Abstract: A device for measuring relative distance between two physical objects includes an elongated inductor coil and a movable core. The movable core includes a slug of magnetically interactive material and is configured to move within the elongated inductor coil and to couple and interact magnetically with the elongated inductor coil. Electric current flowing through the elongated inductor coil generates a magnetic flux within the elongated inductor coil, and the magnetic flux is subsequently modified by moving the movable core within the elongated inductor coil and the modified magnetic flux is used to produce an electric output as a function of the position of the slug within the elongated inductor coil.

Abstract: A resistance welding apparatus characterized by very low output impedance, and providing a substantially constant voltage source to low impedance (e.g., resistances on the order of 1-100 micro-ohms) materials-to-be-joined. The welding apparatus includes one or more primary and secondary winding pairs disposed about a high permeability core with the secondary coil(s) positioned between the primary coil(s) and the core. In a preferred form, the secondary coil(s) are capable of delivering more than 75,000 amperes of welding current. The welding apparatus is lighter, more cost efficient, and more energy efficient than conventional systems.

Abstract: A resistance welding apparatus characterized by very low output impedance, and providing a substantially constant voltage source to low impedance (e.g., resistances on the order of 1-100 micro-ohms) materials-to-be-joined. The welding apparatus includes one or more primary and secondary winding pairs disposed about a high permeability core with the secondary coil(s) positioned between the primary coil(s) and the core. In a preferred form, the secondary coil(s) are capable of delivering more than 75,000 amperes of welding current. The welding apparatus is lighter, more cost efficient, and more energy efficient than conventional systems.

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 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: Denier and other optically transmissivity-dependent parameters of yarn are monitored on-line and in real-time with a preferably microprocessor-controlled high frequency modulated-demodulated optically-based system. An LED is spaced-apart from an array of preferably identical photodetector ("PD") diodes that will track one another, with the yarn spaced between one of the PDs. The LED outputs preferably collimated light in response to a periodic LED drive signal, and yarn characteristics will affect light received by at least one PD in the array. An output signal from a first PD is fedback to the LED driver to continuously compensate the system against dust or other factors affect LED transmission and PD light reception. An output signal from a second PD is coupled to a fraction of the drive signal so as to enhance dynamic range. This signal is amplified and AC-coupled to a sample and hold that samples during a stable active portion of the LED drive signal to demodulate the relevant signal.

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 capacitive sensing circuit and system includes a variable capacitance sensing element as an active element in a circuit to measure changes in capacitance of the sensing element. A switching network in alternate cycles energizes a capacitor to develop a charge which effectively linearizes the sensor's capacitance response. In a push-pull circuit with two active sensing elements, a multi-channel switching network energizes two fixed correction capacitors to provide third or higher order correction, significantly extending the effective scale of the sensor. In a preferred embodiment, a single feedback signal is applied to all capacitors in different switching cycles. Examples include weight and pressure sensing systems.

Abstract: An instrument includes multiple sensing elements of the variable-capacitance type. The sensing elements are placed by a switching network into a single capacitance sensing circuit, and those elements which are not active in the circuit at a given time are switched by another or the same switching network into a ground shunt. The switching is effected at a rate, in relation to the expected vibrational spectrum of the sensor system, to determine a set of readings which are essentially equivalent to a set of simultaneous capacitance measurements of the plural sensing element. A preferred system is a weight sensing system employing three or four load cells to support a scale platform.

Abstract: An oscillator including a first frequency control network having a series coupled inductance and sensor capacitor, a pair of cascaded capacitors, and an emitter follower amplifier coupled thereto. The emitter follower amplifier drives a current limiter and a feedback path, whereby the current through the emitter follower amplifier is divided between the current limiter and the feedback path in a manner establishing an oscillatory potential in the oscillator, while keeping the transistor of the emitter follower amplifier substantially out of its saturation state.

Abstract: An oscillator including a non-inverting amplifier coupled in series with an inverting amplifier. A first feedback network couples the output from the non-inverting amplifier to the input of that amplifier by way of a capacitor C. A second feedback network couples the output of the inverting amplifier to the input of the non-inverting amplifier by way of a series connected resistor R, and includes a capacitor coupled between the input of that non-inverting amplifier and a reference potential. A third feedback network generates a feedback signal proportional to the difference between the average voltage at the output of the non-inverting amplifier and the average voltage at the output terminal of the inverting amplifier, and couples that feedback signal to the input of the inverting amplifier.

Abstract: 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.

Abstract: A temperature-compensated measuring system employs an internal signal-processor to provide high accuracy measurements, correct over a wide range of temperatures. In a calibration mode, the system employs the signal-processor to provide mathematical constants used to generate a temperature-compensation function. In a measurement mode, signals representing the uncompensated quantity and the system temperature are supplied to the signal-processor, which uses them to generate a temperature-compensation function from which it produces a high-accuracy temperature-corrected value of the measured quantity. In various forms, the invention can be used to measure temperature-compensated force, pressure or acceleration.

Abstract: A diaphragm having a pattern of wrinkles adapted so that the diaphragm is both radially and tangentially expandable with respect to a reference point in that central portion.

Abstract: A capacitive sensor system including a sensor with two fixed plate elements having opposed planar, electrically conductive surfaces serving as electrodes. The sensor further includes a movable, electrically conductive diaphragm positioned between the electrodes. At least one diode detector network is coupled across the electrodes. The diode detector networks each include a pair of oppositely directed series connected diodes with the junction between the diodes of each network being coupled to the diaphragm. In embodiments having only one diode detector network, the junction between the two diodes may be directly or capacitively coupled to the diaphragm.