WO2023030618A1

WO2023030618A1 - A sensing device for a people conveyor electrical or safety system, a people conveyor safety system and a people conveyor

Info

Publication number: WO2023030618A1
Application number: PCT/EP2021/074117
Authority: WO
Inventors: Otto Pekander
Original assignee: Kone Corporation
Priority date: 2021-09-01
Filing date: 2021-09-01
Publication date: 2023-03-09

Abstract

The invention relates to a people conveyor, people conveyor safety system (1000) and a sensing device for a people conveyor electrical or safety system, the people conveyor safety system comprising a safety circuit comprising safety sensors and/or safety contacts, e.g. connected in series, and a safety output, wherein a status of the safety output is configured to depend on statuses of the safety sensors or contacts of the people conveyor system. The sensing device comprises a capacitive sensing arrangement for measuring status of at least one safety sensor and/or safety contact of the people conveyor system when installed in connection with the safety system, the capacitive sensing arrangement comprising circuit board (510), such as a printed circuit board. The circuit board comprises a sensing portion comprising an electrically conducting sensing pad (501), wherein the sensing pad is arranged and configured for capacitive coupling with an adjacent electrical circuit or cable of at least one safety sensor and/or safety contact, a shield pad (502) next to the sensing pad, and a measurement amplifier comprising an input connected to the sensing pad and an output connected or configured to be connected to a measurement device, wherein the measurement amplifier is referenced to the shield pad for preventing picking of ambient electrical noise.

Description

A SENSING DEVICE FOR A PEOPLE CONVEYOR ELECTRICAL OR SAFETY SYSTEM, A PEOPLE CONVEYOR SAFETY SYSTEM AND A PEOPLE CONVEYOR

Field of the invention

The invention relates in general to people conveyors. In particular, however not exclusively, the invention concerns people conveyor electrical or safety systems.

Background

Elevators are provided with a safety circuit to ensure safe operation in various operational situations. The safety circuit can contain sensors in the form of safety contacts connected in series. The safety circuit is a critical component for the safety of the elevator.

Elevator is in safe state as long as the safety circuit is complete, with all safety contacts closed. In some prior art systems opening of at least one safety contact indicates that the safety of the elevator is compromised. In certain prior art solutions opening of the safety circuit can be detected, but without identifying the open contact and the root cause of the failure. For example, opening of a landing door into elevator shaft may be diagnosed if landing door safety circuit opens, but it is not possible to identify the landing floor in question.

Most common failures stopping e.g. an elevator are failures relating to the safety circuit. Therefore, reliable operation of safety circuit is important for the reliability and safety of the conveyor system. Measuring the safety circuit might allow to pinpoint the actual source of the failure. This is because the voltage of the safety circuit typically is taken to machine room from multiple different locations in the shaft or elevator car.

To improve diagnosis of an elevator safety circuit, some prior art solutions have been proposed for measuring status of individual safety contacts. One such solution is suggested in W02006108433A1 . In this solution a capacitive sensing arrangement is fitted in connection with plurality of safety contacts to indicate individual safety contact states. The prior art safety systems are designed typically for a specific conveyor system because it is difficult to design one safe method to measure different type of elevator safety circuits which are used in the field. This is especially so if there is galvanic connection between measurement device and the safety circuit since the malfunction of the monitoring device itself could potentially compromise the safety of the elevator.

Capacitive measurement of safety contacts is desirable because of its costefficiency and also safety as measurement is carried out as galvanically isolated from the elevator safety circuit. Therefore, the measurement can be implemented without risk of wrong connections or ground faults in the safety circuit. However, it is technically challenging to obtain reliable measurements with a capacitive sensor, as signal to noise ratio is low and the sensor easily picks noise from the ambient.

Thus, there is a need for a reliable and safe electrical circuit or safety circuit monitoring solution which may be used with different types of conveyor systems and with their safety circuits.

