Patent Publication Number: US-2023160491-A1

Title: Electric field device

Description:
This patent application is the national phase entry into the United States of America of PCT/EP2021/060276, international application filing date Apr. 20, 2021. 
     This patent application claims the benefit and priority of and to German patent application No. 20 2020 102 186.9, filed Apr. 20, 2020. German patent application No. 20 2020 102 186.9, filed Apr. 20, 2020 is incorporated herein by reference hereto in its entirety. PCT/EP2021/060276, international application filing date Apr. 20, 2021, is incorporated by reference hereto in its entirety. 
    
    
     In processes in the chemical and petrochemical industry, the formation of an explosive atmosphere cannot usually be ruled out. In this case, the plant components used, for example electric field devices such as positioners, must meet special explosion protection requirements. In the case of the “Ex d” type of pressure-tight encapsulation, the mode of operation is based on the containment of any explosion that may occur inside the housing, so that a transfer of the explosion to the atmosphere surrounding the housing is prevented. This is achieved by an explosion-proof design of the housing together with flameproof gaps at all openings of the housing, whereby the electrical components that can ignite an explosive atmosphere are enclosed in the housing. The requirements for equipment of the pressure-tight encapsulation type of ignition protection are described in the EN 60079-1 standard. 
     EP 0 866 532 A2 describes a housing for an electrical circuit for use in explosion-hazard areas. A partition provided in the housing divides the latter into an electronics compartment and a terminal compartment. The electronics compartment and the terminal compartment each have a detachable sealed cover member. A flameproof electrical feedthrough is associated with the partition, which feedthrough is electrically connected to electronic boards on the side of the electronics compartment. On the side of the terminal compartment, there is an electrical connection to the terminals and a connection member for an operating unit, which is arranged either at a distance from the location of the housing, or directly on the housing, and is adapted to be rotatable relative to the housing. 
     DE 198 10 350 A1 describes an electric field device of the pressure-tight encapsulation type of ignition protection, which is formed from at least two modules that are coupled both mechanically and electrically. A first module thereof has a terminal compartment for connecting the field device in an explosion-hazard area having a safety barrier arranged therein, and a housing of the pressure-tight encapsulation type of ignition protection. A second module, which has characteristics of a field device of the intrinsically safe ignition protection type, can also be opened in the explosion-hazard area for adjustment and maintenance purposes. The electrical connection between the two modules includes an ignition-proof cored conductor bushing, and the electrical signal connections of the second module are implemented via the cored conductor bushing. 
     EP 2 016 318 B1 discloses a process valve that has a housing assembly with a modular structure for control electronics, i.e. for monitoring, control and/or regulating electronics. According to the requirements of the process valve, the housing assembly is optionally composed of a predetermined limited supply of modules in combination with a cover element which comes in two different types. The respective cover elements are formed with an operating unit, which has a display and operating element, and accommodate the entire control electronics, which control electronics are formed with different circuit boards according to the requirements of the process valve. All modules and the respective cover element can be connected to one another via identical connection points. The housing assembly is connected to a drive housing of the process valve by means of an adapter part. A retaining ring is arranged in the adapter part, which ring enables the housing assembly to rotate relative to the drive housing. 
     It is the object of the invention to improve on an electric field device of the type specified in such a way that the field device can be easily adapted to different space conditions of a process plant, taking into consideration good accessibility, readability and operation as well as simple feed conditions. 
     In a manner known per se, an electric field device of the ignition protection type of pressure-tight encapsulation for use in potentially explosive areas for controlling and/or regulating a valve unit of a process plant, comprises a housing, in which a control unit that comprises electronic components and is used as a monitoring, control and/or regulating unit is arranged. The explosion-proof housing is of a design in accordance with standard EN 60079-1, is provided with seals and has ignition-proof gaps at all openings of the housing, so that pressure-tight encapsulation of the electronic components is ensured, with the result that any possible explosion inside the housing will not affect the surrounding explosive atmosphere. 
     The control unit has a detachable communication connection to an operating unit. The control unit is operationally connected to the operating unit, which can be integrated in the housing, for example, and in particular can comprise display, indicator and/or operating elements. 
     The housing is connected to a drive housing of the valve unit via a mechanical interface. The connection can be made, for example, via a screw connection. 
