EP3532421B1 - Elevator with electric circuit monitoring a switch with alternating current - Google Patents

Description

The present invention relates to an elevator system with a specially designed controller for implementing control functions within the elevator system.

In an elevator system, an elevator car is moved between different levels or floors of a building with the aid of a drive. Movements of the elevator car or an operation of a drive conveying the elevator car are controlled with the aid of a controller.

The controller can, on the one hand, actively control elevator components such as a motor of the drive, for example, in order to move the elevator car to the desired floors. For this purpose, the controller can, for example, control an energy supply from an energy source to the drive. As a rule, the drive is driven by an electric motor, so that the controller controls or regulates a power supply to the electric motor. For this purpose, one or more switches can be used between the electrical energy source and the electric motor, e.g. can be designed as circuit breakers for switching high powers and are sometimes also referred to as contactors, which can be closed in a controlled manner by the controller when the drive is to move the elevator car. The control should be able to monitor an actual closed state of these switches.

On the other hand, the controller can monitor ambient conditions, in particular safety-relevant conditions, within the elevator system and take these into account when controlling the elevator functions. For example, the control can monitor permanently or at short time intervals whether all components of the elevator and thus also the entire elevator system are in a safe state, so that the elevator car can be moved safely.

For example, the control can monitor whether the car door and all shaft doors are correctly closed. This can be done on the door of the elevator car and door switches can be provided on each of the shaft doors, which switch to an associated closed state depending on whether the door in question is open or closed. The various door switches can be connected in series and thus form a safety circuit. For example, the safety circuit can only be closed when all door switches included in it, and possibly also further safety switches integrated therein, are closed. The controller can monitor a state of the safety circuit and, for example, only allow the elevator car to move when the safety circuit is closed

It has been observed that switches contained in a circuit of a control system of an elevator system partially degrade over time. In particular, switches that are used to switch only low electrical power, such as door switches or monitoring switches, tend to adopt incorrect switching states over time. For example, as a result of functional degradation, a switch switched to a closed state may not pass an electrical current through between an input and an output of the switch as desired.

It was also observed that a switching state of such switches could not be reliably recognized or verified under certain conditions. For example, the aim was to monitor a current switching state of the switch by the control or other devices continuously or at time intervals, for example to detect whether the switch is closed. However, this could lead to misdiagnosis, i.e. a e.g. an actually closed switch is falsely recognized as open, which can impair the availability of the elevator.

The EP28 553 23 A1 describes a braking method for controlling an elevator, wherein a solid-state circuit is provided for supplying electrical power from a DC intermediate circuit which drives the elevator car. A brake controller is controlled by means of a pulse signal. But the pulse signal here is used to overcome a possible fault due to contamination at an electrical contact, so that the brake controller can switch correctly. There is a disadvantage that electrocorrosion due to electropolarity that results in a certain Direction is directed at the metal contact of the brake controller would often occur because only a direct voltage or a direct current is applied to the brake controller CN 205 312 843 U discloses a power supply circuit for an elevator car door. At the output of the circuit, two optocouplers are connected in a row with one another in order to weaken the adverse effect of corrosion in the circuit.

WO2005 / 000727A1 also discloses a circuit of an elevator installation, but not a control in which an analog signal with alternating voltage is applied to a switch. Also US5523633A Figure 11 shows a circuit and method for reducing switch corrosion by controlling using pulsed signals of rectified electropolarity. However, the circuit has no control signals in the form of AC voltage.

