Adapter for an automation field device

Abstract

Adapter for insertion into a two-wire line, comprising: an adapter housing (200); adapter electronics (201) which are disposed in the adapter housing and connect a first terminal element (202) to a third terminal element (204) through a first electrical connection line (206) and connect a second terminal element (203) to a fourth terminal element (205) through a second electrical connection line (207), wherein the adapter electronics also comprise an surge arrestor (208) which is designed to limit a voltage applied between the third and fourth terminal elements to a first maximum value in the event of a fault, wherein the adapter electronics also comprise an overcurrent protection device (209) which is designed to prevent the loop current (I) from rising above a maximum current value in the event of a fault, and wherein the adapter electronics also comprise a circuit (600) which is designed, where no fault is present, to adjust a voltage applied to the surge arrestor, starting from a minimum input voltage, to a second maximum value which is smaller than the first maximum value.

Description

[0001] Adapter for a field device in automation technology

[0002] The invention relates to an adapter for insertion into a two-wire line between a field device of automation technology and a non-Ex-capable power supply isolator in order to make the field device Ex-capable, in particular Ex-ia-capable, as well as to an automation technology system.

[0003] In automation technology, particularly in process automation technology, field devices are often used to record and / or influence process variables. Sensors such as level gauges, flow meters, pressure and temperature gauges, pH and redox potential meters, conductivity meters, etc., are used to record process variables and record the corresponding process variables: level, flow, pressure, temperature, pH value, or conductivity. Actuators such as valves or pumps, which can be used to change the flow of a liquid in a pipe section or the fill level in a container, are used to influence process variables. In principle, field devices are all devices that are used close to the process and that supply or process process-relevant information.In the context of the invention, field devices are understood to include, in particular, remote I / Os, radio adapters or, in general, devices that are arranged at the field level.

[0004] A large number of such field devices are manufactured and distributed by Endress + Hauser.

[0005] Many field devices are available as so-called 2-wire versions (also called two-wire field devices). In this case, the field device's power is supplied via the same wire pair (two-wire wire) as the communication cable.

[0006] Particularly in the process industry, but also in automation technology, physical or technical quantities must often be measured or determined by field devices in areas where there is a potential risk of explosion, so-called potentially explosive atmospheres. By implementing appropriate measures in the field devices and evaluation systems (such as voltage and current limitation), the electrical energy in the transmitted signal can be limited so that this signal cannot trigger an explosion under any circumstances (short circuits, interruptions, thermal effects, etc.). Appropriate protection principles for this purpose have been defined in IEC EN DIN 60079-ff.

[0007] According to this standard, design and circuitry measures for field devices for use in potentially explosive atmospheres are defined based on the applicable types of protection. One of these types of protection is the type of protection

[0008] "Intrinsic safety" (Ex-i marking, IEC EN DIN 60079-11, published June 2012). The "intrinsic safety" type of protection is based on the principle of current and voltage limitation in an electrical circuit. The energy in the circuit that could potentially ignite an explosive atmosphere is limited so that neither sparks nor excessive heating of the electrical components can ignite the surrounding explosive atmosphere.

[0009] The "intrinsic safety" type of protection defines three protection levels: Ex-ia, Ex-ib, and Ex-ic. Level a is the highest level, at which two countable faults in combination must not lead to a malfunction and thus cause an ignition (2-fault safety). Level b defines that one countable fault must not lead to a malfunction and thus cause an ignition (1-fault safety). Accordingly, level c defines no fault safety, meaning that even a single malfunction can cause an ignition (0-fault safety).

[0010] In order to achieve the Ex-ia protection level, it is now necessary to use a so-called Ex supply isolator, via which an input current and an input voltage applied to the two connection terminals of a field device are limited, e.g. to an input voltage of less than 35 V and a maximum power of less than 0.8 W.

[0011] However, there are a large number of existing installations in automation systems where the field devices are operated without an Ex power isolator. Such field devices must then comply with the Ex-m encapsulation type of protection or the Ex-d flameproof enclosure type of protection.

[0012] To comply with the Ex-m type of protection, the parts of the field device that could ignite an explosive atmosphere through sparks or heating must be encapsulated in a potting compound in such a way that the explosive atmosphere cannot be ignited. This is achieved by encapsulating the components on all sides with a potting compound that is resistant to physical—particularly electrical, thermal, and mechanical—and chemical influences.