     The housing has connection feedthroughs via which lines are connected. The connection feedthroughs are preferably in the form of cable glands. The lines are connected to the control unit via a connection interface. For this purpose, the connection interface can be designed with connection terminals, for example. The connection terminals may, for example, be integrated in the control unit, or they may be arranged separately from the control unit. 
     According to the invention, the housing is designed as a housing assembly with a modular structure. The modular structure allows individual housing components to be selectively combined for adapting it specifically to the requirements of the process valve. 
     The modular housing assembly has a first module formed with the mechanical interface for connection to a drive housing. Preferably, the mechanical interface of the first module has holes, for example, through which it can in particular be screwed to the drive housing. Positioning the electric field device directly on the drive housing makes it possible to connect the control unit of the electric field device electrically as well as pneumatically to the drive in a simple manner, with the result that positioning and/or control of the actuator of the valve unit can be performed via the control unit. 
     The first module is formed with connection feedthroughs. If the connection feed-throughs are designed in the form of a cable gland, the lines, in particular cables, can be guided through the cable gland into the interior of the module. If the connection feedthrough is designed in the form of plug-in connections, the lines can be connected thereto. The lines are connected to the control unit via the connection interface. 
     The control unit is secured in the first module and is installed in a stationary manner with respect to the first module. Bidirectional communication with the electric field device is possible via the control unit. On the one side, this is possible via the operating unit, which is adapted to be electrically connected to the control unit. The control unit also has an interface to a control center so that the control unit can be alternatively monitored and/or operated from a position remote from the site of the housing. 
     Communication between the control center and the control unit can, for example, take place via a BUS system. This arrangement is particularly advantageous for systems that are difficult to access, are exposed to particularly harsh environmental conditions or increased vibration stresses. 
     The first module can be mechanically connected to a cover element, selectively either directly or indirectly, in a releasable manner. The direct connection of the first module to the cover element features a housing assembly having a short overall length. Advantageously, the housing assembly in this configuration is of low weight as well as small in size. In particular, the housing has a small axial extent, allowing it to be adapted easily to a process plant where only limited space is available for installation of the electric field device. 
     Indirect connection of the first module to the cover element is made with the interposition of a second module. The modular structure of the housing assembly allows for differently assembled configurations of the housing using a uniform cover element as well as a uniform first module. Thus, in an alternative housing assembly, the first module is connected to the second module, which in turn is connected to the cover element. By using a uniform cover element as well as a uniform first module, which serve as the base body for the different housing assemblies, the modular structure has a simplified arrangement with a small number of housing components. 
     The operating unit is arranged in a fixed position in the second module. The second module is designed to accommodate the operating unit. In particular, the second module can have a recess in which the operating unit is arranged, for example, behind a pressure-resistant viewing window. 
     Furthermore, the second module can have a plurality of connection feedthroughs. The connection feedthroughs can be formed at a plurality of positions in the circumferential direction of the second module. Lines can be connected to the connection feedthroughs, which former are electrically connected to the control unit via the connection interface, which can in particular have connection terminals. 
     The second module is adapted to be secured to the first module in different angular orientations about a longitudinal axis of the electric field device with respect to the first module. The longitudinal axis of the electric field device extends orthogonally to the connection plane of the first and second modules. 
     The first module is secured in a fixed position on the drive housing by means of the mechanical interface. Accordingly, the second module can be secured to the drive housing of the valve unit in different angular orientations relative to the first module and relative to the drive housing. As a result, the positions of the respective connection feedthroughs and the operating unit, which are each arranged in a fixed position relative to the second module, can be optimally adapted to the installation space conditions of the process plant via the different angular orientations of the second module. In this way, the position of the operating unit can be easily adapted to the installation space conditions of the plant, in order to ensure good accessibility, easy readability and easy operation. The same is true for the position of the connection feedthroughs which allow easy adaptation of the feed conditions for the electrical lines to the installation conditions of the plant. 
     According to a preferred embodiment, the control unit comprises a circuit board which is connected to the connection interface in an electrically conductive manner, which connection interface may comprise connection terminals that may be spatially separated from the control unit. For example, the connection terminals of the connection interface may be arranged in the second module that is disposed remote from the first module in which the control unit is mounted. Separating the connection interface from the control unit allows to make efficient use of the space available in the housing. The connection interface can be arranged directly in the first module, for example, and as a result, the first module can advantageously have a compact over-all length. 
