Abstract:
A data surge protection module can be added to data and control networks not having such surge protection. The use of quick connect/disconnect connectors allows for the rapid installation and/or replacement of such modules. A built-in ground plate and a braided low impedance conductor offer alternative grounding for the module. The module employs two or more diode steering bridges and uses a diode as a surge suppression element.

Description:
This application is a continuation of Ser. No. 09/192,154 filed on Nov. 13, 1998 now U.S. Pat. No. 6,342,998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to the field of electrical voltage surge protection and more particularly to providing surge protection for data communication circuits. 
     2. Description of the Prior Art 
     Prior art surge protectors for programmable logic controllers (PLC&#39;s) or similar devices, are complex to use and require the attachment of various grounds, conductors and jumpers to protect data communication circuits. This makes the replacement of the surge protector difficult and time consuming. 
     SUMMARY OF THE INVENTION 
     The instant invention overcomes the difficulties noted above with respect to the prior art. The instant invention employs a housing with two complementary ground connects. The first is a notched plate capable of accepting the shaft of an attachment bolt. This bolt fastens the housing ground plate to a ground system. The second ground connection is implemented via a low impedance ground strap. The ground strap is used when dimensional constraints prevent the direct bolting of the notched plate to a ground system. The input data conductors are coupled to a plug-in connector which is received in a suitable header on the housing. The output data conductors are also coupled to a plug-in connector which is received in a suitable header on the housing. The use of the plug-in connectors makes the connection to and from the module quick and easy. A number of diode steering bridges couples selected lines to a silicon avalance diode (SAD) which provides surge protection to one another to protect against surges, line to line, and line to ground. The SAD mounted at the bridge output is the surge suppression element for transient voltage surges. Certain of the input data lines are also fused with automatically resettable positive temperature co-efficient devices contained in the housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawings in which similar elements are given similar reference characters: 
     FIG. 1 is a front elevational view of a programmable logic device, hereafter “PLC” and a plurality of side card modules in an enclosure; 
     FIG. 2 is a front elevational view of the device of FIG. 1, with an electrical voltage surge protection module attached to the enclosure but turned 90° to better illustrate the connections to the module. 
     FIG. 3 is a side elevational view of the enclosure of FIG. 2 with a module attached and grounded by means of a ground plate on the module and a ground strap on the enclosure. 
     FIG. 4 is a side elevational view of the enclosure of FIG. 2 with a module attached and grounded by means of a pigtail of braided metal coupled to the enclosure. 
     FIG. 5 is an exploded, perspective view of the module and its quick connect/disconnect connectors for three data input lines and three data output lines. 
     FIG. 6 is an exploded, perspective view of the module and its quick connect/disconnect connectors for six data input lines and six data output lines. 
     FIG. 7 is a top plan view of the printed circuit board (hereafter “PCB”) for a three data line module. 
     FIG. 8 is a side electrical view of the PCB of FIG.  7 . 
     FIG. 9 is a top plan view of the PCB for a six data line module. 
     FIG. 10 is a side elevational view of the PCB of FIG.  9 . 
     FIG. 11 is an exploded side elevational view of a module according to the invention. 
     FIG. 12 is a schematic drawing of a circuit for protecting a module with three data lines. 
     FIG. 13 is a schematic drawing of a circuit for protecting a module with six data lines. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 there is shown a PLC  24  mounted in a housing  22  of signal loop network  20 . Also mounted in enclosure  22  are a number of “side card” modules  26  which act as input/output control devices. The PLC  24  is connected to a mother board (not shown) across the back of enclosure  22  and the individual side card modules, or daughter boards  26  are connected to the mother board to receive operating voltages and signals. The input lines  28 ,  30  and  32  from a computer or the like are coupled to the PLC  24  and the output lines  34 ,  36  and  38  extend from the first side card module  26  to a circuit to controlled devices, for example, for turning an electrical motor on or off. No surge protection is provided to the PLC or the side card modules  26  and they may be damaged or destroyed by a transient voltage surge. 
     FIG. 2 shows the same arrangement of PLC  24  and side card modules  26  in an enclosure  22  but with an electrical voltage surge protection module  42  added to enclosure  22  to provide signal loop network  40 . Lines  28 ,  30  and  32  are removed from the input terminals of the PLC  24  and are coupled to the input terminals  44 ,  46  and  48  of the module  42 . Lines  50 ,  52  and  54  are coupled between output terminals  56 ,  58  and  60  of the module  42  and the input terminals of the PLC  24 . This wiring of the module  42  places it in series between the input lines  28 ,  30 ,  32  and the input terminals of the PLC and provides transient voltage surge protection at this point. 
