CONTACT MONITORING DEVICE FOR A THREE-POLE CHANGEOVER CONTACT

Description

[0001] The invention relates to a contact monitoring device for monitoring an electrical, three-pole changeover contact (e.g. a relay), in particular for monitoring a switching operation of the changeover contact.

[0002] Changeover contacts with three terminals are generally known in the prior art, with the terminals usually referred to as a COM terminal ("common"), NC terminal ("normally closed"), and NO terminal ("normally open"). A changeover contact typically has the task of establishing electrical contact between a common terminal, the COM terminal, and one of two other terminals, the NC or NO terminal. During normal operation, the changeover contact thus has two operating states: either the COM terminal is connected to the NC terminal, or the COM terminal is connected to the NO terminal.

[0003] In addition to the two aforementioned states, which can also occur in the event of faulty operation of the changeover contact (e.g., if the COM terminal and the NC or NO terminal are welded together), other switching states can also occur in the event of a fault. For example, there may be no connection at all between the three terminals due to worn contact beads. Alternatively, all three terminals may be connected to one another, for example, by an arc or by the contacts welding together due to thermal and / or electrical overload. Furthermore, the NC terminal may only be connected to the NO terminal, but neither may be connected to the COM terminal; however, this condition typically plays a minor role due to the design of a relay.Overall, a number of (fault) states can occur with changeover contacts, which is why there is a need in practice for a simple and reliable way to detect or monitor the switching state of a changeover contact.

[0004] Document CN 109283462 A discloses a portable relay tester comprising a control module, a drive module, and a contact detection module. The relay coil is energized via PWM signals, while a contact detection circuit determines the switching states and contact resistances. The measurement results are evaluated in the control module and presented, for example, via a display and acoustic signals.

[0005] The principle of evaluating the switching state of a contact by applying a test signal to it is known from DE 28 06 294 A1. However, the contact in question is only a single contact with two switching states.

[0006] EP 1 202 313 A1 also discloses a method for monitoring the switch position of mechanical switch contacts, which requires two coupling transformers. Furthermore, the aforementioned method can only distinguish between two switching states.

[0007] Similar solutions for changeover contact monitoring are also known from documents EP 3 396 692 A1, DE 27 29 480 A1, DE 42 21 916 A1, and DE 10 2018 217 135 A1. However, the disadvantage of all these approaches is that they can only distinguish between two switch positions. In particular, in the case of the approach in DE 10 2018 217 135 A1, the condition in which all three terminals—i.e., the COM, NC, and NO terminals—are connected to each other (e.g., by welding the contacts) would be incorrectly interpreted as correct switch function, even though a fault may be present.

[0008] Accordingly, the object of the invention is to provide a cost-effective method for monitoring a three-pole changeover switch, which avoids the disadvantages of previous solutions. In particular, the object of the invention is to provide a solution by means of which as many faults or switching states of a changeover switch as possible can be detected, preferably independently of any external wiring of the changeover contact.

[0009] These objects can be achieved with the features of independent claim 1. Advantageous embodiments and applications of the invention are subject of the dependent claims and are explained in more detail in the following description with partial reference to the figures.

[0010] According to a first aspect, the disclosure relates to a contact monitoring device for monitoring an electrical, three-pole changeover contact (e.g., a relay changeover contact). The changeover contact can comprise three terminals, which will be referred to below as the COM terminal, the NC terminal, and the NO terminal.

[0011] The contact monitoring device comprises a signal generator designed to generate a monitoring signal. The signal generator can be, for example, an oscillator circuit, e.g., a Colpitts oscillator circuit. The monitoring signal is preferably a high-frequency monitoring signal, i.e., a signal in the high-frequency range. For example, the monitoring signal can have a frequency of at least 10 kHz, preferably of at least 100 kHz, or more preferably of at least 1 MHz. The monitoring signal is preferably a voltage signal; however, the monitoring signal can also or alternatively be a current signal and / or a power signal.

[0012] Furthermore, the contact monitoring device comprises one, preferably exclusively one, coupling device (e.g., a transformer) connected downstream of the signal generator, and a sensing circuit connected downstream of the coupling device. In other words, the sensing circuit is coupled to the signal generator via the coupling device. Preferably, the coupling device is an inductive coupling device and / or is designed to galvanically isolate the sensing circuit from the signal generator. The sensing circuit, in turn, is coupled to the changeover contact or can be coupled to it. Preferably, the sensing circuit is coupled to each terminal of the changeover contact or can be coupled to it.

[0013] It is provided that the monitoring signal generation of the signal generator and thus the monitoring signal and / or a signal derived from the monitoring signal can be changed depending on the switching position of the changeover contact by means of the sensing circuit coupled to the signal generator via the coupling device. In other words, the sensing circuit can be designed to change the monitoring signal generation of the signal generator and thus the monitoring signal and / or a signal derived from the monitoring signal depending on the switching position of the changeover contact via its coupling to the signal generator via the coupling device. By way of example only, the sensing circuit can, for example,be designed to change the amplitude and / or frequency of the generated monitoring signal and / or the signal derived from the monitoring signal as a function of the switch position of the changeover contact by influencing the oscillation behavior of the signal generator. A signal derived from the monitoring signal should be understood to be a signal that is functionally related to the monitoring signal (e.g. is proportional to it) and / or can be generated or converted from it. For example, the monitoring signal can be a voltage signal and the signal derived from the monitoring signal can be a current signal. Furthermore, the sensing circuit is designed to change the monitoring signal and / or the signal derived from the monitoring signal differently for at least three, preferably four, particularly preferably five, different switch positions of the changeover contact.In this context, “changing” can also generally be understood as “influencing” or “varying”.

[0014] In other words, for each of the switch positions, a change or influence of the monitoring signal can occur that is characteristic of the respective switch position, which then results, for example, in a different amplitude of the monitoring signal for each of the switch positions.

[0015] Furthermore, the contact monitoring device comprises an evaluation device designed to detect the monitoring signal and / or the signal derived from the monitoring signal and / or a change in the monitoring signal and / or a change in the signal derived from the monitoring signal, in order to thereby monitor the changeover contact. For example, the evaluation device can detect the current amplitude of the monitoring signal and / or a change in the amplitude of the monitoring signal and, based thereon, determine, for example, the current actual switching state of the changeover contact, which can then in turn be compared, for example, with a predetermined target switching state. If the monitoring signal is a pulse-like monitoring signal, detecting a change in the monitoring signal can, for example, be detecting an impulse response.Overall, this advantageously allows for the detection and monitoring of a variety of different switch positions of the changeover contact, enabling reliable diagnosis of the current state of the changeover contact. Particularly from the perspective of functional safety (e.g., according to the IEC 61508 standard), this allows for clear detection of the contact state of the changeover contact, thus achieving a high degree of diagnostic coverage.

