Circuit for managing electric arcs and electrical and / or electronic device comprising such a circuit

Abstract

The present invention relates to a circuit (11) for managing electric arcs for a four-wire electronic and / or electrical measuring device, the circuit (11) comprising a connection point (E1) configured to be connected to a voltage and / or current generator, and at least two connection points (S1, S2) configured to be connected to an intermittent electrical contact element, the circuit (11) being characterised in that it comprises at least: - a capacitive element (C1); - a voltage clipping element (D1); and - a switch (T1) configured to close during a voltage peak; the capacitive element (C1), the voltage clipping element (D1) and the switch (T1) being mounted in parallel with one another and also connected to each of the connection points (E1, S1, S2).

Description

Arc flash management circuit and electrical and / or electronic device comprising such a circuit

[0001] [The present invention relates to the field of electronic and / or electrical devices, as well as to the management of sparks or electric arcs that may occur during connections, disconnections and / or switching of elements of such devices.

[0002] Indeed, it is common for such devices to include connectors, switches, relays, etc., which will switch or connect / disconnect frequently, and sometimes impromptu, while a current is present, thus generating an electric arc that can damage the elements between which said electric arc propagates.

[0003] This problem is particularly present in the field of electrical resistance measurement devices, for example in the aeronautical field.

[0004] Indeed, during the assembly of an aircraft, such as an airplane, a helicopter, a drone, etc., or later during maintenance, operators must verify that the parts are properly assembled (or fixed) to each other.

[0005] These checks can be carried out, in particular, by measuring the resistance values ​​between elements (or parts of an element). It should be noted that this type of measurement also allows for the verification of metallization of parts, the quality of a weld, etc.

[0006] The resistance value is indeed a physical quantity that reflects the quality of the connection between elements; the lower this value, the better the connection. The connections between aircraft components advantageously have a low resistance value to limit damage when the aircraft is struck by lightning.

[0007] Generally, measuring resistance involves applying a predetermined voltage or current to the component whose resistance is being measured. Then, the resulting current or voltage is measured, respectively, as the relationship between voltage and current is, as stated in Ohm's law, the resistance value of the component under test.

[0008] The values ​​of electric current injected into one or more parts to be tested, in order to measure their resistance, are generally at least one ampere, and usually around ten amperes, or even more.

[0009] Such devices generally include a central unit to which Kelvin (or 4-wire) type probes are connected, probes which generally include metallic touch points through which the electrical test stated above is carried out, but the cables connecting said points to the central unit can be of significant lengths, for example lengths of several tens of meters, which can store significant amounts of electrical charge.

[0010] Thus, when the test probes of such a device are incorrectly applied or are no longer in contact with the element being tested during the electrical test, an electric arc may be created between the test probe and the element being tested (the stored energy being a function of the inductance value and the current intensity value).

[0011] Indeed, during a test, and the application of the probes to the element to be tested, a closed electrical circuit is created in which a test current flows; the sudden breakage of one of the probe tips with the test element can cause the discharge of energy stored in the device in the form of an electric arc.

[0012] The electric arc thus generated lasts for a very brief moment, but can have sufficient intensity to weaken, or even damage, the test tip and / or the element being tested, especially since the phenomena of spark creation can be repeated many times during the use of such a device.

[0013] It is therefore necessary to find a solution to limit the creation of electrical arcs in such electrical and / or electronic devices, thereby preventing damage to one or more components of these devices, such as measuring probes, connectors, switches, relays, etc., as well as the element under test. Furthermore, this solution must be compact (for ease of implementation) and inexpensive.

[0014] The invention thus aims to solve at least one of the problems mentioned above by proposing a new type of arc management circuit for a four-wire electronic and / or electrical measuring device, said circuit comprising a connection point configured to be connected to a voltage and / or current generator and at least two connection points configured to be connected to an intermittent electrical contact element, such as a Kelvin or four-wire test probe, characterized in that said circuit comprises at least: - a capacitive element; - a voltage clipping element; - a switch configured to close during a current peak; said capacitive element, the voltage clipping element and the switch being, on the one hand, mounted in parallel with each other and, on the other hand, connected to each of said connection points.

