Patent Publication Number: US-9418811-B2

Title: Relay

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2014-142915 filed on Jul. 11, 2014, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The disclosure relates to a relay; and more particularly, to a relay including an electromagnetic device. 
     BACKGROUND ART 
     As for such a relay, there is known, e.g., a remote control relay (see, e.g., Japanese Unexamined Patent Application Publication No. 2011-249137). 
     In the remote control relay disclosed in Japanese Unexamined Patent Application Publication No. 2011-249137, there is accommodated in a case an electromagnetic device having a plunger moving reciprocally by power supply to a coil and an opening/closing mechanism for switching on/off of a contact part in response to the reciprocating movement of the plunger. 
     The electromagnetic device includes a coil, a coil bobbin, a plunger, two armatures, a yoke, a residual plate, two permanent magnets, and two auxiliary yokes. 
     The coil bobbin has a cylindrical tubular body around which a coil is wound, plate-shaped flanges provided at both end portions in an axial direction of the tubular body, and side pieces protruding from both edges of each of the flanges in a direction opposite to the tubular body. 
     The remote control relay disclosed in Japanese unexamined Patent Application Publication No. 2011-249137 is disadvantageous in that it is difficult for the armature provided between the two side pieces protruding in the same direction from the flange of the coil bobbin to move smoothly due to large friction between the two side pieces and the armature moving along the axial direction of the coil bobbin. 
     SUMMARY OF THE INVENTION 
     In view of the above, the disclosure provides a relay capable of improving an operation stability of an electromagnetic device. 
     In accordance with an aspect of the present invention, there is provided a relay including a fixed contact point; a movable contact member; and an electromagnetic device. The movable contact member is moved between a first position in contact with the fixed contact point and a second position separated from the fixed contact point in response to an operation of the electromagnetic device. The electromagnetic device includes a bobbin, a coil, a movable iron core, a first armature, a second armature, and a ferromagnetic member. The bobbin includes: a tubular body around which the coil is wound, the movable iron core penetrating through the tubular body; a first flange protruding outward from a first end portion in an axial direction of the tubular body; a second flange protruding outward from a second end portion in the axial direction of the tubular body; a pair of first side pieces protruding in a direction opposite to the tubular body from both edges in a width direction of the first flange which is perpendicular to the axial direction of the tubular body; and a pair of second side pieces protruding in a direction opposite to the tubular body from both edges in a width direction of the second flange which is perpendicular to the axial direction of the tubular body. The movable iron core has a first end portion, a second end portion and an intermediate portion therebetween, and cross sectional areas of the first end portion and the second end portion perpendicular to the axial direction of the tubular body are smaller than a cross sectional area of the intermediate portion perpendicular to the axial direction of the tubular body. The first armature has a first hole to which the first end portion of the movable iron core is insertion-fitted. The second armature has a second hole to which the second end portion of the movable iron core is insertion-fitted. The ferromagnetic member has a rectangular frame shape surrounding the bobbin, the coil, the first armature and the second armature, a first insertion hole through which a part of the first end portion of the movable iron core that protrudes beyond the first armature penetrates, and a second insertion hole through which a part of the second end portion of the movable iron core that protrudes beyond the second armature penetrates. The bobbin has at least one first rib formed along the axial direction of the tubular body on each of facing surfaces of the pair of first side pieces and at least one second rib along the axial direction of the tubular body on each of facing surfaces of the pair of second side pieces. The first armature is interposed between the first ribs of the pair of first side pieces and the second armature is interposed between the second ribs of the pair of second side pieces. 
     With such configurations, it is possible to improve the operation stability of the electromagnetic device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures depict one or more implementations in accordance with the present teaching, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements. 
         FIG. 1  is a schematic exploded perspective view of a relay according to an embodiment. 
         FIG. 2  is a schematic front view of the relay when a movable contact member is in a first position in a state where a cover is removed. 
         FIG. 3  is a schematic front view of the relay when the movable contact member is in a second position in a state where the cover is removed. 
         FIG. 4  is a schematic exploded perspective view of an electromagnetic device in the relay according to the embodiment. 
         FIGS. 5 and 6  are schematic cross sectional views of the electromagnetic device in the relay according to the embodiment. 
         FIG. 7  is a schematic perspective view of a bobbin in the relay according to the embodiment. 
         FIG. 8  is a schematic perspective view of principal parts of the electromagnetic device in the relay according to the embodiment. 
         FIG. 9A  is a left side view of the electromagnetic device in the relay according to the embodiment. 
         FIG. 9B  a right side view of the electromagnetic device in the relay according to the embodiment. 
         FIG. 10  is a circuit diagram of a conversion circuit in the relay according to the embodiment. 
         FIG. 11  is a schematic perspective view of principal parts of an electromagnetic device in a relay of a comparative example. 
         FIG. 12A  is a left side view of a first modification of the electromagnetic device in the relay according to the embodiment. 
         FIG. 12B  is a right side view of the first modification of the electromagnetic device in the relay according to the embodiment. 
         FIG. 13A  is a left side view of a second modification of the electromagnetic device in the relay according to the embodiment. 
         FIG. 13B  is a right side view of the second modification of the electromagnetic device in the relay according to the embodiment. 
         FIG. 14A  is a left side view of a third modification of the electromagnetic device in the relay according to the embodiment. 
         FIG. 14B  is a right side view of the third modification of the electromagnetic device in the relay according to the embodiment. 
         FIG. 15  is a schematic view of a load control system including the relay according to the embodiment. 
         FIG. 16  is a view for explaining a transmission signal of the load control system including the relay according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a relay  1  according to an embodiment will be described with reference to  FIGS. 1 to 8, 9A, 9B and 10 . 
     The relay  1  includes a fixed contact point  2 , a movable contact member  3 , and an electromagnetic device  4 . In response to an operation of the electromagnetic device  4 , the movable contact member  3  is moved between a first position in contact with the fixed contact point  2  (see  FIG. 2 ) and a second position separated from the fixed contact point  2  (see  FIG. 3 ). As shown in  FIGS. 4 to 6 , the electromagnetic device  4  has a bobbin  41 , a coil  42 , a movable iron core  43 , a first armature  44   a , a second armature  44   b , and a ferromagnetic member  45 . The bobbin  41  has a tubular body  41   a  around which the coil  42  is wound and through which the movable iron core  43  penetrates. Further, the bobbin  41  has a first flange  41   b  protruding outward from a first end portion  41   aa  in an axial direction of the tubular body  41   a , and a second flange  41   c  protruding outward from a second end portion  41   ab  in the axial direction of the tubular body  41   a.    
