US 4,015,472 AGranted

Two-wire transmission system for vortex flowmeter

AssigneeFischer & Porter Co.

InventorPeter J. Herzl

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Abstract

A two-wire transmission system for a vortex-type flowmeter whose sensor generates a low-level a-c signal having a frequency that depends on flow rate, the signal being fed to the input of a pre-amplifier adjacent the meter. The two-wire system serves to supply d-c power to the pre-amplifier from a remote d-c source and to conduct the a-c output of the pre-amplifier to a remote output point. The system includes a DC-to-DC converter constituted by a high-frequency oscillator whose circuit incorporates the primary of an isolation transformer, the secondary of which is coupled to a rectifier supplying d-c to the power terminals of the pre-amplifier. Connected across the pre-amplifier output is a load resistor which draws a sufficiently heavy current to modulate the d-c power consumed by the pre-amplifier in accordance with the amplified a-c signal. These modulations are reflected in the demand imposed by the converter on the d-c source through the two-wire line, the fluctuating demand being detected at the remote output point to extract the a-c signal from the line.

Claims10

Dependent claims

An isolated two-wire line transmission system for supplying d-c operating power to the power terminals of a pre-amplifier whose input is connected to the transducer of a grounded vortex-type flowmeter yielding a low-frequency a-c signal within a given range as a function of flow rate and for concurrently conveying the amplified low-frequency a-c signal output of the pre-amplifier to a remote terminal, said system comprising:

A. a d-c voltage source;
B. a DC-to-DC converter whose input is connected via said two-wire line to said source and whose output is connected by at least one lead to said amplifier power terminals, whereby the direct-current carried by said lead depends on the power drawn by said amplifier from said converter;
said converter being constituted by a high-frequency carrier oscillator whose operating frequency is substantially higher than the highest frequency in the low-frequency range of said flowmeter, said carrier being applied by a high-frequency isolation transformer to a full-wave rectifier whose output is fed by said lead to said power terminals, said transformer being substantially unresponsive to frequencies in said low-frequency range,
C. a load resistor connected between the output of said amplifier and said lead, said resistor drawing a sufficiently heavy current to modulate the direct-current flowing through said lead in accordance with the amplified low-frequency a-c signal flowing through said resistor, this modulation being reflected in the demand imposed by said converter on said d-c source through said line, whereby the current in said line has an a-c modulation component;
and
D. means coupling said output terminal to said line to extract only the a-c modulation component therefrom.

3 more elements

Dependencies are inferred from the claim text.