RU2786033C2 - Control of contact area in plug device - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to determination of electrical contact properties. In a method for determination of electrical contact resistances, in a contact area between the first contact element of the first plug device and the response second contact element of the second plug device, current circuit resistances are assessed. The current circuit contains the first contact element, the contact area, and only the second contact element of the second plug device. Inductive voltage is induced in the current circuit, so that measurements conducted in the specified current circuit allow for conclusion about contact resistances of interest.

EFFECT: speed of determination of problems is increased.

20 cl, 21 dwg

Description

The invention relates to a method for determining the electrical contact properties, in particular the transient contact resistance in the contact zone between two contact elements (contact pin, socket) of a plug device. In addition, it relates to a plug-in device designed to carry out this method.

Electrical plug devices, such as plugs or sockets or couplings for power supply according to DIN VDE 0623, EN 60309-2 (“CEE-plug connectors”) or according to IEC 62196 (“Charger plugs for electric vehicles”) contain metal contact elements ( pins at the plug and socket at the socket), through which electrical contact occurs in the connected state. Due to pollution, oxidation, weakening of contact forces, etc. in the contact zone between these contact elements, electrical resistances can occur, which cannot be neglected. Particularly with power plug-in devices, in which relatively high currents flow during operation, such transient contact resistances can lead to unacceptable power losses. Since the lost power is converted into heat, there is also a risk of dangerous overheating. Therefore, various measures have been proposed in the prior art to control the temperature in the plug device. However, such systems can only react when heating has already occurred and thus a potentially problematic situation has arisen.

From JP 2007285833 a circuit is known for detecting abnormal conditions on a plug contact. In order to be able to measure the voltage drop across the plug-in contact, an additional plug-in contact is provided. Similar devices are also disclosed in CN 206848406 and CN 202008524.

From EP 2944503 A2 a vehicle power interface is known, comprising a power circuit with first and second power contacts. In addition, it contains an auxiliary contact, which is electrically isolated from the first power contact and is also in contact with the second power contact, and a measuring circuit is connected through the auxiliary contact for recording the electrical contact state between the first and second power contacts.

Against this background, the object of the invention is to provide alternative means for determining or monitoring the function of a plug device. They should primarily ensure that problem situations are detected as early as possible.

This problem is solved by means of a method with the features of claim 1 of the formula and a plug device with the features of claim 9 of the formula. Preferred options are contained in the dependent claims.

The proposed method serves to determine the electrical properties of the contact in the contact zone between the contact element of the first plug device (hereinafter also the "first contact element") and the mating contact element (also the "second contact element") of the mating second plug device. The first plug device can have a socket with sockets as the first contact elements, and the second plug device can have a plug with contact pins as the second contact elements, or vice versa, and the plug devices, in addition to the contact elements, as a rule, also contain additional components. (housings, inserts, etc.). The method is characterized in that the properties of at least one current circuit are evaluated, containing:

- the first contact element,

- contact zone and

- from the second plug device only the second mating contact element and, if necessary, other contact elements of the second plug device.

A current circuit forms, by definition, an electrically conductive connection between two terminals through which direct current or at least alternating current can flow or flow. If these conclusions are identical, then an electrical circuit takes place. Otherwise, a closed loop is usually created by connecting the leads to the evaluation circuit.

The ends or terminals of the current circuit are usually located in the first plug device or are its constituent parts, so that the current circuit is completely accessible from the first plug device.

The electrical conductivity of the current circuit can be conductive, i.e. provide a direct current flow (and the value of the ohmic resistance is usually less than about 100 kOhm). Additionally or alternatively, the current circuit may be capacitively conductive, for example when it contains a capacitance in series (and such capacitance is typically greater than about 10 pF, preferably greater than about 100 pF, greater than 1 nF, or greater than 3 nF).

Determination of electrical contact properties can be carried out both qualitatively and quantitatively. A qualitative definition may consist, for example, in stating that the contact properties are suitable or unsuitable for reliable operation. The quantitative determination may refer in particular to determining the value of the contact resistance between the first and second contact elements.

The method has the advantage that, by using the described current circuit, the determination of the contact properties is only possible from the side of the first plug device. Of the second plug device, for the completeness of the current circuit, only the mating second contact element is used (and, if necessary, or in exceptional cases, one or more other contact elements of the second plug device), which is connected to the first contact element in the connection process. Therefore, as a result, no structural changes to the second plug device are required, so that the method is independent of type, age, manufacturer, and the like. used second plug device.

The specific composition of the current circuit used and the measurement principle used may vary. According to the first variant, the used current circuit contains at least one probe, which is located in the first plug device and, in the connected state of both plug devices, contacts the mating second contact element in the additional (other) contact zone. Such a probe is usually absent in a traditional plug device, but is provided exclusively or including for this method. Due to the probe in the connected state, two contact zones are created between the first plug-in device and the mating second contact element. Therefore, the current circuit implemented mainly in the first plug device can comprise a section of the second contact element lying between the two contact zones (and nothing else from the second plug device). The transient contact resistance in the contact area of interest between the contact elements of the plug-in devices is in this current path and is therefore measurable.

