Device and method for monitoring a switching state of a relay

Abstract

A device and a method for monitoring the switching state of a relay are disclosed. The device includes a relay (3) connected to an electrically conductive line. The relay has two terminals to which the line can be connected. The line can be switched by the relay (3). For monitoring purposes, a predefined signal (1) is coupled onto the line of the first terminal by means of an input coupling (7). The predefined signal (1) is extracted from the line of the second terminal by means of an output coupling (8). The switching state of the relay (3) can then be determined by evaluating the extracted signal.

Description

[0001] The present invention relates to a device and a method for monitoring a switching state of a relay.

[0002] Such monitoring is necessary to determine whether a relay actually achieves the switching state specified for it. Due to mechanical influences or electrical stress, as well as malfunctions, a relay may not achieve the switching state it was intended for. This must be detected early to prevent malfunctions and even damage to the higher-level system that could be caused by the relay.

[0003] Relays and contactors are switches that can be operated electrically. Due to excessive stress, aging, or contamination of the contact surfaces, it can happen that switch contacts, once closed, cannot be opened again. In safety-critical applications, it is therefore necessary to be able to verify the actual switching state of the contacts.

[0004] In order to be able to assess the real switching state, it is advantageous to be able to assess the switching state as independently as possible of existing signals or components in order to also detect a malfunction that is caused depending on existing signals or components.

[0005] For this purpose, relays or contactors with an additional contact pair are known, which is mechanically connected to the contact pair(s) to be monitored. The switching state of the contact pair to be monitored can thus be determined via the switching state of the mechanically coupled contact pair.

[0006] However, the additional contact pair for monitoring the switching state increases the size of the relay or contactor, which is particularly problematic in applications with limited space (e.g., automotive applications). The ability to detect the switching state of a relay or contactor without the need for additional contact pairs is therefore desirable.

[0007] Furthermore, DE 29 21 095 A1 discloses a monitoring system for switching elements, wherein an additional signal is generated, which is compared with the control signal to determine whether the switching element has assumed the state it should have assumed according to the control signal. Thus, the disclosed device is dependent on the control signal for monitoring.

[0008] The object of the present invention is therefore to provide a device and a method for monitoring the switching state of a relay that can reliably monitor the switching state independently of existing signals or components of a higher-level system. Another object of the invention is to keep the relay or contactor as small as possible.

[0009] These objects are achieved by the features of the present claim 1 and by the features of the independent claim 9.

[0010] The invention is based on the assumption that a closed relay transmits a coupled signal better than an open one. By coupling and decoupling a signal before and after the relay or contactor, the switching state can be determined without an additional contact pair. The coupled signal can be modulated and coded as desired. The coupling and decoupling can be inductive or capacitive. A circuit for evaluating the coupled signal can evaluate the switching state.

[0011] For the purposes of this application, a relay is considered an electrical or electronic switch. Therefore, the term "relay" also includes electronic and electromechanical switches, as well as contactors.

[0012] For this purpose, a device is proposed with a relay and an electrically conductive line that is routed through the relay. This means that two terminals are provided on the relay, which are connected to the line, so that the line can be switched or controlled by the relay. The line can conduct an electrical signal.

[0013] Since the relay can also be switched electronically, a control connection can be provided in addition to the two connections, which, however, has no contact points with the cable passing through.

[0014] According to the invention, a predefined signal can now be coupled into the line. For this purpose, the line is connected to the first of the two terminals on the relay, and the predefined signal can be coupled into this line.

[0015] Coupling refers to adding a predefined signal to the signal on the line. This can be achieved, for example, through modulation.

[0016] The predefined signal must be distinguished from a constant voltage level and is preferably designed as a square wave signal, in particular as a symmetrical square wave signal.

[0017] A decoupled signal can still be decoupled from the line. To do this, the line is connected to the second of the two terminals on the relay, and a signal can be decoupled from this line.

[0018] Decoupling refers to the separation of an electrical signal from the signal on the line. This can be achieved, for example, by demodulation.

[0019] If the closed relay is functioning properly, the output signal is identical to the input predefined signal. However, if the relay malfunctions, there will be a difference between the output signal and the predefined signal.

[0020] The coupled, predefined signal is transmitted much better through a closed relay than through an open relay (ideally, an open relay transmits no signal at all). The output signal indicates whether the relay is open or closed.

[0021] Whether the relay is functioning properly can be determined by comparing the actual state of the relay with the desired state of the relay by comparing the predefined signal with the output signal taking the desired state into account.

[0022] This difference can be used to determine the switching state of the relay and also to determine whether the relay is malfunctioning by evaluating the decoupled signal.

[0023] The predefined signal can be coupled in using a high-pass filter. This passes the predefined signal through a high-pass filter, and the predefined signal can then be modulated onto the electrical signal of the line.

[0024] The high-pass filter's function is to isolate a useful voltage on the line (DC or low AC voltage (e.g., 50 Hz or 60 Hz)) that is routed through the relay from the signal generation circuit. At the same time, the high-pass filter allows the predefined signal to couple onto the line.

[0025] The extracted signal can be extracted using a bandpass filter. This filters the extracted signal through a bandpass filter to isolate a specific frequency range of the extracted signal.

[0026] To better evaluate the extracted signal, it may be advantageous to amplify it. Depending on the length of the signal transmission path, the extracted signal can be attenuated and made more easily interpretable again via the amplifier.

[0027] An operational amplifier can be used for this purpose, but amplifiers consisting of several active components would also be conceivable.

[0028] The evaluation can preferably be performed by a microcontroller. This is advantageous because it allows the evaluation to be highly customized to the intended use.

