DEVICE FOR TRANSMITTING SIGNALS FROM A PARTIALLY METALLIC HOUSING

Description

[0001] The invention relates to a device for transmitting signals from an at least partially metallic housing using electromagnetic waves of a specific wavelength, a field device adapter for wireless data transmission and a field device for automation technology.

[0002] In automation technology, particularly in process automation technology, field devices are frequently used to determine, optimize, and / or influence process variables. Sensors, such as level gauges, flow meters, pressure and temperature gauges, conductivity meters, etc., are used to detect process variables, measuring levels, flow rates, pressure, temperature, and conductivity, respectively. Actuators, such as valves or pumps, are used to influence process variables, changing the flow rate of a liquid in a pipe section or the fill level in a container. In principle, field devices are defined as all devices used close to the process that provide or process process-relevant information. In the context of the invention, remote I / Os are also considered field devices.Generally speaking, field devices are those located at the field level. A large number of such field devices are manufactured and distributed by the company Endress+Hauser.

[0003] Currently, many existing automation systems still commonly use two-wire field devices connected to a higher-level unit, such as a PLC, via a two-wire cable. These two-wire field devices are designed so that the measured or manipulated values, as the main process variable, are communicated (i.e., transmitted) analogously as a 4-20 mA signal over the two-wire cable. For transmitting all other data, the HART protocol has proven particularly effective. In HART, a frequency signal is superimposed on the analog 4-20 mA current signal as a digital two-wire signal for data transmission. According to the HART protocol, the data transmission frequency switches between 1200 Hz and 2400 Hz, with the lower frequency representing a logical "0" and the higher frequency a logical "1".In this way, the slowly changing analog current signal remains unaffected by the frequency superposition, so that analog and digital communication are combined using HART.

[0004] However, with increasing digitalization, it is desirable that data can be transmitted not only via two-wire lines, i.e., purely wired, but also wirelessly using electromagnetic waves. This is useful for wirelessly transferring data to a database, such as a cloud database, and making it available there, or for wirelessly transmitting data between a field device and a mobile operating unit, for example, to wirelessly parameterize or configure the field device via the mobile operating unit.

[0005] For this purpose, so-called field device adapters for wireless data transmission are increasingly being used, making it possible to retrofit existing field devices for wireless data transmission. These field device adapters can be directly integrated into the two-wire line. This means the field device adapter is essentially connected as an independent unit between the higher-level unit and the field device. Alternatively, the field device adapter can also be mechanically connected directly to the field device, for example via a cable gland, and electrically connected to the field device electronics.

[0006] Since field device adapters and field devices are often used in potentially explosive environments, the use of metallic housings is mandatory. However, these generally prevent wave radiation for wireless data transmission. Any attachments to the field device adapters or field devices, such as external rod antennas, represent weak points for the housing and are therefore avoided.

[0007] The following patents are known from the prior art: US 2016 / 079677 A1, US 2012 / 268343 A1, EP 3 016 201 A1, US 6 798 385 B2, and DE 10 2009 047535 A1. US 2016 / 079677 A1 discloses a system and a method for wireless communication in a welding system. US 2012 / 268343 A1 discloses an antenna device with a housing made of a conductive material and a slot formed in a first surface. EP 3 016 201 A1 discloses an antenna device with at least two slotted antennas for transmitting and / or receiving electromagnetic waves. US 6 798 385 B2 discloses a consumer electronics device that uses a metal housing as an antenna. DE 10 2009 047535 A1 discloses a method for determining a connection configuration of a field device on a wireless adapter.

[0008] The invention is therefore based on the objective of proposing a device in which the transmission of signals using electromagnetic waves is possible even with metallic housings.

[0009] The problem is solved according to the invention by the device according to claim 1, the field device adapter for wireless data transmission according to claim 8 and the field device of automation technology according to claim 9.