In a first modification of the probe embodiment described above, the voltage drop that occurs when the operating current flows through the contact zone of interest is measured through the formed current circuit. The "operating current" then flows, by definition, during the originally intended operation of the plug-in device through the considered contact elements (and usually through at least two additional ones) for driving, for example, a consumer, such as an electric motor, or charging a battery. With plug-in power devices, this operating current lies in the range of one to three digit values in amperes, so that even a relatively low contact contact resistance leads to a noticeable detectable voltage drop. This voltage drop also occurs in the estimated current path formed and forms an indicator for the contact properties in the contact zone of interest. If the magnitude of the operating current underlying the measurement is additionally known, it is possible, in addition to the detected voltage drop, to also calculate the existing contact resistance in the contact zone.

When using a probe, attention should be paid to the fact that in the contact zone between it and the second contact element of the second plug device, as a rule, unknown contact properties also take place, which make it difficult to determine the contact properties in the contact zone of interest. Therefore, if necessary, before the evaluation or the measurement leading to the evaluation, certain contact properties can be created between the probe and the second contact element of the second plug device. There are various possibilities for this. For example, it would be possible to create as well defined, reproducible contact pressure as possible by design means. The higher the contact pressure, the more likely it is that the oxide layer, foreign layers, etc. will be destroyed. However, there are limits to the increase in contact pressure: the force of the plug should only be increased slightly by means of a probe. Additionally or alternatively, an electrical procedure can be used in which, by applying a suitable voltage (hereinafter "breakdown voltage"), any existing insulating layer (of oxides, foreign layers, etc.) is broken through. At the end of this process, also called "point contact", the stress in the transitional contact zone between the contact elements is, as a rule, a maximum of the order of the melting stress of the material of the contact surface. This ensures a certain value, or at least a certain maximum value.

According to another variant, the first plug device comprises two (or more) probes with their own and separate contact area, respectively, to the second contact element. Therefore, three or more current circuits can be evaluated, comprising various combinations of at least three contact zones formed between (a) the second contact element and (b) the first contact element and/or different probes. Therefore, several independent measurements are possible, from which unknown quantities can be determined, such as transient contact resistances.

In another embodiment, an inductive voltage is induced in the current circuit used. This has the advantage that, without mechanical/electrical contact, measurements of the current in said circuit can be made, which allow inferences to be made about the properties of interest of the contact.

In one special modification of the embodiment described above, the current circuit in question forms a secondary winding (usually with a single turn) on a magnetic core, which is located in the first plug device and on which the primary winding is also located. Through the primary winding, the excitation of the system can then be carried out in a controlled manner, which leads to the induction of an inductive voltage in the secondary winding via the magnetic core, i.e. considered current circuit. In this case, the electrical properties of the current circuit depend on the contact properties of interest in the contact zone and are detected, for example, in the form of a reverse action in the primary winding. For example, on the primary winding, the input impedance of the system can be determined, which in a certain way depends on the transient contact resistance in the contact zone of interest.

Additionally or alternatively, the electrical properties of the current circuit can also be detected in the previous case by means of a separate measuring coil located around the current circuit.

The sockets of plug devices are often designed so that they contain two or more contact fingers arranged in parallel around the cylindrical cavity, which are parallel spaced from the common base of the socket. Each of these contact fingers has its own transitional contact zone to the inserted contact pin and can therefore be considered as an independent "first contact element" within the framework of the method described here. However, for the operation of a plug device, as a rule, only the contact resistance formed by all contact fingers together (in parallel connection) with the corresponding contact pin is of interest, so that the contact fingers of the same socket can be considered as the only one within the framework of the method described here. first contact element. The transient contact resistance to this "first contact element" is then formed by connecting the transient contact resistors in parallel with the individual contact pins.

In sockets with several contact fingers, these fingers can be electrically connected to each other at their free ("distal") ends, for example, by means of a spring ring that wraps around the outside, which presses the contact fingers inward. If, on the other hand, two or more contact fingers of the socket outside the common base are electrically separated from each other, then the current circuit in question can be formed so that they are located in series in it. One part of the contact fingers then forms the first section of the current circuit, and the other part of the contact fingers forms the second section, both of these sections being electrically connected, on the one hand, by the inserted contact pin, and, on the other hand, by the common base of the contact fingers. With such a configuration, one part of the contact fingers may be located on one side, for example, and another part of the contact fingers on the other side of the annular magnetic core, so that a secondary winding as a whole is formed in accordance with the above description.

The above considerations also apply in a similar way to the case of a contact pin divided in the longitudinal direction, with parts of this pin playing the role of contact fingers.

In the case of more general forms of contact elements, a magnetic core can also be located, covering the contact zone between the first and second contact elements. In this case, for example, regardless of the protrusion of the contact fingers, it is possible to induce voltage in the considered current circuit.

Depending on the configuration, the described method interacts differently with the operation of the plug device. With the above definition of the voltage drop in the contact zone of interest, the operation of the plug-in device is necessary, for example, to carry out the method. On the other hand, high currents that flow during operation can interfere with the evaluation of the inductive voltage during induction. Therefore, as a rule, it may be preferable if the evaluation by the proposed method is synchronized with the flow of the operating current. For example, in terms of on/off timing, this could mean that the evaluation occurs only when no operating current is flowing, or conversely, only occurs when the operating current is flowing. In addition, synchronization can also be attributed to the modulation of the operating current, for example, when the measurements are carried out preferably in the region of the passage of the operating AC current through zero.

