EP2337054B1 - Safety relay circuit - Google Patents

Description

The invention relates to a safety relay circuit, as is commonly used in safety-related circuits for industrial applications with danger potential, in particular in an emergency stop circuit, a two-hand trip or for monitoring the position of a protective door.

document WO 2007054187 discloses a safety relay circuit according to the preamble of claim 1.

To avoid errors, safety-related circuits are generally redundant. Such a circuit therefore usually comprises two signal transmitters, one of which is arranged in each case in one of two independent signal circuits. The safety-critical application is only released if both signal generators indicate a safe state in unison. The safety relay circuit is usually interposed within the safety-related circuit the signal generator and a Freigabestrompfad, via which, for example, the engine of a safety-critical industrial plant is controlled.

In terms of the required redundancy, the safety relay circuit (hereinafter referred to as relay circuit) usually comprises two switching relays, which are connected in series in the release current path. The enable current path is thus enabled only when both switching relays are closed (i.e., turned on) simultaneously. Such a relay circuit is usually produced as an integrated circuit (IC).

On the control side, the switching relays are connected as intended to one of the two signal transmitters, so that by switching both signal transmitters switched the switching relay, and thus the Freigabestrompfad, depending on the type of safety-related circuit, open (interrupted) or closed (released) can be.

For example, both signal generator of a redundant door position signaling circuit are closed by the above-mentioned protective door in its closed position, whereby the switching relay of the relay circuit energized, and in turn the Freigabestrompfad be unlocked.

One possible source of error in relay circuits of this type is a so-called cross-circuit, i. a short circuit between the two redundant signal circuits of the safety circuit. Such a cross-circuit can occur, in particular, when the signal line is pinched between the signal generators and the relay circuit. In the worst case, one of the signal transmitters of the safety circuit is bridged by the cross-circuit, so that the redundancy of the safety circuit is canceled.

According to a common principle for cross-circuit detection, the electrical resistance between the signal circuits is tested by the relay circuit during operation at regular intervals. However, such a test requires a comparatively complex switching logic within the relay circuit and is correspondingly expensive. Often, such testing is done by means of a microcontroller. In addition, a failure of the switching logic in this case lead to a - possibly unnoticeable - failure of the cross-circuit detection.

After a simple and fail-safe alternative principle of cross-circuit detection, the two switching relays of the relay circuit are switched via different potential. For example, one of the switching relays is switched on the control side between positive operating potential and ground, while the other switching relay is connected between positive and negative operating potential. In the event of a cross-circuit, due to the potential difference between the signal circuits, a short-circuit current flows, due to which the voltage across at least one of the switching relays collapses so that it triggers and interrupts the enabling current path.

However, in certain safety-related circuits, it may be necessary to use both signal transmitters with the same polarity, ie either positive or negative, Potential to switch, even if in this case cross-circuits can not be detected. In a conventional relay circuit, therefore, one of the switching relay is connected to both control inputs each with an input contact, so that the switching relay associated with this signal generator can be selectively switched between the switching relay and positive operating potential or between the switching relay and negative operating potential. The second switching relay of this relay circuit is internally connected to ground with a control input, while the other control input is connected to a further input contact. The relay circuit also includes output contacts for positive and negative operating potential for wiring to the signal paths. In this design, at least five connection contacts plus the required voltage inputs are thus required for the basic function of the relay circuit including the optional cross-circuit detection. These connection contacts are no longer available for any required or desired additional functions.

Generally, on the other hand, it is desirable to realize a relay circuit with a given range of functions in the smallest possible installation space, in particular in the smallest possible housing. The size of the housing also limits the available number of contacts, especially if the relay circuit is to be implemented in a standard housing.

The invention has for its object to provide a safety relay circuit with two serially connected in a Freigabestrompfad switching relay and a cross-circuit detection function in which at least one of the switching relay is switched both against positive operating potential and negative operating potential, this scope of functions with a very small number of input contacts to be realized.

This object is achieved by the features of claim 1. Accordingly, of the two serially connected in the Freigabestrompfad switching relay of (safety relay) circuit a first switching relay with two control inputs - in particular directly - with a first input contact connected, which is provided for supplying a first switching potential. One of the control inputs of this switching relay is preceded by a pre-circuit with a driver circuit. For this purpose, this ballast circuit is designed to apply a switching potential inverted with respect to the first switching potential to this control input.

