Field device and device arrangement

Abstract

The invention relates to a field device (2) having a wired interface (5) via which the field device (2) can receive electrical power, and having an apparatus for energy harvesting (10) which is designed to receive energy from an environment of the field device (2) and to output electrical power, wherein the field device (2) is configured to feed the electrical power output by the apparatus for energy harvesting (10) to at least one load of the field device (2). According to a further aspect of the invention, a device arrangement (1) is proposed, comprising the field device (1), a supply device (7) and a conductor system (6) via which the field device (2) is coupled to the supply device (7).

Description

[0001] Field device and device arrangement

[0002] The invention relates to a field device with a wired interface. Furthermore, a device arrangement comprising the field device according to the invention is proposed.

[0003] In process automation technology, field devices are frequently used to detect and / or influence process variables. Examples of such field devices include level gauges, limit level gauges, and pressure gauges with sensors that detect the corresponding process variables: level, limit level, or pressure. These field devices are often connected to higher-level units, such as control systems. These higher-level units are used for process control, process visualization, and / or process monitoring. Field devices known from the prior art typically consist of a housing, a sensor, and a control unit or data processing device located within the housing.

[0004] According to current technology, energy and / or signal transmission between field devices and higher-level units is often achieved using the well-known 4 mA to 20 mA standard, which employs a 4 mA to 20 mA current loop or a two-wire connection between the field device and the higher-level unit. Measured values ​​are transmitted by modulating the current. There is also the HART standard, which modulates digital communication data onto the analog 4 mA current value. Besides the 4 mA and HART standards, other common data transmission methods exist, such as Profibus, Foundation Fieldbus, the Modbus protocol, SDI-12, IO-Link, and newer standards like Ethernet APL and Single-Pair Ethernet (SPE).

[0005] A disadvantage of field devices known from the prior art is that they require a constant energy supply from external sources. The invention therefore aims to provide a field device with a lower energy footprint than those known from the prior art. A further objective of the invention is to provide a device arrangement in which such a field device is advantageously used. These objectives are achieved by providing the field device according to claim 1 and the device arrangement according to claim 19.

[0006] It is noted that the features listed in the independent and dependent claims may be combined with one another in any way, provided this is technically feasible. This also applies across the boundaries of the claim categories and even if one claim is not dependent on another. The description further characterizes and specifies the invention, particularly in conjunction with the figures. Where elements in the claims or the description are designated with numerical terms such as "first," "second," etc., these numerical terms serve only to distinguish the elements and do not make any statement about an order, a total number, or other properties of the elements, unless explicitly stated otherwise.

[0007] According to a first aspect of the invention, a field device is proposed, comprising a wired interface through which the field device can receive electrical power, and an energy harvesting device configured to receive energy from an environment of the field device and to deliver electrical power, wherein the field device is configured to supply the electrical power delivered by the energy harvesting device to at least one consumer of the field device.

[0008] Thus, the field device is suitable for providing electrical power by means of the energy harvesting device, which can be used by the at least one consumer of the field device. Consumers of the field device can be various components of the field device that require electrical energy for their function, for example, a sensor for acquiring measured values ​​or a device for data processing of the field device. The data processing device can, for example, be a microcontroller. The data processing device is preferably usable as a control and / or regulation unit of the field device. This can preferably also control energy distribution within the field device. Within the scope of the present invention, the term "energy harvesting device" is understood to mean any device that can harvest energy from the environment of the field device.Examples of energy sources include sunlight, ambient temperature, vibrations, air currents, or water currents. However, according to the invention, it is also conceivable to use other energy sources.