     Turning now to FIGS. 3,  4  and  11  the manner of mounting and grounding the module  42  is shown. Module  42  has a PCB  62  shown in FIG. 11, upon which the circuit components are located and to which is fastened a braided low impedance alternate ground wire  64 . Also present on the PCB  62  are two 3-pin headers or multi-pin connectors  66 , only one of which is visible in FIG.  11 . For six conductor constructions two 6-pin headers or multi-pin connectors are used as will be explained below. The PCB  62  is placed in a housing made up of a top housing portion  68  and a base portion  70 . A grounding plate  72  (FIG. 11) has a plug-in tongue  74  at one end and an upturned tab  76  at an opposite end. Tab  76  extends through base portion  70  of the housing and into the PCB  62  where it is soldered to the PCB  62 . The plug-in tongue  74  is best seen in FIG. 11 is attached to the top housing portion  68  via base portion  70  by means of a bolt  88 . It is generally rectangular in shape and has cut-out  80  to provide two tongues  82  (see FIG. 3) which can be plugged into a grounding stud  84  on the side of enclosure  22  as is shown in FIGS. 3 and 4. The module  42  is assembled by the use of two threaded fasteners  88  as shown by the dashed lines in FIG.  11 . 
     The alternative ground attachment braided conductor  64  is not used in the arrangement of FIG.  3  and may be cut-off and discarded or can be retained if desired. In the event no clearance space is available to attach module  42  to the grounding stud  84  the module  42  may be mounted to the enclosure  22  and to the grounding stud  84  by means of braided low impedance conductor  64 . The conductor  64  is terminated in a connector  86  which may be a ring terminal  86 ′ as shown in FIG. 5 or a spade terminal  86 ″ as shown in FIGS. 7 and 9. Connector  86  is held in place by a suitable fastener. The module  42  can be fastened to enclosure  22  by a crimp type fastener, bonding, pressure sensitive tape, brazing, welding or the like. 
     Referring to FIGS. 5 to  11  the module  42  for use with three conductor cables and the module  42 ′ for use with six conductor cables in shown. The three pin header  66  has three vertical pins  90  which mate with three sockets (not shown) of a 3 pin quick connect/disconnect multi-conductor connector or terminal connector  92 . Conductors such as  28 ,  30  and  32  can be fastened to a 3 pin terminal connector  92  using the screw fasteners  94 . In a similar fashion, the module  42 ′ has two six pin headers  96  each with six vertical pins  98 . The pins  98  mate with six sockets (not shown) of a 6 pin quick connect/disconnect multi-conductor connector or terminal connector  100 . Conductors can be fastened to the terminal connector  100  by use of the screw fasteners  102 . 
     Referring now to FIG. 12, the circuitry for a three conductor electrical voltage surge protection module  42  is shown. A conductor  110  extends from an input J 1 - 3  line 1_IN terminal  112  to one side of a PTC fuse  114  rated at 10 amps at 250 volts. The other side of fuse  114  is connected by conductor  116  to output terminal  118  marked schematically as J 2 - 3  1_OUT. The conductors  110 ,  116  and fuse  114  constitute one signal line from the computer or similar device to a PLC. Conductor  120  extends from input terminal  122  marked J 1 - 1  2_IN to one side of PTC fuse  124 . The other side of fuse  124  is connected by conductor  126  to output terminal  128  marked J 2 - 1  2_OUT. The conductors  120 ,  126  and fuse  124  constitute a second signal line. A third line  130  extends from input terminal  132  marked J 1 - 2  SHLD to output terminal  134  marked J 2 - 2  SHLD. This is the shield line conductor from the input cable that is passed through the device to the output cable and is grounded as at  136 . 
     A first steering bridge  138  is made up of four diodes  140 ,  142 ,  144  and  146 . The anode of diode  140  is connected to the cathode of diode  146  and to line  148  to conductor  116 . The cathode of diode  140  is connected to the cathode of diode  142  and to a line  150 . The anode of diode  142  is connected to the cathode of diode  144 , this junction is connected to line  152  to conductor  126 . Line  152  may be a single line or made up of two sections jumpered together as at  154 . The anode of diode  144  is connected to the anode of diode  146 . This junction is connected to line  156 . A SAD  158  is connected with its cathode connected to line  150  and its anode connected to line  156 . The SAD  158  provides the transient voltage suppression for lines  110 ,  116  and  120 ,  126 , respectively, as will be set forth below. 
     A second steering bridge  160  is made up of four diodes  162 ,  164 ,  166  and  168 . The anode of diode  162  is connected to the cathode of diode  168 . This junction is connected to line  170 . The cathode of diode  162  is coupled to the cathode of diode  164 . This junction is connected to line  150 . The anode of diode  164  is connected to the cathode of diode  166 . This junction is connected to line  170 . Line  170  is connected by conductor  172  to shield line  130 . The anode of diode  166  is connected to the anode of diode  168 . This junction is connected to line  156 . 
