EP1036398B1 - Electromagnetic relay - Google Patents

Description

The invention relates to an electromagnetic relay, according to the general concept of Claim 1, such as known from US-A-4412267.

With conventional solutions to ensure a short-circuit or overload resistance for a relay are predominant Protective devices used, which the load current in Interrupt a fault using thermal effects. These include in particular fuses or bimetallic contact springs.

SU 142 74 72 A1 is a short-circuit protection for a three-phase motor known, which realized with the help of reed relays is. However, the reed relays are separated from the motor relay. In particular, with motor relays, which switch on the motor power supply, No overload or short-circuit status can be queried.

The aim of the invention is to provide an inexpensive, integrated and particularly space-saving solution for a to create short-circuit or overload-proof relay, wherein in particular a differentiated response of the protective devices in the event of a permanent overload of the relay and not already desired with only brief current peaks is.

According to the invention, this goal is achieved by an electromagnetic Relay achieved according to claim 1.

A relay according to the invention can be interrupted reset the control current to a normal operating state. Compared to Hall sensors, which also have one Detection of a magnetic field emanating from an increased load current is possible, reed contacts offer the advantage of a temperature-independent behavior, a simple setting of trigger thresholds and easier to implement Evaluation circuits.

Advantageous embodiments with regard to the arrangement of the Reed contact relative to the load current conductor, the shield the reed contact from the magnetic field of the excitation coil as well as regarding the means for generating and processing the overcurrent signal and to turn off the control current are dependent Claims.

Figur 1 ein erfindungsgemäßes Relais mit einem auf einer Leiterplatte vormontierten Reedkontakt,

Figur 2 den auf einer Leiterplatte vormontierten Reedkontakt mit einem angekoppelten Laststromleiter gemäß Figur 1,

Figur 3 eine Variante eines erfindungsgemäßen Relais mit einem in einen Sockel eingelegten Reedkontakt,

Figur 4 den in einen Sockel eingelegten Reedkontakt mit einem angekoppelten Laststromleiter gemäß Figur 3,

Figur 5 eine weitere Variante eines erfindungsgemäßen Relais mit einem auf einem Sockel vormontierten Reedkontakt,

Figur 6 den auf einem Sockel vormontierten Reedkontakt mit einem angekoppelten Laststromleiter gemäß Figur 5,

Figur 7 ein Prinzipschaltbild eines erfindungsgemäßen Relais mit einem Hilfsreedkontakt und einer Hilfswicklung als Überstromschutzelementen,

Figur 8 ein Prinzipschaltbild einer Ausführungsform mit einem Hilfsrelais als Überstromschutzelement,

Figur 9 ein Prinzipschaltbild einer weiteren Ausführungsform mit einem Kaltleiter und einem Vorwiderstand als Überstromschutzelementen,

Figur 10 ein Prinzipschaltbild einer bistabilen Ausführungsform mit einem Kondensator als Pulsansteuerungselement,

Figur 11 ein Prinzipschaltbild einer Ausführungsform mit einer Auswerteelektronik zur Überstromerkennung und Laststromabschaltung und

Figur 12 eine Realisierung der Auswerteelektronik gemäß Figur 11.

The invention is explained in more detail below using exemplary embodiments with reference to the drawing. It shows

1 shows a relay according to the invention with a reed contact preassembled on a printed circuit board,

FIG. 2 shows the reed contact preassembled on a printed circuit board with a coupled load current conductor according to FIG. 1,

FIG. 3 shows a variant of a relay according to the invention with a reed contact inserted in a base,

FIG. 4 shows the reed contact inserted in a base with a coupled load current conductor according to FIG. 3,

FIG. 5 shows a further variant of a relay according to the invention with a reed contact preassembled on a base,

FIG. 6 shows the reed contact preassembled on a base with a coupled load current conductor according to FIG. 5,

FIG. 7 shows a basic circuit diagram of a relay according to the invention with an auxiliary reed contact and an auxiliary winding as overcurrent protection elements,

FIG. 8 shows a basic circuit diagram of an embodiment with an auxiliary relay as an overcurrent protection element,

FIG. 9 shows a basic circuit diagram of a further embodiment with a PTC thermistor and a series resistor as overcurrent protection elements,

FIG. 10 shows a basic circuit diagram of a bistable embodiment with a capacitor as a pulse control element,

FIG. 11 shows a basic circuit diagram of an embodiment with evaluation electronics for overcurrent detection and load current shutdown and

12 shows a realization of the evaluation electronics according to FIG. 11.