[0009] Since the field device provides additional electrical power via the energy harvesting device, power consumption via the wired interface can be reduced. The field device is preferably a measuring device. According to the invention, the field device can have one or more sensors. The sensor of the field device can be a level sensor or radar sensor, but other types of sensors can also be used. For example, the field device can be configured for flow measurement. It is also possible for the field device to have means for analyzing the measured data. Alternatively or additionally, the field device can be designed as an actuator. For example, it could be used as an actuator or a controllable valve. The wired interface of the field device can be any interface for connecting a cable or...This refers to a wired connection. The wired interface is also preferably suitable as a power electronics interface and / or for data processing of signals transmitted via connected conductors.

[0010] The energy harvesting device is preferably a solar module. A solar module, or photovoltaic module, is capable of generating electrical energy from light. It preferably comprises silicon-based solar cells. The solar module can be a single unit, but it can also consist of several sub-modules. These can preferably be arranged on different sides of the field device to increase the solar module's output power. The solar module is preferably arranged directly on, in, and / or on the field device. According to alternative embodiments of the invention, other energy harvesting devices could be used instead of the solar module. In particular, the use of water turbines or wind turbines is conceivable. Thus, the field device could include a water turbine or a wind turbine.A water turbine or a wind turbine used in conjunction with the field device should preferably be attached directly to it and be dimensioned so that the field device can support it. However, according to the invention, it is also possible for the field device to have a device with which energy can be extracted from the ambient temperature or from vibrations.

[0011] It is advantageous if the field device is further configured to adjust its electrical power consumption via the wired interface depending on the electrical power supplied by the energy harvesting device. If the energy harvesting device provides electrical power that can be used by the at least one consumer, then the field device needs to draw less power via the wired interface. This reduces the field device's energy footprint. Since the energy drawn via the wired interface is often not, or at least not exclusively, based on renewable energy generation, this can potentially also reduce CO₂ emissions. 2-Reduce the footprint of the field device. The resulting energy savings can be quite considerable, especially when using a large number of field devices according to the invention. If the electrical power consumption via the wired interface is adjusted or reduced, then it is possible for the at least one consumer to be supplied in mixed operation, so that the at least one consumer receives both electrical power that the field device draws via the wired interface and electrical power that is provided by the energy harvesting device.

[0012] It is particularly advantageous if the field device is further configured to communicate its required electrical power consumption via the wired interface. In this way, the field device's energy demand can be communicated to a remote device. According to the invention, this can be done, in particular, via an analog or a digital signal. According to advantageous embodiments of the invention, the remote device is configured to adjust the electrical power supplied to the field device depending on the field device's required electrical power consumption or the communicated energy demand. For this purpose, a current and / or voltage supplied by the remote device to the field device via a cable can optionally be adjusted.

[0013] It is advantageous if the field device is further configured to output a signal via the wired interface containing a command to set the electrical power output of a remote device. This refers to the output of electrical power to the field device, particularly via a line connected to the wired interface. The signal can be, in particular, an analog or a digital signal. This allows the remote device to be instructed to output electrical power of a specific level. For example, according to advantageous embodiments, this can be used to instruct the output of a current or voltage of a specific level.

[0014] According to advantageous embodiments of the invention, the field device is further configured to output a signal via the wired interface that switches off the power supply via the wired interface from the remote device. This is particularly useful at times when the energy harvesting device fully covers the energy requirements of the field device. According to the invention, the power supply can be switched off by a signal that cuts off or reduces to zero a voltage and / or current supplied by the remote device. According to a further embodiment of the invention, the signal is configured such that the remote device is switched off or put into a standby mode by the signal.According to alternative versions of the invention, the remote station switches off the power supply if this is necessary depending on the communicated energy demand of the field device. Alternatively or additionally, the remote station uses the communicated energy demand to evaluate and / or predict the energy consumption of the field device or the energy consumption of a group of field devices connected to the remote station.

