DEVICE FOR MEASURING THE ELECTRICAL RESISTANCE OF AN ELEMENT

Abstract

The present invention relates to a device (1) for measuring the resistance of an element (2) comprising: - a digital control circuit (5) configured to control the value of a measurement current (IR) to be injected into the element to be tested (2) and to determine the resistance value of the element tested (2); - a digital-to-analog conversion stage (8); - an analog measurement circuit (7) comprising: • means for generating the measurement current (IR) from a digital setpoint (Cm) from the control circuit (5); • means for measuring an analog value of the voltage (VR) generated by the measurement current (IR);the means for generating a measurement current (IR) comprising a circuit for selecting a reference electrical resistance (RSH) value comprising several reference resistances (RSH1 RSH2), and at least one switch (S1, S2, S3) configured to isolate, connect in series, and / or connect in parallel one or more of said reference resistances (RSH1 RSH2) so as to select a measurement current (IR) intended to flow through the element (2) to be tested. Fig. 5;

Description

Title of the invention: DEVICE FOR MEASURING THE ELECTRICAL RESISTANCE OF AN ELEMENT

[0001] The present invention relates to the field of electrical resistivity measurement devices of an element.

[0002] For example, during the assembly of an aircraft, such as an airplane, helicopter, drone, etc., or later during maintenance, operators must verify that the parts are properly assembled (or fixed) to each other. These checks can be carried out, in particular, by measuring the resistance values ​​between elements (or parts of an element).

[0003] 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 the elements of an aircraft advantageously exhibit a low resistance value to limit the damage caused when the aircraft is struck by lightning.

[0004] It should be noted that this type of measurement also makes it possible to control metallizations of parts, the quality of a weld, etc.

[0005] Generally, measuring a resistance value involves applying a predetermined voltage or current to the element whose resistance is to be measured. Then, the resulting current or voltage value is measured, respectively, the relationship between voltage and current being, as stated in Ohm's law, the resistance value of the element under test.

[0006] It is thus seen that, on the one hand, the value of the voltage or current imposed on the element must be known as accurately as possible, and on the other hand, that the measured value of the resulting current or voltage must also be measured as accurately as possible, in order of course to determine the most accurate possible resistance value relative to the tested element.

[0007] Current electrical conductivity measurement devices are not suitable for testing with good accuracy elements exhibiting resistances of very different orders of magnitude, ranging for example from a few milliohms to a few tens of ohms.

[0008] Furthermore, the power supply to such measuring devices may deliver voltage or current values ​​exhibiting variations or drifts, particularly as a function of wear on electronic components, temperature, or other environmental or intrinsic parameters. These uncontrolled variations may impair the accuracy of the electrical resistance measurement.

[0009] Indeed, since the intensity of the injected current is different from that expected, the calculated resistance value is incorrect.

[0010] Such measurement errors are problematic because an erroneous resistance value can be assumed by the device user or operator to be either a fault in electrical continuity of the conductive network, which can lead to unnecessary maintenance operations, or a correct continuity measurement when this is not the case.

[0011] Thus, the present invention aims to partially remedy at least one of the drawbacks mentioned above by proposing a new type of device for measuring the resistance of an element, in particular an aircraft structural element. According to the invention, said device comprises: - a digital control circuit configured to, on the one hand, control the value of a measurement current to be injected into the element to be tested, and on the other hand, determine, from the voltage value generated by the measurement current (IR), the resistance value of the element being tested; - a digital-to-analog conversion stage configured to convert a digital signal into an analog signal and vice versa; - an analog measurement circuit connected to said control circuit via said converters and comprising: • means of generating the measurement current from a digital setpoint from the control circuit; • means of measuring an analog value of the voltage generated by the measurement current; the means for generating a measurement current being configured to convert a voltage value at the output of the digital-to-analog conversion stage into a measurement current, and include a circuit for selecting a reference electrical resistance value, said selection circuit comprising several reference resistances, and at least one switch configured to isolate, connect in series, and / or connect in parallel one or more of said reference resistances so as to select a measurement current intended to flow through the element to be tested.

[0012] Advantageously, having several reference resistances allows, in particular, several "current ranges" for testing elements with resistances of very different orders of magnitude, thus allowing good accuracy to be maintained for different orders of magnitude of resistance value, whether it be resistance values ​​on the order of milliohms to a few tens of ohms.