There may therefore be a need for an elevator system in which in particular the problems outlined above are avoided or at least reduced. In particular, there may be a need for an elevator system in which a circuit forming part of a controller has at least one switch and the circuit is designed in such a way that a switching state of the switch can be reliably determined over the long term. Such a need can be met with an elevator installation according to the independent claim. Advantageous embodiments are specified in the dependent claims and the description below

According to one aspect of the invention, an elevator installation is described which has an elevator car, a drive for driving the elevator car and a control for controlling at least the drive and optionally further elevator components. The controller comprises a circuit which has a switch to be monitored, a signal transmitter unit and a monitoring unit. The switch to be monitored has an input and an output. The signal transmitter unit is designed to apply an AC voltage signal as an input signal to the input of the switch to be monitored. The monitoring unit is designed to receive an output signal present at the output of the switch to be monitored and, based on a comparison of the output signal with the input signal, to generate a monitoring signal which indicates a current closed state of the switch to be monitored.

Possible features and advantages of embodiments of the invention can be viewed, inter alia and without restricting the invention, as being based on the ideas and findings described below.

As already noted in the introduction, degradations were observed in switches that are connected in a circuit of an elevator system to the effect that their switching status could no longer be reliably controlled over time and / or their current switching status could no longer be reliably recognized.

It has now been recognized that the first-mentioned problem can arise from the fact that two different switching states are usually implemented in simple mechanical switches in that electrically conductive structures are mechanically brought into contact or are mechanically separated from one another to create an electrically closed state or one to generate electrically open state. In the course of time, however, electrically insulating layers, such as oxide layers for example, can form on the surfaces of the electrically conductive structures, for example due to electrocorrosion, which can hinder reliable electrical contact between the electrically conductive structures. Expensive switches or contactors in an elevator system then usually have to be replaced.

It was also recognized that the second-mentioned problem can arise from the fact that a current switching state of a switch is usually determined by applying an electrical voltage to an input of the switch and monitoring whether an electrical current is then established through the switch or not or whether a corresponding resulting electrical voltage is present at the output of the switch. However, a reliable distinction cannot be made here as to whether the setting or absence of the electrical current or the electrical voltage resulting at the output is caused by the electrical voltage applied, or whether other causes such as faulty earth faults, short circuits, leakage currents or the like are responsible for this .

Furthermore, the continuous application of a direct voltage to the switch, in particular to its electrically conductive structures, could contribute to electrical corrosion and thus to the formation of electrically insulating layers between them.

The problems mentioned occur in particular with switches by means of which low electrical powers of less than 50 W, in particular less than 10 W or even less than 2 W, are switched in the elevator system and / or which are switched as mechanical switches are designed. For example, the switch to be monitored can be designed to switch significantly higher powers, but actually only be used in the elevator system to switch low powers. In particular with such switches to be monitored, electrically insulating layers can form during operation on structures to be mechanically and electrically contacted, such as metal structures, for example due to electrocorrosion, the electrically insulating layers can become thicker over time and ultimately lead to a complete interruption of an electrical one Contact inside the switch. While high-performance switches, which often switch powers in the range of several kilowatts, often briefly form sparks or arcs during a switching process, which can virtually remove any previously formed oxide layer, due to the low power to be switched on the switches to be monitored, such oxide layers can occur cannot be removed during normal operation and can therefore increasingly thicken.

It is pointed out that in the present text the terms switch and switch to be monitored are used synonymously, whereas other types of switches such as power switches for switching a power supply to drive the elevator system are specifically designated as such or as "further switches".

Both of the above-mentioned problems can be defused in the elevator system presented here. A main idea can be seen in this, instead of the conventional application of a constant voltage, i. a DC voltage, to monitor the current switching state of the switch using a signal transmitter unit to apply an AC voltage signal to the input of the switch and then using a monitoring unit to monitor an output signal occurring at the output of the switch and to match this with the desired switching state, e.g. correlate with the input signal or be dependent on it.

In the event that the output signal matches the desired switching state in a predetermined manner or at least correlates with it in a predetermined manner, it can be assumed with a very high degree of probability that that the switch is in a closed state. Otherwise it can be assumed that the switch is in its open state. Accordingly, the monitoring unit can generate and output a monitoring signal which, for example, provides the elevator control with the necessary information about the switching state, for example in a power supply or a safety chain of the elevator installation.