     A positive transient voltage on line  110  greater than the breakover point of diode  158  and less than current level of fuse  114  will be conducted from terminal  112 , conductor  110 , fuse  114  to the line  148  to the anode of diode  140 . Diode  140  will conduct and place this transient on line  150 . The current with pass through the diode  158  from cathode to anode and to line  156  and to the junction of the anodes of diodes  166  and  168 . The transient is passed by lines  170  and  172  to the shield line  130  which is grounded, thereby shunting the excess transient current to ground. 
     A negative transient voltage of sufficient magnitude on line  110  from terminal  112  passes fuse  114  and is applied to line  148  and in turn to the cathode of diode  146 . The transient then passes from the cathode of diode  146  is applied to line  156 , through the diode  158  from anode to cathode to line  150 . The transient output on line  150  is divided by the diodes  162 ,  164  whose cathodes are connected to line  150  and anodes are connected to line  170  then to line  172  to the grounded shield conductor  130 . 
     A positive transient voltage signal incurred between line  120  and ground or between lines  120  and  130  passes from terminal  122 , along line  120  through fuse  124  to line  152 . The signal continues from the anode to the cathode of diode  142  to line  150  to diode  158 . The transient signal then passes through diode  158  from cathode to anode and to line  156 . Line  156  applies the signal to the anodes of diodes  166 ,  168 . The cathodes of diodes  166  and  168  are each connected by line  170  to line  172  to the grounded shield conductor  130 . 
     A negative transient voltage signal incurred between line  120  and ground or between lines  120  and  130  passes through fuse  124  to line  152 . The signal passes from cathode to anode of diode  144 , to line  156  and through diode  158  from anode to cathode to line  150 . The signal on line  150  is applied to the cathodes of diodes  162 ,  164  whose anodes provide signals to transient lines  170 ,  172  to the grounded shield line  130 . This arrangement provides transient voltage surge protection for line to line and line to ground surges. 
     The circuitry for a six conductor electrical voltage surge protection module  42 ′ is shown in FIG.  13 . Line  180  from input terminal  182  marked J 1 - 6  TERM_IN is input to fuse  184  the output of which is connected by conductor  186  to output terminal  188  marked J 2 - 6  TERM_OUT. The conductors  180 ,  186  connect to an external resistor (not a part of this device) which terminates the module  42 ′ data line to the PLC. Conductor  190  extends from input terminal  192  marked J 1 - 5  A_IN to fuse  194  which is also connected to conductor  196  which extends to output terminal  198  marked J 2 - 5  A_OUT. This is a first signal line. 
     Conductor  200  extends from input terminal  202  marked J 1 - 4  B_IN to fuse  204  and from fuse  204  via conductor  206  to output terminal  208  marked J 2 - 4  B_OUT which is the second signal line. Conductor  210  extends from input terminal  212  marked J 1 - 3  COMMON_IN to fuse  214 , conductor  216  to output terminal  218  marked J 2 - 3  COMMON_OUT. This is the return line for both of the signal lines A and B. From input terminal  222  marked J 1 - 2  SHLD_IN, conductor  220  connects to fuse  224  to conductor  226  to output terminal  228  marked J 2 - 2  SHLD_OUT. A chassis ground line  230  extends from input terminal  232  marked J 1 - 1  CHS_GND to output terminal  234  marked J 2 - 1  CHS_GND. Line  230  is tied to chassis ground  238  by conductor  236 . 
     A first steering bridge  240  is composed of four diodes  242 ,  244 ,  246  and  248 . The anode of diode  242  is coupled to the cathode of diode  248  and to line  250  connected at its other end to the common line  216 . The cathode of diode  242  is connected to the cathode of diode  244  and to line  252 . The anode of diode  244  is coupled to the cathode of diode  246  and to line  254  coupled to the termination line  186 . The anode of diode  246  is coupled to the anode of diode  248  and to a line  256 . A second steering bridge  260  is made up of four diodes  262 ,  264 ,  266  and  268 . The anode of diode  262  is coupled to the cathode of diode  268  and to a line  270  connecting to the A_IN signal line  196 . The cathode of diode  262  is connected to the cathode of diode  264  and by line  272  to line  252 . The anode of diode  264  is connected to the cathode of diode  266  and line  274  to the B_IN signal line  206 . The anode of diode  266  is connected to the anode of diode  268  and by line  276  to line  256 . A diode  278  has its anode coupled to line  256  while its cathode is coupled to line  252 . 
     A third steering bridge  280  is made up of four diodes  282 ,  284 ,  286  and  288 . The anode of diode  282  is coupled to the cathode of diode  288  and to line  290  connected to shield line  226 . The cathode of diode  282  is connected to the cathode of diode  284  and to line  252 . The anode of diode  284  is connected to the cathode of diode  286  and by line  292  to chassis ground line  230 . The anode of diode  286  is connected to the anode of diode  288  and by line  294  to line  256 . 
