Detection of a switched state of a switch element

Abstract

The invention relates to a circuit assembly and a method for detecting a switched state of a switch element (SW3) within a current supply path. The switch element (SW3) has two connections (11, 12), is arranged in the current supply path between two connection ends (11', 12') of the current supply path, the connections (11, 12) being electrically connected to one each of the connection ends (11', 12'), and is designed to assume a selectively either closing or interrupting switched state. In the closing switched state a switch path running between the two connections (11, 12) is closed in order to close the current supply path between the connection ends (11', 12'), and in the interrupting switched state of the switch path running between the two connections (11, 12) is opened to interrupt the current supply path between the connection ends (11', 12'). A diagnosis circuit comprises an auxiliary circuit designed so as to incorporate the current supply path running at least between the connection ends (11', 12') with switch element (SW3) arranged therebetween, and is designed to supply the auxiliary circuit with an auxiliary voltage, to sense a voltage applied between the two connection ends (11', 12') at the switch element (SW3), to output an output signal corresponding to the sensed voltage, and to evaluate the output signal in relation to the present switched state.

Description

[0001] Detection of a switching state of a switching element

[0002] The invention relates to a circuit arrangement and a method for detecting a switching state of a switching element, in particular within a power supply path.

[0003] Switching elements within the scope of the invention are known to be used to establish or break an electrically conductive connection between two electrically conductive terminals or contacts by means of a switching path running between them, depending on the switching state. Switching elements can generally be designed as a conventional on / off switch, as a normally closed contact, normally open contact, or changeover switch. A conventional on / off switch only requires the action of an external force or control for the switching itself, i.e., for establishing or breaking an electrically conductive connection between the two electrically conductive terminals or contacts. Normally closed and normally open contacts are defined by their respective rest and working positions. When the normally closed contact is in its rest position, it is in its closing switching state (in English, "normally closed" - "NC"), i.e.The electrically conductive connection is established between the two connections or contacts, and in order to assume the interrupting switching state, i.e. to open the electrically conductive connection between the connections or contacts, it must be subjected to a correspondingly permanent force, i.e. to be controlled. The normally open contact, on the other hand, is in its rest position in its interrupting switching state (in English “normally open” - “NO”), i.e. the electrically conductive connection between the two connections or contacts is separated, and in order to assume the closing switching state, i.e. to close the electrically conductive connection between the connections or contacts, it must be subjected to a correspondingly permanent force, i.e. to be controlled. The closing switching state of a normally open contact is therefore its working position. A changeover switch, also known as a throw switch or changeover orA changeover contact, also known as a "double-throw" contact, has at least one additional third terminal in addition to the two previously described terminals or contacts, so that one electrically conductive connection is opened and another is closed simultaneously. A changeover switch thus establishes an electrically conductive connection between two terminals or contacts in every position. One of the terminals or contacts is connected as the common center terminal ("COM") to either one or another contact during switching.

[0004] Normally, normally closed and normally open contacts switch monostable without any special additional precautions, i.e. of two or more possible states, only one is stable (rest position). The other state (operating position) is only maintained as long as an external force acts on it, preventing it from returning to its rest position. The return of a monostable switching element to the rest state can also be delayed by a time constant. A changeover switch, on the other hand, can be designed as a monostable switching element or as a stable switching element, where the effect of the external force is only required for the switching itself. If the third or any further connection is not used in the latter case, the changeover switch can also be used as a conventional on / off switch. Monostable switching elements can, for example, be designed as pushbutton switches, i.e.as switches that are activated by pressing and automatically return to their original position when released, often using a mechanical spring. Further examples include contactors and relays. Contactors are traditionally referred to as electrically or electromagnetically operated switches for high electrical power, while relays are electrically operated, remotely controlled switches with usually two switching positions, which are activated via a control circuit and can switch additional circuits. Unlike contactors, which have only one or several normally closed and normally open contacts, relays can also have changeover contacts (changeover switches).

[0005] Switching elements can also be positively guided, whereby an NC contact and a NO contact are mechanically connected to one another in such a way that the NO contact and NC contact can never be closed together. This means, for example, that a NO contact that is welded due to overload, i.e. that does not open when the coil is de-energized, will result in no NC contact closing. In this case, an NC contact can also be used to diagnose or monitor the status of the NO contact. This circumstance makes positively guided switching elements an ideal standard component in safety-critical applications, in particular, for example, the ideal basic building block of a safety switching device. With integrated diagnostics, such diagnostics or monitoring can even take place during operation.

