Patent Publication Number: US-2021195771-A1

Title: Apparatus and process valve assembly

Description:
The invention relates to an apparatus, in particular a control head, positioner and/or sensor controller, for process automation for use in an environment where there is a risk of explosion and where dusts may occur. The dusts mentioned at this point and in the following are especially electrically conductive dusts. The apparatus is an electrical apparatus. 
     The apparatus includes a wall structure that serves as the housing of the apparatus and includes a first wall structure section that defines a first housing inner area. The wall structure further comprises a second wall structure section defining a second housing inner area separate from the first housing inner area. A first circuit arrangement is arranged in the first housing inner area and the first housing inner area is dust-tightly enclosed by the first wall structure section, so that the dusts cannot penetrate into the first housing inner area and the explosion safety of the first housing inner area is ensured by the dust-tight enclosure. 
     From the prior art, apparatuses with a sealed housing inner area are known. In WO 2009/09569 A1, for example, a positioner is described which has a waterproof housing to protect sensitive electrical components. 
     Furthermore, U.S. Pat. No. 7,647,940 B2 describes a valve controller with separate chambers for mechanical and electrical components. 
     For use in an environment where there is a risk of explosion and where dusts, especially electrically conductive dusts, may occur, the object is to design the apparatus in such a way that explosion safety is ensured without restricting the function and/or adaptation possibilities of the apparatus too much. 
     This object is solved by an apparatus according to claim  1 : One or more electrical circuits are arranged in the second inner area of the apparatus and all electrical circuits arranged in the second inner area form an overall intrinsically safe second circuit arrangement, so that even if the dusts penetrate into the second inner area of the apparatus, no explosion-initiating heating and/or sparking is possible by the second circuit arrangement and the explosion safety of the second inner area of the apparatus is ensured by the overall intrinsically safe design of the second circuit arrangement. 
     This results in a device divided into two housing inner areas, with a different type of ignition protection used in each inner area. In the first housing inner area, explosion protection is achieved in particular by the ignition protection type “protection by enclosure Ex t” and in the second housing inner area by an altogether intrinsically safe design of the first circuit arrangement. An altogether intrinsically safe design can also be described as single circuit intrinsic safety. 
     Since the first housing inner area is sealed dust-tight, the first circuit arrangement does not necessarily have to be designed to be altogether intrinsically safe; i.e. the first circuit arrangement can also be designed in such a way that there is a risk of an explosion-triggering short circuit if dust penetrates. In the case of the not altogether intrinsically safe design, a multi-circuit intrinsic safety can be present, i.e. a plurality of intrinsically safe circuits are present. A design that is not altogether intrinsically safe can also be described as existing multi-circuit intrinsic safety. Consequently, the requirements for the first circuit arrangement accommodated in the first housing inner area are lower, so that the first circuit arrangement can also include very complex circuits. In particular, the first circuit arrangement can also include safety barriers, for example a diode and/or a resistor connected as a safety barrier. 
     The requirements for the second circuit arrangement, which is located in the second housing inner area, are higher—here, all circuits must be intrinsically safe as a whole, i.e. such that no explosion-causing heating and/or sparking is possible even if dust is deposited. Accordingly, only simple circuits, such as analog-digital converters or digital-analog converters, which are also intrinsically safe as a whole, are preferably accommodated in the second inner area of the housing. 
     The second inner area of the housing does not have to be dust-tight and/or verified and/or certified for its dust-tightness, and, expediently, it is not. This makes it possible to modify and/or adapt the second wall structure section without major effort; after all, no dust-tightness needs to be guaranteed for the second inner area of the housing and no verification/certification is required in this respect either, so that an adaptation does not involve any major effort. 
     This means that explosion protection can be guaranteed with the inventive apparatus without limiting the function and/or adaptation possibilities too much. 