1 to 6 show variants of a relay according to the invention with different coupling of a reed contact K _R to a load current conductor 1. In the embodiment according to FIG. 1, the reed contact K _{R is} preassembled on a printed circuit board 4. A magnet system 6 is arranged on a base 5 and has a core, an armature and an excitation coil W _R. The axis of the excitation coil W _R extends parallel to the base plane of the base 6. In an outer area on the base 5, the printed circuit board 4 is fixed standing perpendicular to the base plane of the base 5. Two connection plates 2 and 3 are connected to the reed contact K _R (see also FIG. 2). Switching thresholds for the reed contact K _R can be defined by a suitable choice of the distance between the two connecting plates 2 and 3. The two conductor connection plates 2 and 3 are fitted together with the reed contact K _R on a printed circuit board 4, the reed contact K _{R being} oriented perpendicular to the base plane of the base 5. According to a preferred embodiment, the reed contact K _{R is} thus arranged perpendicular to the axis of the excitation coil W _R , as a result of which the reed contact K _R is insensitive to the magnetic stray flux of the excitation coil W _R. The load current conductor 1 is arranged in a section perpendicular to the reed contact K _R , with a suitable conductor design ensuring that the magnetic field generated by the load current conductor 1 passes through the reed contact K _R centrally and in parallel. In this embodiment, this is achieved in that the relevant section of the load current conductor 1 is formed by a sheet metal strip, the sheet metal plane of which extends parallel to the reed contact K _R.

In the embodiment shown in Figure 3, the magnet system 6 is arranged on the base 5 such that the axis of the excitation coil W _{R runs} parallel to the base plane of the base 5. The reed contact K _R is mounted between the magnet system 6 and the base 5 perpendicular to the axis of the excitation coil W _R and parallel to the base plane of the base 6. In this embodiment too, the reed contact K _{R is} connected to two contacting plates 2 and 3 (see also FIG. 4). The two contact plates 2 and 3 are at a distance from one another which determines the switching threshold of the reed contact K _R. The unit formed from the contacting plates 2 and 3 and the reed contact K _R is inserted into the base 5, the load current conductor 1 being inserted in one section in the middle through a sensor ring R _S formed from the reed contact K _R and the contacting plates 2 and 3. The load current conductor 1 is formed in this section by a bent sheet metal strip, so that the sensor ring R _S lies at a free end of the sheet metal strip perpendicular to the load current conductor 1 and encloses it. As an alternative to the example shown in FIG. 4, the sensor ring R _{S can} also be formed by a U-shaped, magnetically conductive flux ring and a reed contact K _R coupled to it via two air gaps.

FIG. 5 shows an exemplary embodiment of a relay with a reed contact K _R preassembled on a base 5, the reed contact K _{R being} oriented perpendicular to the base plane of the base 5. In this exemplary embodiment, the magnet system 6 is mounted on the base 5 such that the axis of the excitation coil W _R extends parallel to the base plane of the base 5. The load current conductor 1 is essentially formed by a sheet metal strip, a first end of the load current conductor 1 being inserted vertically through the base as a connecting element. The second end of the load current conductor 1 runs parallel to the axis of the excitation coil W _R (see also FIG. 6). In a central section, the load current conductor 1 is formed into a loop surrounding the reed contact K _R. A corresponding shaping of the load current conductor 1 in this central section ensures that the magnetic field coupled into the reed contact K _R by the load current conductor 1 passes through the reed contact K _{R in the} center and in parallel. The reed contact K _R is bent together with its connecting wires in a U-shape and fastened with the ends of the connecting wires to extensions of two connecting loops 7 and 8. The reed contact K _{R can be connected} to the extensions of the connection loops 7 and 8 arranged below the magnet system 6, for example by soldering or resistance welding. The distance between the two connection loops 7 and 8 defines the switching threshold of the reed contact K _R. In all of the exemplary embodiments shown in FIGS. 1 to 6, there is an advantage in that the assembly of the reed contact K _R and the coupling of the reed contact K _R to the load current conductor 1 do not require any significant design changes to the relay.