[0006] However, for the use of generally more cost-effective and less complex non-forced switching elements in safety-critical applications, particularly e.g. within a safety switching device, further measures are necessary.

[0007] It is known, for example, to use "simple" switching elements, e.g. simple relays, instead of positively guided switching elements in the field of safety technology through the use of changeover switches, whereby the monitoring of such non-positively guided switching elements can be carried out, for example, on a microcontroller basis.

[0008] Examples include EP 1 869687 B1 and EP 3 575 900 B1.

[0009] Thus, according to EP 1 869687 B1, in a safety switching device for safely switching off an electrical load with at least one input for connecting a signaling device, an evaluation and control unit is provided for controlling a switching element in order to interrupt a power supply path to the load. The evaluation and control unit is further configured to perform functional tests at defined times to verify a switching function of the switching element, wherein the input for connecting the signaling device is also configured as an input for supplying a supply voltage required for the operation of the switching element.

[0010] According to EP 3 575 900 B1, in a very specific embodiment, an intelligent safety relay is provided with two processing chips, each comprising a plurality of terminals for controlling the safety relay to remain in an output standby state upon receipt of a sensing signal, and with two relay coils, each having a normally closed contact, each of which is connected to a diagnostic signal generating circuit, each having a normally open contact, each of which is connected to a relay output end, and each having a common contact, both common contacts being connected to one another and to a common diagnostic signal detecting circuit, each relay coil being controlled by means of a logic circuit to be switched on or off, such that the respective common contact is electrically connected to the corresponding normally closed or normally open contact;wherein the electrical connections between each common contact and corresponding normally open contact interconnect the relay output ends;

[0011] In summary, according to both of the aforementioned documents, a changeover relay diagnosis is implemented using their NC contacts (NC: "normally closed"). Specifically, this involves diagnosing whether a test signal supplied to the changeover relay via the NC contacts can be read back or not, with each switching element of each changeover switch of the changeover relay being controlled sequentially. The subsequent evaluation can then be performed by a microcontroller. Consequently, the NC path of a changeover relay is used for contact monitoring, and a microcontroller is used for control and evaluation.

[0012] DE 10 2010 060 323 A1 also describes a switching arrangement for monitoring the function of a safety circuit, whereby the switching arrangement exclusively comprises relays with non-forced contacts and a monitoring unit in the form of a microcontroller.

[0013] US 9,989,594 B2, on the other hand, describes a monitoring circuit for monitoring the switching state of an electrical switching contact, which has a monitoring unit and a transformer, wherein the secondary windings of the transformer, together with the switching contact, form a monitoring circuit. Against the background of the cited prior art, one object of the invention is to implement a novel solution for monitoring the switching state of switching elements, which can be implemented in particular with discrete components, i.e. with individual electrical circuit elements that can be arranged in a separate housing, with their own external connections, and with only one functional unit, instead of integrated circuits (ICs), which combine several electronic components in one housing.In particular, the invention is intended to enable such monitoring even with non-positively guided switching elements, preferably simple normally open contacts, and is also suitable for use in safety-critical applications, particularly in safety-related switching devices. Furthermore, it is also desirable that load monitoring can be used.

[0014] The solution according to the invention is provided by the subject matter having the features according to the appended independent claims. Expedient embodiments are the subject matter of the appended claims.

[0015] Accordingly, the invention proposes a method for detecting a switching state of a switching element within a power supply path, in which a switching element arranged between two terminal ends of a power supply path and having two terminals, each of which is electrically connected to a respective terminal end of the power supply path, can be or is controlled to selectively assume a first switching state in which a switching path running between the two terminals is closed to close the power supply path between the two terminal ends, or to assume a second switching state in which the switching path running between the two terminals is open to interrupt the power supply path. The switching element can thus bring about a resistance value between these two terminal ends that is either high-ohmic or low-ohmic depending on the switching state.

[0016] Furthermore, it is provided to form an auxiliary circuit by including the power supply path running at least between the connection ends with a switching element arranged therebetween and to supply this with an auxiliary voltage. According to the invention, a voltage present between the two connection ends on the switching element is then tapped and an output signal corresponding to the tapped voltage is output, which output signal is finally evaluated in relation to the existing switching state.