[0010] The device according to the invention for transmitting signals from an at least partially metallic housing using electromagnetic waves of a specific wavelength, comprising: a transmitter / receiver unit arranged in the housing for generating and receiving electromagnetic waves, at least one primary antenna arranged in the housing for coupling out the generated electromagnetic waves of the transmitter / receiver unit and for coupling in and transmitting received electromagnetic waves to the transmitter / receiver unit, at least one slot-shaped housing opening which is designed such that a length of the slot-shaped housing opening corresponds to an integer multiple of a quarter wavelength of the determined wavelength, preferably an integer multiple of half a wavelength of the determined wavelength, so that the slot-shaped housing opening in conjunction with the primary antenna transmits the signals into and out of the housing using electromagnetic waves.

[0011] According to the invention, an antenna comprising a primary antenna or primary radiator and a secondary antenna or secondary radiator is proposed for transmitting or receiving electromagnetic waves from or in a metallic housing, wherein the secondary antenna or secondary radiator is designed in the form of a slot-shaped housing opening which is at least partially filled with an electrically non-conductive material other than air, and whose length corresponds to the following condition: L = n ⋅ λ / 4 ⋅ √ DK , where: λ = wavelength of the electromagnetic wave with which the signals are transmitted, DK = dielectric constant and n ∈ N.

[0012] The at least one slot-shaped opening in the housing is specifically chosen to be so small that it prevents the transmission of electromagnetic waves with very low frequencies, i.e., frequencies significantly below 1 GHz, preferably frequencies in the range of 1 kHz to 100 MHz, which can cause EMC interference. This means that the slot-shaped opening essentially acts as a high-pass filter for electromagnetic waves, allowing only waves intended for signal transmission to pass through. Waves with a frequency or frequency band of 2.4 GHz are typically used for signal transmission. WLAN according to IEEE 802.11b and g, Bluetooth (IEEE 802.15.1), and ZigBee (IEEE 802.15.4) are among the most prominent examples of the 2.4 GHz category. Other communication technologies based on the IEEE 802.15.4 specification include, for example, 6 LoWPAN, 6TiSCH or ANT or ANT+.From this perspective, for electromagnetic waves with a frequency of 2.4 GHz, a preferred length of at least one slot-shaped housing opening of half a wavelength of 2 λ / 4 = λ / 2 ≅ 12.43 cm results.

[0013] To prevent interference, especially EMC interference, from electronics located inside the housing, the length of the slot-shaped housing opening L can be selected such that the condition n·λ does not apply to a frequency of interference to the electronics (finterference = c / λinterference, where c corresponds to the speed of light), particularly EMC interference, but does apply to the specific wavelength λ used for transmission. Furthermore, to prevent stronger interference, i.e., interference that causes device failure, the length of the slot-shaped housing opening L can also be selected such that the condition (n+0.5)·λ / 4 does not apply to a frequency of strong interference.

[0014] The housing is essentially a metallic housing. The housing can, for example, have a metallic surface area of ​​at least 85%, preferably at least 90%, particularly preferably at least 95%, and most preferably at least 99% of the total surface area of ​​the housing.

[0015] Another advantageous embodiment of the device according to the invention provides that the housing, with the exception of the at least one slot-shaped housing opening and possible cable inlets and / or outlets, has an externally closed housing form.

[0016] Another advantageous embodiment of the device according to the invention provides that the housing has rounded edges in cross-section at least in one section, preferably a rounded housing shape, wherein the at least one slot-shaped housing opening is arranged in the section.

[0017] According to the invention, the housing is designed such that at least two circumferences measured in two spatial directions each correspond to an integer multiple of half a wavelength of the determined wavelength, wherein the measured circumferences each pass through the slot-shaped housing opening, preferably a center point of the housing opening. By appropriately designing the housing, the RF energy is distributed among the individual "circumferences" of the housing in such a way that a uniform radiation pattern is produced overall.In particular, in order to locally delay the orbital period of a wave and thereby significantly improve the radiation pattern in almost all spatial directions, the design may provide that at least one orbital delay element is formed on an outer surface of the housing to delay the electromagnetic waves by one orbital period and / or that the at least one orbital delay element has a groove-shaped or point-shaped structure or is made of a different material than the housing, preferably a dielectric material or a high-frequency metamaterial.

