Drexelbrook Engineering Company

Drexelbrook Controls, Inc.

David M Stern

Frederick L Maltby

L Jonathan Kramer

Leslie D Horrocks, Deceased

By Maureen Horrocks, Executrix

An instrument system provides compensation for signal processing errors by processing both sensor signals and reference signals in a common signal processor. Reference signals may be provided which enable zero compensation, gain compensation, or both. The system outputs compensated signals to a two wire signal loop in either analog or digital form, and selects the form of output signal in accordance with digital input signals received from the signal wires. The system may be embodied as a radio frequency admittance instrument system for monitoring the condition of materials.

Error compensating instrument system with digital communications

An improved system for generating a signal representative of the level of a material having a dielectric constant within a vessel is disclosed. The system features use of a first probe for generating a signal indicative of the dielectric constant of the material which is divided into a signal varying with the level of the material whereby a compensated level signal irrespective of the actual dielectric constant is measured. In a preferred embodiment, a single integrator is used to perform the division operation whereby inaccuracies due to component variation including long-term drift are eliminated. The instrument is disclosed as functioning in a two-wire instrument system having low power requirements, permitting use of conventional signal limits. Means for calibrating the instrument in a fail-safe manner such that the operator is assured of proper calibration are disclosed, as is means whereby bridge circuits used to measure in the capacitance measurements supplied to the division circuit are both supplied by a single oscillator means, again increasing reliability and accuracy of the system.

Two-wire compensated level measuring instrument

Two-wire level measuring instrument

A compensated level measuring system is disclosed for measuring the level of the material housed in a vessel, the system incorporating compensation means for compensating for variations in the dielectric constant of the material. A two element measuring system is used, having a first element mounted at a fixed position within the vessel containing the material for obtaining a level signal which is a function of the material level, and a second element maintained within the vessel and always submerged in the material for obtaining a reference signal. Means are provided for adjusting the reference signal so that it can accurately compensate for variations in the level signal which occur independently of the material level. The compensating means is provided either by a mechanical embodiment in which the reference signal is effectively tuned by modifying the position of the reference probe, or electronic means where the effective reference signal is modified by an error function to compensate for errors introduced by changes in the dielectric constant of the material being measured.

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Merion Station, PA, United States of America

David M Stern