According to the second aspect, the invention relates to a plug device (hereinafter also "first plug device") with at least one first contact element, which in the contact zone contacts the second (reciprocal) contact element of the second mating plug device in the connected state of the plug devices, moreover the plug device is designed to evaluate the properties of at least one current circuit, which contains the first contact element, the contact zone, and from the second plug device - only the second contact element and, as an option, additional contact elements of the second plug device.

The device is designed, therefore, for the implementation of the method according to one of the options described above. The explanations and modifications relating to the method therefore also apply to the plug device and vice versa.

According to one variant, the plug device preferably contains at least one probe, which is located in the first plug device and, in the state connected to the second plug device, contacts the mating second contact element in the additional contact zone. The probe is usually electrically isolated from the first contact element so that it provides separate electrical access to the second contact element.

In another embodiment, the plug device comprises a magnetic core which surrounds a first contact element and/or a probe of the kind described above and/or a contact zone. By means of such a magnetic core it is possible to induce a voltage in the first contact element or probe and thus in the current circuit under consideration. Preferably, a primary winding is provided on the magnetic core for this purpose. As an option, the core can be envelope-closed or have a local or distributed gap ("air gap").

The plug device may also contain an evaluation circuit for evaluating the properties of said current circuit in a manner according to one of the options described above.

Below the invention is explained in more detail on the examples of its implementation shown in the drawings, which show:

fig. 1 - sockets of the first plug device (coupling) and a plug as a second plug device with mating sockets contact pins;

fig. 2 is a schematic diagram of a current circuit comprising a socket, a contact pin and a probe on the socket side which contacts the contact pin inside the socket;

fig. 3 is a schematic diagram of a current circuit containing a contact pin, a socket and a probe on the side of the plug in two versions;

fig. 4 is a schematic diagram of a current circuit containing a socket, a contact pin and two probes from the side of the socket;

fig. 5 is a schematic diagram of a current circuit comprising a socket, a contact pin and a probe on the socket side which contacts a contact pin outside the socket;

fig. 6 - current circuit from FIG. 2 with equivalent circuit diagram superimposed;

fig. 7 is an equivalent circuit diagram for direct measurement of resistance;

fig. 8 is an equivalent circuit diagram of the circuit of FIG. 7, supplemented by a working circuit, designed to measure the voltage drop in the contact zone under operating conditions;

fig. 9 is an equivalent circuit of the circuit of FIG. 8, supplemented with a voltage source to create a breakdown (point contact) in the contact area of the probe;

fig. 10 is a plan view of a device of two contact fingers inside and two contact fingers outside of a magnetic core for generating an inductive voltage;

fig. 11 shows the device of FIG. 10 when viewed from the side;

fig. 12 is an equivalent circuit diagram of the device of FIG. 10 and 11;

fig. 13 are exemplary curves of the real and imaginary parts of the input impedance of the system of FIG. 10 and 11 depending on the transient contact resistance in the contact zone;

fig. 14 - an alternative arrangement of the magnetic core around the contact pin and between two contact zones;

fig. 15 is a perspective view of the location of the magnetic core relative to the contact pin, with the magnetic core enclosing the contact area between the contact pin and the contact finger of the socket (not shown);

fig. 16 is a longitudinal section through the arrangement shown in FIG. 15, with a simultaneous image of the nest;

fig. 17 is a section along line A of FIG. 16;

fig. 18 is a section along line B of FIG. 16;

fig. 19 schematically shows a current circuit comprising a contact pin, a socket and a pressed probe on the socket side for measuring the conductive and/or capacitive conductance of the current circuit;

fig. 20 is a schematic diagram of a current circuit comprising a pin, a socket, and a socket-side probe, as well as a connection state detection circuit mechanically coupled to the probe;

fig. 21 is a modification of the device shown in FIG. 11, with a measuring coil around the current path.

In FIG. 1, for clarity, only the sockets BU are shown, in perspective, from the sleeve, which is the first plug device SV1. In this example, each of the five sockets BU consists of a cylindrical base, from which four parallel spaced contact fingers KF extend, enclosing a cylindrical cavity. The plug is shown below as a second plug device SV2 with socket-matching pins ST. When the plug SV2 is connected to the socket SV1, the contact pins ST in the contact area come into electrically conductive contact with the sockets BU.

Due to aging processes, corrosion, pollution, etc. relatively high contact resistance can occur in the contact zones, which leads to an unacceptably high occurrence of heat losses. Therefore, it is desirable to determine or monitor the electrical properties of the contact in the contact areas, in particular the contact resistance in the contact area between the contact pin ST and the corresponding socket BU.

At the same time, the components necessary for such a determination should be placed, if possible, only in one of the two plug devices SV1, SV2, so that the control does not depend on the type and origin of the mating plug device used. In most of the examples described below, the required components are placed in the sleeve as the first plug device SV1, while the plug as the second plug device SV2 can, in principle, be any. However, the corresponding explanations also apply (with appropriate agreements) to the coupling and the plug, which have switched roles.

In FIG. 2 shows a schematic partial section through the first contact element in the form of a socket BU, in which a contact pin ST is inserted as a counterpart second contact element. The BU socket can be a closed round sleeve or consist of several contact fingers spaced from the base. The latter can be separated at the free distal end (Fig. 1) or electrically connected to each other. Between the pin ST and the socket BU or its contact fingers there is (at least) one contact area through which the operating current flows during operation. The properties of the contact in this contact zone, in particular the contact resistance present there, must be determined according to the invention by the components located in the coupling.

