JPH0219892B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital output pressure sensor that uses a vibrating beam as a sensing element.

Conventionally, various sensors using vibrating beams have been developed. Typically, some type of digital pulse is used to indicate the force or pressure exerted on the beam.

Certain sensors are described in U.S. Patent No. 3,470,400.
No. 3,479,536 utilizes piezoelectric sensing technology. A type of pivoted beam restrained in its path of travel is described in U.S. Pat.
Disclosed in No. 3649857.

Another patent related to vibrating beams of general interest is also No. 3,664,237.
Vibrating beam capacitive sensing techniques are illustrated in US Pat. Nos. 3,187,579 and 3,762,223. In both of these patents, the sensing capacitor plate is on the opposite side of the member from the drive coil.

A piezoelectric beam that bends laterally due to mass acceleration at the end of the beam or due to the impact of a small flow rate is disclosed in US Pat. No. 3,304,773. An accelerometer using a vibrating beam with capacitive sensing means is shown in US Pat. No. 3,505,866.

U.S. Patent No. issued April 17, 1979
No. 4,149,422 has a thin wire that is held under a spring load to create a pretension and whose natural frequency changes with pressure loading. A vibrating wire type pressure sensor is disclosed. The lever used to load the vibrating wire is mounted on the cross-sectional curvature joint for relative freedom of pivot movement.

The sensing means is such that a current from the oscillator flows through the wire and this current reacts with the magnetic field from the permanent magnet to move the wire. This creates an opposing EMF (electromotive force), and positive feedback in the current-generating oscillating circuit sustains the oscillation of the wire. Thus, the sensor disclosed in US Pat. No. 4,149,422 does not utilize capacitive sensing technology.

The present invention relates to a pressure sensor, and particularly to a pressure sensor that applies a load to and influences the natural frequency of a vibrating beam. The vibrating beam is sensed and provides an output in the form of digital pulses that allow for direct digital measurements or a pressure reading to be measured.

The beam is loaded, as shown, by a pivotally mounted lever that helps isolate the beam from unnecessary stress while loading the beam. Excitation to the beam is from a coil driven by an oscillator and the sensing means is a capacitor. In this way, there is little interaction between the excitation and sensing signals, which can improve accuracy.

In the particular embodiment shown, the excitation coil and the extraction capacitor plate are integrally coupled to each other and mounted on the same side of the vibrating beam, so that:
These connections facilitate mounting and shielding, and alignment and adjustment of the spatial arrangement between the drive coil, sense capacitor, and vibrating beam.

Other advantages include ease of manufacture with fewer parts, easier cost reduction, better control of parasitic resonances, and having sensing circuitry components that can be mounted on the extraction member. Regarding the vibrating beam, since there is virtually no current in the beam, the beam has little detrimental effect on the operation of the drive coil or the extraction capacitance.

Hereinafter, specific examples of the present invention will be described with reference to the drawings. 1 and 2 show the general arrangement of a sensor according to the invention. The sensor assembly is indicated at 10, and the outer frame 11 has a substrate for mounting various components. The substrate of the frame indicated by 12 is a flat plate, and the frame has an upright wall 13,1.
It has 4. The outer surface of the outer frame 11 is coated with silicone rubber, preferably about 1.57 mm (0.062 inch) thick, to dampen external vibrations. The wall 13 has an opening and mounting means for mounting the bellows 15,16.

The bellows 16 has a collar 17 at its end. The collar is shaped like a small ring, and the ring partially fits inside the clamp 23A and is held in a recess within the clamp 23A. Clamp 23A is slidingly attached to and slides along a tongue 23, indicated generally at 24, which forms part of the pivoting and loading lever member.

The tongue 23 extends between the bellows 15 and 16. The bellows 15 is connected to the tongue 23 because it has an end ring 17A that is partially fitted into a recess in the sample 23. bellows 15
and 16 transmit the load from the pressure to the tongue 23 which causes the bellows to expand in the axial direction.
The tongue 23 has a dovetail end that slides in tandem with the clamp 23A.

Bellows are of common design used as sensors and are usually placed in a stationary or equilibrium position as shown. First pressure inlet 2
0 is connected to the bellows 15, and the second pressure inlet 21 is connected to the bellows 16. The bellows, of course, tends to expand along its axis under pressure, stretching its inner end against the tongue 23 and clamp 23A. In this way, the pressure difference displaces the position of the tongue 23.

