Device to test the good working order of a magnetic field generator

A device to test the good working order of a magnetic field generator, and namely a demining coil, such device comprising at least one evaluation means for the magnetic field coupled with at least one display means, device wherein said evaluation means comprise at least one wound coil able to be positioned so that the lines of the magnetic field pass through it, said wound coil linked to evaluation electronics powered by said wound coil itself.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The technical scope of the invention is that of devices enabling the functioning of a magnetic field generator to be tested.

The invention is more particularly adapted to testing coils used in demining systems.

2. Description of the Related Art

A test device is known by patent FR-2779529, which enables the intensity level of a variable magnetic field to be assessed.

This device comprises a magnetic field sensor coupled with an electronic signal processing circuit. The circuit makes a comparison between the detected signal and a set point. The comparison results are displayed on a monitor.

This device is well adapted to the mapping of magnetic fields at some distance from the generator and to ensuring a measurement of the level of the field (using means enabling the set point to be varied).

It is, however, far too complex to be used simply to validate or verify that a generator is functioning correctly. Furthermore, the sensor's sensitivity is maximal in a well-defined direction which must be known with respect to the generator to avoid an evaluation error.

There is thus a need for a cheap, robust test device enabling the validation of the good working order of a magnetic field generator to be reliably established.

SUMMARY OF THE INVENTION

The aim of the invention is to supply such a device.

Thus, the invention relates to a device to test the good working order of a magnetic field generator, and namely a demining coil, such device comprising at least one evaluation means for the magnetic field coupled with at least one display means, device wherein the evaluation means comprise at least one wound coil able to be positioned so that the lines of the magnetic field pass through it, such wound coil linked to evaluation electronics powered by the wound coil itself.

The evaluation electronics may comprise at least one calibrated circuit powering the display means.

According to another embodiment, the evaluation electronics may comprise at least two separate channels each enabling a different frequency of the magnetic field to be tested.

Each evaluation channel may associate a filtering stage and an evaluation stage.

The evaluation electronics may associate an evaluation stage configured for a frequency of around ten Hz or so and an evaluation channel configured for a frequency of over one kilo Hz.

Advantageously, the two evaluation channels will be coupled with the same display means.

The evaluation electronics may comprise an energy storage module incorporating at least one capacitor.

The display means may comprise at least one pilot lamp.

The display means may namely comprise a single pilot lamp arranged on an upper face of the device.

The wound coil will preferably be integral with a casing delimiting a bore intended to cap a generator to be tested.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1schematically shows a demining device1comprising a power source2linked to a magnetic field generator3constituted by a cylindrical coil with axis4which is integral with a vehicle (not shown).

Such a demining device is disclosed by patent FR2750204 and thus does not require further description here.

The coil3is shown here capped by a test device5according to the invention.

FIG. 2shows a section of one embodiment of this test device5.

The latter comprises a casing6delimiting a cylindrical bore7with axis25intended to cap the coil3and which thus has a diameter substantially equal to the external diameter of the coil3. The casing6incorporates a cylindrical notch8in which a conductor is wound to form a wound coil9. The wound coil9may be made integral to the casing6by duplicate molding or by bonding.

The wound coil9is linked to measurement electronics10arranged in a case11integral with the casing6. The measurement electronics10are linked to the display means12constituted by a pilot lamp. The wound coil9and measurement electronics10constitute the evaluation means for the magnetic field.

FIG. 3shows an embodiment of these evaluation means. The wound coil9is linked to the pilot lamp12by means of a circuit incorporating at least one calibrated resistor. The circuit thus formed does not comprise a power source. It is powered by the wound coil9when the lines of the field13(FIG. 1) generated by the generator3pass through it and when this field varies as a function of time.

The value of the calibrated resistor10is selected as a function of the level of the magnetic field, which is required to be tested.

For a given wound coil, the electromotive force of the coil is proportional to the intensity of the magnetic field and is furthermore proportional to the variation frequency of this field.

Someone skilled in the art will select the value of the resistor such that the pilot lamp12only lights up if the magnetic field presents the required characteristics from the perspective of intensity and frequency.

Furthermore the number of loops in the wound coil9will be selected so as to ensure (when the coil is coupled with one of the generators3to be tested) an induced current of sufficient intensity to enable the pilot lamp12to be lit.

The device according to the invention is thus particularly simple and robust. Furthermore, the pilot lamp is only able to light up in the presence of a variable magnetic field.

The device thus enables two types of fault to be highlighted: one in which the field is at an insufficient level and one in which the filed is continuous even if its level in absolute value is sufficient.

The good working order of the generator is indicated by the pilot lamp12periodically going on and off. The frequency of its being switched on corresponds to that of the magnetic field generated.

Different variants are possible without departing from the scope of the invention. It is possible for several pilot lamps12to be provided, oriented differently, this in order to make it easier for an operator at a distance to observe whether the device is in working order or not.

