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Abstract

A two-wire signal transmitter which isolates for direct current voltages the transducer input circuitry from the transmitter output circuitry. The transmitter superimposes a controlled current signal on the two-wire transmission line which also conducts a direct current power supply voltage to the transmitter. The direct current power supply voltage is transferred to the transducer input circuitry by means of a series direct current to alternating current and alternating to direct current conversions using a transformer for direct current isolation. The direct current transducer input voltage is converted to an alternating current voltage prior to any active signal processing with the processed or any current signal being transferred to the transmitter output circuitry through a direct current isolation transformer. The transferred alternating current signal is converted to a direct current signal by a synchronous detector. A matched dual current generator is utilized in the transducer input circuitry and in the zero reference circuitry to minimize unequal drift due to environmental temperature changes.

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First Claim