[0015] A circuit according to the invention thus makes it possible to reduce, or even prevent, the occurrence of electrical arcs that could damage components and / or elements of the four-wire electronic and / or electrical measuring device in which said circuit is mounted. Furthermore, the circuit according to the invention has the advantage of being inexpensive, compact, easy to implement, and robust with regard to the overcurrents that the circuit according to the invention is capable of handling.

[0016] According to another possible characteristic, said voltage clipping element is a Transil type diode, for example unidirectional or bidirectional.

[0017] This unidirectional or bidirectional Transil diode is an electronic component used to clip voltages, while being inexpensive and resistant to overvoltages and / or overcurrents. Furthermore, this type of diode has a response time adapted to the duration of the overcurrent to be managed, for example, a response time between 1 ps and 4 ms.

[0018] According to another possible feature, said circuit comprises two electrodes located at a predetermined distance from each other, each electrode being connected to one of said second and third connection points.

[0019] The circuit according to the invention advantageously includes an additional electrical safety feature consisting of two electrodes which, if the overcurrent becomes too high, localize the creation of electrical arcs between the two electrodes, thus preventing the formation of electrical arcs at expensive and / or fragile components or elements, and thus preventing their damage. The electrodes are advantageously mounted in parallel with the capacitive element, the voltage clipping element, and / or the switch.

[0020] According to another possible characteristic, said switch is a transistor, for example a MOSFET type transistor. Advantageously, said switch is a transistor allowing passive control of said switch by voltage variations at said circuit according to the invention.

[0021] According to another possible characteristic, said capacitive element is a capacitor, said capacitor having a capacitance which is a function of the reaction time of said voltage clipping element.

[0022] The said capacitor advantageously has a capacitance of at least 1 nanofarad, and preferably of at least 10 nanofarads (the capacitor advantageously having at most a reaction time of 1.5 ns).

[0023] According to another possible feature, said circuit includes a resistor and a capacitor mounted to form a series RC circuit, said RC circuit being configured to control the state of said transistor.

[0024] The said RC circuit is advantageously configured so that the switch opens after the time required for the current to descend following the occurrence of an overvoltage and can allow its management by said circuit according to the invention.

[0025] According to another possible characteristic, said RC circuit has a time constant T of at least 1 millisecond, and preferably less than 10 milliseconds.

[0026] Advantageously, the time constant T of the RC circuit must have a value low enough not to impact a measurement made by the four-wire electronic and / or electrical measuring device in which said circuit is mounted, but have a value sufficient so that the overvoltage value does not exceed a critical threshold (in particular before the end of the transistor activation and before there is an appearance of a spark or an electric arc).

[0027] According to another possible characteristic, the transistor comprises a gate, a source and a drain, the capacitor of the RC circuit having a capacitance value much greater than the capacitance value of the gate of said transistor.

[0028] Advantageously, the capacitance value of the capacitor in the RC circuit has a value at least 10 times greater than the capacitance value of the gate of said transistor, and preferably a value at least 100 times greater than the capacitance value of the gate of said transistor.

[0029] According to another possible feature, said circuit comprises two assemblies, each comprising a transistor and an RC circuit configured to control the state of said transistor, each of said assemblies being mounted in parallel with each other with respect to said voltage clipping element.

[0030] The said circuit according to the invention may also have variant embodiments allowing it to be mounted interchangeably at various locations of a four-wire electronic and / or electrical measuring device.

[0031] According to another possible characteristic, said circuit exhibits axial (or mirror) symmetry.

[0032] The circuit advantageously exhibits mirror symmetry, optimizing the number of electronic components required and thus the manufacturing cost of a circuit according to the invention. Furthermore, the circuit according to the invention can be mounted interchangeably at various locations within a four-wire (or Kelvin) electronic and / or electrical measuring device, for example, interchangeably at one or both of the test probes of said device.

