Field device, system and method for process automation

Abstract

The invention relates to a field device (16), a system and a method for process automation, comprising a power supply interface via which the field device (16) can be connected to a functional unit (17) in order to receive an interface current (19), comprising a load circuit which is designed to load the functional unit (17), a load circuit voltage is provided on the basis of at least a part of the interface current (19), the load circuit having a voltage limiter (66), which has a load (B1) designed as a controllable load or a Zener diode and is designed to limit the load circuit voltage by means of a first electronic control element (T1) controlled by the load (B1), and wherein the load circuit further comprises a longitudinal voltage stabilizer (63) formed by the load (B1), which longitudinal voltage stabilizer is designed to provide a supply voltage based on the load circuit voltage using the load.

Description

Technical Field

[0001] The invention relates to a field device for process automation, comprising a power supply interface, with which the field device can be connected to a functional unit in order to receive an interface current, and the field device also comprises a load circuit, which is designed to provide a load circuit voltage based on at least a part of the interface current, wherein the load circuit has a voltage limiter, which includes a load designed as a controllable load or a Zener diode and is designed to limit the load circuit voltage by a first electronic control element controlled by the load. Background Art

[0002] DE 10 2019 215 409 B4 discloses a field device having a power supply interface and a load circuit. The load circuit has a voltage limiter with a controllable load of a control transistor. The load circuit voltage dropped across the load circuit is provided as a supply voltage. Summary of the invention

[0003] The object of the present invention is to achieve better stabilization of the supply voltage in an efficient manner.

[0004] This object is achieved by a field device as described below. The load circuit further comprises a longitudinal voltage stabilizer formed by the load, which is designed to provide a supply voltage based on the load circuit voltage using the load.

[0005] By means of the longitudinal voltage stabilizer, an improved stability of the supply voltage can be achieved. As a load for the longitudinal voltage stabilizer, an already existing load for controlling the first electronic control element is used. Therefore, no additional load is required and thus an improved stability can be achieved in an efficient manner.

[0006] Advantageous further developments are the subject of the variants described below.

[0007] The longitudinal voltage stabilizer preferably comprises a second electronic control element which is controlled by the load and is designed to provide the supply voltage using the second electronic control element.

[0008] Preferably, the first electronic control element is a first transistor and / or the second electronic control element is a second transistor.

[0009] The load circuit preferably further has a current limiter comprising a third electronic control element, in particular a third transistor. The current limiter is preferably designed to control the first electronic control element using the third electronic control element in order to limit the first load circuit current flowing through the first electronic control element.

[0010] The longitudinal voltage stabilizer is preferably designed to reduce or prevent the influence of a load circuit voltage increase caused by the current limiter on the supply voltage when limiting the first load circuit current.

[0011] The load preferably has an output terminal, via which the load controls both the first electronic control element and the second electronic control element.

[0012] The load is preferably designed as a controllable load and has an input terminal which is controlled based on a supply voltage.

[0013] The load circuit preferably comprises an output branch leading from the power supply terminals, to which input terminals of the controllable load are connected.

[0014] The output branch preferably comprises a voltage divider which provides a divided voltage, which is supplied to the input terminal, based on the supply voltage.

[0015] The load circuit preferably has a first load circuit connection point and a second load circuit connection point, between which the load circuit voltage drops. The voltage limiter preferably has an input branch extending from the first load circuit connection point to the second load circuit connection point and comprising a first electronic control element.

[0016] The longitudinal voltage stabilizer preferably has a load branch which is connected in parallel with the input branch by way of example and comprises the load.

[0017] The field device preferably comprises a measuring resistor, which is in particular connected in series with the load circuit.The field device is preferably designed to receive communication information transmitted via the interface stream from the functional unit using the measuring resistor.

[0018] The field device preferably comprises a consumer, wherein the field device is designed to provide at least a portion of the energy required for operating the consumer via a supply voltage based on the interface current.

[0019] The invention further relates to a system comprising a field device and a functional unit, wherein the functional unit is connected to a power supply interface.