     Preferably, the operating unit comprises a support element having a display element, an indicator element and/or an operating element arranged thereon. The support element of the operating unit can be designed, for example, as a PCB or board which is used for mechanically fastening and electrically connecting individual electronic elements of the operating unit, e.g. the display, indicator and/or operating elements. 
     The operating unit is arranged in a stationary manner in the second module and can be used for bidirectional communication of the electric field device via the display, indicator and/or operating elements. The arrangement in a stationary manner with respect to the second module can be achieved, for example, via a screw connection of the support element to the second module. 
     An operating element carried by the support element, for example an operating screw, can pass through the second module, in particular via a recess so as to enable operation of the electric field device from outside the housing, for example. 
     The display and/or indicator element can in particular be arranged in a recess in the second module in a stationary manner. In this case, for instance, the recess can be covered by an inspection window, for example a glass pane, which is connected to the second module in a pressure-tight manner. 
     According to a preferred embodiment, the detachable communication connection between the control unit and the operating unit is made via a connection element, by means of which the support element can be flexibly arranged with respect to the circuit board. The support element, to which the display element, indicator element and/or operating element are attached, is arranged in a fixed position with respect to the second module. By means of the connection element, the support element is flexibly connected to the control unit which is arranged in a fixed position in the first module. The flexibility of the connection between the support element and the circuit board via the connection element allows the control unit to be easily adapted to the angular orientation of the second module with respect to the first module. In other words, the support element, as well as the entire operating unit, can be adapted flexibly to a rotation of the second module about the longitudinal axis of the housing assembly, thus ensuring the positionally fixed arrangement of the operating unit with respect to the second module. 
     Preferably, the connection element is formed as a plug-in connector on the circuit board of the control unit, the circuit board having a plurality of plug-in connectors at various positions. The position of the support element on the circuit board of the control unit can be changed by reconnecting it to the plug-in connectors, which reconnection of the support element is done in such a way that the stationary arrangement of the support element with respect to the second module is ensured in the event of a change in the angular orientation of the second module with respect to the first module. For this purpose, the board reflects the symmetry requirements of the second module by means of the arrangement of the plug-in connectors, so that the positions of the display and/or indicator elements and of the operating element, that are arranged on the support element, can be adapted to the position each of the cutout and the recess of the second module, respectively. By flexibly reconnecting it to differently positioned plug-in connectors of the board of the control unit, the support element of the operating unit can be adapted to the angular orientation of the second module with respect to the first module. 
     In an alternative embodiment, the support element is connected to the circuit board by means of a cable connection. The flexible cable connection enables the support element to be rotated around a wide angular range, in particular of more than 180°, so that in particular also an angular range of up to 360° with respect to the circuit board of the control unit is obtained. In this embodiment, the support element may in particular be connected to the second module in a releasable manner, for example using a screw connection. The support element is arranged in a constant position relative to the second module. Thus, the position of the support element, to which the display, the indicator and/or operating element is mechanically connected, can be changed exclusively via the angular orientation of the second module relative to the first module. 
     According to a preferred embodiment, the first module, the second module and the cover element each have a connection area via which they can each be mechanically connected to one another. The respective connection areas are of defined uniformly, so that the first module can be optionally connected to the second module and to the cover element. In the respective connection areas, the first module, the second module and the cover element are centered in relation to one another in an identical manner and can be connected to one another. 
     Preferably, the respective connection areas have a rotationally symmetrical cylindrical transition, with the respective transitions engaging in one another in such a way that they each have axially abutting surfaces. For example, the transition of the cover element may engage the transition of the first module and/or the second module, with the transition of the respective first or second module radially engaging around the transition of the cover element. In the same way, the transition of the second module may engage the transition of the first module. The respective interengaging transitions are rotationally symmetrical and cylindrical in shape and have axially abutting surfaces in the assembled state of the housing assembly. 
     According to a preferred embodiment, the respective connection areas can be connected to one another via a positive and/or non-positive connection. In this way, the connection can be made by the geometric contact of two active surfaces of the respective connection areas and/or the connection is caused by a system of friction-related forces. 
     Preferably, the connection is made in the axial direction via a screw connection of a pair of holes of the respective connection areas. In particular, the respective connection areas can be connected to one another in a releasable manner via a flange, with a screw connection applying a contact pressure to the flange. A respective connection area can, for example, have a flange face with holes that form a hole pattern. By means of a pair of holes of the hole patterns in the respective flange faces, the housing parts to be connected to one another can be positioned in a centered manner relative to one another. In this case, the angular orientation of the second module relative to the first module depends on the narrowness of the grid of the respective hole patterns. 
