EP2045825A1 - Switching element - Google Patents

Abstract

The switching element (S0) has a contact element with a switching contact (5, 6) e.g. break contact, for producing or interrupting an electric circuit. A test element (T) i.e. current controlling element, is provided for monitoring the electric circuit, and is switched in parallel or series with the switching contact. The test element is provided between contacts of the switching contact, and is arranged outside or inside of a housing of the switching element. The test element comprises a circuit formed of ohmic, capacitive and/or inductive resistances and/or diodes i.e. Zener diodes.

Description

The invention relates to a switching element, comprising a switching element with a switching contact for the production or interruption of a circuit. Furthermore, the invention relates to a command device, in particular emergency stop switch, with such a switching element.

Switching elements are used in a variety of command devices and other electromechanical switching devices, such as position switches, contactors or circuit breakers etc.

Switching elements function either on the basis of normally open or normally closed contacts. The normally open contact is open in the de-energized state. Upon actuation, for example by a push button, the circuit is closed and thereby set a machine in operation or started a process. Normally closed contact elements are used to interrupt circuits in order to switch off systems or machines or to end operating states. Special significance and thus special demands on reliability are normally closed contacts, which are used with emergency / off command devices or position switches with personal protection function. In the event of an emergency, the safe shutdown of the machine or system must be ensured.

The emergency / off command device causes by the circuit of the associated switching element interrupting, for example, an armature circuit of a contactor. In the past, the application in combination with an electronic control (PLC) has prevailed, via the control cable, the so-called control input level is transmitted to the electronic control and this tells whether the emergency stop command device was actuated or not. The sole indicator is the actual interruption of the circuit. Thus, the transition of the switching contact from the closed state (impedance / resistance approximately zero) to the opened state (impedance / resistance approximately infinite) is detected.

The problem now is, for example, if lines between switching element and control by damage to the insulation or miswiring are shorted that the circuit remains almost without resistance. For the control input level of the electronic control, it makes no difference whether the circuit is normally closed by the switch contact or, fatally, by a short circuit acting in parallel with it. This type of short circuit is not recognizable on the part of the electronic control. This leads to potential dangers, especially in safety circuits, since it does not interrupt the circuit despite actuation by the user.

Such a short circuit can neither be detected by the operator nor by the electronic control and must be excluded by occasional checks of the functionality. However, this inevitably shuts down entire plants or parts of the plant, which leads to downtimes and disruptions to operations.

The invention has for its object to provide a switching element, which substantially reduces the risk of an unnoticed dysfunctional command device.

The object is achieved by a switching element of the type mentioned, which has at least one test element for monitoring the circuit. The object is further achieved by a command device, in particular emergency stop switch, which has such a switching element.

The invention is based on the finding that a circuit that can be switched on and off by a switching element, both in a closed switching contact even with a short circuit is almost without impedance. Consequently, the triggering criterion chosen so far is problematic because short circuits with sufficiently low impedance can not be detected.

The operation of the switching element according to the invention is based on a test element for monitoring the circuit. This test element is a current-influencing element which has an inductance, capacitance and / or an ohmic resistance. The test element may additionally or exclusively consist of a diode, in particular zener diode, as well as combinations thereof. Importantly, the test element has some type of impedance. As long as the current flow through the circuit is given, i. the plant or machine is operating properly, the test element has at least one particular feature that can be monitored, such as e.g. Voltage, current, phase shift or other electrical quantities. The decisive factor here is that the selected electrical variable assumes a different value if the current flow through the switching contact deviates from the operational value.

Advantageously, the detectable change in state, which is detected by a measurement on the test element, a short-circuit monitoring or a line break monitoring. For a short-circuit monitoring, the test element in series with the switching contact, in particular normally closed, is switched. For a line break monitoring a parallel circuit of the test element to the switching contact is necessary. Both types of monitoring can be realized simultaneously. Here, a plurality of test elements can be used.

Advantageously, test elements are connected in parallel and in series with the switching contact, so that a line break monitoring and a short-circuit monitoring can be realized.

Advantageously, a parallel connection (short circuit) is now easily recognizable by the fact that the electrical properties of the test element (s) change as a result of the unwanted short circuit. If, for example, an ohmic resistor is used as test element, which is connected in series with the normally closed contact, a parallel connection causes the entire current flow to increase significantly. If, for example, this current is detected, it is also recognizable by an electronic controller that the command device has been bypassed. When impressed current and the decreasing voltage value can serve as a criterion.

