FR2681699A1 - System intended to supply data relating to the detection of electrically conducting particles contained in a fluid, and a detector designed for this purpose - Google Patents

Abstract

The invention relates to a system for supplying data relating to the detection of electrically conducting particles contained in a fluid, comprising at least one magnetic detector (3) capable of delivering a signal when it detects such particles, and a logic control circuit (13, 35a, 53, 59, 63) for supplying a logic datum to a visualisation unit (39) when these particles are detected, causing display of the said data on the presence of the particles. The circuit may comprise ZAPPER-effect means (55, 57), and the detector may be of the multichannel type. Application in particular to the detection of metal particles in the oil circuit of an aircraft engine.

Description

 The invention relates to a system adapted to provide information relating to the detection of metallic particles, or generally electrically conductive particles, contained in a fluid, such as oil.

 Systems are already known, particularly in aeronautics, for detecting the presence of metallic particles in the aircraft oil circuit.

 It is generally a device installed on each engine and intended to inform maintenance agents of the degree of pollution of the oil circuit during a visit under the wing, at the end of each flight.

 In general, such systems are mounted on a mechanical assembly with quarter-turn locking, the support of which carries a sealing valve for closing the oil tank during visual checks of the detection means usually employed. , often called "magnetic plugs".

 Still on known systems, the capture of metallic particles present in the oil tank is often carried out by three such plugs housed in the lubrication module of the oil circuit.

 Usually, each plug consists of a magnetic bar surrounded by two conductive parts which form an electrical circuit cut by the bar.

 Until now, however, a complete system has not yet been proposed making it possible to provide a maintenance agent with detection information, this with a degree of sophistication depending on the type of information that it is desired to acquire, depending on that we wish to be informed as soon as possible of the presence of these particles, whatever their size or number, or that we prefer rather to notify the maintenance agent only if the density or the size of captured particles is likely to actually degrade lubrication.

 It should also be noted that existing systems do not always have conditions of reliability, maintenance and electrical consumption compatible with the very strict requirements of the aeronautical industry.

 The invention aims in particular to solve these problems.

For this, it first proposes a system intended therefore to provide information relating to the detection of metallic or electrically conductive particles contained in a fluid, such as oil, this system comprising, according to an important characteristic of the invention
at least one magnetic particle detector capable of delivering a detection signal when particles are thus detected,
a logic control circuit with a CMOS integrated circuit and with bias resistor (s) for supplying a logical data item to a display unit when such particles are detected, causing said particle presence information to be displayed on this unit,
- And means for supplying power to the detector and the logic circuit.

 Insofar as, in certain cases, it may prove to be interesting to know whether the short circuit at the magnetic detector originates from the increasing accumulation of metallic particles on the plugs as a result of the normal progressive wear of oil, or if this short circuit is due to the attraction of large metallic debris from a premature rupture of certain parts, the system of the invention may also include ZAPPER effect means connected to the detector to deliver to it a quantity of electricity capable of breaking the electrical connection established by the particles between the magnetic bar and the surrounding conductive parts of the detector, this if the concentration or the importance of these particles does not exceed this place a predetermined value.

 If, moreover, it is desired to prevent the display unit from being triggered while the detector only fleetingly detects short-circuits, the logic control circuit may moreover include time-delay means so as not to cause the display of particle presence information only if the corresponding signal transmitted by the detector remains at the end of the global delay time.

Insofar as it has further been found that the development of the various versions of the detection system of the invention has been temporarily limited by the lack of advanced magnetic detectors, an improved magnetic detector of the multi-channel type has also been devised including
- a body with an axis and a length in the direction of this axis, this body containing a magnetic axial central bar opening on the outside at a front end of the detector where it is surrounded by a metallic core,
several magnetized pellets distributed around said bar, behind the core, and embedded in an electrically insulating washer,
several electrically conductive pads isolated from the bar and from the pads, these pads being distributed around said bar with an angular arrangement and a radius comparable to those where said pads are arranged, with interposition between two successive pads of a strip of electrically insulating material, each pad being connected, to form a channel, to an electrical conductor transmitting to the control circuit information corresponding to the presence or absence of particle detection.

