Electronic marker locator systems and methods

• US 9,194,978 B2
• Filed: 05/13/2013
• Issued: 11/24/2015
• Est. Priority Date: 05/13/2013
• Status: Active Grant

• Current Assignee: Radiodetection Limited
• Original Assignee: Radiodetection Limited
• Inventors: Pearson, Richard David, Thompson, Jeffrey Richard, Poyner, Julian
• Primary Examiner(s): Koval, Melissa
• Assistant Examiner(s): Farrow, Felicia
• Application Number:
  US13/892,841
• Publication Number:
  US 20140333309A1
• Time in Patent Office: 925 Days
• Field of Search: 324326-329, 324331-332, 324/343, 702/166, 343/728
• US Class Current: 1/1
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• CPC Class Codes: G01V 3/00 Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12
• CPC Class Codes: G01V 3/081 the magnetic field is produced by the objects or geological structures characterised by the method of magnetic field measurement G01R33/00
• CPC Class Codes: G01V 3/083 Controlled source electromagnetic [CSEM] surveying
• CPC Class Codes: G01V 3/104 using several coupled or uncoupled coils G01V3/101 takes precedence
• CPC Class Codes: G01V 3/15 specially adapted for use during transport, e.g. by a person, vehicle or boat

Abstract

A locator for determining the depth of a buried electromagnetic marker includes a transmission antenna and two reception antennas. The locator has a major axis and is configured. The transmission antenna is configured to generate an oscillatory magnetic field parallel to the major axis. The first reception antenna of the two reception antennas is configured to couple with an oscillatory magnetic field parallel to the major axis emitted by the electromagnetic marker and to generate a first detected signal. The second reception antenna is displaced along the major axis from the first antenna and configured to couple with an oscillatory magnetic field parallel to the major axis emitted by the electromagnetic marker and to generate a second detected signal. The locator includes analogue to digital converters and a processor which is configured to calculate the depth of the electromagnetic marker.

Claims

1. A locator for determining a depth of a buried electromagnetic marker, the locator having a major axis and being configured to be used with the major axis substantially perpendicular to a ground surface, the locator comprising:

a transmission antenna configured to generate an oscillatory magnetic field parallel to the major axis,

a first reception antenna configured to couple with an oscillatory magnetic field parallel to the major axis emitted by the electromagnetic marker and to generate a first detected signal,

a second reception antenna displaced along the major axis from the first antenna and configured to couple with an oscillatory magnetic field parallel to the major axis emitted by the electromagnetic marker and to generate a second detected signal,

a first analogue to digital converter configured to generate a first digitised signal from the first detected signal,

a second analogue to digital converter configured to generate a second digitised signal from the second detected signal, and

a processor configured to calculate the depth of the electromagnetic marker from the first digitised signal and the second digitised signal,

wherein the transmission antenna generates the oscillatory magnetic field having the target frequency for a first time interval and the first reception antenna is prevented from generating the first detected signal and the second reception antenna is prevented from generating the second detected signal for at least the first time interval.

2. A locator according to claim 1, wherein

the transmission antenna comprises a winding around a transmission antenna axis, the transmission antenna axis arranged to be substantially parallel to the major axis when the locator is in use,

the first reception antenna comprises a winding around a first reception antenna axis, the first reception antenna axis being arranged to be substantially parallel to the major axis, and

the second reception antenna comprises a winding around a second reception antenna axis, the second reception antenna axis being arranged to be substantially parallel to the major axis.

3. A locator according to claim 2 wherein the transmission antenna axis is arranged to be within 5 degrees of parallel to the major axis when the locator is in use and/or the first reception antenna axis is arranged to be within 5 degree of parallel to the major axis, and/or the second reception antenna axis is arranged to be within 5 degrees of parallel to the major axis.

4. A locator according to claim 1, further comprising a controller configured to cause the transmission antenna to generate an oscillatory magnetic field having a target frequency.

5. A locator according to claim 4, wherein the controller is configured to select the target frequency from a plurality of possible target frequencies in accordance with a target marker type.

6. A locator according to claim 4 wherein the controller is configured cause the transmission antenna to generate the oscillatory magnetic field having the target frequency for a first time interval and to prevent the first reception antenna from generating the first detected signal and the second reception antenna from generating the second detected signal during a settling time after at least the first time interval.

