Abstract:
In distribution networks for safety sensors and devices, aspects of the invention provide routing individualized status signals in parallel to potential safety sensor locations in addition to serially routing safety signals to provide substantially increased protection. A shorting plug that electrically shorts together an individualized status signal to a voltage reference level at a safety sensor location, in addition to electrically shorting together the safety signals for electrical continuity, provides individualized status information for each potential safety sensor location in addition to the serial safety information provided by the safety signals. Another aspect of the invention provides a remote monitoring device coupled to one or more adapter ports, with each adapter port coupled to one or more safety sensors, wherein adapter ports are coupled via cabling with cable endings of the same type, thereby preventing circumvention of a safety sensor simply by coupling together adjacent cables.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to safety applications in industrial environments, and in particular, to distribution networks for safety sensors and devices. 
     Industrial environments typically include numerous mechanical operations, such as doors opening and closing, conveyor systems moving, and so forth. Such mechanical operations may be hazardous if the state is not known or fully appreciated. For example, if a door in the industrial environment is propped open, such as for inspection or diagnostics of machinery, and a conveyor system moves, or if a door in the industrial environment is closed, such as at a receiving station, and the conveyor system moves, a catastrophic condition could potentially result, such as human injury and/or property damage. 
     Safety sensors and safety distributions systems are known techniques for increasing the protection of personnel and equipment in such environments. Safety sensors may monitor, among other things, the status of doors and the motion of equipment. Safety sensors may comprise, for example, various modules with integrated proximity sensors, connectors or other mechanisms for detection, and switches for electrical signaling. Safety sensors are typically dispersed throughout the industrial environment and often attach to a one or more centralized safety distribution boxes as part of a safety sensor distribution network. 
     In operation, a safety signal may be routed to each particular safety sensor and back, such that if electrical continuity of the safety signal is detected, a safe condition is believed to be likely. On the other hand, if electrical continuity of the safety signal is not detected, such as the safety sensor breaking electrical continuity due to detection of an open door that should be closed, an unsafe condition may be presumed, an alert may be triggered, and the related industrial process may be stopped. 
     For additional safety, redundant signals may also be routed to each particular safety sensor and back, such that if electrical continuity is lost among any one of the safety signals, an unsafe condition may again be presumed. In addition, the safety signals are often routed serially through each safety sensor via the safety distribution box, such that if electrical continuity is lost due to any one of the safety sensors, an unsafe condition may again be presumed. 
     The safety distribution box often, in turn, couples to a power supply, a dedicated safety relay or safety programmable logic controller (“PLC”) and/or a general PLC. PLC&#39;s typically include a processor executing software stored in memory and numerous input and output connections for interacting with the industrial environment, including for monitoring safety signals and triggering an alert upon detecting an unsafe condition. 
     Shorting plugs that electrically short together safety signals are also typically used in such environments for maintaining flexibility. If, for example, a safety sensor is no longer needed, the safety sensor may be removed and a shorting plug may be installed in the old safety sensor&#39;s place at the safety distribution box. As such, electrical continuity of the safety signals may be maintained. 
     However, bypassing safety sensors that are still in use in the industrial environment with shorting plugs results in a loss of safety monitoring in the system. As a result, the potential for catastrophic conditions occurring increases. 
     SUMMARY OF THE INVENTION 
     The present inventors have recognized that individualized status signals routed in parallel to each of the potential safety sensor locations provides substantially increased protection. A shorting plug that electrically shorts together an individualized status signal to a voltage reference level at a safety sensor location, in addition to electrically shorting together the safety signals for electrical continuity as described above, provides individualized status information for each potential safety sensor location in addition to the serial safety information provided by the safety signals. 
     A PLC may implement logic, such as by executing computer software, to monitor the individualized status signals in addition to monitoring the safety signals. A table, which may be stored and periodically updated in the PLC, may indicate the presence or absence of safety sensors for each potential location. If electrical continuity in one or more safety signals are broken, such as by a safety sensor indicating an unsafe condition, or if an individualized status signal indicates the absence of a safety sensor and the corresponding table indicates that a safety sensor should be present, the PLC may trigger an alert, which may result in stopping one or more industrial processes, lighting a warning light, sounding an alarm and/or sending an electronic mail or SMS text message. 
