GB2097933A - Means for detecting a metallic object - Google Patents
Means for detecting a metallic object Download PDFInfo
- Publication number
- GB2097933A GB2097933A GB8211642A GB8211642A GB2097933A GB 2097933 A GB2097933 A GB 2097933A GB 8211642 A GB8211642 A GB 8211642A GB 8211642 A GB8211642 A GB 8211642A GB 2097933 A GB2097933 A GB 2097933A
- Authority
- GB
- United Kingdom
- Prior art keywords
- coil
- signal
- metallic object
- transmitter
- transmitter coil
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000005672 electromagnetic field Effects 0.000 claims abstract description 16
- 230000003321 amplification Effects 0.000 abstract description 5
- 238000003199 nucleic acid amplification method Methods 0.000 abstract description 5
- 238000001514 detection method Methods 0.000 abstract description 2
- 239000002800 charge carrier Substances 0.000 description 4
- 230000000977 initiatory effect Effects 0.000 description 4
- 239000003990 capacitor Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000005293 physical law Methods 0.000 description 2
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000010363 phase shift Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
- G01V3/10—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils
- G01V3/104—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils using several coupled or uncoupled coils
- G01V3/105—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils using several coupled or uncoupled coils forming directly coupled primary and secondary coils or loops
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Remote Sensing (AREA)
- Geology (AREA)
- Environmental & Geological Engineering (AREA)
- Electromagnetism (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Geophysics And Detection Of Objects (AREA)
- Control Of Vending Devices And Auxiliary Devices For Vending Devices (AREA)
- Control And Other Processes For Unpacking Of Materials (AREA)
Abstract
Means for detecting a metallic object comprises a coil system with a transmitter coil (5) for generating an electromagnetic field and a receiver coil (6) subject to an electromotive force induced by the resultant of the field generated by a metallic object and the field generated directly by the transmitter coil (5). An oscillator (1) is provided for generating a sinusoidal signal for the transmitter coil (5) and a variable attenuation or amplification circuit (2) is provided for controlling the amplitude of the signal, this circuit (2) being controlled by a signal (Im) emitted by the coil system and then rectified (8) and compared (9) with a reference voltage (Uref), the arrangement being such as to control the amplitude of said electromagnetic field. In an alternative embodiment (Figure 2) the signal emitted by the transmitter coil itself is rectified and compared with Uref. The detection means may be used in an electromagnetic proximity fuze. <IMAGE>
Description
SPECIFICATION
Means for detecting a metallic object
This invention relates to means for detecting a metallic object.
It has been proposed to provide means for detecting a metallic object comprising a coil system with a transmitter coil for generating an electromagnetic field and a receiver coil which is arranged in such a way that an electromotive force is induced in the coil when the coil is affected by the field generated by a metallic object and the field generated directly by the transmitter coil.
Such detection means may for instance be used in apparatus for detecting metallic objects in the earth in connection with geophysical prospecting but can also be used in electromagnetic proximity fuses for initiating the charge of a charge carrier, for instance a missile, projection, shell or the like, when this passes within a certain distance of a metallic object. In both of these applications, signal processing means are arranged to emit an active output signal in dependence upon the interference electromotive force induced in the receiver coil due to the metallic object.
The Specification of our British Patent No.
1,599,779 describes the use of means of the aforementioned type for detecting a metallic object in an electromagnetic proximity fuse for initiating the charge of a charge carrier when a metallic object is located at a well-defined distance from the charge carrier, preferably a small distance of 0.5 to 1.5 m. The advantage of generating an electromagnetic field for use in a proximity fuse is that such a fuse acts independently of the earth's magnetic field and also independently of whether or not the target is constructed of ferrous metal in contrast to previously known magnetic proximity fuses.
In the proximity fuse described in our aforesaid
Patent Specification, the receiver or sensor coil is located in front of and at a certain distance from the transmitter or generator coil, preferably in the nose section of the charge carrier, so that in addition to said interference electromotive force, an electromotive force is also induced in the receiver coil under the direct influence of the electromagnetic field generated by the transmitter coil. Signal processing means are arrange to separate the interference electromotive force from the directly induced electromotive force and to emit an active output signal to means for initiating the charge.
