Locator device for continuously locating a dipole magnetic field transmitter and its method of operation

• US 5,337,002 A
• Filed: 10/09/1992
• Issued: 08/09/1994
• Est. Priority Date: 03/01/1991
• Status: Expired due to Term

• Current Assignee: Digital Control Incorporated
• Original Assignee: Digital Control Incorporated
• Inventors: Mercer, John E.
• Primary Examiner(s): Strecker, Gerard R.
• Assistant Examiner(s): EDMONDS, WARREN
• Application Number:
  US07/958,941
• Time in Patent Office: 669 Days
• Field of Search: 324/207.11-207.26, 324/226, 324/227, 324/202, 324/225, 324/239, 324/66, 324/67, 324/326, 324/329, 455/40
• US Class Current: 324/326
• CPC Class Codes: E21B 47/0228 using electromagnetic energy or detectors therefor
• CPC Class Codes: E21B 47/0232 at least one of the energy sources or one of the detectors being located on or above the ground surface
• CPC Class Codes: E21B 47/024 of devices in the borehole determining slope or direction of the borehole E21B47/022
• CPC Class Codes: G01C 9/06 Electric or photoelectric indication or reading means
• CPC Class Codes: G01C 9/20 the indication being based on the inclination of the surface of a liquid relative to its container
• CPC Class Codes: G01V 3/165 operating with magnetic or electric fields produced or modified by the object or by the detecting device with electromagnetic waves G01V3/17

Abstract

A locator/monitor for locating a boring tool and monitoring the progress of the tool for control purposes. The locator/monitor is used in expedited locating methodology and straightforward calibration techniques of the present invention. A durable and cost effective pitch sensor is also provided by the present invention. In addition, the present invention provides a slotted transmitter housing formed of an electrically conductive material, where the magnetic field generated by the transmitter is capable of penetrating to the surface.

Claims

1. A locator for continuously locating a magnetic field transmitter disposed beneath a surface, comprising:

first and second range sensors capable of measuring the field strength of the signal transmitted by the transmitter and oriented orthogonally to each other,

processor means for generating a vector sum of the field strengths measured by the first and second sensors,

display means for indicating the distance between the locator and the transmitter, and

calibration means including

means for measuring the distance between the locator and a reference surface,

means for storing a measurement of the field strengths sensed by the range sensors at least two distances from the reference surface and for storing the distances from the reference surface at which the field strengths were measured,

means for calculating the proportionality constant of field strength of the signal generated by the transmitter from the stored measurements of field strength and distance, and

wherein the processor means generates a monotonic function indicative of the distance between the locator and the transmitter on the basis of the calculated proportionality constant.

2. A locator according to claim 1, wherein the means for measuring the distance between the locator and the reference surface is an ultrasonic ranging device.

3. A locator according to claim 1, having a forward/rearward axis, wherein the range sensors each comprise an antenna which is located in a vertical plane and each of which is oriented at an angle of 45°

to the forward/rearward axis.

4. A locator according to claim 3 further comprising means for displaying an indication of which of the first and second range sensors is measuring the greater field strength.

5. A method for locating a magnetic field transmitter which is beneath an original point of observation and which is displaced forwardly or rearwardly from the original point of observation, comprising the steps of:

measuring the field strength at the original point of observation with a first and a second field strength measuring means, each measuring means comprising an antenna located substantially within the plane of the transmitter and within which lies the axis along which the transmitter is forwardly or rearwardly displaced, with the first antenna oriented at an angle of 45°

above the horizontal in the forward direction and the second antenna oriented at an angle of 45°

above the horizontal in the rearward direction, with the two antennas at right angles to each other,

moving the detection means along a detection path, which is within the vertical plane in a direction from the original point of observation which causes the field strength measured by the field strength measuring means to increase,

comparing the field strengths measured by each of the field strength measuring means while moving the detection means along the detection path,

identifying a first point along the detection path at which the flux lines emitted by the transmitter are substantially vertical, as indicated by the measurement of equal field strengths by the field strength measuring means,

identifying a second point along the detection path at which the flux lines emitted by the transmitter are substantially vertical, as indicated by the measurement of equal field strengths by the field strength measuring means,

identifying a point between the first and second points at which point the flux lines emitted by the transmitter are substantially horizontal, as indicated by the measurement of equal field strengths by the field strength measuring means, this point being approximately directly above the transmitter.

6. A locator for continuously locating a dipole magnetic field transmitter disposed beneath a generally horizontal surface, comprising:

a main housing defining a forward/rearward axis which extends in a horizontal direction during normal operation of the locator device;

first and second antennae capable of measuring the field strength of the signal transmitted by the transmitter and oriented orthogonally to each other, each of said antennae being carried by said housing in a vertical plane and at an angle of 45°

to said forward/rearward axis during normal operation of the locator device;

processor means contained within said housing for generating a vector sum of the field strengths measured by the first and second antennae; and

display means contained within the housing for indicating the distance between the locator and the transmitter.

