Setra Systems, Inc.

Setray Systems, Inc.

Shih-Ying Lee

Dennis K Briefer

Gino Amaro Pinto

Sen Z Li

Thomas Foley

A capacitive sensor includes an elastic member extending about a central axis, having a central region, a peripheral region, a first side, and a second side. An overpressure stop member has an inner surface and an outer surface. The inner surface of the overpressure stop member has a contour adapted to limit deflection of the elastic member caused by a differential pressure between the two regions across the elastic member. The outer surface of the overpressure stop member has an first electrically conductive region. A second plate is spaced apart from the outer surface of the overpressure stop member, and being connected to the central region of the elastic member by a post, wherein the post transfers deformation of the elastic member caused by differential pressure across the elastic member to movement of the second plate along the central axis. The second plate has a second electrically conductive region opposite the first electrically conductive region, wherein the first electrically conductive region and the second electrically conductive region form a capacitor.

Center-mount capacitive sensor with overload protection

A capacitive pressure transducer includes a conductive diaphragm positioned between pneumatically separated chambers defined by concave body members. The diaphragm is fixed and sealingly coupled at its periphery to the peripheral rim of the concave body members. The diaphragm can be supported in tension by the peripheral rim of the body members. An electrode assembly, supported by one body member, establishes a substantially planar conductive surface opposite to and spaced apart by a nominal gap from the conductive diaphragm. The capacitive pressure transducer further includes a thermal compensation element securely coupled to the inside surface or the outside surface of one of the concave body members and/or to the electrode. The thermal compensation element has a different coefficient of thermal expansion from that of the concave body member or electrode to which it is attached. The combination of the concave body member or electrode and thermal compensation element having different coefficients of thermal expansion results in a bimetallic action which produces a thermally dependent force that compensates or counter-acts the thermally induced changes in the characteristics of the transducer.

Transducer having temperature compensation

A capacitive pressure transducer includes a conductive diaphragm positioned between pneumatically separated chambers. The diaphragm is fixed and sealingly coupled at its periphery to the peripheral rim of a concave body member. The diaphragm is supported in tension by the peripheral rim of the body member. An electrode assembly, supported by the body member establishes a substantially planar conductive surface opposite to and spaced apart by a nominal gap from the conductive diaphragm. The body member includes a yieldable portion that is adapted to radially expand its peripheral rim in response to forces applied to the body member. When the forces are applied, the body member becomes strained beyond its elastic limit and takes a permanent set whereby the peripheral rim is expanded and the diaphragm becomes tensioned. The tension in the diaphragm can be determined as a function of the geometry of the body member and deformation resulting from the forces applied. Additional forces can be applied at a later point in time in order to change or adjust the tension in the diaphragm.

Pressure transducer having a tensioned diaphragm

Method of making a pressure transducer having a tensioned diaphragm

A variable capacitance type pressure sensor with excellent manufacturability center-mounts an electrode on an edge-mounted diaphragm using a metal-glass-metal subassembly. An inner metal post of the assembly is welded to the diaphragm. A solder or flowable cement secures the electrode to an outer metal collar of the assembly with the initial diaphragm-to-electrode spacing set by a temporary shim. The position of the glass and the physical lengths of the metallic members of the assembly are adjusted to provide self-compensation for temperature variations. In a preferred form for low and medium pressure applications, the diaphragm is stamped from sheet metal with a central dimple that resists rotation of the attached assembly and isolates diaphragm deformation stresses from the post-to-diaphragm weld. In a high pressure form, a machined central boss isolates this weld from stress. A fitting that edge-mounts the diaphragm has a thinned end wall, or the diaphragm has a thin-walled skirt, to relieve stress on the diaphragm-to-fitting joint.

