Intrinsically safe automation field device

Abstract

Intrinsically safe automation field device for use in a potentially explosive area, said device comprising: - a first and a second connection terminal (30a, 30b) for connecting a two-wire line (14) that can be used to supply a current; - a sensor and / or actuator module (40) for capturing and / or setting a process variable; - an input / output module (20) having a radio unit (21) for wirelessly transmitting data; - a main electronics module (30) which is separate from the input / output module and has an energy store (34) which is designed to provide energy needed for the radio unit (21) for wirelessly transmitting data, wherein at least the energy store (34) is encapsulated on the main electronics module (30) using a potting compound.

Description

[0001] Intrinsically safe field device in automation technology

[0002] The invention relates to an intrinsically safe field device in automation technology for use in a potentially explosive atmosphere.

[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] 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.

[0006] 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

[0007] “Intrinsic safety” (marking Ex-i, IEC EN DIN 60079-11, published June 2012).

[0008] 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. The "intrinsic safety" type of protection defines three levels of protection: 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).At level c, no fail-safety is defined, so that even a malfunction can cause ignition (0 fail-safety).

[0009] Today, field devices are constructed from modular field device electronics that are electrically connected to one another via a plug-in connection and arranged in a corresponding housing. This modular design allows the individual electronic modules to be prefabricated according to the intended functionality and then assembled to form the field device electronics. Typical modules that are connected via the plug-in connection are: a main electronics module, which, for example, contains a microprocessor for further data processing; a sensor and / or actuator module, which includes a sensor and / or actuator element for detecting and / or adjusting the physical variable; and an input / output module, which, for example, contains a display for displaying information.Since the input / output module is arranged behind a viewing window in a housing wall to allow the display to be read, and thus interference with the radio transmission through the housing wall can be reduced, the input / output module also usually comprises a radio unit.

[0010] Many field devices are designed as so-called 2-wire field devices. In this case, the field device is powered via the same cable pair (two-wire) as is used for communication. The 4-20 mA standard is usually used for this, in which the measured values ​​or control values ​​are communicated, i.e. transmitted, as the main process variable via the two-wire line or two-wire cable in the form of a 4-20 mA loop current or current signal. In this case, an electrical loop current between 4 mA and 20 mA flowing in a current loop represents the value of the physical or technical quantity. Due to drift and inaccuracies, as well as the detection of range overflows, a somewhat larger current range is permitted for the representation of the quantities: 3.8...20.5 mA. Currents less than 3.6 mA orare greater than 21 mA, the evaluation units should no longer interpret them as a representation of the physical or technical quantity, but as error information of the sensor.

[0011] This means that the energy supply is severely limited. Assuming the worst-case scenario, in which the field device signals an error condition and is therefore only supplied with a current of less than 3.6 mA, the field device has access to less than 38.16 mW (= 10.6 V * 3.6 mA) of energy at a supply voltage of 10.6 V. In order to enable wireless communication between the field devices, e.g. via a Bluetooth radio unit, a higher energy level than the currently available is required, at least temporarily. For this purpose, an energy storage device is usually provided on the input / output module of the field device, in which energy is continuously stored so that it is available for the radio unit to send and / or receive communication packets.

[0012] Since such energy storage devices must be able to store a relatively large amount of energy, they are encapsulated with a potting compound to enable the field device to be used in hazardous areas. Encapsulation is achieved using a potting frame that surrounds the energy storage device and is filled with the potting compound. The disadvantage of this is that an additional process step is required during the production of the input / output module for applying the potting frame and filling it with the potting compound. This additional process step results in additional costs.

[0013] A further disadvantage is that the energy storage device creates a short circuit for the main electronics module when the device is switched on or when the input / output module is hot-plugged into a corresponding interface of the main electronics module, thus drawing a significant amount of energy from the main electronics module. This would result in the main electronics module being unable to function for a short time. To prevent this, an additional (active) current limiter is integrated into the input / output module upstream of the energy storage device, which limits or regulates the current at startup. This additional circuit component also results in additional material and production costs.

[0014] The invention is therefore based on the object of remedying this situation.

[0015] The object is achieved according to the invention by the intrinsically safe field device of automation technology according to patent claim 1.