[0013] To comply with the Ex-d type of protection, the parts of the field device that can ignite an explosive atmosphere must be arranged in an enclosure in such a way that, in the event of an explosion of an explosive mixture inside, the enclosure can safely withstand the explosion pressure and the transmission of the explosion to the explosive atmosphere surrounding the enclosure is prevented.

[0014] Such field devices do not require a specially designed Ex isolating power supply, but can be operated with a conventional isolating power supply. If a new field device that is not designed to meet Ex-d and / or Ex-m requirements is to be installed in such existing installations, a conversion to a specially designed isolating power supply is required. This conversion entails increased effort when installing a (new) field device to meet Ex-i requirements.

[0015] The invention is therefore based on the object of demonstrating a possibility how a field device can comply with the protection level Ex-ia without requiring a conversion to a specially designed supply isolator in the existing installation.

[0016] The object is achieved according to the invention by the adapter according to patent claim 1 and the automation technology system according to patent claim 12.

[0017] The adapter according to the invention for insertion into a two-wire line between an automation field device and a non-Ex-capable power supply isolator in order to make the field device Ex-capable, in particular Ex-ia-capable, comprises: an adapter housing with a first and a second connection element for connecting a first two-wire line, via which the adapter can be connected to the power supply isolator, and with a third and fourth connection element for connecting a second two-wire line, via which the adapter can be connected to the field device; adapter electronics arranged in the adapter housing, which connects the first connection element to the third connection element by a first electrical connection line and the second connection element to the fourth connection element by a second electrical connection line,such that the first connecting line conducts a loop current coming from the power supply isolator from the first connection element to the field device connectable to the third connection element, and the second connecting line conducts the loop current coming from the field device via the fourth connection element to the second connection element back to the power supply isolator, wherein the adapter electronics further comprises an overvoltage protection device which is designed to limit a voltage applied between the third and fourth connection elements to a first maximum value in the event of a fault, wherein the adapter electronics further comprises an overcurrent protection device which is designed to prevent the loop current from increasing above a maximum current value in the event of a fault, so that a power to be delivered to the field device is limited, and wherein the adapter electronics further comprises a circuit which is designed toIn the absence of a fault, the voltage applied to the surge protection device is regulated, starting from a minimum input voltage applied between the first and second connection elements, to a second maximum value that is smaller than the first maximum value. According to the invention, an adapter is proposed in which, starting from a defined input voltage at the connection terminals via which the adapter is connected to a supply isolator, the voltage across a surge protection device is limited or regulated to a specific maximum voltage using a circuit, in particular a semiconductor circuit.

[0018] An advantageous embodiment of the adapter according to the invention provides that the minimum input voltage applied between the first and second connection element is greater than 3 volts, preferably greater than 5 volts, particularly preferably greater than 10 volts, most preferably in the range of 10-15 volts.

[0019] A further advantageous embodiment of the adapter according to the invention provides that the second maximum value is in the range from 5 to 25 volts, preferably in the range from 7 volts to 25 volts, particularly preferably in the range from 12 to 25 volts, very particularly preferably in the range from 17 to 22 volts.

[0020] A further advantageous embodiment of the adapter according to the invention provides that the overvoltage protection device has at least three Zener diodes connected in parallel with the third and fourth connection elements, wherein a cathode of the Zener diodes is connected to the first connecting line and an anode of the Zener diodes is connected to the second connecting line. In particular, the embodiment can provide that the Zener diodes are selected such that a Z voltage is in the range of 10-20 V, preferably approximately 16 V.

[0021] A further advantageous embodiment of the adapter according to the invention provides that the circuit has a voltage-controlled switching element, in particular a field-effect transistor, for setting a voltage drop, which is arranged in the first and / or second connecting line in such a way that the switching element serves as a voltage divider to a field device connectable to the third and fourth connection element.

[0022] A further advantageous embodiment of the adapter according to the invention provides that the circuit further comprises an operational amplifier, a voltage divider and a feedback loop, wherein the operational amplifier is designed to regulate the switching element, wherein the voltage divider is preferably designed to control a negative input of the operational amplifier by means of an intermediate tap as a function of an input voltage applied between the first and second connection element and / or the feedback loop is preferably used to return a voltage drop generated by the switching element to a positive input of the operational amplifier.A further advantageous embodiment of the adapter according to the invention provides that the voltage divider is introduced between the first and the second connecting line and is preferably designed as a high-impedance voltage divider, so that a cross current through the voltage divider is not greater than 20 pA, preferably not greater than 10 pA, most preferably not greater than 5 pA.