     Furthermore, according to the invention, an apparatus is provided, in particular a control head, positioner and/or sensor controller, for process automation for use in an area in which there is a risk of explosion and in which dusts can occur, the apparatus comprising a wall structure serving as housing of the apparatus and comprising a first wall structure section defining a first housing inner area and a second wall structure section defining a second housing inner area separated from the first housing inner area, wherein a first circuit arrangement is arranged in the first housing inner area and the first housing inner area is enclosed in a dust-tight manner by the first wall structure section, so that the dusts cannot penetrate into the first housing inner area and the dust-tight enclosure ensures the explosion safety of the first housing inner area, the apparatus having a first circuit board which is part of the first wall structure section and the second wall structure section and separates the first housing inner area from the second housing inner area in a dust-tight manner. 
    
    
     
       Below, exemplary details and embodiments are explained with reference to the figures. 
         FIG. 1  shows a schematic representation of an apparatus and 
         FIG. 2  shows a schematic diagram of a process valve assembly. 
     
    
    
       FIG. 1  shows an apparatus  10 , which here is exemplarily designed as a control head and/or positioner, preferably for controlling a valve drive  20  and/or a valve fitting  30 . Alternatively, the apparatus  10  can also be designed differently, for example, the apparatus  10  can also be a sensor controller; i.e. a device with which sensors are controlled and/or read out. Basically, the apparatus  10  is an electrical device for process automation, which is used in an area where there is a risk of explosion and where dusts, especially electrically conductive dusts, can occur. 
     The apparatus  10  comprises a wall structure  1 . The wall structure  1  serves as housing for the apparatus  10 . The wall structure  1  has a first wall structure section  5  and a second wall structure section  6 . The courses of the two wall structure sections  5  and  6  are marked with dashed lines in  FIG. 1 . 
     The first wall structure section  5  defines a first inner area  11  and the second wall structure section  6  defines a second inner area  12 . The first inner area  11  and the second inner area  12  are separated from each other. In the first inner area  11  a first circuit arrangement  21  is located and in the second inner area  12  a second circuit arrangement  22  is located. 
     Explosion safety in the two housing inner areas  11  and  12  is respectively achieved in a different way: 
     In the first housing inner area  11 , explosion safety is ensured by the first housing inner area  11  being dust-tightly enclosed by the first wall structure section  5 , so that the dusts cannot penetrate into the first housing inner area  11 . 
     This prevents the dusts from penetrating into the first housing inner area  11  and causing a short circuit in the first circuit arrangement  21 , which short circuit could lead to an explosion-causing spark and/or explosion-causing heating. 
     In the first housing inner area  11 , explosion safety is therefore achieved by means of a dust-tight enclosure. 
     In the second housing inner area  12 , however, explosion safety is achieved by an altogether intrinsically safe design of the second circuit arrangement  22 . The second circuit arrangement  22  is formed by all electrical circuits  24  in the second inner area  12 . Due to the altogether intrinsically safe design of the second circuit arrangement  22 , no explosion-causing heating and/or sparking is possible by the second circuit arrangement  22 , even if the dusts penetrate into the second housing inner area  12 . Thus, the explosion safety is achieved in the second inner area of the housing by the altogether intrinsically safe design of the second circuit arrangement  22 . 
     The subdivision into the two housing inner areas  11 ,  12  and the different guarantee of explosion safety in the two housing inner areas  11 ,  12  is advantageous, because the wall structure  1  or the housing of the apparatus can be adapted more simply. 
     Only a part of the wall structure  1 —namely the first wall structure section  5 —must be dust-tight, while the second wall structure section  6  does not necessarily have to be dust-tight. In particular, attachment elements, such as connection elements, which are part of the second wall structure section  6 , can thus be easily adapted, modified or exchanged without having to achieve, verify and/or certify the dust-tightness of the second housing inner area  12 . 
     Complex circuits, for which an altogether intrinsically safe design would be very costly, can be accommodated in the first housing inner area  11 , where they are protected from the electrically conductive dust by the first wall structure section  5  and therefore do not necessarily have to be designed to be intrinsically safe as a whole. 
     Exemplary details of the apparatus  10  are explained below. 