By way of example, a pilot lamp12ais shown inFIG. 2by dotted lines which is positioned on an upper face of the device5and which is connected to measurement electronics10aembedded in the body of the device.

It is naturally possible to implement the invention using different measurement electronics. For example, a circuit comprising a band-pass filter and peak level detector may be employed, such circuit being designed to deliver a discontinuous signal which is an image of the peak-to-peak amplitude of the voltage generated by induction in the wound coil9, thus also of the amplitude of the magnetic field received.

This signal may be directed to a comparator, which will receive a constant signal supplied by set point means. The comparator will control the lighting of the pilot lamp if the signal received is greater than or equal to the set point.

Once again, the supply of electrical energy for the measurement electronics will be ensured using the current induced by the magnetic field in the wound coil.

This type of embodiment will enable the device to be adapted to different types of generators by modifying the set point value.

FIG. 4shows a test device according to a second embodiment of the invention.

In this embodiment, the evaluation electronics10comprise two separate evaluation channels14and15each enabling a different frequency of the magnetic field to be tested.

Indeed, there are demining devices which function at different operating frequencies, for example, low frequency demining devices (frequencies of around ten Hertz or so) and high frequency demining devices (over a kilo Hertz). These devices functioning at high and low frequency may furthermore be associated in the same vehicle.

Each evaluation channel14,15comprises a filtering stage16,17followed by an evaluation stage18,19.

Each filtering stage16,17is made classically by associating resistors and capacitors. They enable only that part of the signal supplied by the wound coil9, which corresponds to the frequency intended to be evaluated by the channel, to pass through to the evaluator18or19.

For example, the low frequency filtering stage16will be calibrated to let frequencies pass of around ten Hz or so and the high frequency filtering stage17will be defined so as to let frequencies pass which are over a kHz.

In parallel to the filtering stages16,17, the wound coil9supplies an energy storage module20. This module associates, for example, a diode21and a capacitor22.

The alternative current supplied by the coil9charges the capacitor22.

The purpose of this module20is firstly to power the evaluators18and19, and secondly to power the pilot lamp12.

The evaluation modules18and19comprise a calibration stage18a,19athat enables only a fraction of the voltage from the filter16,17to be retained. The detection sensitivity is thereby regulated for each evaluation channel. These calibration stages will classically comprise a rectifier followed by a resistor bridge.

The calibration stages18a,19awill be connected to an oscillator18b,19a(made in the form of integrated circuits). Each oscillator will be calibrated at a well defined frequency which will be different for the high frequency channel15and for the low frequency channel14.

Thus, the calibration signals supplied by stages18a,19awill be applied at the “reset” input (RAZ) of each oscillator. This will result in a signal being emitted, or not, by the oscillator in question.

If a current of the required frequency is detected by one of the stages14or15, the calibration stage in question (18aor19a) will apply a voltage to the RAZ input of oscillator18bor19b. The latter is thereafter unlocked and periodically supplies a current to the pilot lamp12causing it to light up at the frequency which has been associated by adjustment to the oscillator18b,19bin question. If the stages14or15do not detect a current, the oscillators are locked and the pilot lamp12remains off. Diodes23,24are positioned between each oscillator and the pilot lamp12. The combination of these two diodes constitutes a logic gate OU. The pilot lamp12is thus lit up indifferently by one or other of the evaluation channels14,15.

FIG. 5shows the test device5implemented to control a demining device1functioning at high frequency. This demining device also comprises a power source2connected to a magnetic field generator3constituted by one or several conductive loops, which will, for example, be integral with a mechanical organ integral with a vehicle, for example a demining plough. To control this magnetic field generator the test device5according to the invention is positioned close to the loop or one of the loops3. The axis25of the test device5will be positioned substantially perpendicularly to the plane26of the loop (more often than not the axis25is thus substantially vertical). In such a position, the lines13of the magnetic field generated by the generator3pass through the wound coil9of the device5, which is thus able to function.

The device5shown inFIG. 5incorporates a single pilot lamp12arranged on an upper face of the device5. This lamp is thus visible form all directions in space. A suitable optical device may be provided to ensure the diffusion of the radiation over 360°. We can thus see that the device according to this embodiment of the invention just as easily enables a low frequency demining device such as that shown inFIG. 1to be tested as a high frequency device such as that shown inFIG. 5.

The device incorporates no onboard power source, no control buttons and no adjustment means. It is extremely robust and enables the presence of an alternative magnetic field of a given intensity to be verified (pilot lamp off in the absence of the field or if the field is continuous, of insufficient level or is not in the correct frequency band). It also enables generators to be tested that function according to different frequencies, and this with no particular adjustment or intervention required on the device.

Furthermore, a user, even an inexperienced one, will easily be able to detect the lighting frequencies of the lamp, which are different for high or low frequency generators.