[0023] An advantageous embodiment of the adapter according to the invention provides that the adapter electronics further comprises a voltage regulation unit for supplying voltage to the operational amplifier, which is preferably incorporated into the first and / or second connecting line in such a way that the voltage regulation unit is connected in series with a field device connectable to the third and fourth connection element, so that no parallel current occurs between the first and second connecting lines. In particular, the embodiment can provide that the voltage regulation unit comprises a diode, another Zener diode, another resistor and / or a voltage-stabilizing circuit, in particulara reference voltage circuit or a voltage regulator and / or the adapter electronics further comprises a further Zener diode which is designed such that it is connected in parallel to the voltage regulation unit in order to limit an operating voltage for the operational amplifier to a maximum value and / or the adapter electronics comprises a series resistor which is connected in front of the Zener diode to protect the operational amplifier and / or the Zener diode.

[0024] The invention further relates to an automation technology system comprising a non-Ex-i capable power supply isolator, an automation technology field device which is designed in such a way that it meets the requirements of the intrinsic safety Ex-i type of protection and an adapter according to one or more of the preceding claims, wherein the adapter is connected to the non-Ex-i capable power supply isolator at the first and second connection element by means of a two-wire line and to the field device at the third and fourth connection element by means of a further two-wire line.

[0025] An advantageous embodiment of the automation technology system according to the invention and of the adapter provides that the field device is further configured to compensate the cross current caused by the voltage divider when transmitting measured and / or control values ​​by means of the loop current.

[0026] The invention is explained in more detail with reference to the following drawings. It shows:

[0027] Fig. 1: an arrangement comprising an adapter according to the invention, a field device of the

[0028] Automation technology and a power isolator, and

[0029] Fig. 2: A detailed view of adapter electronics according to the invention. Figure 1 shows an arrangement typically found in an automation system. Here, a power isolator 100 is connected to a field device 300 via a two-wire cable. Measurement and / or control values ​​can be transmitted between the field device 300 and a higher-level unit (not shown separately in Fig. 1), e.g., a programmable logic controller (PLC), via the two-wire cable. For example, the measurement and / or control values ​​can be transmitted analogously in the form of a 4-20 mA current signal between the field device and the higher-level unit.

[0030] The 100 power supply isolator is not Ex-capable, i.e. it is not approved / suitable for use in a potentially explosive area, as can be found, for example, in an existing installation in an automation system in which Ex-d devices and / or Ex-m devices are used or present.

[0031] The field device 300 can be a field device 300 that is designed to meet the requirements of the Ex-m encapsulation type of protection or the Ex-d flameproof enclosure type of protection. For example, parts of the field device 300 that can ignite an explosive atmosphere through sparks or heating can be embedded in a potting compound so that the explosive atmosphere cannot be ignited and the field device is Ex-m capable. Alternatively, parts of the field device 300 that can ignite an explosive atmosphere can be arranged in a housing such that, in the event of an explosion of an explosive mixture inside, the housing safely withstands the explosion pressure and prevents the transmission of the explosion to the explosive atmosphere surrounding the housing, thus making the field device Ex-d capable.

[0032] To meet the requirements of the Ex-ia protection level of the "intrinsic safety" type of protection, an adapter according to the invention is inserted into the two-wire line such that the adapter 200 is arranged between the non-Ex-capable power supply isolator and the field device 300. The adapter 200 comprises an adapter housing 200 and adapter electronics 201 arranged in the adapter housing 200 with four connection terminals 202, 203, 204, 205 for connecting the two-wire line.

[0033] Fig. 2 shows adapter electronics 201 in detail. The adapter electronics 201 comprises a first and a second connection terminal 202, 203, which serve to connect a wire of the first two-wire line 400 coming from the power supply isolator, and a third and a fourth connection terminal 204, 205, which serve to connect a wire of the second two-wire line 500 leading to the field device 300. Furthermore, the adapter electronics 201 comprises a first line 206 (hereinafter also referred to as the plus line), which connects the first connection terminal 202 to the third connection terminal 204, and a second line 207 (hereinafter also referred to as the minus line), which connects the second connection terminal 203 to the fourth connection terminal 205.