[0029] To do this, the evaluation can first examine the extracted signal for the presence of a signal that can be distinguished from a pure voltage level. If this is present, the relay is closed, since otherwise no signal transmission can take place through the relay.

[0030] Furthermore, the output signal can be compared with the predefined signal. When the relay is closed, the output signal should be identical to the predefined signal.

[0031] In addition to determining the relay's switching state, the evaluation can also detect a malfunction. To do this, the evaluation can compare the detected relay switching state with the desired relay switching state. If it is necessary to determine the relay's desired switching state (e.g., with electronic or electromechanical relays), this desired state can be compared with the detected switching state, and if there is a deviation, a result signal can be generated.

[0032] For the method for monitoring the switching state of a relay using the aforementioned device, the predefined signal is first coupled onto the line at the first terminal. For this purpose, the predefined signal, e.g., a square wave signal, is modulated onto the line signal.

[0033] The decoupled signal is then decoupled from the line at the second connection by a decoupling (8).

[0034] The switching state of relay (3) is then detected by evaluating the output signal. Detection is performed as previously described.

[0035] Further features are shown in the attached drawing. It shows: Fig. 1: Block diagram of a device according to the invention

[0036] Fig. 1 shows a block diagram of an apparatus according to the invention for carrying out the method according to the invention.

[0037] Fig. Figure 1 shows a wire that is routed via two terminals through a relay 3. Relay 3 is shown in the open position. This means that an electrical signal on the wire is not transmitted from the first terminal of the relay to the second.

[0038] A predefined signal 1 is now generated. This can be done, for example, using a voltage generator. In this embodiment, the predefined signal 1 is a symmetrical square wave. This can, for example, be implemented with an amplitude of 5 V, an offset of 2.5 V, and a frequency of 1 MHz.

[0039] The predefined signal 1 is then coupled to the line in front of the relay 3 via a coupling 7, which in the present embodiment is implemented by means of a high-pass filter 2.

[0040] Via an output coupling 8, which in the present embodiment is implemented as a bandpass filter 4, an output signal is output again after relay 3. This signal is conditioned or processed by an amplifier 5. The output signal thus processed can then be evaluated by an evaluation unit, implemented in the present embodiment as a microcontroller 6. This evaluation can then determine the switching state of relay 3.

[0041] Likewise, a result signal can be generated by the evaluation if the determined switching state of relay 3 differs from the expected switching state. For this purpose, the expected switching state must also be fed into the evaluation.

[0042] In the presented embodiment, the coupled signal cannot theoretically match the output signal because relay 3 is open. The coupled signal cannot therefore be transmitted from the first terminal of relay 3 to the second.

[0043] If a malfunction of the relay causes the coupled signal to be transmitted, at least partially, from the first connection of relay 3 to the second connection, this is detected by the evaluation, which can generate a result signal for further processing.

[0044] The present invention is not limited to the aforementioned features. For example, the predefined signal can be implemented as a sawtooth voltage. Likewise, it could be possible to feed the predefined signal back to the amplifier for direct comparison. Finally, the evaluation can be performed by an external computer. This would require appropriate interfaces for signal transmission to the computer. LIST OF REFERENCE SYMBOLS 1 signal 2 high pass 3 relays 4 bandpass 5 amplifiers 6 microcontrollers 7 Coupling 8 Extraction QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 29 21 095 A1

[0007]

Claims

[1] Device for monitoring a switching state of a relay, with a relay (3), with an electrically conductive line which is routed via two terminals of a relay (3) and can be switched by the relay (3), characterized by , that a predefinable signal (1) can be coupled to the line at the first terminal by means of a coupling (7), that a decoupled signal can be decoupled from the line at the second terminal by a decoupling (8) and the switching state of the relay (3) can be determined by evaluating the output signal. [2] Device according to claim 1, characterized by that the predefinable signal (1) is designed as a symmetrical square wave voltage. [3] Device according to claim 1 or 2, characterized by that the coupling (7) and / or the decoupling (8) can be carried out capacitively. [4] Device according to claim 1 or 2, characterized by that the coupling (7) and / or the decoupling (8) can be carried out inductively. [5] Device according to one of claims 1 to 4, characterized by that a high pass filter (2) is included and the coupling (7) can be carried out by means of the high pass filter (2). [6] Device according to one of claims 1 to 5, characterized by that a bandpass filter (4) is included and the coupling-out (8) can be carried out by means of the bandpass filter (4). [7] Device according to one of claims 1 to 6, characterized by that the coupled signal can be amplified by an amplifier (5). [8] Device according to one of claims 1 to 7, characterized by that the evaluation of the coupled signal can be carried out by a microcontroller (6). [9] Method for monitoring a switching state of a relay by means of a device according to one of claims 1 to 8, characterized bythat the predefinable signal (1) is coupled to the line of the first connection by a coupling (7), that the decoupled signal (1) is decoupled from the line of the second connection by a decoupling device (8) and that the switching state of the relay (3) is detected by evaluating the coupled signal. [10] Method according to claim 9, characterized by that the coupling (7) and / or the decoupling (8) is carried out capacitively. [11] Method according to claim 9, characterized by that the coupling (7) and / or the decoupling (8) is carried out inductively. [12] Method according to one of claims 9 to 11, characterized by that the decoupled signal is amplified by the amplifier (5). [13] Method according to one of claims 9 to 12, characterized by that for evaluation the pre-definable signal (1) is compared with the decoupled signal. [14] Method according to one of claims 9 to 13, characterized by that the evaluation generates a result signal which describes the detected switching state of the relay (3) for further processing.

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