     According to a particularly preferred embodiment, the connection area of the second module is continuously adjustable with respect to the connection area of the first module. The respective connection areas of the first module and the second module can, for example, be formed with an external thread which can be screwed into the internal thread of a movable threaded piece, the movable threaded piece being formed, for example, as a union nut. The union nut can, for example, radially embrace the respective connection areas of the first and second modules, and can be fixed to the housing via a shoulder, for example, that is formed on the housing. In this way, the angular orientation of the second module relative to the first module about the longitudinal axis of the electric field device can be adjusted continuously in an advantageous manner so that the operating unit formed on the second module and connection feedthroughs can assume a position that is optimally adapted to the specific installation space of the plant. 
     Preferably, the connection area of the second module has a pattern of elongated holes. In particular, the respective connection areas of the first and second modules can be connected to one another in a releasable manner, via a flange, with the connection area of the second module having a flange face that has a pattern of elongated holes formed in it. This allows continuous adjustment of the angular orientation of the second module relative to the first module. 
     Preferably, the first module has a rotational stop with respect to the second module. A mechanical stop limits the angular orientation of the second module relative to the first module. This makes an angle change of the second module with respect to the first module of nearly 360° possible. In particular, this prevents the cable connection between the control unit and the operating unit from being impaired by overtwisting. 
     According to one embodiment, a position detection sensing means for a position measurement of a valve member position is arranged in the first module. The position detection sensing means may be a magnet whose field strength or field line direction is read by a magnet-sensitive sensor as a function of position. For this purpose, the magnet can be positioned outside the positioner housing and the magnet-sensitive sensor can be positioned inside the positioner, for example, in order to determine a respective position of a valve rod. The position detection sensing means is integrated in the first module, which serves as a base body for the different configurations of the housing assemblies and is arranged immediately adjacent to the drive housing. 
     Preferably, an IP converter is arranged in the first module. The IP converter is electrically connected to the control unit that is used to monitor, control and/or regulate the valve unit. It is used to control the pneumatic drive of the control valve and regulates a discharge pressure as a function of an electrical control signal. 
     Additional advantages, features and possible applications of the present invention will be apparent from the description which follows, in which reference is made to the embodiments illustrated in the drawings. 
    
    
     
       Throughout the description, the claims and the drawings, those terms and associated reference signs are used as are stated in the list of reference signs which follows below. In the drawings, 
         FIG.  1    is an axial longitudinal sectional view of an electric field device according to the invention; 
         FIG.  2    is an axial longitudinal sectional view of an alternative embodiment of an electric field device according to the invention; 
         FIG.  3    is a perspective view of an electric field device according to the invention; 
         FIG.  4    is a perspective view of an electric field device according to the invention with a changed angular orientation of a second module according to  FIG.  3   ; 
         FIG.  5    is a view of an electric field device according to the invention that is arranged on a drive housing of a valve unit; 
         FIG.  6    is a perspective view of an alternative configuration of a housing assembly of an electric field device according to the invention; and 
         FIG.  7    is a perspective axial top view of a first module of an electric field device according to the invention. 
     
    
    
       FIG.  1    is an axial longitudinal sectional view of an electric field device  10 . The electric field device  10  is designed as a positioner  10  for monitoring, controlling and/or regulating a valve unit  14  (not shown here) of a process plant. 
     The electric field device  10  is provided with a housing  12  having a pressure-tight encapsulation for use in potentially explosive atmospheres. The housing  12  is formed as a housing assembly  12  with a modular structure, comprising a first module  16 , a second module  18  and a cover element  20 . The first module  16  can be mechanically connected to the cover element  20  selectively either directly or indirectly in a releasable manner. In the present case, the first module  16  is indirectly connected to the cover element  20  with the interposition of the second module  18 . 
     The connection of the first module  16  to the second module  18  and the connection of the second module  18  to the cover element  20  takes place in a respective connection area  22 ,  24 . Owing to the identical design of each of the connection areas  22 ,  24 , only the connection area  22 , by means of which the first module  16  is connected to the second module  18 , will be described in detail here. 
     In the present case, the connection area  22  has a flange connection  26  that is used to mechanically connect the second module  18  to the first module  16 . A contact pressure is applied to the flange connection  26  via screw connections  28 . The flange connection  26  is formed by the flange face  30  formed on the first module  16  and the flange face  32  formed on the second module  18 . 