Summary

An objective of the invention is to provide a sensing device for a people conveyor electrical or safety system, a retrofittable sensing device for a people conveyor system and a people conveyor safety system.

With the solution of the invention, it’s possible to obtain reliable measurements with a capacitive sensor without noise from the ambient disturbing the measurements. The solution of the invention discloses a galvanically isolated, capacitive sensing device for measuring status of electrical circuit e.g. in a distributed electrical system, in particular an elevator, an escalator or a moving walk. The sensing device is useful for measuring status of individual sensors, such as individual safety contacts. The sensing device can be designed to be EMC compliant and tolerant against noise from the ambient.

The objectives of the invention are reached as defined by the respective independent claims. According to a first aspect, the invention relates to a sensing device for a people conveyor safety system, the people conveyor safety system comprising a safety circuit comprising safety sensors and/or safety contacts, e.g. connected in series or in parallel, and a safety output, wherein a status of the safety output is configured to depend on statuses of the safety sensors or contacts of the people conveyor system. The sensing device comprises a capacitive sensing arrangement for measuring status of at least one safety sensor and/or safety contact of the people conveyor system when installed in connection with the safety system, the capacitive sensing arrangement comprising circuit board, such as a printed circuit board. The circuit board comprises a sensing portion comprising an electrically conducting sensing pad, wherein the sensing pad is arranged and configured for capacitive coupling with an adjacent electrical circuit of at least one safety sensor and/or safety contact, a shield pad next to the sensing pad, and a measurement amplifier comprising an input connected to the sensing pad and an output connected or configured to be connected to a measurement device, wherein the measurement amplifier is configured to be referenced to the shield pad for preventing picking of ambient electrical noise.

In one embodiment of the invention the shield pad is arranged in the same circuit board layer and adjacent to the sensing pad.

In one embodiment of the invention the shield pad is arranged in a separate layer and arranged to cover the sensing pad.

In one embodiment of the invention the circuit board further comprises a ground layer separated from the shield pad by a diode or filtering means, e.g. by a coil and/or a narrow signal trace interconnecting ground layer with the shield pad.

In one embodiment of the invention the capacitive sensing arrangement and/or the sensing portion of the capacitive sensing arrangement comprises an alignment marking and/or a fixing structure for aligning and/or fixing the electrical circuit of the safety sensor and/or safety contact to be measured to the sensing pad, e.g. in such a way that capacitive coupling between the electrical circuit of the safety sensor and/or safety contact and the sensing pad is formed when the electrical circuit of the safety sensor and/or safety contact is aligned according to the marking and/or the fixing structure. In one embodiment of the invention the circuit board comprises a microcontroller comprising an A/D converter connected to an output of the measurement amplifier and a transceiver circuit configured to communicate measurement related information.

In one embodiment of the invention the measurement device comprises wireless data communication means, such as a wireless modem for communicating measurement related information.

In one embodiment of the invention the sensing portion and/or the sensing pad is formed on a flexible printed circuit board.

In one embodiment of the invention thickness of the flexible printed circuit board portion is less than 255 micrometers and/or the flexible printed circuit board comprises flexible solder mask.

According to a second aspect, the invention relates to a retrofittable sensing device for a people conveyor electrical or safety system, the people conveyor electrical or safety system comprising electrical devices, in particular sensors, actuators and one or more control boards connected with electrical cabling, e.g. connected in series or in parallel. The sensing device comprises a capacitive sensing arrangement for measuring status of at least one electrical device of the people conveyor electrical or safety system when installed in connection with the electrical or safety system, the capacitive sensing arrangement comprising circuit board, such as a printed circuit board. The circuit board comprises a sensing portion comprising an electrically conducting sensing pad, wherein the sensing pad is arranged and configured for capacitive coupling with an adjacent electrical cable of at least one electrical device, a shield pad next to the sensing pad, and a measurement amplifier comprising an input connected to the sensing pad and an output connected or configured to be connected to a measurement device, wherein the measurement amplifier is configured to be referenced to the shield pad for preventing picking of ambient electrical noise. The retrofittable device can be easily coupled to existing wiring of the distributed electrical or safety system.

