RU2010202C1 - Capacitive pressure transducer and device to form its output signal - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: capacitive pressure transducer has main membrane with bearing base, electrodes located in central part of membrane and on its bearing base, supplementary membrane with elastic center and bearing base and electrodes, output conductors partially placed into interelectrode gap. Peripheral electrode of supplementary membrane is put on its elastic center. Pressure block is manufactured in the form of plate. Supplementary membrane is hermetically joined to pressure block with the aid of bushing. Dielectric film located on planar surfaces of membranes is used for insulation of electrodes. Sealed coupling of supplementary membrane with main one is accomplished through pressure block and ring. Device to form output signal of capacitive pressure transducer has first and second amplifiers, reference capacitors connected to input of first amplifier through first commutation key and instrument capacitor placed into feedback circuit of first amplifier. Reference and instrument capacitors are by turns connected into feedback circuit through second commutation key. Output of first amplifier is by turns connected through third key in step with first commutation key to non-inverting and inverting inputs of second amplifier which output is linked to integrator. EFFECT: expanded operational capabilities, increased reliability. 2 cl, 2 dwg

Description

 The invention relates to measuring equipment, in particular to capacitive pressure sensors intended for use in various fields of science, technology and national economy.

 Known capacitive pressure sensor containing a curved membrane and a flat metal plate. Two ring-shaped electrodes are installed on the membrane, the first being a measuring one and the second a reference one. The reference plate facing the curved surface of the membrane also contains a sensing element made in the form of an annular electrode, which together with the membrane electrode forms a capacitive sensor. A mechanical spacer installed in the central part of the space between the membrane and the reference plate maintains a constant distance between them, without interfering with the deflection of the membrane. The reference plate is closed by a lid that connects to the membrane along the perimeter. A reference ring-shaped electrode is mounted on the lid, the position of which corresponds to a reference ring-shaped electrode on the membrane. These two ring-shaped electrodes form a reference capacitive sensor [1].

 The closest in technical essence to the proposed design is a pressure sensor containing a housing, a membrane with a rigid center and a support base, a diaphragm mounted on the membrane, and a capacitive strain transducer in the form of two pairs of opposite electrodes located in the center and periphery of the membrane and diaphragm [2 ].

 A disadvantage of the known designs is the inability to measure the excess pressure and the pressure difference due to the need in this case to directly contact the environment or the second measured pressure with the electrodes of the capacitors and the destabilizing effect of the environmental characteristics on the dielectric gaps.

 A known device for generating the output signal of a pressure sensor containing a voltage generator, a reference capacitor with an amplifier, in the feedback circuit of which is included a measuring capacitor of the sensor [3].

 A disadvantage of the known device is the inability to form an output signal when measuring overpressure and pressure difference with sufficiently high accuracy and sensitivity.

 In a capacitive pressure sensor containing the main elastic element in the form of a membrane with a rigid center, made in one piece with the supporting base, the Central and peripheral electrodes located respectively in the Central part of the elastic element and on its supporting base, located with a gap and hermetically connected to the main an elastic element an additional elastic element in the form of an additional membrane with a rigid center, a support base and with response electrodes, forming respectively a measuring and supporting the capacitors, as well as the lead conductors partially located in the interelectrode gap and connected to the contacts of the pressure pad, the peripheral electrode of the additional membrane is placed on its rigid center, and the pressure pad is made in the form of a circuit board with a central hole, the supporting base of the additional membrane with the help of the inserted sleeve is hermetically connected around the periphery with the inner edge of the hole of the board, which with the help of the inserted ring is hermetically connected to the supporting base of the main elastic element, and ktsii sensor connected in a certain ratio.

 In addition, in the device for generating the output signal of the capacitive pressure sensor containing a voltage generator connected through the first reference capacitor to the first amplifier, into the feedback circuit of which the measuring capacitor of the sensor is connected, an additional reference capacitor is introduced, the capacitance of which is equal to the capacity of the first reference capacitor, the second amplifier , an integrator and three switching keys, while an additional reference capacitor is connected through the first key parallel to the first reference cond nsatoru to the first amplifier input, a reference capacitor sensor included in the first amplifier feedback circuit in parallel with the measuring capacitor through the second switch, and the output of the first amplifier is connected via a third switch to the non-inverting and inverting inputs of a second amplifier whose output is connected to the integrator.

 In FIG. 1 shows the proposed capacitive pressure sensor; in FIG. 2 - the proposed device for generating the output signal.

 The relations between the dimensions of the interelectrode gap, the thickness of the electrodes, the thickness of the dielectric substrates and the dimensions of other structural elements have been changed for clarity.

 The capacitive pressure sensor contains the main elastic element in the form of a membrane 1, made integral with the supporting base 2, electrodes 3 and 4, located in the Central part of the main elastic element and on its supporting base, located with a gap and hermetically connected around the periphery with the main elastic element, an additional elastic element in the form of a membrane 5 with a rigid center 6 and a supporting base 7 and with response electrodes 8 and 9, and output conductors 10, partially located in the interelectrode gap. The peripheral electrode 9 of the additional elastic element is placed on its rigid center. Germock 11 is made in the form of a board. An additional elastic element is hermetically connected to the pressure pad using a sleeve 12. To insulate the electrodes on the planar surfaces of the elastic elements, a dielectric film 13 of a composition of aluminum and silicon oxides is located. The tight connection of the additional elastic element with the main is carried out through the pressure pad 11 and the ring 14.

