FR2779529A1 - Magnetic field strength determination device for a variable magnetic field generator, used to determine whether generator is working effectively for use with mine clearance devices - Google Patents

Abstract

The device comprises a magnetic field sensor (6), followed by a processing circuit (7) for treatment of the signal generated by the sensor and a comparison device (8) connected to a command generator (19) which controls a visualization means (10). An Independent claim is included or a process using the above device, in which a control value (9) is preset to a value representing a minimum acceptable magnetic field which when measured indicates that the device is operating correctly. The control value is compared with the measured value at a chosen distance from the magnetic field generator and the display (10) is used to indicate the result of the comparison.

Description

DEVICE FOR EVALUATING THE LEVEL OF THE INTENSITY OF A FIELD

  VARIABLE MAGNETICS AND METHOD FOR MONITORING THE EFFICIENCY OF A MAGNETIC FIELD GENERATOR USING SUCH A DEVICE The technical sector of the present invention is that of devices allowing the measurement or evaluation of the periodic magnetic field produced by materials. of any kind. The device according to the invention is more particularly intended for the evaluation of the periodic magnetic field generated by a terrestrial demining system, evaluation necessary for the operations of checking the effectiveness of the deminer, in particular before a demining operation. The existing measurement systems are

  are in the form of measuring devices or components.

  Measuring devices are most of the time complex laboratory means requiring in their implementation qualified personnel. These means are not suitable20 for operational use, that is to say in the field, due to their lack of robustness and their

  low operating temperature range. In addition, their implementation is long and complex. They cannot therefore allow rapid control of the effectiveness of a deminer25 just before an operation by the personnel in charge of demining.

  With the components, the measured value of the magnetic field is not immediately accessible and must be

  add management and processing electronics and provide adequate packaging to make them operational.

  The known systems are therefore unsuitable for the effectiveness control operations of a deminer in the field of operations.35 The invention therefore aims to provide a simple device, inexpensive and compact, usable in the field in operational environment , and allowing to simply provide an indication of the level of the intensity of the ambient magnetic field by comparison with a reference value. The subject of the invention is therefore a device for evaluating the level of the intensity of a variable magnetic field, a device characterized in that it comprises a magnetic field sensor, followed by a circuit for processing the signal delivered by the sensor, and a comparator in relation to a reference means for controlling a display means. According to a characteristic of the invention, the device

  may include a control means causing its power off and / or automatic power.

  More particularly, the control means may comprise an automatic tensioning means actuated by the magnetic field.15 Advantageously, the tensioning means may

  be constituted by a switch, part of which will be mobile under the action of the magnetic field.

  According to another characteristic of the invention, the control means may include a delay means connected

by means of visualization.

  The processing circuit may include a regulator, a bandpass filter and an amplifier.

  The display means may include a circuit

  electric supply of two electro-diodes

luminescent.

  According to a particular embodiment, the setpoint means may deliver a fixed voltage signal representing a level of magnetic field. According to another embodiment, the setpoint means

  may be adjustable and include a potentiometer connected to a setpoint calculation circuit comprising a display.

  The invention also relates to a method for monitoring the efficiency of a periodic magnetic field generator

  (like a minesweeper) at a given distance.

  This process is characterized in that: - a set value is fixed beforehand, a value giving a minimum level of magnetic field to be measured which is representative of the efficiency of the generator, - it is detected at a given point at a distance from the generator and using a sensor, the magnetic field generated by the generator and the detected signal is processed, - the setpoint is compared with the detected signal, - the display shows the

  result of the signal / setpoint comparison.

  A first advantage of the invention lies in the possibility of determining the extent of the radiation of a magnetic field around its source.10 Another advantage lies in the fact that the device is portable and autonomous and that it does not has no power on or off system. Yet another advantage is that the device is activated or deactivated without intervention

operator manual.

