Hewlett-packard Company

Other

Robert D Albin

John A Cacciola

Frank K David

A liquid level detecting system for detecting a conducting liquid level in a non conductive container which utilizes a grounding rod mounted in a lower portion of the container and a conductive sensing rod mounted at a position above the grounding rod. An oscillator is provided having a frequency in the range of about 600 hertz to about 100 kilohertz. The output of the oscillator is applied to the sensing rod through a high impedance circuit and a high pass filter. In another embodiment, the high pass filter may have the higher end frequencies attenuated to produce a band pass filter which selectively passes the frequency of the oscillator. The voltage drop across the circuit which includes the conductive sensing rod to ground is detected by a voltage peak detector and a threshold detector to produce an output which detects the drops in voltage when the conductive fluid level in the tank rises so that both the sensing rod and the grounding rod are covered, completing the circuit. In another embodiment, multiple sensing rods may be positioned at various heights in the tank to detect various fluid levels. The use of the high pass or band pass filters in series with the sensing rod and ground will eliminate any DC current in the rods thereby reducing electrolysis. The filters also eliminate or significantly reduce interference or artifacts due to DC and 60 hertz.

Liquid level sensor utilizing AC and resistance

A finline structure comprises a dielectric substrate-mounted circuit disposed within a waveguide having on the substrate integrated distributed capacitance elements at least partially formed by laterally separated metallization layers. Thin-film construction techniques may be employed in construction. In general, the distributed capacitance elements permit the biasing of a plurality of circuit elements in a finline transmission medium. In selected structures, r.f. continuity is effected between traces and metallization layers while maintaining d.c. isolation. Examples are described of circuits which can incorporate an integrated capacitor, including but not limited to detectors, r.f. modulators, r.f. attenuators, amplifiers, and multipliers. According to the invention, a plurality of elements, as well as multiple port elements, may be selectively biased while retaining d.c. isolation and r.f. continuity. Moreover, the versatility of construction allows for higher levels of integration as well as the realization of new topologies previously unattainable. Since the capacitance structure is integrated into the thin film circuit, fewer discrete parts are required and the manufacturing process may be precisely controlled by photolithography.

Integrated capacitance structures in microwave finline devices

A microwave frequency multiplier employs a first diode and a second diode each coupled in anti-parallel relationship across a signal input of a finline structure, each of the diodes being associated with signal-induced biasing elements for self biasing the diodes. A bias is caused to occur at internal nodes which increase with increased input power for a broad range of input power levels. The presence of such biasing results in waveform clipping at higher signal levels. Relative to prior art, the conversion loss will remain optimum up to high input power over an entire high-power input range. Additional external bias may be employed in alternative embodiments.

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Santa Rosa, CA, United States of America

Robert D Albin