The application of an AC voltage signal instead of a conventionally used DC voltage signal in the circuit can bring about at least two advantages.

Firstly, the detection of a corresponding AC voltage signal at the output of the switch with the aid of the monitoring unit can indicate with very high reliability that the switch is actually closed. In particular, matches with regard to a frequency behavior or a pulse duration of the detected output signal with the applied AC voltage input signal can only be assumed if the closed switch actually creates an electrical connection between the input of the switch and its output. Any faults in the switch, such as inadequate electrical contact between internal conductive structures due to interposed insulating layers, any short circuits or earth faults, any leakage currents, or the like, cannot generate a corresponding AC voltage output signal with a high degree of probability. Thus, at least the closed state of the switch can be detected with a very high level of reliability, which is essential for safe operation of the elevator system, especially in the event that the switch is part of a safety chain of the elevator system.

Second, by applying an alternating voltage signal to the switch, any possible electrical corrosion of its conductive structures can be prevented or at least reduced.

This is particularly true if, according to one embodiment of the invention, the signal transmitter unit is designed to generate the AC voltage signal with a periodically reversing electrical voltage. In other words, the Signal generator unit generate the alternating voltage signal with a sign that changes over time, so that temporarily a positive voltage and temporarily a negative voltage are applied to the switch. Repeatedly reversing the applied voltage can help prevent electrical corrosion.

In particular if, according to one embodiment of the invention, the signal transmitter unit is designed to generate the alternating voltage signal with positive and negative amplitudes that are symmetrical with respect to a 0V potential, the occurrence of electrical corrosion can be greatly reduced. In other words, the AC voltage signal can preferably be generated by the signal generator unit in such a way that the maximum positive voltages are the same as the maximum negative voltages, with a voltage profile over time preferably being set symmetrically to the 0V potential. As a result, the electrically conductive structures of the switch are exposed to both positive and negative electrical voltages for the same time and with the same strength. Electrochemically induced reactions can be largely reversed when the electrical voltage is reversed, so that overall, hardly any electrocorrosion can occur.

According to one embodiment, the signal generator unit is designed to generate the AC voltage signal with a period that varies over time. In other words, the alternating voltage signal to be applied to the input of the switch is not transmitted by the signal transmitter unit with a time-constant period, i.e. with a fixed frequency, but this period or the frequency are varied over time.

In that the output signal occurring at the output of the switch is compared by the monitoring unit not only with regard to its amplitude, but also with regard to its period or frequency with the applied input signal, it can be recognized even more reliably whether the switch is in its closed state or not and the monitoring signal to be generated by the monitoring unit can be generated with even greater reliability.

According to one embodiment, the signal generator unit has a first microcontroller for generating an electrical signal with a time-varying amplitude, a Output connection and a capacitor which is electrically connected to the microcontroller on the one hand and the output connection on the other hand and is designed to form a galvanic separation between the microcontroller and the output connection. The monitoring unit has a second microcontroller for analyzing an electrical signal with amplitude varying over time and an input connection which is electrically connected to the second microcontroller. The output connection of the signal generator unit is electrically connected to the input of the switch to be monitored and the input connection of the monitoring unit is electrically connected to the output of the switch to be monitored.

The two microcontrollers (MCU - micro controller units) can be designed, for example, as integrated circuits and designed to generate an alternating voltage in the form of time-varying voltage pulses. At least in the case of the signal transmitter unit, however, the alternating voltage is not forwarded directly electrically from the first microcontroller to the output connection of the signal transmitter unit. Instead, a capacitor with a suitable capacitance is connected between the first microcontroller and the output connection. This capacitor creates a galvanic separation between the first microcontroller and the output connection so that only AC components of a voltage generated by the microcontroller are transmitted to the output connection, but DC components do not reach the output connection. In this way, it can be avoided that, in addition to the desired AC voltage signal, also DC voltage components are applied to the input of the switch, which could possibly contribute to electrical corrosion. The capacitance of the capacitor can be dimensioned in such a way that the frequency of the alternating voltage signals generated by the first microcontroller can be passed through to the output connection of the signal transmitter unit.