     The shorting plug may electrically short together a status signal to a positive DC voltage reference level, such as +24 Volts DC, though in other embodiments, other voltage references or ground could be used. Installing the shorting plug may also illuminate a light emitting diode (“LED”) as a result of the electrical shorting which may be visually inspected. The LED may be located on the distribution box, or in an alternative embodiment, on the shorting plug itself. The shorting plug may also have preferred colors, such as red, and/or a preferred connector styles for ensuring its use in the safety system. 
     As such, in accordance with embodiments of the present invention, installation of shorting plugs in the place of safety sensors can be readily recognized and detected, thereby allowing verification of such uses, and possibly corrective actions. 
     Another aspect of the present invention provides a remote monitoring device, such as a PLC, coupled to one or more adapter ports, with each adapter port coupled to one or more safety sensors, wherein adapter ports are coupled via cabling with cable endings of the same type, such as female-to-female cable ends, or male-to-male cable ends. As such, an adapter port, and in turn, a safety sensor, may not be circumvented simply by coupling together adjacent cables. 
     These and other objects, advantages and aspects of the invention will become apparent from the following description. The particular objects and advantages described herein may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made, therefore, to the claims herein for interpreting the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a logical drawing of a distribution box, shorting plugs, safety sensors and remote devices in accordance with an embodiment of the present invention; 
         FIG. 2  is an isometric view of a distribution box in accordance with an embodiment of the present invention; 
         FIG. 3  is an isometric view of a shorting plug in accordance with an embodiment of the present invention; 
         FIG. 4  is a logical pin out drawing for a primary electrical connector for use with a distribution box in communicating with one or more remote devices in accordance with an embodiment of the present invention; 
         FIG. 5  is a logical pin out drawing for a secondary electrical connector for use with a distribution box in communicating with a safety sensor, which may also receive a shorting plug, in accordance with an embodiment of the present invention; 
         FIG. 6  is a schematic diagram of circuitry for a distribution box which may accommodate, for example, eight potential safety sensors, shorting plugs or combinations thereof, in accordance with an embodiment of the present invention; and 
         FIG. 7  is a logical drawing of a safety distribution system using a remote device, adapter ports, safety sensors and cabling with cable endings of the same type in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , various aspects of an embodiment of the present invention will now be described in the context of a safety distribution system  10 . The safety distribution system  10  may comprise a distribution box  12  with a primary electrical connector half  14  and a plurality of secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 . 
     The primary electrical connector half  14  may be used for communicating with one or more remote devices, including a power supply  40 , a dedicated safety relay or safety PLC  42  and/or a general PLC  44 . The power supply  40 , the safety PLC  42  and/or the general PLC  44  may be located together in a single enclosure  46  and may be in proximity to a warning light tower  48  or other alarm indicating device. The safety PLC  42  and the general PLC  44  may each include a processor executing software for monitoring the safety sensors, and in alternative embodiments, the functionality may be combined into a single PLC or other capable device. 
     The primary electrical connector half  14  may extend from the housing of the distribution box  12  for coupling to and communicating with one or more remote devices via a primary electrical cable  60  having an opposing electrical connector half. The primary electrical cable  60  may route signals of different varieties, including power signal conductors  62 , which provides a positive DC voltage reference level via +24V DC signal and a ground via Common signal, pairs of input and output safety signal conductors  64 , which may provide redundant serially connected safety signals throughout the safety system, and individualized status signal conductors  66 , which may provide an individual status signal for each potential safety sensor location. Within the single enclosure  46 , the power signal conductors  62  may couple to the power supply  40 , the safety signal conductors  64  may couple to the safety PLC  42 , and the status signal conductors  66  may couple to the general PLC  44 . Alternative embodiments, however, may provide more or fewer signals and in alternative arrangements, such as single PLC for safety and status signals, or a power supply local to or integrated within the distribution box  12 . 