[0016] According to a first aspect of the invention, the sensing circuit can be configured to change an amplitude, a frequency, a phase position, a decay behavior, a propagation time, and / or a signal shape of the monitoring signal depending on the switch position of the changeover contact. Additionally or alternatively, the sensing circuit can also be configured to change an amplitude, a frequency, a phase position, a decay behavior, a propagation time, and / or a signal shape of the signal derived from the monitoring signal depending on the switch position of the changeover contact. For example, the sensing circuit can be configured to increase the amplitude of the monitoring signal, starting from a first switch position (basic position), if the changeover contact is moved to a second switch position, and to decrease it compared to the amplitude in the first switch position if the changeover contact is moved to a third switch position.The monitoring signal can be a continuous monitoring signal or a pulsed monitoring signal. In principle, the sensing circuit can be designed to change the same characteristic(s) of the monitoring signal and / or the signal derived from the monitoring signal as a function of the switch position (e.g., always the frequency). Alternatively, the sensing circuit can also be designed to change, at least in part, different characteristics of the monitoring signal and / or the signal derived from the monitoring signal depending on the switch position (e.g., the frequency in a first switch position and the amplitude in a second switch position). Changing or influencing the aforementioned characteristics of the monitoring signal and / or the signal derived from the monitoring signal can be achieved, for example, by coupling in variables that influence the oscillation behavior of the signal generator (such as, for example,an impedance) into the signal generator depending on the switch position.

[0017] According to a further aspect of the invention, the changeover contact can comprise a preferably common COM terminal, an NC terminal, and an NO terminal. Furthermore, the sensing circuit can be configured to change the monitoring signal and / or the signal derived from the monitoring signal differently for at least three, preferably four, particularly preferably all of the following switch positions. In other words, the contact monitoring device as a whole can be configured to provide a different monitoring signal for at least three, preferably four, particularly preferably all of the following switch positions. The corresponding switch positions, which can also be referred to as switching states, are: 1. No connection between the COM port, the NC port, and the NO port; 2. Only the COM port and the NC port are connected; 3. Only the COM port and the NO port are connected; 4. Only the NC port and the NO port are connected; 5. All ports, i.e., the COM port, the NC port, and the NO port, are connected.

[0018] The advantage of being able to generate different monitoring signals, i.e. signals characteristic of the respective switch position, from the signal generator for as many of the corresponding switch positions as possible is that this allows a clear assignment of the individual switching states, which advantageously enables the most accurate diagnosis of the changeover contact.

[0019] According to the invention, the sensing circuit comprises one or more impedances.

[0020] Furthermore, the sensing circuit is designed to provide a total impedance to the coupling device with the changeover contact, which varies with the switch position of the changeover contact. In other words, the sensing circuit is designed , Depending on the switch position of the changeover contact, the total impedance applied to the coupling device can be changed. This changed total impedance can then result in a change in the monitoring signal generated in the signal generator or oscillator circuit. For example, an increase in the total impedance can cause a reduction in the amplitude of the monitoring signal.

[0021] Additionally or alternatively, the sensing circuit can also be configured to provide a different total impedance at the coupling device for at least three, preferably four, particularly preferably five switch positions of the changeover contact. For example, a first total impedance can be provided for a first switch position, a second total impedance can be provided for a second switch position, etc. In other words, the sensing circuit can be configured to use the changeover contact to set a characteristic total impedance at the coupling device for at least three, preferably four, particularly preferably five switch positions, which is then coupled via the coupling device into the signal generator to change the monitoring signal generation there.In an advantageous manner, a simple possibility for varying the oscillation signal as a function of the switch position can be provided, which then enables reliable monitoring of the changeover contact.

[0022] According to a further aspect of the invention, the sensing circuit can comprise a first impedance that is or can be coupled to a terminal of the changeover contact, preferably the COM terminal. The first impedance is preferably designed in the form of a series circuit comprising a resistor and a capacitor, whereby the resistor and capacitor, respectively, will be referred to below as the "first" resistor and "first" capacitor for ease of differentiation.

[0023] Additionally or alternatively, the sensing circuit can also comprise a second impedance that can be coupled or is coupled to another terminal of the changeover contact, preferably the NC terminal. This second impedance is preferably also designed in the form of a series circuit comprising a "second" resistor and a "second" capacitor. Additionally or alternatively, the sensing circuit can also comprise a third impedance that can be coupled or is coupled to another terminal of the changeover contact, preferably the NO terminal. This is preferably also designed in the form of a series circuit comprising a "third" resistor and a "third" capacitor.In an advantageous manner, a corresponding interconnection of impedances can be provided, which makes it possible to vary the total impedance applied to the coupling device and thus the monitoring signal generation depending on the switch positions of the changeover contact, thereby enabling a simple monitoring or determination of the changeover contact state.

[0024] According to a further aspect of the invention, the sensing circuit can comprise one to three further impedances, which will be referred to below as fourth, fifth, and sixth impedances for easier differentiation. The respective impedance can be connected downstream of a respective terminal of the changeover contact. For example, the fourth impedance can be connected downstream of the COM terminal, the fifth impedance can be connected downstream of the NC terminal, and / or the sixth impedance can be connected downstream of the NO terminal. The corresponding impedances, which can comprise, for example, an inductance or a ferrite, can serve to attenuate high-frequency signals that are present at the changeover contact and / or at an electrical load and / or voltage source coupled to the changeover contact by means of the coupling device.In other words, the fourth, fifth, and / or sixth impedances can function as filter elements, whereby other filtering options known to those skilled in the art can also be used instead of impedances. The impedances or filter elements are preferably high-impedance in a frequency range from 100 kHz to 100 MHz, so that the monitoring signal is not present, or only present with a reduced signal amplitude, to any loads connected to the changeover contact. This advantageously allows for reliable monitoring of the changeover contact, which has virtually no impact on corresponding useful signals. In other words, the contact monitoring device is advantageously unnoticeable or barely noticeable for typical DC or low-frequency useful signals "from the outside."

[0025] According to a further aspect of the invention, the sensing circuit can comprise at least one further impedance, wherein the at least one further impedance is connected between two terminals of the changeover contact. The sensing circuit preferably comprises one, two, or three further impedances, which will be referred to below as seventh, eighth, and ninth impedances for ease of differentiation. For example, the seventh can be referred to as [the seventh impedance]. Likewise, the eighth impedance can also preferably be designed in the form of a series circuit comprising an eighth inductance and an eighth capacitance. Finally, the ninth impedance can also preferably be designed in the form of a series circuit comprising a ninth inductance and a ninth capacitance. The corresponding impedances can serve to attenuate high-frequency signals between the terminals of the changeover contact.Preferably, the aforementioned LC series resonant circuits have a series resonant frequency that lies in the range of the frequency of the monitoring signal. The impedance of the series resonant circuits at the series resonant frequency is thus determined solely by resistive components of the inductance and capacitance and is therefore very low. This advantageously reduces voltage signals between the terminals and thus electromagnetic interference emissions, while minimizing the influence of any connected loads on the sensing circuit at the operating frequency of the signal generator, since these loads are connected in parallel to the low seventh or eighth impedance.