Low cost, center-mounted capacitive pressure sensor

A capacitance pressure sensor includes a conductive diaphragm positioned between two pneumatically separate chambers. The diaphragm is supported at its periphery by a concave base member. An electrode assembly establishes a substantially planar conductive surface opposite to, and spaced apart by a nominal gap from, the conductive diaphragm. The electrode assembly includes the conductive surface and a single support element secured to, and extending through the base member. A glass dielectric fixes the support element to a collar which may be welded, brazed or soldered to the base member. The glass dielectric provides both mechanical support and high quality electric insulation between the electrode and the housing. By prefabricating the electrode support element with the collar and securing the collar to the housing after the dielectric has cured, problems associated with thermal expansion and contraction are avoided and the dimension of the nominal gap may be precisely controlled at a relatively low cost.

Capacitive pressure sensor having a pedestal supported electrode

A capacitance pressure sensor includes a conductive diaphragm positioned between two pneumatically separate regions. The diaphragm is supported at its periphery by a concave base member. An electrode assembly establishes a substantially planar conductive surface opposite to, and spaced apart by a nominal gap from, the conductive diaphragm. The electrode assembly includes the conductive surface and a plurality of support legs extending through, and secured at, apertures in the base member.

Capacitive pressure sensor

A flush-mounted sensor measures the pressure of a fluid at a given point of a fluid system such as a container or conduit. A sensor head edge-mounts an isolating diaphragm responsive to the pressure of the fluid. The isolating diaphragm has a small diameter in comparison with the dimensions of the fluid system, is adjacent to the fluid in the system to reduce the dead volume of fluid adjacent the diaphragm and may be formed of a material that is compatible with the fluid. A drive rod mechanically couples the isolating diaphragm to a second diaphragm of a variable capacitor assembly, preferbly one of the center-mounted type where the diaphragm is one plate of the capacitor. The second diaphragm is also edge-mounted and produces a counterforce acting on the side of the isolating diaphragm opposite the side adjacent the fluid. The force of the fluid pressure acting on the isolating diaphragm is transmitted by the drive rod to the second diaphragm where changes in the capacitance correspond to changes in the pressure.

Flush-mounted pressure sensor

A transducer measures the pressure of a fluid within a hollow conduit, typically one with a circular cross-section, having a central region that is deformed to a non-circular cross-section. This non-circular portion of the conduit displaces radially and repeatably without hysteresis in response to the pressure of the fluid in the conduit in a manner that corresponds to the pressure. A variable capacitor assembly, or a set of strain gauges mounted on the exterior of the non-circular portion, produce an electrical signal proportional to the radial displacement or to the strain, respectively. In one capacitive form, a pair of electrodes are mounted on opposite sides of the non-circular portion formed as free end portions of metallic sheet members with a central channel. In another capacitive form, electrodes are mounted at one or both ends of lever arms which in turn are coupled to the non-circular portion with a set of flexure plates to produce a mechanical amplification of the radial displacement.

Pressure transducer with flow-through measurement capability

A compact force transducer has at least one flexible beam mounted at one or both its ends to a force summing member or members. The force-to-be-measured is applied to the force summing member along a first axis generally transverse to the beams to deform the beam elastically, without overstressing, through a displacement d. A sensor member carries a conductive surface and is coupled to the beam member. In a parallelogram form, there are a parallel pair of beam members extending between two force summing members and a sensor member is secured to each beam member at or near its point of inflection. One sensor member includes multiple arms that sandwich the other sensor member to produce a linear, push-pull mode of operation. In a low cost cantilevered beam form, the sensor is coupled to the beam at the force summing member in a parallel, spaced relationship. In a hybrid push-pull form, the transducer uses a two beam parallelogram construction with cantilevered sensors (1) coupled rigidly to each beam adjacent one force summing member with a hinge coupling between the beam and this one force summing member, and (2) extending generally in a parallel spaced relationship with respect to an associated one of the beams.

Compact force transducer with mechanical motion amplification

Two pairs of parallel plate electrodes forming respectively a sensor capacitor and a reference capacitor are mounted on a parallelogram structure designed to deform under load in such a way that the gap width of the sensor capacitor changes as a function of load while the gap width of the reference capacitor is unaffected by the load. The capacitance of the reference capacitor is, however, similarly affected by temperature, humidity and other physical properties which may affect the dielectric constant of the medium, and is available for use in a ratio circuit to compensate for spurious changes in the sensor capacitance.

