WO2018059649A1 - Relay circuit - Google Patents

Abstract

A relay circuit has a voltage source (40), a relay (10a, 10b) having a coil (30) connected parallel to the voltage source (40), and a switch (42a, 42b) connected in series with the coil (30) of the relay (10a, 10b). A capacitor (50a, 50b) is connected parallel to the coil (30) of the relay (10a, 10b) so that a resonant circuit is formed, the damping behaviour of which depends on a fault state of the relay (10a, 10b). An evaluation device (54) connected to a signal pickup (52a, 52b) for picking up a voltage signal at the coil (30) of the relay (10a, 10b) is designed such that it detects a damping behaviour over time of the picked-up voltage signal in order to establish a fault state of the relay (10a, 10b) from said detected damping behaviour.

Description

 Relay circuit

The present invention relates to a relay circuit, i. an electronic circuit with at least one relay.

In the case of relays, there is basically the problem in practice that the relay contacts can be welded or glued together. This can then result in an undesired permanent start of the relay, although the control circuit of the relay is open.

Therefore, various measures have already been developed in order to be able to monitor or determine such a fault condition of the relay. Typically, this monitoring is done on the load side of the relay, for example using optocouplers and other additional circuit components. In addition, conventional monitoring usually requires an additional switching operation of the relay.

The invention has for its object to provide an improved relay circuit in which a fault condition of the relay can be reliably detected in a simple manner.

This object is achieved by a relay circuit having the features of claim 1. Particularly preferred embodiments and further developments of the invention are the subject of the dependent claims.

The relay circuit has a voltage source, a relay with a coil, with the coil of the relay to the voltage source connected in parallel, and a switch, which is connected in series with the coil of the relay on. According to the invention, a capacitor is additionally provided, which is connected in parallel with the coil of the relay, so that it forms an LC resonant circuit together with the coil. Furthermore, a signal tap for Picking up a voltage signal to the coil of the relay and an evaluation device which is connected to the signal tap provided. The evaluation device is designed such that it detects a temporal damping behavior of the tapped voltage signal and can conclude from the detected damping behavior on a fault condition of the relay.

The relay circuit according to the invention requires a small number of additional components, in particular the capacitor connected in parallel with the coil of the relay, and has a simple design. In addition, only the control current side of the relay circuit is needed to monitor the fault condition of the relay, while the load current side can remain unchanged. Furthermore, it is possible with the relay circuit of the invention to monitor a fault condition of the relay without additional switching operations of the relay. The invention is based on the following considerations. When closing the control circuit, the coil of the relay is energized, so that the electromagnet formed by this coil attracts a movable ferromagnetic armature, whereby working contacts of the relay contact each other and a load circuit of the relay is closed. Welding these work contacts, the armature of the relay remains even after opening the control circuit in the immediate vicinity of the electromagnet, whereby the armature receives electrical energy from the coil (eddy currents). If the coil of the relay is part of an LC resonant circuit, as in the relay circuit according to the invention, these eddy currents induced in the armature influence the damping behavior of this resonant circuit. In particular, the vibration in the LC resonant circuit is attenuated by these eddy currents stronger or faster than without them. That the oscillation of the LC resonant circuit will fade faster in the case of welded normally open contacts than in the case of a faultless relay. By monitoring the damping behavior of this vibration can be concluded in a simple way to a fault condition of the relay.

The relay circuit of the invention is not limited to any specific type of relay. In particular, relays may be used for AC circuits and for DC circuits on the load side of the relay. The relay can be used as a working current relay or be used as closed-circuit relay. The relay may, for example, be a relay with changeover contacts or a relay with only make contacts.