According to one embodiment, the signal transmitter unit furthermore has a protective diode which is connected between an electrical connection of the first microcontroller and the capacitor on the one hand and an electrical protective potential on the other hand. In other words, one end of a protective diode is connected to an electrical line connected, which connects the first microcontroller to the capacitor and an opposite end of the protective diode is connected to an electrical protective potential such as ground. The protective diode is preferably designed and polarized in such a way that any electrical charges that may be present, such as static charges, for example, can be diverted and thus cannot damage the sensitive first microcontroller.

Similarly, according to one embodiment, the monitoring unit can also have a protective diode, which is connected between an electrical connection of the second microcontroller and the input connection on the one hand and an electrical protective potential on the other hand, in particular in order to be able to protect the second microcontroller against negative voltages.

According to one embodiment, the elevator system also has at least one further switch which is coupled to the switch to be monitored in such a way that the further switch and the switch to be monitored always change their switching states together.

For example, another switch can be designed to switch high electrical powers in the range of a few kilowatts and actually switch such high electrical powers in the elevator system. However, with such a further switch, in view of the high switched powers, it is often not possible without problems to detect its current switching state. It can therefore be advantageous to place a switch to be monitored alongside the further switch. The current switching state of the switch to be monitored is relatively easy to detect. In particular, the circuit described herein with the signal generator unit generating the AC voltage signal and the monitoring unit can be used for this purpose. In the event that it is ensured that the switch to be monitored always changes its switching state together with the at least one further switch, the current switching state of the further switch can be inferred by measuring the switching state of the switch to be monitored. The switch to be monitored can, for example, be mechanically coupled to the further switch in such a way that when internal switching components of the further switch are changed over, forces also necessarily apply to the switch monitoring switch are exercised and move this to switch.

For example, according to one embodiment, the further switch can be connected between the drive and a power source supplying the drive. In this case, the further switch is used to turn on or turn off a power supply for the drive of the elevator system. With the aid of the signal transmitter unit and the monitoring unit, the control proposed here can thus always and with high reliability determine the current switching state of the power supply supplying the drive of the elevator system with the aid of the switch to be monitored that interacts with the further switch.

According to an alternative embodiment, the switch to be monitored is part of a safety chain of the elevator installation. In other words, the switch to be monitored can be a safety switch which, for example, monitors a specific function or a specific state of a component of the elevator system. The switch to be monitored can form a link in a safety chain.

With the aid of the combination of signal transmitter unit and monitoring unit proposed herein, not only can the current switching status of an individual switch to be monitored be determined, but in the case of a safety chain composed of several switches to be monitored, the switching status of the entire safety chain can also be determined. The signal transmitter unit and the monitoring unit do not necessarily need to be wired to each individual switch, but it can suffice to contact both units with end contacts of the safety chain, since the individual links of the safety chain are electrically connected in series with one another.

For example, according to one embodiment, the switch to be monitored can be a door switch. Such a door switch is typically in the closed state when the car or shaft door monitored by it is correctly closed and locked and is opened as soon as the door is not correctly locked and / or begins to open. Such a door switch is therefore, similar to other safety switches, mostly a passive element, which is switched by an active element, such as the door in this case, so that the monitoring signal reproduced state of the switch can be inferred to the current closed state of the door.

It should be noted that some of the possible features and advantages of the invention are described herein with reference to different embodiments. A person skilled in the art recognizes that the features can be combined, adapted or exchanged in a suitable manner in order to arrive at further embodiments of the invention.

Embodiments of the invention are described below with reference to the accompanying drawings, neither the drawings nor the description being to be interpreted as restricting the invention.

Fig. 1 shows an elevator system.

Fig. 2 illustrates a conventional monitoring of a switching state of a switch.