     The bobbin  41  has a pair of first side pieces  41   d  protruding in the opposite direction to the tubular body  41   a  from both edges of the first flange  41   b  in a width direction (right-left direction in  FIG. 9A ) perpendicular to the axial direction of the tubular body  41   a . Moreover, the bobbin  41  has a pair of second side pieces  41   e  protruding in the opposite direction to the tubular body  41   a  from both edges of the second flange  41   c  in the width direction (right-left direction in  FIG. 9B ) perpendicular to the axial direction of the tubular body  41   a.    
     In the movable iron core  43 , cross sectional areas of a first end portion  43   a  and a second end portion  43   b  in a direction perpendicular to the axial direction of the tubular body  41   a  are smaller than a cross sectional area of an intermediate portion  43   c  in a direction perpendicular to the axial direction of the tubular body  41   a.    
     The first armature  44   a  has a first hole  44   aa  to which the first end portion  43   a  of the movable iron core  43  is press-fitted. The second armature  44   b  has a second hole  44   bb  to which the second end portion  43   b  of the movable iron core  43  is press-fitted. 
     The ferromagnetic member  45  has a rectangular frame shape surrounding the bobbin  41 , the coil  42 , the first armature  44   a  and the second armature  44   b . The ferromagnetic member  45  has a first insertion hole  455  (see  FIG. 5 ) through which a part of the first end portion  43   a  of the movable iron core  43  that protrudes beyond the first armature  44   a  penetrates. Further, the ferromagnetic member  45  has a second insertion hole  456  (see  FIG. 5 ) through which a part of the second end portion  43   b  of the movable iron core  43  that protrudes beyond the second armature  44   b  penetrates. The bobbin  41  has first ribs  41   f  formed on facing surfaces of the pair of the first side pieces  41   d  to extend along the axial direction of the tubular body  41   a , and second ribs  41   g  formed on facing surfaces of the pair of the second side pieces  41   e  to extend along the axial direction of the tubular body  41   a . The first armature  44   a  is interposed between the first ribs  41   f  of the pair of the first side pieces  41   d . The second armature  44   b  is interposed between the second ribs  41   g  of the pair of the second side pieces  41   e . Therefore, the relay  1  can improve the operation stability of the electromagnetic device  4 . 
     The relay  1  preferably includes a case  10  for accommodating the fixed contact point  2 , the movable contact member  3 , the electromagnetic device  4  and the like. The relay  1  preferably further includes a first terminal  5 , a second terminal  6 , and a pair of third terminals  7 . The fixed contact point  2  is electrically connected to the first terminal  5 . The movable contact member  3  is electrically connected to the second terminal  6 . In the relay  1 , a series circuit of a load  305  (see  FIG. 10 ) and a commercial power supply  306  (see  FIG. 10 ) can be connected between the first terminal  5  and the second terminal  6 , for example. In the relay  1 , the coil  42  is electrically connected between the pair of third terminals  7 . Therefore, the relay  1  can control on/off of the load  305 . 
     Each of the components of the relay  1  will now be described in detail. 
     The relay  1  is a single winding type bistable relay (latching relay). The bistable relay is an electromagnetic relay that is operated forward or backward when an excitation input is applied to the coil  42  and maintains its state even after the excitation input is removed. Further, the relay  1  is a polar relay having a polarity by the excitation input of the coil  42 . Therefore, the relay  1  needs to reverse a direction of power supply to the coil  42  in order to move the movable iron core  43  reciprocally. The relay  1  is a remote control relay. The relay  1  preferably satisfies standards of a remote control relay standardized as JIS C 8360. 
     The case  10  is preferably set to have a size of an agreement type circuit breaker for use in distribution panel specified in Annex XC of JIS C 8201-2-1, for example. 
     The case  10  is formed by combining a body  11  made of a synthetic resin material and a cover  12  made of a synthetic resin material. As for the resin material of the body  11  and the cover  12 , PBT (polybutylene terephthalate) or the like may be used, for example. In the case  10 , the body  11  and the cover  12  are preferably made of the same material. The body  11  is formed in a box shape having an opening  11   a  at one side thereof. The cover  12  has a flat plate shape that covers the opening  11   a  of the body  11 . The case  10  is formed by combining the body  11  and the cover  12  by using four headed pins  15 . The body  11  has four first through holes  11   b  through which the headed pins  15  penetrate. The cover  12  has four second through holes  12   b  through which the headed pins  15  penetrate. The case  10  is assembled by insertion-fitting the body  11  and the cover  12 , allowing the headed pins  15  to penetrate through the second through holes  12  of the cover  12  and the first through holes  11   b  of the body  11 , and coupling the body  11  and the cover  12  by performing plastic deformation on leading end portions of the headed pins  15 . 
     The body  11  has two parallel partition walls  11   c  and  11   d  formed as one unit. The two partition walls  11   c  and  11   d  protrude toward the cover  12  from the surface of the body  11  which faces the cover  12 . The two partition walls  11   c  and  11   d  are separated from each other in a lengthwise direction of the case  10 . The electromagnetic device  4  accommodated in the case  10  is disposed such that the axial direction of the tubular body  41   a  becomes parallel to the lengthwise direction of the case  10 . In the relay  1 , a plate spring  16  is preferably disposed between the electromagnetic device  4  and the partition wall  11   d . The plate spring  16  has a substantially U shape so that it does not interfere with the movable iron core  43 . For example, the plate spring  16  has a substantially U shape so that it is not brought into contact with the movable iron core  43  moving along the lengthwise direction of the case  10 . In the relay  1 , it is possible to reduce impact generated by the movement of the movable iron core  43  due to the presence of the plate spring  16 . 
     In the relay  1 , the first terminal  5  and the second terminal  6  are arranged in the width direction of the case  10  at a first end portion in the lengthwise direction of the case  10 . Further, in the relay  1 , a pair of third terminals  7  is arranged in the width direction of the case  10  at a second end portion in the lengthwise direction of the case  10 . 
     The first terminal  5  includes a first terminal plate  51 , a first washer  52 , and a conductive first terminal screw  53 . A first shaft portion  53   b  of the first terminal screw  53  is inserted through the first washer  52  and fitted to a first screw hole  51   b  of the first terminal plate  51 . The first terminal plate  51  is partially exposed to the outside of the case  10  and partially accommodated in the case  10 . The first terminal plate  51  is a conductive plate such as a metal plate or the like. The first terminal plate  51  of the first terminal  5  is attached to the body  11  by the first terminal screw  53 . 