[0018] Another advantageous embodiment of the device according to the invention provides that the at least partially metallic housing is essentially made of a metallic material.

[0019] An alternative embodiment of the device according to the invention provides that the housing, which is at least partially metallic, is made of a plastic and that the housing, preferably on an inner surface, has at least a partial metallic covering.

[0020] According to the invention, the device further comprises a printed circuit board arranged within the housing, which is configured as a primary antenna for coupling out the generated electromagnetic waves of the transmitting / receiving unit and for coupling in and transmitting received electromagnetic waves, such that the electromagnetic waves are coupled out of or coupled in laterally from the printed circuit board. The embodiment provides that the printed circuit board is further configured as a primary antenna such that the electromagnetic waves are coupled out or coupled in only in a near field and are only coupled out or coupled into a far field in combination with the at least one slot-shaped opening in the housing. Such a configuration offers the advantage that a complete and therefore complex antenna, such as those known from the prior art for Vivaldi antennas, is not required.Rather, a primary antenna is sufficient, which only radiates into the near field and only acts as a complete antenna with the help of the slot-shaped housing opening as a secondary radiator.

[0021] The invention further relates to a field device adapter for wireless data transmission comprising a device according to one of the previously described embodiments, wherein an adapter housing of the field device adapter comprises the housing.

[0022] The invention further relates to a field device for automation technology comprising a device according to one of the previously described embodiments, wherein a field device housing of the field device comprises the housing at least in one section.

[0023] An advantageous embodiment of the field device according to the invention provides that the section includes at least one cable passage of the field device.

[0024] The invention is explained in more detail with reference to the following drawings. They show: Fig. 1 : a schematic representation of a first embodiment of a device according to the invention, Fig. 2 : a schematic representation of a cross-section through a housing of a second embodiment of the device according to the invention, which has several slot-shaped housing openings, Fig. 3 : a schematic representation of a third embodiment of the device according to the invention, Fig. 4 : the in Fig. 3 Perspective representation of the circumferences U1 and U2 in one plane to illustrate the mode of operation of the delay elements and / or a preferred geometric design of a housing of the device according to the invention, Fig. 5 : a schematic representation of a fourth embodiment of the device according to the invention.

[0025] Figur 1 Figure 1 shows a schematic representation of a first embodiment of a device according to the invention. The device comprises a housing 2, which is essentially made of a metal, preferably stainless steel. Alternatively, the housing 2 can also be made of a plastic and lined with a layer, preferably metallic on its inner surface. The housing 2 is geometrically designed such that it has a closed outer form. It is understood that possible cable inlets and / or outlets 13, 14, as well as a housing opening 5 designed according to the invention, remain unaffected. A cable inlet and a cable outlet each extend from the end faces of the cylindrical housing 2, through which a cable with at least one signal line 2a, 2b is guided into or out of the housing 2. In the figure shown in Figure 2, the housing 2 is designed as a closed outer form. Fig.1 In the illustrated embodiment, the housing 2 has a substantially cylindrical cross-section. Alternatively, the housing 2 can also have other shapes. Preferably, the housing 2 can have a shape as shown in Fig. 2 The depicted case shape has rounded edges.

[0026] A printed circuit board 6 is arranged in the housing 2, to which and from which the cable 1a, 1b with the signal line 2a, 2b leads and departs. The printed circuit board 6 includes a transmit / receive unit 11 for generating and receiving electromagnetic waves. The transmit / receive unit 11 can, for example, be an RF modem implemented as a chip. The printed circuit board also includes a primary antenna 4 for coupling out the generated electromagnetic waves and for coupling in and transmitting the received electromagnetic waves. The in Fig. 1 The transmitter / receiver unit 11 shown is designed to generate or receive electromagnetic waves with a frequency band of 2.4 GHz, so that signals transmitted via the signal lines 2a, 2b can also be transmitted wirelessly by the device using Bluetooth (possibly also Bluetooth Low Energy) or one of the aforementioned variants.