[0017] The method therefore offers the advantage that it can essentially ensure comprehensive recording of the respective switching state, even of non-positively guided switching elements, and thus also test their functional suitability. Since there is generally a higher voltage signal and therefore a corresponding output signal in the open switching state than in the unopened switching state, it is also possible, even when using a normally open contact, to easily check whether the "NO path" to be formed between the two connections is actually high-impedance in its switched-off state, i.e. in its NO status. The auxiliary voltage also makes it possible to carry out a large number of tests, which makes the method ideal for use in safety-critical applications, particularly in safety-related switchgear.

[0018] In a preferred development, the method further comprises, as a further step, selectively opening or disconnecting the auxiliary circuit, preferably in series with the switching element, and evaluating the resulting output signal corresponding to the tapped voltage with respect to a level change. Such a procedure can be used, in particular, to perform a test to verify the presence of an actually open switching state, since in this case, the opening and disconnecting of the auxiliary circuit must be reflected in a corresponding change in the corresponding output signal.

[0019] To selectively open or close the auxiliary circuit, the primary side of an optocoupler, whose secondary side is arranged in series with the switching element as part of the auxiliary circuit, can be controlled by a logic device, for example, and the resulting output signal corresponding to the tapped voltage can be evaluated by the logic device with respect to a level change. Depending on the respective evaluation, the invention thus provides for testing the switching element to be tested for functionality or a fault. As a result, it is possible to detect whether the switching element is functioning properly or whether it is faulty.

[0020] Accordingly, the invention further provides a circuit arrangement for detecting a switching state of a switching element within a power supply path, with which, in particular, the method described above can also be expediently implemented. The circuit arrangement comprises the switching element and the power supply path, wherein the power supply path, in particular for the load current supply, is arranged between two potential terminals, and the switching element has two connections and is arranged in the power supply path between two connection ends of the power supply path, wherein each of the connections is electrically connected to one of the connection ends. The switching element is further configured to assume, in particular by control by means of a voltage to be supplied from outside the circuit arrangement, a selectively either closing or interrupting switching state.wherein in the closing switching state, a switching path running between the two terminals is closed to close the power supply path between the terminal ends and in the interrupting switching state, the switching path running between the two terminals is open to interrupt the power supply path between the terminal ends. According to the invention, the circuit arrangement is further characterized by a diagnostic circuit which comprises an auxiliary circuit formed by including the power supply path running at least between the terminal ends with a switching element arranged therebetween, wherein the diagnostic circuit is at least configured to supply the auxiliary circuit with an auxiliary voltage, to tap off a voltage applied to the switching element between the two terminal ends,for outputting an output signal corresponding to the tapped voltage and for evaluating the output signal in relation to the respective switching state.,

[0021] In addition to the advantages demonstrated with regard to the method, the circuit arrangement thus offers the further advantage that it can, in principle, be constructed using discrete components. In a suitable embodiment, the auxiliary circuit of the diagnostic circuit further includes a resistor arranged in series with the switching element, in particular a resistor whose resistance is many times lower than the resistance created by the switching element in the interrupted switching state between the two terminals. This allows detection and, in particular, the associated testing to be carried out in the simplest way even in the closed switching state, since in such a diagnostic case the auxiliary voltage can also drop across this resistor.Furthermore, by means of such a resistor, a desired or required level difference between the voltage signals in the open and unopened switching state can be easily influenced.

[0022] In a suitable embodiment, it can be provided, alternatively or additionally, that the diagnostic circuit for outputting the output signal corresponding to the tapped voltage includes an operational amplifier, in particular an operational amplifier used as a differential amplifier, with a non-inverting and an inverting input, wherein each of the inputs is electrically connected to one of the two connection ends. Furthermore, in a preferred practical embodiment, each of the inputs of the operational amplifier is electrically connected to the respective connection end via a resistor. This can consequently achieve high-impedance decoupling.

[0023] In particular for carrying out a large number of tests, the diagnostic circuit expediently includes a logic device which is connected in a galvanically decoupled manner to provide the auxiliary voltage for supplying the auxiliary circuit and to evaluate the corresponding output signal.