     The second terminal  6  has a second terminal plate  61 , a second washer  62 , and a conductive second terminal screw  63 . A second shaft portion  63   b  of the second terminal screw  63  is inserted through the second washer  62  and fitted to a second screw hole  61   b  of the second terminal plate  61 . The second terminal plate  61  is partially exposed to the outside of the case  10  and partially accommodated in the case  10 . The second terminal plate  61  is a conductive plate such as a metal plate or the like. The second terminal plate  61  of the second terminal  6  is attached to the body  11  by the second terminal screw  63 . 
     The third terminal  7  has a third terminal plate  71 , a third washer  72 , and a conductive third terminal screw  73 . A third shaft portion  73   b  of the third terminal screw  73  is inserted through the third washer  72  and fitted to a third screw hole  71   b  of the third terminal plate  71 . The third terminal plate  71  is partially exposed to the outside of the case  10  and partially accommodated in the case  10 . The third terminal plate  71  is a conductive plate such as a metal plate or the like. 
     In the relay  1 , the fixed contact point  2  is electrically connected to the first terminal  5  and the movable contact member  3  is electrically connected to the second terminal  6 . Therefore, in the relay  1 , when the movable contact member  3  is in contact with the fixed contact point  2 , the first terminal  5  and the second terminal  6  are electrically connected to each other via the fixed contact point  2  and the movable contact member  3 . When the movable contact member  3  is separated from the fixed contact point  2 , the first terminal  5  and the second terminal  6  are electrically insulated from each other. 
     The fixed contact point  2  is fixed to an extended piece  51  extending from the first terminal plate  51 . The extended piece  51   c  has a substantially J shape. The fixed contact point  2  is fixed to a leading end portion of the extended piece  51   c . The relay  1  includes a partition wall disposed between the first terminal  5  and the second terminal  6 . The partition wall  18  has an electrical insulation property. The partition wall  18  is made of a synthetic resin. 
     The movable contact member  3  includes a plate spring  31  that is a long conductive plate, and a movable contact point  32  that is fixed to the plate spring  31  and can be brought into contact with the fixed contact point  2 . The conductive plate is made of a metal material. In the movable contact member  3 , the plate spring  31  and the movable contact point  32  may be formed as one unit. In the relay  1 , the movable contact member  3  and the fixed contact point  2  form a contact part  100 . 
     The movable contact member  3  has the movable contact point  32  at a first end portion  3   a  in a lengthwise direction thereof. A second end portion  3   b  in the lengthwise direction of the movable contact member  3  is electrically connected to the second terminal  6  through a flexible wire  65 . The wire  65  is a braided conductor formed by braiding several copper wires. 
     In the relay  1 , the bobbin  41  has a pair of supporting pieces  41   h  protruding from the pair of first side pieces  41   d  in the opposite direction to the first flange  41   b . The pair of supporting pieces  41   h  has bearing holes  41   j  through which a cylindrical rod-shaped first shaft pin  101  penetrates. The first shaft pin  101  is accommodated in the case  10  along the width direction of the case  10  and supported by the case  10 . 
     The relay  1  includes a long lever  8  that is rotatable about the first shaft pin  101 . The lever  8  is made of a synthetic resin having an electrical insulation property. The lever  8  has a first bearing hole  81  at a central portion in a lengthwise direction thereof. The first bearing hole  81  allows the first shaft pin  101  to be rotatably supported. Therefore, the lever  8  is rotatably supported by the bobbin  41 . 
     The lever  8  has a second bearing hole  82  at a first end portion  8   a  in a lengthwise direction thereof. In the lever  8 , a cylindrical rod-shaped second shaft pin  102  attached to the first end portion  43   a  of the movable iron core  43  penetrates through the second bearing hole  82 . The second shaft pin  102  is arranged in parallel to the first shaft pin  101 . Accordingly, the lever  8  can rotate about the first shaft pin  101  by the movement of the movable iron core  43 . 
     The lever  8  has a spring receiving portion  83  for holding a coil spring  9  between itself and the movable contact member  3 , the spring receiving portion  83  being formed as one unit with the lever  8 . The coil spring  9  applies a force to the movable contact member  3  so that a desired contact pressure can be obtained when the movable contact member  3  is in contact with the fixed contact point  2 . 
     The spring receiving part  83  has a substantially U shape opened toward the movable contact member  3  side. More specifically, the spring receiving unit  83  has a substantially U shape formed by a central piece  83   a  and a pair of side pieces  83   b  protruding from both ends of the central piece  83   a  along the thickness direction of the central piece  83   a . Formed at the central piece  83   a  of the spring receiving unit  83  is a first protrusion  83   d  to which one end portion of the coil spring  9  is fitted. Formed at an intermediate portion  3   c  in a lengthwise direction of the movable contact member  3  is a second protrusion (not shown) to which the other end portion of the coil spring  9  is fitted. 
     In the movable contact member  3 , a hole  34  is formed between the second protrusion and the first end portion  3   a  while being separated from the second protrusion and the first end portion  3   a . The lever  8  has a third protrusion (not shown) to be inserted into the hole  34  of the movable contact member  3 , the third protrusion being formed as one unit with the lever  8 . Further, the lever  8  has at the first end portion  8   a  a pivot protrusion  85  that can be brought into contact with the movable contact member  3 . 
     A display piece  86  facing a window opening formed at a front surface of the case  10  is formed at a second end portion  8   b  in the lengthwise direction of the lever  8 . The display  86  is formed as one unit with the lever  8 . In the relay  1 , when the lever  8  is rotated by the movement of the movable iron core  43 , an exposed area on a display surface of the display piece  86  is changed. “ON” and “OFF” are displayed on the display surface of the display piece  86 . When the movable contact member  3  is in contact with the fixed contact point  2 , only “ON” on the display surface of the display piece  86  is exposed through the window opening. When the movable contact member  3  is separated from the fixed contact point  2 , only “OFF” on the display surface of the display piece  86  is exposed through the window opening. In the lever  8 , a groove  86   b  is formed on the display surface of the display piece  86  along the width direction of the case  10 . Therefore, in the relay  1 , the lever  8  can be rotated when a user inserts a leading end portion of a minus driver or the like into the groove  86   b  through the window opening and moves the minus driver. 
     The bobbin  41  is made of a synthetic resin having an electrical insulation property. The tubular body  41   a  has a square tube shape. The first flange  41   b  and the second flange  41   c  have a rectangular shape. 
