other with respect to temperature T])
It has a complicated relationship as shown in the formula. 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 Problems> The present invention provides a simple method for differential pressure output while using differential sound sensors, fixed capacitance sensors, and temperature sensors, which have little dependence between temperature and static pressure. A high-precision differential pressure converter that does not have the above-mentioned problems is obtained by performing sophisticated digital correction calculations, and its configuration is such that the first and second electrodes face the moving electrode. a differential capacitance sensor that forms first and second capacitances that differentially vary depending on the differential pressure to be detected when the sealed liquid is filled between them; a detection unit provided with a fixed capacitance sensor for detecting a fixed capacitance formed therein and a temperature sensor for detecting the temperature of a sealed liquid; a differential capacitor 1 corresponding to a first and second capacitance; A microcomputer unit that converts the corresponding fixed capacitance signal and the temperature signal corresponding to the temperature into digital signals and performs arithmetic processing; and a digital-to-analog conversion means that converts the arithmetic results of the microcomputer unit into an analog signal. A differential pressure conversion device having a microcomputer unit that calculates the difference between the sums of the first and second capacitances and outputs a 7'c first differential pressure signal corresponding to the differential pressure. a static pressure calculation means that calculates static pressure applied to the sealed liquid using the pressure calculation means and the temperature signal and the fixed capacitance signal;

Using the static pressure signal and temperature signal corresponding to this static pressure, the first
a correction calculation means for correcting the influence of static pressure and temperature on the differential pressure signal and outputting the second differential pressure signal;
The differential pressure signal is output as an analog signal.

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

FIG. 1 is a diagram showing an embodiment of the present invention.

This is a diagram. 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 detection portion, which is almost the same as the portion mechanically connected to the main body 1 as one body in FIG. 30 is Micro Combita Uni.

It is. 31 is a capacitance/time converter that converts the capacitances CI, C2 and fixed capacitance cK into corresponding time signals, and 32 is a timer counter that converts the time signals into digital values, which perform analog/digital conversion. Vessel 33
It consists of The temperature signal T from the temperature sensor 13 in the detection section 29 is converted into a digital value by an analog/digital converter 34. 35 is RAM (Random Access Memory), 36 is ROM (Read Only Memory), and the addressing of these is CPU (processor).
37 Gara bus 38. This is done via a latch decoder 39. 4o is a data bus. Timer counter 32.
The output data from the analog/digital converter 34 is RA
Stored in M35.

A predetermined calculation program and initial data are stored in the ROM 36, and are 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
Stored in M35. Note that the illustration of the control path is omitted.

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

FIG. 2 shows the capacitance ic1. of the capacitance/time converter 31 in FIG. FIG. 3 is a schematic diagram showing the configuration of a differential capacitance/time conversion section 31a that converts C2 into time.

Transfer! A floating capacitor C8l is formed between the hW1 capacitor 7 and the common potential point COM, and the moving capacitor 7 is connected to the inverter G.
It is connected to the input terminal of 1. The output terminal of inverter G1 is connected to the input terminal CL of counter cT1 via inverter G2.
It is connected to the. One end of the input of the Nandt gate G3 is connected to the output end Q of the counter cT1.

One end of the input of the Nant gate G4 is the n-bit output end Q of the counter CT. and are connected via inverter G5. Nandogelt G3. The other ends of G4 are connected to the output ends of inverter G1, and these output ends are connected to fixed j1 poles 9 and 8, respectively.

Also, Natsutogate G3. Each input terminal of a Nandt 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 CC1. Note that each element is formed of CMO8, for example.

Output terminal Q of counter CT1. is held negative (low level) during the period T gate/gate G4. Capacitance *C1,
A positive feedback loop composed of inverter G1 is formed. Therefore, when the potential at the output terminal of the Nant gate G4 is positive power supply voltage +E()-Irepel), the parallel capacitor C1 is charged and the input voltage of the inverter G1 rises, and when it reaches the threshold voltage vTH, the inverter G1 The potential at the output end of the output terminal falls vertically to a negative power supply voltage -E (low level). Therefore, the output terminal of the Nante gate G4 becomes high level, and the output terminal of the Nante gate G3 remains high level as long as the output terminal Qn of the counter CT1 is held at low level, so the output terminal of the Nante gate G6 becomes high level. The level becomes low and the bidirectional constant current circuit CC1 starts discharging the charge in the capacitor tC1 at a constant current value i. Therefore, the potential at the input end of the inverter G1 decreases at a constant rate, and when it reaches the threshold voltage V T HK, the potential at the output end of the inverter G1 is reversed to the level. The time from the fall of 1 to reaching the threshold voltage vTH due to discharge of the bidirectional constant current circuit CC1,
is proportional to the capacitance C1.