[0027] According to the invention, the housing 2 has an (unfilled) slot-shaped opening 5 with a length L corresponding to an integer multiple of a quarter wavelength n·λ / 4 of the electromagnetic wave. In this embodiment, the opening is filled with nothing other than air. At a frequency of 2.4 GHz, the slot-shaped housing opening 5 thus has a preferred length of 12.43 cm, which corresponds to approximately half a wavelength (2·λ / 4) of the electromagnetic wave. The width B of the slot-shaped opening 5 is chosen to be as small as possible and is largely determined by a suitable manufacturing process. Preferably, the width B is less than 3 mm, and particularly preferably less than 1 mm. The slot-shaped opening 5 has no electrical connection to the circuit board 6 and is illuminated by the primary antenna 4 located inside the housing 2.

[0028] The in Fig. 1 The device shown is connected at one end via cable 1a to a field device 7 and at the other end via cable 1b to a higher-level unit (not shown separately). Cable 1a, 1b forms a two-wire line, with one wire of the two-wire line comprising the signal line 2a, 2b. The other wire of the two-wire line is looped through by the circuit board 6. The measured or control values, for example, are transmitted as the main process variable in analog form as a 4-20 mA signal between the field device and the higher-level unit via the two-wire line. All other data, in particular data relating to parameterization, diagnostics, or similar information, is transmitted via the two-wire line using the HART protocol.The device integrated into the two-wire line allows data transmitted via the HART protocol, especially data transmitted via cable, to also be transmitted wirelessly using electromagnetic waves, for example to a cloud. In this case, the device thus constitutes a field device adapter for wireless data transmission.

[0029] Alternatively, the device can be used in a different manner than described in Fig. 1 In the example shown, the device can also be mechanically attached directly to an (existing) field device, for example by screwing it on. The attachment is preferably made via a screw thread located on the field device housing, which was originally intended for cable entry or strain relief (so-called PG (armored thread)). In this case, the device serves as an adapter (also called a dongle), in particular a Bluetooth adapter, by means of which a field device 7, which was not originally configured for wireless data transmission, can subsequently be retrofitted or supplemented for this purpose.

[0030] The device can also, again deviating from the one described in Fig. 1 The example shown can also be designed as part of the field device 7. In this case, the field device housing has at least one slot-shaped housing opening 5 in at least one section. For example, the field device housing can be designed such that it has at least one outwardly projecting, in particular cylindrical, extension, the contour of which, for example, corresponds to that shown in Fig.1 can correspond to the housing 2 shown and which has at least one slot-shaped opening 5 designed according to the invention.

[0031] Fig. 2 Figure 1 shows a cross-section through a housing 2 of a second embodiment, in which the housing of the device has several slot-shaped openings. Two or four slot-shaped openings 5 ​​in the housing 2 have proven to be particularly preferred. To achieve the most uniform radiation possible from the housing 2, the slot-shaped housing openings 5 ​​can additionally have different lengths L1 to L4, depending on the installation position and / or design of the primary antenna 4, with the following for the length of each slot-shaped housing opening, independent of the other lengths: L = n ⋅ λ / 4 , with: λ = wavelength of the electromagnetic wave that transmits the signals at a frequency of 2.4 GHz, and n ∈ N.