[0033] The invention also relates to a four-wire (or Kelvin type) electrical and / or electronic measuring device, characterized in that said device comprises at least one arc flash management circuit as defined above.

[0034] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of two particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings, in which: - Fig. 1 illustrates a very schematic representation of a four-wire electronic and / or electrical measuring device according to the invention; - [Fig. 2] illustrates a schematic representation of a management circuit according to a first embodiment of the invention; - [Fig. 3] illustrates a schematic representation of a management circuit according to a second embodiment of the invention.

[0035] In the description that follows, the term "include" is synonymous with "include" and is not restrictive, as it allows for the presence of other elements within the structure to which it refers. It is understood that the term "include" includes the terms "consist of." Furthermore, it should be noted that in the various figures, the same references designate identical or similar elements.

[0036] Figure 1 illustrates a highly schematic representation of a four-wire electrical and / or electronic measuring device 1 according to the invention, device 1 configured to measure the electrical resistance value of an element 3 under test. This four-wire device 1 is, for example, intended to measure the electrical resistance value of at least one structural element of an aircraft.

[0037] More specifically, the measuring device 1 is capable of determining the electrical resistance of the element 3 being tested from the value of an injected current called "test current" in the element 3 being tested and the voltage measured across the terminals of said element 3 being tested.

[0038] This type of measuring device 1 is used in particular during the assembly of an aircraft, such as an airplane, a helicopter, a drone, etc. or later during the maintenance operations of these to ensure that the parts are correctly assembled to each other by measuring contact resistances, and more particularly resistances of low value (for example less than or equal to 60 Ohms, preferably a few Ohms, and preferably even less than 0.1 Ohm, down to values ​​on the order of the microohm).

[0039] It should be noted that electrical resistance is understood to be the electrical resistivity value of an element, that is, the tendency of an element to oppose the passage of an electric current. The device 1 according to the invention can directly measure the electrical resistance of element 3 or perform an indirect measurement, that is, by measuring a physical quantity proportional or inverse to the electrical resistance, such as electrical conductivity, to ultimately determine an electrical resistance value.

[0040] The said device 1 comprises the following: - a central unit 5 in which is housed a power supply source, such as a voltage and / or current generator, as well as electronic control and / or measurement circuits (not shown); - a human-machine interface 7, for example located on and in the central unit 5; - an electrical connection (or connector) 9 intended to link the central unit 5, in particular the measurement circuit, to the element 3 whose electrical resistance value we seek to determine, said connection 9 comprising two cables.

[0041] It should be noted that the human-machine interface 7 refers to all the elements that allow the user to interact with the device 1, more specifically to control the device 1 and to exchange information with said device 1. The human-machine interface 7 includes, for example, at least one means of display, such as a touch screen or not, buttons, a keyboard, etc.

[0042] Electrical connection 9 is advantageously a Kelvin or 4-wire type connection. Thus, said Kelvin connection 9 comprises four electrical conductors generally terminated by clips or points which are intended to connect to or be applied to element 3 whose electrical resistance value is to be determined.

[0043] More specifically, the Kelvin connection 9 comprises two measuring conductors 8a and two power conductors 8b, these being distributed between two probes 9a and 9b, each of said probes 9a and 9b comprising one measuring conductor 8a and one power conductor 8b (each of the cables of connection 9 therefore comprises one power conductor and one measuring conductor).

[0044] More specifically, the end of the measuring conductor 8a is a movable metal tip, for example attached to a spring, while the end of the power conductor 8b is a fixed metal tip, the fixed metal tip being in contact with the element to be tested 3 preferably before the movable metal tip reaches the end of its movement (in order to correct manufacturing tolerances and / or tip wear) (i.e. when the spring, making the associated tip movable, is compressed).

[0045] Device 1 is thus configured to trigger the generation of a test current only when the two fixed and mobile metal tips of each of the probes 9a and 9b are in contact with the element 3 to be tested.