[0015] The field device is preferably configured to reduce its electrical power consumption via the wired interface by a first value of electrical power corresponding to a second value of electrical power supplied by the energy harvesting device and delivered to at least one load of the field device. For example, if the energy harvesting device supplies 1 watt of electrical power, and 0.8 watts of this electrical power are used to supply the at least one load of the field device, then the electrical power consumed by the field device via the wired interface can be reduced by 0.8 watts. The field device is preferably configured to deliver at least a portion of the electrical power supplied by the energy harvesting device to the at least one load of the field device.A portion of the delivered electrical power may not be used, may be fed into an energy storage device of the field device, or may be used for other purposes. The power consumption of the field device via the wired interface is preferably adjusted accordingly by the data processing device, by the power electronics of the field device, and / or by the wired interface itself.

[0016] In some applications, it may be possible to reduce electrical power consumption via the wired interface to 0 watts or nearly 0 watts. However, this is only possible if the electrical power supplied by the energy harvesting device fully powers at least one load. If this power is insufficient to operate the load, additional power must be drawn via the wired interface to bridge the power gap. The load(s) can therefore be powered by both the energy harvesting device and the wired interface.

[0017] Preferably, the field device is further configured to communicate the electrical power consumption, reduced by the initial electrical power value, via the wired interface. The field device thus communicates to the remote station the required electrical power consumption, which has decreased because the energy harvesting device is active. This has the advantage that the remote station can reduce its energy supply to the extent that additional energy is supplied by the energy harvesting device.

[0018] According to a particular embodiment of the invention, the field device further comprises an energy storage device, wherein the field device is suitable for supplying the electrical power delivered by the energy harvesting device to the energy storage device, and wherein the field device is further suitable for supplying energy stored in the energy storage device to the at least one consumer of the field device in the form of electrical power. The electrical energy storage device is preferably a rechargeable battery. This can store electrical energy and also release it again. This is particularly advantageous when the energy harvesting device temporarily provides more electrical power than is required by the at least one consumer. In this case, excess electrical power can be supplied to the energy storage device.

[0019] According to the invention, the field device can be configured to supply the energy stored in the energy storage device to the at least one consumer of the field device in the form of electrical power if the electrical power supplied by the energy harvesting device is insufficient to supply the at least one consumer of the field device. For example, if the energy harvesting device temporarily fails to provide electrical power, the at least one consumer of the field device can be operated with stored energy from the energy storage device. The field device is preferably configured to switch the power supply to the at least one consumer in this case so that it receives electrical power from the energy storage device. The electrical power supplied via the wired interface is preferably reduced accordingly.

[0020] The phrase "the power output of the energy harvesting device is insufficient" here means that the energy harvesting device does not output enough electrical power to operate the at least one load of the field device. This includes the fact that at least one load of the field device cannot be operated. It also includes the fact that multiple loads of the field device cannot be operated if they share the power output of the energy harvesting device. In this case, the at least one load must be supplied with energy by an alternative means. According to the invention, it is possible for the energy supply of individual loads to continue to be fully provided by the output power of the energy harvesting device, provided it is sufficient, while other loads are supplied via the energy storage device.The field device is preferably configured so that, in this case, it only supplies energy via the wired interface to those consumers whose power output from the energy harvesting device is insufficient. Operating the field device with an energy storage device is advantageous, for example, if the energy harvesting device is a solar module. Since this may not generate any electrical power at night, the at least one consumer can be supplied by the electrical energy storage device during this period. It is understood that the energy stored in the energy storage device may run out. In this case, the field device is preferably configured to ensure the energy supply to the at least one consumer is restored via the wired interface.

[0021] According to a preferred embodiment of the invention, the field device comprises several consumers, wherein a first subset of the several consumers is formed by at least one primary consumer to which the field device supplies electrical power via the wired interface when the electrical output power of the energy harvesting device is insufficient. A second subset of the several consumers is formed by at least one secondary consumer to which the field device supplies no electrical power or only limited electrical power via the wired interface when the electrical output power of the energy harvesting device is insufficient.In the context of the present invention, the insufficient electrical output power is understood to mean that the at least one consumer of the field device cannot be operated using the output power of the energy harvesting device, including the operation of multiple consumers using the output power of the energy harvesting device.