     The first side piece  41   d  has a rectangular plate shape. A length of the first side piece  41   d  in the axial direction of the tubular body  41   a  is greater than a thickness of the first armature  44   a . A length of the first side piece  41   d  in a direction perpendicular to the facing direction of the pair of first side pieces  41   d  and the axial direction of the tubular body  41   a  is greater than that of the first flange  41   b . The first ribs  41   f  are formed on the facing surfaces of the pair of first side pieces  41   d  to extend along the axial direction of the tubular body  41   a . Two first ribs  41   f  are formed at each of the first side pieces  41   d . The two first ribs  41   f  formed at each of the first side pieces  41   d  are separated from each other in the direction perpendicular to the facing direction of the pair of first side pieces  41   d  and the axial direction of the tubular body  41   a . As shown in  FIG. 9A , a distance H 1  between the first ribs  41   f  facing each other in the facing direction of the pair of first side pieces  41   d  is set to be substantially the same as a length H 12  of the first armature  44   a  in the facing direction of the pair of first side pieces  41   d.    
     The second side piece  41   e  has a rectangular plate shape. A length of the second side piece  41   e  in the axial direction of the tubular body  41   a  is greater than a thickness of the second armature  44   b . A length of the second side piece  41   e  in a direction perpendicular to the facing direction of the pair of second side pieces  41   e  and the axial direction of the tubular body  41   a  is greater than that of the second flange  41   c . The second ribs  41   g  are formed on the facing surfaces of the pair of second side pieces  41   e  to extend along the axial direction of the tubular body  41   a . Two second ribs  41   g  are formed at each of the second side pieces  41   e . The two second ribs  41   g  formed at each of the second side pieces  41   e  are separated from each other in the direction perpendicular to the facing direction of the pair of second side pieces  41   e  and the axial direction of the tubular body  41   a . As shown in  FIG. 9B , a distance H 21  between the second ribs  41   g  facing each other in the facing direction of the pair of second side pieces  41   e  is set to be substantially the same as a length H 22  of the second armature  44   b  in the facing direction of the pair of second side pieces  41   e.    
     The movable iron core  43  has a long plate shape, for example. The movable iron core  43  has a uniform thickness. The width of the first end portion  43   a  and that of the second end portion  43   b  in the lengthwise direction are smaller than the width of the intermediate portion  43   c . Therefore, in the movable iron core  43 , the cross sectional areas of the first end portion  43   a  and the second end portion  43   b  in the direction perpendicular to the axial direction of the tubular body  41   a  are smaller than the cross sectional area of the intermediate portion  43   c  in the direction perpendicular to the axial direction of the tubular body  41   a . The movable iron core  43  has a rectangular cross section in a direction perpendicular to the lengthwise direction. 
     The first armature  44   a  has a rectangular plate shape. A first opening  44   aa  of the first armature  44   a  is formed at a central portion of the first armature  44   a . The first opening  44   aa  has a rectangular shape. The first armature  44   a  is a magnetic body. 
     The second armature  44   b  has a rectangular plate shape. A second opening  44   bb  of the second armature  44   b  is formed at a central portion of the second armature  44   b . The second opening  44   bb  has a rectangular shape. The second armature  44   b  is a magnetic body. 
     The electromagnetic device  4  is magnetized by the power supply to the coil  42  such that polarities of the first armature  44   a  and the second armature  44   b  become different from each other. More specifically, the electromagnetic device  4  can change a state in which one of the first armature  44   a  and the second armature  44   b  is magnetized to the N pole and the other is magnetized to the S pole to a state in which the one is magnetized to the S pole and the other is magnetized to the N pole by reversing a direction of a current flowing through the coil  42 . 
     As shown in  FIGS. 4 to 6 , the electromagnetic device  4  preferably has a non-magnetic plate  48  at a side of the first armature  44   a  which is opposite to the side where the second armature  44   b  is disposed. The plate  48  may be made of, e.g., austenite-based stainless steel. As for the austenite-based stainless steel, it is possible to employ, e.g., SUS304 or the like. 
     The plate  48  has a rectangular plate shape. A third opening  48   a  greater than the first opening  44   aa  of the first armature  44   a  is formed at a central portion of the plate  48 . The plate  48  is preferably fixed to the first armature  44   a . In the electromagnetic device  4  including the plate  48 , the plate  48  is disposed between the first armature  44   a  and the ferromagnetic member  45  when the first armature  44   a  moves toward the ferromagnetic member  45  by the movement of the movable iron core  43 . The plate  48  is preferably thinner than the first armature  44   a.    
     The ferromagnetic member  45  has a rectangular frame shape surrounding the bobbin  41 , the coil  42 , the first armature  44   a , the second armature  44   b  and the like. The ferromagnetic member  45  is disposed such that the axial direction of the ferromagnetic member  45  and the axial direction of the tubular body  41   a  in the bobbin  41  are perpendicular to each other. The axial direction of the ferromagnetic member  45  is in parallel to the facing direction of the pair of first side pieces  41   d  of the bobbin  41 . 
     The ferromagnetic member  45  is formed by combining a pair of yokes  450  each having a substantially U shape. Each of the yokes  450  (hereinafter, referred to as “first yokes  450 ”) has a substantially U shape formed by a central piece  451  and a pair of side pieces  452  protruding from both ends of the central piece  451  in a thickness direction of the central piece  451 . The pair of first yokes  450  is arranged in a direction perpendicular to the facing direction of the pair of first side pieces  41   d  of the bobbin  41  and the axial direction of the tubular body  41   a  of the bobbin  41 . In the first yokes  450 , a distance between the pair of side pieces  452  is set to be longer than a distance between a surface of the first armature  44   a  facing the side piece  452  close thereto and a surface of the second armature  44   b  facing the side piece  452  close thereto. 
     Each of the first yokes  450  has a first recess  453  forming approximately a half of the first through hole  455  at a leading edge of one of the pair of side pieces  452  close to the first armature  44   a . Further, each of the first yokes  450  has a second recess  454  forming approximately a half of the second through hole  456  at a leading edge of the other one of the pair of side pieces  452  close to the second armature  44   b.    