[0024] For a galvanically decoupled connection for evaluating the corresponding output signal, a first optocoupler and a transformer for providing the electrical auxiliary potential can preferably be included.

[0025] Additionally or alternatively, in a particularly preferred embodiment, the diagnostic circuit can further comprise a second optocoupler, the primary side of which can be controlled by the logic device and the secondary side of which is arranged in series with the switching element as part of the auxiliary circuit. In particular, using such a component, the auxiliary voltage can be activated and deactivated extremely flexibly, and a corresponding dynamization of the evaluation signal can be provoked dynamically and depending on the diagnosis to be performed.

[0026] Further advantages and features of the invention will become apparent from the following description of a preferred embodiment with reference to the accompanying drawings, in which:

[0027] Fig. 1 is a simplified circuit diagram of a preferred embodiment of a circuit arrangement according to the invention, and

[0028] Fig. 2 shows two exemplary signal curves for evaluation in relation to a switching state as shown in Fig. 1.

[0029] Fig. 1 shows a simplified circuit diagram of a circuit arrangement according to the invention for detecting a switching state of a switching element SW3 within a power supply path. Accordingly, the circuit arrangement comprises the switching element SW3 and the power supply path, which, as shown, is arranged between two potential terminals 13, 14. The power supply path can thus be provided, in particular, for load current supply, so that, for example, a working voltage is or can be applied to the potential terminal 14 and one or more loads are or can be connected to the potential terminal 13. However, for reasons of clarity, such loads are not shown in the figure.

[0030] The circuit arrangement is shown in Fig. 1 with a switching element SW3 which has two connections 11, 12 and is arranged in the power supply path between two connection ends 11, 12' of the power supply path, wherein each of the connections 11, 12 is electrically connected to one of the connection ends 11', 12'. In Fig. 1, the switching element SW3 is preferably designed as a make contact, but can alternatively also be designed as a break contact or changeover switch. The switching element SW3 can be controlled in a manner known per se. In particular, however, the control can take place within the scope of the invention by means of a voltage supplied from outside the circuit arrangement. Since the type of control and / or a control circuit provided for this purpose is not the subject of the invention, the control of the switching element SW3 is not shown in Fig. 1 for reasons of clarity.

[0031] The switching element SW3 is thus configured to assume either a closing or an interrupting switching state, wherein in the closing switching state, a switching path extending between the two terminals 11, 12 is closed to close the power supply path between the terminal ends 11', 12', and in the interrupting switching state, the switching path extending between the two terminals 11, 12 is open to interrupt the power supply path between the terminal ends 11', 12'. This can therefore be done in a manner known per se.Essential to the invention is that the circuit arrangement has a diagnostic circuit comprising an auxiliary circuit formed by including the power supply path extending at least between the connection ends 1T, 12' with the switching element SW3 arranged therebetween. The diagnostic circuit is configured to supply the auxiliary circuit with an auxiliary voltage, to tap a voltage present between the two connection ends 1T, 12' at the switching element SW3, to output an output signal corresponding to the tapped voltage, and to evaluate the output signal AS with respect to the respective switching state. The diagnostic circuit is thus particularly independent of the control.

[0032] If the switching element SW3 is thus designed as a shooter, it can be checked with this circuit arrangement, ie in particular by means of the diagnostic circuit, whether in the switched-off state of the switching element the "NO path" formed here via the switching path between the terminals 11, 12 or the terminal ends 1 T, 12' is high-resistance and thus the power supply path is interrupted.

[0033] The switching element SW3 thus creates a resistance value between these two connection ends 11', 12', which is either high-impedance or low-impedance depending on the switching state. If the auxiliary circuit formed by including the power supply path running at least between the connection ends 11', 12' with the switching element SW3 arranged therebetween is supplied with an auxiliary voltage and the voltage present at the switching element SW3 between the two connection ends 11', 12' is tapped, the output signal AS corresponding to the tapped voltage can be evaluated with respect to the existing switching state, and thus the switching state of the switching element SW3 within the power supply path can be detected.