 Of course, if this detector is particularly usable with the most advanced versions of the system of the invention, this is not an exclusive application.

 It should be noted, however, that this multi-channel detector may in particular be associated with programming means for transmitting randomly, and from a determined threshold, information on the presence or absence of detection originating from each of its channels.

 And in another application, it may be associated with it means for programming the logic control circuit, and recording the detection signals supplied by the detector, so as to be able to quantify the number of detection events supplied by the latter. .

 In relation to the accompanying drawings appended as nonlimiting examples, we will now describe in more detail some embodiments of the invention.

On the drawings
FIG. 1 shows a possible arrangement of a conventional single-channel magnetic plug such that it can be installed on an aircraft oil tank,
FIG. 2 shows a logic control circuit which can be added to such a single-channel detector,
FIG. 3 shows an alternative embodiment of such a circuit,
FIG. 4 schematically illustrates in longitudinal section a possible embodiment of a multi-channel magnetic detector,
FIGS. 5 and 6 show two transverse sections of the detector of FIG. 3, along lines VV and VI-VI of FIG. 4 respectively,
FIGS. 7A and 7B show another alternative embodiment of a detection circuit usable in association with the detector of FIGS. 4 to 6,
and FIGS. 8A and 8B show the most advanced variant of the detection circuit which can be used in particular in combination with the magnetic detector of FIGS. 4 to 6.

 Firstly, in FIG. 1, there is therefore shown an oil tank 1 through the bottom of which a magnetic detector 3 is mounted in leaktight manner.

In practice, provision could thus be made to have three such magnetic detectors in three places at the bottom of the tank which are distant from each other.
However, we will only deal with the case of a single detector.

 This detector of the single-channel type is, as shown schematically, conventionally constituted by a central magnetic bar 5 extending to the interior of the tank 1 in order to be able to attract any metallic particles which may be contained therein.

 The bar 5 is surrounded by two electrically conductive parts 7a, 7b. These conductive parts form an electrical circuit cut by the magnetic bar.

 At the rear of each sensor, this circuit transmits its information via a conductor 9.

 In 11, there is shown the "common" or "return" cable of the circuit.

 Let us now look at Figure 2 to see a first logic control circuit that can be associated with this type of magnetic plug.

 It will be noted first of all that the recording of the detection of the presence of particles coming from the magnetic plug 3 is here provided by a control logic constituted from CMOS integrated circuits.

 In this first version, the control circuit firstly comprises, at the input, a flip-flop RS with two NAND gates (NAND) 15, 17. The flip-flop RS is intended to receive information relating to any possible short-circuit created at the level of the magnetic plug 3.

 The two NAND gates 13, 17 have their input polarized at logic level "1" (power level), by means of the polarization resistors 19 and 21 connected between the power lines 23 and ground 25 connected to the 'common power supply unit 27 adapted to deliver a DC voltage appropriate to the components used.

When there is no short circuit at the plug, the RS flip-flop is protected by a bi-directional limiting diode 29 intended to limit any power interference which could damage either of the doors
NAND.

 In practice, we could for example provide that a detection short-circuit will be resistant up to 20 Kn to trigger the flip-flop 13. Beyond this, the short-circuit will more or less lead to the earth of the device the current of the bias resistor 19, hence the appearance of a logic level "0" at the input 17a of the flip-flop whose output 17b will then pass to logic level "1" and will remain in this state, this change d state on the input 17a being transmitted, via the inverter 33, to the input 35a of the looped monostable circuit 35 with RC circuit (resistance / capacitance) 37.

 Of course, the flip-flop RS will have initially been polarized when the power supply was switched on, this in this case, via an input capacitor 31 ensuring at the time tO a logic level "0" on its entry 15a.