[0032] Fig. 3 Figure 1 shows a schematic representation of a third embodiment of the device according to the invention, in which the housing 2 has a slot-shaped opening 5. To enable the device to be used in potentially explosive atmospheres (so-called Ex areas), the slot-shaped opening 5 is filled with a material other than air, in particular an electrically non-conductive material, e.g., glass. It is self-evident that if the housing 2 has several slot-shaped openings 5, each opening is filled with an electrically non-conductive material. It should be noted that the dielectric constant DK or (material-dependent) relative permittivity of the electrically non-conductive material used for filling must be taken into account when determining the length of the (filled) slot-shaped housing opening.This means that the length L of the (filled) slotted housing opening corresponds to an integer multiple of a quarter wavelength of the determined wavelength divided by the square root of the dielectric constant DK (L = n·λ / (4·√(DK))), preferably an integer multiple of half a wavelength of the determined wavelength divided by the square root of the dielectric constant DK (L = n·λ / (2·√(DK))). Using an electrically non-conductive material with a dielectric constant DK = 4, this results, for example, in a length L = 6.25 cm instead of the previously described length of L = 12.43 cm for an unfilled slotted housing opening. Ceramics with a dielectric constant in the range of approximately 30–40 have proven to be particularly suitable electrically non-conductive materials.

[0033] Additionally or alternatively, as in Fig. 3 The housing is geometrically designed such that at least two outer circumferences of the housing, measured in two large spatial directions, preferably the outer circumferences in each spatial direction of the housing, correspond to an integer multiple of half a wavelength λ / 2 of the electromagnetic wave with which the signals are transmitted. The circumferences are measured or defined such that they each pass through the slot-shaped opening of the housing. Preferably, the circumferences pass through the center point of the respective slot-shaped opening.

[0034] To clarify the in Fig. 3 The perspectivally depicted circumferences U1 and U2 are these in Fig. 4 a) und b) again shown in one plane. From Fig. 4 It becomes apparent that each circumference U1 and U2 passes through the slotted opening 5 of the housing. It is self-evident that if the housing 2 has multiple slotted openings 5, the circumferences are determined such that each circumference passes through each slotted opening 5 of the housing.

[0035] To locally delay the orbital period of a shaft, one or more orbital deceleration elements 10 can be formed on an outer surface of the housing 2, which are designed such that the corresponding revolution is increased. Fig. 3 Two delay elements 10 are attached to the housing surface as examples. The in Fig. 3 The depicted delay elements 10 are designed as groove-shaped elements. However, point-shaped elements or elements made of a different material than the housing 2, in particular a dielectric material or a high-frequency metamaterial, are also conceivable. As shown, appropriate positioning can be used to... Fig. 4 b) It becomes apparent that the circumference is deliberately changed, and in particular increased, in one or more spatial directions. It should be noted that, depending on the structural size of the orbital delay elements, the RF orbital path is typically slightly smaller than the (mechanical) circumference, since the electromagnetic wave partially passes over particularly small structures, and the interaction of the electric and magnetic fields results in a slight overall "shortcut".

[0036] Fig. 5 Figure 1 shows a schematic representation of a fourth embodiment of the device according to the invention, in which, in addition to or as an alternative to the embodiments described above, the circuit board 6 is designed such that the electromagnetic waves are coupled out of or into the circuit board laterally, so that the circuit board serves virtually as a primary antenna. The circuit board is further designed such that the laterally coupled electromagnetic waves are only emitted into or coupled into a near field 8, so that the laterally emitting circuit board 6 only acts as a "complete" antenna in combination with the slot-shaped housing opening 5. As shown in Figure 1, the circuit board 6 is designed to act as a "complete" antenna. Fig. 5 As can be seen, the near field 8 here includes at least an area between the circuit board 6 and a housing surface in which the slot-shaped opening 5 is formed.