[0013] It should be noted that the term "analog signal" refers to physical quantities (voltage, current, etc.) that vary continuously. Whereas the term "digital signal" refers to a signal that has a finite number of states (or values) and is therefore quantized.

[0014] Furthermore, it should be noted that "electrical resistance" is understood to be a physical quantity reflecting the ability of a material or at least one element to allow the passage of electric current; this electrical resistance is generally expressed in Ohms. However, the invention also covers the case of an indirect measurement of electrical resistance, such as a measurement of the electrical conductivity (which is the inverse of electrical resistance) of at least one element, a physical quantity generally expressed in Siemens.

[0015] According to another possible feature, said device includes a human-machine interface.

[0016] It should be noted that the term human-machine interface refers to all the elements enabling the user to interact with the device according to the invention, more particularly to control the device according to the invention and to exchange information with said device. The human-machine interface includes, for example, at least one display means, such as a touchscreen or non-touchscreen, buttons, a keyboard, etc.

[0017] According to one possible feature, the means for generating a measurement current include a circuit for selecting a test resistance of known value and at least one switch configured to isolate said test resistance so as to verify the value of the injected test current for this known value of electrical resistance.

[0018] According to one possible feature, the digital control circuit is configured to compare the voltage value generated by the measurement current across the test resistor to a known reference value, and to detect and calculate a drift in the injected test current when the calculated difference is greater than a predetermined threshold.

[0019] According to one possible feature, the human-machine interface includes a means for selecting the test resistance corresponding to a self-test function.

[0020] According to one possible feature, the control circuit is configured to take into account the drift of the current calculated to deduce the electrical resistance value of a tested element.

[0021] According to one possible feature, the measuring device includes a reference voltage source connected to said digital-to-analog conversion stage, said digital-to-analog conversion stage being configured to use the voltage value generated by said reference source for the conversion: - of digital signals, such as the digital setpoint that controls the generation of a measurement current by said analog measurement circuit, originating from the circuit digital control in analog signals destined for the analog measurement circuit, and - of analog signals, such as the voltage value measured across the terminals of the element being tested, from the measurement circuit into digital signals destined for the digital control circuit.

[0022] According to one possible feature, said conversion stage comprises two separate signal converters: - a first converter of the digital-to-analog type; - a second analog-to-digital type converter; said reference voltage source being connected to each of said converters.

[0023] It should also be noted that: - An analog-to-digital converter is an electronic device or component whose function is to transform an analog quantity into a digital value coded on several bits, the converted signal generally being an electrical voltage; - A digital-to-analog converter is an electronic device or component whose function is to transform a digital value (coded on several bits) into an analog quantity, for example a voltage, proportional to the coded digital value.

[0024] The reference voltage source is advantageously connected directly to each of said converters, in order to limit the variations in the voltage generated by said source, particularly at the level of the converter inputs.

[0025] According to another possible feature, the analog circuit includes a current generator assembly configured to convert a voltage value at the output of the digital-to-analog converter into a measurement current.

[0026] According to another possible feature, said device includes a stage for amplifying the voltage measured across the terminals of the element tested (voltage generated by the measurement current).

[0027] According to another possible feature, said amplification stage is an instrumentation amplifier assembly. It should be noted that an instrumentation amplifier circuit is an electronic component (or circuit) designed to process weak electrical signals, particularly those from measurement sensors. Furthermore, the instrumentation amplifier circuit largely eliminates common-mode errors.

[0028] According to another possible feature, the amplification stage comprises a plurality of operational amplifiers and a plurality of resistors.

[0029] According to another possible feature, said device includes a filtering stage configured to filter the analog signal intended to be converted by the analog-to-digital converter.

[0030] According to another possible feature, the control circuit is configured to send a current setpoint in the form of a digital setpoint. This digital setpoint actually encodes a voltage value at the output of the analog-to-digital converter, which is transformed into an IR measurement current.

[0031] According to another possible characteristic, the current setpoint voltage at the output of the digital-to-analog converter is a function of the reference voltage Vref, the number of bits ni of the converter, the values ​​of the bits an, and a coefficient k.

[0032] According to another possible feature, the current setpoint voltage is sent to the input of the current generator assembly to generate an IR measurement current.