Clamp 23A slides along tongue 23 transverse to the direction of movement of the bellows and is adjusted so that movement of bellows 16 around a hinge such as the pivot shown at 27 It will be displaced in relation to the movement of the bellows 15. This movement of clamp 23A along tongue 23 allows adjustment of the force from one bellows or the other, so that when equal pressure is applied to bellows 15 and 16, the resultant force ( moment) is zero.

As shown in the plan view, the lever assembly 24 is attached to the mounting block 2 which is in contact with the substrate wall 12 of the frame 11.
5. Lever assembly 24 is made from a single piece of material. A moving lever portion or actuator 30 is connected to block 25 through a hinge-like pivot indicated at 27. the pivot has a substantially thin cross-sectional thickness;
Block 25 and section 30 are connected along the pivot axis. The lever assembly thus has a lever part 30 that pivots with the mounting part 25.
Since the lever portion 30 is not in contact with the base plate 12 of the frame, it pivots when there is a pressure difference. A suitable spacer is placed under the block 25 to keep the lever part 30 on the substrate 1.
It is separated from 2.

The lever portion 30 pivots about a hinge or pivot portion 27 which offers little stiffness to pivoting, but allows the lever portion 30 to pivot about an axis parallel to the plane of pivoting. Strong resistance to twisting (stiffness). This resistance is also effective against acceleration in the direction along the pivot axis. The lever part is connected to the tongue 23 by a coupling 31.

The load beam, designated 35, is made of a single block of magnetic material, preferably Ni-Span C, alloy 902, manufactured by International Nickel Co., Ltd.
is made from. The load beam 35 has a central vibrating beam section 42 which is arranged between and integrally with first and second isolation sections 43 and 44 for supporting it.

The standoff section 43 is attached at its outer end, as indicated at 36, opposite its junction with the vibrating beam to a support handle 37 forming part of the block 25. The outer end of standoff portion 43 may be mounted separately from substrate 12 of the housing. The connection to the support 37 is a fixed connection, by soldering or brass brazing. The outer end of the isolation portion 43 is also
It may be pinned or fixed with suitable cap screws.

The outer end of the isolation part 44 is attached, as indicated at 40, to a support part 41 which is at the end opposite the load beam 35 and projects from the pivot lever part 30. The mounting means may be any suitable method.

The sensor assembly is accelerationally balanced on at least two axes - that is, it is sensitive to little or no acceleration in the "Y" or "X" axes as shown in FIG. This is because the sum of the torque moments on the sensor side of the pivot shaft is the same as the sum of the torque moments on the bellows side. Since the sensor is not balanced on the "Z" axis (see Figure 7), the resistance (stiffness) of the pivot axis
The strength of is effectively subtracting acceleration effects from the forces delivered along this axis.

If necessary, it is also possible to balance the torque moments around this axis. Within permissible limits, each sensor assembly has a somewhat different torque moment. The effect of these tolerances related to acceleration is that by placing a small amount of material, such as solder, at a location near the pivot 27 to equalize the torque moments about the axis, as shown at 27A in FIG. minimized by

The vibrating beam portion 42 thus supports the support member 37.
and 41 and supported by standoff portions 43 and 44. The beam portion 42 is therefore subject to the force exerted by the movement of the pivot lever portion 30. The standoff portions 43 and 44 are deformed at their central portions to form a pair of thin straps.

Thus, movement of the tongue 23 between the bellows 15 and 16 by deflection or movement of the bellows causes the tongue 23 to pivot the pivot lever portion 30 about the pivot 27. This movement changes the tension, compressive stress or load on the vibrating beam section 42. A change in the load on the vibrating beam section 42 changes the resonant frequency of vibration. The change in the resonant frequency is due to the pressure inlets 20 and 21 and therefore the bellows 15 and 16.
is proportional to the difference in pressure at One pressure inlet is open to atmosphere or vacuum, so that each pressure value is measured. Furthermore, one of the bellows can be omitted.

The pressure signal generated by the bellows 15, 16 is transmitted to one end (free end) of the vibrating beam section 42 via the pivot lever section 30 by its link action, so that the pivot lever section 30 has sufficient It only needs to have mechanical rigidity.

