Abstract:
A positioner includes: an explosion proof container containing, in an interior space, an electric circuit module and an electropneumatic converter converting, into pneumatic signals, electric signals processed by the electric circuit module; and a pneumatic amplifier, provided outside of the explosion proof container, amplifying the pneumatic signal converted by the electropneumatic converter. The explosion proof container is formed with air flow paths for the air fed into the pneumatic amplifier and the air fed out of the pneumatic amplifier, in a thick portion between inner and outer wall faces of the container that encompasses the surrounding of the interior space. The air flow paths are formed along an inner wall face of the explosion proof container. The inner wall face of the explosion proof container where on the air flow path is formed is arc-shaped or a shape that uses many curved faces of free curve shapes.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2013-224588, filed on Oct. 29, 2013, the entire content of which being hereby incorporated herein by reference. 
       FIELD OF TECHNOLOGY 
       [0002]    The present invention relates to a positioner for driving a regulating valve by converting an inputted electric signal into a pneumatic pressure signal. 
         [0003]    Conventionally, for this type of positioner there have been known positioners such as illustrated by the block diagram of the internal structure thereof, in  FIG. 11 . See, for example, Japanese Unexamined Patent Application Publication No. H9-242706. In this figure:  1  is an I/F (interface) terminal;  2  is an electric circuit module that is structured from a CPU (Central Processing Unit), a memory and the like,  3  is an electropneumatic converter;  4  is a pilot relay (pneumatic amplifier) for amplifying the nozzle back pressure PN from the electropneumatic converter  3  and supplying it, as the output air pressure Po, to the regulator valve  200 ; and  5  is an angle sensor for detecting the operating position of the regulator valve  200  and feeding it back to the CPU of the electric circuit module  2 , where a positioner  100  ( 100 B) is structured therefrom. 
         [0004]    The electropneumatic converter  3 , as illustrated in  FIG. 12 , for example, is structured from: a permanent magnet  6 ; yokes  7 - 1  and  7 - 2 ; a coil  8  that is disposed between the yokes  7 - 1  and  7 - 2 ; a flapper (armature)  10  that passes through the center of the coil  8 , through disposal in the space facing the yokes  7 - 1  and  7 - 2 , while maintaining an appropriate gap therebetween, with the tip end portion thereof supported, so as to be able to incline freely, by a supporting point spring (leaf spring)  9  on the yoke  7 - 1 ; a spring (for biasing)  12 - 1 , provided between the top face of the flapper  10  and an upper stationary end  11 - 1 ; and a spring (for zero adjustment)  12 - 2 , provided between the bottom face of the flapper  10  and an adjusting screw  13  that is screwed into a lower stationary end  11 - 2 , wherein a nozzle  14  is in proximity to, and faces, the bottom face of the tip end of the flapper  10 . Air of an air pressure (supply air pressure) Ps is supplied, from an air pressure supplying source, through a fixed constriction  15  to the nozzle  14 . 
         [0005]    In a positioner  100 B that is structured in this way, when an input electric signal IIN (between 4 and 20 mA) is provided from a controller  300 , that is, when the input electric signal IIN is applied to the I/F terminal  1  from the controller  300 , the CPU of the electric circuit module  2  performs control calculations from the input electric signal IIN and from the feedback signal IFB, detected by the angle sensor  5 , to apply, to the electropneumatic converter  3 , an electric current I 1  depending on the result thereof. The electric current I 1  is applied to the coil  8  of the electropneumatic converter  3 , to vary the magnetic field thereof, and thus the flapper  10  rotates in the direction of the nozzle or in the direction opposite from the nozzle. 
         [0006]    Because of this, the distance of separation between the nozzle  14  and the flapper  10  changes, changing the back pressure (nozzle back pressure) PN of the nozzle  14 . The nozzle back pressure PN, after being amplified by the pilot relay  4 , is supplied as the output air pressure Po to the regulator valve  200 , where the opening of the regulator valve  200 , that is, the process flow rate, is controlled thereby. Moreover, the opening of the regulator valve  200  is detected by the angle sensor  5 , and returned, as the feedback signal IFB, to the CPU of the electric circuit module  2 . 
         [0007]    This positioner  100 B is required, under explosion proof standards, to have adequate explosion proof performance, so as to enable use in an explosive gas environment. Because of this, the I/F terminal  1 , the electric circuit module  2 , the electropneumatic converter  3 , the angle sensor  5 , and the like are contained within an explosion proof container. The state of containment, in the explosion proof container, of the I/F terminal  1 , the electric circuit module  2 , the electropneumatic converter  3 , the angle sensor  5 , and the like, in the positioner  100 B, is illustrated in  FIG. 13 . 