[0026] According to a further aspect of the invention, the changeover contact can be a changeover contact of a relay. In this context, the changeover contact can also be referred to as a relay changeover contact. The relay can be, for example, an electromechanical relay, in which the changeover contact can be switched by means of a relay coil and a movable relay armature. Alternatively, however, the relay can also be a semiconductor relay. In addition or alternatively, the contact monitoring device can also be part of a relay base. In other words, the contact monitoring device can be integrated into a relay base. The contact monitoring device is preferably enclosed by a relay base housing.

[0027] According to a further aspect of the invention, the coupling device (a) can be an inductive transformer. For example, the coupling device (b) can comprise a transformer, which can have a first inductance (e.g., a first air-core coil) and a second inductance (e.g., a second air-core coil), wherein the first inductance can be inductively coupled to the second inductance (e.g., via a ferrite or magnetic core). The advantage of a corresponding design with air-core coils is that the coils can be manufactured using printed circuit board technology, and the number of discrete electronic components can be reduced accordingly during manufacture of the contact monitoring device. Additionally or alternatively, the coupling device (c) can be designed to galvanically isolate the signal generator and the sensing circuit.Alternatively, however, the coupling device can also be designed as a direct galvanic connection of the sensing circuit to the signal generator (e.g., in the form of a cable or conductor connection). Additionally or alternatively, the coupling device can also be formed from (d) at least two electromagnetically coupled antennas. Additionally or alternatively, the coupling device can also be formed from (e) at least two capacitors. The two capacitors are preferably designed as printed circuit board capacitors.

[0028] Optionally, features (a), (b) and (c) or features (a), (c) and (d) or features (c) and (e) can be combined in pairs or in their entirety.

[0029] According to a further aspect of the invention, the signal generator can be a high-frequency generator designed to generate a high-frequency monitoring signal. For example, the monitoring signal can have a frequency of at least 10 kHz, preferably at least 100 kHz, or more preferably at least 1 MHz. This can achieve the particular advantage that frequency separation of the monitoring signal and the useful signal switched by the changeover contact can be achieved using cost-effective frequency filter elements. Additionally or alternatively, the signal generator can also comprise a Colpitts oscillator circuit. Additionally or alternatively, the signal generator can be connected to the changeover contact via the coupling device and the sensing circuit, for example in parallel.

[0030] According to a further aspect of the invention, the signal generator can have a tap (e.g., a voltage tap). Furthermore, the signal generator can be configured to provide the monitoring signal and / or a signal derived from the monitoring signal to the evaluation device via the tap. In other words, the evaluation device can be connected to the signal generator via the tap. This advantageously allows for a simple connection of the evaluation device to the signal generator.

[0031] According to a further aspect of the invention, the monitoring signal can comprise at least a first monitoring sub-signal and a second monitoring sub-signal. For example, the first monitoring sub-signal can have a different frequency and / or a different signal shape than the second monitoring sub-signal and / or be generated at a different time. In other words, the first monitoring sub-signal and the second monitoring sub-signal can be different or distinguishable, whereby in principle, more than two different or distinguishable monitoring sub-signals (e.g., three monitoring sub-signals) can also be used. In this context, the "monitoring signal" is to be understood as the signal composed of all monitoring sub-signals or consisting of these components.Furthermore, it can be provided that the first monitoring sub-signal and / or a signal derived from the first monitoring sub-signal can be used by means of the sensing circuit depending on a switching position of a first connection subset of the changeover contact, and the second monitoring sub-signal and / or a monitoring sub-signal distinguishable from the second (e.g., three monitoring sub-signals). In this context, the "monitoring signal" is understood to mean the signal composed of all monitoring sub-signals or consisting of these components.Furthermore, it can be provided that, by means of the sensing circuit, the first monitoring sub-signal and / or a signal derived from the first monitoring sub-signal can be changed depending on a switching position of a first connection subset of the changeover contact, and the second monitoring sub-signal and / or a signal derived from the second monitoring sub-signal can be changed depending on a switching position of a second connection subset of the changeover contact. The first connection subset is preferably at least partially different from the second connection subset. For example, the first monitoring sub-signal and / or the signal derived from the first monitoring sub-signal can be changed depending on the switching state of the COM and NO connection, while the second monitoring sub-signal and / or the signal derived from the second monitoring sub-signal can be changed depending on the switching state of the COM and NC connection. I.e.In other words, the respective monitoring sub-signals and / or the signals derived from the monitoring sub-signals can each be assigned to only a part of the connections of the changeover contact or can only react to a change in a part of the connections of the changeover contact.

[0032] According to a further aspect of the invention, the signal generator can comprise a first signal generator device for generating the first monitoring sub-signal and a second signal generator device for generating the second monitoring sub-signal. For example, the first signal generator device can be a first high-frequency generator designed to generate a high-frequency first monitoring signal, and the second signal generator device can be a second high-frequency generator designed to generate a high-frequency second monitoring signal. Additionally or alternatively, the coupling device can also comprise a first coupling element (e.g., a first transformer) for coupling the first signal generator device to the sensing circuit and a second coupling element (e.g., a second transformer) for coupling the second signal generator device to the sensing circuit.For example, the first coupling element can be a first transformer and the second coupling element a second transformer, although other coupling types described above (e.g., capacitive or in the form of a conductor connection) can also be used. Additionally or alternatively, the sensing circuit can also be configured to couple the first monitoring sub-signal to a first subset of terminals of the changeover contact and to couple the second monitoring sub-signal to a second subset of terminals. In other words, the sensing circuit can be configured to couple the corresponding monitoring sub-signals only to specific terminals of the changeover contact.

[0033] According to a further aspect of the invention, the evaluation device can be designed to output a status signal that indicates the switch positions of the changeover contact as a function of the monitoring signal and / or the change in the monitoring signal. In addition or alternatively, the evaluation device can also be designed to output a status signal that indicates the switch positions of the changeover contact as a function of a signal derived from the monitoring signal and / or the change in the signal derived from the monitoring signal. For example, the evaluation device can be designed to provide a status signal that is proportional to the current amplitude, frequency, phase position and / or signal shape of the monitoring signal and / or the signal derived from the monitoring signal. The status signal preferably comprises at least three, preferably four, particularly preferably five, different signal states. I.e.In other words, the status signal can characterize the actual switching state of the changeover contact. Furthermore, the evaluation device can be configured to then compare the aforementioned status signal with a desired switching state signal, e.g., derived from a switching signal generated by the control of the changeover contact, in order to thereby monitor a proper switching process or the state of the changeover contact.