The beam is driven or excited into resonance by using a coil excited by an AC signal controlled at a resonant frequency. Furthermore, during the hiatus,
The beam is in equilibrium, neither in compression nor in tension. That is, there is no creep or loosening of the support structure or beams, contributing to stability.
The beam may be operated at low stresses, preferably within the elastic limits of the beam material.

Isolation sections 43 and 44 have masses 43A and 44A extending perpendicular to beam portion 42, and each have isolated isolation springs 43B and 43.
C, 44B and 44C. These isolation members hold the vibrating beam section 42 uncoupled from the end mounting portions, thereby reducing the "Q" of the beam.
Reduces energy loss. A small stress reduction member (radii) is attached to the vibration beam section 42.
and at the junction between masses 43A and 44A.

In the design of the beam section 42 and isolation sections 43 and 44, it is ensured that none of the components has a natural frequency that can easily be driven by the beam section 42, which must sweep over the wide range of frequencies used. It is important that there is no If the other element is beam part 4
2, the beam section 42 has a natural frequency such that it can be driven by 2, in particular the beam section 42 has a natural frequency equal to or a multiple of the beam frequency, e.g.
1, 2, 3 and 4 times) will excite such elements in the system.

When this occurs, the effectiveness of the isolation member is reduced, reducing the "Q" of the beam and changing its frequency. This results in a discontinuity in the straightness and smoothness of the beam for a given stress. In addition, it can be seen that the central beam is easily driven at its resonant frequency and twice the resonant frequency. This is because for each half cycle of the beam, a tensile force is applied to one end of the vibrating beam section 42. During its operation, the beam deflects in its rest plane to its opposite side.

As a matter of fact, it is not possible for the isolation member to vibrate at such low frequencies that it cannot be driven by the vibrating beam. This is because the separating element must be very long and thin for this purpose. Therefore, the overall sensor size would be large and the device would be difficult to fabricate. As mentioned above, it is possible for the vibrating beam section to drive the isolation spring with second, third or harmonics.

And also, in practice, it is not possible to drive these isolation springs to high frequencies and not to have them maintain the necessary low frequency isolation. In this way, the frequency of the isolation spring is reduced by the frequency of the vibrating beam section 4 in the stressed frequency range.
It will be appreciated that the selection must be made to have a "window" that does not interfere with 2.

That is, when stress is applied to the vibrating beam section 42, its natural frequency and twice this frequency must not coincide with the resonant frequencies of the isolation springs 43B and 43C and 44B and 44C. The widest "window" is one in which the fundamental isolation spring frequency of each of these four springs is greater than the highest frequency of the vibrating beam section corresponding to the maximum stress, and It is set to be lower than twice the natural frequency.

A specific example of beam portion 42 is generally at least about 0.025 mm (0.001 inch) and at most about 0.25 inch.
Within the range of mm (0.010 inch), approximately 0.12 mm (0.0047
inch) thick beam section. The beam section is generally at least about 2.54 mm (0.10 inch) and at most about 12.7 mm (0.50 inch), and about 6.35 mm.
(0.250 inch) and generally at least about 5.08 mm (0.20 inch) and at most about 2.54 mm
(0.100 inch) and has a width of approximately 1.07 mm (0.042 inch).

The natural frequency in a stress-free state is proportional to the thickness of the beam and inversely proportional to the square of the beam length, and when using a material such as Ni-Span C,
It is approximately 14.KHz. Ni-Span C is a composition that exhibits excellent spring properties, with a virtually zero temperature coefficient over a wide temperature range. Other natural frequencies could also be selected.

The change in frequency is determined by the stress in the beam generated by the force on the lever assembly 24. For example, at one atmosphere, this stress is approximately
It is made of 12.7 mm (1/2 inch) diameter bellows and weighs approximately 1.13 Kg (2.5 lbs). The stress in the vibrating beam section 42 is adjusted by changing the width without changing the frequency of the unstressed state of the beam section. As an example, the stress was adjusted to about 703.7 Kg/cm ² (10000 psi) using Ni-Span C.