     First, regarding the basic structure and the basic function of the apparatus  10 : 
     The apparatus  10  is in particular an electrical and/or fluidic device that can be handled as a physical unit and has the housing  2 , which is the outer wall of the apparatus  10 . The housing  2  can be a single piece or can consist of several sections, in which case expediently all sections of the housing  2  are firmly connected to each other. The housing  2  is formed by at least a part of the wall structure  1 —in the example shown, by the outer walls of the wall structure  1 . As an example, the housing  2  has a cuboid basic shape. 
     The direction of the width of the apparatus  10  shall also be called x-direction and the direction of the height of the apparatus  10  shall be called z-direction. The direction of the depth (which is perpendicular to the drawing plane) shall be called y-direction. The x-direction, y-direction and z-direction are orthogonal to each other. 
     The apparatus  10  is expediently designed to be mounted on the valve drive  20  and/or the valve fitting  30 . For this purpose, an mechanical interface may be provided on the bottom of the housing  2  (not shown in  FIG. 1 ). 
     As shown in  FIG. 2  the apparatus  10  can, for example, form a process valve assembly  40  together with the valve drive  20  and the valve fitting  30 . For better visibility, the apparatus  10 , valve drive  20 , and valve fitting  30  are shown spaced apart in  FIG. 2 ; tat but in reality the apparatus  10  may be mounted on the valve drive  20  and the valve drive  20  may be mounted on the valve fitting  30 . 
     As an example, the apparatus  10  has a display  3  located on the outside of the housing  2 , in particular a graphic display with which, for example, an operating status of the apparatus  10  can be displayed. 
     Furthermore, the apparatus  10  is expediently adapted to communicate with a (not shown) higher-level controller, for example a programmable logic controller, PLC, in order to receive commands for controlling the valve drive  20  and/or the valve fitting  30  and/or to transmit a feedback signal, for example a sensor value and/or status information, to the higher-level controller. For this purpose, the apparatus  10  comprises one or more communication circuits  25 , which in particular form part of the first circuit arrangement  21 . 
     Furthermore, the apparatus  10  is exemplarily adapted to provide control of the valve drive  20  and/or the valve fitting  30 , especially by means of fluidic signals, in particular on the basis of commands received from the higher-level controller. For this purpose, the apparatus  10  is equipped with a control circuit  27 , e.g. one or more microcontrollers  37 ,  38 , in which in particular an open-loop control model and/or closed-loop control model is stored, which is adapted to the valve drive  20  and/or the valve fitting  30  and which is used for the control. The control circuit  27  is in particular part of the first circuit arrangement  21 . 
     In addition, the apparatus  10  expediently comprises a fluid device  28 , in particular one or more valves, preferably one or more pilot valves, which is controlled by the control circuit  27  and which, on the basis of this control, provides fluid signals for the valve drive  20  and/or the valve fitting  30 . 
     The apparatus  10  has a number of external ports  16 ,  17 , especially fluidic ports. In particular, ports  16 ,  17  may be located on a detachable connection element  7 , which may in particular form part of the housing  2 . Expediently, the ports  16 ,  17  serve to provide a fluidic connection to the fluid device  28 . Via the ports  16 ,  17 , the fluid device  28  can be fluidically connected, for example, to a (not shown) source of pressurized fluid and/or to one or more pressure chambers  47  of the valve drive  20 . In particular, the apparatus  10  is adapted to output fluidic signals for controlling the valve drive  20  and/or the valve fitting  30  via one or more of the ports  16 ,  17 . 
     For example, fluidic signals are output to one or more pressure chambers  47  of the valve drive  20  to set one or more pistons  46  of the valve drive  20  in motion, which in turn sets a drive shaft  48  in rotation. The drive shaft  48  is coupled to a valve member  49  located in a process fluid channel  51 . The control performed by the apparatus  10  can thus change the position of the valve member  49  and thus influence a process fluid flowing through the process fluid channel  51 . 
     Expediently, the drive shaft  48  is further coupled to a shaft  14  of the apparatus  10 , which shaft  14  is located in the first housing inner area  11 . The shaft  14  is in turn coupled with an angle of rotation measuring unit  15  and/or a position indicator  4 , which is expediently located in the first housing inner area  11 . 