     The flange sheets  30 ,  32  each have holes  34  in them that form a hole pattern. Via a pair of holes of the respective hole patterns, the second module  18  can be arranged in different angular orientations relative to the first module  16  about a longitudinal axis A of the positioner  10 , which longitudinal axis A extends orthogonally to the plane connecting the first module  16  to the second module  18 . In the present embodiment, the change in the angular orientation of the second module  18  relative to the first module  16  depends on the narrowness of the grid of the respective hole patterns. 
     As an alternative, it is conceivable that the flange face  32  of the second module  18  has a pattern of elongated holes. This allows almost continuous adjustment of the angular orientation of the second module  18  with respect to the first module  16 . 
     In the connection area  22 , the first module  16  and the second module  18  presently have a rotationally symmetrical cylindrical transition area  36 . In the region of the transition area  36 , the first module  16  and the second module  18  telescope into one another, or in other words, the second module  18  is circumferentially enclosed by the first module  16 . This means that the first module  16  and the second module  18  each have axially abutting surfaces in the transition area  36 , via which the first module  16  and the second module  18  are centered relative to one another. 
     The second module  18  is connected to the cover element  20  in a connection area  24 , which is of identical form as connection area  22 . For example, the connection area  24  has a flange  38  (not shown here) for connecting the second module  18  to the cover element  20 , and a rotationally symmetrical cylindrical transition  40 , each having axially abutting surfaces, with the second module  18  radially engaging around the cover element  20  in the region of the transition  40 . 
     The housing assembly  12  is connected to a drive housing  56  (not shown here) of the process valve (not shown here either) via a mechanical interface formed on the first module  16 . The connection can be made by means of a screw joint, for example. Furthermore, the first module  16  as well as the second module  18  each have connection feedthroughs  44  (not shown here) by means of which lines (not shown here either) are connected. The lines are connected to a control unit  48  via a connection interface  46 . In the present embodiment, the connection interface  46  is implemented with connection terminals  50 , which are mechanically fastened to a support plate  52 . 
     The connection interface  46  arranged in the second module  18  is spatially separated from the control unit  48  mounted in the first module  16 , thus making clever use of the available installation space of the housing assembly. As a result, the first module  16  can be designed to have a compact overall length, for example. 
     The connection interface is connected to the control unit via electrical wiring  53 , which in the present embodiment is assigned to the feedthrough  55  that can be designed to be pressure resistant. For example, owing to a flameproof feedthrough of the electrical signal connection, the ignition protection provided for the enclosed space between the cover element  20  and the second module  18  can be different or lower as compared to the enclosed space between the first module  16  and the second module  18 . 
     In the present embodiment, the control unit  48  comprises a two-piece circuit board  58 , with the two parts being arranged the one above the other. The circuit board  58  is mounted in a fixed position in the first module  16 . It is used as a monitoring, control and/or regulating unit for the valve unit  14  (not shown here). In the present embodiment, the control unit  48  is electrically connected both to an IP converter  74 , which is arranged in the first module  16 , and to position detection sensing means (not shown here) that is also arranged in the first module  16 . 
     The control unit  48  enables bidirectional communication with the electric field device  10 . For this purpose, the control unit  48  has an interface to a control center, which allows the electric field device  10  to be monitored and/or operated from a distance from its installation site. 
     In the present embodiment, bidirectional communication with the control unit  48  is via an operating unit  62  which comprises a support member  64  which has a display, an indicator and/or a control element arranged thereon. In the present embodiment, the display and/or indicator element  66  is arranged behind a pressure-resistant viewing window  68  in a recess  54  in the second module  18 , and the support element  64  has a releasable mechanical connection  70  to the second module  18 , thus ensuring a stationary arrangement of the support element  64  in a constant position with respect to the second module  18 . The support element  64  of the control unit  62  is electrically connected to the control unit  48  via a detachable communication connection, which in the present case takes the form of a cable connection  60 . 
     When there is a change in angle of the second module  18  relative to the first module  16 , the support element  64  and/or the operating unit  62  undergoes the same change in angle, so as to ensure that the position of the operating unit  62  relative to the second module  18  remains unchanged. Because of the flexibility of the cable connection  60 , the support element  64  can rotate nearly 360° with respect to the circuit board  58  of the control unit  48 . A mechanical stop (not shown here) limits the angular orientation of the second module  18  with respect to the first module  16 , in particular to prevent the cable connection  60  from being impaired by overtwisting. 