By connecting both control inputs of the first switching relay with a common terminal contact and provided in one of these voltage paths ballast is enabled to operate the first switching relay by applying a single switching potential. Thus, we only need a single input contact for wiring this switching relay. The potential gradient required for operating the switching relay, ie the required electrical voltage, is created by inverting the switching potential through the ballast circuit. The driver circuit of the Vorschaltkreises acts as a current source or sink, and allows the required for the actuation of the switching relay current flow. The driver circuit is preferably formed by an operational amplifier. Alternatively, as a driver circuit but also a simple switching transistor can be used.

An inverted switching potential is generally referred to as an electrical potential which has a sign which is opposite to the first switching potential. The inverted switching potential can have a time course which is exactly mirrored with respect to the first switching potential, and thus at any time have the same magnitude as the first switching potential. But this is not mandatory. Rather, the inverted switching potential in the amount and / or the time course may differ from the first switching potential.

Due to the inverting characteristic of the ballast circuit, a positive or negative switching potential can optionally be applied to the (single) input contact connected to the first switching relay, especially since the ballast circuit generates a sufficient potential difference in each case.

In a preferred embodiment of the relay circuit, the pre-circuit comprises, in addition to the driver circuit, a threshold circuit connected upstream of this. In this case, a threshold circuit is generally understood to mean an electrical circuit which switches discontinuously between predetermined potential values on the output side when the input potential rises or falls continuously when the input potential exceeds or falls below predetermined threshold values. Preferably, the threshold circuit is a comparator.

The threshold circuit improves the switching precision of the first switching relay due to the discrete switching characteristic. It has expediently, but not necessarily, a switching hysteresis in the manner of a Schmitt trigger.

Preferably, an inverting threshold circuit in combination with a non-inverting driver circuit is provided in the frame circuit. In an alternative embodiment of the Vorschaltkreises but also a non-inverting threshold circuit may be provided in combination with an inverting driver.

The second switching relay is connected to a control input in an appropriate embodiment of the relay circuit for supplying a second switching potential with a second input contact. The second control input of the second switching relay is - preferably fixed - with a reference potential, in particular ground, connected.

If signal circuits are connected to the input contacts assigned to the first or second switching relay, in which a differently polarized switching potential is applied, a cross-circuit detection is performed. If signal circuits connected to the input contacts assigned to the first or second switching relay are connected, in which an equally polarized switching potential is applied, then - as is also the case with the conventional relay circuit described above - no cross-circuit detection takes place.

Preferably, the two switching relays are formed together with the ballast circuit as an integrated circuit. As a result, the relay circuit can be manufactured and installed as a standard electrical component in mass production. Furthermore, a complex and error-prone manual interconnection and assembly of individual parts is avoided.

Fig. 1

in einem schematisch vereinfachten Schaltplan eine Sicherheitsrelaisschaltung umfassend zwei Schaltrelais, die seriell in einen Freigabestrompfad geschaltet sind, wobei ein erstes Schaltrelais mit beiden Steuereingängen mit einem zur Zuführung eines ersten Schaltpotentials vorgesehenen ersten Eingangskontakt verschaltet ist, und wobei einem der Steuereingänge und den ersten Eingangskontakt ein eine Treiberschaltung umfassender Vorschaltkreis zum Anlegen eines modifizierten Schaltpotentials an diesen Steuereingang zwischengeschaltet ist, und wobei das zweite Schaltrelais mit einem Steuereingang fest mit Masse, und mit dem anderen Steuereingang mit einem zweiten Eingangskontakt verbunden ist,

Fig. 2

in Darstellung gemäß Fig. 1 die dortige Sicherheitsrelaisschaltung, wobei der erste Eingangskontakt mit einem ein positives Schaltpotential führenden ersten Signalkreis beschaltet ist, wobei der zweite Eingangskontakt mit einem ein negatives Schaltpotential führenden zweiten Signalkreis beschaltet ist, und wobei der Freigabestrompfad mit einem Motorstromkreis eines elektrischen Motors beschaltet ist,

Fig. 3

in zwei synchronen Diagrammen den zeitlichen Verlauf des an den ersten Eingangskontakt angelegten Schaltpotentials im Falle eines Querschlusses zwischen den Signalkreisen, und

Fig. 4

in Darstellung gemäß Fig. 2 die dortige Sicherheitsrelaisschaltung, wobei aber sowohl der erste Eingangskontakt als auch der zweite Eingangskontakt mit je einem ein positives Schaltpotential führenden Signalkreis beschaltet sind.