     As already mentioned, the inner area enclosed by the housing  2  is divided into a first housing inner area  11  and a second housing inner area  12 . The first housing inner area  11  and the second housing inner area  12  are exemplarily two non-overlapping partial volumes of a total volume enclosed by the housing  2 . According to a preferred embodiment, the first housing inner area  11  and the second housing inner area  12  together represent the total inner area of the housing  2  or the apparatus  10 . Preferably, the first housing inner area  11  represents more than 50% of the total inner area; and the second housing inner area  12  represents more than 20%, 30% or 40% of the total inner area. 
     The first housing inner area  11  is dust-tightly closed by the first wall structure section  5  against the environment of the apparatus  10  and/or against the second housing inner area  12 , especially according to IP6x. 
     Expediently, the two housing inner areas  11 ,  12  are divided into multiple sub-areas  41 ,  42 ,  43 ,  44 ,  45 , e.g. by the second circuit board  32  and/or the third circuit board  33 . For example, the first housing inner area  11  is divided into sub-areas  41 ,  42 ,  43  and the second housing inner area  12  is divided into sub-areas  44  and  45 . 
     The housing inner areas  11 ,  12  are defined by the wall structure sections  5 ,  6 . Expediently, the wall structure sections  5 ,  6  are integral parts of the wall structure  1  or the apparatus  10 . In particular, the wall structure sections  5 ,  6  are respectively not modules and are expediently not removable from each other or from the apparatus  10 . 
     The subdivision into the two housing inner areas  11 ,  12  is made by means of the wall structure  1 , in particular by means of wall elements  8 ,  9  of the wall structure  1  projecting into the inner area of the housing  2 . As an example, the wall structure  1  has the wall element  8  projecting inwards in x-direction from a side wall of the housing  2  and the wall element  9  projecting upwards in z-direction from the bottom wall of the housing  2 , which wall elements  8 ,  9  meet in the inner area of the housing  2 . The wall elements  8  and  9  are expediently each designed bar-shaped. The wall element  8  is aligned with its largest surface perpendicular to the z-direction and the wall element  9  is aligned with its largest surface perpendicular to the x-direction. The wall element  8  and the wall element  9  are each part of the first wall structure section  5  and the second wall structure section  6 . The wall elements  8  and  9  provide a dust-tight separation of the first housing inner area  11  from the second housing inner area  12 . 
     As an example, part of the first wall structure section  5 , in particular the wall element  8 , is formed by a first circuit board  31  arranged in housing  2 . Preferably the first circuit board  31  is also part of the second wall structure section  6 . 
     The first circuit board  31  is aligned horizontally—i.e. in a y-z plane—as an example and runs expediently over the entire width of the volume enclosed by housing  2 . The first circuit board  31  rests on the wall element  9  and is supported by it. As an example, the first circuit board  31  and the wall element  9  form a T-shaped structure. 
     The contact points between the first circuit board  31  and the side wall of the housing  2  and between the first circuit board  31  and the wall element  9  are dust-tight. The first circuit board  31  itself is also dust-tight. 
     The first circuit board  31  has several layers, which are in particular glued together by means of so-called prepregs—i.e. textile fiber-matrix semi-finished products pre-impregnated with resins. Furthermore, the first circuit board  31  has at least one circuit board core—i.e. two copper foils with a prepreg in between. The prepreg or the circuit board core isolates the two housing inner areas  11 ,  12  of the housing from each other, especially in terms of explosion protection. 
     In addition, the circuit board  31  may include one or two outer prepregs and/or outer circuit board cores between which electrical lines are routed. Expediently, these lines are separated by the one or two prepregs and/or circuit board cores in a dust-tight manner from the second inner area  12  and/or the first inner area  11 . The electrical lines run in particular in inner layers of the first circuit board  31 . 
     Expediently, in the first circuit board  31  an electrical line runs, which provides an electrical connection between the first circuit arrangement  21  and the second circuit arrangement  22 . 