The term fault state of the relay in this context is intended to include in particular the two states of a faultlessly functioning relay (i.e., no welded working contacts) and a defective relay (i.e., welded working contacts). In further developments of the invention, further intermediate states such as, for example, an already existing tendency to weld the working contacts are recognizable. In an advantageous embodiment of the invention, an envelope generator circuit is further provided, which is connected between the signal tap and the evaluation device and which is designed to generate an envelope signal from the tapped voltage signal. The evaluation device is then preferably configured such that it detects a temporal damping behavior of the envelope signal generated by the envelope generator circuit in order to be able to conclude from the detected damping behavior on an error state of the relay. The envelope signal is usually easier to evaluate than the unprocessed voltage signal. In this context, the envelope signal should represent a special case of the voltage signal.

The envelope generator circuit preferably has a rectifier circuit with attenuation. Preferably, the envelope generator circuit includes a rectifier element (e.g., diode) associated with the signal tap. Preferably, the envelope generator circuit includes a smoothing capacitor.

In an advantageous embodiment of the invention, the evaluation device is further configured to detect an opening of the switch to detect a temporal damping behavior of the tapped voltage signal after opening the switch. The opening of the switch may preferably be detected by detecting a drive signal for the switch or monitoring a switching state of the switch.

In a further advantageous embodiment of the invention, the signal tap between the coil of the relay and the switch is provided. Further, the coil of the relay is preferably connected in parallel with a freewheeling diode.

In an advantageous embodiment of the invention, the relay circuit on several relays each with a coil. The coils of the relays are then each a switch in series and a capacitor connected in parallel and assigned a signal tap for tapping the voltage signal to the respective coil of a relay.

Preferably, a common evaluation device is provided for the coils of the plurality of relays.

Preferably, an at least partially common envelope generator circuit is provided for the coils of the plurality of relays. The above and other features and advantages of the invention will become more apparent from the following description of a preferred, non-limiting embodiment thereof with reference to the accompanying drawings. Therein show, in part schematically: FIG. 1 the structure of a relay;

Fig. 2 is a circuit diagram of a relay circuit according to the present invention;

 and FIG. 3 shows voltage-time diagrams of the voltage signals and the envelope signals for two different error states of the relay.

In Fig. 1, the structure of a relay is shown using the example of a relay with changeover contact.

The relay 10 has a common make contact 12 which is connected to a common working port 14, and a first working contact 16 (NC contact), which is connected to a first working port 18, and a second working contact 20 (NO contact), the with a second working connection 22 is bound. The common working contact 12 is provided at a free end of a ferromagnetic anchor 24 which is movably supported by a hinge 26. The armature 24 is held by a tension spring 28 in its rest position shown in Fig. 1. The relay 10 further includes a coil 30 wound around a ferromagnetic core 32 to form an electromagnet. The two ends of the coil 30 are connected to a first coil terminal 34 and a second coil terminal 36, respectively. The electromagnet 30, 32, the working contacts 12, 16, 20 and the armature 24 are preferably housed in a housing 38.

Fig. 1 shows the switching state of the relay 10 in the de-energized state of the coil 30 and in the case of a faultless relay 10. In the de-energized state of the coil 30, the electromagnet exerts no attraction to the ferromagnetic armature 32. By the tension spring 28, the armature 24 and thus the common working contact 12 are pulled upwards. That the common working contact 12 is electrically conductively connected to the first working contact 16. When the coil 30 of the relay 10 is energized, the electromagnet attracts the armature 24 against the force of the tension spring 28. The common working contact 12 on the armature 24 then comes into contact with the second working contact 20. When the current flow through the coil 30 ends, the armature 24 returns to its original position of FIG. In a defective relay 10, in which the common working contact 12 and the second working contact 20 are welded together, the armature 24 is held in the vicinity of the electromagnet even after completion of the current flow through the coil.

The relay 10 shown in Fig. 1 may preferably be integrated into a relay circuit of Fig. 2.

The relay circuit of FIG. 2 has, by way of example, two relays 10a and 10b, but is not limited to this number of relays. There may also be only one relay or more than two relays. Since the present invention advantageously requires only a modification of the control ^¬ circuit of the relay, only the control circuits are shown in Fig. 2. A representation of the load circuits of the relay has been omitted since the invention in this regard is in no way limited.