[0022] The field device's consumers are divided into primary and secondary consumers. According to the invention, primary consumers can be those for which a constant supply of electrical energy is required. These could be, for example, the field device's sensor or its data processing device. These are preferably supplied with energy continuously via the wired interface.

[0023] According to the invention, the secondary consumers can be consumers that do not need to be operated continuously, or for which continuous operation in a high-energy-consumption mode is not required. Nevertheless, it is advantageous if the secondary consumers can be operated at least when the energy harvesting device provides sufficient output power. If the energy harvesting device does not provide sufficient output power, the at least one secondary consumer, according to the embodiment described here, is either no longer operated or is operated only in an energy-saving mode in which it receives only reduced electrical power via the wired interface.

[0024] For example, a secondary load is an additional sensor of the field device that measures a value that only needs to be determined at longer intervals. Advantageously, this additional sensor is only activated if the energy harvesting device provides sufficient output power. If the output power of the energy harvesting device is insufficient to power the additional sensor, it is not supplied with electrical power via the wired interface and remains inactive. Other loads of the field device, which are classified as primary loads, are supplied with electrical power via the wired interface if the output power of the energy harvesting device is insufficient to power them.

[0025] The field device is preferably configured to supply the energy stored in the energy storage device to at least one secondary consumer in the form of electrical power when the electrical output power of the energy harvesting device is insufficient. Thus, it is possible for secondary consumers to be powered by the energy storage device if the output power of the energy harvesting device is insufficient to supply them. However, according to possible embodiments of the invention, it is also possible for the primary consumers to be supplied with electrical energy from the energy storage device if the energy harvesting device does not provide sufficient output power.

[0026] According to one embodiment of the invention, the at least one secondary load can be a light source. In particular, the light source can be a light ring. This light ring can, for example, illuminate brightly in a standard mode as a secondary load if the energy harvesting device provides it with sufficient output power. If, however, the energy harvesting device no longer provides sufficient output power for operation in the standard mode to still be possible, the light ring preferably switches to an energy-saving mode. In the energy-saving mode, according to this embodiment of the invention, the light ring is supplied with electrical power via the wired interface, but consumes less energy than in its standard mode and illuminates with reduced brightness.

[0027] According to the invention, the energy harvesting device can be arranged on a mounting platform of the field device, which can be detachably connected to a main body of the field device. This allows the energy harvesting device to be easily replaced and maintained. The mounting platform preferably has spring contacts through which it can electrically contact the main body of the field device. This enables the transfer of electrical energy between the energy harvesting device and the main body of the field device.

[0028] The wired interface is preferably a two-wire interface. This allows for a simple power supply setup for the field device, resulting in comparatively low cable and material consumption. It is advantageous if the wired interface is also suitable for data transmission. It is particularly beneficial if data transmission occurs over the same cables used for power supply. This minimizes cable consumption and reduces the complexity of the setup. Alternatively, additional cables dedicated solely to data transmission can be included as part of the wired interface.

[0029] It is advantageous if the wired interface for data transmission and power consumption is designed according to one of the following standards: Ethernet-APL, IO-Link, Modbus, SDI-12, Single Pair Ethernet (SPE), Power over Ethernet (PoE), Profibus PA, or Foundation Fieldbus. These are different standards specifically intended for connecting field devices and other industrial equipment. According to these standards, both digital data transmission and power supply to an end device are possible. However, unlike the known 4 mA to 20 mA standard, the amount of energy transmitted is not dependent on the transmitted measurement value. In accordance with the present invention, the energy consumption via the wired interface can be adjusted depending on the output power of the energy harvesting device.