         [0008]    In  FIG. 13 ,  16  is the explosion proof container, where the terminal block  17  that structures the I/F terminal  1 , the electric circuit module  2 , the electropneumatic converter  3 , and the angle sensor  5  are contained within this explosion proof container  16 . Note that in  FIG. 13 , the electropneumatic converter  3  is secured to the back portion of the interior surface of the explosion proof container  16 , where the detailed structure is illustrated in  FIG. 12 , and only the structures of the critical portions are illustrated here. Moreover, in  FIG. 13 , the pilot relay  4  is secured to the outside of the explosion proof container  16 , where air, of the supply air pressure Ps, is applied through a reduction valve  401  to the electropneumatic converter  3  and the pilot relay  4 . In addition, the angle sensor  5  detects the degree of opening of the regulator valve  200 , through a feedback lever  18 .  402  and  403  are pressure gauges,  19 - 1  and  19 - 2  are flame arrestors,  20  is an Auto/Manual switch,  21  is a connector for connecting the electric circuit module  2  and the electropneumatic converter  3 , and  22  is an O-ring. 
         [0009]    Moreover, the explosion proof container  16  is formed with air flow paths such as a flow path L 1  through which flows air of the supply air pressure Ps, a flow path L 2  through which flows air of the nozzle back pressure PN, a flow path L 3  through which flows air of the output air pressure Po, and the like, and the pilot relay  4  is provided with, for example, a poppet valve  23 , a valve driving member  24  for driving the poppet valve  23 , diaphragms  25  and  26  for holding the valve driving member  24 , and the like. 
         [0010]    In this positioner  100 B, air of the supply air pressure Ps is provided to a supply air pressure chamber  27  of the pilot relay  4  through the flow path L 1  of the explosion proof container  16 , where the nozzle back pressure PN is guided to an input air pressure chamber  28  of the pilot relay  4  through the flow path L 2  of the explosion proof container  16 . When the nozzle back pressure PN increases, the diaphragms  25  and  26  move in the direction of the arrow A, pressing the valve driving member  24  downward. As a result, the poppet valve  23  is pushed down, opening a through hole  29  in the surface of the supply air pressure chamber  27 , increasing the output air pressure Po on the regulator valve  200 . When the nozzle back pressure PN decreases, the diaphragms  25  and  26  move in the direction of the arrow B, pushing the valve driving member  24  upward. As a result, the poppet valve  23  is pushed upward, closing the through hole  29  in the surface of the supply air pressure chamber  27 , reducing the output air pressure Po that is outputted to the regulator valve  200 . 
         [0011]    However, in the structure illustrated in  FIG. 13 , the flow path resistance is increased, having a deleterious effect on the dynamic characteristics of the positioner, due to the air flow path that is provided separately, to the outside of the interior space of the explosion proof container, being in the form of a pipe, in combination with a straight line and a 90-degree bend. Moreover, in this structure the explosion proof container and the pneumatic circuit area are structured completely independently and separately, causing the efficiency of the distribution of the various elements within the positioner to be poor, and there are also limitations on the exterior shape, and thus there is a problem in that there is little freedom in the exterior visual design, and the exterior shape is large. 
         [0012]    Note that in the pilot relays there are the single-action type wherein, for a single nozzle back pressure PN, a single output air pressure Po is outputted, and a double-action type wherein, for a single nozzle back pressure PN, two different output pressures Po1 and Po2 are outputted. See, for example, Japanese Unexamined Patent Application Publication No. 2012-207746. In the double-action pilot relay, when the regulator valve is caused to undergo forward operation, the output air pressure Po1 is caused to be higher than Po2, and when undergoing reverse operation, the output air pressure Po2 is higher than Po1. While  FIG. 13  shows the structure for the case of a single-action pilot relay, a double-action pilot relay would require two air flow path systems adjacent to the explosion proof container, and thus the interior shape would be larger than that of the single-action type and the pneumatic circuit structure would also be more complex, making the exterior visual design more difficult, when considering design properties, and causing the combination of the straight line and the 90° bend in the pneumatic circuit to have a complex structure, further increasing the flow path resistance, and having a deleterious impact on the controllability of the positioner. 
