EP2826052B1 - Safety relay circuit - Google Patents

Description

The invention relates to a circuit arrangement for switching a load circuit in safety technology, with error states of the relay to be detected.

In particular, the currentless circuit of the load circuit ("switch-off safety relay circuit") or the switching on ("switch-on safety relay circuit") of the load circuit should be ensured.

In order to safely comply with the open position of a load circuit, electromagnetic relays are preferably used. In safety technology, the switching position of mechanical switching contacts is checked, whereby it is known ( EP 1 202 313 A1 ), apply a high-frequency signal to the control circuit with the switch to be tested and determine the switch position with a high-frequency detector. To increase safety, it is also known to arrange two relay switches in a row in the load circuit. The check of the switch position by means of a high-frequency control circuit, however, is complex and does not detect certain error conditions. Thus, the relay switch can assume its open position, which can be determined, but if it comes through a foreign body or by metal break a bridge between the normally open contact and the normally closed relay switch, this fault condition can not be determined with the known device. Such a circuit arrangement is also from the document EP 2 256 777 A2 known.

The invention has for its object to offer a safety relay circuit, can be reliably detected in the fault conditions at the relay switch. In particular, the currentless circuit of a load circuit, or the switching of the load circuit, can be safely brought about.

According to the invention, a monitoring circuit is provided which logically links the command input to an electromechanical relay with a circuit indicating the relay switch position or the relay switch state and obtains an error error signal therefrom.

To ensure the Stromlosschaltung the load circuit, the relay switch of two relays are connected in series in the load circuit in the invention. Thus, if one of the switches does not reach its open state, then the other relay switch causes the current path to be de-energized to the load.

To ensure the switching on of the load circuit, the relay switch of two relays in the load circuit are connected in parallel with each other in the invention. Thus, if one of the switches does not reach its closed state, then the other relay switch causes the current path to close to the load.

In terms of safety technology, it must be required that faults are detected, even if they do not immediately lead to a faulty circuit, because the fault in one of the relay switches is cured by the correct operation of the other relay switch. In each relay switch, a display circuit is provided, however, is able to detect disturbances due to erroneous bridging at the respective relay switch by current detection means.

In the preferred embodiment, each display circuit has a light emitting diode driven by an associated auxiliary voltage source. When an appropriate relay switch is opened, the associated LED illuminates fully, signaling the correct state of the switch in the quiescent state of the circuit. In contrast, if the load circuit is active and there is no fault in the relay switches, then the LEDs are switched dark.

If, in the off-load safety relay circuit, one of the series-connected relay switches should not drop when the load circuit is de-energized, say because the contacts are welded, then the associated indicator circuit will not close and the associated LED will remain dark. This is detected as an error in the relay in question and it can be prevented that the load circuit is turned on again.

In the turn-off safety relay circuit, when the load circuit is activated, a fault occurs in one of the relays such that all three terminal contact points of the failed relay switch are electrically connected, then the associated LED lights up due to operation Auxiliary voltage source and it is possible to turn off the load circuit by switching the non-faulted relay. This can be done within a safety period.

A fault in the switch-off safety relay circuit can occur even when the load circuit is de-energized, namely that in one of the display circuits, the current flow of the auxiliary voltage source is disturbed and the LED does not light properly. As a result, it can be recognized that the relevant relay is no longer safe. The switching on of the load circuit can be prevented.

If in the switch-on safety relay circuit one of the relay switches is welded to the contact point of the monitoring circuit ("hanging contacts") or if a "three-point contact override" occurs in one of the relay switches, then this is detected when the display circuit is interrogated due to the LED lighting up , The safe switch-on state of the load circuit is maintained via the undisturbed, parallel-connected relay.

If in the switch-on safety relay circuit at one of the relay switches, the switchless contacts are bridged by mistake ("two-point contact bridging") then this is detected when switching on the faulty relay. The load current can possibly lead to an overload of the current detection means, which can be averted by a fuse ("polyfuse").