Embodiments of the invention will be explained in more detail with reference to a drawing. Show:

Fig. 1

in a schematically simplified circuit diagram, a safety relay circuit comprising two switching relays, which are connected in series in a Freigabestrompfad, wherein a first switching relay is connected to both control inputs provided with a first switching potential for supplying a first input contact, and wherein one of the control inputs and the first input contact a Driver circuit comprehensive Vorschaltkreis for applying a modified switching potential is connected to this control input, and wherein the second switching relay is connected to a control input fixed to ground, and to the other control input to a second input contact,

Fig. 2

in illustration according to Fig. 1 the local safety relay circuit, wherein the first input contact is connected to a first switching circuit leading to a positive switching potential, wherein the second input contact is connected to a second signal circuit carrying a negative switching potential, and wherein the Freigabestrompfad is connected to a motor circuit of an electric motor,

Fig. 3

in two synchronous diagrams, the time profile of the applied to the first input contact switching potential in the event of a cross-circuit between the signal circuits, and

Fig. 4

in illustration according to Fig. 2 the local safety relay circuit, but both the first input contact and the second input contact each having a positive switching potential leading signal circuit are connected.

Fig. 1 shows a (safety) relay circuit 1. The relay circuit 1 comprises a first switching relay 2a and a second switching relay 2b and a first switching relay 2a circuitry zugeordneten Vorschaltkreis. 4

The relay circuit 1 is formed as an integrated circuit (IC) in a standard case 5. In principle, a housing with eight (input or output) contacts K1 to K8 suffices for the range of functions described below. For any further additional functions not described in detail below, further contacts may be provided.

Each of the switching relays 2a, 2b comprises according to conventional design, a magnetic excitation coil 6a and 6b and an electrical switching contact 7a and 7b, which is switchable via one of the excitation coil 6a, 6b associated iron anchor. The switching relays 2a, 2b are connected with their respective switching contact 7a, 7b serially in a Freigabestrompfad 8, which is formed between the (input) contacts K4 and K5. The excitation coil 6a, 6b of each switching relay 2a and 2b respectively comprises two control inputs 9a, 9b and 10a, 10b, via which the excitation coil 6a, 6b can be energized to actuate the associated switching contact 7a, 7b.

The control input 9a of the switching relay 2a is connected directly to the (input) contact K3. The control input 10a of the switching relay 2a is also connected to the contact K3. However, the contact circuit K3 and the control input 10a of the ballast circuit 4 is interposed, wherein the ballast circuit 4 is connected on the one hand directly to the contact K3, and on the other hand directly to the control input 10a.

The control input 9b of the switching relay 2b is connected directly to the (input) contact K7. The control input 10a is placed inside the circuit directly to ground potential M.

The pre-circuit 4 is formed by a threshold circuit 11 in the form of a Schmitt trigger and by a driver circuit 12 in the form of an operational amplifier. The threshold circuit 11 is on the input side directly to the contact K3, and the output side connected to the input of the driver circuit 12. The driver circuit 12 has its output directly connected to the control input 10a.

The remaining contacts K1, K2, K6 and K8 serve as voltage inputs and outputs. Thus, the relay circuit 1 is supplied via the (input) contact K2 and K6 intended with an AC voltage U~ or ground potential M. From this the relay circuit 1 generates by rectification a positive switching potential U + and a negative switching potential U- and provides these switching potentials U + and U- via the (output) contacts K1 and K8, respectively.

As part of a safety-related circuit 20 with cross-circuit detection is in accordance with Fig. 2 between the contacts K1 and K3 of the relay circuit 1 as intended, a first electrical signal circuit 21 a connected to a first signal generator 22a. Between the contacts K8 and K7 of the relay circuit 1, a second electrical signal circuit 21 b is connected to a second signal generator 22b as intended. The signal generators 22a, 22b are, for example, electrical switches which are actuated by a protective door in its closed position. The protective door secures, for example, the working area of a machine whose motor 23 is supplied via a - here simplified - directly connected to the Freigabestrompfad 8 motor circuit 24. In practice, a contactor is actuated in most cases deviating from this via the enable path 8, which then switches the motor circuit 24.

The signal generator 22a and 22b are closed in the actuated state, so that when the protective door is properly closed via both signal circuits 21 a, 21 b, a conductive connection between the contacts K1 and K3 or between the contacts K8 and K7 is formed.

At the contact K7 is in this case the negative switching potential U-. Thus falls above the excitation coil 6b a potential U- from the ground potential M corresponding voltage from, under the action of the exciting coil 6b is energized and closes the switching contact 7b. The applied to the contact K3 input potential Ue corresponds in this case the positive switching potential U +.

As a result of the connection with the contact K3, the potential Ue ≈ U + is present both at the control input 9a and at the input side of the threshold circuit 11. The threshold circuit 11 inverts this input potential Ue and outputs an inverted (thus negative here) potential Ui to the input of the driver circuit 12.