Fig. 3 shows a circuit of a control of an elevator installation according to an embodiment of the present invention.

Fig. 4 Fig. 10 illustrates a circuit for monitoring a power supply for a drive of an elevator installation.

The figures are only schematic and not true to scale. In the various figures, the same reference symbols denote the same or identically acting features

Fig. 1 shows an elevator installation 1 in which an elevator car 3 can be moved within an elevator shaft 5 with the aid of a drive 7. The elevator car 3 is held by a rope or belt-like suspension element 9. This suspension element 9 is driven by a drive pulley 11 of the drive 7. The suspension element 9 also holds a counterweight 13.

Operation of the drive 7 is controlled by a controller 15. The controller 15 controls a power supply of an electric motor accommodated in the drive 7 by a power source 17. The power source 17 can, for example, be a multi-phase power connection whose power supply to the drive 7 is controlled with the aid of a switch arrangement 19. It can be important here to be able to detect a current switching state of the switch arrangement 19 and to be able to communicate with the controller 15 for control purposes, for example.

The controller 15 is also connected to a plurality of safety switches. Each of the safety switches is designed as a switch 21 and is used, for example, to monitor a specific safety-relevant state within the elevator installation 1. For example, safety switches can be provided as door switches 22 on shaft doors 23 and monitor a current closed state of an associated shaft door 23. Other types of switches 21, such as shaft limit switches, door zone switches, etc., can also be monitored.

Fig. 2 illustrates how a switching state of a switch, in particular of a mechanically operating switch 21, is conventionally monitored. An input voltage U of, for example, 5 V is applied from a voltage source 25 to an input connection 27 of the switch 21. An output connection 29 of the switch 21 is connected to a monitoring unit 31 in which a microcontroller 33 monitors the voltage at the output connection 29. If the input voltage U is measured at the output connection 29, it is assumed that the switch 21 is closed. If there is no voltage at the output connection 29, it is assumed that the switch 21 is open.

However, the permanent application of the input voltage U to the switch 21 can over time lead to electrical corrosion on its electrically conductive switching components. In particular, a corroded switch 21 can result in no voltage being applied to the output terminal 29, although the switch 29 is closed. In addition, short circuits, shunts or the like can lead to voltages similar to the input voltage U being present at the output terminal 29, although the switch 21 is open.

Fig. 3 therefore shows a circuit 35 as it can be integrated, for example, in the controller 15 of an elevator system 1, and with the aid of which the switching state of a switch 21 can be reliably monitored and the risk of electrical corrosion can be minimized.

In addition to the switch 21, the circuit 35 has a signal transmitter unit 37 and a monitoring unit 39. If necessary, the signal transmitter unit 37 and the monitoring unit 39 and possibly other units, for example the elevator control, can be included in a common overall unit. The signal transmitter unit 37 is electrically connected to an input 41 of the switch 21. The monitoring unit 39 is electrically connected to an output 43 of the switch 21.

The signal transmitter unit 37 has a first microcontroller 45 which is designed to generate an AC voltage signal 47. The first microcontroller 45 is electrically connected to a connection of a capacitor 51 via a resistor 49. The second connection of the capacitor 51 is connected to the input 41 of the switch 21 via an output connection 42. A capacitance of the capacitor 51 is suitably adapted so that although the AC voltage signal 47 can pass through the capacitor 51, any DC voltage components, however, do not reach the switch 21.

A protective diode 53 is also provided in the signal transmitter unit 37. One end of this protective diode 53 is connected to the electrical connection of the first microcontroller 45 to the capacitor 51. The other end of the protective diode 53 is electrically connected to a protective potential, for example a ground potential 54. In this way, the protective diode 53 can prevent static electrical charges from damaging the first microcontroller 45, for example.

