Abstract: Apparatus for non-contact determination of wafer resistance of a semiconductor wafer includes a first sensor element, separated from a surface of the wafer by a first air gap, for capacitively coupling an AC drive signal into a portion of the wafer. A second sensor element, separated from the surface of the wafer by a second air gap, capacitively couples an AC output signal out of the wafer portion. An inductor, in series connection with the sensor elements is included in the sensor/wafer circuit. A frequency of the AC drive signal is automatically tuned to a resonant frequency at which capacitance impedance of the first air gap and of the second air gap is canceled by inductive impedance of the inductor. A voltage value of the drive signal required to drive an AC current signal of fixed magnitude through the wafer portion is automatically determined. The voltage value provides a measure of wafer resistance.

Abstract: Apparatus for non-contact determination of wafer resistance of a semiconductor wafer includes a first sensor element, separated from a surface of the wafer by a first air gap, for capacitively coupling an AC drive signal into a portion of the wafer. A second sensor element, separated from the surface of the wafer by a second air gap, capacitively couples an AC output signal out of the wafer portion. An inductor, in series connection with the sensor elements is included in the sensor/wafer circuit. A frequency of the AC drive signal is automatically tuned to a resonant frequency at which capacitance impedance of the first air gap and of the second air gap is canceled by inductive impedance of the inductor. A voltage value of the drive signal required to drive an AC current signal of fixed magnitude through the wafer portion is automatically determined. The voltage value provides a measure of wafer resistance.

Abstract: A control system for a magnetic bearing includes a sensor which generates an output representative of the relative shaft position. The signal from the sensor is processed by an integrator and offset adjustment block and a difference amplifier to subtract the processed sensor signal from a reference voltage. The difference signal result is fed to a bias control circuit including voltage dividers which generates a voltage which is received by coil current power amplifiers for both the upper and lower magnetic coils. Coil currents are then generated to stabilize the magnetic bearing.

Abstract: The present invention relates to an active mount system in which a vibration sensor such as a force gauge or an accelerometer senses vibrational forces transmitted through a resilient mount by a load such as a machine. The invention further includes a digital narrow-band least mean square filter that receives a sinusoid synchronous with the rotating machinery and an error signal from the load cell and generates a corrective signal to be amplified and transmitted to the electromagnet which supplies an attenuating force to the resilient mount in response to the signal. As an alternative, a wide frequency range control can be realized by the use of a wide frequency range, high gain amplifier and multi-filter phase compensation circuitry to generate the corrective force signal which is amplified and transmitted to the electromagnet.

Abstract: A tachometer signal conditioner circuit functions to accept a wide range of input signals and produces a digital pulse signal which indicates a gear shaft phase reference position. Tachometer input signals of either a true 1/revolution or an N/revolution signal with a single pulse or N pulses of different amplitude than the other pulses during the same shaft revolution can be used. The circuit comprises tachometer signal conditioner circuitry for amplifying and filtering the input from the tachometer, tachometer signal detector circuitry to produce digital pulses synchronous with the tachometer signal cycles and to detect the occurrence of a tachometer signal with a different amplitude during each 1/revolution or N/revolution period, a blanking signal generator which prevents tachometer signal noise from generating spurious 1/rev pulses during operation in the N/rev mode, and an output driver which produces signals to the remaining signal circuitry and to a front panel indicator lamp.

Abstract: A fiber optic sensor probe system comprises an electromechanical arrangement system which enables a fiber optic probe to lock onto a null point relative to a target which null point represents an in focus condition for the probe relative to the target. A servomechanism feedback circuit maintains the probe in an in focus condition relative to the target if the target moves. A dithering motion is provided to the probe such that, when the electrical output of the probe has a frequency component which is the same frequency as that of the dither, an out of focus condition of the probe relative to the target exists and the servomechanism feedback system operates to correct it. A monochromatic light source is used to eliminate the problem of different spectral components of light having slightly different focal lengths.

Abstract: This invention relates to a detection circuit for use in a servo controlled fiber optic sensor. A low noise signal with an amplitude proportional to the magnitude of the synchronous detection output is produced without the use of filter by a calculation of the average vale of the synchronous detector output signal driving one complete cycle of the dither signal cycle. This value is fed into sample and hold circuitry, which in turn controls the series motor.

Abstract: A new variable impedance type system is described for measuring a preselected physical parameter such as spacing, displacement, pressure, vibration, etc. A sensor/transducer is positioned to provide the variable impedance. The sensor/transducer is part of a self-oscillatory circuit which produces pulses having a pulse rate proportional to the physical parameter being measured.