[0020] The present invention also relates to a method for operating the system, comprising the following steps: receiving an interface current from a functional unit at a field device; providing a load circuit voltage based on at least a portion of the interface current through a load circuit; limiting the load circuit voltage through a voltage limiter; and providing a supply voltage based on the load circuit voltage through a longitudinal voltage stabilizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Exemplary details and embodiments are explained below with reference to the drawings.

[0022] Figure 1 It is a schematic diagram of a system consisting of functional units and field devices. DETAILED DESCRIPTION

[0023] Figure 1 A system 10 is shown, which includes a functional unit 17 and a field device 16. Figure 1 In the embodiment, the functional unit 17 is connected to a power supply connection of a field device 16. The field device 16 is preferably a position controller, in particular for process automation.

[0024] According to one possible design, the system 10 further comprises a valve (and / or a valve drive) (not shown in the figure). The valve and / or the valve drive are actuated by the field device 16. The system 10 is, for example, an industrial device, in particular a process technology device.

[0025] The system 10 serves as an exemplary application environment for the field device 16. The field device 16 can also be provided alone—ie in particular without the other components of the system 10.

[0026] The functional unit 17 is designed, for example, as a sensor, an actuator or a superordinate controller. For example, the functional unit 17 is a sensor designed as an active current generator. As an example, the functional unit 17 is a displacement sensor. The functional unit 17 advantageously includes its own functional unit housing and is preferably arranged to be spaced apart from the field device 16.

[0027] The functional unit 17 comprises a first functional unit connection point 41 and a second functional unit connection point 42, via which the functional unit 17 is connected to a power supply interface of the field device 16. The functional unit 17 provides an interface current 19, which flows, for example, from the first functional unit connection point 41 (via the field device 16) to the second functional unit connection point 42.

[0028] Functional unit 17 is advantageously designed to transmit communication information, such as sensor values, in particular measured values, or control values, in particular setpoints, to field device 16 via interface circuit 19. Field device 16 is preferably designed to perform actions according to the communication information, such as actuating valves and / or valve drivers.

[0029] The communication between the functional unit 17 and the field device 16 preferably takes place via the current strength of the interface current 19 . For example, the functional unit 17 maps the communication information to be transmitted to the field device 16 onto the current strength of the interface current 19 .

[0030] The functional unit 17 is advantageously also designed to supply the field device 16 with energy via the interface current 19 , optionally all the electrical energy available to the field device 16 .

[0031] The functional unit 17 and the field device 16 are preferably connected to each other via electrical cables (e.g., one or more cables). For example, a first electrical cable extends from a first control connection point 41 to a first interface connection point 37 of the field device 16, and a second electrical cable extends from a second control connection point 42 to a second interface connection point 38 of the field device 16.

[0032] The field device 16 includes a power interface, through which the field device 16 is connected (or can be connected) to the functional unit 17 to receive the interface current 19. The field device 16 is preferably communicatively connected to the functional unit 17 via the power interface. The power interface is preferably a 4-20mA power interface. For example, the power interface is an analog power interface. The circuit formed by the functional unit 17 and the power interface can also be called a current loop.

[0033] The field device 16 is implemented particularly by 2-wire technology, wherein the power interface is a 2-wire terminal. Optionally, the power interface is the only power supply for the field device 16. According to a feasible design, the field device 16 has another power interface (not shown in the figure), in particular for connection to a superior controller, such as a PLC (programmable logic controller). In this case, the field device can be powered by both power interfaces, or can also be powered by only one of the two power interfaces.

[0034] The field device 16 advantageously comprises a consumer 43. The consumer 43 is powered (in particular exclusively) by electrical energy provided via the power supply interface. The consumer 43 is preferably an electronic processing device for processing the communication information.

[0035] As mentioned above, the field device 16 is particularly used for actuating a valve (and / or a valve driver). The field device 16 is preferably designed as a position regulator and particularly comprises an electro-pneumatic converter to provide a pneumatic actuation signal for actuating a valve (and / or a valve driver). According to a possible design, the consumer comprises an electro-pneumatic converter. Optionally, the consumer 43 comprises a pilot valve, particularly a solenoid valve. The consumer 43 may preferably comprise a field device control unit, particularly a processor, such as a microcontroller.