In an advantageous embodiment, the or the test elements are arranged in close proximity to the switching contact. Since it is the parallel shorts that have a fatal effect, it makes sense to keep the line length between the switch contact and test element small, so that the probability of such a short circuit is significantly reduced.

In an advantageous embodiment, at least one test element outside or inside the housing of the switching element can be arranged or arranged. It can thereby be achieved that conventional switching elements can still be equipped with such a test element or such a test element can be retroactively upgraded.

In an advantageous embodiment, the test elements form a circuit of ohmic, capacitive and / or inductive resistors, which lead to a more comfortable detection of a short circuit or line break. An evaluating controller undertakes the initiation of appropriate measures if the characteristic measured variables indicate a short circuit.

Advantageously, the switching contact of the switching element is a normally closed contact, but this can also consist of a normally open contact.

Further advantageous embodiments and preferred developments of the invention can be taken from the description of the figures and / or the dependent claims.

In the following the invention will be described and explained in more detail with reference to the embodiments illustrated in the figures.

FIG 1

ein Not/Aus-Befehlsgerät mit getrenntem Betätiger und einem Schaltelement,

FIG 2

bis 10 Schaltkontakte für Schaltelemente mit in Reihe geschalteten Testelementen,

FIG 11

Befehlsgerät mit elektronischer Steuerung,

FIG 12

Befehlsgerät mit elektronischer Steuerung bei Kurzschluss,

FIG 13

und 14 Schließerkontakte mit in Reihe und parallel geschalteten Testelementen,

FIG 15

und 16 Schaltkontakte für Schaltelemente mit in den Schaltmechanismus integrierten Testelementen,

FIG 17

Schaltelement mit externem Testelement.

Show it:

FIG. 1

an emergency stop device with separate actuator and a switching element,

FIG. 2

up to 10 switching contacts for switching elements with test elements connected in series,

FIG. 11

Control unit with electronic control,

FIG. 12

Control unit with electronic control in case of short circuit,

FIG. 13

and 14 normally open contacts with test elements connected in series and in parallel,

FIG. 15

and 16 switching contacts for switching elements with test elements integrated into the switching mechanism,

FIG. 17

Switching element with external test element.

FIG. 1 shows an emergency stop device with separate actuator B and a switching element S0. The actuator B is shown in relation to the switching element S0 in a mounting position. The dotted arrow indicates in this case the unlocking of the actuator B, including the actuating parts of the same, to the switching element S0, in particular to the plunger 10 at. The switching element S0 has a switching bridge 11 of an NC contact, which via the two contacts 5.6 the close or open the circuit to be monitored if actuated. The moving parts of the switching element S0 are countered with a return spring 12, which counteracts the actuating movement. About the screw terminals 13,14 takes place the electrical connection to the outboard (and not shown) circuit.

There is a test element T between the contact 6 and the screw terminal 13. In this case, the test element T can consist of a number of components, in particular a combination of components. Decisive in this context is the fact that the test element T can be distinguished in impedance from the wiring and thus enables detection of a short circuit, which changes the operational characteristic of the test element.

Advantageously, the test element T is in the vicinity or even in the immediate vicinity of the contact 6, so that an inadvertent contacting of the conduction path between the test element T and the contact 6 is as improbable as possible. A short circuit that includes this pole would not be detectable by the test device.

The following FIG. 2 such as FIGS. 4 to 10 show possible electrical diagrams of the switching element S0. In this case, the normally closed contact is connected in series with various test elements. Advantageously, these test elements or their characteristics can be detected outside the switching element S0, so that no additional lines need to be guided into the switching element S0.

FIG. 2 shows a switching contact for the switching element S0 with a series-connected test element T1. The externally detectable characteristic here consists in the zener voltage of the Zener diode, which acts as a test element T1. As soon as a short circuit of the command device occurs, the Zener voltage drops to zero due to the short circuit. This is recognizable from the outside, namely by the fact that the zener voltage no longer measurable to the same extent as before. The change gives a clear indication of the short circuit.

From the short circuit scenario, the operational shutdown is easy to distinguish. If, with the circuit intact, the mechanical switching contact is opened by a scheduled actuation, the current is interrupted, which is recognized and evaluated by the control.

FIG. 3 shows a make contact with the test element T1, which is formed of a zener diode. The remarks to FIG. 2 apply here accordingly, with the difference that a review of the characteristic Zener voltage is only feasible after closing the normally open contact. This means that after the contact has been closed, the user can obtain information about short-circuit safety if a statement about it can be derived from the measured voltage.