Force transducer

A force transducer has (1) a pair of opposed rigid-body force summing members that each include a sensor member and (2) a pair of beam members that each extend between and couple the force summing members. These sensor members have opposing sensing portions which are mutually offset. A force-to-be-measured is applied to a summing member, either directly or through a rigid input force member. The force deforms the beams so that the sensing members are displaced with respect to each other while maintaining their parallel relationship. In one form the entire force transducer is formed from a single piece of material. A conductive material coated on a pair of small ceramic inserts that are bonded to the sensor portions form an accurate capacitor to measure the applied force. In another form, the sensor members are secured to the flexible beams. When the length of the force summing members exceeds the length of the flexible beam members, a deflection of the transducer in response to the applied force produces an amplification of this deflection at the opposed sensor portions. In yet another form, the transducer has a 'sandwich' construction where the beams are each an integral, monolithic member with a thin, central portion that is flexible about only one axis and a pair of end pieces that have a much larger cross-sectional area than the thin central portions. A thin layer of bonding material couples these large end pieces to an interposed force summing member.

A weighing system includes a weighing pan connected to a rigid armature by a mechanical filter constraining the armature to motion along a reference axis with respect to a housing and damping out transient forces along this axis resulting from the placement of objects on the pan. The mechanical filter includes spring and damping elements that provide a low-pass filter, that is, one that efficiently and quickly eliminates high frequency oscillations. In one form, the mechanical filter couples the pan to the armature. Because of this connection, friction in the mechanical filter does not result in frictional errors in the weighing measurement. In another form, a mechanical linkage couples the armature to the housing. A force transducer, comprising a pair of complementary opposed surfaces having a mutual separation which is related to the force across the transducer, is coupled between the armature and the housing. Coupled to the transducer is a position sensor which generates a signal representative of the separation between the complementary opposed surfaces of the transducer.

Weighing system

A force transducer includes a pair of rigid force summing members that each extend toward one another along a central axis and a pair of beam members that each extend along the central axis and couple the force summing members to form a parallelogram frame. More specifically, the beam members are mounted to the force summing members to provide a frame such that a force applied to one force summing member along a first reference axis and resisted on the opposite side of the other force summing member produces a flexing of the beam members. The force summing members each include sensing members that also extend along the central axis toward one another. The sensing members are spaced from one another in the direction of the first reference axis. Electrically conductive members mounted on the opposite faces of the sensor form a variable gap capacitor that is integral with the frame. The flexing of the frame produces a change in the gap that relates to the applied force. The force summing and beam members are formed of a dielectric material. In one form each beam member is integral with an associated force summing member, the beam member being defined by an open slot. The beam members are each tapered along the central axis and toward the variable gap. In one form of the construction the beam member portions associated with each force summing member are joined at a point of inflection (i.e. the zero bending moment point) of the beam as joined. In the preferred form, the beam members and the associated force summing members are integral, monolithic and each force summing member and associated beam and sensor portions is identical to the other.

A force transducer includes a pair of rigid force summing members that each extend toward one another along a central axis and a pair of beam members that each extend along the central axis and couple the force summing members to form a parallelogram frame. More specifically, the beam members are mounted to the force summing members to provide a frame such that a force applied to one force summing member along a first reference axis and resisted on the opposite side of the other force summing member produces a flexing of the beam members. The force summing members each include sensing members that also extend along the central axis toward one another. The sensing members are spaced from one another in the direction of the first reference axis. Electrically conductive members mounted on the opposite faces of the sensor form a variable gap capacitor that is integral with the frame. The flexing of the frame produces a change in the gap that relates to the applied force. The force summing and beam members are formed of a dielectric material. In one form each beam member is integral with an associated force summing member, the beam member being defined by an open slot. In one form of the construction the beam member portions associated with each force summing member are joined at a point of inflection (i.e. the zero bending moment point) of the beam as joined. In the preferred form, the beam members and the associated force summing members are integral, monolithic and each force summing member and associated beam and sensor portions is identical to the other.

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Lincoln, MA, United States of America

Shih-Ying Lee