[0034] Fig. 2 shows, by way of example, a roughly sketched curve of a stimulus signal generated to check the diagnostic circuit and the curve of a corresponding output signal AS (diag. input) received for evaluation in the case of a switching element SW3 in the state shown in Fig. 1, i.e. open. If no stimulus signal is applied (stimuli OFF), the corresponding output signal AS is also zero or almost zero (diag. input OFF). If the stimulus signal is switched on and the switching element SW3 is open and thus has a high impedance (stimuli ON), a corresponding output signal AS is also applied (diag. input ON). By means of such a stimulus signal, a corresponding dynamization of the evaluation signal can thus also be provoked.

[0035] For this purpose, the auxiliary circuit of the diagnostic circuit is preferably constructed, as shown in Fig. 1, with a resistor R7 arranged in series with the switching element SW3, in particular a resistor R7 whose resistance value is many times lower than a resistance value caused by the switching element SW3 in the interrupted switching state between the two terminals 11, 12. In the open switching state of the switching element, a series circuit of resistor R7 and the high-impedance switching contact SW3 can be formed by means of the diagnostic circuit, so that it is possible to check whether the switching path in the open state, i.e. according to Fig. 1 in particular the “NO path” in the switched-off state of the switching element, has a high resistance. In this case, a corresponding voltage applied to the switching element SW3 can therefore also be tapped. As a result, the switching state of the switching element SW3 within the power supply path can be detected.It is advantageous that such a voltage divider can be formed in particular without a reference potential, i.e. independently of the working voltage applied to the potential terminals 13, 14 and the connected loads. To output the output signal corresponding to the tapped voltage, an operational amplifier A3, in particular an operational amplifier used as a differential amplifier, with a non-inverting and an inverting input can preferably be part of the diagnostic circuit, as shown in Fig. 1, wherein each of the inputs is electrically connected to one of the two connection ends 1T, 12', in particular via a resistor R8, R9. Decoupling, in particular high-impedance decoupling, can therefore be achieved via the resistors R8, R9 and are also relevant for fault exclusion when preferably carrying out various functional tests.The resistors R8, R9 should therefore preferably be in the range of 1MOhm or even larger.

[0036] In other words, in a preferred embodiment, not only the switching state of the switching element SW3 can be detected within the power supply path, in particular in the case of a non-forced switching element. Rather, the switching element to be tested can also be checked for functionality or a fault. Thus, depending on the evaluation, a functional switching element SW3 can be detected, in particular in the case of a non-forced switching element, i.e. in particular when monitoring the contacts of a non-forced relay, or a fault. The invention is therefore particularly suitable for use in safety-critical applications, in particular in safety-related switching devices.

[0037] To provide the auxiliary voltage to supply the auxiliary circuit and to evaluate the corresponding output signal, a galvanically decoupled logic device can be part of the diagnostic circuit, as can be seen in Fig. 1.

[0038] In this case, it has proven expedient to provide an optocoupler, designated OC4 in Fig. 1, for the galvanically isolated connection for evaluating the corresponding output signal, and a transformer, designated T3 in Fig. 1, for providing the auxiliary electrical voltage. Additionally or alternatively, the diagnostic circuit can also comprise an optocoupler, designated OC3 in Fig. 1, whose primary side can be controlled by the logic device and whose secondary side is arranged in series with the switching element SW3 as a component of the auxiliary circuit. By means of the optocoupler OC3, for example, by switching off the auxiliary voltage (e.g. as also shown in Fig. 2) in the direction of the switching element SW3, a malfunction of the operational amplifier A3 can also be detected by provoking a change of state at its inputs.This type of dynamization of the evaluation signal can also be used in particular to exclude or detect a stuck-at error (in particular a malfunction of the operational amplifier A3) in the diagnostic chain.

[0039] Preferred procedures for selectively opening or disconnecting the auxiliary circuit in series with the switching element SW3 in the further course to detect the switching state and to evaluate the output signal corresponding to the tapped voltage with respect to a level change are described below.

[0040] As can be seen from these procedures, in order to selectively open or close the auxiliary circuit, the primary side of the optocoupler OC3 is preferably controlled by the logic device logic and the output signal corresponding to the tapped voltage is then also evaluated by the logic device logic with regard to a level change.

[0041] With reference to Fig. 1, it is assumed that the auxiliary circuit of the diagnostic circuit is supplied with an auxiliary voltage via the transformer T3 and the circuit part U3, wherein this auxiliary voltage is independent of the potentials connected to the potential terminals 13, 14 and only serves the diagnostic circuit for its function.