         [0013]    The present invention was created in order to solve such problems, and an aspect thereof is to provide a positioner having an explosion proof container structure that is able to reduce the flow path resistance of the pneumatic circuit along with increasing the freedom in the exterior visual design, while increasing the efficiency of the placement of the various elements within the positioner. 
       SUMMARY 
       [0014]    The present invention, in order to achieve the aspect set forth above, a positioner for driving a regulator valve by converting an inputted electric signal into a pneumatic signal, includes: an electric circuit module that processes electric signals; an electropneumatic converter that converts, into pneumatic signals, electric signals that have been processed by the electric circuit module; an explosion proof container that contains, in an interior space, the electric circuit module and the electropneumatic converter; and a pneumatic amplifier, provided outside of the explosion proof container, that amplifies the pneumatic signal converted by the electropneumatic converter. The explosion proof container is formed with air flow paths for the air that is fed into the pneumatic amplifier and the air that is fed out of the pneumatic amplifier, in a thick portion between an inner wall face and an outer wall face of the container that encompasses the surrounding of the interior space. The air flow paths are formed along an inner wall face of the explosion proof container. The inner wall face of the explosion proof container where on the air flow path is formed is arc-shaped or a shape that uses many curved faces of free curve shapes. 
         [0015]    In this invention, air flow paths are formed along an inner wall face that is shaped as an arc, for example, in a thick portion between the inner wall face and the outer wall face of the explosion proof container. In this case, the entirety of the inner wall face need not necessarily be formed in arc shapes. That is, only one portion need be formed as an arc shape, with the air flow path formed along with the inner wall face that is formed as the arc shape. This reduces the curves in the air flow path in the explosion proof container, causing the air flow path to be smooth, producing a flow path shape wherein there is little variation in the cross-sectional area, thereby reducing the flow path resistance. 
         [0016]    Note that, in the present invention, the air flow path is provided with a resonator that reduces the flow path resistance before or after a part wherein the flow path resistance is large, such as a part with a sharp bend such as being bent at a right angle or being bent back sharply, a part wherein there is a rapid change in cross-sectional area, a part wherein there is a small cross-sectional area, or the like. For example, the cross-sectional area of the flow path can be secured, and the flow path resistance can be reduced, through the provision of an air reservoir as a resonator in the air flow path. 
         [0017]    Because, in the present invention, the air flow paths are formed along the interior wall face in arc shapes or in shapes that use many free curve-shaped curved faces, in a thick portion between the inner wall face and the outer wall face of the explosion proof container, that is, because the explosion proof container is integrated with the pneumatic circuit parts as a two-layer structure, the efficiency with which the various components within the positioner are disposed can be increased, and the flexibility in the external visual design can be increased as well. For example, the outer wall face of the explosion proof container may be used as one portion of the exterior shape of the positioner, and the exterior shape of the positioner can be formed in a streamlined shape, making it possible to both reduce the flow path resistance and improve the external visual design. 
         [0018]    Because, in the present invention, the airflow paths are formed along the interior wall face in arc shapes or in shapes that use many free curve-shaped curved faces, in a thick portion between the inner wall face and the outer wall face of the explosion proof container, the flow path resistance is low and the flexibility for the exterior visual design is high in the explosion proof container, enabling a reduction in the flow path resistance and an improvement in the external visual design, and also enabling a reduction in the exterior size. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0019]      FIG. 1  is an exterior perspective diagram illustrating an example of a positioner according to the present invention. 
           [0020]      FIG. 2  is a diagram illustrating the state wherein the cover, provided on the front face of the positioner, has been removed. 
           [0021]      FIG. 3  is a block diagram illustrating the interior structure of this positioner (a positioner that uses a double-action pilot relay). 
           [0022]      FIG. 4  is a diagram illustrating the structure of the double-action pilot relay in this positioner. 
           [0023]      FIG. 5  is a diagram wherein the positioner, illustrated in  FIG. 1 , is viewed from the back. 
           [0024]      FIG. 6  is a diagram illustrating the explosion proof container of the positioner alone, viewed from the back. 
           [0025]      FIG. 7  is a diagram illustrating the air inlet portion for the supply air pressures Ps1 and Ps2 in the explosion proof container. 
           [0026]      FIG. 8  is a diagram illustrating the air inlet portion for the supply air pressures Ps1 and Ps2 in the explosion proof container. 
           [0027]      FIG. 9  is a diagram illustrating the air outlet portion for the output air pressure Po1 in the explosion proof container. 
           [0028]      FIG. 10  is a diagram illustrating the air outlet portion for the output air pressure Po2 in the explosion proof container. 