The construction described above corresponds to the case of traditional plug-in devices and also forms the starting position in the following FIGS. 3-5, 19, 20.

In the variant in FIG. 2, starting from this starting position, it is provided that at the bottom of the socket BU there is an electrically conductive probe F, the tip of which contacts the pin ST when it is fully inserted into the socket. In this case, the touch occurs with a normal contact force, and this almost does not affect the insertion and extraction forces. The stylus F can be made, for example, of nickel silver or bronze spring wire (both materials have very good spring properties, good to very good corrosion resistance and do not necessarily require a coating). In addition, the probe is electrically isolated from socket BU and brought out to terminal b.

The second conclusion a is made to the socket material BU. Between terminals a, b, thus, a current circuit is formed, containing the following components:

- socket BU;

- contact pin ST in contact with the socket in the contact area of interest;

- Probe F in contact with pin ST in a separate second contact zone.

A suitable evaluation circuit (not shown) can be connected to terminals a, b to determine the properties of the current circuit and in particular the contact area of interest.

In FIG. 3 shows a variant in which the contact properties are measured from the side of the plug. For this purpose, two terminals a, b are provided, of which one (b) is connected to pin ST, and the other (a) separately from it to probe F, which, when inserted, contacts externally with socket BU.

The insert in Fig. 3 at the bottom right shows an alternative embodiment in which the contact pin ST' has an axially extending recess or groove. In this groove, insulated from the pin ST', there is a probe F', which can contact the socket BU from the inside.

In FIG. 4 shows a variant similar to that of FIG. 2, however, in addition to the first probe F1, a second probe F2 is provided which contacts the contact pin ST in a separate third contact area and, being electrically separated from the socket and the first probe F1, leads to terminal c. In this case, a suitable evaluation circuit can use all three outputs a, b and c.

In FIG. 5 shows an alternative construction to FIG. 2, in which the probe F does not rest on the bottom of the socket BU, but contacts the contact pin ST outside the socket.

In FIG. 6 shows the equivalent circuit of the generated circuit for the device of FIG. 2. The current circuit lying between terminals a, b passes through the base and the contact fingers of the socket, from there through the contact resistance Ü _Ü of interest to the pin, from it through the additional contact resistance R _F in the second contact zone between the pin and the probe into the probe and ends at last in output b. Inside the massive material of the socket and the contact pin, the resistance can, as a rule, be neglected in comparison with the transient contact resistances R _Ü , R _F in the contact zones.

In FIG. 7 shows again the equivalent circuit diagram of FIG. 6, moreover, between the terminals a, b, a measuring device is connected. In this case, we can talk about an ohmmeter, which measures the resistance in the current circuit, which consists mainly of two series transient contact resistances R _Ü , R _F . However, since both resistances are not known in advance, such a measurement of the sum (R _Ü + R _F ) would not allow one to draw conclusions about the transient resistance R _Ü of interest.

The way out of this situation is provided by the device of FIG. 4, in which there are two probes F1, F2 and thus three (unknown) contact resistances R _Ü , R _F1 , R _F2 . Due to three independent measurements of the total resistance R1 = (R _Ü + R _F1 ) between a and b, the total resistance R2 = (R _Ü + R _F2 ) between a and c, as well as the total resistance R3 = (R _F1 + R _F2 ) between b and c it is then possible to determine the transitional contact resistance R _Ü of interest. The condition is that the three contact resistances R1, R2, R3 can be measured with sufficient accuracy.

Fig. 8 illustrates another principle of measurement, which is bypassed by a single probe (see Fig. 2, 3, 5) and is carried out in the working state of the plug device. On the right side of Fig. 8 shows a working circuit containing an alternating voltage source Q, a transient contact resistance R _Ü of interest, and a consumer R _X . The operating current I _B flowing in this circuit creates a voltage drop U _B across the contact resistance R _Ü . This drop can be measured with a voltmeter across terminals a, b.

The unknown transient contact resistance R _F between the probe and the contact pin does not interfere with such a voltage measurement, if it is sufficiently small compared to the internal resistance of the voltmeter. For the voltage drop U _B created in the working circuit across the transient contact resistance R _Ü creates a measuring current through terminal a, voltmeter, terminal b and transient contact resistance R _F , which is small due to the high internal resistance in the voltmeter. In addition, the high internal resistance compared to the transient contact resistance R _F ensures that basically the entire voltage drops across the voltmeter.

In FIG. 9 shows an extension of the circuit from FIG. 8, with which it is possible to achieve the mentioned condition, namely, that the contact resistance R _F on the probe must be small compared to the internal resistance of the voltmeter. To do this, a breakdown voltage U _D of sufficient magnitude is applied through the switch S to the terminals a, b. In detail, the following exemplary process may take place.

First, switch S is closed for about 1 s ("phase 1"). A voltage U _D of about 50 V causes insulating oxides, foreign layers, etc. that are present even on aged contacts. break through, as a result of which a current of approx. After breakdown/point contact, the voltage at the junction between probe and contact pin is in the order of the melting stress of the material of the contact surface. For example, for nickel, the melting temperature is 1453°C and the corresponding melting voltage is 0.65 V. The contact resistance R _F,fritt created as a result of point contact between the probe and the contact pin is therefore of the order of 1V/100 mA = 10 Ohm.