• Fig. 1 eine Sicherheitsrelaisschaltung im Ruhezustand,
• Fig. 2 im aktiven Zustand,
• Fig. 3 im Fehlerzustand I (hängende oder verschweißte Kontakte)
• Fig. 4 im Fehlerzustand II (Dreipunktkontakt-Überbrückung)
• Fig. 5 im Fehlerzustand III (Zweipunktkontakt-Überbrückung)
• Fig. 6 eine Ausschalt-Sicherheitsrelaisschaltung gemäß Erfindung,
• Fig. 7 eine schematisierte Darstellung von Anzeigestromkreisen der Ausschalt-Sicherheitsrelaisschaltung im Ruhezustand des Laststromkreises,
• Fig. 8 die Ausschalt-Sicherheitsrelaisschaltung im aktiven Zustand des Laststromkreises,
• Fig. 9 die Ausschalt-Sicherheitsrelaisschaltung in einem Fehlerzustand I,
• Fig. 10 die Ausschalt-Sicherheitsrelaisschaltung in einem Fehlerzustand II,
• Fig. 11 die Ausschalt-Sicherheitsrelaisschaltung in einem Fehlerzustand III,
• Fig. 12 eine schematische Darstellung von Überwachungsstromkreisen der Einschalt-Sicherheitsrelaisschaltung im Ruhezustand des Laststromkreises,
• Fig. 13 die Einschalt-Sicherheitsrelaisschaltung im aktiven Zustand des Laststromkreises,

Embodiments of the invention will be described with reference to the drawing. Showing:

• Fig. 1 a safety relay circuit at rest,
• Fig. 2 in the active state,
• Fig. 3 in error state I (hanging or welded contacts)
• Fig. 4 in error state II (three-point contact bridging)
• Fig. 5 in error state III (two-point contact bridging)
• Fig. 6 a switch-off safety relay circuit according to the invention,
• Fig. 7 a schematic representation of display circuits of the shutdown safety relay circuit in the idle state of the load circuit,
• Fig. 8 the switch-off safety relay circuit in the active state of the load circuit,
• Fig. 9 the switch-off safety relay circuit in an error state I,
• Fig. 10 the switch-off safety relay circuit in one Fault condition II,
• Fig. 11 the switch-off safety relay circuit in a fault state III,
• Fig. 12 a schematic representation of monitoring circuits of the switch-on safety relay circuit in the idle state of the load circuit,
• Fig. 13 the switch-on safety relay circuit in the active state of the load circuit,

It will be related to the Fig. 1 to 5 taken showing a safety circuit in different correct and faulty states. The safety circuit comprises a load circuit LN between the terminals L and N, which can be turned on and off by a relay K1, a display circuit A1 indicating the switch position of the relay, and an evaluation circuit indicating the display state of the display circuit A1 with the command input the relay K1 logically linked and from the overall condition of the circuit as "error-free" or evaluated as "faulty". One can designate the display circuit together with the evaluation circuit as a monitoring circuit.

The relay K1 has as an electromechanical relay on a switch tongue k1, which switches between a closing point S1 and an opening point Ö1 and is connected to a common point G1. The display circuit A1 comprises an auxiliary power source H1 and current detection means in the form of a light emitting diode LED1 and is connected to the switching points G1 and Ö1. Depending on the position of the switch k1, the light-emitting diode LED1 is in operation or out of operation. The switched-on state of the light-emitting diode is indicated by arrows, while in the switched-off state the arrows are omitted.

The evaluation circuit comprises an integrated circuit IC1, which can make logic operations in such a way that two similar input signals give an output signal "error-free", which is represented here by a "0", and two dissimilar input signals leads to the output of an error signal, which symbolized here by a "1". As an input signal to the integrated circuit IC1 on the one hand the command input to the relay K1 and on the other hand the signal of an opto-coupler is used, which converts the signal of the LED LED1 into a corresponding input signal to the integrated circuit IC1. The optocoupler consists of a circuit with switching transistor Q1, which is turned on by the light of LED1 and otherwise switched off. In the circuit of the optocoupler is a resistor in series with the transistor Q1 and a tap leads the signal of the optocoupler to the integrated circuit IC1 of the evaluation circuit.