[0034] According to a further aspect of the invention, the evaluation device can be designed to detect a switching signal (e.g. generated by a control of the changeover contact) for switching the changeover contact. For this purpose, the evaluation device can be connected to the corresponding control, e.g. via a switching control connection. Furthermore, the evaluation device can be designed to output a control signal depending on the switching signal and the monitoring signal and / or the change in the monitoring signal, which indicates whether the changeover contact is switched according to the switching signal. In addition or alternatively, the evaluation device can also be designed to output a control signal depending on the switching signal and a signal dependent on the monitoring signal and / or the change in the signal dependent on the monitoring signal, which indicates whether the changeover contact is switched according to the switching signal.By way of example, the control signal may be a binary signal having a first signal value and a second signal value, wherein the first signal value indicates a correct switching operation and the second signal value indicates an incorrect switching operation.

[0035] According to a further aspect of the invention, the evaluation device can further be designed to detect the monitoring signal and / or the change in the monitoring signal within a predetermined time interval upon receiving the switching signal in order to determine whether the changeover contact is switched within the predetermined time interval in accordance with the switching signal. In addition or alternatively, the evaluation device can also be designed to detect the signal derived from the monitoring signal and / or the change in the monitoring signal and / or the signal derived from the monitoring signal within a predetermined time interval upon receiving the switching signal in order to determine whether the changeover contact is switched within the predetermined time interval in accordance with the switching signal. The predetermined, i.e. previously defined, time interval can be, for example, 50 ms.This advantageously allows for needs-based monitoring of the changeover contact. In one embodiment, the contact monitoring device can comprise an optical display element configured to indicate the detection of the switching signal and a corresponding detected switching of the changeover contact, or a deviation from the expected switching signal.

[0036] According to a further aspect of the invention, the contact monitoring device can comprise a control for controlling the switching state of the changeover contact. In other words, the switching state of the changeover contact can be specified via the control. For this purpose, the control can be configured to output a corresponding switching signal to the changeover contact (e.g., to energize a relay coil associated with the changeover contact). Preferably, the control is also signal-connected to the evaluation device in order to provide the evaluation device with the switching signal and / or a desired switching state signal derived therefrom.

[0037] According to a further aspect of the invention, the contact monitoring device and the changeover contact can be housed in a common housing. In other words, the contact monitoring device and the changeover contact can form a structural unit. The housing preferably comprises a plurality of connections, which can be designed, for example, in the form of socket plugs. For example, the housing can comprise a supply connection 11d for supplying power to the contact monitoring device, two control connections for controlling the switching state of the changeover contact, three load connections for connecting to a load to be switched, and / or an output connection for outputting a status and / or control signal. Overall, a structurally compact, integrated solution for monitoring a changeover contact can thus be provided in an advantageous manner.Alternatively, the contact monitoring device can also be a separate device from the changeover contact. For example, the contact monitoring device can be part of a module base into which a corresponding switching module with a changeover contact can be plugged. In this case, the contact monitoring device or the module base can further comprise three contact connections, which can be designed, for example, as socket connectors, and are configured to receive corresponding contacts on the changeover contact or switching module. Furthermore, the contact monitoring device or the module base can comprise one or more switching signal outputs for providing a switching signal for the changeover contact, wherein the switching signal outputs can in turn be configured to receive corresponding switching contacts on the changeover contact or switching module.

[0038] The above-described aspects and features of the invention can be combined with one another in any desired manner. Further details and advantages of the invention are described below with reference to the accompanying drawings. They show: Figure 1: a schematic representation of a three-pole changeover contact according to a general embodiment; Figure 2: a schematic representation of a contact monitoring device for a three-pole changeover contact according to an embodiment of the invention; Figure 3: a schematic representation of a contact monitoring device for a three-pole changeover contact according to a further embodiment of the invention; Figure 4: a tabular listing of selected states of the changeover contact and the resulting interconnection of the impedances for the Figure 3shown embodiment; Figure 5: a tabular list of selected states of the changeover contact and the resulting connection of the impedances for a further development of the Figure 4 described embodiment; Figure 6: frequency-dependent curves of the magnitude of the impedance on the signal generator side of the coupling device of a contact monitoring device in one embodiment for different states of the changeover contact; Figure 7: a schematic representation of a contact monitoring device for a three-pole changeover contact according to a further embodiment of the invention; and Figure 8: a tabular list of selected states of the changeover contact and the monitoring signals resulting therefrom for the Figure 7 shown embodiment.

[0039] Identical or functionally equivalent elements are described in all figures with the same reference numerals and some are not described separately.

[0040] Figure 1shows a schematic representation of a three-pole changeover contact 2 according to a general embodiment. In this case, the changeover contact 2 is—merely by way of example—part of an electromechanical relay 10 or changeover relay. The relay 10 comprises three terminals assigned to the changeover contact 2, which will be referred to below—according to the usual convention—as COM terminal 2a, NC terminal 2b, and NO terminal 2c. Furthermore, the relay 10 comprises two relay coil terminals 3a and 3b, via which a relay coil 3 of the relay 10 can be energized. Via the current flow, the relay coil 3 creates a magnetic field which is guided in a magnetic core 4 and exerts a force on a movable relay armature 5, which in turn causes a movement of one or more contact elements or contact pills 7a, 7b, 7c assigned to the respective terminals 2a, 2b, 2c via a slider 6.For example, in the present - merely exemplary - case, when current flows through coil 3, the COM contact plug 7a is connected to the NO contact plug 7c. If the current flow through coil 3 is interrupted, the contact plugs 7a, 7b, 7c are returned to their original position, e.g., due to a corresponding resilient tension of the COM contact element 7a, i.e., in this case, the COM contact plug 7a is contacted with the NC contact plug 7b. In addition to the embodiment shown here, in which a changeover contact 2 is part of an electromechanical relay 10, the generic changeover contact 2 can also be integrated into other devices, such as a changeover switch.

[0041] Figure 2shows a schematic representation of a contact monitoring device 100 for a three-pole changeover contact 2 according to an embodiment of the invention. A "three-pole" changeover contact 2 is generally understood to mean a changeover contact 2 with three poles or three terminals 2a, 2b, 2c. For example only, the switching position of the changeover contact 2 can be specified via a control 8, which controls a relay coil 3, wherein the relay coil 3 is connected to the changeover contact 2 or its contact elements, as described above in connection with Figure 1described. The contact monitoring device 100 for monitoring the changeover contact 2 has a signal generator 110, which is designed to generate a monitoring signal Sü. The monitoring signal S Ü can generally be a high-frequency auxiliary energy. By way of example only, the signal generator 110 can have a Colpitts oscillator for this purpose, which includes a transistor 111, the operating point of which can be adjusted via a base voltage divider with resistors 112 and 113 and an emitter resistor 114. The base of the transistor 111 is also connected to ground via a capacitor 115 in order to short-circuit high-frequency components present at the base to ground.Furthermore, the Colpitts oscillator comprises an oscillating circuit, which determines the frequency of the monitoring signal S Ü , consisting of two series-connected capacitors 116 and 117 and an inductor 121, which in this case is designed as a coil and can also be considered part of a coupling device 120, described in more detail below. Furthermore, a voltage component determined by the capacitance ratio of the capacitors 116 and 117 (capacitive voltage divider) is fed back to the emitter of transistor 111 via capacitor 117, whereby an overall monitoring signal S Ü can be generated in the form of a periodic alternating voltage signal.