     In the following, the first housing inner area  11  will be discussed in more detail: 
     The x-z cross-section of the first housing inner area  11  corresponds to an L (rotated 180 degrees). The first wall structure section  5 , which encloses the first housing inner area  11 , comprises the top wall of the housing  2 , a first (right) side wall of the housing  2 , a section of the bottom wall of the housing  2 , the wall elements  8 ,  9  and a section of a second (left) side wall of the housing  2 . The first housing inner area  11  is dust-tightly sealed according to IP6x. 
     The first housing inner area  11  serves in particular to accommodate the main part of the electrics and electronics of the apparatus  10 . The entire electrics and electronics housed in the first housing inner area  11  shall also be referred to as the first circuit arrangement  21 . 
     The first circuit arrangement  21  comprises one or more communication circuits  25  for communication with an external unit, in particular the higher-level controller. The communication circuit  25  comprises, for example, one or more digital and/or analog interfaces  26 ,  36 , in particular an analog current interface  26 . Furthermore, the first circuit arrangement preferably comprises the control circuit  27 . Expediently, the first circuit arrangement  21  further comprises electrical terminal clamps. 
     As an example, the control circuit  27 , the analog current interface  26  and/or a safety barrier  35  are located on the first circuit board  31 . 
     Expediently, a third circuit board  33 , which runs parallel to the first circuit board  31  as an example, is arranged in the first housing inner area  11 . On the third circuit board  33 , the digital/analog interfaces  36  and/or the angle of rotation measuring unit  15  are arranged. The third circuit board  33  runs exemplarily between the wall element  9  and the first (right) side wall of the housing  2 . 
     The various circuits of the first circuit arrangement  21  each comprise one or more electric circuits  23 . The electric circuits  23  are each designed intrinsically safe, i.e. each of the electric circuits  23  fulfils, by itself, the ignition protection type intrinsically safe (Ex i). As long as no electrically conductive dust penetrates into the first housing inner area  11 , the explosion safety of the first housing inner area  11  is guaranteed. 
     According to a possible embodiment, the first circuit arrangement  21  is not altogether intrinsically safe. For example, the first circuit arrangement  21  can be designed in such a way that potential differences between nodes of different electric circuits  23  can form an explosion-causing spark and/or an explosion-causing heating in case of dust accumulation and short circuit. Furthermore, the first circuit arrangement  21  may include one or more protective barriers  35  which could be bridged by the dust, which in turn would cancel the intrinsic safety and would allow heating and/or sparking caused by an electrical short circuit. The first circuit arrangement  21  can be designed in this way since the penetration of dust is prevented by the dust-tight first wall structure section  5 . Therefore, the risk of dust penetration does not have to be considered when designing the first circuit arrangement  21 . 
     One, several or all of the electrical/electronic functional units contained in the first housing inner area  11 , in particular the first circuit arrangement  21 , are not contained in the second housing inner area  12 . 
     Now to the second housing inner area  12 : 
     The second housing inner area  12  has an exemplarily rectangular x-z cross section. The second housing inner area  12  is enclosed by the second wall structure section  6 , which exemplarily includes a section of the bottom wall of the housing  2 , the wall element  9 , the wall element  8 , a section of the second (left) side wall of the housing  2  and the connection element  7 . 
     The second housing inner area  12 —in contrast to the first housing inner area  11 —does not necessarily have to be dust-tight, especially not according to IP6x, and, as an example, is not. 
     The second housing inner area  12  is used in particular to accommodate the main part, preferably all, of the fluidic functional units of the apparatus  10 . The fluidic functional units in the second housing inner area  12  can altogether be referred to as the fluid device  28 . 
     The fluid device  28  expediently includes one or more valves, for example one or more pilot valves and/or a pressure amplifier or booster. 
     Further, an actuator device  34  and/or a sensor device  29  can be arranged in the second housing inner area  12 . The actuator device  34  is, for example, an electromagnetic or electrodynamic actuator, especially a plunger coil. The sensor device  29  comprises for example a pressure sensor. 