[0033] According to another possible characteristic, the input voltage of the analog-to-digital converter generates at the output a digital signal Lu ext is a function of the reference voltage Vref, of the number of bits n2 of the converter.

[0034] According to another possible feature, said device includes a Kelvin electrical connection, an electrical connection also referred to as a "four-wire connection".

[0035] A Kelvin connection is a means of establishing electrical contact with a component while eliminating or significantly reducing the effect of parasitic resistances related to the connection itself, such as contact resistance and / or conductor resistance. This is particularly critical when measuring electrical quantities that need to be measured as precisely as possible, for example, small resistance values, especially those less than 1 Ohm.

[0036] According to another possible feature, the control circuit and the measurement circuit are arranged on two separate electronic boards. Having two separate cards helps to reduce noise on the measurement circuit.

[0037] According to another possible feature, said device includes an alerting means, for example configured to indicate to the operator (or user) the injection of an IR measuring current, the end of the measurement and / or the determination (and display via the human-machine interface) of the electrical resistance value of a tested element, that said measurement is correct, etc. Said alerting means is, for example, an audible and / or visual indicator.

[0038] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of a particular embodiment of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings, in which: - Fig. 1, referenced as Fig. 1, illustrates a very schematic representation of a resistance measurement device according to the invention; - the [Fig.2], referenced [Fig.2], is a very schematic and enlarged view of the part of the device dedicated to measuring the [Fig.1]; - [Fig.3], referenced [Fig.3], is a very schematic and detailed view of the part of the device illustrated in [Fig.2]; - the [Fig.4], referenced [Fig.4], is a block diagram illustrating the conversion of electrical signals carried out in the device of the [Fig.1];

[0039] - [Fig. 5], referenced [Fig. 5], is a block diagram partially illustrating the circuit generating a measurement current from the device of [Fig.1] according to a particular embodiment;

[0040] - [Fig.6], referenced [Fig.6], is a block diagram partially illustrating the circuit of generation of a measurement current of the device of [Fig.1] according to another particular embodiment;

[0041] - [Fig.7], referenced [Fig.7], is a block diagram illustrating an example of a circuit self-test of the device in [Fig.1] to detect any drift in the injected test current.

[0042] Fig. 1 is a very schematic representation of a device 1 according to the invention intended to measure the electrical resistance value of at least one element 2, such as structural elements of an aircraft.

[0043] The measuring device 1 is capable of determining the electrical resistance of the element 2 tested from the value of an injected current called a measurement current in the element 2 tested and the voltage measured across the terminals of the element 2 tested.

[0044] 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 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 1 Ohm, down to values ​​on the order of milliohms) with an accuracy of at least 1%.

[0045] It should be noted that electrical resistance is understood to mean the electrical resistivity value of an element, that is to say, 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 the element 2 or perform an indirect measurement, that is to say by measuring a physical quantity proportional or inverse to the electrical resistance, such as electrical conductivity, to ultimately determine an electrical resistance value.

[0046] Said device 1 thus comprises a housing 100, for example made of plastic, in which are housed: - a power supply source 3 which is for example a reference voltage source; - electronic control circuits 5 and measurement circuits 7, advantageously two separate electronic boards; - a digital-to-analog conversion stage 8 linking the control circuit 5 to the measurement circuit 7 and which is configured to convert a digital signal into an analog signal and vice versa; - an electrical connection 9 intended to connect the device 1, in particular the measuring circuit 7, to the element 2 whose electrical resistance value we seek to determine.

[0047] The electrical connection 9 is advantageously a Kelvin or 4-wire connection. Thus, said Kelvin connection 9 comprises four electrical conductors 11a, 11b, 13a, 13b, generally terminated by clips or prongs intended to connect to or be applied to the element(s) 2 whose electrical resistance is to be determined. More particularly, the Kelvin connection 3 comprises two power conductors 11a, 11b and two measuring conductors 13a, 13b.

[0048] The power conductors 1a and 11b, more particularly visible in [Fig.2], are thus configured to inject an IR electric current, called "measurement current", into the element 2 being tested, while the measurement conductors 13a and 13b are configured to allow the measurement of a voltage across the terminals of the element 2.

[0049] In the present case, the Kelvin connection 9 allows the VR voltage generated by the IR measurement current to be measured by limiting, or even canceling, the effects of the resistances related to the contact resistances and / or the conductors of said connection 9.