In one embodiment of the invention information sensed by the sensing device and/or safety system utilizing the sensing device may be gathered and sent to a remote cloud system where it may be analyzed and e.g. a maintenance visits to the elevator site may be scheduled based on the analyzing results.

According to a third aspect, the invention relates to a people conveyor safety system comprising a safety circuit comprising safety sensors and/or safety contacts e.g. connected in series or in parallel, and a safety output, wherein a status of the safety output is configured to depend on statuses of the safety sensors and/or safety contacts. The safety system comprises at least one capacitive sensing device for measuring status of at least one safety sensor and/or safety contact of the people conveyor system, wherein the capacitive sensing device is the capacitive sensing device according to the invention.

In one embodiment of the invention at least part of the electrical circuit of the safety sensor and/or safety contact is arranged near and/or essentially around the sensing pad of the capacitive sensing device in such a way that capacitive coupling between the electrical circuit of the safety sensor and/or safety contact and the sensing pad is formed.

In one embodiment of the invention the sensing device is configured to measure status of individual sensor or individual safety contacts.

According to a fourth aspect, the invention relates to a people conveyor comprising the safety system according to the solution of the invention.

In one embodiment of the invention the people conveyor is an elevator, an escalator, or a moving walk.

Various other advantages will become clear to a skilled person based on the following detailed description.

The terms “first”, “second” and “third” are herein used to distinguish one element from other element, and not to specially prioritize or order them, if not otherwise explicitly stated.

The exemplary embodiments of the invention presented herein are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used herein as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objectives and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

Brief description of Figures

Some embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings:

Figure 1 illustrates schematically an elevator according to an embodiment of the invention,

Figure 2 illustrates schematically an escalator according to one embodiment of the invention,

Figure 3 illustrates schematically an elevator safety chain according to an embodiment of the invention,

Figure 4 illustrates schematically one implementation example of a part of a safety system according to an embodiment of the invention, and

Figure 5 illustrates a part of the sensing device according to one example embodiment of the invention.

Detailed description of some embodiments

Figure 1 illustrates schematically an example conveyor system in which the sensing device or electrical or safety system utilizing the sensing device of the invention can be used. The conveyor system of Figure 1 is an elevator 100 according to an example embodiment of the invention with which the sensing device of the invention can be used, e.g. in the safety system of the elevator. The elevator 100 may comprise an elevator car 10 arranged to be moved in an elevator shaft 12. The moving of the elevator car 10 may be implemented, by a hoisting rope or belt 13 in connection with a traction sheave 14 or the like. Furthermore, the elevator 100 comprises an elevator motor 20 arranged to operate, such as rotate by the rotor thereof, the traction sheave 14 for moving the elevator car 10, if not essentially directly coupled to the hoisting rope 13. The traction sheave 14 may be connected, via a mechanical connection 22, directly or indirectly via a gear to a shaft of the motor 20. The elevator 100 may comprise a machine room or be machine roomless, such as have the motor 20 in the elevator shaft 12.

The elevator 100 may preferably comprise at least one, or at least two, hoisting machinery brake(s) 16 configured for resisting or, preferably, preventing the movement of the motor 20, that is the rotor thereof, directly or via the traction sheave 14 or components thereof and/or therebetween. Furthermore, the elevator 100 may comprise a brake controller 25 configured to operate at least one of the at least one hoisting machinery brake 16. The brake controller 25 may further be in connection with other elements of the elevator 100, such as an elevator control unit and/or a safety system 1000. The brake controller 25 may comprise an actuator (not shown) for operating the brake 16 or at least be in connection with such an actuating device.