[0036] The field device 16 comprises a coupling mechanism 30, by means of which the field device is connected (or can be connected) to the functional unit 17. The coupling mechanism 30 comprises a power supply interface. By way of example, the field device 16 comprises its own field device housing, in which the coupling mechanism 30 and / or a consumer 43, such as an electronic processing device, are arranged. Advantageously, the field device 16 is fixed to the valve (or valve drive) with its field device housing, for example, by a mechanical interface arranged on the field device housing.

[0037] The field device 16 comprises a load circuit, which is exemplarily part of the coupling mechanism 30. The load circuit is designed to provide a load circuit voltage based on at least a part of the interface current 19, advantageously based on the entire interface current 19. The load circuit voltage is generated in particular as a product of the part of the interface current 19 flowing from the first load circuit connection point 45 to the second load circuit connection point 46, preferably the entire interface current 19, and a resistance acting between the first load circuit connection point 45 and the second load circuit connection point 46. The load circuit voltage is advantageously present at the first circuit node K1 (with respect to the reference potential).

[0038] The load circuit also has a voltage limiter 66, which comprises a load B1 designed as a controllable load or a Zener diode. The voltage limiter 66 is designed to limit the load circuit voltage via a first electronic control element T1 controlled by the load B1. Advantageously, the load circuit regulates the load circuit voltage via the voltage limiter.

[0039] The load circuit further comprises a longitudinal voltage stabilizer 63 formed by the load B1, which is designed to provide a supply voltage based on the load circuit voltage using the load B1. The supply voltage is present, for example, at the supply terminal 56 (relative to the reference potential). The longitudinal voltage stabilizer 63 is in particular connected between the first circuit node K1 and the supply terminal 56. The load B1 is both part of the voltage limiter 66 and part of the longitudinal voltage stabilizer 63. In particular, a voltage stabilizer which separates the output voltage (here the supply voltage) from the input voltage (here the load circuit voltage) (here, for example, by the second electronic control element T2) is referred to as the longitudinal voltage stabilizer 63.

[0040] The field device 16 is preferably designed to provide at least a portion of the energy required for operating the consumer 43 (or all of the energy required for operating the consumer 43) via a supply voltage based on the interface current 19. In particular, the consumer is supplied with electrical energy via the supply voltage applied to the supply terminal 56.

[0041] The coupling mechanism 30 comprises a first interface connection point 37 and a second interface connection point 38, through which the field device 16 is connected to the functional unit 17. The coupling mechanism 30 also comprises a power supply terminal 56 and a reference potential terminal 65, between which a supply voltage is provided. The consumer 43 is connected to the power supply terminal 56 and the reference potential terminal 65. The reference potential terminal 65 is, for example, a ground terminal. A reference potential, for example ground, is provided at the reference potential terminal 65. The coupling mechanism 30 also comprises a communication terminal 67, at which the coupling mechanism 30, for example, provides a measurement voltage corresponding to the communication information (particularly relative to the reference potential terminal 65).

[0042] The field device 16, in particular the coupling mechanism 30, comprises a measuring resistor R9, which is connected in series to the load circuit (and may also be referred to as a ninth resistor R9). The field device 16 is designed to receive communication information transmitted via the interface current 19 from the functional unit 17 using the measuring resistor R9. For example, the interface current 19 flows through the measuring resistor R9, and the communication information is acquired by the consumer 43 based on the measured voltage drop across the measuring resistor R9.

[0043] The load circuit comprises a first load circuit connection point 45 and a second load circuit connection point 46, via which the load circuit is connected between the interface connection points 37, 38, in particular in series with the measuring resistor R9. The interface current 19 flows through the load circuit from the first load circuit connection point 45 to the second load circuit connection point 46. The load circuit voltage drops between the first load circuit connection point 45 and the second load circuit connection point 46.