[0050] Furthermore, said device 1 advantageously includes a human-machine interface (not shown). The human-machine interface corresponds to all the elements enabling the user to interact with the device 1 according to the invention, more particularly to control the device 1 and / or to exchange information with said device 1. Thus, the human-machine interface includes, for example, at least one display means, such as a touch screen or not, buttons, a keyboard, etc.

[0051] More specifically, said device 1 comprises two electronic circuits 5 and 7 which are: - a control circuit 5 which is, on the one hand, a digital circuit, and on the other hand, configured to control the value of an IR measurement current to be injected into element 2; - a measurement circuit 7 which is an analog circuit, connected to said control circuit 5, and which is configured, on the one hand, to generate a measurement current IR according to a digital setpoint from said control circuit 5, and on the other hand, to measure an analog value of the voltage VR generated by the measurement current IR. It should also be noted that the control circuit 5 is connected to the human-machine interface and also has the function of managing said interface.

[0052] It should also be noted that the control circuit 5 is an electronic entity, comprising for example one or more components, such as microcontrollers, and which is notably configured to send and receive signals, process data, store data, etc.

[0053] The conversion stage 8 is, for its part, configured to use the voltage value generated by said power supply 3 for the conversion of: - digital signals (in particular the digital setpoint which will give rise to the creation of a measurement current IR by the measurement circuit 7) from the control circuit 5 into analog signals for the measurement circuit 7, and - analog signals (in particular a voltage value VR measured across the terminals of the tested element 2) from the measurement circuit 7 into digital signals for the control circuit 5.

[0054] Thus, during a test of an element 2, the control circuit 5 sends a digital setpoint Cm (which is a digital signal) which is converted into an analog signal by the conversion stage 8 to be transformed by the measurement circuit 7 into a measurement current IR which is injected through the electrical connection 9 to the element 2 (in particular via the power conductors 1la and 11b).

[0055] The flow of a measurement current IR in the element 2 causes the creation of a voltage VR across the terminals of said element 2. The value of the voltage VR is measured via the electrical connection 9, in particular by means of the measurement conductors 13a and 13b.

[0056] The value of the voltage VR is an analog signal which is processed (for example filtered and / or amplified) by the measuring circuit 7, in order to be converted into a digital signal by the conversion stage 8 for the control circuit 5.

[0057] Therefore, the control circuit 5 is configured to command a measurement current value IR to be injected into element 2 and to retrieve a voltage value VR (in digital form), in order to determine the electrical resistance value of said element 2 from said IR and VR values ​​in their digital forms. The stage of conversion 8 thus converts the digital and analog signals flowing between said circuits 5 and 7.

[0058] The control circuit 5 is therefore configured to send a current setpoint in the form of a voltage-coded digital signal, which is then converted into an electrical current value. The current setpoint voltage Vc at the output of the digital-to-analog converter is a function of the reference voltage Vref, the number of bits ni of the converter, the values ​​of the bits an, and a coefficient k.

[0059] Fig. 2 is a schematic and enlarged view of a part of device 1 of Fig. 1, and more particularly of the power supply 3 serving as the reference voltage source Vref, the conversion stage 8 and the measurement circuit 7.

[0060] The conversion stage 8 comprises a digital-to-analog converter 11 and an analog-to-digital converter 13, each of them connecting the control circuit 5 to the measurement circuit 7. The transmission of analog signals and digital signals between said circuits 5 and 7 is carried out respectively through said converters 11 and 13.

[0061] It should be noted that an analog-to-digital converter is an electronic device or component whose function is to transform an analog quantity into a digital value coded on several bits (the converted signal generally being an electrical voltage).

[0062] It should also be noted that a digital-to-analog converter is an electronic device or component whose function is to transform a digital value (coded on several bits) into an analog quantity, for example a voltage, proportional to the coded digital value.

[0063] Said reference voltage source 3 is, for its part, connected (preferably directly) to each of said converters 11 and 13 to serve as the sole reference during the conversion of digital signals into analog signals and vice versa, during signal exchanges between said circuits 5 and 7.

[0064] Having a single and identical reference voltage source for converting the different signals from the control circuit and the measurement circuit helps to limit the risks of error related to these conversions and therefore to improve the accuracy with which the electrical resistance value of the tested element is determined.