 To avoid bouncing or doubling of the control function and ensuring the correct display on the display unit 39, it has been provided that the logic level "0" of the input 17a is also transmitted to the diode 41 and therefore to the second monostable circuit 43, image of the first, and connected between the unit 39 and the output of the inverter 45 itself connected to the output of the NAND gate 15.

 The display unit 39 is in this case formed from a bistable magnetic circuit with two windings 47, 49.

 In other words, it is a "pop out" display unit normally switched off when no presence of particles is detected.

 With such an arrangement, it is understood that any short circuit transmitted by the detector 3 will be displayed on the unit 39 and will remain so even after the power supply has been cut off.

 As for the return to the initial state of the circuit with erasure of the signal, it will take place quite naturally under the aforementioned conditions on the branch of the circuit comprising the monostable circuit 43.

 Thus, a pulse produced by the monostable circuit 43, under the control of the flip-flop RS 13, will trigger the energization of the winding 47, thus erasing the previous event this by means of an external reset button 51 can be operated by the operator.

 However interesting it may be, such a circuit does not, however, allow the different forms of pollution that may exist in the oil tank to be distinguished.

However, it appeared that two kinds of "pollution" can exist
First of all, it can happen that an increasing pile of metallic particles gradually accumulates on the detector, sign of a normal wear of the oil.

 However, the detector may also attract larger debris as a result of premature failure of certain parts, such as ball bearings.

 In practice, it turned out that it would be interesting to be able to remove the doubt about the origin of the short-circuits.

 To do this, provision has been made for using "ZAPPER effect" means capable of delivering to the detector (s) a quantity of electricity capable of breaking the electrical connection established by the particles, between the magnetic bar 5 and the outer conductive parts 7a, 7b, this if the concentration or the importance of these particles (or debris) does not exceed, at this location, a predetermined value, the electric discharge then causing a dispersion of the particles and therefore the opening of the circuit.

 If, in addition, provision has been made to add time-delay means, it will then be possible to trigger the lighting of the display unit only if the short-circuit remains at the end of the time-delay.

 To explain these principles present in the circuit of figure 3, (where one kept the same reference marks for the same components as in figure 2), one will consider that one is in the presence of a short circuit on one of the magnetic plugs.

 The detection of this short circuit always arrives, first, as input to the flip-flop RS 13 whose logic output level goes from "0" to "1".

 This output information is then transmitted to a first timer 53 with delay t1 for example of the order of 50 ms.

 This delay is used, in steady state, to correctly bias the transistor 55 which, with the capacitor 57, in this case constitute the aforementioned ZAPPER effect means.

 If the short-circuit of the detector still remains after t1, this transistor 55 will then ensure the discharge of the capacitor 57, and the output information of the timer 53 will again make the transistor 55 conductive and trigger the second circuit of timer 59 connected after the first.

 As before, the delay time t2 of the second circuit 59 will be chosen to ensure that the capacitor 57 has the time to discharge in the short-circuit of the detector concerned in order to try again to break the link.

 If the short-circuit disappears at the end of t2, the output information emanating from the timer 59 will then trigger the monostable circuit 61 which will return the flip-flop RS 13 to its initial state, the latter causing a reset (logic level "0") of the visual indicator 39, via the monostable circuit 63. The indicator will therefore remain off.

 If on the other hand the short circuit still exists, the input NAND gate 65 which receives the information emanating from the detector at the same time as the flip-flop RS 13, will then trigger the lighting of the indicator 39, via the monostable circuit 67, the NAND input gate 69 of this monostable then receiving on its two terminals 69a, 69b logic information of level "1" originating respectively from the timer 59 and from the NAND gate 65.

 As before, the entire circuit can be reset by manual reset via the push button 51.

 Before describing the two other detection circuits illustrated in FIGS. 7A, 7B and 8A, 8B, we will now present the new type of multi-channel magnetic detector that the invention proposes to use in particular with these last two most advanced versions of the detection circuit.

 As illustrated in FIGS. 4 to 6, it is a magnetic detector marked 70 comprising a body, for example made of stainless steel, 71 with a longitudinal axis 73, the body being elongated in the direction of this axis.