The monitoring unit 39 has a second microcontroller 55. This is electrically connected to the output 43 of the switch 21 via an input connection 44. Furthermore, there is a protective diode 57 between the electrical connection of the microcontroller 55 to the input connection 44 on the one hand and a protective potential such as a ground potential 58 interposed in order to protect the second microcontroller 55, for example against negative voltages.

The second microcontroller 55 is designed to record and analyze electrical voltages present at its input connection 44, in particular electrical AC voltage signals present there. In particular, the second microcontroller 55 can be designed to compare the output signals of the switch 21 recorded by it with the alternating voltage signals 47 which were applied to its input 41.

For this purpose, information about the applied alternating voltage signals 47 can be stored in the second microcontroller 55, for example stored in a memory. Alternatively, the second microcontroller 55 can be in communication with the first microcontroller 45 via a data connection 59 (shown in dashed lines) and receive information from the first microcontroller 45 regarding the alternating voltage signals 47 applied by the latter to the switch 21.

If the second microcontroller 55 of the monitoring unit 39 detects that the output signals present at the output 43 of the switch 21 essentially correspond to the AC voltage signals 47 present at its input 41, it can be assumed that the switch 21 is in its closed state. If, however, no voltage or only a direct voltage is present at the output 43 of the switch 21, although the alternating voltage signal 47 is present at its input 41, it can be assumed that the switch 21 is open or defective.

An essential feature that indicates whether the incoming alternating voltage signal 47 corresponds to the output signal read out is a time profile of the two signals, in particular a frequency of the two signals. If necessary, a difference signal between the incoming AC voltage signal 47 and the output signal read out can be analyzed. Any attenuation of the AC voltage signal 47 or superimpositions of additional DC voltage signals can be suitably taken into account in the analysis or ignored as irrelevant for the decision as to whether the switch 21 to be monitored is closed or not.

It can be assumed that any errors in the circuit 35 can lead to additional DC voltages being applied to the output 43 of the switch 21, for example due to short circuits, shunts or the like, but when the switch 21 is open, no AC voltage is applied to the Output 43 can be generated which falsely "plays" a closed switch to the monitoring unit 39.

The AC voltage signals 47 are preferably generated by the signal generator unit 45 in such a way that an AC voltage signal 48 is set at the switch 21, in which the voltage U periodically reverses its polarity with an amplitude symmetrical to an OV potential (zero volt potential). For example, the AC voltage signal 48 can be sinusoidal, rectangular or with any other periodic curve and move symmetrically around a time axis t. Times in which the alternating voltage signal 48 is positive and times in which it is negative are essentially of the same length, so that any electrochemical reactions can repeatedly take place in alternating directions, but not a build-up of, for example, an electrochemically generated oxide layer on electrically conductive ones Structures of the switch to be monitored 21 comes.

Fig. 4 shows an embodiment of how the power supply to a motor 61 of the drive 7 can be controlled and monitored with the aid of the circuit 35 in an elevator installation. The circuit 35 forms part of the controller 15. The signal transmitter unit 47 with its first microcontroller 45 and the monitoring unit 39 with its second microcontroller 55 can be integrated into the controller 15 (for the sake of clarity, details of the two units 37, 39 are shown in FIG Fig. 4 not shown).

The controller 15 is connected to the switch arrangement 19. A contactor 63 is provided in the switch arrangement 19, with the aid of which three phases of a power supply can be connected to the motor 61. The contactor 63 serving as a further switch is switched via a relay 65 controlled by the controller 15.

The contactor 63 is coupled to a switch 21 to be monitored in such a way that in the event that the contactor 63 changes its switching state, the switch 21 to be monitored also inevitably changes its switching state. A switching state of the switch 21 to be monitored can then be monitored in the manner described above with the aid of the signal transmitter unit 37 and the monitoring unit 39 of the circuit 35 in a simple and reliable manner, and electrical corrosion can be avoided in the process.

