Emhart Industries, Inc.

P. R. Mallory Co.

Louis M Sandler

Charles E Scott

Walter R Spofford

Daniel I Pomerantz

Robert G Bristol

John N Oliver

The present invention utilizes the fact that the rate of change of the amplitude of a sinusoidal waveform is substantially constant within an interval of such waveform near its zero crossing. A circuit for measuring peak amplitudes of sinusoidal waveforms includes a voltage differentiator for differentiating between a first and second reference selected within the interval of a sinusoidal waveform wherein the rate of change of the amplitude is substantially constant; a time interval calculator for measuring a time interval between the references; a frequency determinator for determining the frequency of oscillation of the waveform; and a processing unit responsive to the voltage differentiator, the time interval calculator, and the frequency determinator for determining a peak amplitude of the waveform. In accordance with the present invention, a method of controlling the operation of an induction motor of the type having a main winding and at least one start winding utilizes the circuit for measuring peak amplitudes of sinusoidal waveforms. The motor start control system includes a current sensing device for producing a waveform proportional to the main winding current of the motor and a control circuit responsive to the waveform for deenergizing the start winding of the motor when the amplitude of the waveform is less than a threshold level wherein the threshold level is variable in accordance with the start main winding current. By continuously determining peak amplitudes of the waveform which is proportional to main winding current of the motor and storing an initial peak amplitude of the waveform, the start winding is deenergized when a peak amplitude of the waveform becomes less than a defined percentage of the stored initial peak amplitude.

Control system and method for motor starting

An oscillator circuit having a variable duty cycle for controlling the power level of a microwave oven provides an adjustable RC time constant circuit including a capacitance branch and a resistance branch and coupling means therebetween, the resistance branch including a pair of alternately selectable current paths for the charging and discharging of the capacitance branch, the coupling means including semiconductor switch means for selecting and coupling either of the current paths to the capacitance branch for changing the charging and discharging of the capacitance branch in accordance with the selected current path, and one of the current paths including a pair of parallel connected portions with each of the parallel portions having a diode connected therein for controlling the direction of current flow, the diodes being connected with opposite respective polarities for allowing current flow only in opposite directions in the respective portions, the one current path further including a potentiometer having a pair of fixed terminals each of which is connected to a separate parallel portion and a variable wiper terminal connected to the first coupling means for simultaneously inversely varying the resistance in the parallel portions.

Oscillator circuit for controlling the power level of a microwave oven

A circuit for controlling the application of alternating current power to an apparatus provides a triac having a pair of main terminals adapted for being coupled in series between the apparatus and a source of alternating current power, the triac also having a gate terminal, nonregulated direct current power supply adapted to receive alternating current power from the source thereof, the power supply including a rectifier and a filter and having a pair of output terminals for distributing direct current power, circuitry for maintaining an approximately constant load on the nonregulated direct current power supply and for switching current therefrom to the triac gate terminal including a semiconductor junction switch having a gate terminal, a first main terminal coupled to one output terminal of the power supply and the triac gate terminal and a second main terminal coupled to the other output terminal of the power supply, and circuitry coupled to the switch gate terminal for activating and deactivating current flow in the switch to deactivate and activate, respectively, current flow through the triac by shunting current from the one terminal of the power supply away from the triac gate and to the other power supply terminal, thereby providing control of the application of alternating current power to the apparatus.

Alternating current power control circuit

Disclosed herein is an improved means for detecting a half-cycle voltage crest of an alternating voltage waveform which includes means for protecting the detecting means from current surges associated with the initial random application of the alternating voltage waveform to the detecting means.

Crest firing means

An apparatus for detecting the presence of a substance on a liquid surface utilizes a single semiconductor sensing element having a thermal resistance which is related to the thermal conductivity of the environment surrounding it. A control logic sequentially and periodically samples and stores ambient temperatures of the environment surrounding the sensing element, subsequently heats the sensing element, samples and stores peak temperatures of the sensing element resulting from the heating, and finally differentiates between the ambient temperatures and peak temperatures to detect any change in the difference therebetween.

Apparatus and method for detecting the presence of a substance on a

In a touch control system including one or more touch sensitive devices which capacitively transmit a relatively large electrical signal when not touched and transmit a relatively small electrical signal when touched an improved means for detecting the touch and no-touch conditions of the touch sensitive devices includes a comparator having positive feedback associated therewith. By increasing or decreasing the positive feedback the touch control system is operable either asynchronously or synchronously with an external control system. Furthermore, a plurality of touch sensitive devices may be multiplexed utilizing a single detection means constructed in accordance with the invention disclosed herein while requiring a relatively low voltage drive signal.

Detection means for touch control switches

A vacuum fluorescent display system for displaying a plurality of illuminable characters includes a plurality of segmented anodes, at least one cathode filament, a plurality of control grids interposed between the anodes and the cathode filament and circuitry for controllably powering the cathode filament and for sequentially driving the control grids whereby selected segments of the anodes are sequentially illuminated and the luminous intensity of the segments of each of the anodes is substantially the same. The cathode filament is controllably powered by removing and applying heating power in response to driven and undriven states respectively of the control grids. By controlling when heating power is applied to the cathode filament the voltage along the cathode filament is the same for each anode when the selected anode segments are sequentially illuminated thereby substantially eliminating variation in luminous intensity.

Drive means and method for vacuum fluorescent display systems

Electrodes are disposed on portions of a container comprising dielectric material, an electrical signal is capacitively transmitted between said electrodes, said electrical signal is shunted by the presence of a liquid in close proximity to said electrodes, and said shunting is detected.

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North Reading, MA, United States of America

Louis M Sandler