[0030] Ethernet-APL is a special 2-wire Ethernet based on 10BASE-T1L according to IEEE 802.3cg with additional provisions for the process industry. IO-Link is a communication system for connecting intelligent sensors and actuators to an automation system, standardized in IEC 61131-9. Modbus is a protocol based on a client / server architecture where data transmission can occur via a serial interface or Ethernet. The protocol is part of the IEC 61158 standard. SDI-12 is an asynchronous protocol for serial communication, designed especially for use in remote locations and for low power consumption. Single Pair Ethernet (SPE) is a two-wire Ethernet interface designed for applications including factory automation and the Industrial Internet of Things (IIoT), standardized in various versions under IEEE 802.3.Power over Ethernet (PoE) encompasses various standards and systems that allow power to be supplied via Ethernet connections. Well-known examples include the IEEE 802.3af-2003, IEEE 802.3at-2009, IEEE 802.3bt-2018, and IEEE 802.3bu-2016 standards. Profibus PA is a Profibus variant with a transmission layer suitable for process automation. The two-wire bus line of this transmission layer handles not only communication but also the power supply to the connected devices. Foundation Fieldbus is a fieldbus system for data and power transmission developed by the FieldComm Group.

[0031] It is understood that the invention can also be used with other wired interfaces. For example, the use of three- or four-wire interfaces is possible, as is the use of other cable interfaces and transmission protocols.

[0032] According to a further embodiment of the invention, the field device has a radio interface for transmitting measured values. Thus, a wired interface can be used where the transmitted power can be freely regulated, while data is transmitted exclusively via the radio interface. For example, Bluetooth, LoRaWAN (Long Range Wide Area Network), NB-IoT (NarrowBand-IoT), LTE-M (Long-Term Evolution), or any other radio transmission technology can be used as the radio transmission technology. The field device can optionally have multiple radio interfaces, preferably utilizing different radio transmission technologies. Data transmission via both the wired and radio interfaces is also possible according to the invention. However, the use of a radio interface is not required.

[0033] According to a further aspect of the invention, a device arrangement is proposed comprising the field device described above, a power supply unit configured to provide energy to the field device and to receive data from the field device, and a conductor system via which the field device is coupled to the power supply unit. The power supply unit is understood to be a counterpart of any configuration. For example, the power supply unit can be configured to receive and, if necessary, evaluate measured values ​​from one or more field devices. The power supply unit can be configured to control the field device either alternatively or additionally. Preferably, the power supply unit provides electrical energy to the field device via the conductor system. The conductor system is preferably formed by a two-wire line.

[0034] Further features and advantages of the invention become apparent from the drawings, which are intended to clarify the invention for the person skilled in the art, enabling them to carry it out. The drawings do not, however, limit the invention. Nevertheless, the drawings illustrate advantageous aspects of the invention, the features of which – possibly even individually – can be used to specify the invention to be protected. This shows:

[0035] Fig. 1 shows a schematic representation of a device arrangement with a field device according to the invention and

[0036] Fig. 2 shows a flowchart of the operating sequence of the field device according to the invention.

[0037] Fig. 1 shows a schematic representation of a device arrangement 1 with a field device 2 according to the invention. The field device 2 has a sensor 3, which is a radar sensor. The sensor 3 is connected to a control unit 4 of the field device 2. The control unit 4 performs measurements using the sensor 3. The control unit 4 outputs the measured values ​​obtained in this way via a wired interface 5 of the field device 2. A conductor system 6, comprising two conductors and designed for data and power transmission according to the Ethernet-APL standard, is connected to the wired interface 5. The field device 2 is coupled to a power supply unit 7 via the conductor system 6.The power supply unit 7 supplies the field device 2 with electrical energy via the conductor system 6 according to the Ethernet-APL standard and also receives the measured values ​​from the sensor 3 via the conductor system 6, which the field device 2 outputs via the wired interface 5.