[0044] The first load circuit connection point 45, the first interface connection point 37, the first voltage stabilizer connection point 64 and the first voltage limiter connection point 68 are, for example, directly connected to the first circuit node K1. The first load circuit connection point 45, the first interface connection point 37, the first voltage stabilizer connection point 64 and the first voltage limiter connection point 68 are, for example, at the same potential, the potential of the first circuit node K1.

[0045] The second load circuit connection point 46 is, for example, at a reference potential, in particular at ground potential. Advantageously, the second load circuit connection point 46 is (in particular directly) connected to a reference potential terminal 65, in particular a ground terminal. The second load circuit connection point 46 and / or the second voltage stabilizer connection point 69 are directly connected to the second circuit node K2 and are at the potential of the second circuit node K2.

[0046] The voltage limiter 66 will be discussed in more detail below. The voltage limiter 66 is designed in particular as a parallel voltage limiter.

[0047] By way of example, the voltage limiter 66 has an input branch 48 which extends from the first load circuit connection point 45 to the second load circuit connection point 46 and comprises a first electronic control element T1. By way of example, the first electronic control element T1 is a first transistor. The first transistor is designed, for example, as a bipolar transistor, in particular as a PNP transistor.

[0048] The first load circuit current flows through the input branch 48 and thus through the first electronic control element T1. The first load circuit current is part of the interface current 19 flowing through the load circuit. The input branch 48 is used to set, in particular increase, the first load circuit current, more precisely, to set, in particular increase, by the first electronic control element T1 in order to limit the load circuit voltage.

[0049] The first electronic control element T1 is controlled by the load B1, for example, by connecting the first load output terminal 52 (eg, via the second resistor R2) to the control terminal 9 of the first electronic control element T1. For example, the first load switching current is determined by the control of the first electronic control element T1 by the load B1.

[0050] The input branch 48 exemplarily comprises a first resistor R1 which is connected in series with the first electronic control element T1. The input branch 48 comprises a third circuit node K3 which is arranged, for example, between the first electronic control element T1 and the first resistor R1.

[0051] The first electronic control element T1 has a first current-carrying terminal 7, a second current-carrying terminal 8 and a control terminal 9. The first current-carrying terminal 7 is, for example, connected to the first resistor R1. The second current-carrying terminal 8 is exemplarily connected to the second load circuit connection point 46. The control terminal 9 is connected to the fourth circuit node K4 (for example via the second resistor R2). For example, the first current-carrying terminal 7 is an emitter terminal, the second current-carrying terminal 8 is a collector terminal, and the control terminal 9 is a base terminal.

[0052] The voltage limiter 66 comprises a load B1 which is exemplarily connected between the fourth circuit node K4 and the second circuit node K2. The voltage limiter 66 further comprises a voltage divider formed by a third resistor R3 and a fourth resistor R4.

[0053] The load circuit B1 preferably has an output branch 47 leading from the power supply terminal 56, and the load input terminal 51 of the load B1 is connected to the output branch 47. The output branch 47 includes a voltage divider, which provides a divided voltage based on the power supply voltage supplied to the load input terminal 51. The output branch 47 includes a fifth circuit node K5, and the load input terminal 51 is connected to the fifth circuit node K5. The fifth circuit node is arranged between the third resistor R3 and the fourth resistor R4.

[0054] The load B1 comprises a first load output terminal 52 and a second load output terminal 53. The first load output terminal 52 may also be referred to as a cathode, and the second load output terminal 53 may also be referred to as an anode. The load input terminal 51 may also be referred to as a reference terminal. The first load output terminal 52 is connected to the control terminal 9 of the transistor T1, for example, via a second resistor R2. The load B1 controls the first electronic control element T1 via the first load output terminal 52. The second load output terminal 53 is connected to the second circuit node K2.