FIG. 7 shows a basic circuit diagram of a relay with an auxiliary reed contact and an auxiliary winding as overcurrent protection elements. The relay R has a control circuit, which is associated with an excitation winding W _R through which a control current I _S is assigned, and a load circuit, the load current I _L being controllable by a movable contact element K _B and a fixed contact element K _{F of} the relay R. A reed contact K _{R is} arranged in the control circuit, through which the control current I _S can be controlled by the excitation coil W _R. The reed contact K _R is coupled to a load current conductor through which the load current I _L flows. The magnetic coupling between the load current conductor and the reed contact K _R is subsequently symbolized by a load current conductor winding W _L. In the exemplary embodiment according to FIG. 7, the reed contact K _{R has} a movable contact element E1 and two fixed contact elements E2 and E3. Furthermore, an auxiliary winding W _{H1 is} coupled to the reed contact K _{R in} such a way that, in an overcurrent operating state, the auxiliary winding W _{H1 emits} a magnetic field which is in the same direction as a magnetic field caused by a load current winding W _L.

The load current I _L is switched directly via the movable contact element K _B and the fixed contact element K _{F of} the relay R. The reed contact K _R can be arranged axially within the load current winding W _L. A reed contact K _R lying outside the load current winding W _L , which is arranged parallel to the winding axis, is also possible. An alternative to coupling the reed contact K _R to a load current winding W _L is to arrange the reed contact K _R within a loop-shaped section of a load current conductor.

In order to prevent the reed contact K _R from being influenced by the magnetic field of the excitation coil W _{R of} the relay R, the reed contact K _{R is} advantageously to be arranged perpendicular to the axis of the excitation coil W _R. Alternatively, the aforementioned influence can be prevented by a magnetically conductive shielding plate between the excitation coil W _R and the reed contact K _R. A magnetic stray field originating from the excitation coil W _{R is} short-circuited by the shielding plate. Another possibility is to selectively introduce the magnetic stray flux emanating from the excitation coil W _R into the reed contact K _R. This is possible, for example, by regulating the control current I _S. As a result, a constant magnetic flux acts as an offset on the reed contact K _R. By defining corresponding threshold values at the reed contact K _R , it is possible to use the stray magnetic field.

In a normal operating state, the reed contact K _R connects the excitation coil W _{R of} the relay _R to a control voltage source U _S via a first fixed contact element E2 of the reed contact K _R. In this state, the auxiliary winding W _H coupled to the second fixed contact element E3 is separated from the movable contact element E1 of the reed contact K _R and thus from the control voltage source U _S. In contrast, in an overcurrent operating state, the movable contact element E1 of the reed contact K _{R is} connected to the second fixed contact element E3 and separated from the first fixed contact element E2. As a result, the excitation winding W _{R of} the relay R is separated from the control voltage source U _S , while the auxiliary winding W _{H is} connected to the control voltage source U _S. Even after the load circuit has been interrupted, the connection between the movable contact element E1 of the reed contact K _R and the second fixed contact element E3 is maintained due to the magnetic flux emanating from the auxiliary winding W _H. Only after disconnection from the control voltage source U _S does the relay R return to the normal operating state.

FIG. 8 shows a basic circuit diagram of an alternative configuration option for a short-circuit-proof relay, in which the overcurrent protection function is implemented by means of an auxiliary relay R _H1 . The auxiliary relay R _H1 has a movable contact element E4 and two fixed contact elements E5 and E6, the movable contact element E4 being connected to the first fixed contact element E5 in the normal operating state. The movable contact element E4 is connected directly to a control voltage input terminal, so that the control voltage U _{S is applied} directly to the excitation coil W _{R of} the relay R. The reed contact K _R is connected between the contact element E4 of the auxiliary relay R _H1 and the second fixed contact element E6.