In geophysical prospecting as well as in proximity fuses it is desirable to keep the amplitude of the generated electromagnetic field constant, i.e. independent of frequency, temperature, and different disturbing factors which may affect the detector means. It is therefore an object of the invention to design the transmitter unit in such a way as to facilitate the maintenance of a constant amplitude for the electromagnetic field. This also has an advantage with respect to the manufacture of the detector means, as the tolerance requirements of for instance the transmitter coil can be reduced.
According to the present invention there is provided means for detecting a metallic object, wherein a coil system comprises a transmitter coil for generating an electromagnetic field, and a
receiver coil which is arranged in such a way that an electromotive force is induced in the coil when the coil is affected by the field generated by a metallic object and by the field generated directly by the transmitter coil, there being an oscillator for generating a sinusoidal signal for the transmitter coil of the coil system, and wherein means for controlling the amplitude of the sinusoidal signal include a feed-back circuit comprising means for rectifying a signal emitted by the coil system and means for comparing said rectified signal with a reference voltage and, in dependence upon said comparison, for generating an output signal to said means for controlling the amplitude of the sinusoidal signal, thereby to maintain the amplitude of the electromagnetic field generated by the transmitter coil substantially constant.
In one embodiment of the present detector means it is the signal emitted by the receiver coil due to the directly induced electromotive force in the coil which is fed back but in a second embodiment it is a signal emitted by the transmitter coil which is fed back.
In order to enable the invention to be more
readily understood, reference will now be made to the accompanying drawings which illustrate
diagrammatically and by way of example two
embodiments thereof, and in which Figure 1 and
Figure 2 each show a block circuit diagram of a
respective embodiment of means for detecting a
metallic object in accordance with the invention.
Referring now to Figure 1 , there is shown a
block circuit diagram illustrating the basic function of the detector means according to the
invention. The detector means may for instance be utilized in a metal detector for geophysical
prospecting or in a proximity fuse for initiating a charge near a metallic object (the target). In both of these applications, the detector means includes
a coil system which comprises a transmitter unit
in the form of a transmitter or generator coil for
generating an electromagnetic field which is distributed in space according to known physical
laws and a receiver unit in the form of a receiver or sensor coil which is located so that it is
affected by an electromagnetic field generated by the metallic object in which case an interference electromotive force is induced in the coil.The
receiver coil is also located in such a way that a
part of the electromagnetic field generated by the transmitter coil, directly affects the receiver coil and gives rise to a directly induced electromotive force in the coil. By means of signal processing
means, this interference electromotive force is
then separated from the directly induced electromotive force and an active output signal is provided in dependence upon the interference electromotive force only.
The signal processing of the interference electromotive force is described in the
Specification of our aforesaid British Patent No.
1,599,779 and is therefore not described in further detail here. The present invention is particularly concerned with the transmitter unit of the detector means which comprises a feed-back circuit which makes it possible to keep the amplitude of the electromagnetic field generated by the transmitter coil substantially constant.
The circuit illustrated in Figure 1 comprises an oscillator 1 for generating a sinusoidal signal X of a specific frequency and amplitude. This signal is fed via a variable attenuation or amplification circuit 2 to a tuned circuit comprising a current feed-back ampiifier 3, a capacitor C, a drive unit 4 and a transmitter or generator coil 5. The amplifier 3 and the drive unit 4 provide the necessary current ls for the transmitter coil 5. The transmitter coil then generates an electromagnetic field at the same frequency as the sinusoidal signal X. This field is distributed in space according to known physical laws and part of the field impinges on a receiver or sensor coil 6 located close to the transmitter coil 5 or spaced a certain distance from said coil, depending on the field of use.An electromotive force is then induced in the receiver coil 6 and gives rise to a receiver signal 1m which is fed to an integrator 7 and a rectifier 8 in which the signal is integrated and rectified, respectively. The signal is then compared with a reference voltage, Uref and if the sum of the rectified signal and the reference voltage is not equal to zero, then an error signal is obtained which is integrated by means of an integrator 9, giving rise to a signal Y which is used to control the variable attenuation or amplification circuit 2 for the sinusoidal signal X.