In a manner similar to circuit 35 in the in Fig. 4 Example shown a single switch 21 is monitored in order to monitor the function or the switching state of a power switching contactor 63, the controller 15 provided with the circuit 35 can also be used to monitor the switching state of a safety chain in which several switches 21 such as for example door switches 22 are connected in series.

Finally, it should be pointed out that terms such as “having”, “comprising”, etc. do not exclude any other elements or steps and that terms such as “a” or “an” do not exclude a plurality. It should also be pointed out that features or steps that have been described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps of other exemplary embodiments described above. Reference signs in the claims are not to be regarded as a restriction.

Claims (13)

1. Elevator system (1), comprising:

   an elevator cabin (3);

   a drive (7) for driving the elevator cabin (3);

   a control means (15) for controlling at least the drive (7) and optionally further elevator components;

   wherein the control means (15) comprises a circuit (35) and the circuit (35) has:

   a switch (21) to be monitored comprising an input (41) and an output (43);

   a signal transmitter unit (37) which is designed to apply an AC voltage signal (47) as an input signal to the input (41) of the switch (21) to be monitored;

   a monitoring unit (39) which is designed to record an output signal applied to the output (43) of the switch (21) to be monitored and, on the basis of a comparison of the output signal with the input signal, to generate a monitoring signal which indicates a switching state of the switch (21) to be monitored.
2. Elevator system according to claim 1, wherein the signal transmitter unit (37) is designed to generate the AC voltage signal (47) so as to have a periodically reversing electrical voltage.
3. Elevator system according to either of the preceding claims, wherein the signal transmitter unit (37) is designed to generate the AC voltage signal (47) so as to have positive and negative amplitudes that are symmetrical with respect to a 0V potential.
4. Elevator system according to any of the preceding claims, wherein the signal transmitter unit (37) is designed to generate the AC voltage signal (47) so as to have a temporally varying period.
5. Elevator system according to any of the preceding claims, wherein the signal transmitter unit (37) has:

   a first microcontroller (45) for generating an electrical signal having a temporally varying amplitude;

   an output terminal (42);

   a capacitor (51) which is electrically connected at one end to the first microcontroller (45) and at the other end to the output terminal (42) and is designed to form a galvanic isolation between the first microcontroller (45) and the output terminal (42);

   wherein the monitoring unit (39) has:

   a second microcontroller (55) for analyzing an electrical signal having a temporally varying amplitude;

   an input terminal (44) which is electrically connected to the second microcontroller (55);

   wherein the output terminal (42) of the signal transmitter unit (37) is electrically connected to the input (41) of the switch (21) to be monitored and the input terminal (44) of the monitoring unit (39) is electrically connected to the output (43) of the switch (21) to be monitored.
6. Elevator system according to claim 5, wherein the signal transmitter unit (37) also comprises a protective diode (53) which is connected between an electrical connection of the first microcontroller (45) to the capacitor (51) at one end and an electrical protection potential (54) at the other end.
7. Elevator system according to either claim 5 or claim 6, wherein the monitoring unit (39) also comprises a protective diode (57) which is connected between an electrical connection of the second microcontroller (55) to the input terminal (44) at one end and an electrical protection potential (58) at the other end.
8. Elevator system according to any of the preceding claims, wherein the switch (21) to be monitored in the elevator system switches low electrical powers of less than 50W.
9. Elevator system according to any of the preceding claims, wherein the switch (21) to be monitored is a mechanical switch.
10. Elevator system according to any of the preceding claims, also comprising at least one further switch (63) which is coupled to the switch (21) to be monitored such that the at least one further switch (63) and the switch (21) to be monitored always change their switching states together.
11. Elevator system according to claim 10, wherein the at least one further switch (63) is connected between the drive (7) and a power source (17) supplying the drive (7).
12. Elevator system according to any of the preceding claims 1 to 9, wherein the switch (21) to be monitored is part of a safety chain of the elevator system (1).
13. Elevator system according to claim 12, wherein the switch (21) to be monitored is a door switch (22).

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