     In the present embodiment, the position of the operating unit  62 , which comprises the support element  64  and the display and/or indicator element  66 , can be changed exclusively via the angular orientation of the second module  18  relative to the first module  16 , with the position of the operating unit  62  relative to the second module  18  remaining unchanged. This allows the position of the operating unit  62  to be easily adapted to the specific installation space conditions of the plant to ensure good accessibility, simple readability and easy operation. 
     The same is true for the connection feedthroughs (not shown here) of the second module  18 , whose position can be adapted to the specific installation space conditions of the process plant by changing the angular orientation of the second module  20  with respect to the first module  18 . 
       FIG.  2    is an axial longitudinal sectional view of an alternative embodiment of the positioner  10 . The housing assembly  12  comprises the first module  16 , the second module  18  and the cover element  20 , which are each connected to one another via the connection areas  22 ,  24 . The connection areas  22 ,  24  each have a rotationally symmetrical cylindrical transition  36 ,  40 . In the regions of the respective transitions  36 ,  40 , the respective housing components  16 ,  18 ,  20  telescope into one another and each have axially abutting surfaces via which the housing components  16 ,  18 ,  20  are centered relative to one another. 
     In the connection areas  22 ,  24 , the housing components  16 ,  18 ,  20  can be connected to one another, as already described above with respect to  FIG.  1   , for example via a flange  26 ,  38  (not shown here). As an alternative, it is conceivable that the second module  18  is continuously adjustable relative to the first module  16 , in that the first module  16  as well as the second module  18  have an external thread formed in the connection area  22 , which thread can be screwed into an internal thread of a movable threaded piece, for example a union nut. In an advantageous manner, the connection via a rotary joint has a small gap. In particular, the movable threaded piece can radially engage around the connection area  22  and can be secured in place via a shoulder formed on the housing  16 , for example. The continuously adjustable angular orientation of the second module  18  relative to the first module  16  allows the second module  18  to be optimally adapted to the installation space conditions of a process plant by means of rotating it with respect to the first module  16 . 
     As already described with regard to  FIG.  1   , the first module  16  has a mechanical interface  42  for fixing it to a drive housing  56  (not shown here) of a process valve (not shown here either). The first module  16  as well as the second module  18  each have connection feedthroughs  44  (not shown here) which are used to connect lines (not shown here either) that are electrically connected to a control unit  48  of the positioner  10 . 
     The control unit  48 , which is installed in a stationary manner relative to the first module  16 , comprises in particular a two-piece circuit board  58 , as described with regard to  FIG.  1   . The control unit  48  and a support element  64  of the operating unit  62  are connected to one another via a detachable communication connection. In particular, they are connected via a plug-in connector  72  formed on the circuit board  58  which receives the support element  64  to which a display, indicator and/or operating element is attached. The circuit board  58  has a plurality of plug-in connectors  72  in different positions, so that the position of the support element  64  on the circuit board  58  can be changed by replugging. 
     The circuit board  58  reflects the symmetry requirements of the second module  18  via the plug-in connectors  72 , which allows the position of the display and/or display element  66  to be optimally adapted to the position of the recess in the second module  18 . In the case of an angular orientation of the second module  18  with respect to the first module  16 , replugging the support element  64  is done in such a way that the stationary arrangement of the support element  64  with respect to the second module  18  will be ensured. This means that the support element  64  is replugged in such a way that the display and/or indicator element  66  of the operating unit  62  remains arranged behind a pressure-resistant viewing window  68  in a recess of the second module  18 . In addition to being connected to the circuit board  58  by means of a plug-in connection  72 , the support element  64  may be connected to the second module  18  by means of a mechanical connection  70 . 
       FIG.  3    is a perspective view of an electric field device  10  according to the present invention, which is configured as a positioner  10  and comprises a housing assembly  12  with a modular structure having a first module  16 , a second module  18  and a cover element  20 . 
     The first module  16  has a mechanical interface  42 , via which it can be connected in a stationary manner to a drive housing  56  (not shown here) of a process valve. 
     The first module  16  as well as the second module  18  have connection feedthroughs  44 , to which lines (not shown here) can be connected which serve to electrically connect the positioner  10  to a drive of the process valve. In the circumferential direction, the second module  18  has a plurality of terminal feedthroughs  44 . 