For control, it is possible to measure the voltage with the closed switch S. Otherwise, phase 1 serves only to create a transient contact resistance R _F,fritt between probe and pin, which is at least one order of magnitude lower than the high internal resistance with which the voltage measurement takes place.

By the beginning of the next "phase 2" switch S opens. The voltage measurement now gives the desired voltage drop U _B between pin and socket during operation of the plug device.

If, on the other hand, the operating current I _B is known, then the evaluation circuit can calculate the contact resistance R _Ü from the voltage drop U _B and the current I _B . However, even without knowing the operating current, the voltage drop is valuable information: with a plug-in device, when the voltage drops between pin and socket, for example, up to 25 mV, stable operation can still be said, but at the latest, starting from about 50 mV, continuous operation can be delivered. questionable (for a 125 A plug device, this corresponds to a contact resistance between pin and socket of 0.4 mΩ; other voltage limits are possible).

Since the decisive feature is the measurement of the voltage drop in phase 2, phase 1 can, if necessary, be omitted entirely if the probe design is suitably stable.

Phase 2 can be immediately followed again by phase 1. A rest phase ("phase 3") can also be included between the two phases.

An alternative measurement process for a device with two probes could be as follows (with reference to Fig. 4):

Phase 1: short-term current through a and b to "prepare" the transition between the first probe F1 and the contact pin ST.

Phase 2: Terminal a (socket BU) and terminal b (second probe F2) are briefly supplied with a current of the order of the later operating current (via socket BU and pin ST). This measures the voltage drop between a and b (first probe F1).

Phase 3: If phase 2 shows "OK", then, for example, the operating voltage/operating current is connected via a contactor. Otherwise, a warning message is issued.

The method can thus be used in order to check the properties of the transition between the contact pin and the socket before connecting the operating current.

The advantage of the methods described is that they function independently of the type of pin-socket contact ("X-Contact" according to WO 2016/184673 A1, torsion spring, etc.). In addition, they can be carried out during ongoing operation, and the operating current does not distort the measured values.

In FIG. 10-18 shows another method that uses an inductive voltage in a current circuit. Such a method is carried out, in particular, with those shown in FIG. 1 sockets BU, in which two (or more) contact fingers KF are parallel to each other on a common base, without contacting at the distal end.

In FIG. 10 shows a schematic top view of a socket BU with four individual contact fingers KF1, KF2, KF3, KF4 extending in a circular sector of about 90°, respectively. Approximate dimensions (diameter, gap) are indicated in mm. Two contact fingers KF1, KF3 are enclosed in a magnetically soft core MK (for example, from a nanocrystalline or amorphous material, ferrite or similar magnetic material), and on the portion of the envelope-closed core MK lying outside the socket, in turn, a multilayer primary winding PSP is wound, for example from lacquered copper wire. The primary winding PSP is connected to an evaluation circuit AS, by means of which suitable current and/or voltage characteristics can be generated.

According to the principle of a transformer, current fluctuations create a changing magnetic field in the primary winding of the PSP, which is concentrated by the MK core and directed further. As the side view in FIG. 11, the contact fingers KF1, KF3 surrounded by the MK core and the outer contact fingers KF2, KF4, due to the inserted contact pin ST, form a closed current circuit around the MK core, which can be considered as a secondary winding with one turn. Therefore, an alternating magnetic field in the MK core induces an induction voltage U _ind and the corresponding induction currents inside the current circuit (see the arrowheads in the contact fingers KF1, KF3 and the ends of the arrows in the contact fingers K2, KF4 indicated in Fig. 10). These induced currents must flow through the contact areas between the contact fingers and the contact pin ST and thus constitute the desired sensor for transient contact properties or transient contact resistance in the contact areas.

The construction described is, after all, two series-connected parallel circuits of respectively two contact fingers according to the equivalent circuit diagram shown in FIG. 12, with material resistances neglected for simplicity. The total resistance in this "secondary winding" inductive circuit is calculated at

R ₁₃ = R _Ü1 R _Ü3 / (R _Ü1 + R _Ü3 )

R ₂ 4 = R _Ü2 R _Ü4 / (R _Ü2 + R _Ü4 )

How

_Rges,ind = R ₁₃ + R ₂₄

Unlike the diagram in Fig. 12, during the rest of the operation of the plug device, a parallel circuit of the contact fingers takes place. Its total resistance is then

R _{ges, B} = R ₁₃ R ₂₄ / (R ₁₃ + R ₂₄ )

If all transient contact resistances have the same value, i.e.

R _Ü1 = R _Ü2 = R _Ü3 = R _Ü4 = R _Ü

then it is fair:

R _ges,ind = R _x1 , and R _ges,B = R _x /4, i.e. _Rges,B = _Rges,ind /4

If the four contact resistances have different values (in practice, they are statistically distributed), then the measured value R _ges,ind detected by the method described here may exceed the value R _ges,B , however, lies, thus, "on the safe side".