Abstract: A device for counting objects in a stacked relationship which includes a bifurcated optical cable, a light source for directing light through the bundle at the stack and a sensor for generating a signal proportional to the light reflected by the stack. The signal is digitized and fed to a digital counter. Various displays connected to the counter indicate the count results.

Abstract: A displacement measuring instrument for measuring the displacement of a target including in combination a fiber optic lens assembly including means for maintaining said assembly in space relation with said target, dither means for vibrating said assembly toward and away from said target about the lens null along the axis of said assembly, first electronic means for providing a first output voltage proportional to displacement of said assembly from said target, second electronic means cancelling that portion of said first output voltage resulting from displacement due to said dither means and providing a second voltage resulting from displacement due to means other than said dither means, servo means receiving said second output voltage and moving said assembly with respect to said target to null said second output voltage and measurement means measuring the movement of said servo means.

Abstract: This invention provides for the use of two similar fiber optic probes set at a fixed position differential relative to each other in order that a calibration correction signal can be obtained which may be used to create a common output signal having a gap calibration which is independent of surface reflectance.

Abstract: A method and apparatus for controlling a resonant piston compressor of the type comprising an electrodynamic linear reciprocating motor adapted to be driven cyclically by an alternating current power source and having at least one piston coupled to and adapted to be driven within a selectively valved working cylinder by the linear reciprocating motor in synchronism with the frequency of the alternating current power source. Enclosed volumes of gas act as resilient gas springs coacting with the piston and with the linear reciprocating motor to form a mechanical resonant system having a resonant frequency substantially centered on the frequency of the alternating current power source. A midstroke porting arrangement is responsive to the position of the resonant piston for selectively communicating a gas spring control valve with said gas springs.

Abstract: A control system for controlling the operation of a reciprocating resonant free-piston variable stroke compressor of the type driven by electrodynamic linear motors wherein the spring-mass system of the compressor which is forced into vibration by the linear motor, is arranged to have a selectively variable mechanical resonant frequency generally centered on the power line frequency of the alternating current power source used to drive the linear motor. The control system provided by this invention variably controls the opening and closing of a gas spring control valve that in turn regulates the pressure of gas filled volumes selectively connected to a manifold vented by the valve. The volumes comprise the resilient gas springs for the resonant piston compressor.

Abstract: A control method and system for quasi-proportionally controlling the magnitude of DC excitation current supplied to the DC field coil windings of a linear reciprocating motor in proportion to the magnitude of the AC excitation current supplied to the AC field coil windings of the motor.

Abstract: A fiber optic proximity measuring instrument for measuring dynamic changes in the gap between a probe tip and a target includes a light source, two sensors for measuring reflected light and lamp brightness, and a light conducting cable for transmitting light to the target and conducting light reflected from the target back to the reflected light sensor. The lamp intensity is set by a brightness control during setup to produce a mean level of reflected light intensity, and then is automatically regulated to maintain an equal mean intensity at the reflected light sensor despite changes in target reflectivity and cable light conductance.

Abstract: A controlled carrier current measuring sensor/transducer signal amplifier system comprising a carrier oscillator for providing a carrier voltage oscillatory signal of known frequency and fixed voltage magnitude. A differential amplifier has the carrier voltage oscillatory signal supplied to one of its inputs. A reference impedance and a variable impedance sensor transducer are connected in a series circuit across the output of the differential amplifier and a first feedback signal is fed back to a second input of the differential amplifier with the first feedback signal comprising the sum of the voltage across the reference impedance and the variable impedance sensor transducer. A buffer amplifier has its input connected to the juncture of the reference impedance and the variable impedance sensor/transducer for deriving an output voltage representative of the instantaneous value of the voltage across the variable impedance sensor/transducer.

Abstract: A new capacitance type non-contact displacement and/or vibration measurement instrument sensing head is described together with a novel method of maintaining calibration of the instrument using such sensing head. The invention takes the form of a central probe member having a first guard ring disposed in coaxial, electrically insulated relationship about the central probe member and driven at the same potential and frequency as the probe member. A secondary driven guard ring coaxially surrounds the first guard ring and is electrically isolated from it and is driven at the same alternating current frequency but at a higher voltage of the order of 1.5 to 1 times higher. The additional secondary guard ring, driven at a suitably boosted voltage level and the same frequency as the central probe member, serves to focus the otherwise divergent electric field, thus producing a very significant improvement in the output linearity when operated at relatively large displacements.