[0055] The load B1 is designed to set the current (also referred to as the second load circuit current) flowing from the first load output terminal 52 to the second load output terminal 53 based on the voltage applied to the load input terminal 51, such as the divided voltage provided by the voltage divider. In particular, the load B1 is designed to compare the voltage applied to the load input terminal 51 with a reference voltage (such as an internal reference voltage), and to set the second load circuit current based on the comparison. The reference voltage is, for example, 2.5V. For example, the load B1 is designed to increase the second load circuit current in response to the voltage applied to the load input terminal 51 being greater than the reference voltage. In addition, the load B1 is advantageously designed to reduce the second load circuit current in response to the voltage applied to the load input terminal 51 being less than the reference voltage.

[0056] Preferably, in the case of load B1, the current / voltage characteristic curve between the first load output terminal 52 and the second load output terminal 53 is changed by controlling the load input terminal 51. For example, load B1 is a shunt voltage regulator or a shunt voltage regulator. For example, a Zetex ZHT431 device from Diodes Incorporated can be used as load B1, or a device with the same function as this device, such as a "TL431" device, can be used. For example, load B1 is designed as an "Adjustable Precision Zener Shunt Regulator", that is, an adjustable precision Zener shunt regulator. Load B1 can also be called an adjustable Zener diode. Load B1 is in particular a reference diode. Load B1 is preferably used as a voltage reference.

[0057] The longitudinal voltage stabilizer 63 will be discussed in more detail below.

[0058] The longitudinal voltage stabilizer 63 is preferably designed to reduce or prevent the effect of a load circuit voltage rise caused by the current limiter 62 (explained in more detail below) on the supply voltage when limiting the first load circuit current.

[0059] The longitudinal voltage stabilizer 63 is designed in particular as a longitudinal voltage regulator. In particular, the longitudinal voltage stabilizer 63 is designed to regulate the supply voltage to a predetermined voltage value.

[0060] The longitudinal voltage stabilizer 63 has a first voltage stabilizer connection point 64, a second voltage stabilizer connection point 69 and a third voltage stabilizer connection point 70. The longitudinal voltage stabilizer 63 is connected to the power supply terminal 56 via the third voltage stabilizer connection point 70.

[0061] The longitudinal voltage stabilizer 63 has a load branch 49, which extends exemplarily from the first voltage stabilizer connection point 64 to the second voltage stabilizer connection point 69. The second load circuit current flows through the load branch 49. The second load circuit current is part of the interface current 19 flowing through the load circuit. The load branch 49 is connected in parallel with the input branch 48, for example, and includes a load B1. The load branch 49 also includes a fifth resistor R5 connected between the fourth circuit node K4 and the first circuit node K1.

[0062] The longitudinal voltage stabilizer 63 preferably comprises a second electronic control element T2 controlled by the load B1 and is designed to use the second electronic control element T2 to provide, in particular to regulate, the supply voltage. For example, the load B1 controls the second electronic control element T2 using the first load output terminal 52 of the second electronic control element T2. The second electronic control element T2 is in particular a second transistor. The second transistor is designed, for example, as a bipolar transistor, in particular as an NPN transistor.

[0063] The second electronic control element T2 has a first current carrying terminal 71, a second current carrying terminal 72 and a control terminal 73. The first current carrying terminal 71 is exemplarily connected to the first voltage stabilizer connection point 64. The second current carrying terminal 72 is exemplarily connected to the third voltage stabilizer connection point 70 and thus to the supply terminal 56. The control terminal 73 is connected to the fourth circuit node K4 (for example via the sixth resistor R6). For example, the first current carrying terminal 71 is a collector terminal, the second current carrying terminal 72 is an emitter terminal, and the control terminal 73 is a base terminal.

[0064] The longitudinal voltage stabilizer 63 comprises an output branch 47 which extends from the third voltage stabilizer connection point 70 to the second voltage stabilizer connection point 69 and comprises, for example, a voltage divider formed by a third resistor R3 and a fourth resistor R4.

[0065] The load circuit preferably further comprises a voltage limiter 62 comprising a third electronic control element T3, in particular a third transistor. The voltage limiter 62 is designed to control the first electronic control element T1 using the third electronic control element T3 so as to limit the first load circuit current flowing through the first electronic control element T1.

[0066] The third electronic control element T3 is designed, for example, as a bipolar transistor, in particular as a PNP transistor.