The coil of the first relay 10a is connected in parallel with a power supply 40. In series with the coil, a first switch 42a is connected, which is a switching transistor in this embodiment. When the first switch 42a is closed, the control circuit of the first relay 10a is closed, so that its coil is energized, in order to electrically connect the common working contact 12 to the second make contact 20 in a relay designed according to FIG.

In order to avoid destruction of the first switching transistor 42a by a self-induced in the coil of the first relay 10a high reverse voltage when opening the control circuit, i. Switching off the current through the coil, a first free-wheeling diode 44a is optionally connected in parallel to the coil of the first relay 10a.

The first switch 42a is driven by a first control signal source 46a in this exemplary embodiment. The control signal for opening or closing the first switch 42 is supplied to the first switch 42a, for example via a first resistor.

As illustrated in FIG. 2, a first capacitor 50a is connected in parallel to the coil of the first relay 10a. The first capacitor 50a and the coil of the first relay 10a together form an LC resonant circuit.

As illustrated by way of example in FIG. 3, when the first switch 42 is opened, ie when the current through the coil of the first relay 10a is switched off, a voltage signal U0 is produced first and then-in the case of a fault-free first relay 10a -by the LC resonant circuit of the capacitor 50a and coil a voltage signal U1 with a damped oscillation. If, on the other hand, the common make contact 12 and the second make contact 20 of the first relay 10b are welded together, in the ferromagnetic armature 24 of the first relay 10a, which is located in the immediate vicinity of the electrode. romagneten 30, 32 remains, eddy currents induced. These eddy currents in the armature 24 influence the damping behavior of the oscillation of the LC oscillation circuit in such a way that a voltage signal U2 with a stronger damping arises. The voltage signals U1, U2 can be tapped at a first signal tap 52a between the first switch 42a and the coil of the first relay 10a or the LC resonant circuit. The first signal tap 52a is connected to an evaluation device 54, which can detect the temporal damping behavior of the voltage signal U1, U2 and can recognize a fault condition (fault-free relay, welded working contacts) from this.

The evaluation device 54 has for this purpose, for example, a microcontroller or a comparator circuit. The evaluation device 54 detects the opening of the first switch 42a, for example, based on the voltage signal U0. Alternatively, the evaluation device 54 can also be supplied with the drive signal of the first control signal source 46a or the evaluation device 54 can itself monitor the switching state of the first switch 42a. In order to simplify the evaluation of the voltage signals on the coil of the first relay 10a for the evaluation device 54, the evaluation device 54 is preferably preceded by an envelope generator circuit 56. This envelope generator circuit 56 generates from the voltage signals U1 and U2 corresponding envelope signals U1 'and U2', which are also exemplified in FIG. The attenuation behavior of the voltage signals can be more easily detected from the envelope signals.

In the embodiment of FIG. 2, the envelope generator circuit 56 has a rectifier circuit with attenuation. In particular, the envelope generator circuit 56 may include a first rectifier element 58a in the form of, for example, a diode between the first signal tap 52 and the evaluation device 54 and a smoothing capacitor 60 with a resistor 62 connected in parallel.

The control circuit of the second relay 10b is constructed analogously to the control circuit of the first relay 10a. That is, a second switch 42b, which is controlled by a second control signal source 46b is connected in series with the coil of the second relay 10b, and an optional second free-wheeling diode 44b is connected in parallel to the coil of the second relay 10b. The coil of the second relay 10b is connected in parallel to the common voltage source 40 of the relay circuit. Alternatively, separate power sources may be provided for the control circuits of the various relays 10a, 10b.

For monitoring the fault condition of the second relay 10b, a second capacitor 50b is connected in parallel with the coil of the second relay 10b to form an LC oscillation circuit. A second signal tap 52b for the voltage signals U1, U2 on the coil of the second relay 10b is provided between this LC resonant circuit and the second switch 42b.