The coil W _{H2 of} the auxiliary relay R _H1 is de-energized in the normal operating state. In the overcurrent operating state, the reed contact K _{R is} closed, as a result of which the control voltage U _{S is applied} directly to the coil W _{H2 of} the auxiliary relay R _H1 . As a result, the movable contact element E4 is connected to the second fixed contact element E6 of the auxiliary relay R _H1 and separated from the first fixed contact element E5. Because of this, the excitation coil W _{R of} the relay R is de-energized in the overcurrent operating state. Because the load circuit and the control circuit of the auxiliary relay R _H1 are connected in series in the overcurrent operating state, the auxiliary relay R _H1 maintains its switch position even after the load circuit of the relay R has been interrupted by actuating the contact element K _B and opening the reed contact K _R. If a time delay unit is additionally arranged between the reed contact K _R and the second fixed contact element E6 of the auxiliary relay R _H1 , brief load current peaks do not trigger the overcurrent protection device. Instead of the auxiliary relay R _H1 , a second reed contact can be used, which is then coupled to an associated auxiliary winding.

FIG. 9 shows a further alternative for implementing overcurrent protection with a _PTC thermistor R _PTC and a series resistor R _{v connected in series} . These two overcurrent protection elements are connected in series with the reed contact K _R to the control voltage source U _S , the reed contact K _{R being} initially closed in the overcurrent operating state and opened in the normal operating state. The excitation coil W _{R of} the relay R is connected in parallel with the reed contact K _R and the series resistor R _V and in series with the _PTC thermistor R _PTC . Since the series resistor R _V is low-ohmic in comparison with the internal resistance of the excitation coil W _{R of} the relay R, an increased current flows through the _PTC thermistor R _PTC after the reed contact K _{R is closed, as} a result of which the latter heats up and becomes high-impedance. As a result, the voltage drop across the excitation coil W _{R of} the relay decreases, so that the load circuit is interrupted. Depending on the heating behavior of the _PTC thermistor R _PTC , a time delay is reached, which means that short-term load current peaks do not trigger protection. In addition, the _PTC thermistor R _PTC performs a status memory function if the residual current through the excitation coil W _{R of} the relay R is sufficient to maintain the required _PTC thermistor temperature. In this case, the _PTC thermistor R _PTC remains in a high-resistance state even after the reed contact K _{R is} reopened. Only after disconnection from the control voltage source U _S and cooling of the _PTC thermistor R _PTC can the relay R be activated again.

10 shows a basic circuit diagram of an embodiment with a bistable relay R _2S and a capacitor C _S. The bistable relay R _2S is equipped with a first field winding W _R1 and a second field winding W _R2 . The first field winding W _{R1 of} the relay R _2S is connected in series with the capacitor C _S to the control voltage source U _S. The second excitation winding W _R2 is connected in series with the reed contact K _R to the control voltage source U _S and has an opposite winding sense compared to the first excitation winding W _R1 . A positive pulse of the current I _S1 through the first field winding W _R1 thus causes the load circuit to be closed, while a positive pulse of the current I _S2 through the second field winding W _R2 interrupts the load circuit. In the event of an overcurrent, the reed contact K _R first connects the second excitation winding W _R2 to the control voltage source U _S , whereupon the relay R _{2S changes} to a stable switched-off state. Only after the control voltage U _S is switched off and on again does the first excitation winding W _R1 receive a positive current pulse via the capacitor C _{S, as} a result of which the relay R _{2S changes} to a stable switched-on state.

In the basic circuit diagram of a variant of the short-circuit or overcurrent-proof relay shown in FIG. 11, the overcurrent protection functions are integrated in an overcurrent protection device which is implemented by an electronic circuit CCU. The electronic circuit CCU has four connections, the control voltage U _{S being} present between a first control voltage connection K1 and a second control voltage connection K2. Furthermore, the electronic circuit CCU has a first excitation coil connection K3 and a second reed contact connection K4. The first reed contact connection and the second excitation coil connection are connected to the second control voltage connection K2. The electronic circuit CCU can be integrated as an application-specific integrated circuit (ASIC) in a very simple manner into the circuit board 4 of the relay shown in FIG. 1 or also into the base 5 of the relay shown in FIGS. 3 and 5.

A possible implementation in terms of circuitry for the overcurrent protection device according to FIG. 11 is shown in FIG. The electronic circuit CCU is divided into a timing element U1, a switch-on path U2 for the excitation coil W _R and a switch-off path U3. The switch-on path U2 for the relay coil W _R consists of a pnp transistor T1 connected in series with the relay coil W _R between the two control voltage connections K1 and K2 and a series resistor R2. The transistor T1 is connected with its emitter to the first control voltage connection K1 and with its collector to the first excitation coil connection K3. The series resistor R2 of the switch-on path U2 is connected between the base of the transistor T1 and the second control voltage connection K2.