     In the electromagnetic device  4 , an electromagnetic force can be generated when the current is made to flow through the coil  42  and an attractive force can be generated by the electromagnetic force between one of the first armature  44   a  and the second armature  44   b  and the ferromagnetic member  45 . In the relay  1 , when the first armature  44   a  becomes close to the first yoke  450  in the electromagnetic device  4 , the movable contact member  3  is located at the first position in contact with the fixed contact point  2 . Further, in the relay  1 , when the second armature  44   b  becomes close to the first yoke  450  in the electromagnetic device  4 , the movable contact member  3  is located at the second position separated from the fixed contact point  2 . 
     The electromagnetic device  4  includes permanent magnets  46 . The permanent magnets  46  have a rectangular plate shape. Each of the permanent magnets  46  is magnetized such that polarities of a first surface  461  and a second surface  462  in a thickness direction thereof become different from each other. Each of the permanent magnets  46  is magnetized such that the first surface becomes the S pole and the second surface becomes the N pole. Each of the permanent magnets  46  is disposed at a surface side of the central piece  451  of the first yoke  450  which faces the coil  42 . Each of the permanent magnets  46  is disposed such that the first surface  461  is positioned at the central piece  451  side of the first yoke  450  and the second surface  462  is positioned at the coil  42  side. Accordingly, in the electromagnetic device  4 , the ferromagnetic member  45  is magnetized to the same pole as that of the first surfaces  461  of the permanent magnets  46 . More specifically, in the electromagnetic device  4 , the pair of first yokes  450  forming the ferromagnetic member  45  is magnetized to the S pole. 
     The electromagnetic device  4  further includes a pair of second yokes  47  smaller than the first yokes  450 . The second yoke  47  has a substantially L shape formed by a rectangular plate-shaped main piece  471  and a side piece  472  protruding from one end of the main piece  471  in a thickness direction of the main piece  471 . The second yoke  47  is disposed between the permanent magnet  46  and the bobbin  41 . More specifically, the second yoke  47  is disposed between the permanent magnet  46  and the coil  42  such that the main piece  471  faces the permanent magnet  46 . In the electromagnetic device  4 , the second surface  462  of the permanent magnet  46  faces the second yoke  47  side, so that the second yoke  47  is magnetized to the same pole as that of the second surface  462  of the permanent magnet  46 . More specifically, in the electromagnetic device  4 , the second yoke  47  is magnetized to the N pole. Therefore, in the electromagnetic device  4 , the second yoke  47  and the first yoke  450  are magnetized to different polarities. 
     The second yoke  47  is disposed such that the side piece  472  faces a surface of the second flange  41   c  which faces the second armature  44   b . The size of the second yoke is set such that the side piece  472  and the second armature  44   b  become close to each other when the first armature  44   a  becomes close to the ferromagnetic member  45  and the other end of the main piece  471  and the first armature  44   a  become close to each other when the second armature  44   b  becomes close to the ferromagnetic member  45 . Therefore, in the electromagnetic device  4 , if the movable iron core  43  is moved until the first armature  44   a  or the second armature  44   b  becomes close to the ferromagnetic member  450 , even when the power supply to the coil  42  is stopped, the position of the movable iron core  43  can be maintained by the magnetic force of the permanent magnet  46 . Accordingly, in the relay  1 , it is possible to maintain, even after the power supply to the coil  42  is stopped, the state of the contact part  100  (hereinafter, referred to as “first contact part  100 ”) formed by the fixed contact point  2  (hereinafter, referred to as “first fixed contact point  2 ”) and the movable contact member  3  (hereinafter, referred to as “first movable contact member  3 ”). 
     In the electromagnetic device  4 , a magnetic circuit including the first armature  44   a , the first yoke  450 , the permanent magnet  46 , the second yoke  47  and the movable iron core  43  is formed when the first armature  44   a  becomes close to the ferromagnetic member  45 . Further, in the electromagnetic device  4 , a magnetic circuit including the second armature  44   b , the first yoke  450 , the permanent magnet  46 , the second yoke  47  and the movable iron core  43  is formed when the second armature  44   b  becomes close to the ferromagnetic member  45 . 
     As described above, the relay  1  is a single winding type bistable relay. The relay  1  includes a conversion circuit  20  (see  FIG. 10 ) for switching a direction of power supply to the coil  42  in order to reciprocally move the movable iron core  43 . The conversion circuit  20  includes a first diode D 1 , a second diode D 2 , a second contact part  200 , a capacitor C 1 , and a resistor R 1 . 
     In the conversion circuit  20 , an anode of the first diode D 1  and a cathode of the second diode D 2  are connected to one of the pair of third terminals  7 . The second contact part  200  is configured to selectively connect one of the cathode of the first diode D 1  and the anode of the second diode D 2  to one end of the coil  42 . The other end of the coil  42  is connected to the other third terminal  7  of the pair of third terminals  7 . Therefore, in the relay  1 , the current flows through the coil  42  in opposite directions between a case where a series circuit of the coil  42  and the first diode D 1  is connected between the pair of third terminals  7  and a case where a series circuit of the coil  42  and the second diode D 2  is connected between the pair of third terminals  7 . 
     As shown in  FIGS. 2 and 3 , the second contact part  200  includes a second fixed contact point  202 , a third fixed contact point  203 , a second movable contact member  212  facing the second fixed contact point  202 , and a third movable contact member  213  facing the third fixed contact point  203 . The relay  1  includes a supporting plate  220  for supporting the second movable contact member  212  and the third movable contact member  213 . The supporting plate  220  is a conductive plate such as a metal plate or the like. In the second contact part  200 , the supporting plate  220  is electrically connected to one of the pair of third terminals  7  via the coil  42 . Further, in the second contact part  200 , the second fixed contact point  202  and the third fixed contact point  203  are electrically connected to the other one of the pair of third terminals  7  via the first diode D 1  and the second diode D 2 , respectively. 
     The supporting plate  220  has a substantially U shape. The supporting plate  220  has a substantially U shape formed by a central piece  221  and a pair of side pieces  222  having different lengths. In the second contact part  200 , the second movable contact member  212  is supported by a longer one of the pair of side pieces  222 , and the third movable contact member  213  is supported by a shorter one of the pair of side pieces  222 . 
     The second movable contact member  212  includes a plate spring  212   a  that is a long conductive plate, and a second movable contact point  212   b  that is fixed to the plate spring  212   a  and can be brought into contact with the second fixed contact point  202 . The plate spring  212   a  has a spring force acting in a direction that brings the second movable contact member  212  into contact with the second fixed contact point  202 . In the second movable contact member  212 , the second movable contact point  212   b  and the plate spring  212   a  may be formed as one unit. 
