Abstract: A variable reluctance transducer system incorporating digital control of parallel resonant circuits including two inductive sensors L1 and L2 on each side of a flat diaphram. The dual variable reluctance elements provide dual frequency signals for digital calculation to obtain a quotient of the frequencies, thereby substantially eliminating the resonant frequencies as a variable in the accuracy of the device. Manipulation of the produced quotient by a micro-controller 10 employing digital calibration tables stored in a programmable read only memory 14 allows calibration reponsive to a temperature sensor 16, thereby substantially eliminating temperature induced errors in the system, further increasing accuracy.

Abstract: The present invention comprises an oscillator including a transformer having a first winding with a power feed to the center tap. A first pair of transistors in a push-pull configuration are connected at the emitter electrodes across the second winding of the transformer. A center tap on the second winding is provided for a negative polarity power return. The base electrodes of the transistors are commonly connected to receive a control current and the collector electrodes of the transistors are connected across a first winding of the transformer. A capacitive element is connected across the first winding to create a tuned circuit within an oscillator.

Abstract: An improved control circuit for maintaining constant amplitude of the sinusoidal output signal of an oscillator circuit by synchronously demodulating the signal using a push-pull transistor pair operating in saturation to generate a control signal for comparison with a reference voltage in a direct coupled negative feedback loop to the oscillator. The configuration of the feedback loop provides effectively instantaneous control response to eliminate low frequency modulation propagated internally in the oscillator due to noise generation in circuit components.

Abstract: A high-accuracy system for gaging liquid height in storage tanks. A pair of standpipes are arranged to be pumped to several accurately predetermined liquid levels to enable zero and sensitivity calibration of a differential-pressure transducer which normally monitors the pressure head of a column of liquid in the tank. The entire system is filled with tank liquid (eliminating condensation and vapor bubble problems encountered if the transducer is vented to atmosphere), and sharp-edged standpipes provided to minimize meniscus error when one or both standpipes are completely full.