The circuit illustrated in Figure 2 is similar to that illustrated in Figure 1 but in this embodiment the transmitter coil voltage signal is is fed back and rectified by the rectifier 8. The feed-back circuit is connected to the terminal 11 between the capacitor C and the transmitter coil 5 in the tuned circuit. The receiver coil is not illustrated here.
Another difference between the first and second embodiments relates to the variable attenuation or amplification circuit 2. In the second embodiment this circuit is comprised in an oscillator feed-back circuit, but in a manner similar to the first embodiment, the integrated error signal Y is also used to control the variable attenuation or amplification circuit 9.
It is not always necessary to include an integrator 7 in the feed-back circuit and Figure 2 shows an example in which this integrator is not included in the circuit.
An advantage of the circuits just described is that the field of tolerance of the frequencies of the oscillator 1 and the tuned circuit is increased.
Moreover, possible variations of the loss resistances of the transmitter coil or temperature variations of the capacitor C of the tuned circuit have little or no influence on the amplitude of the field generated by the transmitter coil 5. By rectifying the receiver signal, the detector means are also insensitive to phase shifts in the coils and the drive unit 4. The amplitude of the electromagnetic field can easily be controlled by means of the direct reference voltage U,,,.
Claims (7)
1. Means for detecting a metallic object wherein a coil system comprises a transmitter coil for generating an electromagnetic field; and a receiver coil which is arranged in such a way that an electromotive force is induced in the coil when the coil is affected by the field generated by a metallic object and by the field generated directly by the transmitter coil, there being an oscillator for generating a sinusoidal signal for the transmitter coil of the coil system, and wherein means for controlling the amplitude of the sinusoidal signal include a feed-back circuit comprising means for rectifying a signal emitted by the coil system and means for comparing said rectified signal with a reference voltage and, in dependence upon said comparison, for generating an output signal to said means for controlling the amplitude of the sinusoidal signal, thereby to maintain the amplitude of the -electromagnetic field generated by the transmitter coil substantially constant.
2. Means as claimed in Claim 1, wherein an integrator and a rectifier are provided for integrating and rectifying, respectively, the signal emitted by the coil system.
3. Means as claimed in Claim 2, wherein a further integrator is provided for integrating the signal emitted by the comparison means.
4. Means as claimed in any one of Claim 1 to 3, wherein the arrangement is such that the signal emitted by the coil system is a signal emitted by the receiver coil due to the directly induced electromotive force in the coil.
5. Means as claimed in any one of Claims 1 to 3, wherein the arrangement is such that the signal emitted by the coil system is a signal emitted by the transmitter coil.