[0038] The control unit 4 receives electrical power via the wired interface 5 and supplies it to various consumers of the field device 2, for example, the sensor 3, as well as to an energy storage device 8 and a light ring 9 of the field device 2. The energy storage device 8 is a battery that can store electrical energy. The energy storage device 8 can release the stored energy as electrical power, and the control unit 4 can supply the released electrical power to the consumers. The control unit 4 is also coupled to an energy harvesting device 10 of the field device 2. The energy harvesting device 10 is a solar module. The solar module is attached to a mounting platform 11 of the field device 2, which is detachably connected to a main body 12 of the field device 2. The control unit 4 is electrically connected to the energy harvesting device 10 via a platform interface 13.When the Energy Harvesting device 10 emits electrical power, this power can be received by the control unit 4 and supplied to the consumers of the field device 2.

[0039] Fig. 2 shows a flowchart of the operating sequence of the field device according to the invention. The field device begins operating in an initial state 14. In a first query step 15, it is checked whether the electrical power supplied by the energy harvesting device is sufficient to operate the various loads of the field device. If this is the case, the field device transitions to a first supply state 16. In the first supply state 16, the loads are supplied with electrical power supplied by the energy harvesting device. The illuminated ring of the field device operates in a standard mode in the first supply state 16, in which it shines brightly. Furthermore, in the first supply state 16, the energy storage device is charged if the electrical power supplied by the energy harvesting device is not fully supplied to the loads.The field device periodically returns from the first supply state 16 to the first query step 15 to check whether the electrical power supplied by the energy harvesting device is still sufficient to operate the loads. If the electrical power supplied by the energy harvesting device is no longer sufficient to operate the loads, a second query step 17 is performed.

[0040] In the second query step 17, the charge level of the field device's energy storage is checked. If the energy storage charge is sufficient to power the loads, the field device transitions to a second supply state 18. In this second supply state 18, the loads are supplied with electrical power provided by the energy storage. The control unit ensures that the electrical power is delivered to the loads. In this second supply state 18, the indicator ring operates in its standard mode, where it shines brightly. The field device periodically returns to the first query step 15 to check whether it can transition to the first supply state 16, allowing the loads to be powered again via the energy harvesting device.Furthermore, the second query step 17 is also performed periodically to determine whether an energy supply from the energy storage device is still possible. As soon as the energy storage device is discharged, this is no longer the case, and the field device transitions to a third supply state 19.

[0041] In the third supply state 19, the power supplies cannot be operated with electrical power supplied by either the energy harvesting device or the energy storage device. Therefore, in this third supply state 19, the control unit supplies the loads with electrical power that the field device receives via the wired interface. The control unit also puts the light ring into an energy-saving mode. In this energy-saving mode, the light ring illuminates at a lower intensity than in the standard mode. Furthermore, the light ring has a lower electrical power consumption in this energy-saving mode than in the standard mode, so the load on the power supply unit is limited when the light ring is operated in the third supply state.From the third supply state 19, the field device periodically returns to the first query step 15 and to the second query step 17 to check whether, if necessary, an energy supply to the consumers is again possible through the energy harvesting device or through the energy storage.

[0042] Reference symbol list

[0043] 1 Device arrangement

[0044] 2 Field device

[0045] 3 Sensor

[0046] 4 Control unit

[0047] 5 Wired interface

[0048] 6-wire system

[0049] 7 Power supply unit

[0050] 8 Energy storage

[0051] 9 Light ring

[0052] 10 Energy Harvesting Device

[0053] 11. Attachment platform

[0054] 12 main bodies

[0055] 13 Platform interface

[0056] 14 Initial state

[0057] 15 First query step

[0058] 16 Initial supply status

[0059] 17 second query step

[0060] 18 second supply state

[0061] 19 third supply state

Claims

Patent claims 1. Field device (2) with a wired interface (5) through which the field device (2) can receive electrical power, and with an energy harvesting device (10) configured to receive energy from an environment of the field device (2) and to deliver electrical power, wherein the field device (2) is configured to supply the electrical power delivered by the energy harvesting device (10) to at least one consumer of the field device (2).