Next, when the potential at the output end of the inverter G1 goes to -E level, the potential at the output end of the gate G4 goes to the low level, and the capacitor C1 is charged in the opposite direction.

In this case, the potential at the output terminal of the Nant gate G6 becomes 71 level, and from the bidirectional constant current circuit CC1, the capacitance C1
is charged with a constant current value i, the potential at the input terminal of the inverter G1 increases at a constant rate, and the threshold voltage vT
When reaching H, the potential at the output end of inverter G1 is inverted to low level. The time 1, / for this inverter G1 to reverse is also proportional to the capacitance C1. The above operation is repeated until the counter CT1 counts n bits. Therefore, the potential at the output terminal Q of the counter CT1 has a value proportional to the capacitance C1 by the period T1 during which the potential at the output terminal Q of the counter CT1 is held at a low level.

When the counter CT1 counts n bits, the potential at its output terminal Q is inverted to high level, and the Nant gate G3. Capacitance tc2. A positive feedback loop constituted by inverter G1 is selected and oscillates in the same manner as when the output terminal of counter CT1 is held at a low level. Therefore, the period T2 during which the output terminal Q of the color/return CT1 is held at a high level is proportional to the capacitance C2.

As above, differential capacity! The t/time converter 31a converts the capacitance CC periodically for times TI and T2K.

1' 2 Converted time T1. T2 is converted into a digital value by a timer counter 32, and the temperature signal TVi is converted into a digital value by an A/D'R converter 34.

FIG. 3 is a block diagram showing the configuration of a regular customer f1'/time converter 31b of the capacity/time converter 31 in FIG. 1, which converts the regular customer "iCK" into time.

The connection point between one end of the fixed customer iIt'CK that detects fluctuations in the static pressure P8 and the common potential point COM is connected to the input end of the inverter G7, and a bidirectional constant current circuit CC2 is connected between the output end and the input end of the inverter G7. It is connected. The input end of the inverter G8 is connected to the output end of the inverter G7, the output end of which is connected to the other end of the fixed capacitor CK, and the input end CL of the Kn-bit counter CT2. Counter CT2
A time signal is obtained from the output terminal Qn of the fixed customer, which is converted into a time signal.

The input terminal of inverter G7 is at that level, the shoulder voltage vT
When the voltage exceeds H and suddenly becomes low, the output terminal becomes low level. Therefore, a constant current i is generated from the bidirectional constant current circuit CCK from the input end to the output end of the inverter G7.
to start discharging. As the discharge progresses and reaches the threshold voltage vTH of inverter G7, its output terminal suddenly...
The other end of the regular customer aCK becomes low level. As a result, the input terminal of the inverter G7 becomes a low level, the output terminal becomes an I/I level, and the fixed capacitor is charged with a constant current 1 from the bidirectional constant current circuit CC2. As a result of charging, the voltage at the input terminal of inverter G7 becomes the threshold voltage V.
When TH is reached, the level at the output terminal is inverted. The oscillation continues by repeating the above operation, but at this time of discharge 1i
ft and the charging time are values proportional to the fixed customer ryccK, so the output terminal Q of the counter CT2. A time signal proportional to the fixed volume is obtained.

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

First, electrostatic window-1c1. The relationship between c2 and the differential pressure ΔPfx before correction will be explained. If the value of each capacitance CC when the differential pressure ΔP is zero is C8, and the spring constant of the moving electrode 7 is K, then the electrostatic window 1tc1. C2 appears as. From these equations, the differential pressure ΔP is determined.

