GB2270981A

GB2270981A - Locating magnetically tagged concealed equipment.

Info

Publication number: GB2270981A
Application number: GB9217238A
Authority: GB
Inventors: Graham Brindley; Eric Anthony Forrester; David Robert Jackson
Original assignee: Minister of Agriculture Fisheries and Food UK
Current assignee: Minister of Agriculture Fisheries and Food UK
Priority date: 1992-08-12
Filing date: 1992-08-12
Publication date: 1994-03-30
Also published as: GB9217238D0

Abstract

Concealed, eg buried, equipment is located by incorporating a magnet 11 with the equipment (10) prior to its being positioned in a concealed position 13, and of locating the position of the equipment (10) by means of apparatus 20 which detects the magnetic field associated with the magnet 11 and converts the magnetic field into an electrical signal. The magnet is preferably horizontal when the equipment is concealed. The dector preferably comprises one or more linear Hall effect sensors 15 and an associated power supply circuitry and display 20. The sensitivity of the detector can preferably be altered to assist location of the magnet. <IMAGE>

Description

POSITION DETECTORS The present invention is concerned with methods and apparatus for marking and detecting a position or equipment which is to be positioned in a concealed environment and later recovered.

There are many instances where concealed equipment has to be accessed, for example for maintainance or for the collection of data.

One example is in the agricultural industry, where porous pots are buried in soil, left for a substantial period, and then recovered for examination to determine the degree of nitrate contamination in the soil. It is frequently desirable that the pots be recovered with minimal disturbance of the surrounding soil and this requirement, the time between burial and recovery, and the number of pots involved, makes schemes involving mapping or marking (for example, by flags) impractical. The use of electronic circuitry, such as a transmitter, with each pot, is inordinately expensive , especially in view of the harsh conditions to which the pots might be subjected.

There is a therefore a requirement for a method and for apparatus for marking equipment which is to be stored in a concealed position and later recovered.

According to one aspect of the present invention a method of marking a piece of equipment, positioning the equipment in a concealed position, and accurately locating the concealed equipment, involves the steps of incorporating a magnet with the equipment prior to its being positioned in the concealed position, and of locating the position of the equipment by means of apparatus which detects a magnetic field associated with the magnet and converts the magnetic field into an electrical current.

The magnet is advantageously positioned in the equipment in such a manner that it will lie horizontally when the equipment is in the concealed position.

The applicant has discovered that conventional metal detectors do not give results of sufficient accuracy and reliability when used for the marking of buried porous pots used in the investigation of soil nitrate levels.

According to another aspect of the present invention apparatus for detecting the location of a concealed magnet includes detection means for detecting a magnetic field, means for converting an output of the detection means into an electrical signal, and means for processing the electrical signal to enable the position of the magnet to be identified.

The apparatus might consist of a case containing a power supply, for example one or more electric storage batteries, a magnetic field detector which might be, for example, one or more linear Hall effect sensors, and appropriate circuitry. The circuitry will preferrably contain means for altering the sensitivity of the device to aid in accurate location of a magnet.

Some aspects of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which; Figure 1 is an elevation of a piece of equipment with a magnet attached thereto, Figure 2 is a view of a magnet detector being used to locate a magnet, Figure 3 is a view of a magnet detector control and display panel, Figure 4 is a magnet detector circuit diagram, and Figure 5 shows a magnet detector component layout.

A piece of equipment 10, intended for use in a concealed position, (Figure 1) has a magnet 11 attached thereto, the alignment of the magnet 11 being such that when the equipment 10 is in the concealed position the magnet 11 will lie substantially parallel to a surface 12 (Figure 2) adjacent to which locating means will operate.

In use, the equipment is placed in a concealed position 13 (Figure 2, only magnet 11 being shown), which might be, for example, buried in soil 14 beneath the surface 12.

Apparatus 50 for locating the magnet 11, and hence the equipment 10, has a detector unit 15 (Figure 2), containing two linear Hall effect sensors 16 (Figure 4), mounted on a first end 18 of an arm at the second end 19 of which is a control box 20 on which is a control and display panel 21 (Figure 3).

The control box 20 contains a power supply consisting of two nine amp batteries 22 connected by a ganged switch 23 to a circuit, shown generally in Figure 4, which controls the circuit voltage to five volts and which includes a (VCO) gain stage 24 and a VCO pitch offset 25. The ganged switch 23 is controlled by an on/off/volume control 26 on the control and display panel 21, the VCO gain stage 24 is contolled by the control 26 and by a gain control 27 and the VCO pitch offset 25 is controlled by a VCO pitch control 28.

The circuit of Figure 4 also contains, inter alia, an auto zero sub-circuit 29 operated by an auto zero button 30 and a close range sub-circuit 31 controlled by a close range switch 32.

An intensity meter 33 on the control and display panel 21 is calibrated to indicate North and South.

In use, when it is required to recover concealed equipment 10 the apparatus 50 is switched on and a suitable volume set by operation of the on/off/volume control 26, and a suitable time, for example thirty seconds, is allowed for the apparatus to stabilize. The auto-zero button 30 is then pressed and the VCO pitch and gain are set by operation of the controls 28, 27. If required, the auto zero button is pressed again, and then the detector unit 15 is moved over the surface 12 until a reading is obtained on the meter 33. The meter 32 will give a reading in either the North or the South sector, depending on whether the unit 15 is closest to a North or a South magnet pole.By suitable searching movements of the unit 15 the rough position of a magnet 11 can be identified, and then accurate location of the position under the surface 12 of the magnet 11 can be completed after operation of the close range switch 32. The equipment 10 on which the magnet is positioned can then be recovered.

It has been found that, using the method and apparatus of the invention, equipment buried in earth at a depth of about one metre can be located to an accuracy of six centimetres.

It will be realised, of course, that whilst the method and apparatus described above have related mainly to agricultural items buried in earth they can used for many other purposes- for example in the location of service conduits in buildings and under road surfaces.

Details of the circuit shown in Figure 4 will be readily understood by those skilled in the electronic arts, and will not therefore by described in detail herein.

It will also be realised that a position can be identified by positioning a magnet and using the apparatus and method of the invention to locate the magnet.

Claims

What is claimed is; 1. A method of marking a piece of equipment, positioning the equipment in a concealed position, and accurately locating the concealed equipment, including the steps of incorporating a magnet with the equipment prior to its being positioned in the concealed position, and of locating the position of the equipment by means of apparatus which detects a magnetic field associated with the magnet and converts the magnetic field into an electrical current.
2. A method as claimed in Claim 1 wherein the magnet is positioned in the equipment in such a manner that it will lie horizontally when the equipment is in the concealed position.
3. Apparatus for detecting the location of a concealed magnet including detection means for detecting a magnetic field, means for converting an output of the detection means into an electrical signal, and means for processing the electrical signal to enable the position of the magnet to be identified.
4. Apparatus as claimed in Claim 3 including a case containing a power supply.
5. Apparatus as claimed in Claim 4 wherein the power supply includes one or more electric storage batteries.
6. Apparatus as claimed in any one of Claims 3 to 5 wherein the magnetic field detector includes one or more linear Hall effect sensors, and appropriate circuitry.
7. Apparatus as claimed in Claim 6 wherein the circuitry contain means for altering the sensitivity of the device to aid in accurate location of a magnet.
8. A method of marking a piece of equipment, positioning the equipment in a concealed position, and the locating the equipment substantially as herein described with reference to Figutes 1 to 5 of the accompanying drawings.
9. Apparatus for locating a magnet substantially as herein described with reference to Figures 2 to 5 of the accompanying drawings.