Fig. 1 shows the error-free state of the safety relay circuit in the idle state. The relay K1 has turned off the load circuit LN and turned on the display circuit A1. The LED LED1 lights up and turns on the transistor Q1, so that the optocoupler outputs the signal "0". This agrees with the command signal "0" to the relay K1. The integrated circuit IC1 then outputs the error-free signal "0".

Fig. 2 shows the active state of the safety relay circuit. With the signal "1", a switch-on command to the relay K1 is given, which turns on the load circuit LN and turns off the display circuit A1. As a result, the optocoupler no longer receives a flashing signal and transmits the signal "1" to the integrated circuit IC1. Since both inputs of the integrated circuit IC1 are equivalent to the evaluation circuit, the signal "error-free", symbolized by "0", is output.

Fig. 3 shows a fault condition I, which can be characterized by suspended or welded contacts. This fault state I occurs when switching off the relay K1 and means that the relay is no longer safe. Because of the faulty position of the switching tab k1, the diode LED1 in the indicator circuit A1 does not light, so that the optocoupler outputs the signal "1" to the integrated circuit IC1, which detects the inconsistency between the command input to the relay K1 and the reaction of the indicator circuit A1 and as error signal "1" outputs.

Fig. 4 shows an error state II, which can be referred to as "three-point contact override", because the switching points S1, G1 and Ö1 have contact with each other. In error state II, the diode LED lights up. When the relay K1 is switched on with the command signal "1", should open the display circuit A1, which does not happen because of the three-point contact bridging. This leads to a mismatch between the input signals of the integrated circuit IC1 and thus to a delivery of an error signal "1".

With Fig. 5 is a fault state III outlined, which consists in a kind of two-point contact bridging. During operation, when the display circuit A1 should be off, the LED receives an overcurrent LED1, which is mitigated by a (not shown) protective resistor. The thereby emitting light makes the optocoupler give the signal "0", which is detected by the integrated circuit IC1. There is a discrepancy between the input signal "1" to the relay K1 and the signal "0" of the display circuit A1, which can be evaluated for error message. As an error message, the change between short-time lighting of the LED and the extinction of the LED in the evaluation circuit can be exploited, as would occur in the destruction of the LED.

In the Fig. 6 shown circuitry can be referred to as a safety relay with optical diagnosis. The circuit includes two electromagnetic relays K1 and K2 of a simpler, conventional design, which are connected in parallel to each other to a control source, not shown, so that the relay coils are energized or not energized. It is also possible to control the relays K1 and K2 by separate control circuits. The relays K1 and K2 each have associated switches k1 and k2 which are at rest, as in FIG Fig. 7 represented, and one Working position ( Fig. 8 ) depending on the excitation state of the relay coils. In their working position, the relay switches k1 and k2 close a load circuit extending between the terminals L and N. Each relay switch k1, k2 is associated with a display circuit A1 or A2, which indicate the position of the switch k1 or k2 and each contain a light emitting diode LED1 or LED2 as current detection means and each an auxiliary voltage source H1, H2 for operating the respective associated light emitting diode. The relay switch k1 in the illustrated rest position ( Fig. 7 ) bridges the otherwise open display circuit A1 to two (G1, Ö1) of the three terminal contact points (S1, G1, Ö1) of the relay K1 and in the same way connects the switch k2 the corresponding terminal contact points (S2, G2, Ö2) of the Relay K2 to close the second display circuit Ü2. If the relay switches k1 and k2 from their illustrated rest position ( Fig. 7 ) into the working position ( Fig. 8 ), the display circuits A1 and A2 are opened and the load circuit LN is closed.

As an auxiliary voltage source H1, H2 can be used any type of power source, with the current detection means and especially light emitting diodes can be operated. In case of switching to Fig. 6 For example, a transformer having a primary winding and two secondary windings is used as auxiliary voltage sources H1, H2. The transformer forms a first transformer T1 as a first auxiliary voltage source H1 and a second transformer T2 as a second auxiliary voltage source H2. The primary winding is supplied with voltage pulses to the respective auxiliary voltage sources H1, H2 cyclically to be effective and thereby query the respective state of the display circuits A1, A2.