     The secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30  each are used to communicate with one or more safety sensors of various configurations and types, and in this example, safety sensors  50 ,  52 ,  54 ,  56  and  58 . Safety sensors may include, for example, safety switches for detecting the change in position of objects and/or machinery, such as the SensaGuard™ system available from Rockwell Automation, Inc. of Milwaukee, Wis. Intermediate cables, such as cables  70  and  72 , cables  78  and  80 , cables  82  and  84 , and cables  86  and  88 , may be used for coupling the distribution box  12  to the safety sensors, such as safety sensors  50 ,  52 ,  54 ,  56 , and  58 , respectively, as the safety sensors may be widely dispersed throughout the industrial environment. Safety sensors  50 ,  52 ,  54 ,  56  and  58  have two jointly acting electrical switches controlled by a sensed condition, with one switch across a different input and output pair. 
     Through the primary electrical connector half  14 , the safety signal conductors  64  redundantly join the secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 , and safety sensors coupled thereto, in series from first to last, such that safety signal outputs of each secondary electrical connector half are coupled to safety signal inputs of a next secondary electrical connector half until reaching the last secondary electrical connector half. In this way, the safety signal conductors  64  couple serially from the safety PLC  42  to the primary electrical connector half  14 , via the primary electrical cable  60 , then to the first secondary electrical connector half  16 , then to any safety sensor attached to the first secondary electrical connector half  16 , then back out of the first secondary electrical connector half  16 , then to the next secondary electrical connector half  18 , and so forth. At the last secondary electrical connector half  30 , the safety signal conductors  64  continue to couple serially to the primary electrical connector half  14 , then back to the safety PLC  42  via the primary electrical cable  60 . 
     The safety PLC  42  may monitor electrical continuity of the safety signals  64 . If electrical continuity is lost on any of the serially connected safety signals  64 , such as by removal a safety sensor from a connector half, or by a safety sensor triggering an unsafe condition, or by faulty operation of a single safety signal, the safety PLC  42  detects the condition and responds accordingly by triggering an alert, such as illuminating a red light at the light tower  48 , sounding an alarm, and/or sending an electronic mail or SMS text message, and putting the system and/or machine into a safe state, such as stopping one or more industrial processes or machines. 
     If a safety sensor is not to be attached at a secondary electrical connector half, a shorting plug may be used in its place to maintain electrical continuity. For example, in the safety distribution system  10 , the safety signal conductors  64  couple serially from the safety PLC  42  to the primary electrical connector half  14 , via the primary electrical cable  60 , then to the first secondary electrical connector half  16 , then through a shorting plug  90  attached, which maintains serial electrical continuity across the first secondary electrical connector half  16 , then to the next secondary electrical connector half  18 , and so forth. The shorting plug  90  may have unique characteristics for distinguishing it from other types of shorting plugs and connectors, such as unique shapes, colors and/or markings. 
     In addition to safety signal conductors  64 , the safety distribution system  10  and the distribution box  12  also utilizes the status signal conductors  66 . The status signal conductors  66  provide an individualized status signal conductor to each potential safety sensor location via each secondary electrical connector half. The status signal conductors  66  may default to a particular condition when monitored, such as ground or floating high impedance, and upon insertion of a shorting plug at particular secondary electrical connector half, the corresponding status signal may be driven to a different condition, such as a DC voltage level, via electrical shorting by the shorting plug. This may allow, for example, detection of a shorting plug where a safety sensor is expected, thereby triggering an alert and putting the system and/or machine into a safe state. 
     In the safety distribution system  10 , the status signal conductors  66  couple individually, in parallel, from the general PLC  44  to the primary electrical connector half  14  via the primary electrical cable  60 . Then, a first status signal of the status signal conductors  66  couples to the first secondary electrical connector half  16 , a second status of the status signal conductors  66  couples to the next secondary electrical connector half  18 , and so forth, until each potential safety sensor location is coupled to a status signal. If a safety sensor is attached at a secondary electrical connector half, the respective status signal may simply default to the first condition, such as grounding or floating. However, if a shorting plug is attached to the secondary electrical connector half, the respective status signal may then be driven to the second condition, such as the DC voltage reference level, via the shorting plug. 