The switch-off path U3 for the excitation coil W _R is formed by a first resistor R4 and a second resistor R3. The first resistor R4 is connected in parallel to the excitation coil W _R , while the second resistor R3 of the switch-off path U3 is connected between the first excitation coil connection K3 and the second reed contact connection K4.

The timing element U1 has a comparator CMP and an RC element on, the capacitor C1 of the RC element having a first Connection connected to the first control voltage connection K1 is. The resistance R1 of the RC element is between that second terminal K5 of the capacitor C1 and the second reed contact terminal K4 connected. The comparator CMP itself consists of a pnp transistor T2 and a zener diode D1, the transistor T2 of the comparator CMP with its emitter is connected to the first control voltage connection K1, while the collector of transistor T2 with the base of Transistor T1 of the switch-on path U2 is connected. The base of the transistor T2 of the comparator CMP is at the cathode the Zener diode D1 connected, the anode between the Capacitor C1 and the resistor R1 of the RC element connected is.

When the control voltage U _{S is applied} to the control voltage connections K1 and K2 of the electronic circuit CCU, a control current flows through the emitter-base path of the transistor T1 of the switch-on path U2 and turns on the transistor T1. As a result, the excitation coil W _{R of} the relay R is supplied with a switching voltage, whereupon the load circuit is closed. The transistor T1 is switched via the resistor R2, the switching speed of the transistor playing an important role. Before activating the timer U1 it must be ensured that the relay R switches through first when the control voltage U _{S is} applied. The timing element U1 has the task of blocking the transistor T2 of the comparator CMP until the transistor T1 of the switch-on path U2 is turned on. The transistor T2 of the comparator CMP then changes to a stable, blocked state, which is achieved by the feedback of the collector voltage of the transistor T1 via the resistors R3, R1 and the zener diode D1.

In the event of an overcurrent, the reed contact K _R closes and connects the base of the transistor T2 directly to the second control voltage connection K2. This causes capacitor C1 to discharge through resistors R1 and R3. After the breakdown voltage at the Zener diode D1 has been exceeded, a control current flows through the emitter-base path of the transistor T2, which turns on the transistor T2 and electrically connects the base of the transistor T1 of the switch-on path U2 to the first control voltage terminal K1. The switch-off path U3 is then activated via the transistor T2 of the timer U1, as a result of which the transistor T1 of the switch-on path U2 changes to the blocked state. As a result, the excitation coil W _{R of} the relay R is separated from the control voltage source U _S , so that the load circuit is interrupted. The result of this is that the reed contact K _R opens again, since no overcurrent now flows through the load circuit. The switch-off path U3 remains activated since the transistor T2 of the comparator CMP remains in the conductive state unchanged. This operating state is maintained or stored until the control voltage U _S at the control voltage connections K1 and K2 of the electronic circuit CCU is switched off.

An unwanted activation of the overcurrent protection device at Inrush or switching current peaks, which are usually less than a few 100 milliseconds, Timer U1 prevented. By appropriate dimensioning the resistor R1, the capacitor C1 of the timer U1, of the resistors R3 and R4 of the switch-off path U3 and the selection of a Zener diode D1 with a suitable breakdown voltage can the timing of the electronic Switching CCU to the duration of expected inrush or switching current peaks be adjusted. At the same time, through the timing element U1 also generates interference pulses at the control voltage connections K1 and K2 filtered out.