[0042] Furthermore, the contact monitoring device 100 comprises a coupling device 120, which is connected downstream of the oscillator circuit or the signal generator 110. In the present case, the coupling device 120 is, for example, an inductive transmitter in the form of a transformer, which is designed to inductively couple the signal generator 110 to a sensing circuit 130, which will be described in more detail below. For this purpose, the transformer has a first inductance 121 (e.g., a first planar coil) and a second inductance 122 (e.g., a second planar coil), wherein the first inductance 121 is inductively coupled to the second inductance 122, e.g., via a magnetic core (not shown).As mentioned above, the first inductance 121 fulfills a dual function in the present embodiment, in that, on the one hand, it represents an element of the oscillator's resonant circuit and, on the other hand, forms the connection between the coupling device 120 and the signal generator 110. However, for a formally unambiguous assignment of the corresponding components, the first inductance 121 can be assigned to the signal generator 110, and the second inductance 122 or the magnetic core can be assigned to the coupling device 120. Preferably, the coupling device 120 provides galvanic isolation between the signal generator 110 and the sensing circuit 130.

[0043] The contact monitoring device 100 further comprises a sensing circuit 130, which is connected downstream of the coupling device 120 and is coupled to the changeover contact 2. By means of the aforementioned sensing circuit 130, which is coupled to the signal generator 110 via the coupling device 120, the oscillation behavior of the signal generator 110 and thus the monitoring signal S Ü and / or a signal derived from the monitoring signal (e.g., a current signal if the monitoring signal is a voltage signal) can be changed depending on a switching position of the changeover contact 2. In particular, the sensing circuit 130 is designed to change the monitoring signal S Ü generated by the signal generator 110 and / or the signal derived from the monitoring signal differently for at least three, preferably four, different switch positions of the changeover contact 2, which in connection with the Figures 3 to 6will be described in more detail later. In the present case, the sensing circuit 130 comprises, by way of example, a plurality of impedances, which is why the sensing circuit 130 can also be referred to as an impedance circuit in this embodiment. In order to change or influence the oscillation behavior of the signal generator 110 or the monitoring signal S Ü generated by it, the present sensing circuit 130 generally comprises three impedances 131, 132 and 133, which are each assigned to one of the connections 2a, 2b or 2c. A first impedance 131 is coupled to the COM connection 2a, a second impedance 132 to the NC connection 2b and a third impedance 133 to the NO connection 2c. Depending on the design, one or more of these three impedances can be omitted or be zero. Merely as an example, in the present embodiment, for example. B. the first impedance 131 is zero or a simple direct electrically conductive connection.The second and third impedances 132 and 133 can further be realized, for example, in the form of a series circuit comprising a second or third resistor 132a, 133a and a second or third capacitor 132b, 133b.

[0044] The sensing circuit 130 can also comprise further, but fundamentally optional, impedances, in particular if the contact monitoring device 100, as in the present embodiment, is merely an example of part of a relay base in which the COM, NC and NO connections 2a, 2b, 2c are electrically connected to corresponding load connections 9a, 9b, 9c for connection to corresponding loads (here, for example, load 12 or load 13). For example, the COM connection 2a can be electrically connected to the load connection 9a via a fourth impedance 134. The NC connection 2b can be electrically connected to the load connection 9b via a fifth impedance and the NO connection 2c can be electrically connected to the load connection 9c via a sixth impedance. Here, too, depending on the design, individual ones of these optional impedances can be omitted, i.e., for example, be zero or direct electrical connections can be made, e.g. B. can be realized via conductor tracks.In the present case, the fourth, fifth, and sixth impedances 134, 135, 136 are embodied, for example, in the form of ferrites, which are preferably low-impedance for low-frequency alternating current signals and high-impedance for high-frequency alternating current signals. The advantage of these additional impedances, i.e., the fourth, fifth, and sixth impedances 134, 135, 136, is that they can attenuate high-frequency signals at the load terminals 9a, 9b, 9c due to the coupling to the signal generator 110. This advantageously makes it possible to functionally isolate the contact monitoring device 100 from external circuitry at the load terminals 9a, 9b, 9c, while simultaneously allowing low-frequency signals with high current intensities to be efficiently conducted to terminals 2a, 2b, 2c.In other words, when viewed from the outside, the terminals 9a, 9b and 9c are virtually identical to the respective terminals 2a, 2b and 2c due to the low impedances 134, 135, 136 for a useful signal, so that a relay socket with a contact monitoring device 100 according to the embodiment shown does not differ or hardly differs from a conventional standard relay socket.

[0045] Additionally or alternatively, the optional impedances 137 and 138 can also be provided in the sensing or impedance circuit 130, which will be referred to below as seventh impedance 137 and eighth impedance 138. These impedances 137 and 138 can serve different purposes, e.g., for interference immunity and independence from external circuitry. For example only, they can consist of series resonant circuits with a seventh or eighth inductance 137a, 138a and a seventh or eighth capacitance 137b, 138b, respectively, wherein the series resonant circuits preferably each have a series resonant frequency at the operating frequency of the signal generator 110. The impedance of the series resonant circuits at the series resonant frequency is thus determined solely by resistive components of the inductance and capacitance and is therefore very low. In this way, on the one hand, an injected high-frequency voltage signal can be advantageously applied between the terminals 9a and 9b or9a and 9c, thus minimizing electromagnetic interference emissions at the connection terminals. Furthermore, the influence of any connected loads on the sensing circuit 130 can be minimized at the operating frequency of the signal generator 110, since these loads are connected in parallel with the low impedances 137 and 138.

[0046] Overall, preferably, all impedances present in the sensing or impedance circuit 130 are dimensioned such that they pose virtually no impairment to the wanted signal. For example, the capacitors 132b, 133b, 137b, and 138b of the impedances 132, 133, 137, and 138 can be very small, so that they have a very high impedance for the wanted signal and, consequently, are barely noticeable or unnoticeable. In this respect, the sensing circuit 130 or the contact monitoring device 100, viewed from the outside, behaves as if it were unnoticeable for a (DC or AC or low-frequency) wanted signal compared to a conventional circuit or simple connection. In other words, the components of the sensing circuit 130 are preferably designed so that they do not affect the impedance between the terminals 9a, 9b and 9c at the operating frequency of the loads to be switched (typically DC voltage or 50 Hz or 60 Hz).Furthermore, it should be noted that the components exemplified here as load connections 9a, 9b, 9c do not necessarily have to be actually accessible connections. Thus, the corresponding components can also simply be taps for internal signals of a complex product, e.g., a product with multiple functional units, so that connections 9a, 9b, 9c are only present indirectly or as internal signals / potentials.

