Abstract: A pressure sensor (40) useful as a vacuum manometer. A reference pressure cavity (50) of the sensor is evacuated through an evacuation opening (72) located behind a plate portion (54) of the sensor electrode (52) having a non-planar surface for supporting the diaphragm (44) during an overpressure event. The electrode is hermetically sealed to the body (42) of the sensor by a brazed joint with a ceramic seal member (60) disposed there between. The brazed joint may include a layer of buffer material (79) which provides a degree of malleability to the joint to avoid cracking of the ceramic seal member. The brazed ceramic/metal joint permits the selection of materials such that differential thermal expansion effects can be passively minimized. The electrode is connected to the sensor circuitry (84) by a wire having a spring section (53), thereby providing a stress free interconnection.

Abstract: A surface mounted instrument (20) that is easily installed to seal (110, 120) against a mounting surface (150) in spite of imprecise installation of a standard rough-in box (145) or irregularities in the surface. A cover plate (60) overlays the installed instrument housing (10) without the use of outwardly visible mechanical connectors by use of a pawl (65) that engages the housing. An oversized display (50) is mounted for easy replacement on a moveable display module (45) for unobstructed access to the interior (35) of the housing. Subsurface channels (90) formed in the housing are used to deliver a working fluid from a measured location to a sensor (85) inside the housing.

Abstract: An environmental condition monitor (200) configured for simple upgrade from analog signal output to any of a plurality of digital communication protocols. A display board (202) includes the analog signal acquisition and processing elements of the device and also includes a pre-positioned but initially inoperative digital communication output connector (214). A connector board (204) associated with the display board includes a connector (212) to which any one of a plurality of digital communication boards (210) may be selectively connected, depending upon which of a plurality of digital communication protocols is desired. Selective connection of a digital communication board completes a circuit whereby an analog output signal is converted to the desired digital output format and is then communicated back to the now-activated digital communication output connector (214).

Abstract: An apparatus (10) for sensing a condition, such as humidity, through an opening (20) in a surface (12) such as a duct or wall. A housing (14) includes an outer section (16) mounted on the surface and a probe section (18) extending into the duct or wall. A circuit board assembly (32) is mounted within the housing and includes a user interface section (34) within the housing outer section and a sensor section (36) rigidly connected to the user interface section and extending into the housing probe section. The sensor section may be integrated into the circuit board assembly by a rigid connector (42) allowing easy removal and field replacement of the sensor section. A sealing device (56) isolates the housing outer section from the air within the duct or wall. A flexible grounding connection (66) provides electrical grounding of the circuit board assembly and a degree of mechanical support.

Abstract: A capacitive pressure sensor for measuring a pressure applied to an elastic member includes a capacitive plate disposed adjacent to the elastic member so as to define a gap between a planar conductive surface of the elastic member and a corresponding planar surface of the capacitive plate. The gap, capacitive plate and elastic member together define a capacitor having a characteristic capacitance. The sensor further includes an elongated electrical conductor characterized by an associated inductance value. The conductor is fixedly attached to and electrically coupled with the capacitive plate. The gap between the capacitive plate and the elastic member varies as a predetermined function of the pressure applied to the elastic member so as to vary the characteristic capacitance. The capacitor and the electrical conductor together form an electrical resonator having a characteristic resonant frequency. Varying the capacitance of this tank circuit varies the resonant frequency of the tank circuit.

Abstract: A capacitive pressure sensor for measuring a pressure applied to an elastic member includes a capacitive plate disposed adjacent to the elastic member so as to define a gap between a planar conductive surface of the elastic member and a corresponding planar surface of the capacitive plate. The gap, capacitive plate and elastic member together define a capacitor having a characteristic capacitance. The sensor further includes an elongated electrical conductor characterized by an associated inductance value. The conductor is fixedly attached to and electrically coupled with the capacitive plate. The gap between the capacitive plate and the elastic member varies as a predetermined function of the pressure applied to the elastic member so as to vary the characteristic capacitance. The capacitor and the electrical conductor together form an electrical resonator having a characteristic resonant frequency. Varying the capacitance of this tank circuit varies the resonant frequency of the tank circuit.

Abstract: A temperature compensated pressure sensor network for providing an output sensing signal representative of an applied pressure includes a reference oscillator circuit for providing a reference signal having an associated reference frequency. The oscillator circuit includes a first inductor pair electrically coupled in series, wherein the reference frequency is a predetermined function of a first inductance associated with the first inductor pair. The sensor network further includes a sensor circuit for providing a sensing signal having an associated sensing frequency. The sensor circuit includes a second inductor pair and a sensing capacitor electrically coupled in series, wherein the sensing frequency is a predetermined function of a second inductance associated with the second inductor pair and the applied pressure. The sensor network also includes a processor for receiving the reference signal and the sensing signal, and producing the output sensing signal.

