Optical current transducer with offset cancellation and current linearization

Patent metadata

Field	Value
Publication number	US-10197603-B2
Application number	US-201514676427-A
Country	US
Kind code	B2
Filing date	Apr 1, 2015
Priority date	Apr 1, 2015
Publication date	Feb 5, 2019
Grant date	Feb 5, 2019

Abstract

There is provided a system for use with a fiber-optic current transducer. The system includes a processing unit configured to transduce a first light signal into a first electrical signal. The processing unit is further configured to transduce a second light signal into a second electrical signal. The processing unit is configured to remove offsets from the first electrical signal and the second electrical signal by forcing the first electrical signal and the second electrical signal to be on the same per unit basis. Furthermore, the processing unit is configured to combine the first electrical signal and the second electrical signal to produce a composite signal, the composite signal being free of the offsets. And the processing unit is further configured to linearize the composite signal to produce an output current indicative of a current flowing in a conductor disposed proximate the FOCT.

First claim

What is claimed is:

1. A system, for use with a fiber-optic current transducer (FOCT), the system comprising:
a processing unit configured to:
transduce a first light signal into a first electrical signal;
transduce a second light signal into a second electrical signal;
calculate a first direct current (DC) offset of the first electrical signal;
calculate a second direct current (DC) offset of the second electrical signal;
calculate a difference value by subtracting the first DC offset of the first electrical signal from the second DC offset of the second electrical signal;
calculate, based on the difference value, a first gain for the first electrical signal and a second gain for the second electrical signal;
calculate a first adjusted DC offset by multiplying the first DC offset by the first gain;
calculate a second adjusted DC offset by multiplying the second DC offset by the second gain;
wherein the first gain and the second gain are determined such that the first adjusted DC offset is equal to the second adjusted DC offset;
calculate a first adjusted electrical signal by multiplying the first electrical signal by the by the first gain;
calculate a second adjusted electrical signal by multiplying the second electrical signal by the second gain;
calculate a current output signal based on subtracting the first adjusted electrical signal from the second adjusted electrical signal;
calculate a current correction factor by:
adding the first adjusted electrical signal and the second adjusted electrical signal to form a composite signal;
detecting a maximum value of a cycle the composite signal; and
calculating the current correction factor based on a ratio of the composite signal to the maximum value; and

calculate a corrected current output signal by multiplying the current output signal by the current correction factor.

2. The system of claim 1 , wherein the current correction factor is calculated if the current output signal is above a threshold of 4000 Amperes.

3. The system of claim 1 , wherein the first light signal and the second light signal are provided by light in a fiber that is reflected via a first path and a second path.

4. The system of claim 3 , wherein the fiber is positioned around a conductor.

5. The system of claim 1 , further comprising a crystal in the FOCT, the crystal configured to route the first light signal and the second light signal.

6. The system of claim 1 , wherein the first DC offset is determined by integrating the first electrical signal with an integrator and the second DC offset is determined by integrating the second electrical signal with the integrator.

7. The system of claim 1 , wherein the first DC offset is provided to a first summing junction to remove the first DC offset from the first electrical signal and the second DC offset is provided to a second summing junction to remove the second DC offset from the second electrical signal.

Assignees

• Gen Electric

Inventors

• Wallace Daniel Robert
• Korot Daniel
• Serradimigni Charles Max

Classifications

• G01R15/247

  Details of the circuitry or construction of devices covered by G01R15/241 - G01R15/246 · CPC title

• G01R15/24 Primary

  using light-modulating devices · CPC title

• G01R15/246 Primary

  based on the Faraday, i.e. linear magneto-optic, effect · CPC title

• G01R19/0092

  Measuring current only · CPC title

• G01R15/005

  Circuits for altering the indicating characteristic, e.g. making it non-linear · CPC title