The evaluation device 54 is connected as a common evaluation device of the relay circuit with the signal taps 52a, 52b of both relays 10a, 10b. Likewise, the envelope generator circuit 56 is assigned to both relays 10a, 10b as a common envelope generator circuit of the relay circuit. As illustrated in FIG. 2, a second rectifier element 58b of the envelope generator circuit 56 is provided between the second signal tap 52b and the evaluation device 54. Alternatively, both signal taps 52a, 52b may be connected to the evaluation device 54 via a common rectifier element.

REFERENCE NUMBER LIST

10 relays

10a, 10b relay

 12 common working contact

 14 shared work connection

 16 first working contact

 18 first work connection

20 second contact

 22 second work connection

 24 anchors

 26 joint

 28 spring

30 coil

 32 core

 34 first coil connection

 36 second coil connection

 38 housing

40 voltage source

 42a, 42b switch

 44a, 44b freewheeling diode

 46a, 46b control signal source

 48a, 48b resistance

50a, 50b capacitor

 52a, 52b signal tap

 54 evaluation device

 56 Envelope generator circuit

 58a, 58b Rectifier element, esp. Diode

60 capacitor

 62 resistance

 U0 Voltage signal when opening the relay

 U1 voltage signal with open, properly controlled relays

UV envelope signal on open, properly driven relays Voltage signal with open, defective relay Envelope signal with open, defective relay

Claims

Relay circuit, comprising:  a voltage source (40);  a relay (10, 0a, 10b) having a coil (30), the coil (30) of the relay being connected in parallel with the voltage source (40); and  a switch (42a, 42b) connected in series with the coil (30) of the relay (10, 10a, 10b),  marked by  a capacitor (50a, 50b) connected in parallel with the coil (30) of the relay (10, 10a, 10b) so as to form a resonant circuit together with the coil;  a signal tap (52a, 52b) for picking up a voltage signal (U1, U2) on the coil (30) of the relay (10, 10a, 10b); and  an evaluation device (54) which is connected to the signal tap (52a, 52b) and is designed to detect a temporal damping behavior of the tapped voltage signal (IM, U2) and from the detected attenuation behavior to an error state of the relay (10, 10a, 10b). Relay circuit according to claim 1, wherein  Furthermore, an envelope generator circuit (56) is provided, which is connected between the signal tap (52a, 52b) and the evaluation device (54) and is designed to generate an envelope signal (U1 \ U2 ') from the tapped voltage signal (IM, U2). to create; and the evaluation device (54) is designed to detect a temporal damping behavior of the envelope signal (LH ¹ , U2 ') generated by the envelope generator circuit (56) and to deduce from the detected damping behavior an error state of the relay (10, 10a, 10b). 3. Relay circuit according to claim 2, wherein the envelope generator circuit (56) comprises a rectifier circuit with attenuation. Relay circuit according to one of the preceding claims, wherein the evaluation device (54) is designed to detect an opening of the switch (42a, 42b) and a temporal damping behavior of the tapped voltage signal (U1, U2) after opening the switch (42a , 42b) to detect and from the detected damping behavior on a fault condition of the relay (10, 10a, 10b) to close. Relay circuit according to one of the preceding claims, wherein the signal tap (52a, 52b) between the coil (30) of the relay (10, 10a, 10b) and the switch (42a, 42b) is provided. Relay circuit according to one of the preceding claims, in which the coil (30) of the relay (10, 10a, 10b), a freewheeling diode (44a, 44b) is connected in parallel. Relay circuit according to one of the preceding claims, which  a plurality of relays (10a, 10b) each having a coil (30),  wherein the coils (30) of the relays (10a, 10b) each have a switch (42a, 42b) in Row and a capacitor (50a, 50b) are connected in parallel and a signal tap (52a, 52b) for picking up the voltage signal (U1, U2) at the respective coil (30) is associated with a relay (10a, 10b). Relay circuit according to claim 7, wherein  for the coils (30) of the plurality of relays (10a, 10b) a common evaluation device (54) is provided. 9. Relay circuit according to claim 7 or 8, wherein  for the coils (30) of the plurality of relays (10a, 10b) an at least partially common envelope generator circuit (56) is provided.