[0046] Figure 2 illustrates, for its part, a very schematic representation of an arc management circuit 11 according to a first embodiment of the invention, circuit 11 intended to be mounted in device 1.

[0047] The arc flash management circuit 11 is, for example, located in one or both of the probes 9a and 9b of the device 1, which are intended to be in contact with the element 3 under test. The circuit 11 thus comprises a connection point Ei configured to be connected to a current and / or voltage generator, also referred to as the "first connection point," and at least two connection points Si and S2, referred to respectively as the second and third connection points, which are connected respectively to the power conductor 8b and the measuring conductor 8a.

[0048] Circuit 11 thus includes at least: - a capacitive element Ci, said capacitive element Ci being advantageously a capacitor, also referred to as the first capacitor; - a voltage clipping element D1, for example a unidirectional Transil type diode; - a T1 switch configured to close during a voltage spike; - two electrodes located B1 and B2 at a predetermined distance from each other, each electrode being connected to one of the second and third connection points Si and S2.

[0049] The capacitive element Ci, the voltage clipping element Di, and the switch Ti are, on the one hand, mounted in parallel with each other and, on the other hand, each connected to the first, second, and third connection points Ei, Si, and S2. The electrodes B1 and B2 are also advantageously mounted in parallel with the capacitive element Ci, the voltage clipping element D1, and / or the switch T1.

[0050] Said switch T1 is advantageously a transistor, for example a MOSFET transistor, and said circuit 11 comprises a resistor Ri and a capacitor C2, called the second capacitor, mounted to form a series RC circuit, said RC circuit being configured to control the state of said transistor T1, that is to say, to allow or prevent the passage of a current through transistor T1. The series RC circuit associated with transistor T1 thus forms an assembly referenced 13 in [Fig. 2].

[0051] It should be noted that circuit 11 includes a first node Ni and a second node N2, the first node Ni being connected to one of the terminals respectively of the first capacitor Ci, the Transil diode D1, the RC circuit, and the switch T1, while the other terminal respectively of the first capacitor Ci, the unidirectional Transil diode D1, the RC circuit, and the switch T1 is connected to the second node N2.

[0052] The said series RC circuit thus has two opposite terminals, one corresponding to a terminal of the second capacitor C2 which is connected to the first node Ni, and the other corresponding to a terminal of the first resistor Ri which is connected to the second node N2. Furthermore, the first node Ni is connected to the first and second connection points E1 and Si, while the second node N2 is connected to the third connection point S2.

[0053] In addition, transistor T1 includes a gate, a source and a drain, the source and drain being respectively connected to the second and third connection points Si and S2, while the gate of said transistor T1 is connected to a node N3, called third node, located between the first resistor Ri and the second capacitor C2 of the series RC circuit.

[0054] The grid is therefore connected respectively to one of the terminals of the resistor Ri and the second capacitor C2 of the RC circuit, while the opposite terminals respectively of the resistor Ri and the capacitance C2 are connected to one of the second and third connection points Si and S2 (or respectively to the first and second nodes Ni and N2).

[0055] Advantageously, the second capacitor C2 of the RC circuit has a capacitance value much greater than the capacitance value of the gate of said transistor Ti, the capacitance value of the second capacitor C2 having a value at least 10 times greater than the capacitance value of the gate of said transistor T1, and preferably a value at least 100 times greater than the capacitance value of the gate of said transistor Ti.

[0056] Note that the gate capacitance of transistor T1 is in series with the capacitance of the second capacitor C2, and that the value of this set must be much lower than the value of the capacitance of the first capacitor Ci, thus preventing the value of current flowing through the gate of transistor T1 from being too high, or even damaging said transistor T1.

[0057] Furthermore, the first capacitor Ci has a capacitance that is a function of the reaction time of the Transil diode D1, the first capacitor Ci having for example a capacitance of at least 1 nanofarad, and advantageously a capacitance of at least 10 nanofarads.