Abstract: A capacitance measurement system amenable to implementation on an integrated circuit includes a switching network, a voltage driving element, a sensor network, and a feedback network. The sensor network includes a fixed capacitor connected in series to a variable sensing capacitor. The feedback network receives the voltage generated at the junction node between the two capacitors, and the other side of the sensor capacitor is connected to system ground. The voltage driving element, responsive to a signal from the switching network, shifts the local voltage which supplies power to the feedback network. The feedback network generates a feedback signal representative of the difference in the charge stored on the series capacitors from a predetermined value.

Abstract: A capacitive pressure sensor includes a housing element, a first electrode assembly and a second electrode assembly. The first electrode assembly includes a deformable elastic member, and a plurality of petal electrodes. The petal electrodes are attached to the elastic member and extend from the elastic member in a direction which is substantially perpendicular to the surface of the elastic member. The elastic member of the first electrode assembly is secured at its perimeter to the housing element at an aperture in the housing, so that the petal electrodes are enclosed within the housing. The second electrode assembly is also enclosed within the housing and is surrounded by the elongated electrodes. The spatial relationship between the petal electrodes and the second electrode assembly is directly related to the capacitance measured between them.

Abstract: 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.

Abstract: A pulse width modulation digital to analog converter includes a pulse generator, a combiner and a filter. The pulse generator receives an n-bit digital word, partitions the input digital word into a plurality of sub-words, and produces a plurality of periodic pulse width modulated waveforms, each waveform's duty cycle and amplitude being representative of one of the plurality of sub-words. Since the sub-words have unique magnitude significance relative to the n-bit input word and relative to the other sub-words, each of the plurality of pulse width modulated waveforms are weighted according to the corresponding sub-word significance. The combiner receives the plurality of weighted pulse width modulated waveforms and combines them into a composite pulse width modulated waveform.

Abstract: An improved mixing scale, such as a paint mixing scale, includes a base which supports a scale pan in a substantially horizontal position. The scale pan supports a receiver container for holding the contents of that which is to be weighed. The mixing scale also includes a backing member which extends upwardly from the base and includes an output display near a top end of the member for presenting the measurement values produced by the scale. Proximate to the output display is a visual flow monitoring device, such as a reflector. Placement of the reflector proximate to the output display allows a user of the mixing scale to monitor the measurement value presentation and the flow of an additive being delivered into the receiver container simultaneously, or at the very least without requiring a physical shift in position by the user which might otherwise disrupt the delivery operation.

Abstract: 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.

Abstract: 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.

Abstract: A circular membrane diaphragm is edge-mounted on a generally cylindrical housing structure that allows the diaphragm to deform when a differential pressure is applied across it. The housing structure also supports a circular electrode in an internal chamber and in close proximity to the back surface of the diaphragm to form a variable capacitor. The outer side of the membrane is exposed to a second chamber defined by the housing structure and a cover. A tube connects the second chamber to a gas whose pressure is to be measured. The back of the housing structure is exposed to atmospheric pressure and other ambient atmospheric conditions. The housing structure is characterized by double flanges spaced axially by a deep lateral groove. A central cylindrical boss extends axially from the back side of the housing. The outer diameter B of the boss is at least equal to the diameter E of the groove. This housing structure provides the membrane with a high degree of isolation from external pressure fluctuations.

Abstract: A differential pressure transducer includes a pair of interior chambers separated by a peripherally supported, nominally planar electrically conductive diaphragm. A magnetic assembly is positioned on at least one chamber wall opposite to a central portion of the diaphragm. The magnetic assembly includes an electrical conductor and preferably a magnetic field permeable electric field shield between the electrical conductor and the chamber so that as the central portion of diaphragm is displaced from its nominal plane in response to an applied pressure differential, the inductance of the magnetic assembly changes. The transducer may be a portion of a tank circuit of an oscillator having a frequency of oscillation that varies with the pressure differential applied across the diaphragm.

Abstract: A differential pressure transducer includes a pair of interior chambers separated by a peripherally supported, nominally planar electrically conductive diaphragm. A magnetic assembly is positioned on at least one chamber wall opposite to a central portion of the diaphragm. The magnetic assembly includes an electrical conductor and preferably a magnetic field permeable electric field shield between the electrical conductor and the chamber so that as the central portion of diaphragm is displaced from its nominal plane in response to an applied pressure differential, the inductance of the magnetic assembly changes the transducer may be a portion of a tank circuit of an oscillator having a frequency of oscillation that varies with the pressure differential applied across the diaphragm.

Abstract: An apparatus is disclosed for measuring the pressure of a liquid column enclosed within a pressurized tank or cell, and for deriving the height and/or density of the liquid column based on the measured pressure. The apparatus includes a first pressure sensor for differentially measuring the pressure within the cell relative to a reference pressure at a first height, and further includes a second pressure sensor for differentially measuring the pressure within the cell relative to a reference pressure at a second height. A feedback network is operative to match the reference pressure to the pressure within the cell at one of the first and second heights. The feedback network ensures that the sensor detecting the one region is maintained at a zero or null differential pressure condition, enabling the use of a small dynamic range sensor.

Abstract: 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.

Abstract: 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.