7. A locator according to claim 6, further comprising a third reception antenna configured to couple with a magnetic field generated by a buried current carrying conductor, wherein the controller is configured to enable signals generated by the third reception antenna to be processed for a time interval excluding the first time interval.

8. A locator according to claim 1 wherein the processor is configured to calculate the d depth of the electronic marker using the following equation:

9. A locator according to claim 1, further comprising a display configured to display an indication of a calculated depth, wherein the locator is configured such that the calculated depth is displayed on the display only when one or more predetermined criteria are satisfied.

10. A locator according to claim 9 wherein the processor is configured to calculate the standard deviation of the depth calculation referred to in a 10 Hz bandwidth and a predetermined criterion is that the standard deviation of the depth calculation is less than 20%.

11. A locator according to claim 10, wherein the processor is operable to calculate the first derivative with respect to time of the field detected at the antennas and a predetermined criterion is that the first derivative of the field detected at the antennas is less than 20% of the signal/s.

12. A locator according to claim 10, wherein the processor is further configured to calculate the first derivative with respect to time of the calculated depth and a predetermined criterion is that the first derivative of the calculated depth is less than 20% of the calculated depth/s.

13. A method of determining a depth of buried electromagnetic marker, the method comprising

transmitting, from a transmission antenna of a locator, an oscillatory magnetic field to the electronic marker;

receiving, at a first reception antenna of the locator, an oscillatory magnetic field emitted by the electronic marker and generating a first detected signal indicative of the strength of the oscillatory magnetic field emitted by the electronic marker at the first reception antenna;

receiving, at a second reception antenna of the locator separated from the first reception antenna along a major axis of the locator, an oscillatory magnetic field emitted by the electronic marker and generating a second detected signal indicative of the strength of the oscillatory magnetic field emitted by the electronic marker at the second reception antenna;

preventing the first reception antenna from generating the first detected signal and the second reception antenna from generating the second detected signal while the oscillatory magnetic field is transmitted from the transmission antenna to the electronic marker;

digitising the first detected signal to generate a first digitised signal;

digitising the second detected signal to generate a second digitised signal; and

calculating the depth of the electromagnetic marker from the first digitised signal and the second digitised signal.

14. A method according to claim 13, further comprising preventing the first reception antenna from generating the first detected signal and the second reception antenna from generating the second detected signal during a settling time after the oscillatory magnetic field is transmitted from the transmission antenna to the electronic marker.

15. A method according to claim 13 wherein calculating the depth of the electronic marker comprises calculating the depth d as:

16. A method according to claim 13, further comprising determining if one or more predetermined criteria are satisfied and if one or more predetermined criteria are satisfied displaying an indication of a calculated depth.

17. A method according to claim 16, further comprising calculating the standard deviation of the depth calculation referred to in a 10 Hz bandwidth and wherein a predetermined criterion is that the standard deviation of the depth calculation is less than 20%.

18. A method according to claim 16, further comprising calculating the first derivative with respect to time of the field detected at the reception antennas and a predetermined criterion is that the first derivative of the field detected at the reception antennas is less than 20% of the signal/s.

19. A method according to claim 16, further comprising calculating the first derivative with respect to time of the calculated depth and a predetermined criterion is that the first derivative of the calculated depth is less than 20% of the calculated depth/s.

20. A tangible non-transitory carrier medium carrying computer readable instructions for execution by a processor in a locator, the locator having a major axis and being configured to be used with the major axis substantially perpendicular to a ground surface, the locator comprising a transmission antenna configured to generate an oscillatory magnetic field parallel to the major axis, a first reception antenna configured to couple with a oscillatory magnetic field parallel to the major axis emitted by the electromagnetic marker and to generate a first detected signal, a second reception antenna displaced along the major axis from the first antenna and configured to couple with a oscillatory magnetic field parallel to the major axis emitted by the electromagnetic marker and to generate a second detected signal, a first analogue to digital converter configured to generate a first digitised signal from the first detected signal, and a second analogue to digital converter configured to generate a second digitised signal from the second detected signal, wherein the instructions comprise:

instructions for preventing the first reception antenna from generating the first detected signal and the second reception antenna from generating the second detected signal while the oscillatory magnetic field is transmitted from the transmission antenna;

instructions for controlling the processor to calculate a ratio of the magnitudes of the first detected signal and the second detected signal; and

instructions for calculating the depth of the electronic marker from the ratio.