This stress is ideal because it is very low compared to the allowable strength of Ni-Span C, and the resulting hysteresis error is very low. In addition,
There is no long-term change in frequency. As a result, the frequency change of the vibrating beam portion 42 is approximately 2300Hz, which also
It is approximately 16% of the maximum scale frequency when the beam is placed in either compression or tension. in this way,
For example, the change from zero atmosphere to 1 atmosphere is 14.5KHz
This causes a resonant frequency change from 16.8KHz to 16.8KHz.

As mentioned above, the frequency for the isolation spring is greater than 16.8KHz and twice 14.5KHz or
The vibration beam portion 42 is set so that the frequency is lower than 29KHz.
It is adjusted in the same way as for. In fact, it was found that the vibration frequency of the separation spring works well from 22KHz to 24KHz. When the springs 43B and 43C and 44B and 44C have a normal configuration,
Approximately 0.3mm for a length of approximately 8mm (0.315 inches)
(0.012 inch) thick.

The separation masses (43A and 44A) are adjusted to produce a separation system frequency of 2600 Hz. This frequency then provides an excellent isolation system for the frequency ratio of the vibrating beam section and therefore also a very low transmissibility.

The mechanical structure of the coil and take-out part is 1st to 4th.
As shown in the figure. As shown, a ceramic mounting block 50 is mounted on the disk member 51. The disk member is metal and is brazed to block 50 in a conventional manner. Blocks may be pinned to disks if desired.

The disk member 51 is the substrate of the frame (see Fig. 2).
The block 50 projects into the frame. The disc is adapted to be rotated within the recess 52 and assumes the desired position. The disk is then soldered to ensure that it is held precisely in rotational position during use. Block 50 is made of a non-magnetic and non-conducting material such as alumina or ceramic material.

As shown, the block 50 is connected to the vibrating beam section 42.
It has a protrusion 53 having a surface 53A that is close to and parallel to the plane of . Block 53 fits between each end of separators 43 and 44. Block 5
3 has a cylindrical recess 54 extending inwardly from a surface 57 opposite surface 53A (see FIG. 3).

A mandrel 55 is mounted in this recess and is connected to the block 53 by conductive epoxy or solder.
is fixed to. The mandrel 55 is preferably made of magnetic stainless steel, and is preferably a material with high mu (μ), that is, high magnetic permeability.

The mandrel has a disc-shaped end 56 and between the face 57 of block 53 and disc 56 is a coil indicated at 58. This is a single coil with the appropriate number of turns to create the magnetic force necessary to drive the beam.

On the face 53A of the block 53 adjacent to and facing the vibrating beam section 42, a conductive strip 61 forming a capacitor plate is provided on the ceramic material and sintered. Capacitor plate 61 is shown in FIG. Other electrical components are mounted directly on the surface of the ceramic block 50,
Various components are connected to capacitor plates mounted on strips of conductive material. Such components are discussed later in this specification.

Block 5 adjacent to coil 58 and opposite block 53 with respect to capacitor plate 61
The surface 57 of 3 may be metallized to shield interference from the current in the coil 58 so as not to affect the capacitance sensed between the vibrating beam section 42 and the capacitor plate 61.

By rotating the disc 51, the spacing between the capacitor plate and the vibrating beam section 42 is adjusted during assembly. Block 50 and plate or disk 51
are attached after the beams 35 are placed.
The space between the plate 61 and the vibration beam portion 42 is approximately 0.13 mm.
(0.005 inch).

The vibrating portion 42 of the beam forms the other electrode of the variable capacitor plate formed in conjunction with the plate 61, and this portion is grounded. Block 50 may be formed into a circuit that is powered through pin 50A and connection port 50B, if desired.

A modified configuration is shown in FIGS. 6 and 7. The attachment means for beam 35, lever assembly 24 (particularly pivot shaft section 30) and bellows are substantially the same. The mounting block 25 has been modified to mount a modified drive and extraction sensor assembly 74.

The shaft 75 is mounted in an opening provided in the block 25, as shown in FIG. 6, and a screw 76 provides longitudinal adjustment of the shaft 75 with respect to the vibrating beam portion 42. On the other hand, the shaft 75 is connected to a disk 79, and the disk 79 has a rod 7 extending outside thereof to support the coil.
It has 8. Disc 76 is connected to one end of shaft 75 by epoxy or other adhesive material in a conventional manner.