 Internally, the body 71 contains a magnetic axial central bar 75.

 To ensure its magnetic attraction function, the bar 75 opens onto the outside at 75a at a front end AVT of the detector.

 On this side, the bar 75 is surrounded by a metallic core 77, for example made of stainless steel.

 Further back, the detector further comprises several magnetized pads 79a, 79b, 79c, ..., 79f distributed regularly in groups of two around the bar, behind the core and embedded in an electrically insulating washer 81. In FIG. 5 the arrangement of the N / S poles (north / south) of the pellets has been indicated, the role of which is of course to correctly polarize the attracted particles and the bar.

 Several electrically conductive pads 83a, 83b, ... 83h also allow the magnetic field created to be transmitted to coaxial electric wires or cables 85a, ..., 85h (see Figures 4 and 6), the number of which is equal to that of studs, an additional central wire 85i ensuring the role of common with its stripped end 86i connected to the rear of the magnetic bar 75.

 Of course, to avoid electrical disturbances and ensure good connections, the wires will preferably pass through the body of the detector inside an insulating ring 87 which electrically insulates the body 71 from the bar 75, an insulating sealing washer 89 now. all in position.

 Concerning the studs 83a, 83b, ..., 83h, it will also be noted that, like the magnetized pads 79, they will preferably be distributed regularly around the bar, with an angular arrangement and a radius comparable to those where the pads are placed.

 Of course, the pads are electrically isolated from the magnetic bar 75, for example via the threaded part of the washer 81.

 As can be seen in FIG. 6, between two successive studs is also interposed a strip of electrically insulating material, which may for example be constituted by radiating extensions of the ring 87 (see FIGS. 4 and 6).

 In the illustrated version, it will be noted that the detector comprises six magnetized pads 79a, ..., 79f and eight equidistant conductive pads 83a, ..., 83h, forming as many channels for transmitting information to the control circuit concerned presence or absence of particles, this way by way.

 Let us now turn to Figures 7A and 7B to present a first logic circuit usable with such a multi-channel detector.

 This circuit is a direct evolution of the circuit of Figure 3 which it takes the general architecture.

 In fact, its evolution is intended to allow the control logic to receive several pieces of information from the detectors, since, having the multi-channel detector having several independent channels per plug, it was then imagined to allow the logic to command to detect several short circuits on the same plug, thus making this logic capable of programming several possible detection channels.

Thus, in FIG. 7A, do we find the doors
Input NAND 13, 65, with their bias resistors 19, 21, timers 53, 59, monostable circuits 61, 63, 67, the display unit 39 and the discharge capacity for the ZAPPER 57 effect , the network of NPN transistors 91 (with as many transistors as there are channels per detector) here replacing the previous single transistor 55.

 FIG. 7 having been divided into two parts, the end of the circuit cable which is connected in FIG. 7B to the corresponding end A2 at the output of the NOR gate 93 has been shown under the reference A1. collects information from the network of NOR (NOR) doors 95a, 95b, 95c, ... 95h polarized by the resistor network 96 and whose switching is programmed via the associated contactors 97a, 97b, 97c, ... 97h in number of course equal to the number of channels per detector, this programmed triggering being ensured by the "SHUNT" box (or junction box) 99 making it possible to activate this or that channel, taking into account the detection information received from the detector.

 It will also be noted in this FIG. 7B that the emitter of each transistor of the network 91 has been associated with a number to which corresponds an identical number on the circuit between the junction box 99 and the NOR gates 95a, ....

95h thus indicating the "downstream" connection of each transistor making it possible to inject into the detector circuit the break discharge of the ZAPPER effect, the transistors being moreover "upstream" connected by their collector, and via connection B2, at connection B1 in FIG. 7A, the same for the common connection of the bases between C2 and C1.

 Finally, in 85i, the wire or ground line of the detector concerned has again been shown.