  Other characteristics, details and advantages of the invention will appear more clearly on reading the

  additional description which follows of an embodiment given by way of example in relation to drawings on which:

  - Figure 1 shows, in the form of a functional diagram, the structure of the device, - Figure 2 illustrates the more specific structure of certain components of the device, - Figure 3 is a diagram showing an implementation mode in the field of device according to the invention,

  - Figure 4 partially illustrates in the form of a functional diagram a variant of the invention.

  The device according to the invention is in the form of a portable housing 1, for example made of plastic, equipped with a window 2 in which two light-emitting diodes 3 and 4 of different colors appear and with a hatch 5 of access to the device supply housing. In FIG. 2, the functional diagram of the device is shown schematically. The particular structure of each of the elements is known to those skilled in the art in its particular function and need not be described in more detail. The device comprises a single-axis magnetic field sensor 6 constituted by a commercially available component (for example a so-called "fluxgate" sensor). The sensor is positioned in the housing 1 so that its sensitivity axis Z is substantially perpendicular to the longitudinal generatrices of the housing body 1 (i.e. in the plane of the display 2) .10 The role of this sensor is to '' measure the level of an ambient variable magnetic field emitted by a source (not shown) such as a minesweeper. The measurement will be carried out in the direction Z which will be operationally the

  vertical direction, the case being positioned flat15 horizontally.

  The sensor 6 sends its signal to a processing circuit 7 which includes a bandpass filter 16 and an amplifier 17. The circuit 7 supplies the sensor 6 with voltage from a regulator 15.20 The processing circuit 7 is designed so as to deliver a continuous signal which is an image of the peak-to-peak voltage of the variable magnetic field received by the sensor (field level). Any continuous component of the magnetic field is eliminated. We are thus guaranteed to measure only the variations of the field due to the source and we are freed from the fluctuations of the terrestrial magnetic field from one place to another. The amplified signal is directed to a comparator 8 which also receives a signal of constant and adjustable intensity

  delivered by a setpoint means 9, such as a potentiometer.

  According to a preferred embodiment of the invention, the setpoint means has a fixed value set at the factory and corresponding to the level of magnetic field to be detected. The comparator 8 controls a display means 10 as a function of the result of the comparison between the setpoint supplied by the means 9 and the measurement supplied by the

treatment 7.

  The display means 10 comprises an electrical circuit for lighting the two diodes 3 and 4. The diode 3, of red color for example, may light up when the field level measured by the sensor 6 is less than the value delivered by the setpoint 9. The diode 4, of green color for example, may light up when the measured field level

  is greater than the set value.

  The entire device as surrounded by dotted lines 23 in FIG. 2 is of course supplied by a battery 14 (of 9 volts for example) connected individually to the different components of the device or else in a coupled manner, by connecting the different means between them. Advantageously, the electrical circuit of the display means 10 will include an oscillator making it possible to make the light-emitting diodes 3 and 4 flash. This arrangement makes it possible to extend the life of the battery 14. The device is advantageously supplemented by a control means 11 for power-up, means actuated by the magnetic field and comprising for example a switch 12 having a flexible blade sensitive to the ambient magnetic field. This component is commercially available and comes in the form of a glass bulb containing a normally open contact, the moving part of which closes under the influence of a sufficiently strong magnetic field.

  (contact usually known as "reed switch").

  The device is automatically powered up

  without pressing any switch.

  The power off is obtained automatically using a timing means 13 connected to the display means 10. This means 13 detects the lighting of the diode 3 and it includes a clock and countdown means activated during of the diode 3 lighting and which control the power off of the device if the diode 3 remains lit

  for a predetermined time. The operation of the device is as follows.

  To quantify the range of a periodic magnetic field generator, we first detect the field of the

  generator by approaching him. The tensioning means 12 is activated and ensures the supply of all 5 of the electronic components of the device.

  LED 4 (green) lights up.

  When moving away from the magnetic field source the device constantly compares the level of the magnetic field

  measured and set it until LED 3 (red) 10 lights up and LED 4 (green) goes out.