7. A locator according to claim 6 further comprising means for displaying an indication of which of the first and second antennae is measuring the greater field strength.

8. A method for determining the distance between a point of observation and a generally horizontally extending dipole magnetic field transmitter which is beneath the point of observation and disposed within a given vertical plane, comprising the steps of:

measuring the field strength of the magnetic field at the point of observation with two antennae disposed within said given vertical plane and oriented orthogonally to each other at angles of 45°

with the horizontal,

calculating the distance between the point of observation and the transmitter as a function of the vector sum of the field strengths measured by the sensors, and

displaying the calculated distance.

9. A locator for continuously locating a magnetic field transmitter which is disposed beneath a surface and which transmits a magnetic field signal, comprising:

first, sensor means for measuring the field strength of the signal transmitted by the transmitter,

second, processor means connected with said first means for electronically processing said measured field strength,

third, display means connected to said second means and responsive to said processed field strength for indicating the distance between the locator and the transmitter, and

calibration means including

means for measuring the distance between the locator and a reference surface when the locator is at two different distances from the reference surface,

means for storing a measurement of the field strengths measured by the sensor means when the locator is at said two distances from the reference surface and for storing the distances from the reference surface at which the field strengths were measured,

means for calculating the proportionality constant of field strength of the signal generated by the transmitter from the stored measurements of field strength and distance, and

wherein the processor means generates the monotonic function indicative of the distance between the locator and the transmitter on the basis of the calculated proportionality constant.

10. A method of continuously locating a dipole magnetic field transmitter disposed beneath a generally horizontal surface, comprising:

measuring the field strength of the signal transmitted by the transmitter using a locator including a housing which defines a forward/rearward axis which is held in a horizontal direction and first and second antennae oriented orthogonally to each other, each of said antennae being carried by said housing in a vertical plane and at an angle of 45°

to said forward/rearward axis,

generating a vector sum of the field strengths measured by the first and second antennae, and

indicating the distance between the locator and the transmitter.

11. A method of locating a magnetic field transmitter located beneath the ground from a point above the ground, comprising:

(a) positioning the magnetic field transmitter within the ground;

(b) causing the transmitter to produce a magnetic field which is independent of roll by the boring tool about its axis;

(c) from above ground, using a locator measuring the field strength of said magnetic field at a number of different points and from said measurements determining the location of said transmitter; and

(d) calibrating said locator by

(i) measuring the distance between the locator and a reference surface,

(ii) storing a measurement of the field strengths sensed by the locator at at least two distances from the reference surface and for storing the distance from the reference surface at which the field strengths were measured,

(iii) calculating the proportionality constant of field strength of the signal generated by the transmitter from the stored measurements of field strength and distance, whereby said locator is able to generate a monotonic function indicative of the distance between the locator and the transmitter on the basis of the calculated proportionality constant.

12. A method of locating an elongated boring tool located beneath the ground from a point above ground, comprising:

(a) positioning a dipole magnetic field transmitter within said boring tool such that the transmitter extends substantially coaxial with the axis of the tool;

(b) causing the transmitter to produce a dipole magnetic field which is independent of roll by the boring tool about its axis; and

(c) from above ground, using a locator having a pair of orthogonally positioned antennae, measuring the vector sum of the field strength of said magnetic field at a number of different points and from said measurements determining the location of said boring tool.

13. A method according to claim 12 wherein said locating device includes:

first and second range sensors capable of measuring the field strength of the signal transmitted by the transmitter and oriented orthogonally to each other,

processor means for generation a vector sum of the field strengths measured by the first and second sensors, and

display means for indicating the distance between the locator and the transmitter.

14. A method according to claim 12 including calibrating said locator by:

(a) measuring the distance between the locator and a reference surface,

(b) storing a measurement of the field strengths sensed by the range sensors at least two distances from the reference surface and for storing the distance from the reference surface at which the field strengths were measured,

(c) calculating the proportionality constant of field strength of the signal generated by the transmitter from the stored measurements of field strength and distance, and whereby the locator is able to generate a monotonic function indicative of the distance between the locator and the transmitter on the basis of the calculated proportionality constant.

15. An arrangement for locating an elongated boring tool located beneath the ground from a point above ground, comprising:

(a) a dipole magnetic field transmitter positioned within said boring tool such that the transmitter extends substantially coaxial with the axis of the tool;

(b) means for causing the transmitter to produce a magnetic field which is independent of roll by the boring tool about its axis; and

(c) a locator device having two orthogonally positioned antennae positionable above ground for measuring the vector sum of the field strength of said magnetic field at a number of different points and from said measurements determining the location of said boring tool.

16. An arrangement according to claim 15 wherein said locating device includes:

first and second range sensors capable of measuring the field strength of the signal transmitted by the transmitter and oriented orthogonally to each other,

processor means for generating a vector sum of the field strengths measured by the first and second sensors, and

display means for indicating the distance between the locator and the transmitter.