In principle, both normally closed and normally open contacts can be used in a switching element according to the invention.

4 to 7 show circuits with Öffnerschaltkontakten, which in each case a test element T2, T3, T4, T5 are connected in series. Each of these test elements T2, T3, T4, T5 can be detected and monitored by an impedance characterizing them.

The test element T2 consists for example of two zener diodes, which are connected in opposite directions. Regardless of the current direction, a voltage is applied to one of the zener diodes, which dominates the total voltage across both zener diodes. The polarity of the connections is advantageously irrelevant.

Test element T3 consists of a capacitor which is only suitable for applications with alternating current. The characteristic of the intact circuit is the capacitive reactance.

The test elements T4 and T5 have an ohmic resistance, which also represents an impedance. The current flow consequently changes with a short circuit of the switching contact. An advantage of the use of the test element T5, which includes or forms a luminaire, is the fact that the user can visually recognize a short circuit based on the luminosity. The user is not dependent on any electronic evaluation or voltage measurement. The lighting element of the test element T5 lights up in the operating state, that is, when the circuit is closed. In the event of a saturated short circuit the luminous element remains off.

FIGS. 8 and 9 Show normally closed contacts for switching elements with series-connected test elements T6, T7, which are formed of a circuit of diodes and a resistor.

The test element T6 consists of an optical diode and a resistor, the resistor being designed to produce the optimum operating current for the light-emitting diode. Otherwise, the test element T6 functions in accordance with the test element T5, as described in FIG FIG. 7 is shown. In order to ensure greater flexibility and to avoid a negative influence on the optical diode by the circuit to be monitored, the optical diode including resistor can be connected in parallel with a Zener diode, so that larger currents can flow through the normally closed contact, without the choice of optical To influence diode. Instead, the optimum operating state for the optical diode is ensured by the choice of the optimum, ohmic resistance.

FIG. 10 shows a Öffnerschaltkontakt for the switching element S0 with series-connected test element T8, which here with a more complex electrical / electronic circuit is formed to realize a current control.

FIG. 11 shows a command device 15, in particular an emergency stop command device, with electronic control 16. The electronic control 16 is provided for voltage monitoring of the command device 15. When operatively closed NC, the voltage U _T caused by the test element T2 is measured and monitored. The measured voltage is designated by U. Consequently, when the normally closed contact is closed and the circuit is connected according to the operation: U = U _T. In this case, as shown in the preceding exemplary embodiments, the voltage U _T can be generated by a Zener diode contained in the test element T12. As long as U = U _T , the system is short-circuit-free.

When the normally closed contact triggers, the measuring voltage U jumps to a constant value, which is defined by the internal resistance of the control.

FIG. 12 shows the command device 15 FIG. 11 with electronic control 16 in case of short circuit.

The voltage U _{T of} the test element T12 can not build up because of the short circuit shown as a lightning, so that this voltage can no longer be taken up by the measured variable U. In the case of a short circuit, U is at U = 0. This state is of the other two possible states, as in FIG. 11 easily distinguishable, so that a short circuit is reliably detectable.

FIGS. 13 and 14 show test elements, as they are already known from previous FIG, which are connected in series or parallel to the Schliesserkontakt.

The problem is to make it apparent to the electronic controller whether the circuit has not become inoperative due to an interruption of the circuit.

For this purpose, a (further) defined voltage or current level is generated by a further parallel branch to the mechanical switching contact with a suitable test element on / via the open switch contact. This level can be detected by monitoring outside or inside the switching element. Such a level is for example in FIG. 14 defined by the sum of the zener voltages.

In connection with the exemplary embodiments of the preceding figures, switching elements are now conceivable which can generate a total of four different levels, each of which indicates the proper operating state "on" or "off", a short circuit and line breaks.

In an advantageous embodiment, even beyond running test routines, e.g. by modulation of the voltage over the resulting current waveform for a targeted monitoring provided. The corresponding characteristic which results from the test elements is not merely a specific voltage, but rather a temporal behavior which can be used as a criterion for monitoring. Such test routines can be used, for example, when starting up or restarting the plant or machine, or can be initiated continuously / temporarily during operation in order to ensure regular monitoring.