     The third movable contact member  213  includes a plate spring  213   a  that is a long conductive plate, and a third movable contact point  213   b  that is fixed to the plate spring  213   a  and can be brought into contact with the third fixed contact point  203 . The plate spring  213   a  has a spring force acting in a direction that brings the third movable contact member  213  into contact with the third fixed contact point  203 . In the third movable contact member  213 , the third movable contact point  213   b  and the plate spring  213   a  may be formed as one unit. 
     In the relay  1 , the lever  8  has a manipulation unit  87  that is formed as one unit therewith and selectively presses the second movable contact member  212  and the third second movable contact member  213 . The manipulation unit  87  protrudes from a portion of the second end portion  8   b , in the lengthwise direction, of the lever  8  which is closer to the first bearing hole  81  than the display piece  86 . A leading end portion of the manipulation unit  87  is disposed between a leading end portion of the second movable contact member  212  and a leading end portion of the third movable contact member  213 . The manipulation unit  87  is separated from one of the second movable contact member  212  and the third movable contact member  213  and presses the other one. The second movable contact member  212  comes in contact with the second fixed contact part  202  when it is not pressed by the manipulation unit  87  and becomes separated from the second fixed contact point  202  when it is pressed by the manipulation unit  87 . The third movable contact member  213  comes in contact with the third fixed contact point  203  when it is not pressed by the manipulation unit  87  and becomes separated from the third fixed contact point  203  when it is pressed by the manipulation unit  87 . 
     In the relay  1 , when the first armature  44   a  becomes close to the ferromagnetic member  45 , the first movable contact member  3  is brought into contact with the first fixed contact point  2 ; the second movable contact member  212  is brought into contact with the second fixed contact point  202 ; and the third movable contact member  213  is separated from the third fixed contact point  203 . Further, in the relay  1 , when the second armature  44   b  becomes close to the ferromagnetic member  45 , the first movable contact member  3  is separated from the first fixed contact point  2 ; the second movable contact member  212  is separated from the second fixed contact point  202 ; and the third movable contact member  213  is brought into contact with the third fixed contact point  203 . Therefore, in the relay  1 , the current flows through the coil  42  in opposite directions between a state where the first armature  44   a  is close to the ferromagnetic member  45  and a state where the second armature  44   b  is close to the ferromagnetic member  45 . 
     Hereinafter, the operation of the relay  1  will be described briefly. 
     As shown in  FIG. 3 , in the relay  1 , if the current flows through the coil  42  so that the magnetization state of the movable iron core  43  is changed in a state where the movable contact member  3  is separated from the fixed contact point  2 , the movable iron core  43  is moved so that the first armature  44   a  becomes close to the ferromagnetic member  45 . Thus, in the relay  1 , the lever  8  is rotated in a clockwise direction in  FIG. 3  about the first shaft pin  101  as a rotation axis. In the relay  1 , the movable contact member  3  comes in contact with the fixed contact point  2  as shown in  FIG. 2  by the clockwise rotation of the lever  8 . Further, in the relay  1 , the third movable contact member  213  is pressed by the manipulation unit  87  to be separated from the third fixed contact point  203  by the clockwise rotation of the lever  8 . Accordingly, in the relay  1 , even if the power supply to the coil  42  is stopped, the state in which the first movable contact member  3  is brought into contact with the first fixed contact point  2  is maintained by the magnetic force of the permanent magnet  46 . 
     In the relay  1 , if the current flows through the coil in a reversed direction, the movable iron core  43  is moved so that the second armature  44   b  becomes close to the ferromagnetic member  45 . Thus, in the relay  1 , the lever  8  is rotated in a counterclockwise direction in  FIG. 2  about the first shaft pin  101  as the rotation axis. In the relay  1 , the movable contact member  3  becomes separated from the fixed contact point  2  as shown in  FIG. 3  by the counterclockwise rotation of the lever  8 . Further, in the relay  1 , the second movable contact member  212  is pressed by the manipulation unit  87  to be separated from the second fixed contact point  202  by the counterclockwise rotation of the lever  8 . Accordingly, in the relay  1 , the state in which the first movable contact member  3  is separated from the first movable contact point  3  is maintained even if the power supply to the coil  42  is stopped. 
     The present inventors have studied a relay of a comparative example which has the same configuration as that of the remote control relay disclosed in Japanese Unexamined Patent Application Publication No. 2011-249137. The relay of the comparative example is different from the relay  1  in the shape of the bobbin  41  of the electromagnetic device  4 . 
     As shown in  FIG. 11 , the bobbin  41  in the relay of the comparative example does not include the first ribs  41   f  and the second ribs  41   g  of the bobbin  41  in the relay  1 . In the comparative example, in order to prevent wobbling occurring during the movement of the movable iron core  43 , a length of the first armature  44   a  in the facing direction of the pair of first side pieces  41   d  of the bobbin  41  is set to be approximately equal to a distance between the pair of first side pieces  41   d . In the same manner, in the comparative example, a length of the second armature  44   b  in the facing direction of the pair of second side pieces  41   e  of the bobbin  41  is set to be approximately equal to a distance between the pair of second side pieces  41   e.    
     However, in the relay of the comparative example, the first armature  44   a  and the second armature  44   b  are not smoothly moved. The present inventors consider that this is caused by a large friction force occurring during the movement of the first armature  44   a  along the pair of first side pieces  41   d  and a large friction force occurring during the movement of the second armature  44   b  along the pair of second side pieces  41   e.    
     In the relay of the comparative example, the pair of first side pieces  41   d  of the bobbin  41  is apt to be warped so that the dimension between the pair of first side pieces  41   d  is locally decreased and the first armature  44   a  cannot be inserted between the pair of first side pieces  41   d  in assembling the electromagnetic device. Further, in the relay of the comparative example, the pair of second side pieces  41   e  of the bobbin  41  is apt to be warped so that the dimension between the pair of second side pieces  41   e  is locally decreased and the second armature  44   b  cannot be inserted between the pair of second side pieces  41   e  in assembling the electromagnetic device. The present inventors have found that, in the relay of the comparative example, by winding the coil  42  around the tubular body  41   a  of the bobbin  41 , the pair of first side pieces  41   d  and the pair of second side pieces  41   e  are apt to be warped so that the dimension between the pair of first side pieces  41   d  and the dimension between the pair of second side pieces  41   e  are locally increased. Moreover, in the relay of the comparative example, when the movable iron core  43  is moved, the first armature  44   a  and the second armature  44   b  are wobbled and, thus, attractive force characteristics may become non-uniform. 