[0042] For resistors R7, R8, and R9, MELF resistors (“MELF” - Metal Electrode Leadless Faces) are used in a particularly practical design. MELF (especially mini / micro MELF) resistors offer the well-known advantage of better achieving specific parameters such as pulse load capacity, temperature stability, long-term stability, and dielectric strength, as well as precisely specified behavior in the event of a fault (fuse resistance). Thus, MELF resistors can also essentially eliminate the risk of a short circuit in the component in the event of a fault.

[0043] In order to correctly detect the voltage which is present in the high-impedance state of the switching contact SW3, ie between the terminals 11, 12, an operational amplifier is used as a differential amplifier A3.

[0044] To make the diagnostic result more dynamic, it is also provided, as indicated above, to switch off the auxiliary voltage to the switching contact SW3. This switch-off is preferably implemented using the optocoupler OC3, e.g., an opto-FET, which is controlled via the logic device.

[0045] The detection of the switching state of the switching element SW3, in particular including the associated diagnosis of the switching contact SW3, can then always be carried out according to the same procedure.

[0046] If the logic device logic knows the control state in an appropriate design, the diagnosis of the switching element SW3 is preferably carried out in the open state of the switching element SW3, ie in the non-controlled state with a normally open contact as shown in Fig. 1.

[0047] In the non-activated state, the normally open contact thus creates a high-impedance resistance between the two connections 11 and 12 or between the connection ends 11' and 12' of the power supply path. The auxiliary voltage is enabled by the logic device, galvanically isolated by OC3, and is then applied to the series circuit formed thereby, comprising the resistor R7 and the high-impedance switching contact SW3. As previously described, the resistance value of the resistor R7 is expediently many times lower than the resistance value created by the switching element SW3 in the interrupted switching state, i.e. Rsw3_open » R7. By tapping the voltage applied between the two connection ends 11', 12' on the switching element SW3, the operational amplifier A3 can measure the auxiliary voltage across the switching contact SW3 and output a corresponding output signal for evaluation.If almost the entire auxiliary voltage can be measured via the switching element SW3, the switching element SW3 is high-resistance, i.e. open.

[0048] The corresponding output signal AS output at the output of the differential amplifier A3 therefore assumes a high signal level, i.e., a HIGH level. The output signal AS is then conveniently passed through the optocoupler OC4 to the logic device for evaluation.

[0049] To prevent a stuck-at fault in operational amplifier A3, the optocoupler OC3 is preferably deactivated by the logic device after this pass, meaning that no auxiliary voltage can be measured at switching element SW3. Consequently, an output signal AS with a lower signal level, i.e., a LOW level, is generated at the output of operational amplifier A3, which is then passed to the logic device via optocoupler OC4.

[0050] If the resulting signal sequence of the measurement corresponds to a pattern expected by the logic device (see Fig. 2), it is ensured that the switching contact is open and, in this example, has also assumed a safe state.

[0051] Appropriately based on the embodiment shown in Fig. 1, the following further tests can be carried out, ie in particular with appropriately provoked dynamization of the output signal to be evaluated, hereinafter also referred to as evaluation signal.

[0052] With regard to the switching element SW3, the following errors and their effects can be considered in particular.

[0053] If the switching element SW3 is "welded", i.e. permanently closed, and thus the resulting resistance value is permanently low-impedance regardless of the respective control, no or only a small auxiliary voltage can be tapped across it. At the operational amplifier A3, an output signal AS with a lower signal level, i.e. a LOW level, would therefore be established at the output, regardless of whether or not a stimulus signal is applied. Based on the circuit arrangement according to Fig. 1, in the case of a diagnosis, essentially the entire auxiliary voltage, preferably provided via the transformer T3 and the circuit part U3, would drop across OC3 or R7.

[0054] However, any voltage measured by operational amplifier A3 would permanently result in a low output signal AS, i.e., a permanently LOW signal. Since this signal contradicts the pattern expected by the logic, i.e., a correspondingly provoked dynamization of the evaluation signal fails to occur, an error response can be triggered.