Claims (24)

1. An electromagnetic relay, having

   a magnet system (6) containing: an exciter coil (W_R) through which there flows a control current (I_S) and which is connected to a control voltage (U_S); a core; and an armature, with the core and the armature forming at least one operative air gap,

   at least one movable contact element (K_B) and at least one fixed contact element (K_F) through each of which a load current circuit can be completed,

   coil and contact terminal elements,

   a reed contact (K_R) for each load current circuit, which is coupled to a load current conductor (1) through which a load current (I_L) flows, and

   means, coupled to the reed contact (K_R), for generating and processing an overcurrent signal and for switching off the control current (I_S),

      characterised in that
      these means generate an overcurrent signal and continue to process such that the switched-off condition of the control current (I_S) is maintained until the control voltage (U_S) is switched off.
2. A relay according to Claim 1, characterised in that the reed contact (K_R) is integrated in an electrically and magnetically conductive, open flux ring which surrounds the load current conductor (1).
3. A relay according to Claim 1, characterised in that the reed contact (K_R) is coupled by way of two air gaps to an electrically and magnetically conductive, open flux ring which surrounds the load current conductor (1).
4. A relay according to Claim 1, characterised in that the load current conductor (1) is in one section shaped into a loop which surrounds the reed contact (K_R).
5. A relay according to one of Claims 1 to 4, characterised in that the load current conductor (1) is arranged in a section perpendicular to the reed contact (K_R), with the magnetic flux fed from the load current conductor (1) into the reed contact (K_R) passing through the reed contact (K_R) centrally and parallel.
6. A relay according to Claim 1, characterised in that the load current conductor (1) is in one section wound into a coil (W_L), with the reed contact (K_R) being arranged axially in the coil (W_L).
7. A relay according to Claim 1, characterised in that the load current conductor (1) is in one section wound into a coil (W_L), with the reed contact (K_R) being arranged outside the coil (W_L) and parallel to its axis.
8. A relay according to one of Claims 1 to 7, characterised in that the reed contact (K_R) is arranged perpendicular to the axis of the exciter coil (W_R).
9. A relay according to one of Claims 1 to 7, characterised in that between the reed contact (K_R) and the exciter coil (W_R) there is arranged a magnetically conductive plate.
10. A relay according to one of Claims 1 to 7, characterised in that the exciter coil (W_R) is coupled to a current regulator in order to introduce a defined magnetic flux into the reed contact (K_R).
11. A relay according to one of Claims 1 to 10, characterised in that the means for generating and processing the overcurrent signal and for switching off the control current (I_S) are grouped together to form an overcurrent protection unit.
12. A relay according to Claim 11, characterised in that the reed contact (K_R) has a movable contact element (E1) and two fixed contact elements (E2, E3), in that the overcurrent protection unit is formed by an auxiliary winding (W_H1) coupled to the reed contact (K_R), in that the movable contact element (E1) of the reed contact (K_R) is connected to a first control voltage terminal, in that a first terminal of the exciter coil (W_R) is connected to a first fixed contact element (E2) of the reed contact (K_R), in that a first terminal of the auxiliary winding (W_H1) is connected to the second fixed contact element (E3) of the reed contact (K_R), in that the second terminal of the exciter coil (W_R) and the second terminal of the auxiliary winding (W_H1) are connected to the second control voltage terminal, in that the movable contact element (E1) of the reed contact (K_R) is connected, in a normal operating condition, to the first fixed contact element (E2) of the reed contact (K_R), and in that the movable contact element (E1) of the reed contact (K_R) is connected, in an overcurrent operating condition, to the second fixed contact element (E3) of the reed contact (K_R).
13. A relay according to Claim 12, characterised in that the auxiliary winding (W_H1) is coupled to the reed contact (K_R) such that in the overcurrent operating condition there is emitted from the auxiliary winding (W_H1) through which current flows a magnetic field which at the reed contact (K_R) is in the same direction as the magnetic field created by the load current (I_L).
14. A relay according to Claim 11, characterised in that the overcurrent protection unit is formed by an electromagnetic switching unit which has a movable contact element (E4), two fixed contact elements (E5, E6) and a coil (W_H2), in that the movable contact element (E4) of the switching unit is connected to a first control voltage terminal, in that a first terminal of the exciter coil (W_R) is connected to a first fixed contact element (E5) of the switching unit, in that a first terminal of the coil (W_H2) of the switching unit is connected to the second fixed contact element (E6) of the switching unit, in that the second terminal of the exciter coil (W_R) and the second terminal of the coil (W_H2) of the switching unit are connected to the second control voltage terminal, in that the reed contact (K_R) is connected between the first control voltage terminal and the first terminal of the coil (W_H2) of the switching unit, in that the movable contact element (E4) of the switching unit is connected, in a normal operating condition, to the first fixed contact element (E5) of the switching unit, and in that the movable contact element (E4) of the switching unit is connected, in an overcurrent operating condition, to the second fixed contact element (E6) of the switching unit.
