SU1696920A1 - Capacitive pressure pickup - Google Patents

Abstract

The invention can be used to measure absolute pressure. The purpose of the invention is to increase the sensitivity and vibration impact resistance, as well as to ensure high accuracy by reducing the hysteresis. In the sensor, the force transmitting and compensation systems are made in the form of two identical beams 20 and 21, integral with the cover 1 of the body. One end of the force-transmitting beam 20 is integral with the membrane 4, and the other end is integral with the elastic non-sliding hinge 22 with the housing cover 1 and attached to the moving electrode of the flat rocker arm, made by milling the rectangular plate with the outer frame 11. The compensation beam 21 is made similarly, it is rotated 180 °. in relation to the beam 20 7 Il.

Description

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The invention relates to a measuring and control technique, in particular to sensors for measuring absolute pressure.

The aim of the invention is to increase the sensitivity and vibration impact resistance and to ensure high accuracy.

FIG. Figure 1 shows the proposed pressure sensor; in fig. 2 is a section A-A in FIG. one; in fig. 3 is a section BB in FIG. one ; in fig. 4 - electronic frame, oazrez; in fig. 5 - section bb In Fig 4; in fig. 6 is a view A of FIG. five; in fig. 7 is a measurement block diagram.

The sensor body consists of three parts: 1 - the top cover, 2 - the middle part for fixing stationary electrodes and 3 - the bottom cover. In the top cover 1, two are offset along the axis of symmetry.

membranes 4 and 5 with rigid centers. The membrane 5 is tightly closed by the cap 6. The housing 1 is supported on a flat electrode frame 7 with reinforcing ribs 8, 9 and

10 (Fig. 1 and 4). Fixed exterior frame

11 obtained by milling along with a flat beam 12 inside it, where the beam moves into the frame through elastic elements in the form of necks 13 and 14. The beam 12 at the ends of one side has rectangular electrodes 15 and 16 obtained by processing in the transverse direction in the form of a flat cut 17 The rectangular electrodes in two places, displaced from the center in different directions, through the rods (rods) 18 and 19 with double-sided cuts, are pivotally connected to the cone of two beams 20 and 21 and also through elastic non-shifting hinges.

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The rings 22 and 23, which are made integral in the upper case cover 1 with the inner wall of the latter. The other ends of the beams 20 and 21 are made integral with the rigid centers of the membranes 4 and 5. Fixed are connected to the bottom of the middle part 2 of the case through insulating gaskets 24-27. rectangular electrodes 28 and 29, the adjusting rods 30 and 31 of which at the end have holes for attaching a current-carrying wire and leading it to a printed circuit board (not shown in Fig. 1), on which the measurement circuit is assembled. Stationary electrodes with insulating attachments are attached to the bottom of the middle part 2 of the housing, made in the form of a strip console by milling.

To facilitate the deformation of the cantilever, in order to adjust the capacitive gaps, its supporting section has a transverse groove 32 at the bottom. After grinding the electrode part, the fixing surfaces of the housing parts 1 and 2 and to obtain the necessary initial clearance between the electrodes 15, 28 and 16, 29 are used foil gasket 33 required thickness. After the hermetic closure of the housing, welding is performed around the perimeters of the adjacent portions, for example electron beam welding. To increase temperature stability, a vacuum of 10 mm Hg is created inside the sensor. The cap 34 has a pressure fitting.

FIG. 7 shows a measurement circuit where capacitors C1 and C2, formed respectively between electrodes 15, 28 and 16, 29, are included in the circuit of autogenerators 35 and 36 whose output signals with frequencies f 1 and fa are fed to mixer 37. The difference frequency is supplied to meter 38 frequencies.

The proposed capacitive pressure sensor operates as follows.

Through the nozzle of the cap 34, pressure P is applied to the membrane 4 with a rigid center and in the form of a force is transmitted to the end of the power-transmission beam 20, to the other end of which a compliant force-transmitting rod 18 is attached, which transmits the pressure in the form of force to the moving electrode 15 of the flat rocker 12. If The electrode approaches the stationary electrode 28, increasing the capacitance, then the second movable electrode 16 of the rocker arm moves away from the stationary electrode 29, reducing the capacitance. With full symmetry, the change in both capacities is ± DS. If the oscillator 35 reduces its frequency by the value of A f, then the oscillator 36

increases frequency by the same amount. Since the output signals of the autogenerators are fed to the mixer 37, at the output its frequency change will be ± 2 Af. From the magnitude of the measured frequency, the frequency meter 38 can judge the magnitude of the pressure.

Temperature compensation and increase in vibro-impact resistance is carried out by a temperature-compensating beam 21,

which is connected at one end to the housing

1 through the elastic non-moving hinge 23, and the other with the rigid center of the membrane 5. Due to the asymmetrical attachment of the force-transmitting pliable rods 18, 19 to

Electrodes 15 and 16 of the flat rocker under shock loads may cause torsional inertia moments and therefore the flat rocker on the reverse side has reinforcing ribs located

symmetrically along the diagonal of this rocker, allowing adjustment of asymmetrical inertia moments by moving the screws on the extreme edges 8 and 10 on the rocker with the possibility of adding inertial loads to the same screws.