[0047] Finally, the contact monitoring device 100 also comprises an evaluation device 140, which is designed to detect the monitoring signal Sü and / or the signal derived from the monitoring signal and / or a change in the monitoring signal S Ü and / or a change in the signal derived from the monitoring signal, in order to thereby monitor the changeover contact 2. For this purpose, the evaluation device 140 can be connected to the signal generator 110, for example, via a tap 118, wherein the monitoring signal S Ü generated by the signal generator 110 and a signal derived from the monitoring signal are present at the tap 118. In the present case, the evaluation device 140 is designed - merely as an example - in the form of a Greinacher circuit with two capacitors 141 and 142, two diodes 143 and 144 and resistor 145, wherein the circuit is designed to provide a rectified state signal SZ which is proportional to the oscillation amplitude of S Ü.The status signal SZ can characterize the actual switching state of the changeover contact 2 and can then be compared with, for example, a target switching state signal derived from a switching signal SS generated by the control 8 for the changeover contact 2, in order to thereby monitor a proper switching process or the state of the changeover contact 2.

[0048] Figure 3 shows a schematic representation of a contact monitoring device 100 for a three-pole changeover contact 2 with three terminals 2a, 2b, 2c according to a further embodiment of the invention. The structure basically corresponds to that of the Figure 2illustrated embodiment, wherein for the following discussion of the modification or influencing of the monitoring signal S Ü only the essential components are shown, without detailed circuits. In addition, the present embodiment of the contact monitoring device 100 has a supply connection 11d for the energy supply and two control connections 11a and 11b, which are connected to the control 8 for controlling the relay coil 3 and via which the switching state of the changeover contact 2, which in this case - again merely by way of example - is designed as a relay changeover contact, can be controlled. The evaluation device 140 is connected both to the control 8 and to the signal generator 110. The evaluation device 140 is designed to compare an actual switching state of the changeover contact 2, which is monitored or determined by the control 8, with a target switching state specified by the control 8.A control signal can then be output via the output terminal 11c, for example, which indicates whether the specified target switching state and the monitored actual switching state of the changeover contact 2 match.

[0049] The actual switching state of the changeover contact 2 is monitored in the evaluation device 140, for which purpose the monitoring signal S Ü, which varies depending on the switch position of the changeover contact 2, and / or a signal derived from the monitoring signal is detected. In the present embodiment, the changing or influencing of the monitoring signal S Ü or the signal derived from the monitoring signal takes place by the different interconnection of the impedances 131-138 of the sensing circuit 130 depending on the switch position of the changeover contact 2, so that depending on the switch position of the changeover contact 2, a preferably different total impedance is coupled into the signal generator 110 via the coupling device 120, which in turn results in different amplitudes of the monitoring signal S Ü.In other words, by suitable design of the impedances for the typically four distinguishable states of the changeover contact 2 at the frequency of the signal generator 110, four distinguishable signal amplitudes of Sü can be generated, which - as will be explained below in connection with . Figure 6 will be carried out - allow a clear assignment between signal amplitude and actual switch position.

[0050] Figure 4 shows a tabular list of selected states of the changeover contact 2 and the resulting connection of the impedances 131 to 138 of the sensing circuit 130 as an equivalent circuit diagram for the above-mentioned Figure 2or 3 respectively. Merely as an example, to simplify the discussion, the seventh and eighth impedances 137 and 138 are chosen as zero. If the changeover contact 2 is in "state 1", in which the COM terminal 2a is connected to the NC terminal 2b, the first impedance 131 is electrically connected to the second impedance 132 and the total impedance Z NC of the corresponding impedance circuit is given by Z NC = ((Z 133 + Z 136 + Z 134 )∥(Z 132 )) + Z 131 , where the symbol | | symbolizes a parallel connection and + a series connection. Furthermore, the respective index of the impedances Z is intended to refer to the correspondingly referenced impedance of the sensing circuit 130. That is, the designation "Z 133 " shall abbreviate the impedance 133, the designation "Z 134 " shall abbreviate the impedance 134, etc.If the changeover contact 2 is in "state 2", in which the COM terminal 2a is connected to the NO terminal 2c, the total impedance Z NO is Z NO = ((Z 132 + Z 135 + Z 134 ) ∥ Z 133 ) + Z 131 . If the changeover contact 2 is in "state 3", in which the COM terminal 2a is connected to the NC terminal 2b, the latter in turn being connected to the NO terminal 2b, the total impedance ZS is ZS = (Z 132 ∥ Z 133 ) + Z 131 . If the changeover contact 2 is in "state 4", in which there is no electrical connection between the three terminals 2a, 2b and 2c, the total impedance ZO is ZO = ((Z 133 + Z 136 )∥(Z 132 + Z 135 ))+ Z 131 + Z 134 . Overall, by appropriately designing the respective impedances 131-138 for the individual switching states of the changeover contact 2, different total impedances, i.e., total impedances characteristic of a respective switching state, can be provided.These then result in the signal generator 110 - mediated by the coupling to the signal generator 110 via the coupling device 130 - in the generation of different monitoring signals S Ü , ie monitoring signals which are characteristic of a respective switching state, which can then be evaluated by the evaluation device 140 in order to allow conclusions to be drawn about the corresponding switching state of the changeover contact 2.

[0051] Figure 5 shows the tabular list according to Figure 4with the further development that the fifth and sixth impedances 135 and 136 are chosen to be infinitely high and the first and fourth impedances 131 and 134 are chosen or approximated as zero. In switching state 1 of the changeover contact 2, the impedance 135 is bridged, resulting in a total impedance Z NC = Z 132. In switching state 2, the impedance 136 is bridged and the total impedance Z NO = Z 133 . In switching state 3, both impedances 135 and 136 are bridged, resulting in a total impedance ZS of ZS = Z 132 ∥ Z 133. In switching state 4 of the changeover contact 2, neither of the two impedances 135 and 136 is bridged and the total impedance ZO is a high impedance. It can be seen again that by appropriately dimensioning the impedances of the sensing circuit 130, different total impedances can be provided depending on the switch position, which can be evaluated accordingly.

[0052] Figure 6shows exemplary frequency-dependent curves of the impedance magnitude on the signal generator side of the coupling device 130 of a contact monitoring device 100 in one embodiment for four different states of the changeover contact 2. The corresponding changeover contact 2 should in turn comprise a common COM terminal 2a, an NC terminal 2b, and an NO terminal 2c. The impedance curves 61, 62, 63, and 64—which will be referred to below as the first, second, third, and fourth impedance curves for ease of differentiation—have a maximum dependent on the switching state of the changeover contact 2. The first impedance curve 61 is assigned to a switch position in which the COM, NC, and NO terminals 2a, 2b, 2c, i.e., all three terminals, are connected. The second impedance curve 62 is assigned to a switch position in which only the COM terminal 2a and the NC terminal 2b are connected.The third impedance curve 63 is assigned to a switch position in which only the COM terminal 2a and the NO terminal 2c are connected. The fourth impedance curve 64 is assigned to a switch position in which there is no connection between the COM, NC, and NO terminals 2a, 2b, 2c. The contact monitoring device 100 is designed to separate the impedance curves 61, 62, 63, and 64 by the largest possible amplitude difference by appropriately dimensioning the electrical components, in particular by suitably selecting the impedances 132 and 133.