     The second circuit arrangement  22  is located in the second inner area  12  of the housing  2 . The second circuit arrangement  22  comprises all the electrics/electronics located in the second inner area  12  of the housing. In particular, the second circuit arrangement  22  comprises all circuits or electric circuits  24 , which belong to the fluid device  28 , the sensor device  29  and/or the actuator device  34 . 
     For example, the second circuit arrangement  22  comprises a control and/or readout circuit of the actuator device  34 , of the sensor device  29  and/or of the fluid device  28 , for example of one or more valves, in particular pilot valves. 
     The control and/or readout circuit comprises in particular an analog-to-digital converter and/or a digital-to-analog converter. 
     For example, the second circuit arrangement  22  receives analog sensor signals from the sensor device  29 , converts them into digital signals by means of the readout circuit and makes the digital signals available to the control circuit  27  in the first housing inner area  11 , for example via the electrical connection running through the first circuit board  31 . 
     Furthermore, the second circuit arrangement  22  can receive digital control signals from the control circuit  27  via the electrical connection running through the first circuit board  31 , convert these signals into analog control signals by means of the control circuit (of the second circuit arrangement  2 ) and control the actuator device  34  with the analog control signals. 
     As an example, a second circuit board  32  is located in the second housing inner area  12 . On the second circuit board  32 , the second circuit arrangement  22 , the sensor device  29  and/or the actuator device  34  is located. 
     The apparatus  10  has an exchangeable attachment element, in particular a connection element  7 , which is part of the second wall structure section  6 . The attachment element is, for example, a connection plate. 
     As an example, the attachment element is part of the housing  2 —and thus of the outer wall of the apparatus  10 . The attachment element is part of the second wall structure section  6  and separates the second housing inner area  12  from the environment of the apparatus  10 . The attachment element can be detached and replaced by another attachment element. The attachment element is especially non-metallic. 
     Since the second housing inner area  12  does not have to be sealed dust-tight, the requirements for the attachment element are less stringent, so that it can be adapted or modified without any major effort. 
     As an example, the attachment element is designed as a connection element  7  and has one or more fluid ports—here the fluid ports  16  and  17 . Expediently, the attachment element is fastened with a in particular detachable fastener  18 , for example a screw. 
     One, several or all fluidic and/or electrical/electronic functional units contained in the second housing inner area  12 , in particular the second circuit arrangement  22 , the fluid device  28 , the sensor device  29  and/or the actuator  34 , are expediently not contained in the first housing inner area  11 . Expediently, the first wall structure section  5  does not include the attachment element. 
     In the second inner area  12  of the housing, explosion safety is ensured by the second circuit arrangement  22  (which comprises all circuits  24  arranged in the second inner area  12 ) is designed to be altogether intrinsically safe. The “altogether intrinsically safe design” can also be referred to as “single circuit intrinsic safety”. What is meant is that the second circuit arrangement  22  remains intrinsically safe even if the dusts penetrate into the second housing inner area  12 . The risk of sparking or inadmissibly high heating due to electrical short circuits caused by electrically conductive dust is eliminated in this case. 
     This single circuit intrinsic safety can be achieved in several ways. 
     For example, the second circuit arrangement  22  as a whole can be designed like a single intrinsically safe circuit or consist of a single intrinsically safe circuit only. 
     If there is only one single (intrinsically safe) circuit, there is no possibility that penetrated dusts can establish an electrical connection between two (intrinsically safe) circuits and thus cancel the respective intrinsic safety. 
     Furthermore, the single-circuit intrinsic safety of the second circuit arrangement  22  can be achieved by there being no safety barrier, in particular no Zener barrier, no diode acting as a safety barrier and/or no current-limiting resistor acting as a safety barrier, in the second housing inner area  12 . 
     If there is no safety barrier in the second housing inner area  12 , then no safety barrier can be bridged by penetrating electrically conductive currents (which in turn would result in the intrinsic safety being cancelled). 
     At least one safety barrier  35 , in particular at least one Zener barrier, is expediently arranged in the first housing inner area  11 . The safety barrier  35  is electrically connected to the second circuit arrangement  22  and limits a voltage and/or a current of the second circuit arrangement  22 . The electrical connection between the safety barrier  35  and the second circuit arrangement  22  expediently runs through the first circuit board  31 . 