[0065] The measuring circuit 7 further comprises: - a current generator assembly 17 configured to generate an IR measurement current intended to flow through the element 2 being tested; - an analog signal amplification stage 19, such as the voltage measured across element 2 (voltage generated by the measurement current IR).

[0066] Furthermore, the digital-to-analog converter 11 connects the control circuit 5 to the current generator assembly 17 of the measuring circuit 7, while the analog-to-digital converter 13 connects the amplification stage 19 to the control circuit 5.

[0067] More particularly, the control circuit 5 is configured to send a digital setpoint Cm, therefore a digital signal which encodes a voltage value, which will be converted into an analog signal corresponding to a voltage value at the output Vc of the digital-to-analog converter, the assembly 17 being configured to convert (or transform) this voltage value at the output Vc of the converter 11 into a measurement current IR.

[0068] Fig. 3, on the other hand, is a schematic and more detailed view of the measuring circuit 7 of Fig. 2.

[0069] As illustrated in more detail therein, the current generator circuit 17 comprises a circuit for selecting a reference resistance value RSH (and therefore a measurement current IR), which will be described in relation to [Fig. 5], a first and a second operational amplifier AO1 and AO2 respectively, as well as a transistor T1

[0070] The assembly of said operational amplifiers respectively AOi and AO2, the transistor TH and the circuit for selecting a reference resistance value RSH forms a circuit of the voltage-current converter type.

[0071] More specifically, the output of the first converter 11 (digital-to-analog converter) is connected to the non-inverting input of the first operational amplifier AOp, while the output of the first operational amplifier AOi is connected to the transistor Ti.

[0072] The transistor Ti is, for example, a MOSFET-type transistor whose gate is directly connected to the output of the operational amplifier AOi, while its source is directly connected to the non-inverting input of the second operational amplifier AO2 and to one of the terminals of the reference resistance selection circuit RSH, the other terminal of the reference resistance selection circuit RSH being connected to the inverting input of the second operational amplifier AO2 and to the power conductor 1 of the electrical connection 9. The inverting and non-inverting inputs of the second operational amplifier AO2 are thus connected to the terminals of the reference resistance selection circuit Rsh. The transistor Ti therefore regulates the value of the measurement current IR as a function of the voltage value Vc, the gain of the second operational amplifier AO2, and the selected value of the resistance RSH.

[0073] Furthermore, the output of the second amplifier AO2 is connected to the input of the first operational amplifier AOi. Thus, the voltage Vc at the output of the first converter 11 is compared to the voltage across the terminals of the selection circuit for a reference resistance value RSH, to which a gain is applied by the second operational amplifier AO2.

[0074] More particularly, said amplification stage 19 includes an instrumentation amplifier assembly 21, as well as a filtering stage 23 configured to filter an analog signal (in particular noise) intended to be converted by the analog-to-digital converter, such as the value of the voltage VR across the terminals of element 2.

[0075] The instrumentation amplifier assembly thus comprises a plurality of operational amplifiers AO3, AO4 and AO5, as well as a plurality of resistors Ri, R2 and R3, respectively first Rh second R2 and third R3 resistance.

[0076] More particularly, the measuring conductors 13a and 13b are respectively connected to the non-inverting inputs of the third and fourth operational amplifiers AO3 and AO4, so a voltage difference VR across the terminals of the tested element 2 is applied to the non-inverting inputs of said operational amplifiers AO3 and AO4.

[0077] The first, second and third resistors RB R2 and R3 are, for their part, arranged in series, the terminals of this plurality of resistors being connected to the respective outputs of the said third and fourth operational amplifiers AO3 and AO4.

[0078] One of the terminals of the first resistor Ri is therefore connected to the output of the fourth amplifier AO4, while the other terminal is connected to both the second resistor R2, but also to the inverting input of the fourth amplifier AO4.

[0079] Furthermore, one terminal of the third resistor R3 is therefore connected to the output of the third amplifier AO3, while the other terminal is connected to both the second resistor R2 and the inverting input of the third amplifier AO3. The terminals of the second resistor R2 are connected respectively to each of the inverting inputs of the third and fourth operational amplifiers AO3 and AO4 and to the outputs of the third and fourth operational amplifiers AO3 and AO4, respectively, via the first and third Riet resistors R3.