[0037] The circuit board can be held in the housing in a position necessary for the slot-shaped opening of the housing by means of appropriate retaining elements, e.g. rails. Bezugszeichenliste

[0038] 1a, 1b Cable 2 Housing 2a, 2b Signal line 3 Electromagnetic waves 4 Primary antenna 5 Slotted housing opening(s) 6 Circuit board 7 Field device 8 Near field 9 Far field 10 Rotation delay element 11 Transmit / receive unit 12 Electrically non-conductive material 13 Cable entry 14 Cable exit L, L1-L4 Length of the slotted housing opening B Width of the slotted housing opening DK Dielectric constant of the electrically non-conductive material or (material-dependent) relative permittivity λ Wavelength of the electromagnetic waves U1, U2 Outer circumferences of the housing

Claims

1. A device for transmitting signals from an at least partially metal housing (2) using electromagnetic waves (3) of a specific wavelength (A) for use in an potentially explosive atmosphere, comprising: A transmitter / receiver unit (11) arranged in the housing (2) for generating and receiving the electromagnetic waves (3), at least one primary antenna (4) arranged in the housing (2) for removing the electromagnetic waves (3) generated by the transmitter / receiver unit (11) and for coupling and transmitting received electromagnetic waves (3) to the transmitter / receiver unit (11), at least one slotted housing opening (5), a PCB (6) arranged inside the housing which is configured as a primary antenna (4) for removing the electromagnetic waves (3) generated by the transmitter / receiver unit (11) and for coupling and transmitting received electromagnetic waves (3) in such a way that the electromagnetic waves (3) are removed from or coupled into the PCB (6) at the side, wherein the PCB (6) is further configured as a primary antenna (4) in such a way that the electromagnetic waves are only removed from or coupled into a near field (8) and are only removed from or coupled into a far field (9) in conjunction with the at least one slotted housing opening (5), wherein the at least one slotted housing opening (5) is filled with an non-conductive material (12) that is not air, so that the slotted housing opening (5), in conjunction with the primary antenna (4), transmits the signals into or out of the housing using the electromagnetic waves (3), wherein the at least one slotted housing opening (5) is configured in such a way that a length (L) of the slotted housing opening (5) is equal to a whole multiple of quarter of the wavelength of the specific wavelength divided by the square root of a dielectric constant DK of the non-conductive material (L = n·λ / (4-√(DK))), preferably a whole multiple of half of the wavelength of the specific wavelength divided by the square root of the dielectric constant (L = n·λ / (2-√(DK))), and wherein the housing (2) is configured in such a way that at least two circumferences (U1, U2) measured in two spatial directions are each equal to a whole multiple of half of the wavelength of the specific wavelength (n·λ / 2), wherein the measured circumferences (U1, U2) each pass through the slotted housing opening (5), preferably a center point of the housing opening.

2. The device as claimed in claim 1, wherein the housing (2), with the exception of the at least one slotted housing opening (5) and possible cable inlets and / or outlets, has a housing form that is externally contained.

3. The device as claimed in one of the preceding claims, wherein the housing (2) has round edges (2a) in the cross-section, preferably a round housing form, at least in one section, wherein the at least one slotted housing opening (5) is arranged in the section.

4. The device as claimed in one of the preceding claims, wherein at least one wave period delay element (10) for delaying a period of the electromagnetic waves (3) is formed on an outer surface of the housing (2).

5. The device as claimed in the preceding claim, wherein the at least one wave period delay element (10) has a grooved or dot-like texture, or is made from a different material from that of the housing, preferably a dielectric material or a high-frequency metamaterial.

6. The device as claimed in one of the preceding claims, wherein the at least partially metal housing (2) is mostly made from a metallic material.

7. The device as claimed in one of claims 1 to 6, wherein the at least partially metal housing (2) is made from a plastic and the housing at least partially has metal cladding, preferably on an inner surface.

8. A field device adapter for wireless data transmission, comprising a device as claimed in one of the preceding claims, wherein an adapter housing of the field device adapter comprises the housing.

9. An automation technology field device, comprising a device as claimed in one of the preceding claims 1 to 7, wherein a field device housing of the field device comprises the housing in at least one section.

10. The field device as claimed in the preceding claim, wherein the section comprises at least one cable gland for the field device.