Cable detection apparatus with a comb filter

• US 10,310,130 B2
• Filed: 02/18/2015
• Issued: 06/04/2019
• Est. Priority Date: 02/19/2014
• Status: Active Grant

• Current Assignee: Metrotech Corporation (L'Air Liquide SA)
• Original Assignee: Metrotech Corporation (L'Air Liquide SA)
• Inventors: Overby, Johan, Royle, John Mark
• Primary Examiner(s): Reisner, Noam
• Application Number:
  US14/625,496
• Publication Number:
  US 20150234076A1
• Time in Patent Office: 1,567 Days
• CPC Class Codes: G01V 13/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00
• CPC Class Codes: G01V 3/10 using induction coils
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005

Abstract

An apparatus that uses harmonics of the power line frequency at which electrical power is distributed is presented. The apparatus includes a sensor antenna to detect an electromagnetic field produced by a cable. The output of the sensor is fed to a mixer together with a signal from a sine wave generator at less than the fundamental power frequency to frequency shift the signals from the sensor. The mixed output is then amplified to provide an audible output. A single comb filter receives signals from the mixer and outputs a filtered signal removing non-harmonic frequencies but preferably passing both odd and even harmonics. The output of the comb filter is then integrated at and displayed to indicate the detection of a cable based on the filtered signal.

Claims

1. A cable detection apparatus comprising:

a sensor to detect an electromagnetic field produced by a cable and provide signals, the electromagnetic field expected to have a component at a first frequency;

a frequency shifter to frequency shift the signals from the sensor by a second frequency of half the first frequency;

an amplifier that receives the frequency shifted signals;

a first filter to receive signals from the amplifier and output a filtered signal, the first filter having a higher transmittance at the second frequency and at the second frequency shifted by whole multiples of the first frequency than at least one frequency between two of said shifted frequencies; and

an indicator to indicate the detection of the cable based on the filtered signal.

2. The cable detection apparatus of claim 1, wherein the whole multiples include both odd and even multiples.

3. The cable detection apparatus of claim 1, wherein there is only a single comb filter between the sensor and the indicator.

4. The cable detection apparatus of claim 1, wherein the first filter is a comb filter.

5. The cable detection apparatus of claim 1, wherein the frequency shifter includes a mixer and a sine wave generator operating at the second frequency.

6. The cable detection apparatus of claim 1, further comprising a second filter between the amplifier and the first filter, the second filter being a high-pass filter to remove a B-field of the earth from the signals received from the amplifier.

7. A method of cable detection, the method comprising:

sensing an electromagnetic field produced by a cable to provide signals, the electromagnetic field expected to have a component at a first frequency;

frequency shifting the signals by a second frequency of half the first frequency;

amplifying the frequency shifted signals;

filtering, using a first filter, the amplified signals, the first filter having a higher transmittance at the second frequency and at the second frequency shifted by whole multiples of the first frequency than at least one frequency between two of said shifted frequencies; and

indicating detection of the cable based on the filtering.

8. The method of claim 7, wherein the whole multiples include both odd and even multiples.

9. The method of claim 7, further comprising filtering using only a single comb filter.

10. The method of claim 7, wherein the first filter is a comb filter.

11. The method of claim 7, wherein the frequency shifting includes mixing in a sine wave having the second frequency.

12. The method of claim 7, further comprising filtering, using a high-pass filter, the amplified signals to remove a B-field of the earth from the amplified signals.