     On the other hand, in the relay  1  of the present embodiment, the first armature  44   a  is interposed between the first ribs  41   f  of the pair of first side pieces  41   d  and the second armature  44   b  is interposed between the second ribs  41   g  of the pair of second side pieces  41   e . Therefore, the relay  1  can reduce the friction force occurring during the movement of the first armature  44   a  along the pair of first side pieces  41   d  and the friction force occurring during the movement of the second armature  44   b  along the second side piece  41   e . Further, the relay  1  can reduce wobbling of the movable iron core  43  during the movement of the movable iron core  43 . Therefore, in the relay  1 , the first armature  44   a  and the second armature  44   b  can be moved more smoothly, which makes it possible to improve the operation stability of the electromagnetic device  4 . Moreover, the relay  1  can suppress the non-uniformity of the attractive force characteristics. In the relay  1 , the first ribs  41   f  facing each other have a function of guiding the first armature  44   a . Further, in the relay  1 , the second ribs  41   g  facing each other have a function of guiding the second armature  44   b.    
     In the relay  1 , two first ribs  41   f  are formed at each of the first side pieces  41   d . Therefore, it is possible to further suppress the rotation of the first armature  444   a  in the plane perpendicular to the lengthwise direction of the movable iron core  43  compared to when one first rib  41   f  is formed at each of the first side piece  41   d . Further, in the relay  1 , two second ribs  41   g  are formed at each of the second side pieces  41   e . Therefore, it is possible to further suppress the rotation of the second armature  44   b  in the plane perpendicular to the lengthwise direction of the movable iron core  43  compared to when one second rib  41   g  is formed at each of the second side piece  41   e . In the relay  1 , since the two first ribs  41   f  are formed at each of the first side piece  41   d  and the two second ribs  41   g  are formed at each of the second side piece  41   e , it is possible to suppress the warpage of the pair of first side pieces  41   d  and the pair of second side pieces  41   e . The number of the first ribs  41   f  and the number of the second ribs  41   g  are not limited to two. Since, however, the friction force tends to be increased as the number thereof is increased, two first ribs  41   f  and two second ribs  41   g  are more preferable than three or more first ribs  41   f  and three or more second ribs  41   g.    
     The first rib  41   f  preferably has a first round part  41   fa  at a leading end thereof as shown in  FIG. 9A . In the same manner, the second rib  41   g  preferably has a second round part  41   ga  at a leading end thereof as shown in  FIG. 9B . In the electromagnetic device  4 , when the first rib  41   f  has the first round part  41   fa  at the leading end thereof, the friction force can be reduced compared to when the first rib  41   f  has a rectangular part at the leading end thereof as shown in  FIG. 12A  and, thus, the operation stability can be improved. In other words, in the electromagnetic device  4 , the friction force can be reduced compared to when the facing surfaces of the first rib  41   f  and the first armature  44   a  are approximately in parallel to each other. In the electromagnetic device  4 , when the second rib  41   g  has the second round part  41   ga  at the leading end thereof, the friction force can be reduced compared to when the second rib  41   g  has a rectangular part at the leading end thereof as shown in  FIG. 12B  and, thus, the operation stability can be improved. 
     In the electromagnetic device  4 , when the first rib  41   f  has the first round part  41   fa  at the leading end thereof, the formability of the bobbin  41  can be improved compared to when the first rib  41   f  has a triangular part at the leading end thereof as shown in  FIG. 13A . In the same manner, when the second rib  41   g  has the second round part  41   ga  at the leading end thereof, the formability of the bobbin  41  can be improved compared to when the second rib  41   g  has a triangular part at the leading end thereof as shown in  FIG. 13B . 
     The shape of the first round part  41   fa  and that of the second round part  41   ga  are not limited as long as they do not have at least a right-angled part and the friction force can be reduced. The shapes of the first round part  41   fa  and the second round part  41   ga  seen in the lengthwise direction of the first rib  41   f  and the second rib  41   g  are identical to the cross sectional shapes of the first rib  41   f  and the second rib  41   g  in a direction perpendicular to the axial direction of the tubular body  41 . The first round part  41   fa  and the second round part  41   ga  have a circular shape when seen in the lengthwise direction of the first rib  41   f  and the second rib  41   g . However, the shape thereof is not limited thereto and may be, e.g., a shape with rounded corners or a semi-elliptic spherical shape. 
     In the electromagnetic device  4 , it is preferable to form a first recess  44   ac  (see  FIG. 14A ), into which the first rib  41   f  is inserted, at a side surface of the first armature  44   a  and form a second recess  44   bc  (see  FIG. 14B ), into which the second rib  41   g  is inserted, at a side surface of the second armature  44   b . Accordingly, the relay  1  can further suppress the wobbling of the first armature  44   a  and the second armature  44   b  in a direction perpendicular to the axial direction of the tubular body  41   a  and the pair of first side pieces  41   d  and the pair of second side pieces  41   e . As a result, the operation stability can be further improved. 
     Hereinafter, an example of a load control system  300  including the relay  1  will be described with reference to  FIGS. 15 and 16 . 
     The load control system  300  includes the relay  1 , a first terminal  301  for controlling the relay  1 , a second terminal  302  for monitoring a manipulation state of a switch, a transmission control unit  303 , and a transformer  304 . In the load control system  300 , the first terminal  301  and the second terminal  302  are electrically connected to the transmission control unit  303  via a two-wire signal line Ls. In the relay  1 , the series circuit of the load  305  and the commercial power supply  306  is connected between the first terminal  5  and the second terminal  6 . Further, in the relay  1 , one of the pair of third terminals  7  is connected to the transformer  304  and the other third terminal  7  is connected to the first terminal  301 . The load control system  300  does not include, as constituent components, the load  305  and the commercial power supply  306 . However, the load  305  may be included as a constituent component of the load control system  300 . 
     The first terminal  301  and the second terminal  302  have their own addresses. 
     The transmission control unit  303  is configured to transmit a transmission signal Vs (see  FIG. 16 ) containing address data between the first terminal  301  and the second terminal  302  via a signal line Ls. 
     The second terminal  302  is configured to transmit monitoring data describing a manipulation state of the switch  312  to the transmission control unit  303  via the signal line Ls. 
     In the load control system  300 , when the relay  1  is controlled by the first terminal  301 , a power is supplied in a pulsed manner from a remote control transformer  304  to the relay  1 . The transformer  304  is connected to an AC power supply that is a commercial power supply. The transformer  304  is configured to transform an AC voltage of 100V and supply an AC voltage of 24V to each of the relay  1  and the first terminal  301 . The transformer  304  is a remote control transformer for supplying a predetermined voltage (AC voltage of ±24V) to the relay  1 . 