Fig. 7 shows a schematic diagram of the shutdown safety relay circuit in the idle state. The auxiliary voltage sources H1, H2 are shown in simplified form as DC voltage sources. The connection contact points are indicated by S1, G1 and Ö1 or S2, G2 and Ö2. The first relay switch k1 closes the first display circuit A1 between the contact points G1 and Ö1 and the second relay switch S2 closes the second display circuit A2 between the contact points G2 and Ö2. Arrows at the LEDs LED1 and LED2 indicate the lighting status of these diodes. If both diodes are fully lit, there is no fault condition in the current circuit of the load circuit, as with Fig. 1 has been explained.

Fig. 8 shows the turn-off safety relay circuit in its active state, in which the load circuit LN is turned on. The switch k1 connects the contact points S1 with G1 and the switch k2 connects the contact points S2 with G2. The display circuits A1 and A2 are open and the LEDs LED1 and LED2 are not lit. As with Fig. 2 explained, is thus the error-free active state.

With Fig. 9 an error state I ("hanging contacts") is explained at the switch k1. While the switch k2 has gone to sleep when the load circuit is switched off, the switch k1 has become stuck at the contact point S1 (eg because of welded contacts). Accordingly, the first display circuit A1 is left open and the LED LED1 does not light up. This error state I can be detected, as with Fig. 3 explained in detail. In addition, the discrepancy between the lighting states of LED1 and LED2 can be detected as an error. The renewed restart of the load circuit can be prevented.

Fig. 10 outlines another fault state II ("three-point contact override") that can come to light when the load circuit LN is switched on. The fault occurs due to a short circuit between the contact points S1, G1 and Ö1, such as when a spring in the relay is broken. With Fig. 4 explains how this error condition II can be detected. In order to detect the fault, it can also be utilized that the light-emitting diode LED1 of the indicator circuit A1 lights up in the event of this fault, while the light-emitting diode LED2 of the indicator circuit A2 goes out. When this error occurs, the load circuit should be de-energized immediately. Immediate switch-off is possible via the relay K2.

Fig. 11 shows a fault state III ("two-point contact override"), in which break contact of a metal part, the points S1 and Ö1 with each other. This can be detected before switching on the load circuit, because in the idle state of the circuit ( Fig. 7 ) both LEDs LED1 and LED2 should be lit, but in fault condition III LED1 goes out. Then the load circuit should not be turned on. If the fault condition III occurs during operation, this error will be detected according to the procedure Fig. 5 detected.

The described circuit arrangement thus comprises a monitoring circuit, which display circuits A1, A2 and evaluation circuits according to the Fig. 1 to 5 having. In this case, the evaluation circuits A1, A2 associated with integrated circuits may be combined with each other and additionally contain a further integrated logic circuit to record the positions of the relay switch k1, k2 and the response states of the LEDs LED1, LED2 and evaluate by logical link and optionally perform safety switching measures.

To realize the switch-on safety relay circuit is Fig. 6 modified such that the switches k1, k2 are parallel to each other in the load circuit LN, as is also the case of the FIGS. 12 and 13 evident. Thus, if one of the switches k1 or k2 should fail, the other switch can ensure that the load circuit is safely turned on or stays on.

In contrast to the switch-off safety relay circuit according to Fig. 7 - 11 is preferred in the switch-on safety relay circuit to operate the relays K1, K2 in the fallen state of the switch k1, k2 for switching on the load circuit LN. However, this is not mandatory and in the Fig. 12, 13 Terminal contact points are provided with the same reference numerals as in the embodiment of the Fig. 6 to 11 underlie. Fig. 12 shows the idle state of the switch-on safety relay circuit and Fig. 13 their active state. At rest, both LEDs light up LED1 and LED 2 of the two display circuits A1 and A2, and in the active state of the switch-on safety relay circuit, the LEDs LED1 and LED2 are dark.