     Furthermore, the single-circuit intrinsic safety can be achieved by the second circuit arrangement  22  being designed in such a way that, during specified normal operation of the second circuit arrangement  22 , the maximum potential difference occurring between two nodes of the second circuit arrangement  22  is below a predetermined threshold value, so that even in the event of a short circuit between two nodes of the second circuit arrangement caused by penetrating dust, no explosion-causing sparking and/or explosion-causing heating, for example by a glow nest, occurs. 
     Preferably all possible potential differences between all possible combinations of nodes are below the threshold. 
     According to a possible embodiment, the second circuit arrangement  22  is not designed to be altogether intrinsically safe. According to another possible embodiment, there is no second circuit arrangement  22  in the second housing inner area  12 . 
     In the following, further aspects and advantages of the apparatus  10 , in particular compared to the prior art, will be discussed in more detail. 
     The prior art is that an explosion-proof apparatus or its housing as well as all attachments that are part of the housing, and thus contribute to the tightness of the housing, are subject to the requirements of the ignition protection type (Ex t) if multiple intrinsically safe circuits are present in the housing and the apparatus is to comply with specific standards for operation in areas with electrically conductive flammable dusts, e.g. IEC/EN 60079-31 and IEC/EN 60079-0. 
     Apparatuses in process automation are often designed for areas where there is a risk of explosion, e.g. according to the ATEX directives and/or IECEx. 
     Areas where there is a risk of explosion are e.g. areas where flammable gases or flammable dusts occur. 
     The environments (zones) for flammable gases or flammable dusts are defined separately; they usually do not occur together. Nevertheless, apparatuses are usually designed for both zones simultaneously in order to keep the number of different designs low. Since both areas must be considered, the design of such apparatuses can be very complex. In addition, an apparatus designed as positioner and/or control head includes fluidic, especially pneumatic, as well as electrical functional units. 
     Typically, such apparatuses are designed with the ignition protection type “protection by housing” (Ex t). Such apparatuses often have several circuits (e.g. supply lines with several control circuits, in particular communication and/or control circuits), which are each designed intrinsically safe (Ex i), but where it is possible that in the presence of electrically conductive dust (e.g. Zone  20 ; Zone  21 ) an electrical short circuit between two intrinsically safe circuits may occur, which in turn may cause sparks and/or heating. For this reason, a defined housing protection type (e.g. IP6x according to IEC/EN 60529) is usually mandatory for such apparatus. 
     A dust-tight design of the housing involves a lot of effort, in particular in the presence of non-metallic housing parts (e.g. seals). To verify the dust-tightness, extensive tests are required under, for example, extended temperature requirements, ageing through storage, UV light tests, impact tests, etc. It is particularly problematic that these extensive tests are also required for modifications to an already verified housing and must be verified by a designated body (approval authority). 
     This considerably limits changes, especially in the fluidic functional units of the apparatus. Those fluidic functional units that form part of the housing must also be dust-tight so that the housing is dust-tight overall. A high degree of flexibility is often desired for these fluidic functional units in particular. For example, the possibility of changing or replacing an attachment element mounted on the outside with another one is desired. Furthermore, it may be desired to change the material of an attachment element that forms part of the housing, for example of a pressure amplifier housing and/or of a cassette for pneumatic functions. However, to ensure a dust-tight design, all such modifications would require the extensive testing described above, especially if non-metallic parts of the housing are involved. 
     Furthermore, it is usually necessary to provide electrical functional units with the pneumatic functional units; for example, circuits for controlling pilot valves and/or pressure sensors. 
     From the point of view of explosion protection, the housing  2  is divided into two parts: a first housing part with the first housing inner area  11  and a second housing part with the second housing inner area  12 . 
     The first part of the housing is subject to the requirements of “protection by housing” and the second part is not. 