[0080] In addition, the outputs of the third and fourth operational amplifiers AO3 and AO4 are connected respectively to the inverting and non-inverting inputs of the fifth operational amplifier AO5, said fifth amplifier AO5 performing a subtraction between the output signals from the third and fourth operational amplifiers AO3 and AO4.

[0081] The output of the fifth operational amplifier AO5 is connected to the input of the filtering stage 23. Thus, at the output of the filtering stage 23, the measured voltage VR is therefore amplified then filtered, and sent to the input of the analog-to-digital converter 13. The amplification stage 19 allows, for example, the input signal to be amplified by a factor of 1000.

[0082] The gain of the fifth operational amplifier AO5 is substantially equal to 1, but can be modified by changing the values ​​of the first, second, and third resistors Rb, R2, and R3, for example, by adding resistors that can be arranged in series and / or parallel with said resistors Ri, R2, and R3 via one or more switches. The presence of additional resistors and switches allows, for example, the gain of said fifth operational amplifier AO5 to be varied by a factor of 1000, 100, and / or 10.

[0083] It will be noted that said device 1 may include an alerting means (not shown), for example at the control circuit 5, configured to indicate to the operator the injection of an IR measurement current, the end of the measurement and / or the determination (and display via the human-machine interface) of the electrical resistance value of a tested element.

[0084] Said alerting means is, for example, an audible, haptic and / or visual indicator. Said alerting means can also be configured to indicate that the measurement has been carried out and / or that it is correct or not, in particular with respect to one or more predetermined values ​​of electrical resistance.

[0085] Advantageously, said current generator assembly 17 includes a circuit for selecting a reference resistance value, and therefore a measurement current IR, in which several reference resistances are implemented, as well as switches configured to isolate, connect in series, and / or connect in parallel one or more of said reference resistances.

[0086] In the particular embodiment illustrated in [Fig.5], said current generator assembly selection circuit 17 comprises two reference resistors RSHi and RSH2 and three switches Sb S2 and S3. One of the terminals (called first terminal) of the resistor RSHi is connected to the source of the transistor Ti and, via the first switchsi, to the non-inverting input of the second operational amplifier AO2.

[0087] The other terminal (called the second terminal) of resistor RSHi is connected to the inverting input of the second operational amplifier AO2 via the second switch S2. The second terminal of resistor RSHi is connected to the first terminal of resistor RSH2, the latter being connected to the non-inverting input of the second operational amplifier AO2 via the first switch B. The other terminal (second terminal) of resistor RSH2 is connected to the inverting input of the second operational amplifier AO2 is connected via the second switch S2 to the power conductor 1 of electrical connection 9. A third switch S3 connects the two terminals of resistor RSH2-

[0088] Depending on the position of the three switches Si, S2 and S3, it is possible to vary the value of the reference resistance RSH across the inverting and non-inverting inputs of the second operational amplifier AO2, and thus to calibrate the measuring device 1 differently depending on the resistance to be measured in element 2. The value of the reference resistance RSH across the inverting and non-inverting inputs of the second operational amplifier AO2 is equal to: - Rsm when switches Si and S2 are each in a first position (corresponding to that of [Fig. 5]) and connected respectively to the first and second terminals of the resistance RSHi, with switch S3 open, - the sum of the resistances RsHi and RSH2 when switch S3 is closed, with switch Si in the first position (and therefore connected to the first terminal of resistance RSHi) and switch S2 in a second position (and therefore connected to the second terminal of resistance Rsœ), - RSH21 when switch S3 is closed, switch S1 is in a second position (and therefore connected to the second terminal of resistor RS1 and the first terminal of resistor Rs1) and switch S2 is in the second position (and therefore connected to the second terminal of resistor RSH2)-

[0089] This circuit thus makes it possible to isolate or put in series the resistances RSHietRsH2, and to vary the value of the reference resistance RSHaux terminals of the inverting and non-inverting inputs of the second operational amplifier AO2.