As in Fig. 3 the error state I at the relay K1 is in the catching of the switch k1 at a contact point (here Ö1). This can be determined according to the monitoring procedure, as in Fig. 3 described. Alternatively or additionally, the error state I ("hanging contact") when querying the display circuits A1 and A2 can be determined by the fact that the light states of the LEDs LED1 and LED2 do not match. In this case, the on state of the load circuit LN is ensured by the switch S2.

When fault condition II ("three-point contact override") all three terminal contact points S1, G1, Ö1 of the relay K1 have electrical contact with each other. This can, as with Fig. 4 be described. In addition, the fault state II can be detected when tightening the relay K1, because the light states of the LEDs LED1 and LED2 differ.

When fault state III ("two-point contact override"), there is a bridging between the connection contact points S1 and Ö1. The can according to the method Fig. 5 be determined. In addition, there is a Fehlerprüfmöglichkeit based on different luminous intensities of the diodes LED1 and LED2. As long as the switch k2 of the relay K2 closes the current path of the load circuit LN, the current has little Reason to flow over the fault location at relay K1. However, when the switch k2 is opened, the applied voltage may lead to an excessive current across the diode LED1, which is why the light-emitting diodes are expediently secured by a fuse ("polyfuse"). When the switch game of the switch k2 there are different degrees of light of the diodes LED1 and LED2, which detects that the relay K1 is no longer safe.

The two described methods of fault detection are suitably combined with each other in the monitoring circuit, wherein the control positions of the relay switches k1 and k2 and the response states of the diodes LED1 and LED2 are logically linked together to detect the error conditions at the respective relay switches k1, k2. The monitoring circuit used for this purpose may include the two display circuits A1, A2 and associated evaluation circuits and additional logic circuits to perform the described logical operations. Advantageously, the evaluation circuits and the additional logic circuits are combined in a common integrated circuit.

Claims (11)

1. Circuit arrangement for switching a load current circuit in fail-safe technology, said circuit arrangement comprising:

   at least one electromagnetic relay (K1) with a controlled switch (k1), which in the active state of the relay takes its closed working position and, in so doing, is located in the load current circuit (LN), while in the idle state of the relay the switch (k1) takes an open idle position with respect to the load current circuit (LN),

   at least one monitoring circuit, which comprises:

   a switch position indicator circuit (A1), which includes an auxiliary voltage source (H1) and current detecting means and in the idle state of the relay (K1) allows the current detection means to respond,

   an evaluation circuit, which compares the response of the current detection means with the command input "on" or "off" to the relay (K1) and from the comparison derives the state of the circuit arrangement "faultless" or "defective",

   wherein in the faultless idle state the relay (K1) de-energizes the load current circuit (LN) and energizes the indicator circuit (A1),

   wherein in the faultless active state the relay (K1) energizes the load current circuit (LN) and de-energizes the indicator circuit (A1),

   wherein when the load current circuit (LN) is disconnected, a fault state "hanging contacts" can be detected by means of the discrepancy between the command input to the relay and the response state of the current detection means,

   wherein when the load current circuit (LN) is connected up, a fault state "three point contact bridge" becomes apparent due to the discrepancy between the command input to the relay and the partially persisting response state of the current detection means, and

   wherein during the ongoing operations a fault state "two point contact bridge" can be detected by means of the discrepancy between the command input to the relay and an incorrect response state of the current detection means.
2. Circuit arrangement, as claimed in claim 1,
   wherein upon the switch on command of the relay a logic command signal "1" is outputted to the evaluation circuit, and upon the switch off command a logic command signal "0" is outputted to the evaluation circuit,
   wherein in the positive response state of the current detection means a logic status signal "0" is generated, and in the negative response state, a status signal "1" is generated, and
   wherein in the event that the status signal agrees with the command signal, the evaluation circuit indicates the absence of a fault, and in the event of non-agreement, the presence of a fault.
3. Circuit arrangement, as claimed in claim 1 or 2,
   wherein the objective is to ensure the de-energization of the load current circuit (LN), said circuit arrangement comprising:

   a first electromagnetic relay (K1) having a first switch (k1),

   a second electromagnetic relay (K2) having a second switch (k2 ),

   a first switch position indicator circuit (A1),

   a second switch position indicator circuit (A2), and

   an evaluation circuit, which compares the command inputs of the relays (K1, K2) with the current states of the indicator circuits (A1, A2) and from said comparison derives the state of the circuit arrangement as "faultless" or as "defective."
4. Circuit arrangement, as claimed in claim 3,
   wherein the monitoring circuit includes integrated circuits, which are assigned to the respective evaluation circuits (A1, A2), and also includes additional logic circuits, in order to evaluate for agreement the positions of the relay switches (k1, k2) in relation to each other,
   wherein in the faultless active state the first and second switches (k1, k2) close the load current circuit (LN) and open the respectively associated indicator circuit (A1, A2), which is manifested by means of the non responsiveness of the current detection means,
   wherein a state "hanging contacts" at one of the relays allows the assigned indicator circuit (A1, A2) to remain in its state prior to the de-energization of the load current circuit (LN), a situation that can be evaluated as a fault state of the relevant relay,
   wherein a fault state "three point contact bridge" becomes apparent due to the partial response of the current detection means of the defective relay, when the load current circuit (LN) is connected up, and
   wherein a fault state "two point contact bridge" at one of the relays does not allow the current detection means of the assigned indicator circuit to respond or allows only a weak response of said current detection means, when the relays are brought into the circuit.
5. Circuit arrangement, as claimed in claim 1 or 2, wherein the objective is to ensure the energization of the load current circuit, said circuit arrangement comprising:

   a first electromagnetic relay (K1) having a first switch (k1),

   a second electromagnetic relay (K2) having a second switch (k2),

   a first indicator circuit (A1),

   a second indicator circuit (A2), and

   an evaluation circuit, which compares the command inputs of the relays (K1, K2) with the current states of the indicator circuits (A1, A2) and from said comparison derives the state of the circuit arrangement as "faultless" or as "defective."
6. Circuit arrangement, as claimed in claim 5,
   wherein the monitoring circuit includes integrated circuits, which are assigned to the respective evaluation circuits (A1, A2), and also includes additional logic circuits, in order to evaluate for agreement the positions of the relay switches (k1, k2) in relation to each other,
   wherein in the faultless active state both the first and the second switches (k1, k2) close the load current circuit (LN) and open the respectively assigned indicator circuit (A1, A2), which is manifested by means of the non-responsiveness of the current detection means,
   wherein a state "hanging contacts" at one of the relays allows the assigned indicator circuit to remain in its state prior to switching over the load current circuit (LN), a situation that can be evaluated as a fault state of the relevant relay,
   wherein a fault state "three point contact bridge" becomes apparent due to the partial response of the current detection means of the defective relay, when the load current circuit (LN) is energized, and
   wherein a fault state "two point contact bridge" at one of the relays allows the current detection means of the assigned indicator circuit to respond intensively, when the other relay is switched into the idle state.
7. Circuit arrangement, as claimed in any one of the claims 1 to 6, wherein the current detection means are designed as light emitting diodes (LED1, LED2), which are arranged in series with a respective auxiliary voltage source (H1, H2) and with two (G1, 01; G2, 02) of the three contact points (S1, G1, 01; S2, G2, 02) of a respective relay (K1, K2).
8. Circuit arrangement, as claimed in any one of the claims 3 to 7,
   wherein a first auxiliary voltage source (H1) of the first indicator circuit (A1) includes a first transformer (T1), to which a current/voltage pulse can be intermittently applied, and
   wherein a second auxiliary voltage source (H2) of the second indicator circuit (A2) includes a second transformer (T2), to which a current/voltage pulse can be intermittently applied.
9. Circuit arrangement, as claimed in claim 8,
   wherein the first and second transformers (T1, T2) are structurally combined and form a transformer having a common primary winding and two secondary windings.
10. Circuit arrangement, as claimed in any one of the claims 3 to 9, wherein the first and the second electromagnetic relays (K1, K2) are connected to a control current circuit.
11. Circuit arrangement, as claimed in any one of the claims 1 to 10, wherein an optocoupler circuit connects the respective indicator circuit (A1) to the respective evaluation circuit.

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