There may additionally be, at least in some embodiments, a counterweight 18 arranged in connection with the elevator car 10 such as is known to a person skilled in the art of elevators. Still further, the elevator 100 may additionally comprise a guide rail 17 or rails 17 arranged into the elevator shaft 12 for guiding the movement of the elevator car 10.

The elevator 100 of Fig. 1 can further comprise a converter unit 30. The converter unit 30 may comprise, or substantially be, an inverter or a frequency converter, for connecting to, and controlling the operation of, the motor 20, and a controller in connection with the converter unit 30, wherein the controller is configured to operate the converter unit 30 to provide electrical power (signals), such as having variable voltage and variable frequency, to the windings of the motor 20. The controller may be a separate controller device or be comprised in the converter unit 30, for instance. Still further, the converter unit 30 may be arranged to be fed by an electrical power source 150, such as of the elevator 100, for example from an external electrical power grid or mains power supply, or another power source, for example, a battery system. Additionally, the electrical power source 150 may intake electrical power from the converter unit 50.

Even though the electrical power source 150 is shown to be directly connected to the converter unit 30, it is to be noted that there may be one or several devices arranged therebetween, such as input filter(s), circuit breaker(s), and/or contactor(s) or relay(s), and/or a device for charging the energy storage element(s) of the converter unit 30.

The elevator 100 preferably comprises landings 19 or landing floors 19 and, for example, landing floor doors and/or openings, between which the elevator car 10 is arranged to be moved during the normal operation of the elevator 100, such as to move persons and/or items between said floors 19.

Figure 2 schematically illustrates an embodiment according to the present invention in which the solution of the invention is also used in the connection with a people conveyor system. In this case the people conveyor system is an escalator 200. The sensing device of the invention for the people conveyor electrical or safety system can be arranged in connection with the escalator, e.g. with escalator safety system. The escalator may comprise a step-chain coupled to a motor 206 via a transmission 202 comprising at least a chain or belt or similar. The motor 206 may generate a rotational force via the transmission causing the step-chain to move in an intended travelling direction. A brake may be arranged to the conveyor system so that when de-energized it is configured to meet the rotating axis of the transmission and, in that manner, to brake movement of the step chain or keep the step chain standstill when the escalator system is idle. When energized, the brake opens, allowing movement of stepchain. The transmission may comprise, in the context of escalator system, a gearbox with the mentioned entities. Furthermore, the escalator system may comprise an escalator control unit 210 which may e.g. be configured to control the movement of step-chain through a control of a power supply to the motor 202 and to the escalator brake. In one embodiment of the invention the conveyor system can comprise a processing unit 204. In some embodiments a second motor 207 with a second transmission 203 may be provided, for example, at the opposite end of the step-chain. Then a second processing unit 205 may be mounted to the in connection with the second motor.

In various embodiments, such as in the one shown in Figure 1 and Figure 2, the elevator 100 or escalator 200 may comprise a safety system 1000.

In the solution of the invention the people conveyor, such as an elevator, escalator or moving walk, e.g. the elevator 100 or escalator 200, can comprise a safety system 1000 for performing safety functions of the people conveyor. The safety system 1000 may, for example, comprise at least part of a safety circuit of the people conveyor. The safety circuit for a people conveyor system safety circuit can comprise a series chain of switch contacts connected in series or in parallel to monitor equipment related to the safety of the operation of the installation, an electric power supply connected to one end of the series chain, and at least one switching device connected to another end of the series chain and which generates a control signal for an installation operation control depending on the switching status of the switch contacts. The chain of switch contacts, such as door contacts of a hoistway door, can be connected in series, and a switch contact can be provided for the purpose of, for example, monitoring the position of a hoistway door. Further contacts or switches for the purpose of monitoring, for example, the position of the elevator car door, the position of the brake, equipment serving the safety of the elevator operation, can be connected into the safety circuit and the series chain, respectively.