[0090] In the other particular embodiment illustrated in [Fig. 6], said current generator assembly selection circuit 17 comprises two reference resistors RS1 and RS2 and two switches S1 and S2. One of the terminals (the first terminal) of resistor RS1 is connected to the non-inverting input of the second operational amplifier AO2, and one of the terminals (the first terminal) of resistor RS2 is connected to the same non-inverting input of the second operational amplifier AO2. These two terminals are also connected to the source of transistor Th. The other terminal (the second terminal) of resistor RS1 is connected to the inverting input of the second operational amplifier AO2 via the first switch S1.The other terminal (the second terminal) of the resistor RSH2 is connected to the inverting input of the second operational amplifier AO2 via the second switch S2. The second terminal of the resistor RSHi is connected to the power conductor 1 of the electrical connection 9.

[0091] Depending on the position of the three switches Sb S2 and S3, it is possible to vary the value of the reference resistance RSH across the inverting and non-inverting inputs of the second operational amplifier AO2, and thus to calibrate the measuring device 1 differently depending on the resistance to be measured of element 2. The value of the reference resistance RSH across the inverting and non-inverting inputs of the second operational amplifier AO2 is equal to: - Rsml when switch S2 is open and switch Si is closed, - the equivalent resistance of RSH in parallel with Rsml when switch S2 is closed and switch Si is closed, - Rsml when switch S2 is closed and switch Si is open.

[0092] This circuit thus makes it possible to isolate or put in parallel the resistances RSHietRSH2 and to vary the value of the reference resistance RSHaux terminals of the inverting and non-inverting inputs of the second operational amplifier AO2.

[0093] The user can therefore calibrate the measuring device 1 differently according to the approximate value of the resistance to be measured via the human-machine interface.

[0094] The measuring device 1 is suitable for measuring low value resistances with good accuracy, for example less than or equal to 60 Ohms, preferably a few Ohms, and preferably even less than 1 Ohm, in particular the measurement of resistance values ​​on the order of milliohms, with an accuracy of at least 1%.

[0095] The [Fig.4] is a block diagram of the signal processing carried out during the test of an element 2 by the device 1 according to the invention.

[0096] The operator thus connects terminal 9 to the element 2 to be tested and initiates the test to determine the resistance value of element 2. The control circuit 5 generates a digital setpoint Cm which corresponds to a measurement current value related to the order of magnitude of the resistance value sought. To do this, the user calibrates the measuring device 1 according to the approximate value of the resistance to be measured via the human-machine interface.

[0097] The digital setpoint Cm is therefore then converted into a current setpoint voltage Vc at the output of the digital-analog converter 11, said voltage Vc being among other things a function of the reference voltage Vref, the number of bits ni of the converter 11, the values ​​of the bits an, and a coefficient k.

[0098] This current setpoint voltage Vc is then transformed, by the current generator assembly 17, into a measurement current IR, said measurement current IR being among other things a function of the selected value of resistance RSH, of the gain of the operational amplifier AO2.

[0099] The measurement current IR thus generated is injected into element 2, and generates a voltage VR across the terminals of element 2. This voltage VR is amplified and filtered by the amplification stage 19 to generate a voltage VR'.

[0100] This voltage VR' is the input voltage of the analog-to-digital converter 13 and generates at the output of said converter a digital signal L(: ext, said digital signal L(: ext being a function of the reference voltage Vref, of the number of bits n2 of the converter.

[0101] According to one possible embodiment, said measuring device 1 includes a self-test function for verifying the value of the injected test current. It may be necessary to take into account drifts resulting from the electronic components of the device 1 and / or environmental parameters and material wear. To this end, as illustrated in the example in [Fig. 7], said current generator assembly 17 includes a precision test resistor RSH 3 and is configured to be able to self-test this RSH idc resistance (a known value) to detect any drift in the injected test current and evaluate it based on the voltage measured across this test resistor RSH 3.

[0102] The value of the voltage measured across this test resistor RSH3 corresponds to an analog signal intended to be converted by said analog-to-digital converter 11 for the control circuit 5. The latter is configured to compare the converted value to a known reference value, and to detect and evaluate a drift in the injected test current when the calculated difference is greater than a predetermined threshold.

[0103] In the illustrated position of switches S4, S5, S6 and S7, the value of the electrical resistance across the inverting and non-inverting inputs of the second operational amplifier AO2 is equal to the value of the resistance RSH-

[0104] This RSH resistance value can be selected by means of a circuit such as that described in relation to [Fig.5] or [Fig.6], in which several resistors are implemented, as well as switches configured to isolate, connect in series, and / or connect in parallel one or more of said resistors.