In a modified concept, the evaluation circuit AS on the primary winding PSP could be designed in such a way that not only the complex input impedance Z and thus R _ges,ind is determined, but also with I _B13 , in addition, the fraction of the operating current _IB , which flows through the contact fingers KF1, KF3 enclosed in the magnetic core of the MC in Fig. 10 (transformer/current converter principle). If the evaluation circuit also knows the current I _B24 through other contact fingers KF2, KF4 or the operating current I _B itself (for example, by measuring), then the following relationships are used:

I _B = I _B13 + I _B24

I _B24 R ₂₄ = I _B13 R ₁₃

_Rges,ind = R ₁₃ + R ₂₄

R _{ges, B} = R ₁₃ R ₂₄ / (R ₁₃ + R ₂₄ )

The last two relations have already been used. If we solve this system of equations for R _ges,B , then this will lead to:

R _ges,B = R _ges,ind I _B13 I _B24 / (I _B13 + I _B24 ) ²

With this formula, the scoring schema AS can provide information not only about R _ges,B , but also R _ges,B itself.

To determine R _ges,ind using the AS scoring scheme in FIG. 10, 11 the (complex) input impedance Z of the PSP primary winding is measured, which depends inter alia on R _ges,ind .

In FIG. 13 shows the simulation result with typical parameters for the components used. This shows the real part Re(Z(R _Ü )) and the imaginary part Im(Z(R _Ü )) of the complex input impedance Z as a function of the transient contact resistance R _Ü (under the above assumption that all individual transient contact resistances have the same value). The graph illustrates that the input impedance Z of the measuring circuit changes significantly with changes in the transient contact resistance R _Ü . The evaluation circuit AS connected to the measuring circuit can therefore determine the desired transitional contact resistance using the input impedance.

When modeling, it was assumed that the magnetic core of the MC is designed in such a way that, upon excitation with 127 A, a magnetic flux density of 1 T is achieved. With even stronger excitation, one should reckon with the gradual saturation of the magnetic circuit. This saturation can occur when, during a heavy start-up, currents noticeably higher than the rated current flow for several seconds, of which about half falls on both contact fingers enclosed in the core. The connected electronics will therefore measure distorted Z values in the region of the peak value of the operating current, but will detect rational values near the passage of the operating current through zero. Therefore, as an option, the AS evaluation circuit can be configured such that it measures synchronously with the operating current (50 Hz), in particular only close to zero crossing of the operating current.

The described method with induction of the measuring current can optionally also be carried out using a probe. For example, probe F in FIG. 2 can play the role of lying outside (or inside) the magnetic core of the contact fingers. In addition, instead of several contact fingers, a divided contact pin can also protrude.

The principle underlying the concepts described is that with each excitation by means of a magnetic core, the contact points between the socket and the pin can be investigated if a closed path (curve, line) leading through the electrically conductive material that passes through the surface formed by the magnetic core can be formed only with the simultaneous participation of the contact elements of the first and second plug devices.

These conditions can be achieved, in addition to what has already been described, also under other circumstances. (Note: for clarity, the turns of the primary winding, which cover the magnetic core in the same way as a transformer, are not shown in Figs. 14-18).

So, in Fig. 14 shows the location of the magnetic core MK, which passes inside the socket BU around the pin ST, and in the axial direction on both sides near the core MK there are contact zones between the pin ST and the socket BU. A current circuit of a suitable form then passes from the ST pin through the first of the pin/socket contact areas to the BU socket (or its contact pin), and from there through the second of the pin/socket contact areas back to the ST pin.

Another concept is shown in Fig. 15-18. In this case, only the contact zone between pin ST and socket BU effectively passes through the surface of the magnetic core MK.

As the perspective view in FIG. 15, the magnetic core MK, rectangular in top view, is adjacent in the shape of a semi-cylinder to the pin ST.

In axial section in Fig. 16, this three-dimensional shape of the MK magnetic core is represented as a rectangle. In FIG. 16 also shows a socket BU containing two parallel contact fingers KF1, KF2. In the area of the outer sleeve spring HF extending through 360°, the contact fingers KF1, KF2 touch the pin ST in the first and second contact areas, respectively. The first of these two contact zones between the first contact finger KF1 and the contact pin ST (on the left in Fig. 18 in section along line B) is covered by the magnetic core MK.

The current circuit in which the required inductive voltage is generated passes from the pin ST through the first contact area KF1/ST, the first contact pin KF1, the socket bottom BU and/or the sleeve spring HF to the second pin KF2 and from there through the second contact area KF2/ ST back into the ST pin.

This embodiment has the advantage of being applicable to both free-standing contact finger sockets and (as shown) distally connected contact finger sockets.

In the examples presented, it was not discussed whether the considered current paths were conductive or (only) capacitive. In any case, all examples operate with conductive conduction, in which a continuous continuous current can flow through the current circuit.

However, it is also possible that the considered current circuit at least in one place has only capacitive conduction, i.e. contained the capacitance in the following diagram. Such a current circuit may not conduct any continuous direct current, but only alternating current. However, despite this, the described examples function without changes.

The use of a current circuit with only capacitive conduction is illustrated in FIG. 19. It schematically shows the current circuit containing the contact pin ST, the socket BU and the probe F from the side of the socket. Unlike the device in FIG. 2, an electrically insulating pressure pad DK is provided inside the socket BU, which presses the probe F against the contact pin ST. In this way, a sufficiently tight contact between probe F and pin ST must be guaranteed. Therefore, even if the oxide layers and the like prevent conductive conduction from the probe F to the contact pin ST, then a sufficiently high capacitance is formed between them, which allows the flow of a usable high (alternating) current in the current circuit. Therefore, measures such as, for example, the described point contact would not be required.