           [0029]      FIG. 11  is a block diagram illustrating the interior structure of a positioner that uses a single-action pilot relay. 
           [0030]      FIG. 12  is a diagram illustrating details of the electropneumatic converter in the positioner. 
           [0031]      FIG. 13  is a vertical sectional diagram of a conventional positioner. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Examples according to the present disclosure will be explained below in detail, based on the drawings. 
         [0033]      FIG. 1  is an exterior perspective diagram illustrating an example of a positioner according to the present invention. In this positioner  100  ( 100 A), the exterior shape is of a streamlined shape, with a distinctive exterior visual design that has not existed heretofore. 
         [0034]      FIG. 3  shows a block diagram of the interior structure of this positioner  100 A. In  FIG. 3 , the structural elements that are identical or equivalent to the structural elements explained in reference to  FIG. 11  are indicated by codes that are identical to those of  FIG. 11 , and explanations thereof are omitted. 
         [0035]    In this positioner  100 A, a double-action pilot relay, defined as pilot relay  4 , is used. This double-action pilot relay  4  has two output ports, where if the regulator valve  200  is undergoing forward operation, the output air pressure Po1 of the first output port P1 is higher than the output air pressure Po2 of the second output port P2, and when undergoing reverse operation, the output air pressure Po2 of the second output port P2 is higher than the output air pressure Po1 of the first output port P1. 
         [0036]    In this positioner  100 A, the I/F (interface) terminal  1 , the electric circuit module  2 , the electropneumatic converter  3 , and the angle sensor  5  are contained within the interior space of the case  101  ( FIG. 1 ). That is, an explosion proof container is used for the case  101  (where, in the below, the case  101  will be termed an “explosion proof container”), where the I/F (interface) terminal  1 , the electric circuit module  2 , the electric pneumatic converter  3 , and the angle sensor  5  are contained within this explosion proof container  101 . 
         [0037]    In this explosion proof container  101 , a cover  102  is attached to the front face thereof, and, as illustrated in  FIG. 2 , when this cover  102  is removed, the main cover  104 , which is a portion of the explosion proof container  101 , is visible. Moreover, a cover  103  is attached to the back face of the explosion proof container  101 , where the double-action pilot relay  4  is attached in the space that is covered by this cover  103 . 
         [0038]    A structure of a double-action pilot relay  4  is illustrated in  FIG. 4 . In this figure,  41  is a housing, where an input air pressure chamber  42 , a first supply air pressure chamber  43 , a second supply air pressure chamber  44 , a first output air pressure chamber  45 , a second output air pressure chamber  46 , a first discharge air chamber  47 - 1 , a second discharge air chamber  47 - 2 , and a biasing chamber  48  are provided within the housing  41 . 
         [0039]    In this housing  41 , the first discharge air chamber  47 - 1  is adjacent to the first output air pressure chamber  45  with a first diaphragm  49 - 1  interposed therebetween, and adjacent to the biasing chamber  48  with a second diaphragm  49 - 2  interposed therebetween. Moreover, the input air pressure chamber  42  is adjacent to the bias chamber  48  with a third diaphragm  49 - 3  interposed therebetween, and adjacent to a second discharge air chamber  47 - 2  with a fourth diaphragm  49 - 4  interposed therebetween. Moreover, the second discharge air chamber  47 - 2  is adjacent to the second output air pressure chamber  46  with a fifth diaphragm  49 - 5  interposed therebetween. The first through fifth diaphragms  49 - 1  through  49 - 5  are provided between the housing  41  and a spool (movable body)  50 , where the spool  50  is supported by these first through fifth diaphragms  49 - 1  through  49 - 5  so as to be able to move in the direction of the arrow A and in the direction of the arrow B. 
         [0040]    The spool  50  has a first opening  50   a  that is located at the first output air pressure chamber  45 , a second opening  50   b  that is located at the second output air pressure chamber  46 , a first discharge air duct  50   c   1  for connecting a first opening  50   a  to the first discharge air chamber  47 - 1 , and a second discharge air duct  50   c   2  for connecting a second opening  50   b  to the second discharge air chamber  47 - 2 . In the spool  50 , the first discharge air duct  50   c   1  and the second discharge air duct  50   c   2  are divided by a non-duct portion  50   d.    