[0067] The third electronic control element T3 has a first current carrying terminal 75, a second current carrying terminal 76 and a control terminal 77. The first current carrying terminal 75 is exemplarily connected to the first current limiter connection point 68. The second current carrying terminal 76 is connected (for example via a seventh resistor R7) to the control terminal 9 of the first electronic control element T1. The control terminal 77 is connected (for example via an eighth resistor R8) to the third circuit node K3.

[0068] For example, the first current carrying terminal 75 is an emitter terminal, the second current carrying terminal 76 is a collector terminal, and the control terminal 77 is a base terminal.

[0069] According to a feasible design, the coupling mechanism 30, in particular the load circuit, is designed to have Figure 1 The design shown has the opposite polarity. For example, in this possible design, the first electronic control element T1 and the third electronic control element T3 are both designed as NPN transistors, and the second electronic control element T2 is designed as a PNP transistor.

[0070] Furthermore, according to a feasible design, one, more than one or all of the electronic control elements T1 , T2 , and T3 may be designed as field effect transistors, in particular, metal oxide semiconductor field effect transistors.

[0071] The operation of system 10 will be discussed in more detail below.

[0072] In operation, the field device 16 receives the interface current 19 from the functional unit 17 and provides a load circuit voltage via the load circuit based on at least a portion of the interface current 19. The voltage limiter 66 limits the load circuit voltage, and the longitudinal voltage stabilizer 63 provides a supply voltage based on the load circuit voltage. The load circuit advantageously serves as a voltage source for the consumer 43. The load circuit is in particular a low impedance device.

[0073] Advantageously, the load circuit regulates the supply voltage to a predetermined voltage value by means of a longitudinal voltage stabilizer. For example, the predetermined voltage value can be set by means of a third resistor R3 and a fourth resistor R4, in particular by means of a resistance ratio of these two resistors. For example, the set supply voltage is 3 V. In particular, the load voltage on the load B1 can be adjusted by means of the resistance ratio. The supply voltage is generated, for example, from the load voltage and the base-emitter voltage of the second transistor, in particular as a difference or a sum of the load voltage and the base-emitter voltage.

[0074] The load circuit voltage is preferably also regulated to a predetermined voltage value, in particular by means of a voltage limiter 66 .

[0075] By means of the longitudinal voltage stabilizer 63, in particular the field device 16 can be prevented from being damaged in the event of an incorrect connection of its power supply interface, for example if the field device 16 is (incorrectly) connected with its power supply interface to a power supply with an excessively high voltage, for example a supply voltage of 24 V. If a simple Zener diode were used instead of the longitudinal voltage stabilizer, in the event of a fault, i.e. for example when a 24 V supply voltage is connected, a short circuit and an overcurrent would occur and the Zener diode (and / or the ninth resistor R9) would be destroyed.

[0076] In the case of the current load circuit, if there is a fault in which an excessive interface current 19 is present or an excessively high voltage is connected at the current interface (i.e., for example, when an inappropriate 24V is connected between the first interface connection point 37 and the second interface connection point 38), the first load circuit current flowing through the first electronic control element T1 first increases. As the first load circuit current increases, the voltage limiter 62 conducts a larger current through the third electronic control element T3 and controls the first electronic control element T1 so that the first load circuit current no longer increases or decreases. For example, the voltage limiter 62 causes the voltage at the control terminal 9 of the first transistor T1 to increase when the first load circuit current increases, thereby causing the first transistor T1 to close and the first load circuit current to decrease. This results in an increase in the load circuit voltage, in particular the voltage present at the first node K1. For example, from a certain load circuit voltage, the load circuit can no longer adjust the load circuit voltage to its predetermined voltage value. The increase in the load circuit voltage is compensated by the longitudinal voltage stabilizer in such a way that its influence on the supply voltage is reduced or prevented. Thus, even if the load circuit voltage increases (which is no longer limited by the voltage limiter 66), the increase in the supply voltage at the power supply terminal 56 can be reduced or prevented, and a stable supply voltage can be advantageously provided.