[0053] The above discussion primarily focused on influencing or changing the amplitude of the monitoring signal as a function of a varying total impedance for monitoring the changeover contact. However, it is immediately apparent to those skilled in the art that other parameters of the monitoring signal, such as its frequency, phase position, decay behavior, propagation time, and / or signal shape, can also be used for changeover contact monitoring by appropriately adapting the units of the contact monitoring device. As already described, for example, in Figure 6As can be seen, the maximum of the impedance curves 61, 62, 63 and 64 does not lie at exactly the same frequency. In addition to the change in the amplitude of S Ü, the oscillator in the present embodiment thus oscillates at a (slightly) different frequency in each of the four switching states. By specifically optimizing the impedances 131, 132 and 132 - e.g. by using different capacitances in the impedances 131, 132 and 133, which in interaction with the inductance(s) 121, 122 of the coupling device 120 result in different LC resonance frequencies depending on the contact state - the distance between the resonances, i.e. the maximum of the impedance curves 61, 62, 63 and 64, could be increased even further and thus, additionally or alternatively, a differentiation of the switch position based on the respective characteristic frequency change could be realized.

[0054] Alternatively, it is also possible for signal generator 110 to generate a pulse-like monitoring signal S Ü , which, depending on the state of changeover contact 2, is influenced to varying degrees by the various impedances 131 to 138, or, for example, is attenuated to varying degrees, which in turn can be evaluated. In other words, the distinction can also be made based on a decay or oscillation behavior characteristic of the respective switching state.

[0055] Figure 7shows a schematic representation of a contact monitoring device 100 for a three-pole changeover contact 2 with three terminals 2a, 2b, and 2c according to a further embodiment of the invention. In contrast to the previous embodiments, the monitoring signal S Ü in the present case has at least a first monitoring sub-signal S Ü1 and a second monitoring sub-signal S Ü2. To generate them, the signal generator 110 of the contact monitoring device 100 comprises a first signal generator device 110-1 (e.g., a first high-frequency generator) and a second signal generator device 110-2 (e.g., a second high-frequency generator). For example only, the first monitoring sub-signal S Ü1 and the second monitoring sub-signal S Ü2 can, for example, contain different frequencies or be generated at different times.Furthermore, in the present embodiment, the coupling device 120 comprises a first coupling element 120-1 (e.g., a first inductive transformer) for coupling the first signal generator device 110-1 to the sensing circuit 130 and a second coupling element (e.g., a second inductive transformer) for coupling the second signal generator device 110-2 to the sensing circuit 130. The sensing circuit 130, in turn, is configured to couple the first monitoring sub-signal S Ü1 to a first connection subset of the changeover contact 2 and to couple the second monitoring sub-signal S Ü2 to a second connection subset. In the present case, for example, the first monitoring sub-signal S Ü1 is to be coupled to the connections 2a and 2b, and the second monitoring sub-signal S Ü2 is to be coupled to the connections 2a and 2c.In other words, the switching state with respect to the connections 2a and 2b can be monitored by means of the first monitoring sub-signal S Ü1 and the switching state with respect to the connections 2a and 2c can be monitored by means of the second monitoring sub-signal S Ü2. This means that the respective monitoring sub-signals S Ü1 and S Ü2 should each only react to a change in a part or a subset of the three connections 2a, 2b, 2c of the changeover contact 2. Overall, the first monitoring sub-signal S Ü1 and / or a signal derived from the first monitoring sub-signal S Ü1 can be changed by means of the sensing circuit 130 depending on a switching position of a first connection subset of the changeover contact 2 and the second monitoring sub-signal S Ü2 and / or a signal derived from the second monitoring sub-signal S Ü1 can be changed depending on a switching position of a second connection subset of the changeover contact 2, which e.g.by appropriate dimensioning of the impedances 131-138 of the sensing circuit 130. Finally, the contact monitoring device 100 in turn comprises an evaluation device 140, which is designed to detect the first and second monitoring sub-signals S Ü1 and S Ü2 and thus the monitoring signal S Ü, in order to monitor the changeover contact 2. In addition or alternatively, the evaluation device 140 can also be designed to detect a signal derived from the first and / or second monitoring sub-signals S Ü1 and S Ü2, in order to monitor the changeover contact 2. As explained below in connection with . Figure 8 is executed, four different switch positions of the changeover contact 2 can be reconstructed using appropriate logic.

[0056] Figure 8shows a tabular list of selected states of the changeover contact 2 and the resulting monitoring signals S Ü1 , S Ü2 and S Ü for the Figure 7 The embodiment shown here is exemplary. Digital signals with the respective states 1 (closed) and 0 (open) are generated from the two signals S Ü1 and S Ü2. This can, of course, also be implemented the other way around. Using suitable logic, the total of four changeover contact states can be reconstructed from this, as shown. List of reference symbols

[0057] 2 Changeover contact 2a COM connection 2b NC connection 2c NO connection 3 Relay coil 3a, 3b Relay coil connection 4 Magnetic core 5 Relay armature 6 Slider 7a COM contact cap 7b NC contact cap 7c NO contact cap 8 Control 9a, 9b, 9c Load connection 10 Relay 11a, 11b Control connection 11c Output connection 11d Supply connection 12, 13 Load 100 Contact monitoring device 110 Signal generator 110-1 First signal generator device 110-2 Second signal generator device 111 Transistor 112, 113 Resistor 114 Emitter resistor 115, 116,117Capacitor 118Tap 120Coupling device 120-1First coupling element 120-2Second coupling element 121First inductance 122Second inductance 130Sensing circuit 131First impedance 132Second impedance 132aSecond resistor 132bSecond capacitor 133Third impedance 133aThird resistor 133bThird capacitor 134Fourth impedance 135Fifth impedance 136Sixth impedance 137Seventh impedance 137aSeventh inductance 137bSeventh capacitance 138Eighth impedance 138aEighth inductance 138bEighth capacitance 140Evaluation device 141, 142Capacitor 143, 144Diode 145Resistance,

Claims

1. A contact-monitoring device (100) for monitoring an electrical, three-pole changeover contact (2), comprising: - a signal generator (110) that is configured to generate a preferably high-frequency monitoring signal (SÜ); - a preferably inductive coupling device (120), which is arranged downstream of the signal generator (110); - a sensing circuit (130), which is arranged downstream of the coupling device (120) and is coupled or couplable to the changeover contact (2); wherein by means of the sensing circuit (130), which is coupled to the signal generator (110) via the coupling device (120), the monitoring-signal generation of the signal generator (110) and thus the monitoring signal (SÜ) and / or a signal derived from the monitoring signal (SÜ) is changeable depending on a switching position of the changeover contact (2); - an evaluation device (140), which is configured to detect the monitoring signal (SÜ) and / or the signal derived from the monitoring signal (SÜ) and / or a change in the monitoring signal (SÜ) and / or a change in the signal derived from the monitoring signal (SÜ) in order thereby to monitor the changeover contact (2), characterized in that the sensing circuit (130) is configured to change the monitoring signal (SÜ) and / or the signal derived from the monitoring signal (SÜ) differently for at least three, preferably four, different switching positions of the changeover contact (2), and the sensing circuit (130) comprises one or more impedances (131 - 138) and is configured to provide, together with the changeover contact (2), a total impedance at the coupling device (120) that varies with the switching position of the changeover contact (2).