     This is achieved by a defined separation of the two housing parts. This is achieved in particular by means of the first circuit board  31 , which can also be described as the main circuit board. A part of this first circuit board makes the partition wall. Furthermore, a part of the first circuit board  31  can also serve as a line feed-through, especially in its inner layers. The upper and lower prepregs or cores of the circuit board  31  then serve as insulation between the housing parts/walls for explosion protection purposes. 
     The electric circuits (an electric circuit from the explosion protection point of view), which run from the first part of the housing into the second part of the housing, are fed through in the inner layers of the circuit board  31 . These fed-through circuits can tolerate a dust accumulation by penetration of electrically conductive dust into the housing  2  without endangering safety. This “one” circuit is then designed intrinsically safe for dust and gas from the point of view of explosion protection and remains so even with the aforementioned dust accumulation. 
     In the first part of the housing there is a (not shown) connection space, for example with electrical terminals. Furthermore, the first part of the housing contains the main part of the electronics, preferably more than 90% of the electronic components of the apparatus. 
     In the first part of the housing, the protection types intrinsic safety (Ex i), encapsulation (Ex i) and/or protection by housing (Ex t) are expediently used. Expediently, the first housing part meets the requirements for non-metallic housing parts in terms of explosion protection (Ex t) and the requirements for shock resistance, for example according to IEC 60079-0 and/or IEC 600079-31. 
     In the second part of the housing, especially pneumatics, for example pilot valves and/or boosters, are located. Furthermore, one or more pressure sensors and/or a displacement measuring unit, for example a potentiometer, can be arranged in the second part of the housing. 
     For the second part of the housing, in particular the protection type that intrinsic safety (Ex i) for gas and dust is fulfilled even when dust is deposited, is used. 
     For the second part of the housing there are expediently no increased requirements for non-metallic housing parts due to intrinsic safety for dust (Ex i). Furthermore, there are no increased requirements for shock resistance and/or UV resistance of the plastics. 
     In summary, this results in an electrical apparatus  10  for the area where there is a risk of explosion with combustible and/or conductive dusts, the apparatus  10  having a housing  2 , which is divided into at least two parts. For the division, expediently the first circuit board  31  is used, which can also be used to feed circuits from the first part of the housing into the second part. The circuit board is part of the electronics. The first part of the housing is preferably subject to the more stringent requirements of IEC/EN 60079-31 in the protection type “protection by housing” (Ex t), whereas these requirements expediently do not apply to the second part of the housing. 
     The second housing part B is expediently only subject to the normal functional requirements of the housing without consideration of the special requirements for non-metallic housing parts. 
     Expediently, only one circuit between the first housing part and the second housing part is designed intrinsically safe in terms of explosion protection for gas and dust. 
     For example, an intrinsically safe circuit can be defined according to the DIN/EN/IEC 60079-11 standard. Preferably, an intrinsically safe circuit can be designed in such a way that no ignition sparks (opening and closing sparks) and no impermissibly high heating according to the temperature class can occur. Expediently, an intrinsically safe circuit is limited in its maximum voltage, the maximum possible current, the maximum possible output power, its effective electrical storage, its internal effective capacity and its internal effective inductance. 
     For example, a single-circuit intrinsically safe circuit arrangement contains only components that are not directly responsible for intrinsic safety. Preferably, none of the components of a single circuit intrinsically safe circuit arrangement has an active and/or designated safety-relevant function. 
     Furthermore, a single-circuit intrinsically safe circuit arrangement preferably does not include any electrical energy storage components such as capacitors or inductors, which would require additional protective elements also present in the circuit to achieve intrinsic safety. The single-circuit intrinsically safe circuit arrangement does not include such protective elements, in particular resistors that limit the maximum discharge current of capacitors and/or clamping diodes (e.g. Zener diodes) that limit the counter-induction and thus voltage increases at an inductor. 
     Finally, a single-circuit intrinsically safe circuit arrangement is expediently designed in such a way that any circuit node of the single-circuit intrinsically safe circuit arrangement can be connected to any other circuit node of the same single-circuit intrinsically safe circuit arrangement without impairing the intrinsic safety and/or the explosion protection of the single-circuit intrinsically safe circuit arrangement.