[0016] The intrinsically safe field device of automation technology according to the invention for use in a potentially explosive area comprises: a first and a second connection terminal for connecting a two-wire line via which a current can be supplied; a sensor and / or actuator module for detecting and / or setting a process variable; an input / output module with a radio unit for wirelessly transmitting data; a main electronics module connected to the first and second connection terminal and formed separately at least from the input / output module, which main electronics module conducts the current that can be supplied via the two-wire line via a current path from the first to the second connection terminal, wherein the main electronics module has a voltage regulator incorporated in the current path, which is configured to provide a power supply at least for the input / output module based on the supplied current, wherein the main electronics module is further configured toto transmit the process variable detected by the sensor element by setting the current to a corresponding value and / or to receive a process variable to be set by the actuator element by reading the current and to set the actuator element accordingly, wherein the main electronics module further comprises an energy storage device designed to provide the energy required by the radio unit for wirelessly transmitting data, wherein at least the energy storage device is encapsulated on the main electronics module with a potting compound.

[0017] An intrinsically safe field device for automation technology designed according to the invention offers the advantage of eliminating the need for additional encapsulation of the energy storage device on the input / output module using a encapsulation frame. This, in turn, saves space on the input / output module, thus reducing the module's manufacturing costs.

[0018] An advantageous embodiment of the field device according to the invention for automation technology provides that the energy storage device has at least one capacitor which has a capacitance of at least 10 pF, preferably of at least 250 pF, particularly preferably of at least 1 mF.

[0019] A further advantageous embodiment of the field device according to the invention in automation technology provides that the energy storage device is arranged in front of the voltage regulator on the main electronics module.

[0020] A further advantageous embodiment of the field device according to the invention in automation technology provides that the input / output module further comprises a current limiting or control which limits a current from the main electronic module to a value in the range of 0.1-100 mA, in particular in the range of 0.1-25 mA, very particularly in the range of 1-5 mA 10-100 mA.

[0021] A further advantageous embodiment of the field device according to the invention in automation technology provides that the input / output module does not have a capacitor with a capacitance of greater than 100 pF, in particular of approximately 500 pF.

[0022] A further advantageous embodiment of the field device according to the invention in automation technology provides that the input / output module and the main electronics module are connected to one another via an electrical interface, which is preferably designed to be pluggable.

[0023] A further advantageous embodiment of the field device according to the invention for automation technology provides that the input / output module is arranged in a cover of the field device, preferably behind a viewing window. A further advantageous embodiment of the field device according to the invention for automation technology provides that the input / output module further comprises a display for displaying information and / or for operating the field device.

[0024] A further advantageous embodiment of the field device according to the invention in automation technology provides that the display is a color display.

[0025] The invention is explained in more detail with reference to the following drawing. It shows:

[0026] Fig. 1 : a schematic representation of a field device which is connected to a higher-level unit via a two-wire cable for signal and energy transmission.

[0027] Figure 1 shows a schematic representation of a field device 10 with modular field device electronics. In the present example, the field device electronics comprises a main electronics module 30, a sensor module 40, and an input / output module 20. The input / output module 20 and the sensor module 40 are each electrically connected to the main electronics module 30 via an interface 22a, 22b and 23a, 23b, which can be designed, for example, as a plug-in connection. The field device 10 is connected via a first and second connection terminal 30a and 30b to a two-wire line 14 for signal and power transmission. The two-wire line 14 is, in turn, connected at the other end to a higher-level unit 12. In the illustrated example, the field device 10 is a measuring point in which a measured value or process variable (e.g., temperature, pressure, humidity, fill level, flow rate) is recorded using a sensor module 40.The field device could just as well be an actuator point in which a process variable is set using an actuator module instead of the sensor module.

[0028] The field device 10 does not contain its own power source, but draws the supply current required for its operation via the two-wire line 14. This can be provided, for example, by a voltage source 18 contained in the higher-level unit 12. A measured value signal representing the currently measured value is transmitted from the field device 10 to the higher-level unit 12 via the same two-wire line 14. For this purpose, the field device electronics are configured to transmit a measured value via the two-wire line 14 according to the 4 to 20 mA standard. The voltage source 18 supplies a direct voltage Uv, and the measuring current Is is a direct current.

[0029] The higher-level unit 12 contains an evaluation circuit 26, which extracts the measured value information from the signal current Is transmitted via the two-wire line 14. For this purpose, a measuring resistor 28 is inserted into the two-wire line, across which a voltage UM is generated that is proportional to the signal current Is transmitted via the two-wire line and is fed to the evaluation circuit 26. The signal current Is is conducted in the field device 10 from the first to the second connection terminal 30a, 30b via a current path 31 formed on the main electronics module.