[0055] Is the switching element SW3 "broken", i.e. permanently in the open state, and thus the resulting resistance value is permanently high regardless of the respective control. In order to diagnose this fault, the diagnosis would have to be carried out when the switching element SW3 is controlled to assume the closing switching state. If, when the auxiliary voltage is applied, an output signal AS with a high signal level, i.e. a HIGH level, is generated at the output of the operational amplifier A3, it can be assumed that the switching element SW3 is not responding as expected. If, in the case of a switching element SW3 designed as a normally open contact, the auxiliary voltage is measured at the switching element SW3, it can be assumed that, contrary to expectations, the normally open contact is not closed. However, for a Stop Category 0 device (Safe State OFF), this is the safe state. Nevertheless, an error reaction / error feedback can be triggered.

[0056] With regard to a change in the characteristics of R7, the following errors and their effects can be considered in particular.

[0057] A short circuit is essentially eliminated by a MELF design. Increasing, e.g., doubling, the resistance of R7 has no negative effects, at least as long as the resistance value induced by the switching element SW3 in the interrupting state is several times greater than the resistance value of R7, ie, Rsw3_open » R7.

[0058] Even a reduction, e.g., halving the resistance of R7, has no negative effects. If R7 is open-circuited, no auxiliary voltage would be measurable at switching element SW3, so the presence of such a fault can be detected.

[0059] With regard to a change in the characteristics of R8 and R9, which serve for the high-impedance decoupling of the operational amplifier A3, the following errors and their effects can be considered in particular.

[0060] A short circuit is essentially eliminated by a MELF design.

[0061] An increase, e.g. doubling of one or both resistance values ​​generally has no negative effects.

[0062] A reduction, e.g. halving one or both resistance values, has basically no negative effects

[0063] If there is an open-circuit behavior, an auxiliary voltage would never be measurable at the switching element SW3, so that the presence of such a fault can also be detected.

[0064] With regard to the optocoupler OC3, the following errors and their effects can be considered in particular.

[0065] If this is permanently conductive, the auxiliary voltage to the switching element SW3 can no longer be switched off. A voltage would be continuously measured at the switching element SW3 via operational amplifier A3 when the switching element SW3 is open. This would cause an expected output pattern to be faulty, which could be detected, particularly by the logic device, and trigger an error response.

[0066] If the optocoupler OC3 is permanently high-impedance, i.e., open, no auxiliary voltage can be measured by the operational amplifier A3 at the switching element SW3. This results in an error in the expected output pattern. This can also be detected, particularly by the logic device, and trigger an error response. With regard to the optocoupler OC4, the following errors and their effects can be considered in particular.

[0067] If the optocoupler OC4 is continuously conductive, the output signal of operational amplifier A3 is continuously detected as a HIGH signal, which in turn causes an expected output pattern to be faulty. The presence of such a fault can therefore also be detected and subsequently trigger an error response.

[0068] If the optocoupler OC4 is permanently high-impedance, i.e., open, the output signal of operational amplifier A3 is permanently detected as a LOW signal, which in turn causes an expected output pattern to be faulty. The presence of such an error can therefore also be detected and subsequently trigger an error response.

[0069] With regard to the transformer T3, the following errors and their effects can be considered in particular.

[0070] If there is a wire break in the primary and / or secondary winding, no voltage can be transmitted. Even if such a fault occurs, the output signal of operational amplifier A3 would be permanently detected as a LOW signal, which in turn would cause an expected output pattern to be faulty and could subsequently trigger an error response.

[0071] If there is a short circuit in the primary and / or secondary winding, no voltage can be transmitted. Even if such a fault occurs, the output signal of operational amplifier A3 would be permanently detected as a LOW signal, which in turn would cause an expected output pattern to be faulty and could subsequently trigger an error response.

[0072] The inventive method and the inventive circuit arrangement are therefore also highly suitable for the use of more cost-effective and less complex non-forced switching elements, i.e., in particular for contact monitoring of a non-forced relay, in safety-related applications. With appropriate use, the safe failure fraction (SFF) can be increased through a variety of diagnostic measures, thus also reducing the hardware fault tolerance (HFT) to be implemented. For a quantification of the aforementioned SFF and HFT parameters, reference can be made in particular to IEC EN 61508-2 in the version applicable on the filing date, in particular to Table 2 / 3 therein.