Next, the relationship between the static pressure P8, the fixed capacity record, and the temperature T will be explained. @When the degree T increases, the fixed customer tCK decreases as the dielectric constant C of the sealing liquid 5 decreases, and when the static pressure P8 increases, the fixed customer 1C increases as the conductivity 518Xg increases, so let a and b be constants. Then, the fixed expression domain is expressed by the following equation.

CK=aPs-bT (6)
From this relationship, the static pressure P8 is calculated as 1 b (7) PS-7C
It becomes K+〒T. If α and β are respectively correction coefficients for T, then, (8) where α=1/a and β=−b/a, Ps”αCK−βT(8) is obtained.

On the other hand, the differential pressure ΔP is expressed by equation (5), and this equation (5) is expressed in the ideal case, that is, the fixed electrodes 8, 9. This equation holds true in the case where the moving electrodes 7 are parallel to each other and the spring constant is also constant. However, in reality, when the static pressure P8 or the temperature T changes, the main body 1 deforms (
5) The differential pressure ΔP obtained by formula changes. Therefore, the differential pressure Δ
It is necessary to correct P. The correction coefficient for static pressure P8 is set to 1. Assuming that the correction coefficient for temperature is 2, the corrected differential pressure ΔPC is as follows.

ΔP = ΔP(]+klps+2T)
(9) The microcomputers 22 and 30 are operated in consideration of all the above points. Prior to calculation, ROM
In step 36, the static pressure PS and temperature T are set as initial data as shown in step and step ■, and further in step and step (5),
(8).

The calculation procedure for each equation (9) is stored. RAM 35
K is.

1 as a correction factor. 2. α, β, and spring constant K are set in steps and steps ■.

In the above state, the electrostatic window flk CI and C2 are read by the detection section 29 under the control of the CPU 37 (Step 2) and stored in the RAM 35. Using the stored data, the differential pressure calculation shown in equation (5) is executed by the calculation program stored in the ROM 36 and stored in the RAM 35.

Next, the calculation program stored in the ROM 36 uses the static pressure Ps set in step and step ①, the submergence temperature, and the data of ∆P obtained by calculating the differential pressure in equation (5) as initial values, and executes (9). Execute the differential pressure calculation (steps, steps) shown in the formula. The calculation result is output via the digital/analog converter 44.

Because the temperature T and static pressure P8 do not change in a short time.

Compared to the calculation cycle of differential pressure ΔP in equation (5), (9
) Correction term for the differential pressure ΔP of the differential pressure ΔPo shown in equation 11
The temperature T and static pressure P8 may be read and corrected in cycles of 5 to 1/10. Therefore, this correction cycle is determined in steps and steps (3). If the predetermined correction cycle has not been reached, the capacitances C1 and C2 are repeatedly read. When the predetermined correction cycle is reached, proceed to step ■ and set the fixed capacitance C.
Read K. Next, Ste.

Step a) reads the hot water temperature T, calculates the static pressure P8 shown by equation (8), and returns to step ■) and step ■.

The calculations in the next step and step q) are executed using the temperature T read in step and step ① and the static pressure Ps obtained in step and step ①.

The same procedure is repeated below.

FIG. 5 is a block diagram in which the differential capacitance/time converter 31a and the fixed capacitance/time converter 31b shown in FIGS. 2 and 3 are integrated into a capacitance/time converter 31.

By applying a control signal to the terminal 45, it is switched to either the differential capacitance/time conversion section 31a shown in FIG. 2 or the fixed capacitance/time conversion section 31b shown in FIG. 3, and the obtained signal is output. obtained from terminal 46.

The input end of inverter G9 is connected to terminal 45. Nantes Gate 6
4' and 03', and its output terminal is connected to one input terminal of the Nandt gate 08'. The output end of Nantes Gate G8' is connected to the other end of fixed customer tCK and
are connected to one end of the input gate G6', and the third
It has the same function as inverter G8 in the figure. One end of capacitance J1kC1, C2 and fixed capacitance CK is floating capacitance f
It is coupled to the common potential point COM at C83. Nant gate G3', 04' is G3.04' in FIG. It functions similarly to G4.

Next, the operation of the capacitance/time converter 31 shown in FIG. 5 will be explained using the waveform diagram shown in FIG. 6.