15. A relay according to Claim 14, characterised in that a time delay unit is placed between the reed contact (K_R) and the coil (W_H2) of the switching unit.
16. A relay according to Claim 14 or 15, characterised in that the electromagnetic switching unit is in the form of an auxiliary relay (R_H1).
17. A relay according to Claim 14 or 15, characterised in that the electromagnetic switching unit is in the form of an auxiliary reed contact.
18. A relay according to Claim 11, characterised in that the overcurrent protection unit is in the form of a PTC thermistor (R_PTC) and a serially connected series resistor (R_V) which is connected, in series with the reed contact (K_R), to the control voltage source (Us), in that the reed contact (K_R) is opened (contact broken) in a normal operating condition and closed (contact made) in an overcurrent operating condition, and in that the relay coil (W_R) is placed in parallel with the reed contact (K_R) and the series resistor (R_V) and in series with the PTC thermistor (R_PTC).
19. A relay according to Claim 11, characterised in that the overcurrent protection device is integrated in the magnet system (6), which in order to create two stable switching conditions has an additional, second exciter coil (W_R2), with the exciter coils (W_R1, W_R2) being wound in opposing directions and with a control current (I_S1) through the first coil (W_R1) putting the relay into a switched-on condition, while a control current (I_S2) through the second coil (W_R2) puts the relay into a switched-off condition, in that the first coil (W_R1) is connected in series with a capacitor (C_S) to the control voltage source (Us), and in that the second coil (W_R2) is connected in series with the reed contact (K_R) to the control voltage source (U_S).
20. A relay according to Claim 11, characterised in that the overcurrent protection device is in the form of an electronic circuit (CCU) which has a first control voltage terminal (K1) and a second control voltage terminal (K2), and in that the circuit (CCU) has a timer member (U1), a switch-on section (U2) for the exciter coil (W_R), and a switch-off section (U3).
21. A relay according to Claim 20, characterised in that the switch-on section (U2) for the exciter coil (W_R) comprises a pnp transistor (T1), connected in series with the exciter coil (W_R) between the two control voltage terminals (K1, K2), and a series resistor (R2), in that the transistor (T1) of the switch-on section (U2) is connected by means of its emitter to the first control voltage terminal (K1) and by means of its collector to a first exciter coil terminal (K3), in that the exciter coil (W_R) is connected by means of its second terminal to the second control voltage terminal (K2), and in that the series resistor (R2) of the switch-on section (U2) is connected between the base of the transistor (T1) of the switch-on section (U2) and the second control voltage terminal (K2).
22. A relay according to Claim 21, characterised in that the switch-off section (U3) for the exciter coil (W_R) is formed by a first resistor (R4) and a second resistor (R3), in that the first resistor (R4) of the switch-off section (U3) is placed in parallel with the exciter coil (W_R), in that the reed contact (K_R) is connected by means of a first terminal to the second control voltage terminal (K2), and in that the second resistor (R3) of the switch-off section (U3) is connected between the first terminal (K3) of the exciter coil (W_R) and the second terminal (K4) of the reed contact (K_R).
23. A relay according to Claim 22, characterised in that the timer member (U1) has a comparator (CMP) and an RC element, in that the capacitor (C1) of the RC element is connected by means of a first terminal to the first control voltage terminal (K1), and in that the resistor (R1) of the RC element is connected between the second terminal (K5) of the capacitor (C1) and the second terminal (K4) of the reed contact (K_R).
24. A relay according to Claim 23, characterised in that the comparator (CMP) comprises a pnp transistor (T2) and a Zener diode (D1), in that the transistor (T2) of the comparator (CMP) is connected by means of its emitter to the first control voltage terminal (K1), in that the transistor (T2) of the comparator is connected by means of its collector to the base of the transistor (T1) of the switch-on section (U2), in that the transistor (T2) of the comparator is connected by means of its base to the cathode of the Zener diode (D1), and in that the Zener diode (D1) is connected by means of its anode between the capacitor (C1) and the resistor (R1) of the RC element.

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