The device for generating the output signal of the capacitive pressure sensor contains the first and second amplifiers U1 and U2, respectively, the reference capacitors C _e1 and C _e2 connected to the input of the first amplifier U1 through the first switching key K1, and a measuring capacitor C _x included in the feedback circuit of the first amplifier U1. The reference capacitor C _{o is} included in the feedback circuit of the first amplifier, and the reference Co and measuring C _x capacitors are alternately connected to the feedback circuit through the second switching key K2, and the output of the first amplifier is alternately connected through the third key K3 synchronously to the first switching key to the non-invertible and invertible the inputs of the second amplifier U2, the output of which is connected to the integrator I.

 Capacitive pressure sensor operates as follows.

 Under the influence of the first measured pressure, the membrane of the main elastic element 1, and, consequently, its rigid center with the electrode 3 located in the central part of the main elastic element, bend towards the additional elastic element. As a result, the capacitance of the measuring capacitor formed by the electrodes 3 and 8 located in the central part of the main and additional elastic elements increases. The capacity of the reference capacitor formed by the electrodes 4 and 9 located on the periphery of the main and additional elastic elements does not depend on the magnitude of the first measured pressure due to the significantly greater rigidity of the support base compared to the rigidity of the membrane 1 of the main elastic element. Atmospheric pressure (in the case of measuring overpressure) or the second measured pressure (in the case of measuring the pressure difference) acts on an additional elastic element. As a result, the rigid center 6 of the additional elastic element moves toward the main elastic element. In connection with the placement of the electrodes 8 and 9 of the additional elastic element on its rigid center, the electrodes 8 and 9 of the additional elastic element move towards the electrodes 3 and 4 of the main elastic element. As a result, the capacitance of the capacitors increases. In the case of a decrease in atmospheric pressure (in the case of measuring excess pressure) or a second measured pressure (in the case of measuring the pressure difference), the electrodes 8 and 9 of the additional elastic element are removed from the electrodes 3 and 4 of the main elastic element, as a result of which the capacitance of the capacitors decreases. Thus, the capacitance of the reference capacitor uniquely reflects the value of atmospheric or second measuring pressure. The capacity of the central condenser depends on both the first measured pressure and the second. Thus, by measuring the capacitance of the central and peripheral capacitors, it is possible to unambiguously judge the magnitude of the overpressure or pressure difference.

The formation of the output signal is as follows. The voltage from the generator is supplied to the reference capacitor. In the first step, the keys K1, K2, K3 are in the upper position. Therefore, the voltage from the generator passes through parallel-connected capacitors C _e1 and C _e2 to the input of the amplifier U1, in the feedback circuit of which at the given moment the capacitor C _{o is} connected. The voltage from the output of amplifier U1 is supplied in this case to the non-invertible input of amplifier U2, and then to integrator I. In the next step, the keys K1, K2, K3 are in the lower position. In this case, the signal from the generator is supplied through the capacitor C _e1 to the input U1, in the feedback circuit of which a capacitor C _x is connected. The voltage from the output of the amplifier U1 is fed to the inverting input of the amplifier U2, and from its output to the integrator I, which together with the amplifier U2 provides a signal equal to the difference in voltage supplied to the inputs of the amplifier U2. As a result of this, an output signal is formed at the output of the integrator, the amplitude of which uniquely characterizes the pressure difference acting on the main and additional elastic elements. (56) 1. U.S. Patent No. 4,562,742, cl. G 01 L 9/12, 1985.

 2. USSR author's certificate N 1702197, cl. G 01 L 9/12, 1989.

 3. USSR patent N 593674, cl. G 01 L 9/12, 1974.

Claims (2)

CAPACITIVE PRESSURE SENSOR AND DEVICE FOR FORMING ITS OUTPUT SIGNAL
1. A capacitive pressure sensor containing the main elastic element in the form of a membrane with a rigid center, made in one piece with the support base, the central and peripheral electrodes, located respectively in the central part of the elastic element and on its support base, located with the gap and the gap the main elastic element is an additional elastic element in the form of an additional membrane with a rigid center, a support base, and with response electrodes forming respectively measuring and supporting capacitors, and t Also, the lead-out conductors, partially located in the interelectrode gap and connected to the contacts of the thermal pad, characterized in that the peripheral electrode of the additional membrane is located on its rigid center, and the thermal pad is made in the form of a board with a central hole, an opaque base peripherally connected to the internal edge of the hole of the board, which, using the entered ring, is sealed to the support base of the main elastic element, and the structural elements sensor s
h _o =

,
where h _x , h ₀ - the thickness of the membrane of the main and additional elastic elements, respectively;
R _x , R ₀ - the radius of the membrane of the main and additional elastic elements, respectively
A _o =

·

;
^A x ⁼

^·

;
K ₀ = R ₀ / r ₀ ;
K _x = R _x / r _x ;
R _x , R ₀ - the radius of the main and additional elastic elements, respectively;
r _x , r ₀ is the radius of the rigid center of the main and additional elastic elements, respectively;
μ _x , μ _o - Poisson's ratio of the main and additional elastic elements, respectively;
E _x , E ₀ - the elastic modulus of the primary and secondary elastic elements, respectively;
S _x , S ₀ - the area of the Central and peripheral electrodes, respectively.  2. A device for generating the output signal of a capacitive pressure sensor containing a voltage generator, connected through a first reference capacitor to a first amplifier, into the feedback circuit of which a measuring capacitor of the sensor is included, characterized in that an additional reference capacitor is inserted into it, a capacitor capacitor a capacitor, a second amplifier, an integrator and three switching keys, while an additional reference capacitor is turned on through the first switch in parallel with the first reference cond to the sensor at the input of the first amplifier, the reference capacitor of the sensor is connected to the feedback circuit of the first amplifier in parallel with the measuring capacitor through the second key, and the output of the first amplifier is connected through the third key to the non-inverting and inverting inputs of the integrator.

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