The electrical equivalent circuit of such a device is shown in Fig. 19 superimposed, where C _F denotes the capacitance and R _F the ohmic resistance between probe F and contact pin ST. R _Iso denotes the insulation resistance between probe F and socket BU, which is usually of the order of at least 5 MΩ.

As an option, in this variant, first of all, only the relationship at the transition between the probe F and the contact pin ST is determined by means of a separate measurement, i.e. C _F and R _F , for example by measuring without operating current and/or measuring without an inserted contact pin ST. The result of this determination can then be included in the performance and/or evaluation of the subsequent actual measurement to improve its reliability.

Another extension of the invention is illustrated in FIG. 20. In this concept, it is an independent detection whether the contact pin ST is inserted into the socket BU at all. Thus, it is possible to distinguish between the cases of "contact pin not inserted" and "infinitely high contact resistance".

Preferably, the detection of the inserted state occurs mechanically so as to be independent of the passage of current. As seen in FIG. 20, the probe F may, for example, be mechanically connected to a switch of the detection circuit DS. As a result of touching the inserted contact pin ST, the probe F moves, and this movement is mechanically converted into an opening (or closing) of the switch of the detection circuit DS. The state of the switch can, in turn, be read from the outside.

In FIG. 21 shows a modification of the device from FIG. 11, with only the differences being described below, otherwise reference is made to the preceding description.

In the modified device, an alternating magnetic field is also induced through the primary winding PSP in the magnetic core of the MK due to the fact that an alternating voltage source U _P is connected to it (this alternating voltage source is in Fig. 11 part (not shown) of the evaluation circuit AS).

The (reactive) effects of the current induced by the alternating magnetic field of the core in the current circuit of interest are no longer detected in this device via the PSP primary. Instead, an additional winding is located around the current circuit, which is connected as a measuring coil MS to the evaluation circuit AS. In the measuring coil MS, a measurable electrical quantity (eg voltage) is induced directly by the flow of current in the current circuit it surrounds.

In this case, the entire current circuit can pass through the measuring coil MS when the measuring coil MS embraces all the contact fingers of the same current direction (here KF2 and KF4 or KF1 and KF3). Alternatively, it was also possible to detect only a part of the current path, for example when the measuring coil MS is located only around a single contact finger.

In conclusion, the most important aspects of the invention are listed once again, which can be implemented individually or in combination, and the reference numbers enclosed in brackets refer to exemplary embodiments of the figures:

A) a method for determining the electrical contact properties (R _Ü ) in the contact zone between the first contact element (BU) of the first plug device (SV1) and the second contact element (ST) of the second plug device (SV2) corresponding to it, and the properties of the current circuit are evaluated, which contains the first contact element (BU), the contact area, and from the second plug device (SV2) only the following: the second contact element (ST) and, if necessary, additional contact elements of the second plug device (SV2),

and

a) an inductive voltage (U _ind ) is induced in the current circuit in such a way that measurements can be made in the current circuit that allow inferences to be made about the contact properties of interest, and/or

b) the current circuit contains at least one probe (F, F1, F2), which is located in the first plug device (SV1) and in the connected state contacts the second contact element (ST), and/or

c) the current circuit contains at least two probes (F, F1, F2), which are located in the first plug device (SV1) and in the connected state come into contact with the second contact element (ST), and/or

d) the current circuit contains at least one probe (F, F1, F2), which is located in the first plug device (SV1) and in the connected state is in contact with the second contact element (ST), and between the probe (F, F1, F2) and a breakdown voltage (U _D ) is applied to the second contact element (ST), and/or

e) the evaluation is synchronized with the flow of the operating current (I _B ) through the contact area and/or

e) the current circuit contains at least one probe (F, F1, F2) which is located in the first plug device (SV1) and in the connected state contacts the second contact element (ST), and in the current circuit there is a capacitance of more than about 10 pF, which ensures the flow of alternating current in the current circuit, and / or

g) through the current circuit, the voltage drop (U _B ) that occurs when the operating current (I _B ) passes through the contact zone is measured, and / or

h) the current circuit forms a secondary winding on a magnetic core (MC), on which the primary winding (PSP) is also located.

B) A plug-in device (SV1) with at least one first contact element (BU) which, in the connected state, contacts in the contact zone with a mating second contact element (ST) of the second plug-in device (SV2), moreover, it has a current circuit, containing the first contact element (BU), the contact area, and from the second plug device (SV2) only the following: the mating second contact element (ST) and, if necessary, additional contact elements of the second plug device (SV2),

and

a) it contains means for inducing an inductive voltage (U _ind ) for the method according to item A) and/or

b) it contains at least one probe (F, F1, F2), which in the connected state is in contact with the mating second contact element (ST) of the second plug device (SV2), and/or

c) it contains at least two probes (F, F1, F2), which in the connected state are in contact with the mating second contact element (ST) of the second plug device (SV2), and/or

d) it contains at least one probe (F, F1, F2), which in the connected state is in contact with the mating second contact element (ST) of the second plug device (SV2), and means for generating breakdown voltage (U _D ) and /or

e) it contains a magnetic core (MK) which surrounds the first contact element (BU) and/or the probe (F) and/or the contact zone, and/or

e) it contains an evaluation circuit (AS) for evaluating the properties of the current circuit by the method of point A).