The safety circuit is usually supplied with a supply voltage from either an AC or DC voltage source connected to one end of the series chain. At least one switching device is usually connected to another end of the series chain, the switching device being for example a safety relay. If all switch contacts of the series chain are closed, the safety relay is activated. On the other hand, if one of the switch contacts is in a disconnected condition, the safety relay is deactivated. An elevator operation control monitors the status of the safety relay and if the safety relay is activated, the elevator operation control releases, for example, a pending travel command. Such safety circuit described with reference to an elevator installation may be applied in a similar manner in an escalator installation. Figure 3 illustrates schematically as an example a people conveyor safety system 1000 according to an embodiment of the invention with which the sensing device can be used. The safety system can be e.g. an elevator safety system, an escalator safety system and/or a moving walkaway safety system. The safety system 1000 may comprise a safety circuit 101 1 comprising safety contacts 1010 and a safety output 1001 , wherein a status of the safety output 1001 is, preferably, arranged to depend on statuses, such as on a combination thereof, of the safety circuit 101 1. The safety contacts are arranged in series with each other in this embodiment. In one example embodiment at least some of the safety contacts can be for example landing door safety contacts and/or they can be connected in series. These can be for example force-controlled switches which open when landing door opens into elevator shaft. In this case if certain safety contact is open, the status of the whole safety circuit, e.g. safety chain, is open, i.e. the system is not considered safe to operate. This causes change in the safety chain status, and, consequently, safety shutdown of the elevator. In one embodiment of the invention the safety system 1000 may be configured to perform or at least initiate a safety shutdown depending on the status of the safety output.

The switching device may be a safety relay which actuates a relay contact which closes a control signal loop connected to an installation operation control applying a signal voltage to the relay contact. With closing of the relay contact a control signal for the installation operation control is generated which releases, for example, a pending travel command. According to another embodiment, the switching device may be part of a variable frequency control device for driving, e.g., a drive motor of an elevator hoisting system. Here, the variable frequency control device monitors the status of the switching device and actuates a drive command signal if the switching device is activated. As a result, the switching device acts as a energy-flow controlling contactor.

The statuses of the safety contacts can be monitored with the sensing device according to the solution of the invention. The safety chain can have, such as in a safety logic unit thereof, at least one safety output which provides a safety signal following the combined status of the safety contacts. Safety signal may be, for example, a digital one-bit signal or an output of a safety relay. In an embodiment, the status of the safety output changes from “1 ” to “0” when one or several of the safety contacts open(s). The statuses of the safety contacts may be received and monitored by a safety chain logic unit 1 100. The safety chain logic unit 1 100 may then determine the status of the safety output 1001 based on the combined status of the safety contacts. The information about the status of the safety output 1001 may then be provided to an elevator control unit and/or safety system, and/or utilized directly in determining the operating condition, such as an emergency condition, of the elevator 100. The monitoring of the safety contact can be implemented based on the solution of the invention.

The safety system 1000 may further comprise a converter unit 30 connected to and configured to operate e.g. an elevator, escalator motor 20 for enabling operation of the people conveyor system.

The safety system 1000 may also comprise a brake contactor or relay, such as comprising one or contacts C1 , configured to selectively supply or interrupt electrical power to e.g. at least one hoisting machinery brake 16, or at least to or via the brake controller 25 thereof, by closing or opening at least one primary contact C1 , of the brake contactor or relay. The hoisting machinery brake 16 can comprise an actuating device. Furthermore, the brake contactor or relay may comprise, at least one auxiliary contact, such as normally open (NO) contacts, configured to operate together with, in tandem with, or in response to operation of the at least one primary contact

The brake contactor or relay may preferably be in connection with the safety output 1001 and configured to operate based on the status of the safety output 1001 . Still further, the auxiliary contacts of the brake contactor or relay may be configured to control the operation of the safety input of the converter unit 30 so that the generation of torque is prevented during the safety shutdown. In various embodiments, at least the primary contact or contacts may be NO type of contacts, thereby closing only if control signal, such as in a suitable form and having sufficient amount of electrical power, is applied to the control device, such as the control coil, of the brake contactor or relay. The auxiliary contacts may also be NO type of contacts.