     The first terminal  301  can control relays  1  of up to four circuits and thus has a 2 bit load number for recognizing each relay  1 . Hereinafter, a channel of the first terminal  301  and a load number will be referred to as an address. In other words, in the load control system  300 , each relay  1  has its own address. 
     The first terminal  301  controls a relay  1  having the same load number as that in the address data, thereby controlling a load corresponding thereto. 
     In the load control system  300 , the correspondence relation between the address of the second terminal  302  and the address of the relay  1  is managed by the transmission control unit  303 . Therefore, in the load control system  300 , relays  1  of multiple circuits can be controlled by a single second terminal  302  based on the relation data between addresses of the relays  1  of the multiple circuits and an address of the single second terminal  302  in the transmission control unit  303 . In this specification, such control is referred to as batch control. Particularly, the batch control in which a plurality of loads  305  is controlled to the same state is referred to as group control and the batch control in which a plurality of loads  305  is individually controlled to a preset state is referred to as pattern control. The group control or the pattern control is especially effective when the load  305  controlled by the relay  1  is an illumination load. The group control or the pattern control can be used when a plurality of illumination loads is simultaneously turned on/off in an office or the like where the plurality of illumination loads is arranged. 
     In the load control system  300 , the transmission control unit  303 , the first terminal  301 , the relay  1  and the transformer  304  are preferably disposed inside a distribution board (not shown). 
     The transmission control unit  303  transmits the transmission signal Vs having a format (signal type) shown in  FIG. 16A  to the signal line Ls. The transmission signal Vs is a bipolar (±24V) time division multiplex signal and the data is transmitted by pulse width modulation (see  FIG. 16B ). The transmission signal Vs contains a start pulse signal SY, a mode data MD, an address data AD, a control data CD, a checksum data CS and a signal return period WT. The start pulse signal SY indicates a signal transmission start. The mode data MD indicates a mode of the transmission signal Vs. The address data AD calls the first terminal  301  or the second terminal  302  individually. The control data CD controls the relay  1  or the load  305 . The checksum data detects a transmission error. The signal return period WT is a time slot for receiving a return signal from the first terminal  301  or the second terminal  302 . 
     Each of the first terminal  301  and the second terminal  302  takes the control data CD from the transmission signal Vs when its address coincide with the address data AC of the transmission signal Vs received through the signal line Ls. Further, each of the first terminal  301  and the second terminal  302  returns the monitoring data as a current mode signal in the signal return period WT of the transmission signal Vs. The current mode signal is sent out by short-circuiting the signal line Ls through a proper low impedance. 
     When the data is transmitted to a desired one of the first terminal  301  and the second terminal  302 , the transmission control unit  303  sets the mode data MD to the control mode and sends out the transmission signal Vs having the address of the desired one of the first terminal  301  and the second terminal  302  as the address data AD. In the load control system  300 , the first terminal  301  or the second terminal  302  which has the address that coincides with the address data AD receives the control data CD and returns the monitoring data in the signal return period WT. The transmission control unit  303  checks that the control data CD has been transmitted to the desired one of the first terminal  301  and the second terminal  301  based on the relation between the transmitted control data CD and the monitoring data received in the signal return period WT. 
     The first terminal  301  controls the relay  1  based on the received control data CD. The second terminal  302  controls the display unit  313  based on the received control data CD. 
     The transmission control unit  303  sends out, in a normal state, the transmission signal Vs with the mode data MD set to a dummy mode at a regular time interval (constant normal polling). When there is an information to be transmitted to the transmission control unit  303 , the second terminal  302  generates an interrupt signal shown in  FIG. 16C  in synchronization with a start pulse signal SY of the transmission signal Vs having the dummy mode. At this time, the second terminal  302  sets an interrupt flag to prepare information exchange with the transmission control unit  303 . 
     When the interrupt signal is received, the transmission control unit  303  sets the mode data MD to an interrupt polling mode and sends the transmission signal while increasing high-order half bits (high-order 4 bits when the address data AC has 8 bits) of the address data AD sequentially. The second terminal  302  that has generated the interrupt signal returns, when the high-order 4 bits of the address thereof coincide with the high-order 4 bits of the address data AD of the transmission signal Vs having the interrupt polling mode, low-order 4 bits of the address to the transmission control unit  303  in the signal return period WT. Hence, the transmission control unit  303  can recognize the second terminal  302  that has generated the interrupt signal. 
     When the address of the second terminal  302  that has generated the interrupt signal is acquired, the transmission control unit  303  sets the mode data MD to the monitoring mode and sends out the transmission signal Vs having the address data AD of the acquired address to the signal line Ls. With respect to the transmission signal Vs, the second terminal  302  returns the monitoring data as a transmission target information in the signal return period WT. 
     Lastly, the transmission control unit  303  sends out a signal that instructs an interrupt reset to the second terminal  302  that has generated the interrupt signal and releases the interrupt flag of the second terminal  302 . 
     In this manner, the transmission of the monitoring data from the second terminal  302  to the transmission control unit  303  is completed by four signal transmission (the dummy mode, the interrupt polling mode, the monitoring mode and the interrupt reset). 
     In the transmission control unit  303 , when the monitoring data is received through a series of interrupt processes, there is created the control data CD to be transmitted to the first terminal  301  previously made to correspond to the second terminal  302 . The transmission control unit  303  performs time division multiplex transmission of the created control data CD together with the address AD of the first terminal  301  by using the transmission signal Vs. The first terminal  301  accessed by the transmission signal Vs controls on/off of the power supply to the load  305  by controlling the relay  1  based on control contents of the control data CD. In other words, in the load control system  300 , the first terminal  301  can control the on/off of the power supply to the load  305  through the relay  1  by manipulating the switch  312  of the second terminal  302  corresponding thereto. 
     In  FIG. 15 , there are illustrated a single first terminal  301  and a single second terminal  302 . However, there may be provided a plurality of first terminals and a plurality of second terminals. The first terminal  301  and the second terminal  302  are connected to the signal line Ls through extended connections. 
     The diagrams describing the above embodiments are schematic diagrams and the ratio of dimensions or thicknesses of the respective components are not necessarily the same as the actual dimension ratio. Further, the materials, the numerical numbers and the like described in the above embodiments are only desired examples and are not limited thereto. Moreover, the disclosure can be modified without departing from the scope thereof.