[0034] In order to limit the voltage at the third and fourth connection terminals 204, 205 in the event of a fault, several, preferably three, Zener diodes D1, D2, D3 are connected in parallel to the connection terminals. The Zener diodes D1, D2, D3 are connected in such a way that a cathode of the Zener diodes is connected to the positive line and an anode to the negative line, so that a Zener voltage of the Zener diodes is applied across the third and fourth connection terminals 204, 205 and thus defines an output voltage of the adapter for the downstream field device 300 during faulty operation (explosion protection measure). The Zener diodes D1, D2, D3 are selected such that the Zener voltage is in the range of 10-20 V, preferably approximately 16 V.

[0035] In order to limit the current flowing from the third terminal 204 to the field device 300 and back again via the fourth terminal 204 in the event of a fault, an overcurrent protection device 209, for example in the form of a fuse, is incorporated in the positive line. The overcurrent protection device 209, in combination with the Z voltage of the Zener diodes D1, D2, D3, is designed such that the power provided to the field device connected to the third and fourth terminals 204, 205 is limited to a maximum value (Ex power). For example, the overcurrent protection device 209 can be designed to prevent the current from rising above a maximum current value of 32mA. Thus, in the circuit shown in Fig.2, an Ex power provided at the third and fourth connection terminal is limited to 870 mW (= 32mA * 16V * 1.7), whereby the factor 1.7 represents a safety factor according to the standard DIN EN 60079-11.

[0036] In order that the Zener diodes D1, D2, D3 are or become non-conductive in the event that an input voltage greater than the Z voltage of the diodes D1, D2, D3 is applied to the first and second connection terminals 202, 203, the adapter electronics 201 according to the invention has a circuit 600 which is designed to regulate or limit a voltage drop across the Zener diodes D1, D2, D3.

[0037] For this purpose, the circuit 600 comprises a voltage-controlled switching element 601 for setting a voltage drop, wherein the switching element 601 is arranged in the first and / or second line 206, 207 such that the switching element 601 serves as a voltage divider for a field device 300 connected to the third and fourth connection terminals 204, 205. The switching element 601 can be a transistor, in particular a field-effect transistor, in particular an n-channel field-effect transistor. To regulate the switching element 601 accordingly, the circuit 600 further comprises an operational amplifier 602, a voltage divider 603, and a feedback loop 604a, 604b. The voltage divider 603 serves to drive a negative input of the operational amplifier 602. For this purpose, the voltage divider 603 is inserted between the plus and minus lines 206, 207 and is preferably designed as a high-impedance voltage divider.High-impedance here means that a cross-current flowing through the voltage divider is no greater than 20 pA, in particular no greater than 10 pA, and most especially no greater than 5 pA. The voltage divider 603 is preferably designed in a ratio of 1:10. For example, a first resistor connected to the positive line can have 1 megohm, and the second resistor connected to the negative line can have 100 kiloohms.

[0038] A further Zener diode D5 is also incorporated into the cross line of the voltage divider 603, the cathode of which is preferably connected to the positive line 206 and the anode of which is preferably connected to the negative line 207. The further Zener diode D5 is dimensioned such that a Z voltage is not greater than the Z voltage of the other Zener diodes D1, D2, D3.

[0039] For example, the additional Zener diode D5 can have a Zener voltage of approximately 13. The Zener voltage of the additional Zener diode defines / specifies an output voltage of the adapter or an input voltage for the field device in fault-free operation as soon as the Zener voltage is reached or exceeded.

[0040] The feedback loop 604a, 604b comprises a voltage divider formed from two resistors 604a and 604b. The voltage divider is connected in parallel with the switching element 601, so that a voltage drop generated by the switching element 601 is present across the voltage divider, and a positive input of the operational amplifier 602 is connected to a center tap of the voltage divider. The voltage divider can be configured in a ratio of 1:10, with the resistor with the higher value being applied to the higher voltage potential. For example, the voltage divider can be formed from a 100 kiloohm and a 10 kiloohm resistor.The feedback loop 604a, 604b controls the operational amplifier 602 in such a way that it closes at its output until the voltage drop across the switching element 601 is so large that the voltage applied via the voltage divider to the positive input of the operational amplifier 602 approximately corresponds to the voltage at the negative input of the operational amplifier 602.