     Furthermore, the second module  18  has a viewing window  68  which is provided with a pressure-resistant glass pane, for example, behind which a display and/or indicator element  66  of an operating unit  62  is located that is arranged in a stationary manner with the second module  18 . In the present embodiment, the operating unit  62  also has an operating element  65 , for example an operating screw  65 , which passes through the second module  18  and which can be used to operate the electric field device  10  from outside of the housing  12 . 
     In the present embodiment, the first module  16  is indirectly connected to the cover element  20  with the second module  18  interposed therebetween. The connection of the respective housing components  16 ,  18 ,  20  is made in a respective connection area  22 ,  24 . The respective connection areas  22 ,  24  are uniformly defined, so that the first module  16  can be connected to the cover element  20  selectively either indirectly, via the second module  18 , or directly to the cover element  20 . For this purpose, in the present embodiment, the connection areas  22 ,  24  each have a flange  26 ,  38  via which the respective housing components  16 ,  18 ,  20  are connected to one another in a releasable manner. The flanges  26 ,  38  have bores  34  for screw connections  28 , via which a contact pressure is applied to the respective flange  26 ,  38 . 
     It is apparent from the view of  FIG.  4    that the second module  18  of the housing assembly  12  can be fixed relative to the first module  16  in different angular orientations about the longitudinal axis A, with the longitudinal axis A extending orthogonally to the plane connecting the first module  16  to the second module  18 . This means that the second module  20  can be axially aligned with respect to the first module  18  at different rotational angles, as can be seen from a comparison of the views of  FIGS.  4  and  3   . 
     In particular, the connection region  22  has a flange  26  for connecting the first module  16  to the second module  18 . The flange  26  has flange faces  30 ,  32  formed on the first module  16  and the second module  18 , respectively. The respective flange faces  30 ,  32  have holes  34  that form a hole pattern. The first module  16  and the second module  18  are centered relative to each other via a pair of holes of the hole patterns of the respective flange faces  30 ,  32 . The angular orientation of the second module  18  relative to the first module  16  can be varied via the pair of holes of the flange  26 , the change in angular orientation being dependent on the narrowness of the grid of the respective hole patterns of the flange faces  30 ,  32 . In the present embodiment, the second module  18  is rotated, for example, by 90° about the longitudinal axis A relative to the second module  18  shown in  FIG.  3   . This allows the angular orientation of the second module  18  relative to the first module  16  about the longitudinal axis of the electric field device  10  to be adjusted in an advantageous manner, with the result that the operating unit  62  formed on the second module  18  and connection feed-throughs  44  can assume a position that is optimally adapted to the available installation space of the plant. 
       FIG.  5    is a view of the positioner  10  shown in  FIG.  3    and  FIG.  4    in an arrangement with a drive housing  56  of a drive of a valve unit  14 . The housing assembly  12  with a modular structure shows the first module  16  that is connected to the second module  18  via the flange  26 , which second module  18  in turn is connected to the cover element  20  via the flange  38 . 
     The first module  16  is provided with a mechanical interface  42  that is used for connection to the drive housing  56 . In particular, this connection can be made via a screw connection. Integrated in the first module  16  are the IP converter  74  for controlling the discharge pressure and the position detection sensing means for detecting the actuator position of the valve unit  14 . These components communicate with the control unit  48  for positioning and/or controlling the actuator of the valve unit  14 . The first module  16  as well as the second module  18  comprise connection feed-throughs  44 , via which lines (not shown here) are connected, for an electrical connection of the positioner. 
     In addition to the connection feedthroughs  44 , the second module  18  has an operating unit  62  that has a display element, an indicator element and/or operating element. The display element and/or the indicator element is arranged in a recess in the second module  18 , behind a pressure-resistant viewing window  68 . The positioner  10  can be operated from outside of the housing  12  via the operating element  65  of the operating unit  62 . 
     The first module  16  is secured to the actuator housing  56  in a stationary position via the mechanical interface  42 . The second module  18  can be fixed in different angular orientations about the longitudinal axis A relative to the first module  16  and, consequently, relative to the drive housing  56 . As a result, the positions of the respective connection feedthroughs  44  and of the operating unit  62  or of the display, indicator and/or operating elements  66 ,  65 , which are each arranged in a stationary manner relative to the second module  18 , can be optimally adapted to the specific installation space of the process plant via the different angular orientations of the second module  18 . This allows the position of the operating unit  62  to be easily adapted to the specific installation space of the plant, in order to ensure good accessibility, simple readability and easy operation. The same is true for the position of the connection feed-throughs  44  by means of which the supply conditions of the electric lines can be easily adapted to the installation conditions of the plant. 