 With the circuit which has just been presented, the detection of the particles present around the detector will therefore be able to be carried out in a random manner, this detector by detector, the programming means 95a ..., 97a ..., 99a ... allow defining the critical threshold from which the visual indicator 39 can display the presence information.

 Let us now refer to Figures 8A and 8B to present the most advanced version imagined.

 This latter circuit was illustrated in its adaptation to three magnetic detectors DM1, DM2 and DM3.

In input, the information transmitted by the detectors is taken into account in the same way as in FIGS. 7A or 3, via the rocker RS 13 and the door.
NAND 65 associated with their respective bias resistors 19 and 21.

 A delay circuit 101 associated with a monostable circuit 103 makes it possible to delay the triggering of the display unit and to reset the circuit if, at the end of the delay intervals t1 and t2 of the successive circuits 101 and 103, the generator short-circuit of the detection signal has disappeared.

 Thus, the event of presence of particles will only be taken into consideration if it is stable and still exists at the end of time delay t1, then allowing the switching of the NAND gate 105 whose input terminals 105a, 105b are respectively connected at the output of circuit 101 and the NAND input gate 65.

 If such a short circuit or of constant value is established on the flip-flop 13, the NAND gate 105 will then control the monostable circuit 107 which will trigger the display of the visual indicator (s) concerned. 39a, 39b, 39c (of the same type as the indicator 39 of the previous figures), this via the network of NOR gates 109a, 109b, 109c and the NPN villa transistors, it, lîlc associated.

 As for the reset (extinction) of the displays, it will operate in the same way as previously via the monostable circuit 113 and its associated OR (OR) gate 115, this always under the control of the manual contactor 51.

 In FIG. 8A, the connection ends of the illustrated circuit have also been shown in D1 with the programming and processing part of the recorded signals which will now be presented in relation to FIG. 8B in which only the programming and processing circuit associated with a single detector (Thus, one of the three branches of the connection D1 of FIG. 8A is to be connected to the branch D2 of FIG. 8B, the two other connections operating in the same way way with two other identical circuits).

 In this case, the programming and processing means comprise a programmed random access memory (EPROM) 117 receiving as input the logic signals transmitted by each of the channels of the magnetic detector 70 concerned, with polarization by the network of resistors 118.

 The programmable memory 117 comprises in this case four binary outputs connected to a bit comparator 119 intended to compare the value of the output bits of the memory 117 and of the associated programmer (or coding wheel) 121 also with four output bits, intended to program a determined number of short-circuits as a function of the channels of each detector, this following for example a chart corresponding to a potential number of hours of operation of the device (motor) to be monitored.

 Advantageously, this memory 117 will be programmed to ensure the random sum of the events of presence of particles on for example 256 combinations under 8 bits.

 In practice, the number of bits to be compared by the comparator 119 may be pre-selected by the encoder wheel 121 (from 1 to 8) making it possible to program the number of short circuits per detector (1 to 8 in this case).

 If the logic levels received from memory 117 and from the encoder wheel 121 are identical, then a logic level "O" will be transmitted to the anti-bounce circuit or component 123, via the inverter 125.

 This anti-rebound component (for example of the MC 14990 type) will include an internal oscillator (or timing clock) and will ensure the delayed transmission of the signal to its output D2, then, via the OR gates 110a, 110b, 110c connected between the NAND gate 105 and the entrance to the monostable 107, towards the NOR lO9a, 109b, 109c doors and the display unit to trigger the second winding of the display concerned, with erasure of the previous information.

In the meantime, its oscillator will, via outputs 7 and 9 and the feedback circuit 126 with series inverters 127, 129, reset the programmable memory 117, via the input
CK 131 of the latter, allowing to control again the change of events at the input of each magnetic detector.

 For all practical purposes, it will be recalled that the circuit of FIG. 8B which has just been presented must of course be present at the output of each detector considered.