Since the force-transmitting system in the form of beams, non-moving elastic hinges and power-transmitting rods and membranes with rigid centers are made in one piece with the housing 1 and since under the action of pressure P the membrane 4 moves slightly, the hysteresis value can be neglected.

The movement of the flat rocker is opposed by narrow necks 13 and 14, which play the role of supporting elastic hinges. The sizes and the stiffness and elasticity of both the membranes and the non-displaceable elastic hinges determine the resolution and sensitivity of the sensor. With a thickness of 3 mm and with a height of

The 2mm lower limit of the measured pressures can be increased to 1.5-2.0 mm Hg. The resolution of the sensor can be increased by lengthening the rocker arms and changing the size of the necks,

The change in capacitance C1 and C2 is made by moving the end of the bottom of the body console by moving towards the support with the help of a regulating system,

To convert the construction to the state of measuring the pressure difference, it is necessary to replace the second cap 6 of the membrane 5 with a cap with a fitting similar to the cap 34.

The sensitivity of the capacitive sensor increases by as many times as the ratio of the centering distance of the support and the membrane is greater than the distance of the centers of the power-transmitting rod and the support. The sensitivity of the sensor is also increased by making the surface of the electrode rectangular in shape compared to a round one when the sensor is in the shape of a rectangular prism.

The creation of flat rectangular electrodes is connected by a transverse cut of the central part of the flat rocker. Such cuts lead to a decrease in the strength of the pole arm, which can be broken off under shock loads; bending of the ends of the rocker arm with the production of false signals is also possible. Therefore, reinforcing ribs located symmetrically with respect to its diagonal are made on the back side of the electrodes of the rocker arm. In addition, due to the asymmetric attachment of the force-transmitting rods to the movable rectangular electrodes, under shock loads, torsional moments of inertia may occur, the outer edges compensate for the occurrence of such moments, at the same time increasing the strength of the cord.

In addition, in the proposed sensor, it is much easier to obtain a plane-parallel arrangement of electrodes by milling and grinding the rectangular part of the force-transmitting part of the body and the flat rocker with its outer frame. After fixing the stationary electrodes on the housing, the adjacent outer surface is polished, and when using a foil gasket between the housing 2 and the frame 7, it is possible to easily locate the plane-parallel arrangement of the moving and stationary electrodes that are spaced apart from each other by the thickness of the foil gasket.

Due to the use of the second beam, a full thermal compensation of the sensor's force-transmitting system is created, since the effect of these two beams upon changing the temperature on the movable electrodes gives the same changes and therefore there will be no false signal at the output (all sensor assemblies are made of the same metal).

In the sensor, due to the performance of necks at the same time between the outer frame and the strip arm, as well as due to the monolithicity of the force-transmitting system, i.e. due to the absence of separate attachments, the possible hysteresis is significantly reduced, and consequently, the accuracy is increased.

The design of the sensor allows, without any special changes, only by replacing the cap of a tightly closed membrane with a lid with a socket, to measure the differential pressure.

The presence of a gap of 50 microns, where the air layer is half replaced by mica, allows the capacitance of each capacitor to be increased 1.5-2.0 times. A change in the capacitive gap of only 2-3%, within which the linear characteristic is maintained, leads to a change in the frequency of each oscillator of 25 kHz (the fundamental frequency of the oscillator was 10 MHz).

By selecting the thickness of the membranes with a rigid center and the size of elastic necks (2x2 mm), the lower limit of the measured pressures was brought to 1-2 mm Hg. Sensor weight does not exceed 500 g.

The vibration test of the sensor showed no output spurious signals. The characteristic between the change in frequency of the output signal and the applied pressure was linear.

Claims (1)

Claims of Invention A capacitive pressure sensor comprising two membranes mounted in a housing connected via transmitting elements with movable electrodes placed on opposite arms on one side of a flat rocker, whose axis of rotation is connected to a rectangular support frame fixed to the housing through elastic jumpers, made in one piece with the frame, and fixed electrodes installed with an adjustable gap relative to the moving electrodes, characterized in that, in order to increase the sensitivity stability and vibro-impact resistance, as well as ensuring high accuracy, in it the power-transmitting elements are made in the form of two identical cantilever beams with elastic resistors fixed on opposite sides of the body, connected at one end to the centers of the corresponding membranes, and This beam is placed with the possibility of angular displacement relative to the corresponding elastic supports in two parallel planes, perpendicular to the axis of rotation of the rocker arm and symmetrical from ositelno its longitudinal axis, and are integrally formed with the membranes and the housing, and the rocker arm is provided with ribs disposed on the opposite side with respect to the movable electrodes parallel to the longitudinal axis of the rocker and its diagonally symmetric and balancing mass, // rf / U //////////////////////////. 32 31 / 1 - ,one installed on extreme stiffness pebpax. Aa :; To 25 thirty -) © Jl ig.2 one | g 4s one Oh - oh O5 o you about N gb Sa four T sixteen -G Vida J l X 15 // X fiui.e