[0030] The input / output module 20 comprises, as already mentioned, the radio unit 21 for wirelessly transmitting and receiving data. For example, the radio unit 21 can be a Bluetooth radio unit for wirelessly transmitting data using the Bluetooth standard or a modified variant thereof, e.g., Bluetooth Low Energy. Alternatively, the radio module can also be a WLAN, ZigBee, NFC, IoT, 5G, or WirelessHART radio module. The data can be, for example, configuration and / or parameterization data for the field device. Furthermore, the input / output module can have a display 27 for displaying information and / or for operating the field device. The display 27 can, for example, be a color display. If the display 27 is a monochrome display, a charge pump can also be provided on the input / output module 20, which serves to control the monochrome display.In the case that the display 27 is a color display, the input / output module 20 does not have a charge pump.

[0031] For measured value acquisition, the field device electronics includes the aforementioned sensor module 40, which is connected to the main electronics module 30 via the electrical interface 23a, 23b. The electrical interface 23a, 23b can be designed as a pluggable interface. Via the electrical interface 23a, 23b, both measured values ​​from the sensor module to the main electronics module 30 and power to the sensor module 40 from the main electronics module 30 are transmitted. The electrical interface 23a, 23b can be designed as a pluggable electrical interface.

[0032] The main electronics module, in turn, comprises a transducer circuit 37, which, via a control line 24, controls or drives a current controller or current source 32, also arranged on the main electronics module, such that the measuring current Is is set to a value (signal current) representing the detected measured value. The current source 32 can, for example, comprise a transistor that is controlled via the control signal from the transducer circuit 37. If the field device is designed as an actuator, i.e., has an actuator module instead of a sensor module, current control is omitted. The transducer circuit 37 can, for example, comprise a microprocessor.

[0033] The main electronics module further comprises a low-impedance shunt resistor 33, through which the set signal current Is is read back by the transducer circuit 37 via a readback line 25. According to Ohm's law, a voltage U_Shunt = R_Shunt • Is is dropped across the shunt resistor 33. The voltage U_Shunt is thus proportional to the current Is flowing through the field device. To regulate the set signal current Is, the voltage drop across the shunt resistor 33 is fed to the transducer circuit. Such shunt resistors 33 typically have a resistance value in the range of 5-40 ohms, preferably 7-30 ohms, and particularly preferably in the range of 10-25 ohms.

[0034] The main electronics module further comprises a voltage regulator 36, for example in the form of a switching or linear regulator, which is designed to provide the most constant operating voltage possible for the individual modules. The input voltage for the voltage regulator 36 can be stabilized or supported, for example, by an energy storage device 34, in particular in the form of a capacitor. The energy storage device 34 can, for example, have a capacitor of at least 10 pF, preferably of at least 250 pF, particularly preferably of at least 1 mF. For reasons of clarity, the voltage source arranged on the main electronics module 30 is not shown in Fig. 1.

[0035] Furthermore, the main electronics module includes circuit components for explosion protection and / or EMC measures. In Fig. 1, these circuit components are indicated by the block with reference number 38. Depending on the desired level of protection and the specifications of the corresponding standard, e.g., IEC EN DIN 60079-11, published in June 2012, regarding explosion protection measures and / or, for example, the standard DIN EN 61000-1-2, published in July 2017, regarding EMC measures, the circuit components are designed differently.

[0036] According to the invention, the main electronics module further comprises an energy storage device configured to continuously store energy transmitted via the two-wire line 14 and, as needed, to deliver it to a radio unit arranged on another module of the field device electronics for wireless data transmission during a transmission or reception process. In the present case, the radio unit 21 is located on the input / output module. The energy storage device 34 can, for example, be a capacitor, preferably having a capacitance greater than 100 pF, preferably approximately 500 pF.

[0037] Advantageously, the energy storage device 34 is arranged on the main electronics module 30 in such a way that it is positioned upstream of the voltage regulator 36, so that the energy storage device 34 is subjected to a higher voltage than would be the case if it were positioned downstream of the voltage regulator 36. This offers the advantage that significantly more energy can be stored in the energy storage device, since the voltage is proportional to the square of the amount of energy to be stored (E = % * C * U 2 ). Thus, in an arrangement upstream of the voltage regulator 36, the capacitance can be reduced since the amount of energy required for the transmission and / or reception process does not change.

[0038] To meet the requirements of the intrinsic safety type of protection, at least the energy storage device 34 on the main electronics module 30 is encapsulated with a potting compound. Typically, however, at least the voltage regulator, the current regulator, and the energy storage device, or all electronic components on the main electronics module, are encapsulated with the potting compound.