Control signal S. When set to high level (FIG. 6(A)), the Nand gate G', 04' becomes the Nand gate G3.04 shown in FIG. It has the same functions as G4. Also, at this time, the Nant gate 08' is kept off and does not function. Also,
(S/Toge) G6' is because the output of Nantes gate 08' is held at high level.

It has the same function as the gate G6 in FIG.

Therefore, during the period in which the control signal Sc is at a high level, the block diagram becomes the same as that shown in FIG. 2, as shown in FIG. 6 (b).

As shown in (c), at the output terminal 46, a time T1 corresponding to the capacitance fC1 is obtained at the high level, and a time T2 corresponding to the capacitance C2 is obtained at the low level.

Next, the control signal S. When set to low level (Fig. 6 (a)), the output terminals of Nant gates 03' and 04' become high level, and the output terminal of Nant gate 06' becomes the output terminal of inverter G1 via Nant gate G8'. The level changes in phase with the level of . Therefore, the control signal S. During the period when is at a low level, the curve shown in FIG. 3 is obtained.

In the above description, as shown in FIGS. 2 and 3, output signals are obtained as times TT and TK corresponding to the capacitance it ct , C2 and the fixed capacity, and 1'
2. The timer counter 32 inputs data as a digital signal to the microconbeater unit 30.

This is not limited to this, and any device that can convert an analog signal into a digital signal may be used.

Also, in equation (9), static pressure p8. Although linear correction was performed for m degree TK, non-linear (quadratic or cubic) correction may be performed if necessary.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, slight correction is made by digital calculation using a differential pressure capacitance sensor with little interdependence, a fixed capacitance sensor, and a temperature sensor. Since the structure is configured to do this, correction calculations are simpler than in the past, and moreover, correction can be performed with high precision.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention. Figure 2 is a block diagram showing the configuration of a part of the capacity/time converter in Figure 1, and Figure 3 is a block diagram showing the configuration of another part of the capacity/time converter in Figure 1. Figure 4 is a flowchart diagram showing the calculation procedure in Figure 1, Figure 5 is a professional diagram showing another configuration of capacity/time conversion* in Figure 1;
6 is a waveform diagram explaining the operation of the embodiment shown in FIG. 5, and FIG. 7 is a configuration diagram showing the configuration of a conventional differential pressure converting device. FIG. 8 is a configuration diagram showing the configuration of another conventional differential pressure converter. 1... Main body, 5... Sealing liquid, 7... Moving electrode, 8,
9... Fixed electrode, 11... Arithmetic circuit, 19,
29...Detection section, 20...Diaphragm, 21.
... Differential pressure sensor, 22... Static pressure sensor. 23...Temperature sensor? , 30... Microcomputer unit, 31... Capacity/time converter, 33.3
4...Analog/digital converter, 35...RAM
, 36...ROM, 37...CPU, 44...
・Digital/analog converter, CIl C2...Capacitance, C...Fixed customer 11. CC, CC2... 1 current circuit for both identification, CT1. CT2...Counter. Fig. 2 31a Difference tIJ capacity 78 Aoma t' exchange Fig. 3 31b Fixed official amount/Shima Fyo Juku Fig. 4

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 detection unit provided with a differential capacitance sensor that forms a capacitance, a fixed capacitance sensor that detects a fixed capacitance formed in the filled liquid, and a temperature sensor that detects the temperature of the filled liquid; A microcomputer unit that converts a differential capacitance corresponding to the second capacitance, a fixed capacitance signal corresponding to the fixed capacitance, and a temperature signal corresponding to the temperature into digital signals and performs arithmetic processing; digital-to-analog converting means for converting a calculation result into an analog signal, wherein the microcomputer unit calculates a difference between sums of the first and second capacitances, differential pressure calculation means for outputting a first differential pressure signal corresponding to the pressure; static pressure calculation means for calculating the static pressure applied to the sealed liquid using the temperature signal and the fixed capacitance signal; correction calculation means for correcting the influence of the static pressure and the temperature on the first differential pressure signal using the static pressure signal corresponding to the pressure and the temperature signal, and outputting a second differential pressure signal; , a differential pressure conversion device that outputs this second differential pressure signal as the analog signal.