FIGS. 15 and 16 show the two test elements T9, T10, which are integrated in the switching mechanism of the switching contact. The advantage of this is the immediate proximity of the respective test element to the switching contact to be monitored in the switching elements S2, S3. In this way, an undetectable short circuit in which a pole lies between the test element T9, T10 and a contact is extremely unlikely due to the immediate proximity.

This solution with a placed directly on the mechanically moving part of the switch contacts test element T9, T10 is for example, by means of a corresponding Isolierschaltbrücke ceramic, or the like, implemented. For this purpose, a zener diode (as contained in test element T9) or a suitable resistor (as contained in test element T10) can be soldered or bonded onto this insulating switching bridge, whereby the connection at the switching element is then made at all. Thus, the test elements T9, T10 represent an indispensable part for the production and interruption of the conductivity and are indispensable for the functionality.

FIG. 17 shows a switching element S4 with external test element T11. The switching element S4 is substantially identical in construction to the switching element S0 FIG. 1 , with the difference that it contains no test element within the housing. Instead, a test element T11 can be docked from the outside to the housing of the switching element S4. For this purpose, the test element T11 is provided with its own housing and its own screw terminal 17. The circuit here is to be connected to the screw 13 of the switching element S4 and to the screw 17 of the test element T11.

Advantageously, two snap hooks 18 are integrally formed on the housing of the switching element S4, whereby a mechanical connection between the housings is easy to manufacture and the electrical connection of the test element 11 is shielded with the electrical components of the switching element S4.

Advantageously, with this embodiment, a retrofitting of standard switching elements is possible, with a selection with respect to the test element T11 can be performed with special consideration of the monitored circuit with respect to current, voltage and current influencing behavior.

The switching elements according to the invention are advantageously in all electromechanical switching devices, such as command devices, position switches, contactors, circuit breakers, etc., applicable. In all, a continuous monitoring of circuits during operation is possible.

In summary, the invention relates to a switching element, comprising a switching contact for interrupting or producing a circuit. The stated aim of the invention is first to detect a parallel circuit of the circuit in which the switching element is used, and thus to eliminate the risk of an unnoticed malfunctioning command device and secondly to detect a line break in a control or signaling circuit at the time of occurrence and thus measures such as initiate controlled shutdown of a process. For this purpose, a test element for monitoring the circuit is provided, which allows a differentiation of various states, in particular on state, off state, short circuit due to its electrical or electronic characteristic. Advantageously, such a switching element in almost all electromechanical switching devices, such as command devices, position switches, contactors or circuit breakers, can be used.

Claims (13)

Switching element (S0..S4) comprising a switching element with a switching contact (5,6) for the production or interruption of a circuit, characterized - characterized in that at least one test element (T0-T11) is provided for monitoring the circuit. Switching element (S0..S4) according to claim 1, wherein the test element (T0..T11) is connected in parallel or in series with the switching contact (5,6). Switching element (S0..S4) according to one of the preceding claims, wherein the test element (T9, T10) between the contacts of the switching contact (5,6) is arranged and is provided for contacting. Switching element (S0-S4) according to one of the preceding claims, wherein test elements (T9, T10) are connected in parallel and in series with the switching contact (5, 6). Switching element (S0-S4) according to one of the preceding claims, wherein the one or more test elements (T0-T11) is / are located in the immediate vicinity of the switching contact (5, 6). Switching element (S0-S4) according to any one of the preceding claims, wherein at least one test element (T0-T11) outside or inside the housing of the switching element (S0-S4) can be arranged or arranged. Switching element (S0-S4) according to one of the preceding claims, wherein the test element (T0-T11) is a current-influencing element. Switching element (S0-S4) according to one of the preceding claims, wherein the test element (T0-T11) has an ohmic, capacitive and / or inductive resistance and / or a diode, in particular a Zener diode. Switching element (S0-S4) according to one of the preceding claims, wherein the test elements (T0-T11) form a circuit of ohmic, capacitive and / or inductive resistors and / or diodes, in particular zener diodes. Switching element (S0-S4) according to one of the preceding claims, wherein a monitoring unit for current and / or voltage measurement can be connected or connected to the test element (T0-T11). Switching element (S0-S4) according to claim 10, wherein the monitoring unit for delivering an electronic, audible and / or visual warning signal to a data processing unit or a user is provided. Switching element (S0-S4) according to one of the preceding claims, wherein the switching contact (5,6) is a normally closed contact or a normally open contact. Command device (15), in particular emergency stop switch, with a switching element (S0-S4) according to one of claims 1 to 12.

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