6. Means for detecting a metallic object substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.
7. Means for detecting a metallic object substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8102827A SE426269B (en) | 1981-05-06 | 1981-05-06 | DEVICE FOR THE DETECTION OF METAL FORMS |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2097933A true GB2097933A (en) | 1982-11-10 |
| GB2097933B GB2097933B (en) | 1985-05-15 |
Family
ID=20343740
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8211642A Expired GB2097933B (en) | 1981-05-06 | 1982-04-22 | Means for detecting a metallic object |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS57192887A (en) |
| BE (1) | BE893088A (en) |
| CA (1) | CA1198165A (en) |
| CH (1) | CH656231A5 (en) |
| DE (1) | DE3217033A1 (en) |
| FR (1) | FR2505508B1 (en) |
| GB (1) | GB2097933B (en) |
| IT (1) | IT1147941B (en) |
| NL (1) | NL8201811A (en) |
| NO (1) | NO821485L (en) |
| SE (1) | SE426269B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0622642A2 (en) * | 1993-04-26 | 1994-11-02 | Kabushiki Kaisha Honda Denshi Giken | An object detecting device |
| WO2009155668A1 (en) * | 2008-06-27 | 2009-12-30 | Minelab Electronics Pty Limited | Constant current metal detector with driven transmit coil |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59141001A (en) * | 1983-02-01 | 1984-08-13 | Mitsubishi Electric Corp | Detecting method for effective end position of metallic pipe |
| SE9203256L (en) * | 1992-11-04 | 1994-01-10 | Bofors Ab | Magnetic zone tube |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB835128A (en) * | 1955-09-17 | 1960-05-18 | Asea Ab | Apparatus for examining a substance utilising the effect of the substance on the q factor of a resonant circuit |
| DE2052989C3 (en) * | 1970-10-30 | 1973-11-08 | Guenther Dipl.-Ing. 2209 Sushoern Weber | Switching device triggered by one or more moving objects |
| GB1448877A (en) * | 1973-09-04 | 1976-09-08 | Weber G | Electronic switching device for sensing a body and for converting such sensing into an electrical signal |
| GB1561641A (en) * | 1976-08-05 | 1980-02-27 | Redland Automation Ltd | Presence detector apparatus |
| LU75628A1 (en) * | 1976-08-19 | 1978-04-13 | ||
| DE2722511A1 (en) * | 1977-05-18 | 1978-11-30 | Voll Walter | METAL DETECTOR |
| DE2722498C3 (en) * | 1977-05-18 | 1982-02-04 | Walter Ing.(Grad.) 8728 Hassfurt Voll | Device on a motor vehicle for displaying a minimum distance |
-
1981
- 1981-05-06 SE SE8102827A patent/SE426269B/en not_active IP Right Cessation
-
1982
- 1982-04-22 GB GB8211642A patent/GB2097933B/en not_active Expired
- 1982-05-03 NL NL8201811A patent/NL8201811A/en not_active Application Discontinuation
- 1982-05-04 JP JP57075053A patent/JPS57192887A/en active Pending
- 1982-05-05 FR FR8207818A patent/FR2505508B1/en not_active Expired
- 1982-05-05 IT IT48333/82A patent/IT1147941B/en active
- 1982-05-05 CA CA000402340A patent/CA1198165A/en not_active Expired
- 1982-05-05 CH CH2774/82A patent/CH656231A5/en not_active IP Right Cessation
- 1982-05-05 NO NO821485A patent/NO821485L/en unknown
- 1982-05-06 BE BE0/208015A patent/BE893088A/en not_active IP Right Cessation
- 1982-05-06 DE DE19823217033 patent/DE3217033A1/en active Granted
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0622642A2 (en) * | 1993-04-26 | 1994-11-02 | Kabushiki Kaisha Honda Denshi Giken | An object detecting device |
| EP0622642A3 (en) * | 1993-04-26 | 1995-02-22 | Honda Denshi Giken Kk | An object detecting device. |
| WO2009155668A1 (en) * | 2008-06-27 | 2009-12-30 | Minelab Electronics Pty Limited | Constant current metal detector with driven transmit coil |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3217033A1 (en) | 1982-11-25 |
| GB2097933B (en) | 1985-05-15 |
| FR2505508A1 (en) | 1982-11-12 |
| CH656231A5 (en) | 1986-06-13 |
| IT8248333A0 (en) | 1982-05-05 |
| SE8102827L (en) | 1982-11-07 |
| SE426269B (en) | 1982-12-20 |
| NL8201811A (en) | 1982-12-01 |
| DE3217033C2 (en) | 1991-01-03 |
| FR2505508B1 (en) | 1985-11-29 |
| NO821485L (en) | 1982-11-08 |
| BE893088A (en) | 1982-08-30 |
| IT1147941B (en) | 1986-11-26 |
| CA1198165A (en) | 1985-12-17 |
| JPS57192887A (en) | 1982-11-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19930422 |