Claims

1. Circuit arrangement for detecting a switching state of a switching element (SW3) within a power supply path, comprising the switching element (SW3) and the power supply path, wherein the power supply path, in particular for load current supply, is arranged between two potential terminals (13, 14), and wherein the switching element (SW3) has two terminals (11, 12), is arranged in the power supply path between two terminal ends (1T, 12') of the power supply path, each of the terminals (11, 12) being electrically connected to one of the terminal ends (1T, 12'), and is configured to assume, in particular by means of a voltage supplied from outside the circuit arrangement, a selectively either closing or opening switching state, wherein in the closing switching state a connection exists between the two terminals (11, 12').12) the switching path for closing the power supply path between the terminal ends (11', 12') is closed and in the interrupting switching state the switching path between the two terminals (11 , 12) for interrupting the power supply path between the terminal ends (1 T, 12') is open, a diagnostic circuit which comprises an auxiliary circuit formed by including the power supply path running at least between the terminal ends (1 T, 12') with a switching element (SW3) arranged in between and wherein the diagnostic circuit is further configured to supply the auxiliary circuit with an auxiliary voltage, to tap a voltage applied to the switching element (SW3) between the two terminal ends (11 ', 12'), to output a corresponding output signal and to evaluate the output signal with respect to the respective switching state.

2. Circuit arrangement according to claim 1, wherein the auxiliary circuit of the diagnostic circuit includes a resistor (R7) arranged in series with the switching element (SW3), in particular a resistor (R7) whose resistance value is many times lower than a resistance value caused by the switching element (SW3) in the interrupting switching state between the two terminals (11, 12). Circuit arrangement according to claim 1 or 2, wherein the diagnostic circuit for outputting the output signal corresponding to the tapped voltage includes an operational amplifier (A3), in particular an operational amplifier used as a differential amplifier, with a non-inverting and an inverting input, wherein each of the inputs is electrically connected, in particular via a resistor (R8, R9), to one of the two terminal ends (11', 12'). Circuit arrangement according to claim 1, 2 or 3, wherein the diagnostic circuit includes a logic device which is galvanically isolated for providing the auxiliary voltage to supply the auxiliary circuit and for evaluating the corresponding output signal.Circuit arrangement according to claim 4, wherein a first optocoupler (OC4) is included for the galvanically isolated connection for evaluating the corresponding output signal, and a transformer (T3) is included for providing the auxiliary electrical voltage. Circuit arrangement according to claim 4 or 5, wherein the diagnostic circuit further comprises a second optocoupler (OC3), the primary side of which can be controlled by the logic device, and the secondary side of which is arranged in series with the switching element (SW3) as part of the auxiliary circuit.Method for detecting a switching state of a switching element (SW3) within a power supply path, in particular with a circuit arrangement according to one of claims 1 to 6, comprising the following steps: Controlling a switching element (SW3) which is arranged between two terminal ends (1T, 12') of a power supply path and has two terminals (11, 12), each of which is electrically connected to one terminal end (11', 12') of the power supply path, for selectively assuming a first switching state in which a switching path running between the two terminals (11, 12) is closed to close the power supply path between the two terminal ends (1T, 12'), or for assuming a second switching state in which the switching path running between the two terminals (11, 12) is open to interrupt the power supply path. Power supply path is open, wherein the switching element (SW3) causes a resistance value between these two terminal ends (1 T, 12') which is either higher or lower depending on the switching state, supplying an auxiliary circuit formed by including the power supply path running at least between the terminal ends (11 ', 12') with an intermediate switching element (SW3) with an auxiliary voltage, Tapping a voltage applied between the two terminals (1 T, 12') at the switching element (SW3), outputting an output signal corresponding to the tapped voltage and evaluating the output signal with respect to the current switching state.

8. Method according to claim 7, wherein in a further step the auxiliary circuit in series with the switching element (SW3) is selectively opened or disconnected and the output signal corresponding to the tapped voltage is evaluated with respect to a level change.

9. Method according to claim 8, wherein, for selectively opening or closing the auxiliary circuit, the primary side of an optocoupler (OC3), the secondary side of which is arranged in series with the switching element (SW3) as part of the auxiliary circuit, is controlled by a logic device, and the output signal corresponding to the tapped voltage is evaluated by the logic device with respect to a level change.

10. Method according to claim 7, 8 or 9, wherein, depending on the evaluation, a functional switching element (SW3) or a fault is detected.

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