         [0041]    Moreover, at the end portion on one side of the housing  41 , a duct  51  wherein the opening portion  51   a  thereof faces the outside of the housing  41  is provided as a first poppet valve assembly installing portion  52 , and at the end portion on the other side of the housing  41 , a duct  53  wherein the opening portion  53   a  thereof faces the outside of the housing  41  is provided as a second poppet valve assembly installing portion  54 . 
         [0042]    A first poppet valve assembly  55  is installed slidably, along the inside wall face of the duct  51 , from the opening portion  51   a  of the duct  51  that faces the outside of the housing  41  into the first poppet valve assembly installing portion  52 , where the space remaining at the bottom portion of the duct  51  is defined as the first output air pressure chamber  45 . A second poppet valve assembly  56  is installed slidably, along the inside wall face of the duct  53 , from the opening portion  53   a  of the duct  53  that faces the outside of the housing  41 , into the second poppet valve assembly installing portion  54 , where the space remaining at the bottom portion of the duct  53  is defined as the second output air pressure chamber  46 . 
         [0043]    The first poppet valve assembly  55  is a divided structure of a cylindrical pipe seat portion  57  and a cylindrical column seat retaining portion  58 , having the seat portion  57  attached removably to the front face thereof, where an interior space  59  is formed between the seat portion  57  and the seat retaining portion  58 . A first connecting hole  57   b  for connecting between the interior space  59  and the first output air pressure chamber  45  is formed in the top face  57   a  of the seat portion  57 . This top face  57   a  of the seat portion  57  fulfills the role as a first dividing wall for partitioning between the first supply air pressure chamber  43  and the first output air pressure chamber  45 . 
         [0044]    A first spring  60  is contained in the interior space  59  between the seat portion  57  and the seat retaining portion  58 , where the first poppet valve  61  is held between the seat portion  57  and the seat retaining portion  58  in a state wherein the first spring  60  is stressed. The interior space  59  is connected to the first supply air pressure chamber  43 . The first poppet valve  61  has a discharge air valve  61   a  at the tip end portion thereof, and a supply air valve  61   b  to the rear of the discharge air valve  61   a . Moreover, the first poppet valve  61  has a through hole  61   c  that passes through the axis thereof. 
         [0045]    In this held state, the first poppet valve  61  penetrates through the first connecting hole  57   b  that is formed in the seat portion  57 , and is biased by the first spring  60  so as to be able to move to the left and right. Moreover, the supply air valve  61   b  is biased in the direction so as to close the first connecting hole  57   b , and the discharge air valve  61   a  protrudes from the first connecting hole  57   b . Note that a fine connecting duct  61   d  that connects to the through hole  61   c  that is formed on the interior of the first poppet valve  61  is formed between the discharge air valve  61   a  and the supply air valve  61   b  of the first poppet valve  61 . 
         [0046]    The second poppet valve assembly  56  is also structured identically to the first poppet valve assembly  55 . That is, the second poppet valve assembly  56  is a divided structure of a cylindrical pipe seat portion  62  and a cylindrical column seat retaining portion  63 , having the seat portion  62  attached removably to the front face thereof, where an interior space  64  is formed between the seat portion  62  and the seat retaining portion  63 . A second connecting hole  62   b  for connecting between the interior space  64  and the second output air pressure chamber  46  is formed in the top face  62   a  of the seat portion  62 . This top face  62   a  of the seat portion  62  fulfills the role as a second dividing wall for partitioning between the second supply air pressure chamber  44  and the second output air pressure chamber  46 . 
         [0047]    A second spring  65  is contained in the interior space  64  between the seat portion  62  and the seat retaining portion  63 , where the second poppet valve  66  is held between the seat portion  62  and the seat retaining portion  63  in a state wherein the second spring  65  is stressed. The interior space  64  is connected to the second supply air pressure chamber  44 . The second poppet valve  66  has a discharge air valve  66   a  at the tip end portion thereof, and a supply air valve  66   b  to the rear of the discharge air valve  66   a . Moreover, the second poppet valve  66  has a through hole  66   c  that passes through the axis thereof. 
         [0048]    In this held state, the second poppet valve  66  penetrates through the second connecting hole  62   b  that is formed in the seat portion  62 , and is biased by the second spring  65  so as to be able to move to the left and right. Moreover, the supply air valve  66   b  is biased in the direction so as to close the second connecting hole  62   b , and the discharge air valve  66   a  protrudes from the second connecting hole  62   b . Note that a fine connecting duct  66   d  that connects to the through hole  66   c  that is formed on the interior of the second poppet valve  66  is formed between the discharge air valve  66   a  and the supply air valve  66   b  of the second poppet valve  66 . 