[0077] It should be noted that the terms "first", "second", "third", etc. used are only used to give clear names to the corresponding devices. These terms are not intended to imply how many devices there are. For example, the name "eighth resistor" is not intended to imply that there must be eight resistors.

Claims

1. A field device (16) for process automation, comprising a power supply interface, via which the field device (16) can be connected to a functional unit (17) in order to receive an interface current (19), the field device further comprising a load circuit, the load circuit being designed to provide a load circuit voltage based on at least a portion of the interface current (19), wherein: The load circuit has a voltage limiter (66), the voltage limiter has a load (B1) designed as a controllable load or a Zener diode, and the voltage limiter is designed to limit the load circuit voltage through a first electronic control element (T1) controlled by the load (B1), and wherein the load circuit also includes a longitudinal voltage stabilizer (63) formed by the load (B1), the longitudinal voltage stabilizer is designed to provide a supply voltage based on the load circuit voltage using the load.

2. The field device (16) according to claim 1, wherein: The longitudinal voltage stabilizer (63) comprises a second electronic control element (T2) controlled by the load (B1) and is designed to provide the supply voltage using the second electronic control element (T2).

3. The field device (16) according to claim 1 or 2, wherein: The first electronically controlled element (T1) is a first transistor, and / or the second electronically controlled element (T2) is a second transistor.

4. The field device (16) according to the preceding claim, wherein: The load circuit further comprises a voltage limiter (62), which comprises a third electronic control element (T3), in particular a third transistor, wherein the voltage limiter (62) is designed to control the first electronic control element (T1) using the third electronic control element (T3) in order to limit the first load circuit current flowing through the first electronic control element (T1).

5. The field device (16) according to claim 4, wherein: The longitudinal voltage stabilizer (63) is designed to reduce or prevent the influence of the load circuit voltage increase caused by the voltage limiter (62) on the supply voltage when limiting the first load circuit current.

6. The field device (16) according to claim 2, wherein: The load (B1) has a load output terminal (52), and the load (B1) controls both the first electronic control element (T1) and the second electronic control element (T2) by means of the load output terminal.

7. The field device (16) according to any one of the preceding claims, wherein: The load (B1) is designed as a controllable load and has a load input terminal (51) controlled based on the supply voltage.

8. The field device (16) according to any one of the preceding claims, wherein: The load circuit (B1) comprises an output branch (47) extending from the power supply terminal (56), and a load input terminal (51) of the controllable load (B1) is connected to the output branch.

9. The field device (16) according to claim 8, wherein: The output branch (47) includes a voltage divider that provides a divided voltage supplied to the load input terminal (51) based on the supply voltage.

10. The field device (16) according to any one of the preceding claims, wherein The load circuit (66) has a first load circuit connection point (45) and a second load circuit connection point (46), between which the load circuit voltage drops, wherein the voltage limiter has an input branch (48) which extends from the first load circuit connection point (45) to the second load circuit connection point (46) and includes the first electronic control element (T1).

11. The field device (16) according to claim 10, wherein: The longitudinal voltage stabilizer (63) has a load branch (49) which is connected in parallel with the input branch (48) and includes the load (B1).

12. The field device (16) according to the preceding claim, further comprising a measuring resistor (R9) connected in series with the load circuit, wherein The field device (16) is designed to receive communication information transmitted via the interface current (19) from the functional unit (17) using the measuring resistor (R9).

13. The field device (16) according to any one of the preceding claims, further comprising a consumer (43), wherein: The field device (16) is designed to provide at least a portion of the energy required for operating the consumer (43) via a supply voltage based on the interface current (19).

14. A system (10) comprising a field device (16) according to any one of the preceding claims and the functional unit (17), wherein: The functional unit (17) is connected to the power supply interface.

15. A method for operating the system according to claim 14, comprising the following steps: An interface current (19) is received from a functional unit (17) at a field device (16); a load circuit voltage is provided based on at least a portion of the interface current (19) through a load circuit; the load circuit voltage is limited through a voltage limiter (66); and a supply voltage is provided based on the load circuit voltage through a longitudinal voltage stabilizer (63).

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