The coil 82 is connected to the inner surface of the disk 79 and a ceramic disc-shaped pick-up member 84.
It is wound around the mandrel 78 between the surface 83 of the
A coil core 78 extends into a recess in ceramic disk 84 a desired distance, and
is fixed to the ceramic take-out body and integrally supports both in a predetermined position after the coil is wound around the coil core.

Ceramic disk 84 has a conductive surface, as shown in shading in FIG. 8, to allow the circuit or its components to be mounted close to the beam. The components attached to disk 84 preferably include a capacitor plate 85 and a thick film capacitor 88, with appropriate connecting pieces 86 and corresponding to plate 61. The connecting piece 86 is connected to a thick film hybrid resistor 87, while the thick film capacitor 88 is electrically connected to the connecting piece 86 by cementing.

Appropriate contacts 87A and 88A connect capacitor 88
and is connected to the other end of the resistor 87. As can be seen from the figure, the hybrid capacitor 88 and resistor 87 are
Mounted in close proximity to capacitor plate 85 and protruding from the ceramic disk member, vibrating beam portion 42 is sandwiched between these two parts. The vibrating beam portion 42 is located close to and generally parallel to the capacitor plate 85.

In operation, in either version of the invention, the beam is caused to vibrate by energizing the associated coil. A magnetic flux is generated which deflects the vibrating beam section 42 to either side in a direction perpendicular to its longitudinal plane. The mandrel 55 or 78 extends a considerable length through the ceramic block 53 or 84 and the magnetic field is coupled to the beam section 42. The change in capacitance of the capacitor is sensed and actually controls the drive circuit to cause the vibrating beam to resonate and provide a frequency output.

The change in pressure differential induces a movement of the tongue 23 which causes the lever part 30 to rotate about the pivot axis 27, thereby changing the compressive or tensile load on the vibrating beam section 42 and causing the beam to move. Change the resonant frequency. This change is caused by the vibration beam portion 42
and is sensed by the frequency change of the signal from the capacitor plate formed between either plate 61 or 85, depending on the sensor placed close to this beam section.

This signal change represents the difference in pressure with respect to the frequency of the reference pressure. Preferably, the beam is driven at its fundamental frequency, but capacitor pick-off involves repositioning the pick-off to be sensitive to a desired harmonic of the fundamental frequency or other desired frequency. make it possible to

FIG. 9 is a simplified diagram of a circuit for extracting a frequency output signal from the vibrating beam of the present invention. This circuit can take several different implementations. In FIG. 9, vibrating beam section 42 is shown supported between isolation members 43 and 44 as described above. Capacitor pickup electrode shown at 61 (this is also 85)
is spaced apart from the vibrating beam portion 42 and forms a variable capacitor.

The circuit of FIG. 9 has an applied voltage terminal 90, a ground terminal 91, and an output terminal 92. A power source (not shown) with an applied voltage V+ is connected to the applied voltage terminal 90. A resistor 93 is connected between the terminal 90 and the ground terminal 91.
and the coil 58 (or 82) are connected.

When direct current flows through resistor 93 and coil 58, a steady magnetic field is created from mandrel or magnetic core 54 (or 75). The steady magnetic field created by the direct current flowing through coil 58 may be replaced by permanent magnets if desired.

A bias resistor 88 is also connected between the terminal 90 and the extraction electrode 61 (in FIG.
(attached to the ceramic disc). Bias resistor 88 applies a DC bias to connection point 95 where resistor 88 and electrode 61 are connected. As a result, the voltage generated across the variable capacitor formed by the vibrating beam portion 42 and the extraction electrode 61 is a function of the direct current and the frequency of vibration of the vibrating beam member 42.

The signal derived from node 95 is applied to amplifier 97 through filter capacitor 87 (FIG. 9). The amplified output of amplifier 97 is supplied to output terminal 92 as an output signal of the circuit. amplifier 9
The output of 7 passes through a feedback capacitor 98 to a connection point 94 between the resistor 93 and the drive coil 58.
connected to.

When the circuit is activated, the magnetic field from coil 58 displaces beam portion 42. Beam part 42 and plate 6
The capacitor capacity between 1 and 1 is the bias resistor 88
and the input supplied to amplifier 97 through capacitor 87. The output of amplifier 97 changes the feedback signal applied to capacitor 98, which in turn affects the current through coil 58.