Claims (14)

 1 - System for providing information relating to the detection of metallic or electrically conductive particles contained in a fluid, such as oil, comprising  - at least one magnetic detector (3, 70) of such particles capable of delivering a detection signal when particles are detected,  - a control logic circuit (13, 35, 43, 53, 59, 61, 63) with CMOS integrated circuit and with bias resistor (s) (19, 21) for supplying data to a display unit (39) logic when such particles are detected, causing the display of said particle presence information on this unit,  - And power supply means (27) of the detector and the logic circuit.  2 - system according to claim 1 characterized in that the logic control circuit comprises  - at input, at least one NAND gate (13, 17, 65) coupled to said bias resistor (19, 21) to switch from one logic state to another when it receives a said detection signal from the detector ( 3, 70),  - and at least one monostable circuit (35, 43, 61, 63, 67, 107, 113) controlled by the signal emitted by this door NAND AND, to trigger the display unit (39).  3 - System according to claim 2 characterized in that the logic circuit comprises  - at the input, two so-called NAND gates forming an RS flip-flop (13),  - two inverters (33, 45) connected at the output of said NAND gates to invert their logic output signal,  - and two said monostable circuits (35, 43) looped, connected at the output of said inverters and each controlling one of the coils (47, 49) of a bi-stable magnetic circuit with two coils belonging to the display unit ( 39), one of these monostable circuits controlling the triggering of this display unit when a detection signal is transmitted by the detector (3), the other circuit controlling the triggering of this same unit with erasure of the information above when a signal transmitted via a reset button (51) reaches it via the RS lever (13) and one of said reversers (45) (Figure 2).  4 - System according to any one of claims 1 or 2 characterized in that it further comprises timing means (53, 59, 101) so as not to cause the display on the display unit (39) of the information relating to the presence of particles only if the corresponding signal transmitted by the detector (3, 70) remains at the end of the time delay.  5 - System according to any one of claims 1, 2 or 4 characterized in that the detector (3, 70) comprising a magnetic bar (5) surrounded by electrically conductive parts (7a, 7b; 83a, 83b, ... ), this bar being able to attract the particles which may be contained in the fluid to establish an electrical connection between it and its surrounding conductive parts, the logic control circuit comprises effect means ZAPPER (55, 57, 91) connected to the detector (3, 70) to deliver to it a quantity of electricity capable of breaking the electrical connection established by the particles between the magnetic bar (5, 75) and its conductive parts (7a, 7b; 83a, 83b, ...), if the concentration or the size of its particles does not exceed, at this location, a predetermined value.  6 - System according to claim 5 characterized in that the ZAPPER effect means comprise a capacitor (57) and at least one transistor (55, 99).  7 - System according to claim 6 characterized in that it further comprises  - a first entrance with two so-called NO doors AND forming an RS flip-flop (13),  - a second entrance with a third door NO AND (65),  - three so-called monostable circuits (61, 63, 67),  - two cascade timing circuits (53, 59) placed one after the other at the output of the scale RS (13) and coupled to said ZAPPER effect transistor, either to control, via the first monostable circuit (67), one of the coils (47) of a bi-stable magnetic circuit with two coils belonging to the unit display (39), if a detection signal transmitted by the detector (3) is still present at the end of the delay time for the second timer (59), i.e. to reset the logic level of the RS flip-flop via the second monostable circuit ( 61) if said detection signal transmitted by the detector is no longer present at the end of the delay times and to then command, via the third monostable circuit (63), the triggering of the second winding (49) of the display unit deleting the previous information (figure 3).  8 - System according to claim 7 characterized in that  - the particle detector (70) is a multi-channel detector comprising  a body (71) with an axis (73) and a length in the direction of this axis, the body containing a central axial magnetic bar (75) opening onto the outside at a front end of the detector or it is surrounded by a metallic core (77),  several magnetized pads (79a, 79b, ..., 79f) distributed around said bar, behind the core, and embedded in an electrically insulating washer (81),  several electrically conductive pads (83a, 83b, ... 83h) isolated from the bar and pads, these pads being distributed around said bar, according to an angular arrangement and a radius comparable to those of the pads, with interposition between two successive pads of a strip of electrically insulating material (87), each pad being connected, to form a channel, to an electrical conductor (85a, 85b, ... 