In various embodiments, the auxiliary contact(s) may be arranged integrated, optionally removable, to the brake contactor or relay. Thus, the auxiliary contact(s) may be arranged to close based on the control signal to the control coil of the brake contactor or relay.

The statuses of the safety contacts are in the solution of the invention determined with a capacitive sensing arrangement which measures electrical field in order to sense or determine status of safety contacts. The capacitive sensing arrangement may comprise a circuit board, such as a printed circuit board. The circuit board may comprise a sensing portion comprising an electrically conducting sensing pad. The sensing pad is arranged and configured for capacitive coupling with an adjacent electrical circuit of at least one safety sensor and/or safety contact. The capacitive sensing arrangement and/or the circuit board may further comprise a shield pad next to the sensing pad, a measurement amplifier comprising an input connected to the sensing pad, and an output connected or configured to be connected to a measurement device. The measurement amplifier is referenced to the shield pad for preventing picking of ambient electrical noise.

In one embodiment of the invention the sensing device connects to the wire of dielectric layer (insulator) part of the safety circuit instead of the wire itself. This way the sensing device will form capacitor between the wire of the safety circuit and the measurement device. When the impedance of the sensing device is high enough, the change of the safety circuit voltage is being coupled to the sensing device by capacitance. In the solution of the invention this voltage shift can be measured even when the measurement device is fully floating and e.g. not connected to the same ground with the elevator under test.

The solution of the invention can be used also in other electrical systems than safety systems. In one embodiment of the invention the sensing device is a retrofittable sensing device for a people conveyor electrical or safety system. The people conveyor electrical or safety system can comprise electrical devices, in particular sensors, actuators and one or more control boards connected with electrical cabling, e.g. connected in series or in parallel.

In one embodiment of the invention the retrofittable sensing device can be used in existing, old elevator systems. In those old systems, this galvanically isolated sensing device can be easily coupled to any old, existing electrification cabling, to gather data for preventive maintenance. Said data can be sent from elevator site to e.g. a cloud server, and maintenance need is determined therein, and maintenance visits can be scheduled in the cloud system, based on the data.

Figure 4 presents one example embodiment of a high-level electrical circuit which can be used to implement at least part of the sensing device of the invention. The sensing device of the invention can be implemented in many other ways but Figure 4 presents one implementation example. For example, all parts or components presented in Figure 4 are not essential for implementing the solution of the invention.

The implementation example of Figure 4 comprises an amplifier circuit using a differential amplifier U1. In this implementation example of Figure 4 the shield pad, e.g. the shield pad 502 of fig. 5, is connected in inverting input pin (point “To LTC Shield”) of the differential amplifier U1 such that noise induced into the shield pad 502 will be canceled from output signal of the differential amplifier. Diode D1 used in the example circuit of Figure 4 prevents saturation of the amplifier while still providing very high input impedance for the amplifier. The amplifier can be also plain J-Fet transistor or any other amplifier with high input impedance, e.g. a differential amplifier of an instrumentation amplifier. Capacitor C3 and R1 are not essential for the implementation of the invention, and they can be used for example for testing purposes.

Figure 5 illustrates a part of the sensing device 500 according to one example embodiment of the invention. In the example embodiment of Figure 5 the sensing device is arranged so that there is an area 501 which is placed close by the wire of the monitored circuit or wrapped around the wire. In Figure 5 the sensing area or sensing pad is the middle part, e.g. a middle copper part 501 , which can e.g. be directly connected to D1 in the example schematics of Figure 4. In one embodiment of the invention the sensing portion and/or the sensing pad is formed on a flexible printed circuit board 510. In one embodiment of the invention thickness of the flexible printed circuit board portion is less than 255 micrometers and/or the flexible printed circuit board comprises flexible solder mask. The shield pad 502 is arranged around or next to this sensor trace and/or above it which can be used as reference input for the amplifier. This reference will help to separate the measurement signal from the noise caused by the ambient electrical field. Since circuit is referenced against ambient electrical field, any noise can be cancelled from the measurement signal or at least noise level may be substantially reduced. Thus, it is possible for example to cancel noise from the ambient from a measurement signal picked up from the safety circuit, e.g. to cancel 50 Hz ambient noise.