[0058] The electrodes B1 and B2 are advantageously metallic tracks (for example, on a printed circuit board), or electrical conductors arranged opposite each other and located at a constant and predetermined distance from one another. Furthermore, one of the electrodes B1 is connected to the first node Ni, while the second electrode B2 is connected to the second node N2.

[0059] The said electrodes B1 and B2 have, for example, complementary shapes, such as interdigitated shapes, so that the edge or edges of each of the said electrodes B1 and B2 are at a predetermined distance from each other.

[0060] Thus, when testing an element 3, a test current flows from the first connection point E1 to the second connection point Si, but when there is a break in the electrical continuity of the electrical circuit formed by the probes 9a and 9b with the element 3, for example by loss of contact of one of the probes 9a or 9b, then the energy stored in the power conductors 8b (sometimes having lengths of several tens of meters) connecting the device 1 to the probe 9a or 9b causes an overvoltage which is managed by the management circuit 11.

[0061] The said RC circuit is thus advantageously configured so that the switch T 1 opens after the time necessary for the current to descend following the occurrence of such an overvoltage and can allow its management by the said circuit 11, in order to avoid the occurrence of an electric arc.

[0062] Furthermore, the time constant T of the RC circuit must be sufficiently low so as not to affect a measurement made by the four-wire measuring device 1 in which said circuit 11 is mounted, but sufficient so that the overcurrent value does not exceed a critical threshold for the transistor Ti. For example, said RC circuit has a time constant T of at least 1 millisecond, and preferably less than 10 milliseconds.

[0063] Fig. 3 illustrates, for its part, a very schematic representation of an arc management circuit 11' according to a second embodiment of the invention, circuit 1T also intended to be mounted in device 1.

[0064] The said 1T circuit also includes second and third connection points Si and S2 connected respectively to the power conductor 8b and measuring conductor 8a and a first connection point E1, as well as two nodes Ni' and N2', respectively first node and second node, the first node Ni' being connected to the second connection point Si and the second node N2' being connected to the third connection point S2.

[0065] Furthermore, as with circuit 11 illustrated in [Fig. 2], said circuit 1T comprises: - a capacitive element Ci, said capacitive element Ci is advantageously a capacitor, also referred to as the first capacitor; - a voltage clipping element D1, for example a bidirectional Transil type diode; - at least one switch T1 configured to close during a current peak, said switch T1 advantageously being a transistor, for example a MOSFET type transistor; - two electrodes located B1 and B2 at a predetermined distance from each other, each electrode being connected to one of said second and third connection points Si and S2.

[0066] The capacitive element Ci and the voltage clipping element D1 are, on the one hand, mounted in parallel with each other and, on the other hand, each connected to the second and third connection points Si and S2 and to the first connection point E1. The electrodes B1 and B2 are also advantageously mounted in parallel with the capacitive element Ci and the voltage clipping element D1.

[0067] However, unlike circuit 11 of [Fig. 2], said circuit 11' consists of two sets 13' which each include at least one transistor T1 acting as a switch, a resistor Ri and a capacitor C2, called the second capacitor, mounted to form a series RC circuit, said RC circuit being configured to control the state of said associated transistor Ti, i.e. to allow or not the passage of a current through the transistor Ti.

[0068] Furthermore, the transistor Ti in each of the 13' assemblies comprises a gate, a source, and a drain. The drain of each of the transistors T1 is connected to the second and third connection points Si and S2 (or nodes N2' and Ni'), respectively, while the gate of said transistor T1 is connected to a node N3', called the third node, located between the resistor Ri and the second capacitor C2 of the RC circuit. Moreover, the source of each of the transistors T1 in the 13' assemblies is connected to the first connection point E1.

[0069] It should also be noted that, by design, MOSFET transistors advantageously incorporate a diode, "connected in reverse," between the drain and source of the transistor. This has the advantage of avoiding the need to add a diode to limit current flow in an undesired direction in circuit 11' and assemblies 13'.

