# US 10,274,352 B2 · Method and apparatus for interference reduction

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- Number: US 10,274,352 B2
- Document ID: US10274352B2
- Status: Granted
- Kind: B2
- Application number: 15/268,911
- Filed: 2016-09-19
- Published: 2017-03-23
- Granted: 2019-04-30
- Earliest claimed: 2015-09-21
- Assignees: ABB AB
- Applicants: ABB Limited
- Inventors: Ray Keech
- Web page: https://patentgrep.com/patent/US10274352B2

## CPC

- G01F 1/584: {constructions of electrodes, accessories therefor}
- G01F 1/60: Circuits therefor
- H04L 25/08: Modifications for reducing interference; Modifications for reducing effects due to line faults {; Receiver end arrangements for detecting or overcoming line faults}
- H04L 43/028: by filtering
- H04L 5/06: the signals being represented by different frequencies (combined with time-division multiplexing H04L5/26)
- G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A method and apparatus are for processing a periodic data-carrying signal to reduce periodic interference at either of a first fundamental frequency or a second fundamental frequency, the second fundamental frequency being different from the first fundamental frequency. The periodic data-carrying signal is derived from an excitation signal having an excitation frequency, the excitation frequency being a sub-multiple of the first fundamental frequency. The data-carrying signal is subjected to both a comb filter to reject interference at the first fundamental frequency, and an averaging/integrating filter to reject interference at the second fundamental frequency. A comb filter delay period is related to the first fundamental frequency and the averaging/integrating filter averages or integrates over a period related to the second fundamental frequency.

## Claims

### Claim 1

A method performed by signal processing circuitry of processing a periodic data-carrying signal produced by an electromagnetic flowmeter to reject periodic interference from the data-carrying signal at a first fundamental frequency and a second fundamental frequency, the second fundamental frequency being different from the first fundamental frequency,
the periodic data-carrying signal being derived from an excitation signal having an excitation frequency, the excitation frequency being a sub-multiple of the first fundamental frequency,
the method comprising:
subjecting the data-carrying signal to a comb filter operation performed by comb filter circuitry to reject interference at the first fundamental frequency and harmonics of the first fundamental frequency;
wherein the comb filter operation has a comb filter delay period related to the first fundamental frequency;
wherein the comb filter operation rejects interference at only the first fundamental frequency and harmonics of the first fundamental frequency;
subjecting the data-carrying signal to an averaging or integrating filter operation performed by averaging or integrating circuitry to reject interference at the second fundamental frequency and harmonics of the second fundamental frequency; and
wherein the averaging or integrating filter operation averages or integrates over a period related to the second fundamental frequency.

### Claim 2 (depends on 1)

The method as claimed in claim 1, wherein the excitation frequency is given by:
(the first fundamental frequency)/n,
where n is an integer.

### Claim 3 (depends on 1)

The method as claimed in claim 1, wherein the comb filter delay period is given by:
1/(2×the excitation frequency)
or
1/(the excitation frequency).

### Claim 4 (depends on 1)

The method as claimed in claim 1, wherein the averaging or integrating filter operation averages or integrates over a period given by:
m/(the second fundamental frequency),
where m is an integer.

### Claim 5 (depends on 1)

The method as claimed in claim 1, wherein the comb filter operation precedes the averaging or integrating filter operation.

### Claim 6 (depends on 1)

The method as claimed in claim 1, wherein the averaging or integrating filter operation precedes the comb filter operation.

### Claim 7 (depends on 1)

The method as claimed in claim 1, wherein the first fundamental frequency is 50 Hz and the second fundamental frequency is 60 Hz.

### Claim 8 (depends on 1)

The method as claimed in claim 1, wherein the first fundamental frequency is 60 Hz and the second fundamental frequency is 50 Hz.

### Claim 9 (depends on 1)

The method as claimed in claim 1, wherein the excitation signal has an alternating form, for example a form selected from a group comprising:
a square wave, a non 50:50 pulse, a sine wave, a triangular wave, a saw-tooth wave.

### Claim 10 (depends on 1)

The method as claimed in claim 1, wherein the method is performed by said flowmeter.

### Claim 11 (depends on 1)

The method as claimed in claim 1, wherein the method is performed by signal processing circuitry separate from said electromagnetic flowmeter.

### Claim 12

An apparatus comprising signal processing circuitry for processing a periodic data-carrying signal produced by an electromagnetic flowmeter to reject periodic interference from the data carrying signal at a first fundamental frequency and a second fundamental frequency, the second fundamental frequency being different from the first fundamental frequency,
the periodic data-carrying signal being derived from an excitation signal having an excitation frequency, the excitation frequency being a sub-multiple of the first fundamental frequency,
the apparatus comprising:
comb filter circuitry configured to reject interference from the data-carrying signal at the first fundamental frequency and harmonics of the first fundamental frequency;
wherein the comb filter circuitry has a comb filter delay period related to the first fundamental frequency;
wherein the comb filter operation is configured to reject interference from the data-carrying signal at only the first fundamental frequency and harmonics of the first fundamental frequency;
averaging or integrating filter circuitry in series with the comb filter circuitry, the averaging or integrating circuitry being configured to reject interference at the second fundamental frequency and harmonics of the second fundamental frequency; and
wherein the averaging or integrating filter circuitry is configured to average or integrate over a period related to the second fundamental frequency.

### Claim 13 (depends on 12)

The apparatus as claimed in claim 12, wherein the excitation frequency is given by:
(the first fundamental frequency)/n,
where n is an integer.

### Claim 14 (depends on 12)

The apparatus as claimed in claim 12, wherein the comb filter delay period is given by:
1/(2×the excitation frequency)
or
1/(the excitation frequency).

### Claim 15 (depends on 12)

The apparatus as claimed in claim 12, wherein the averaging/integrating filter circuitry is configured to average or integrate over a period given by:
m/(the second fundamental frequency),
where m is an integer.

### Claim 16 (depends on 12)

The apparatus as claimed in claim 12, wherein the comb filter circuitry precedes the averaging or integrating filter circuitry.

### Claim 17 (depends on 12)

The apparatus as claimed in claim 12, wherein the averaging or integrating filter circuitry precedes the comb filter circuitry.

### Claim 18 (depends on 12)

The apparatus as claimed in claim 12, wherein the first fundamental frequency is 50 Hz and the second fundamental frequency is 60 Hz.

### Claim 19 (depends on 12)

The apparatus as claimed in claim 12, wherein the first fundamental frequency is 60 Hz and the second fundamental frequency is 50 Hz.

### Claim 20 (depends on 12)

The apparatus as claimed in claim 12, wherein the excitation signal has an alternating form, for example a form selected from a group comprising:
a square wave, a non 50:50 pulse, a sine wave, a triangular wave, a saw-tooth wave.

### Claim 21 (depends on 12)

The apparatus as claimed in claim 12, further comprising a signal generator configured to generate the excitation signal.

### Claim 22 (depends on 21)

The apparatus as claimed in claim 21 wherein the apparatus is said electromagnetic flowmeter.

### Claim 23 (depends on 12)

The apparatus as claimed in claim 12 being signal processing circuitry operable to receive and process a data-carrying signal produced by said electromagnetic flowmeter.