[0039] In order to be able to transmit the required current from the main electronics module 30 to the module on which the radio unit 21 is arranged during a transmission and / or reception process by the radio unit 21, a current limiter or control 26 can be provided on the module and designed such that a current required for the transmission and / or reception process, which current is, for example, in the range of approximately 10-100 mA, can flow.

[0040] List of reference symbols

[0041] 10 field device

[0042] 11 Cover of the field device

[0043] 11 a Viewing window

[0044] 12 Higher-level unit, e.g. programmable controller (PLC)

[0045] 14 Two-wire cable

[0046] 18 Voltage source

[0047] 20 Input / output module

[0048] 21 radio unit

[0049] 22a, 22b Electrical interface

[0050] 23a, 23b Electrical interface

[0051] 24 control line

[0052] 25 Readback line

[0053] 26 Current limitation or control

[0054] 27 Display

[0055] 28 measuring resistor

[0056] 30 Main electronics module

[0057] 30a, 30b connection terminals

[0058] 31 current path

[0059] 32 Current control

[0060] 33 Shunt resistance

[0061] 34 Energy storage, e.g. capacitor

[0062] 36 voltage regulators, e.g. switching regulators or linear regulators

[0063] 37 Instrument transformer circuit

[0064] 38 Circuit part for explosion protection and / or EMC measures

[0065] 40 Sensor and / or actuator module

[0066] Is measuring current

[0067] Uk terminal voltage

[0068] Uv voltage of the voltage source

[0069] Ue input voltage at the voltage regulator

[0070] UM voltage at the measuring resistor

Claims

Patent claims 1. Intrinsically safe field device for automation technology for use in a potentially explosive atmosphere, comprising: a first and a second terminal block (30a, 30b) for connecting a two-wire line (14) through which current can be supplied; a sensor and / or actuator module (40) for sensing and / or setting a process variable; an input / output module (20) with a radio unit (21) for wireless data transmission; a main electronics module (30) connected to the first and second terminals (30a, 30b) and designed separately from the input / output module, which carries the current (Is) that can be supplied via the two-wire line from the first to the second terminal (30a, 30b) via a current path (31), wherein the main electronics module (30) has a voltage regulator (36) inserted into the current path (31) which is configured to provide a power supply at least for the input / output module (20) on the basis of the supplied current (Is),wherein the main electronics module (30) is further configured to transfer the process variable detected by the sensor element (40) to a corresponding value by adjusting the current (Is) and / or to receive a process variable to be adjusted by the actuator element (40) by reading the current (Is) and adjusting the actuator element (40) accordingly, wherein the main electronics module (30) further comprises an energy storage device (34) which is designed to provide energy required for the radio unit (21) for wireless data transmission, wherein at least the energy storage device (34) on the main electronics module (30) is encapsulated with a potting compound.

2. Intrinsically safe field device of automation technology according to claim 1, wherein the energy storage device (34) has at least one capacitor having a capacitance of at least 10 pF, preferably at least 250 pF, particularly preferably at least 1 mF.

3. Intrinsically safe field device for automation technology according to one or more of the preceding claims, wherein the energy storage device (34) is arranged upstream of the voltage regulator (36) on the main electronics module (30).

4. Intrinsically safe field device for automation technology according to one or more of the preceding claims, wherein the input / output module (20) further comprises a current limiting or control (26) which limits a current from the main electronics module (30) to a value in the range of 0.1-100 mA, in particular in the range of 0.1-25 mA, and especially in the range of 1-5 mA to 10-100 mA.

5. Intrinsically safe field device for automation technology according to one or more of the preceding claims, wherein the input / output module (20) does not have a capacitor with a capacitance greater than 100 pF, in particular of approximately 500 pF.

6. Intrinsically safe field device for automation technology according to one or more of the preceding claims, wherein the input / output module (20) and the main electronics module (30) are connected to each other via an electrical interface (22a, 22b), which is preferably pluggable.

7. Intrinsically safe field device for automation technology according to one or more of the preceding claims, wherein the input / output module (20) is arranged in a cover of the field device (11), preferably behind a viewing window.

8. Intrinsically safe field device for automation technology according to one or more of the preceding claims, wherein the input / output module (20) further comprises a display (27) for displaying information and / or for operating the field device.

9. Intrinsically safe field device of automation technology according to the preceding claim, wherein the display is a color display.

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