The change in the current through the coil 58 causes the vibration beam section 4 to
By changing the magnetic field passing through 2, the vibrating beam section 42 is again displaced. The vibrating beam section 42 is thus excited to its natural frequency and the output of the amplifier 97 varies at this vibration frequency. Each component is selected to allow appropriate phase adjustment to produce oscillation in the desired frequency range.

The circuit of FIG. 9 thus provides a time-varying output signal such that the frequency of the output signal is a function of the vibration frequency of the beam section 42. This output signal can be converted to a digital or analog signal. The output signal gives an indication of the tensile or compressive force on the beam section 42 varying its frequency, which is also a function of the pressure to be sensed.

The actual circuit components for amplifier 97 and other components for converting the signal at output terminal 92 into a digital or analog signal can be mounted as shown schematically in FIG. Alternatively, if desired, all components may be mounted on block 50, as shown in FIG.

If low frequency vibrations from external sources (such as aircraft vibrations when the sensor is used in an aircraft) cause low frequency oscillations in the output signal, then use a suitable filter. Such undesired oscillations can be eliminated.

[Brief explanation of drawings]

Fig. 1 is a plan view of a pressure sensor having a sensing means according to the present invention, Fig. 2 is a front view taken from line 2-2 in Fig. 1, and Fig. 3 is a section taken along line 3-3 in Fig. 2. 4 is a front view taken from the line 4--4 in FIG. 3, FIG. 5 is a partial sectional view taken from the line 5--5 in FIG. 1, and FIG. 6 is a modified portion of the present invention. 7 is a side view of the coil and pickup member used in the device shown in FIG. 6, taken from line 7-7 in FIG. 6, and FIG. 8 is a side view taken from line 8-8 in FIG. 7. The front view, FIG. 9, is a schematic diagram of the driving and sensing circuitry used in the sensor of the present invention. 10...Pressure sensor, 12...Frame body, 15,1
6... Bellows, 20, 21... Pressure inlet, 23
...Tang, 27...Pivot, 42...Vibration beam, 58...Coil, 61...Electrode.

Claims (1)

[Scope of Claims] 1. A base body, a vibrating beam having a longitudinal axis, means for mounting one end of the vibrating beam in relation to the base body, and a lever member pivotably attached to the base body. a first end of the actuator operatively coupled to an end of the vibrating beam opposite the attachment of the vibrating beam to the substrate; means for applying a pressure signal to a second end of the actuator such that the actuator varies the force exerted by the actuator on the vibrating beam in a direction along the vibrating beam; and vibrating the vibrating beam at its natural frequency. and a frequency detecting means for detecting the frequency of vibration of the vibrating beam, and means for pivotally attaching the lever member to the base body includes a support mounted on the base body. The support block and the lever member are made from a single piece of material with a pivot axis formed therebetween, the pivot axis extending in a direction perpendicular to the pivot axis and the longitudinal axis of the vibrating beam. A vibrating beam pressure sensor configured to exhibit a hinge action through a reduced thickness section of a single piece of material. 2. a base body, a vibrating beam having a longitudinal axis, means for mounting one end of the vibrating beam in relation to the base body, an actuator comprising a lever member pivotably attached to the base body, and the vibration beam; a first end of the actuator operatively coupled to an end of the vibrating beam opposite the attachment of the beam to the substrate; means for supplying a pressure signal to a second end of the actuator such that the actuator changes the force exerted by the actuator on the vibrating beam; and drive means for causing the vibrating beam to vibrate at its natural frequency. , a vibrating beam type pressure sensor comprising a frequency detection means for detecting the frequency of vibration of the vibrating beam, further comprising means for mounting the first end of the vibrating beam on the base; means for attaching a second end of the vibrating beam to a second end of the actuator, the means for attaching the first and second ends of the vibrating beam each having a second end forming an isolated portion; the first and second spring assemblies have a higher natural frequency than the natural frequency of the vibrating beam when the vibrating beam located between them receives sufficient stress; Further, when the vibrating beam portion is under a stress state lower than that, the vibrating beam is configured to include separate bodies each having a fundamental natural frequency lower than twice the characteristic frequency of the vibrating beam portion. Beam type pressure sensor.