  In tipping places, the intensity of the field measured by the device is equal to the setpoint. We thus define

  near and near a perimeter within which the electromagnetic radiation is above a certain threshold.

  The device is switched off automatically after a certain time predetermined by

  construction (3 minutes for example) using timer 13 when the measured magnetic field is less than the setpoint.

  Concretely, the device according to the invention is implemented in the field as follows.

  FIG. 3 shows a deminer 18 generating a magnetic field. The correct operation of the minesweeper is ensured if the level of the vertical magnetic field measured is greater than or equal to a given setpoint along a curve

  S positioned at a certain distance from the minesweeper and defining the scope of the minesweeper. We will determine several measurement points A, B, C, D ...

  placed at a distance from the minesweeper 18, points at which the level of the vertical magnetic field measured must be greater than or equal to the set value. The device according to the invention is successively placed horizontally at the various measurement points. If LED 4 (green) lights up at each measurement point, the deminer works correctly and can start its demining operation.

  If LED 3 (red) lights up at one or more measuring points, the minesweeper has a fault.

  It can thus be seen that the device according to the invention is extremely simple to use and that it quickly makes it possible to conclude that an electromagnetic minesweeper is working properly. By way of a variant and with reference to FIG. 4, it is possible to replace the fixed reference means 9 by a variable reference means 19, adjustable in the field. This means 10 will include a potentiometer 20 accessible to the user and coupled to a setpoint calculation circuit 21

  comprising a display 22 (for example with light-emitting diodes or liquid crystals) making it possible to display the reference value corresponding to the position 15 chosen for the potentiometer 20. The calculation circuit will of course be calibrated at the factory.

  Such a variant will make it possible to measure the level of magnetic field at a given point. It will suffice at this point to

  vary the setpoint to the value ensuring the passage from switching on of diode 3 to that of diode 4 or vice versa.

  The display 22 will then give the value of the level of ambient magnetic field.

Claims (5)

  1- Device for evaluating the level of the intensity of a variable magnetic field, characterized in that it comprises a magnetic field sensor (6), followed by a processing circuit (7) of the signal delivered by the sensor (6), a comparator (8) and a display means (10), the   comparator comparing the detected signal to a setpoint value supplied by a setpoint means (9,19), the display means displaying the result of the signal / setpoint comparison.   2- Device according to claim 1, characterized in that it comprises a control means (11) causing its power off and / or under automatic power. 3- Device according to claim 2, characterized in that   that the control means (11) comprises means (12) for automatic tensioning actuated by the magnetic field.   4- Device according to claim 3, characterized in that the means (12) for tensioning is constituted by a   switch, part of which is movable under the action of the magnetic field.   - Device according to claim 2, characterized in that the control means (11) comprises a means of   timer (13) connected to the display means (10). 6- Device according to any one of claims 1   to 5, characterized in that the processing circuit (7) comprises a regulator (15), a bandpass filter (16) and a   amplifier (17). 7- Device according to any one of claims 1   6, characterized in that the display means (10) comprises an electrical circuit for supplying two diodes electroluminescent (3, 4).   8- Device according to one of claims 1 to 7, characterized in that the setpoint means (9) delivers a   fixed voltage signal representing a magnetic field level.   9- Device according to one of claims 1 to 7, characterized in that the setpoint means (19) is adjustable   and comprises a potentiometer (20) connected to a setpoint calculation circuit (21) comprising a display (22). 10- Method for controlling the efficiency of a periodic magnetic field generator at a given distance, characterized in that: - a set value (9) is fixed beforehand, value giving a minimum level of magnetic field to be measured which is representative of the efficiency of the generator, - the magnetic field generated by the generator is detected at a given point at a distance from the generator and using a sensor (6), and the detected signal is processed, - the setpoint and detected signal,   - The result of the signal / setpoint comparison is displayed using a display means (10).