Claims (20)

1. A method for determining electrical contact resistances (R _Ü ) in the contact zone between the first contact element (BU) of the first plug device (SV1) and the second contact element (ST) of the second plug device (SV2), which includes estimating the resistance of the current circuit, when In this case, the current circuit comprises a first contact element (BU), a contact area, and from the second plug device (SV2) only a second contact element (ST), characterized in that an inductive voltage (U _ind ) is induced in said current circuit, so that the measurements taken in the indicated current circuit, made it possible to draw conclusions about the contact resistances of interest. 2. The method according to claim 1, characterized in that said current circuit comprises at least two probes (F, F1, F2) which are located in the first plug device (SV1) and contact the second contact element (ST) in the connected state . 3. The method according to claim 1 or 2, characterized in that said evaluation is synchronized with the passage of the operating current (I _B ) through the contact zone. 4. A method according to any one of claims 1 to 3, characterized in that a capacitance of more than about 10 pF is formed in the current circuit, which allows the flow of alternating current in the current circuit. 5. A method for determining electrical contact resistances (R _Ü ) in the contact zone between the first contact element (BU) of the first plug device (SV1) and the second contact element (ST) of the second plug device (SV2), which includes estimating the resistance of the current circuit, when In this case, the current circuit contains the first contact element (BU), the contact zone, and from the second plug device (SV2) only the second contact element (ST), characterized in that said current circuit contains at least two probes (F, F1, F2), which are located in the first plug device (SV1) and contact the second contact element (ST) in the connected state. 6. The method according to claim 5, characterized in that said evaluation is synchronized with the passage of the operating current (I _B ) through the contact zone. 7. A method according to claim 5 or 6, characterized in that a capacitance of more than about 10 pF is formed in the current circuit, which allows the flow of alternating current in the current circuit. 8. A method for determining electrical contact resistances (R _Ü ) in the contact zone between the first contact element (BU) of the first plug device (SV1) and the second contact element (ST) of the second plug device (SV2), which includes estimating the resistance of the current circuit, when In this case, the current circuit contains the first contact element (BU), the contact zone, and from the second plug device (SV2) only the second contact element (ST), characterized in that the specified evaluation is synchronized with the passage of the operating current (I _B ) through the contact zone. 9. Method according to claim 8, characterized in that said current circuit comprises at least two probes (F, F1, F2) which are located in the first plug device (SV1) and contact the second contact element (ST) in the connected state . 10. The method of claim 8 or 9, wherein the current circuit has a capacitance of greater than about 10 pF that allows alternating current to flow in the current circuit. 11. A method for determining electrical contact resistances (R _Ü ) in the contact zone between the first contact element (BU) of the first plug device (SV1) and the second contact element (ST) of the second plug device (SV2), which includes estimating the resistance properties of the current circuit, while the current circuit contains the first contact element (BU), the contact area and from the second plug device (SV2) only the second contact element (ST), the current circuit also contains at least two probes (F, F1, F2), which are located in the first plug device (SV1) and contact with the second contact element (ST) in the connected state, characterized in that a capacitance of more than about 10 pF is formed in the current circuit, which allows the flow of alternating current in the current circuit. 12. The method according to any one of claims 1 to 11, characterized in that the voltage drop (U _B ) on the specified current circuit, which occurs when the operating current (I _B ) flows through the contact zone, is measured. 13. Method according to any one of claims 2, 5, 9, 11, characterized in that certain contact properties are created between the probe (F, F1, F2) and the second contact element (ST), preferably by applying a breakdown voltage (U _D ) . 14. The method according to any one of claims 1, 5, 8, 11, characterized in that the current circuit forms a secondary winding on a magnetic core (MC), on which the primary winding (PSP) is also located. 15. The method according to any one of claims 1, 5, 8, 11, characterized in that the current circuit contains at least two contact fingers (KF1, KF2, KF3, KF4), which both contact the same contact pin ( ST). 16. Plug device (SV1), containing at least one first contact element (BU), which contacts in the contact zone with the mating second contact element (ST) of the second plug device (SV2) in the connected state, while the plug device contains a current circuit , which contains the first contact element (BU), the contact area and from the second plug device (SV2) only the second contact element (ST), characterized in that it contains means for inducing an inductive voltage (U _ind ) in the specified current circuit for implementing method for determining electrical contact resistance according to claim 1. 17. The plug device according to claim 16, characterized in that it comprises at least two probes (F, F1, F2) that contact the mating second contact element (ST) of the second plug device (SV2) in the connected state. 18. Plug device containing at least one first contact element (BU), which is in contact in the contact zone with the mating second contact element (ST) of the second plug device (SV2) in the connected state, while the plug device contains a current circuit that contains the first contact element (BU), the contact area and from the second plug device (SV2) only the mating second contact element (ST), characterized in that it contains at least two probes (F, F1, F2) that are in contact with the mating second contact element (ST) of the second plug device (SV2) in the connected state. 19. A plug device according to any one of claims 16 to 18, characterized in that it comprises a magnetic core (MC) which surrounds the first contact element (BU) and/or the probe (F) and/or the contact area. 20. A plug device according to any one of claims 16 to 19, characterized in that it comprises an evaluation circuit (AS) for evaluating the properties of the current circuit when carrying out the method for determining electrical contact resistances according to any one of claims 1 to 15.

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