In one embodiment of the invention the shield pad is arranged in the same circuit board layer and adjacent to the sensing pad. In one embodiment of the invention the shield pad is arranged in a separate layer. In one embodiment of the invention the circuit board further comprises a ground layer separated from the shield pad by a diode or filtering means, e.g. by a coil and/or a narrow signal trace interconnecting ground layer with the shield pad.

In one embodiment of the invention the capacitive sensing arrangement and/or the sensing portion of the capacitive sensing arrangement comprises an alignment marking and/or a fixing structure for aligning and/or fixing the electrical circuit of the safety sensor and/or safety contact to be measured to the sensing pad, e.g. in such a way that capacitive coupling between the electrical circuit of the safety sensor and/or safety contact and the sensing pad is formed when the electrical circuit of the safety sensor and/or safety contact is aligned according to the marking and/or the fixing structure.

In one embodiment of the invention the circuit board comprises a microcontroller comprising an A/D converter or a comparator connected to an output of the measurement amplifier and a transceiver circuit configured to communicate measurement related information.

The people conveyor may comprise a control unit control unit for controlling the operation of the people conveyor and/or the safety system. The control unit may be a separate device or may be comprised in the other components of the conveyor such as in or as a part of the electrical drive. The control unit may also be implemented in a distributed manner so that, e.g., one portion of the conveyor control unit may be comprised in the electrical drive and another portion in the elevator car. The control unit may also be arranged in distributed manner at more than two locations or in more than two devices. In one embodiment of the invention the control unit is configured to control the power units supplying power to the conveyor system.

The control unit or controller of the system may comprise one or more processors, one or more memories being volatile or non-volatile for storing portions of computer program code and any data values and possibly one or more user interface units. The mentioned elements may be communicatively coupled to each other with e.g. an internal bus.

The processor of the control unit or controller is at least configured to implement some functionality of the invention. The implementation of a solution of the invention may be achieved by arranging the processor to execute at least some portion of computer program code stored in the memory causing the processor, and thus the elevator control unit, to implement one or more method steps as described. The processor is thus arranged to access the memory and retrieve and store any information therefrom and thereto. For sake of clarity, the processor herein refers to any unit suitable for processing information and control the operation of the elevator control unit, among other tasks. The operations may also be implemented with a microcontroller solution with embedded software. Similarly, the memory is not limited to a certain type of memory only, but any memory type suitable for storing the described pieces of information may be applied in the context of the invention.

The embodiments of the invention described herein before in association with the figures presented and the summary of the invention may be used in any combination with each other. At least two of the embodiments may be combined together to form a further embodiment of the invention.

The specific examples provided in the description given above should not be construed as limiting the applicability and/or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.

Claims

1. A sensing device for a people conveyor safety system (1000), the people conveyor safety system comprising a safety circuit comprising safety sensors and/or safety contacts, e.g. connected in series or in parallel, and a safety output, wherein a status of the safety output is configured to depend on statuses of the safety sensors or contacts of the people conveyor system, wherein the sensing device comprises a capacitive sensing arrangement (500) for measuring status of at least one safety sensor and/or safety contact of the people conveyor system when installed in connection with the safety system, the capacitive sensing arrangement comprising circuit board (510), such as a printed circuit board, which comprises:

- a sensing portion comprising an electrically conducting sensing pad (501 ), wherein the sensing pad (501 ) is arranged and configured for capacitive coupling with an adjacent electrical circuit or cable of at least one safety sensor and/or safety contact,

- a shield pad (502) next to the sensing pad, and

- a measurement amplifier comprising an input connected to the sensing pad and an output connected or configured to be connected to a measurement device, wherein the measurement amplifier is referenced to the shield pad for preventing picking of ambient electrical noise.