[0041] To supply the operational amplifier 602, the adapter electronics can have a voltage regulation unit 605, which is preferably introduced into the first and / or second line 206, 207 in such a way that it is connected in series with a field device 300 connected to the third and fourth connection terminals 204, 205. This offers the advantage that there is no parallel current to the third and fourth connection terminals, so that any influence on the 4-20 mA current can be avoided. The voltage regulation unit 605 can, for example, have a diode, another Zener diode, another resistor and / or a reference voltage circuit. The adapter electronics can further comprise another Zener diode D4, which is designed such that it is connected in parallel with the voltage regulation unit 605 and limits an operating voltage for the operational amplifier to a maximum value, e.g., 2 V.Furthermore, the adapter electronics 201 can have a series resistor R1, which is connected in front of the operational amplifier 602 and / or the further Zener diode D4 to protect them.

[0042] Adapter electronics 201 configured in this way ensures that, when the input voltage provided by the supply isolator 100 at the first and second connection terminals 202, 203 is lower than the diode voltage / Z-voltage of the Zener diode D1, e.g., 12V, the Zener diode D1 does not yet allow any current to flow, and thus the negative input of the operational amplifier 602 is "low" and the positive input is "high," so that the output of the operational amplifier 602 also goes "high." This causes the switching element 602 to become conductive, and almost the entire voltage is available for the field device 300 via the third and fourth connection terminals 204, 205.

[0043] At a higher input voltage at the first and second terminals 202, 203, e.g., 30 V, the adapter electronics 201 ensures that the additional Zener diode D5 allows a current to flow, thus maintaining a defined voltage value at the negative input of the operational amplifier 602. The voltage value is set via the voltage divider 603. This voltage is now dependent on the input voltage at the first and second terminals 202, 203. As soon as the input voltage rises above the diode voltage of the Zener diode D1, the input voltage at the operational amplifier 602 also rises proportionally.

[0044] The operational amplifier 602 thus ensures that a voltage difference between the negative and positive inputs is minimized by changing its output voltage and thus regulating the voltage across the switching element 601. The voltage regulated by the switching element 601 is applied to the positive input of the operational amplifier 602 via the feedback loop 604a, 604b. This results in the operational amplifier 602 controlling the switching element 601 when the input voltage at the first and second connection terminals 202, 203 increases, causing it to close until the voltage at the positive input of the operational amplifier 602 is approximately equal to the voltage at the negative input of the operational amplifier 602. List of Reference Symbols

[0045] 100 Non-Ex-capable power supply isolator

[0046] 200 adapter housings

[0047] 201 adapter electronics

[0048] 202 First connecting element

[0049] 203 Second connecting element

[0050] 204 Third connecting element

[0051] 205 Fourth connecting element

[0052] 206 First connecting line

[0053] 207 Second connecting line

[0054] 208 Surge protection device

[0055] 209 Overcurrent protection device

[0056] 300 field devices in automation technology

[0057] 400 First two-wire line

[0058] 500 two-wire cable

[0059] 600 Circuit for regulating the voltage on the surge protection device

[0060] 601 switching element, in particular a field-effect transistor

[0061] 602 O pe ra ti ons amplifier

[0062] 603 voltage divider

[0063] 604a, feedback loop 604b 605 voltage regulation unit

[0064] I loop current

[0065] D1 First Zener diode of the overvoltage protection device

[0066] D2 Second Zener diode of the overvoltage protection device

[0067] D3 Third Zener diode of the overvoltage protection device

[0068] D4 Additional diode to limit the operating voltage of the operational amplifier

[0069] R1 series resistor, which is connected in front of the further diode D4

Claims

Patent claims 1. Adapter for insertion into a two-wire line between a field device of automation technology (300) and a non-Ex-capable power supply isolator (100) in order to make the field device Ex-capable, in particular Ex-ia-capable, comprising: an adapter housing (200) with a first and a second connection element (202, 203) for connecting a first two-wire line (400) via which the adapter can be connected to the power supply isolator (100) and with a third and fourth connection element (204, 205) for connecting a second two-wire line (500) via which the adapter can be connected to the field device (300); an adapter electronics (201) arranged in the adapter housing (200), which connects the first connection element (202) to the third connection element (204) by means of a first electrical connection line (206) and the second connection element (203) to the fourth connection element (205) by means of a second electrical connection line (207),such that the first connecting line (206) conducts a loop current (I) coming from the power isolator (100) from the first terminal element (202) to the field device (300) which can be connected to the third terminal element (204), and the second connecting line (207) conducts the loop current (I) coming from the field device via the fourth terminal element (205) to the second terminal element (203) back to the power isolator (100), wherein the adapter electronics (201) further comprises an overvoltage protection device (208) which is configured to limit a voltage present between the third and fourth terminal elements (204, 205) to a first maximum value in the event of a fault, wherein the adapter electronics further comprises an overcurrent protection device (209) which is configured to prevent an increase of the loop current (I) above a maximum current value in the event of a fault, so that a power output to the field device (300) is limited.and wherein the adapter electronics (201) further comprises a circuit (600) which is configured, in the absence of a fault, to regulate a voltage applied to the overvoltage protection device (208), from a minimum input voltage applied between the first and second terminal elements (202, 203), to a second maximum value which is smaller in relation to the first maximum value.