         [0049]    After attaching the first poppet valve assembly  55  to the first poppet valve assembly installing portion  52 , that is, after the first poppet valve assembly  55  is pushed into the duct  51  from the opening portion  51   a  that faces the outside of the housing  41 , in relation to this first poppet valve assembly  55 , a ring-shaped stopper plate  67  is attached to the opening portion  51   a  of the duct  51 . That is, the ring surface of the stopper plate  67  is put into facial contact with the surface of the first poppet valve assembly  55  that faces the outside of the housing  41  (the bottom face  58   a  of the seat retaining portion  58 ), to control the location of the first poppet valve assembly  55  in the first poppet valve assembly installing portion  52 . 
         [0050]    Similarly, after attaching the second poppet valve assembly  56  to the second poppet valve assembly installing portion  54 , that is, after the second poppet valve assembly  56  is pushed into the duct  53  from the opening portion  53   a  that faces the outside of the housing  41 , in relation to this second poppet valve assembly  56  as well, a ring-shaped stopper plate  68  is attached to the opening portion  53   a  of the duct  53 . That is, the ring surface of the stopper plate  68  is put into facial contact with the surface of the second poppet valve assembly  56  that faces the outside of the housing  41  (the bottom face  63   a  of the seat retaining portion  63 ), to control the location of the second poppet valve assembly  56  in the second poppet valve assembly installing portion  54 . 
         [0051]    In this double-action pilot relay  4 , air at the supply air pressure Ps  1  is supplied to the first supply air pressure chamber  43  and the biasing chamber  48  through the explosion proof container  101 , and air of the supply air pressure Ps1 is supplied to the second supply air pressure chamber  44 , so the air with the nozzle back pressure PN is directed to the input air pressure chamber  42 . Moreover, air of the output air pressure Po1 is supplied to the regulator valve  200  through the explosion proof container  101  from the first output air pressure chamber  45 , and air of the output air pressure Po2 is supplied to the regulator valve  200  through the explosion proof container  101  from the second output air pressure chamber  46 . 
         [0052]    Note that the first discharge air chamber  47 - 1  and the second discharge air chamber  47 - 2  are connected to atmosphere, and O-rings  73  and  74  are provided between the housing  41  and the seat portion  57  and the seat retaining portion  58  of the first poppet valve assembly  55 . Additionally, O-rings  75  and  76  are provided between the housing  41  and the seat portion  62  and the seat retaining portion  63  of the second poppet valve assembly  56 . Moreover, in the first poppet valve assembly  55 , an O-ring  77  is installed between the first poppet valve  61  and the seat retaining portion  58 , and in the second poppet valve assembly  56 , an O-ring  78  is installed between the second poppet valve  66  and the seat retaining portion  63 . 
         [0053]    In this double-action pilot relay  4 , when the nozzle back pressure PN is increased, the diaphragms  49 - 1  through  49 - 5  move in the direction of the arrow A, and, accordingly, the spool  50  that is supported on the diaphragms  49 - 1  through  49 - 5  also moves to the side of the arrow A. At this time, the spool  50 , through this movement, presses the first poppet valve  61  downward against the biasing force of the first spring  60 , and, as a result, the supply air valve  61   b  of the first poppet valve  61  opens the first connecting hole  57   b . At this time, the first opening  50   a  of the spool  50  is closed by the discharge air valve  61   a  of the first poppet valve  61 . On the other hand, the second poppet valve  66  is pushed upward by the biasing force of the second spring  65 , and, accordingly, the supply air valve  66   b  of the second poppet valve  66  closes the second connecting hole  62   b . At this time, the second opening  50   b  of the spool  50  is opened by the discharge air valve  66   a  of the second poppet valve  66 . 
         [0054]    As a result, the air of the supply air pressure Ps1 that is supplied to the first supply air pressure chamber  43  through the explosion proof container  101  enters into the interior space  59  of the first poppet valve assembly  55 , and after entering into the first output air pressure chamber  45 , through the first through hole  57   b , is sent to the explosion proof container  101  as air at the output air pressure Po1, to be supplied to the regulator valve  200  through the explosion proof container  101 . On the other hand, after the air from the regulator valve  200  returns into the second output air pressure chamber  46  through the explosion proof container  101 , it enters into the discharge air duct  50   c   2  through the second opening  50   b  of the spool  50 , to be discharged into the discharge air chamber  47 - 2 . 