85h) transmitting to the control circuit information corresponding to a presence or an absence particle detection,  - And said logic circuit further comprises, between its said first and second inputs (13, 65) and the detector channels, programming means (95a, ..., 95h 97a, ..., 97h; 99) for transmit randomly, and from a predetermined threshold, the presence or absence of detection information transmitted by each channel of the detector (FIGS. 7A, 7B).  9 - System according to any one of claims 1 or 4 characterized in that  - the particle detector (70) is a multi-channel detector comprising  a body (71) with an axis (73) and a length in the direction of this axis, the body containing a central axial magnetic bar (75) opening onto the outside at a front end of the detector or it is surrounded by a metallic core (77),  several magnetized pads (79a, 79b, ..., 79f) distributed around said bar, behind the core and embedded in an electrically insulating washer (81),  several electrically conductive pads (83a, 83b, ... 83h) isolated from the bar and pads, these pads being distributed around said bar, according to an angular arrangement and a radius comparable to those of the pads, with interposition between two successive pads of a strip of electrically insulating material (87), each pad being connected, to form a channel, to an electrical conductor (85a, 85b, ... 85h) transmitting to the control circuit information corresponding to the presence or absence of particle detection,  - And said control circuit comprises means (117, 119, 121, 123) for programming said circuit and for processing the detection signals to quantify the number of particle detection events transmitted by the detector.  10 - System according to claim 9 characterized in that the control circuit also comprises  a first entrance with two said doors NO AND forming an RS flip-flop (13),  a second entrance with a third door NO AND (65),  - three monostable circuits (103, 107, 113),  - a timing circuit (101) placed at the output of the flip-flop RS, either to control, via the first monostable circuit (107) and at least one NOR gate (109a, 109b, 109c), one of the windings of a bistable magnetic circuit with two coils belonging to the display unit (39a, 39b, 39c), if a detection signal is transmitted by at least one of the detector channels, either to reset the logic level of the RS flip-flop (13) via the second monostable circuit (103), if said detection signal transmitted by the detector is no longer present at the end of the time delay and to then control, via the third monostable circuit (113), the triggering of the unit display with erasure of the previous information when a reset signal transmitted, via a reset button (51), reaches it via the RS flip-flop (13).  11 - System according to claim 9 or claim 10 characterized in that the programming and processing means comprise  - a random access programmable memory EPROM (117) each input of which is connected to one of the detector channels (70),  - a coding wheel (121) for programming a number of short-circuits according to the channels, according to a pre-determined chart,  - a bit comparator (119) associated with said programmable memory and with the coding wheel,  - an anti-rebound component (123) with internal oscillator connected to the comparator to transmit a timed detection signal if two identical logic levels are transmitted by the programmable memory (117) and the coding wheel (121) (FIGS. 8A, 8B).  12 - System according to claim 11 characterized in that the programmable random access memory (117) is programmed to ensure the random sum of the particle detection events.  13 - System according to one of claims 11 or 12 characterized in that the programming and processing means further comprise a feedback circuit (126) connecting the anti-rebound component (123) and the programmable memory (117) for reset this memory, via the internal oscillator of the anti-rebound component.  14 - Multi-channel magnetic detector intended in particular for the detection system according to claims 8 or 9 and comprising  - a body (71) with an axis (73) and a length in the direction of this axis, the body containing a magnetic axial central bar (75) opening on the outside at a front end of the detector or it is surrounded by a metallic core (77),  several magnetized pellets (79a, 79b, ..., 79f) distributed around said bar, behind the core and embedded in an electrically insulating washer (81),  - Several electrically conductive pads (83a, 83b, ... 83h) isolated from the bar and the pads, these pads being distributed around said bar, according to an angular arrangement and a radius comparable to those of the pads, with interposition between two successive pads a strip of electrically insulating material (87), each pad being connected, to form a channel, to an electrical conductor (85a, 85b, ... 85h) suitable for transmitting information corresponding to the presence or absence of particles.