2. Adapter according to claim 1, wherein the minimum input voltage between the first and second connection element (202, 203) is greater than 3 volts, preferably greater than 5 volts, particularly preferably greater than 10 volts, and most preferably in the range of 10-15 volts.

3. Adapter according to one or more of the preceding claims, wherein the second maximum value is in the range of 5 to 25 volts, preferably in the range of 7 to 25 volts, particularly preferably in the range of 12 to 25 volts, most preferably in the range of 17 to 22 volts.

4. Adapter according to one or more of the preceding claims, wherein the overvoltage protection device (208) has at least three Zener diodes (D1 , D2, D3) connected in parallel to the third and fourth connection element (204, 205), wherein a cathode of the Zener diodes (D1 , D2, D3) is connected to the first connecting line (206) and an anode of the Zener diodes (D1 , D2, D3) is connected to the second connecting line (207).

5. Adapter according to the preceding claim, wherein the Zener diodes (D1 , D2, D3) are selected such that a Z voltage is in the range of 10-20 V, preferably approximately 16 V.

6. Adapter according to one or more of the preceding claims, wherein the circuit (600) comprises a voltage-controlled switching element (601), in particular a field-effect transistor, for adjusting a voltage drop, which is arranged in the first and / or second connecting line (206, 207) such that the switching element (601) serves as a voltage divider to a field device (100) that can be connected to the third and fourth connection element (204, 205).

7. Adapter according to one or more of the preceding claims, wherein the circuit (600) further comprises an operational amplifier (602), a voltage divider (603) and a feedback loop (604a, 604b), wherein the operational amplifier (602) is configured to control the switching element (601), wherein the voltage divider (603) is preferably configured to drive a negative input of the operational amplifier (602) by means of an intermediate tap depending on an input voltage applied between the first and second terminal element (202, 203) and / or the feedback loop (604a, 604b) preferably serves to feed a voltage drop generated by the switching element (601) back to a positive input of the operational amplifier (602).

8. Adapter according to the preceding claim, wherein the voltage divider (603) is placed between the first and the second connecting line (206, 207) and is preferably designed as a high-impedance voltage divider, so that a cross-current through the voltage divider is not greater than 20 pA, preferably not greater than 10 pA, and most preferably not greater than 5 pA.

9. Adapter according to claim 8 or 9, wherein the adapter electronics (201) further comprises a voltage control unit (605) for supplying voltage to the operational amplifier (602), which is preferably integrated into the first and / or second connecting line (206, 207) such that the voltage control unit (605) is connected in series to a conductor connected to the third and fourth connection element (204, 205) is connected to the field device (100), so that there is no parallel current between the first and the second connecting line (206, 207).

10. Adapter according to the preceding claim, wherein the voltage regulation unit (605) comprises a diode, a further Zener diode, a further resistor and / or a reference voltage circuit and / or the adapter electronics (201) further comprises a further Zener diode (D4) configured in such a way that it is connected in parallel to the voltage regulation unit (605) in order to limit an operating voltage for the operational amplifier (602) to a maximum value and / or the adapter electronics (201) comprises a series resistor (R1) connected in front of the further Zener diode (D4) to protect the operational amplifier (602) and / or the further Zener diode.

11. Automation system comprising a non-Ex-i capable power isolator (100), an automation field device (300) designed to meet the requirements of the intrinsic safety type of protection Ex-i, and an adapter according to one or more of the preceding claims, wherein the adapter is connected to the non-Ex-i capable power isolator (100) at the first and second connection elements (202, 203) by means of a first two-wire line (400) and to the field device (300) at the third and fourth connection elements (204, 205) by means of a second two-wire line (500).

12. Automation system according to the preceding claim and adapter according to claim 9, wherein the field device (300) is further configured to compensate the cross current caused by the voltage divider (603) when transmitting measured and / or actuated values ​​by means of the loop current (I).

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