2. Field device (2) according to claim 1, characterized in that the device for energy harvesting (10) is a solar module.

3. Field device (2) according to one of the preceding claims, characterized in that the field device (2) is further configured to adapt an electrical power consumption of the field device (2) via the wired interface (5) depending on the electrical power supplied by the device for energy harvesting (10).

4. Field device (2) according to claim 3, characterized in that the field device (2) is configured to reduce the electrical power consumption of the field device (2) via the wired interface (5) by a first value of electrical power which corresponds to a second value of electrical power which is supplied by the energy harvesting device (10) and to which at least one consumer of the field device (2) is supplied.

5. Field device (2) according to one of claims 1 or 2, characterized in that the field device (2) is further configured to communicate a required electrical power consumption via the wired interface (5).

6. Field device (2) according to claims 4 and 5, characterized in that the field device (2) is further configured to communicate the electrical power consumption, reduced by the first value of electrical power, via the wired interface (5).

7. Field device (2) according to one of the preceding claims, characterized in that the field device (2) is further configured to output a signal via the wired interface (5) which contains a command to adjust an electrical power output of a remote station.

8. Field device (2) according to one of claims 1 to 6, characterized in that the field device (2) is further configured to output a signal via the wired interface (5) which switches off a power supply via the wired interface by a counterpart.

9. Field device (2) according to one of the preceding claims, characterized in that the field device (2) further comprises an energy storage device (8), wherein the field device (2) is suitable for supplying the electrical power delivered by the energy harvesting device (10) to the energy storage device (8), and wherein the field device (2) is further suitable for supplying energy stored in the energy storage device (8) to the at least one consumer of the field device (2) in the form of electrical power.

10. Field device (2) according to claim 9, characterized in that the field device (2) is configured to supply the energy stored in the energy storage device (8) to the at least one consumer of the field device (2) in the form of electrical power when the electrical power delivered by the energy harvesting device (10) is required The supply to at least one consumer of the field device (2) is insufficient.

11. Field device (2) according to one of the preceding claims, characterized in that the field device (2) has several consumers, wherein a first subset of the several consumers is formed by at least one primary consumer to which the field device (2) supplies electrical power via the wired interface (5) when an electrical output power of the energy harvesting device (10) is insufficient, and wherein a second subset of the several consumers is formed by at least one secondary consumer to which the field device (2) supplies no electrical power or only limited electrical power via the wired interface (5) when the electrical output power of the energy harvesting device (10) is insufficient.

12. Field device (2) according to claims 10 and 11, characterized in that the field device (2) is configured to supply the energy stored in the energy storage device (8) to the at least one secondary consumer in the form of electrical power when the electrical output power of the energy harvesting device (10) is insufficient.

13. Field device (2) according to claim 11 or 12, characterized in that the at least one secondary consumer is a light source.

14. Field device (2) according to one of the preceding claims characterized in that the energy harvesting device (10) is arranged on a mounting platform (11) of the field device (2) which can be detachably connected to a main body (12) of the field device (2).

15. Field device (2) according to one of the preceding claims, characterized in that the wired interface (5) is a two-wire interface.

16. Field device (2) according to one of the preceding claims, characterized in that the wired interface (5) is suitable for data transmission.

17. Field device (2) according to claim 16, characterized in that the wired interface (5) for data transmission and power consumption is designed according to one of the standards Ethernet-APL, SPE (Single Pair Ethernet), Power over Ethernet (POE), Modbus, SDI-12, IO-Link, Profibus PA or Foundation Fieldbus.

18. Field device (2) according to one of the preceding claims, characterized in that the field device (2) has a radio interface for transmitting measured values.

19. Device arrangement (1) with a field device (2) according to one of the claims 1 to 18, with a power supply unit (7) which is equipped to supply power to the field device (2) and to receive data from the field device (2), and with a conductor system (6) via which the field device (2) is coupled to the power supply unit (7).

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