The driver circuit 12 is operated in the illustrated embodiment with a gain of about 1. The driver circuit 12 thus does not actually serve to amplify the potential Ui. Rather, it gives the inverted potential essentially unchanged to the control input 10a. Rather, the main task of the driver circuit 12 is in its effect as a current source or current sink to allow a current flow through the exciter coil 6a.

In exemplary circuit dimensioning, the inverted potential Ui corresponds to the absolute value after the input potential Ue ≈ U +. Thus, a voltage equal to twice the switching potential U + drops across the exciting coil 6a, under the action of which the energizing coil 6a is energized and closes the switching contact 7a.

After closing both switch contacts 7a and 7b of the Freigabestrompfad 8 is conductive and thus allows a current flow in the motor circuit 24. The motor 23 is thus released for operation.

When opening the door, one or both of the signalers 22a, 22b are opened. As a result, the switching potential Ue ≈ U + or U- breaks down at the respective contact K3 or K7, whereby the associated switching relay 2a, 2b triggers and the release current path 8 interrupts. The same happens when the applied to the contact K2 AC voltage U- fails.

At one (in Fig. 2 dashed lines indicated) cross-circuit 25, the signal circuits 21 a and 21 b are inadvertently shorted together. At the in Fig. 2 shown circuitry of the relay circuit 1, a short circuit is formed in this case between the contacts K1 and K8. Due to this cross-circuit 25, the voltage drop across the excitation coils 6a and 6b collapses causing the switching relays 2a and 2b to trip and interrupting the enabling path 8. The cross-circuit detection of the relay circuit 1 is based on the principle of the potential difference between the signal circuits 21 a and 21 b. The relay circuit 1 requires and does not include logic for cross-circuit detection.

The course of the input potential Ue ≈ U + and the inverted potential Ui before and after the formation of the cross-circuit 25 is in Fig. 3 in two synchronous diagrams against the time t schematically contrasted. The cross-circuit occurs at a time tq.

Fig. 4 shows the relay circuit 2 with an alternative circuit in which both contacts K3 and K7, and thus both excitation coils 6a, 6b are connected to the negative switching potential U-. The threshold circuit 11 and the driver circuit 12 generates under the action of the now negative input potential Ue ≈ U- again (now positive) inverted potential Ui, which forwards the driver circuit 12 to the control input 10a, so that in turn a twice the switching potential U- corresponding voltage falls over the excitation coil 6a, under the action of the switching relay 2a closes the switching contact 7a.

Since lead in this case, both signal circuits 21 a and 21 b the same potential, a cross-circuit detection in this Beschaltungsvariante is not possible.

LIST OF REFERENCE NUMBERS

1

(Safety) relay circuit

2a, 2b

switching Relays

4

ballast

5

casing

6a, 6b

excitation coil

7a, 7b

switching contact

8th

Enabling current path

9a, 9b

control input

10a, 10b

control input

11

threshold circuit

12

driver circuit

20

(safety-related) circuit

21 a, 21 b

signal circuit

22a, 22b

signaler

23

engine

24

Motor circuit

25

cross circuit

t

Time

tq

time

K1-K8

Contact

M

ground potential

U +

switching potential

U-

switching potential

Ù~

AC

Ue

input potential

Ui

(inverted) potential

Claims (5)

1. Safety relay circuit (1) comprising two switching relays (2a, 2b), which are switched in series in an enabling current path (8), wherein one of the switching relays (2a) is connected with both control inputs (9a, 10a) having a first input contact (K3), provided for the supply of a first switching potential (U+, U-), characterised in that a ballast circuit (4), comprising a driver circuit (12), is connected to one of the control inputs (10a) and to the first input contact (K3), said ballast circuit (4) being used for applying a potential (Ui) to this control input (10a), said potential being inverted in relation to the first switching potential (U+, U-).
2. Safety relay circuit (1) according to claim 1,
   wherein the ballast circuit (4) comprises a threshold circuit (11), upstream of the driver circuit (12).
3. Safety relay circuit (1) according to claim 1 or 2,
   wherein the driver circuit (12) is formed by an operational amplifier.
4. Safety relay circuit (1) according to one of claims 1 to 3,
   wherein the second switching relay (2b) is connected to a control input (9b) having a second input contact (K7), which is provided for supplying a second switching potential (U-), and firmly to the second control input (10b) having a reference potential (M).
5. Safety relay circuit (1) according to one of claims 1 to 4,
   wherein both switching relays (2a, 2b) are configured together with the ballast circuit (4) as an integrated circuit.

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