2. A sensing device according to claim 1 , wherein the shield pad is arranged in the same circuit board layer and adjacent to the sensing pad.

3. A sensing device according to claim 1 , wherein the shield pad is arranged in a separate layer and arranged to cover the sensing pad.

4. A sensing device according to any preceding claim, wherein the circuit board (510) further comprises a ground layer separated from the shield pad by a diode or filtering means, e.g. by a coil and/or a narrow signal trace interconnecting ground layer with the shield pad.

5. A sensing device according to any preceding claim, wherein the capacitive sensing arrangement and/or the sensing portion of the capacitive sensing arrangement comprises an alignment marking and/or a fixing structure for aligning and/or fixing the electrical circuit of the safety sensor and/or safety contact to be measured to the sensing pad, e.g. in such a way that capacitive coupling between the electrical circuit of the safety sensor and/or safety contact and the sensing pad is formed when the electrical circuit of the safety sensor and/or safety contact is aligned according to the marking and/or the fixing structure.

6. A sensing device according to any preceding claim, wherein the circuit board comprises a microcontroller comprising an A/D converter connected to an output of the measurement amplifier and a transceiver circuit configured to communicate measurement related information.

7. A sensing device according to any preceding claim, wherein the measurement device comprises wireless data communication means, such as a wireless modem for communicating measurement related information.

8. A sensing device according to any preceding claim, wherein the sensing portion and/or the sensing pad is formed on a flexible printed circuit board.

9. A sensing device according to claim 8, wherein thickness of the flexible printed circuit board portion is less than 255 micrometers and/or the flexible printed circuit board comprises flexible solder mask.

10. A retrofittable sensing device for a people conveyor safety system (1000) and/or an electrical system, the people conveyor safety system or electrical system comprising electrical devices, in particular sensors, actuators and one or more control boards connected with electrical cabling, e.g. connected in series or in parallel, wherein the sensing device comprises a capacitive sensing arrangement for measuring status of at least one electrical device of the people conveyor electrical system when installed in connection with the electrical system, the capacitive sensing arrangement comprising circuit board (510), such as a printed circuit board, which comprises:

- a sensing portion comprising an electrically conducting sensing pad (501 ), wherein the sensing pad is arranged and configured for capacitive coupling with an adjacent electrical circuit or cable of at least one electrical device, 18

- a shield pad next to the sensing pad, and

1 1. A people conveyor safety system (1000) for a people conveyor, comprising: a safety circuit comprising safety sensors and/or safety contacts e.g. connected in series or in parallel, and a safety output, wherein a status of the safety output is configured to depend on statuses of the safety sensors and/or safety contacts, wherein the safety system comprises at least one capacitive sensing device (500) for measuring status of at least one safety sensor and/or safety contact of the people conveyor system, wherein the capacitive sensing device is the capacitive sensing device according to any claim 1 - 10.

12. A people conveyor safety system according to claim 1 1 , wherein at least part of the electrical circuit of the safety sensor and/or safety contact is arranged near and/or essentially around the sensing pad of the capacitive sensing device in such a way that capacitive coupling between the electrical circuit of the safety sensor and/or safety contact and the sensing pad is formed.

13. A people conveyor safety system according to claim 1 1 or 12, wherein the sensing device is configured to measure status of individual sensor or individual safety contacts.

14. A people conveyor comprising the safety system of any claim 1 1 - 13.

15. A people conveyor according to claim 14, wherein the people conveyor is an elevator (100), an escalator (200) or a moving walk.