         [0055]    On the other hand, when the nozzle back pressure PN is decreased, the diaphragms  49 - 1  through  49 - 5  move to the side of the arrow B, and, concomitantly, the spool  50  that is supported on the diaphragm  49  moves to the side of the arrow B. At this time, the spool  50 , through this movement, presses the second poppet valve  66  downward against the biasing force of the second spring  65 , and, as a result, the supply air valve  66   b  of the second poppet valve  66  opens the second connecting hole  62   b . At this time, the second opening  50   b  of the spool  50  is closed by the discharge air valve  66   a  of the second poppet valve  66 . On the other hand, the first poppet valve  61  is pushed upward by the biasing force of the first spring  60 , and, accordingly, the supply air valve  61   b  of the first poppet valve  61  closes the first connecting hole  57   b . At this time, the first opening  50   a  of the spool  50  is opened by the discharge air valve  61   a  of the first poppet valve  61 . 
         [0056]    As a result, the air of the supply air pressure Ps2 that is supplied to the second supply air pressure chamber  44  through the explosion proof container  101  enters into the interior space  64  of the second poppet valve assembly  56 , and after entering into the second output air pressure chamber  46 , through the second connecting hole  62   b , is sent to the explosion proof container  101  as air at the output air pressure Po2, to be supplied to the regulator valve  200  through the explosion proof container  101 . On the other hand, after the air from the regulator valve  200  returns into the first output air pressure chamber  45  through the explosion proof container  101 , it enters into the discharge air duct  50   c   1  through the first opening  50   a  of the spool  50 , to be discharged into the discharge air chamber  47 - 1 . 
         [0057]    In this way, the spool  50  and the pair of poppet valves  61  and  66  is operated by the nozzle back pressure PN that is directed into the input air pressure chamber  42  through the explosion proof container  101 , where this operation causes the amplified output air pressures Po1 and Po2 to be outputted to the regulator valve  200  through the explosion proof container  101 . In this case, the output air pressure Po1 can be adjusted through adjusting the pressure of the nozzle back pressure PN in the increasing direction when operating the regulator valve  200  in the forward direction, and the output air pressure Po2 can be adjusted through adjusting the pressure of the nozzle back pressure PN in the decreasing direction when operating the regulator valve  200  in the reverse direction. 
         [0058]      FIG. 5  shows a diagram showing the positioner  100 A, illustrated in  FIG. 1 , when seen from the back face side.  FIG. 6  shows a diagram of the explosion proof container  101  of the positioner  100 A alone, when viewed from this back face side. An interior space  101   a  is formed in the center portion of the explosion proof container  101 , where flow paths for the air that is fed into the pilot relay  4  and air that is returned from the pilot relay  4  are formed in a thick portion (a trunk portion)  101   d  between the inner wall face  101   b  and the outer wall face  101   c  of the explosion proof container  101  that encompasses, in a ring shape, the surrounding of the interior space  101   a.    
         [0059]    In this example, a flow path Ls1 through which air of the supply air pressure Ps1 flows, a flow path Ls2 through which air of the supply air pressure Ps2 flows, a flow path Lo1 through which air of the output air pressure Po1 flows, and a flow path Lo2 through which air of the output air pressure Po2 flows are provided in the trunk portion  101   d  of the explosion proof container  101 . 
         [0060]    Note that  101   e  through  101   i , and the like, are holes of gauging, where  101   j  is an inlet for air of the supply air pressure Ps,  101   k  is an outlet for air of the output air pressure Po1,  101   l  is an outlet for air of the output air pressure Po2,  101   m  is a discharge outlet for air within the explosion proof container  101 ,  101   n  and  1010  are conduits for routing electric wiring, and  101   p  is a chamber for housing a terminal block to which the wiring carried in the conduits  101   n  and  1010  is connected, where the chamber  101   p  that contains the terminal block is tightly closed by a cover  105  ( FIG. 5 ) as a portion of the interior space of the explosion proof container  101 . 
         [0061]    In this explosion proof container  101 , the flow path Ls1 through which flows the air of the supply air pressure Ps1 is a groove, with a depth of 10 mm, that is connected to the inlet  101   j  for the air of a supply air pressure Ps, formed along the inner wall face  101   b  of the explosion proof container  101 . That is, the inner wall face  101   b  of the explosion proof container  101  has a ring shape, where the flow path Ls1 is formed as an arc-shaped groove along the ring-shaped inner wall face  101 . 