[0105] In the other position illustrated by dotted lines of switches S4, S5, S6 and S7, the value of the electrical resistance across the inverting and non-inverting inputs of the second operational amplifier AO2 is equal to RSH 3, which corresponds to the self-test configuration.

[0106] The user can therefore self-test the measuring device 1 via the human-machine interface.

[0107] Testing a precision resistor of known value makes it possible to take into account drifts resulting from wear of electronic components and / or parameters environmental factors, with the control circuit configured to take these deviations into account to deduce the electrical resistance value of a tested element.

Claims

1. Claims Device (1) for measuring the resistance of an element (2), in particular an aircraft structural element, said device (1) comprising: - a digital control circuit (5) configured to, on the one hand, control the value of a measurement current (IR) to be injected into the element to be tested (2), and on the other hand, determine, from the voltage value (VR) generated by the measurement current (IR), the resistance value of the element tested (2); - a digital-to-analog conversion stage (8) configured to convert a digital signal into an analog signal and vice versa; - an analog measuring circuit (7) connected to said control circuit (5) via said converters and comprising: • means for generating the measurement current (IR) from a digital setpoint (Cm) from the control circuit (5); • means for measuring an analog value of the voltage (VR) generated by the measurement current (IR); the means for generating a measurement current (IR) being configured to convert a voltage value (Vc) at the output of the digital-analog conversion stage (8) into a measurement current (IR), and comprise a circuit for selecting a reference electrical resistance value (RSh), said selection circuit comprising several reference resistors (RSHi Rsœ), and at least one switch (Si, S2, S3) configured to isolate, put in series, and / or put in parallel one or more of said reference resistors (RSHi Rsœ) so as to select a measurement current (IR) intended to flow through the element (2) to be tested, characterized in that it comprises a reference voltage source (3) connected to said digital-analog conversion stage (8), said digital-analog conversion stage (8) being configured to use the voltage value (Vref) generated by said reference source (3) for the conversion: - digital signals (Cm), such as the digital setpoint (Cm) which controls the generation of a measurement current (IR) by said analog measurement circuit (7), from the digital control circuit (5) in analog signals (Vc) intended for the analog measurement circuit (7), and - analog signals, such as the voltage value (VR) measured at the terminals of the element under test (2), from the measuring circuit (7) into digital signals (LUext) intended for the digital control circuit (5).

2. Device (1) according to claim 1, characterized in that it comprises a human-machine interface comprising means for selecting a reference resistance value (RSH)-

3. Device (1) according to claim 1 or 2, characterized in that the means for generating a measurement current (IR) comprise a circuit for selecting a test resistor (Rsœ) of known value and at least one switch (S4, S5, S6, S7) configured to isolate said test resistor (Rsœ) so as to verify the value of the test current injected for this known value of electrical resistance.

4. Device (1) according to claim 3, characterized in that the digital control circuit (5) is configured to compare the voltage value (VR) generated by the measurement current (IR) at the terminals of the test resistor (Rsœ) with a known reference value, and to detect and calculate a drift of the injected test current when the calculated difference is greater than a predetermined threshold.

5. Device (1) according to claims 2 and 4, characterized in that the human-machine interface comprises means for selecting the test resistance (RSH3) corresponding to a self-test function.

6. Device (1) according to claim 4 or 5, characterized in that the control circuit (5) is configured to take into account the drift of the calculated current to deduce the electrical resistance value of a tested element (2).

7. Device (1) according to any one of the preceding claims, characterized in that the analog measurement circuit (7) comprises a current generator assembly (17) configured to convert a voltage value (Vc) at the output of the digital-analog converter (11) into a measurement current (IR).

8. Device (1) according to any one of the preceding claims, characterized in that there is a stage for amplifying the measured voltage (19) generated by the measuring current (IR).

9. Device (1) according to any one of the preceding claims, characterized in that the control circuit (5) is configured to send a current instruction in the form of a digital signal (Cm).

10. Device (1) according to the preceding claim, characterized in that the set voltage (Vc) of current at the output of the digital-analog converter (11) is a function of the reference voltage (Vref), the number of bits ni of the converter, the values ​​of the bits an, of a coefficient k.

11. Device (1) according to the preceding claim, characterized in that the current reference voltage (Vc) is sent to the input of the current generator assembly (17) to generate a measurement current (IR).

Images