     In  FIGS.  1  to  5   , the electric field devices  10  according to the invention each have a housing assembly  12  in which the first module  16  is mechanically connected indirectly to the cover element  20  with the interposition of the second module  18 . 
       FIGS.  6  and  7    each are a perspective view of an alternative configuration of the housing  12  of the positioner  10 , using a uniform first module  16  as well as a uniform cover element  20 . The first module  16  as well as the cover element  20  both serve as base bodies for the respective different configurations of the housing assembly  12 . Due to the fact that the first module  16 , the second module  18  and the cover element  20  each have uniformly defined connection areas  22 ,  24  via which they can be connected to one another, the first module  16  can be directly connected to the cover element  20 , as is shown in  FIG.  6   . 
     In the present embodiment, the connection area  22  of the first module  16  and the connection area  24  of the cover element  20  are centered in relation to one another. The connection areas  22 ,  24  each have a flange face  30 ,  76  with holes that form a hole pattern. Via a pair of holes of the respective hole patterns, the flange faces  30 ,  76  are screwed together in the present case. 
     Advantageously, the present configuration of the housing assembly  12  comprising the first module  16  and the cover member  20  has a simplified arrangement with a reduced number of housing components  16 ,  20 . As a result, the positioner  10  is smaller in size, in particular has a smaller axial extent. Due to the short overall length of the present housing  12 , the positioner  10  can be easily adapted to a process plant which only has a small installation space available, for example. The positioner is connected to a drive housing  56  of a valve unit  14  via the mechanical interface  42  formed on the first module. The positioner is electrically connected to a drive of the valve unit via connection feedthroughs  44  (not shown here) that are also formed on the first module  16 . 
       FIG.  7    is a perspective axial top view of the first module  16  of the housing  12  according to  FIG.  6   . 
     The IP converter  74  (not shown here) for controlling the discharge pressure, the position detection sensing means (not shown here either) for detecting the actuator position of the valve unit  14 , and the control unit  48  are all arranged in the first module  16 . 
     The control unit  48  is arranged in a stationary manner relative to the first module  16 . In the present embodiment, it has a PCB or board  58 , which is in particular mounted in the first module  16 . Plug-in connectors  72  are arranged on the circuit board  58 , via which the support element  64  of the operating unit  62  can be electrically connected to the control unit  48 . The positions of the plug-in connectors  72  reflect the symmetry of the bores of the flange face  30  and thus the symmetry requirements of the second module  18 . In the present configuration of the housing  12  of the positioner  10 , the support element  64  or the operating unit  62  and the second module  18  are eliminated. 
     For bidirectional communication with the electric field device  10 , the control unit  48  includes an interface to a control center. The control center can be electrically connected to the control unit  48  via the connection interface  46 , which is formed separately from the control unit  48 . For this purpose, the connection interface  46  of the present embodiment has connection terminals  50  which are attached to a support plate  52 . The support plate  52  can, for example, be mounted in a stationary manner in the first module  16 . 
     Communication between the control center and the control unit  48  is done via a BUS system, for example. This for example allows the control unit  48  to be monitored and/or operated from a distance from the installation location of the housing  12  of the electric field device  10 . The present arrangement of the electric field device  10  is advantageous, for example, for process plants that are difficult to access, are exposed to particularly harsh environmental conditions or to increased vibration loads. 
     LIST OF REFERENCE SIGNS 
       10  electric field device 
       12  housing 
       14  valve unit 
       16  first module 
       18  second module 
       20  cover element 
       22  connection area 
       24  connection area 
       26  flange 
       28  screw connection 
       30  flange face 
       32  flange face 
       34  bores 
       36  transition area 
       38  flange 
       40  transition area 
       42  interface 
       44  connection feedthroughs 
       46  connection interface 
       48  control unit 
       50  terminals 
       52  support plate 
       53  electrical wiring 
       54  recess 
       55  feedthrough (optionally pressure-resistant) 
       56  drive housing 
       58  two-piece circuit board 
       60  cable connection 
       62  operating unit 
       64  support element 
       65  operating element 
       66  display and/or indicator element 
       68  viewing window 
       70  mechanical joint 
       72  plug-in connector 
       74  IP converter 
       76  flange face