         [0062]    The air of the supply air pressure Ps, from the inlet  101   j , as illustrated in  FIG. 7  and  FIG. 8 , passes through a pipe-shaped straight line duct  101   q  that is connected to the inlet  101   j , and then turns back at a sharp angle to enter into the arc-shaped flow path Ls1, to rise at a perpendicular at the end of this arc-shaped flow path Ls1 (referencing  FIG. 9 ), to be sent to the pilot relay  4  as air of the supply air pressure Ps1. In this case, the air flows along the arc-shaped flow path Ls1, that is, the air flows along a smooth flow path with little curvature, so there is little variation in cross-sectional area, reducing the flow path resistance. 
         [0063]    In the present invention, in the part of the flow path Ls1 wherein it bends back at a sharp angle, that is, at the part wherein the straight line duct  101   q  and the flow path Ls1 are joined, an air reservoir  101   r  with a depth of 30 mm is provided. This air reservoir  101   r  serves as a resonator, making it possible to reduce the flow path resistance through the effects of this chamber. 
         [0064]    Furthermore, the air of the supply air pressure Ps from the inlet  101   j  rises at a perpendicular from this air reservoir (resonator)  101   r , to be sent to the pilot relay  4  as air of the supply air pressure Ps2. The flow path through which the air of this supply air pressure Ps2 flows is the flow path Ls2. In this flow path Ls2 as well, the flow path cross-sectional area is secured by the air reservoir (resonator)  101   r , to achieve a reduction in the flow path resistance. 
         [0065]    The air of the output air pressure Po1 from the pilot relay  4 , as illustrated in  FIG. 9 , enters into the flow path Lo1, and passes through the outlet  101   k  to be fed to the regulator valve  200 . Moreover, the air of the output air pressure Po2 from the pilot relay  4 , as illustrated in  FIG. 10 , enters into the flow path Lo2, and passes through the outlet  101   l  to be fed to the regulator valve  200 . 
         [0066]    In this case, the output air pressure Po1 and Po2 from the pilot relay  4  turns back at a right angle to exit from the outlets  101   k  and  101   l , and in order to cause the flow path resistance here to be extremely small, in the present example, the openings of the flow path Lo1 and Lo2, for the straight line paths  101   s  and  101   t  into the outlets  101   k  and  101   l , are widened in stages, or the openings of these flow paths Lo1 and Lo2 are connected smoothly to the straight line paths  101   s  and  101   t.    
         [0067]    Moreover, in the present example, the explosion proof container  101  has a two-layer structure, due to the formation of the air flow paths in the thick portion (the trunk portion)  101   d  between the inner wall face  101   b  and the outer wall face  101   c  of the explosion proof container  101 . As a result, the outer wall face  101   c  of the explosion proof container  101 , as a portion of the outer shape of the positioner  100 A, not only reduces the flow path resistance, but also increases the flexibility in the exterior visual design, making it possible to produce exterior visual designs of a distinctive streamlined shape that has not existed heretofore. Note that having a streamlined shape for the external shape of the positioner  100 A produces the additional benefit of being able to get by with less installation space on the work floor. 
         [0068]    Note that while in the example set forth above the positioner  100 A was given an exterior visual design that had a streamlined shape, it need not, of course, be given an exterior visual design with a streamlined shape. Moreover, while in the example set forth above the inner wall face  101   b  of the explosion proof container  101  has a ring shape; that is, while all of the inner wall faces  101   b  are arc-shaped faces, this is not necessarily be all faces, but rather the flow path may be formed along the arc-shaped face by having only a portion of the inner wall face  101   b  have an arc-shaped face. Moreover, the shape may be one that uses many curved faces of free curve shapes, and the flow path may be formed along the curved faces of the free curve shapes. 
         [0069]    Moreover, while in the example set forth above, an air reservoir (resonator)  101   r  was provided at the part of the flow path Ls1 wherein there was a bend at a sharp angle, providing a similar resonator either before or after a part wherein the flow path resistance is large, such as a part wherein there is a rapid change in cross-sectional area or a part wherein there is a small cross-sectional area, or a part wherein there is a perpendicular bend or a sharp angle bend in the air flow path provided in the trunk portion  101   d  of the explosion proof container  101 , can achieve a reduction in the flow path resistance through securing the cross-sectional area of the flow path and through the use also of the chamber effects. 
       Extended Examples 
       [0070]    While the present disclosure has been explained in reference to the above examples, the present disclosure is not limited to the examples set forth above. The structures and details in the present disclosure may be varied in a variety of ways, as can be understood by one skilled in the art, within the scope of technology in the present disclosure.