[0070] Each of the said sets 13' is connected on one side to one of the nodes Ni' or N2', and on the other side, to the input E1, the presence of the two sets 13' allows to manage indifferently the fact that the first node Ni' and the second node N2' are connected indifferently to the power conductor 8b and to the measurement conductor 8a of the probe 9a or 9b (the current flow being different in one case compared to the other).

[0071] The said 1T circuit thus exhibits axial (or mirror) symmetry; axial symmetry is understood to be a functional symmetry, the components forming the said 1T circuit being able to be arranged in any way in space.

[0072] Thus, functionally speaking, and regardless of the connection of said second and third connection points Si and S2 to the power conductors 8b and measurement conductor 8a of the probe 9a or 9b, the first capacitor Ci, the bidirectional Transil diode D1 and the electrodes B1 and B2 have the same functions as those described in the first embodiment of the circuit according to the invention.

[0073] While only the 13' assembly connected to the node or connection point linked to the power conductor 8b and measurement conductor 8a is configured to handle overvoltage, notably by closing transistor T1.

[0074] In an alternative embodiment of the invention, not shown, the switch in the control circuit according to the invention is a triac. It should be noted that when the switch is a triac, it remains closed (or conducting) as long as the current in the power conductor is not zero.

Claims

Demands [Claims 1] [Arc control circuit (11; 1T) for a four-wire electronic and / or electrical measuring device (1), said circuit (11; 11') comprising a connection point (Ei), referred to as the first connection point, configured to be connected to a voltage and / or current generator and at least two connection points (Si, S2), referred to respectively as the second and third connection points, configured to be connected to an intermittent electrical contact element (9a, 9b), characterized in that said circuit (11; 1T) comprises at least: - a capacitive element (Ci); - a voltage clipping element (D1); - a switch (T1) configured to close during a voltage spike; said capacitive element (Ci), the voltage clipping element (D1) and the switch (T1) being, on the one hand, mounted in parallel with each other and, on the other hand, connected to each of said connection points (E1, Si, S2). [Claims 2] Circuit (11; 1T) according to the preceding claim, characterized in that said voltage clipping element (D1) is a Transil type diode (D1). [Claims 3] Circuit (11; 11') according to any one of the preceding claims, characterized in that said circuit (11; 11') comprises two electrodes (B1, B2) located at a predetermined distance from each other, each electrode being connected to one of said second and third connection points (Si, S2). [Claims 4] Circuit (11; 1T) according to any one of the preceding claims, characterized in that said capacitive element (Ci) is a capacitor, said capacitor (Ci) having a capacitance which is a function of the reaction time of said voltage clipping element (D1). [Claims 5] Circuit (11; 11') according to any one of the preceding claims, characterized in that said switch (T 1) is a transistor, for example a MOSFET type transistor. [Claims 6] Circuit (11; 1T) according to the preceding claim, characterized in that said circuit (11; 11') comprises a resistor (Ri) and a capacitor (C2) mounted to form a series RC circuit, said RC circuit being configured to control the state of said transistor (T1). [Claims 7] Circuit (11; 1T) according to the preceding claim, characterized in that said RC circuit has a time constant T of at least 1 millisecond, and preferably less than 10 milliseconds. [Claims 8] Circuit (11; 1T) according to any one of claims 6 or 7, characterized in that the transistor (Ti) comprises a gate, a source and a drain, the capacitor (C2) of the RC assembly having a capacitance value at least 10 times greater than the capacitance value of the gate of said transistor (T1). [Claims 9] Circuit (1T) according to any one of claims 6 to 8, characterized in that said circuit (1T) comprises two assemblies (13') each comprising a transistor (T1) and an RC circuit configured to control the state of said transistor (T1), each of said assemblies (13') being mounted in parallel with each other with respect to said voltage clipping element (D1). [Claims 10] Circuit (11') according to the preceding claim, characterized in that said circuit (11') has axial symmetry. [Claims 11] Four-wire electrical and / or electronic measuring device (1), characterized in that said device (1) comprises at least one arc control circuit (11; 1T) according to any one of the preceding claims.

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