     A positive transient voltage surge pulse incurred between input terminal  182  and input terminal  222  or between terminals  182  and  212  would pass along conductor  180  through fuse  184 , line  254  to the anode of diode  244 , the cathode of diode  244  to line  252  to the cathode of the diode  278 . From the anode of the diode  278  the signal passes to line  256  to the anodes of diodes  286 ,  288 . The signal through diode  286  passes from its anode to line  292  to chassis ground conductor  230  while the signal through diode  288  passes from its cathode to line  290  to shield conductor  226 . For terminal A_IN positive transient voltage surge pulses incurred between terminals  192  and  202 , or  192  and  182 , or  192  and  212  on terminal  192 . The transient is conducted along conductor  190  to fuse  194 . From fuse  194  the transient travels along line  196  to line  270  to the anode of diode  262 , the cathode of diode  262  the line  272  to the line  252  and the cathode of diode  278 . From the anode of diode  278  the pulse travels along line  256  to the anodes of the diodes  286  and  288  whose cathodes steer the transient to chassis ground line  230  and the shield line  226 , respectively. For a transient pulse incurred between lines  200  and  190 ,  200  and  210  or  200  and  180  the flow is via B_IN signal line  200  to input terminal  202  to fuse  204  to line  274  to the anode of diode  264  whose output at the cathode is applied over line  272  to line  252  and through diode  278  from cathode to anode to line  256 . This signal divides between diodes  286  and  288 , as explained above, and is coupled to the chassis ground conductor  230  and the shield conductor  226 . The application of a transient pulse to terminal  212  of conductor  210  is passed through fuse  214  to the anode of diode  242 , the cathode of diode  242 , line  252  to the diode  278 . The remainder of this circuit is the same as described with respect to the A_IN signal line  196  described above. A surge transient on shield line  220  from input terminal  222  is coupled by fuse  224  to line  226  and by line  290  to the anode of diode  282 , through diode  282  to the line  252  and through the diode  278 , cathode to anode to line  256  to line  294  to the anode of diode  286  and from the cathode of diode  286  to the chassis ground conductor  230 . The chassis ground line  230  is directly connected to an equipment ground and will ground any surge pulse applied to it. 
     A negative transient voltage surge pulse incurred between terminals  182  and  212 , or  182  and  222  or  182  and  232  is conducted through conductor  180 , fuse  184  to line  254 , through diode  246  from cathode to anode, line  256  to diode  278  where it passes anode to cathode to the cathodes of diodes  282  and  284 . The signal divides with a portion applied to each diode. The anode of diode  282  is coupled by line  290  to the shield line  226  while the anode of diode  284  is connected by line  292  to the chassis ground line  230 . A negative transient voltage surge pulse incurred between terminals  192  and  202 ,  192  and  222 , or  192  and  232  is conducted through terminal  192  as the A_IN terminal along conductor  190 , through fuse  194  to line  270  to the cathode of diode  268 . From the anode of diode  268  the pulse travels along line  276  to line  256  to diode  278  where it passes from anode to cathode to the line  252  and the juncture between diodes  282 ,  284  which operate in the same manner as set forth above with respect to the termination line  150 . A negative transient voltage surge pulse incurred between terminals  202  and  192 ,  202  and  222 , or  202  and  232  is conducted from input terminal J 1 - 4  B_IN to signal line  200  from terminal  202  is conducted through fuse  204  to conductor  206 . From conductor  206  it passes along line  274  to the cathode of diode  266 , from the anode of diode  266  along line  276  to line  256  to the diode  278 . The further connections are as described above. When the common line  210  incurs a negative transient voltage surge pulse between terminals  212  and  222  and  212  and  232  it is conducted via terminal  212  by fuse  214  to conductor  216 . From conductor  216  the pulse passes along line  250  to the cathode of diode  248 , from the anode of diode  248  to the line  256  to the diode  278  and through the diodes  282  and  284  as explained above. The presence of a negative surge pulse on the shield conductor  226  from terminal  222  via fuse  224  and lines  226  and  290  is applied to the cathode of diode  288 . The diode conducts via its anode to line  294 , line  256  to the anode of diode  278  which conducts anode to cathode and applies the transient to the cathode of diode  284  whose anode is connected via line  292  to the chassis ground conductor  230 . A negative voltage surge pulse applied to the chassis ground conductor  230  is directly connected to the system ground via line  236  and ground connection  238 . This circuit provides surge protection for line to line, line to shield and line to ground. 
     While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, as are presently contemplated for carrying them out, it will be understood that various omissions and substitutions and changes of the form and details of the devices illustrated and in their operation may be made by those skilled in the art, without departing from the spirit of the invention.