2. The contact-monitoring device (100) according to claim 1, characterized in that the sensing circuit (130) is configured to change an amplitude, a frequency, a phase angle, a decay behavior, a propagation time and / or a signal shape of the monitoring signal (SÜ) and / or the signal derived from the monitoring signal (SÜ) in dependence on the switching position of the changeover contact (2).

3. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the changeover contact (2) comprises a COM terminal (2a), an NC terminal (2b), and an NO terminal (2c), and that the sensing circuit (130) is configured to change the monitoring signal (SÜ) and / or the signal derived from the monitoring signal (SÜ) differently for at least three, preferably four, particularly preferably all, of the following switching positions: (a) no connection between the COM, NC, and NO terminals (2a, 2b, 2c); (b) only the COM terminal (2a) and the NC terminal (2b) are connected; (c) only the COM terminal (2a) and the NO terminal (2c) are connected; (d) only the NC terminal (2b) and the NO terminal (2c) are connected; and (e) COM, NC, and NO terminals (2a, 2b, 2c) are connected.

4. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the sensing circuit (130) is configured to provide a different total impedance at the coupling device (120) for at least three, preferably four, particularly preferably five switching positions of the changeover contact (2).

5. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the sensing circuit (130): (a) comprises a first impedance (131), preferably in the form of a series circuit made of a first resistor and a first capacitance, which is coupled to one terminal of the changeover contact (2); and / or (b) comprises a second impedance (132), preferably in the form of a series circuit made of a second resistor (132a) and a second capacitance (132b), which is coupled to another terminal of the changeover contact (2); and / or (c) comprises a third impedance (133), preferably in the form of a series circuit made of a third resistor (133a) and a third capacitance (133b), which is coupled to another terminal of the changeover contact (2).

6. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the sensing circuit (130) comprises one to three impedances (134, 135, 136), wherein each impedance (134, 135, 136) is arranged downstream of one terminal of the changeover contact (2) in order to attenuate high-frequency signals which, by means of the coupling device (120), are applied to the changeover contact (2) and / or to an electrical load and / or a voltage source coupled to the changeover contact (2); optionally wherein the sensing circuit (130) comprises at least one further impedance (137, 138), preferably each in the form of a series circuit consisting of an inductance (137a, 138a) and a capacitance (137b, 138b), wherein the at least one further impedance (137, 138) is respectively connected between two terminals of the changeover contact (2) in order to attenuate high-frequency signals between the terminals of the changeover contact (2).

7. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the coupling device (120) is either (a) an inductive transformer, or (b) comprises a transformer having a first inductance and a second inductance, wherein the first inductance is inductively coupled to the second inductance, or (c) is configured to galvanically isolate the signal generator (110) and the sensing circuit (130), or (d) is formed from at least two electromagnetically coupled antennas, or (e) is formed from at least two capacitors, preferably implemented as printedcircuit-board capacitors, optionally wherein features (a), (b), and (c) or features (a), (c), and (d) or features (c) and (e) can be combined pairwise or all together.

8. The contact-monitoring device (100) according to one of the preceding claims, characterized in that (a) the signal generator (110) is a high-frequency generator configured to generate a high-frequency monitoring signal (SÜ); and / or (b) the signal generator (110) comprises a Colpitts oscillator circuit; and / or (c) the signal generator (110) is connected, for example in parallel, to the changeover contact (2) via the coupling device (120) and the sensing circuit (130).

9. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the signal generator (110) has a tap (118) and is configured to provide the evaluation device (140) with the monitoring signal (SÜ) and / or the signal derived from the monitoring signal (SÜ) via the tap (118).

10. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the monitoring signal (SÜ) comprises at least a first monitoring partial signal (SÜ1) and a second monitoring partial signal (SÜ2), and that, by means of the sensing circuit (130), the first monitoring partial signal (SÜ1) and / or a signal derived from the first monitoring partial signal (SÜ1) is changeable in dependence on a switching position of a first subset of terminals of the changeover contact (2), and the second monitoring partial signal (SÜ2) and / or a signal derived from the second monitoring partial signal (SÜ2) is changeable in dependence on a switching position of a second subset of terminals of the changeover contact (2).

11. The contact-monitoring device (100) according to claim 10, characterized in that (a) the signal generator (110) comprises a first signal generator device (110-1) for generating the first monitoring partial signal (SÜ1) and a second signal generator device (110-2) for generating the second monitoring partial signal (SÜ2); and / or (b) the coupling device (120) comprises a first coupling element (120-1) for coupling the first signal generator device (110-1) to the sensing circuit (130) and a second coupling element (120-2) for coupling the second signal generator device (110-2) to the sensing circuit (130); and / or (c) the sensing circuit (130) is configured to couple the first monitoring partial signal (SÜ1) to a first subset of terminals of the changeover contact (2) and to couple the second monitoring partial signal (SÜ2) to a second subset of terminals of the changeover contact (2).

12. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the evaluation device (140) is configured to output a state signal (SZ) in dependence on the monitoring signal (SÜ) and / or the signal derived from the monitoring signal (SÜ), said state signal (SZ) indicating the switching positions of the changeover contact (2).

13. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the evaluation device (140) is configured to detect a switching signal (SS) for switching the changeover contact (2) and, in dependence on the switching signal (SS) and the change in the monitoring signal (SÜ) and / or the change in the signal derived from the monitoring signal (SÜ), to output a control signal (SK) which indicates whether the changeover contact (2) is switched in accordance with the switching signal (Ss), optionally that the evaluation device (140) is configured, upon receiving the switching signal (SS), to detect the monitoring signal (SÜ) and / or the signal derived from the monitoring signal (SÜ) and / or the change in the monitoring signal (SÜ) and / or the change in the signal derived from the monitoring signal (SÜ) within a predetermined time interval to determine whether the changeover contact (2) is switched in accordance with the switching signal (SS) within the predetermined time interval.

14. The contact-monitoring device (100) according to one of the preceding claims, characterized in that the contact-monitoring device (100) comprises an actuation (8) for controlling the switching state of the changeover contact (2).

15. A system, comprising: - a relay (10) having a changeover contact (2), and - a relay socket for receiving the relay (10), characterized in that the system further comprises a contact-monitoring device (100) according to one of claims 1 to 14 for monitoring the changeover contact (2) of the relay (10), and the contact-monitoring device (100) is part of the relay socket.