     In an alternative embodiment, safety signal conductors  64  and status signal conductors  66  may both be monitored by the safety PLC  42 , or may both be monitored by the general PLC  44  or by another device. 
     Referring now to  FIG. 2 , an isometric view of the distribution box  12  in accordance with an embodiment of the present invention is shown. The distribution box  12  may have varying standard and/or non-standard shapes, such as appearing long and rectangular with beveled edges, contours, mounting shapes and/or holes adequate for mechanically and functionally integrating into the industrial environment. 
     The primary electrical connector half  14  may be round with exterior circumferential threading  100  to allow an opposing electrical connector half, such as the connector on the primary electrical cable  60 , to attach. The primary electrical connector half  14  also includes a plurality of pins  102 , for example, nineteen pins here, for coupling the power signal conductors  62 , the pairs of input and output safety signal conductors  64  and the individualized status signal conductors  66 , and possibly others, to the power supply  40 , the safety PLC  42  and/or the general PLC  44 . 
     The secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30  may be round in shape with interior circumferential threading  102  to allow an opposing electrical connector half, such as a connector and cable leading to a safety sensor, or a connector on a shorting plug, to attach. The secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30  also each include a receiving block  104  for receiving the power signal conductors  62 , the safety signal conductors  64  and a particular status signal of the status signal conductors  66  and routing to the safety sensor or shorting plug. 
     In alternative embodiments, other connector shapes, sizes, configurations and/or styles for the primary electrical connector half  14  and/or the secondary electrical connectors halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30  may be used. 
     The distribution box  12  may also include labels  106  in proximity to the primary electrical connector half  14  and the secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 . The labels  106  may be manually updated with text or symbols for increased safety in the industrial environment, such as indicating no safety sensor in a particular position, and hence a shorting plug is expected, or a safety sensor in a particular position, and hence a safety sensor (and not shorting plug) is expected. 
     The distribution box  12  may also include a plurality of light emitting diodes (“LED&#39;s”) (not shown), including, for example, a power LED which may be green when lit for indicating the distribution box  12  is receiving power, and a plurality of status LED&#39;s which may be amber when lit for indicating if a particular status signal is being driven to the second condition by a shorting plug as described above with respect to  FIG. 1 . Each LED may be visually inspected and compared to the industrial environment and operating software for increased safety. 
     Referring now to  FIG. 3 , an isometric view of the shorting plug  90  in accordance with an embodiment of the present invention is shown. The shorting plug  90  may be generally cylindrical in shape, though other standard and/or non-standard shapes may apply, including beveled edges and ergonomic contours. The electrical connecting end of the shorting plug  90  may be round with exterior circumferential threading  150  to allow attachment to one of the secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 . The shorting plug  90  also includes a plurality of pins  152 , for example, eight pins here, for coupling with the receiving block  104  of one of the secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 . 
     In an alternative embodiment, the shorting plug  90  may also include an LED that may be lit when attached to a secondary electrical connector half for indicating that the particular status signal is being driven to the second condition as described above with respect to  FIG. 1 . The LED may be visually inspected and compared to the industrial environment and operating software for increased safety. The shorting plug may also have a preferred color, such as red, and/or a preferred connector style, for ensuring its use in the system. 
     Referring now to  FIG. 4  and to Table 1 below, a logical pin out drawing and related description for the primary electrical connector half  14  is shown in accordance with an embodiment of the present invention. The example primary electrical connector half  14  here has nineteen connector pins  201 - 219 , with certain connector pins being no-connects and/or reserved for future use, an electrical shrouding  222  and a notch  224  for facilitating a keyed insertion. Table 1 also includes wiring colors for distinguishing each conductor signal in use. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Connector Pin 
                 Description 
                 Wiring Color 
               
               
                   
               
             
             
               
                 201 
                 — 
                 — 
               
               
                 202 
                 Safety A+ (OSSD) 
                 Red 
               
               
                 203 
                 Safety B (OSSD) 
                 Grey 
               
               
                 204 
                 Aux J2 
                 Red/Blue 
               
               
                 205 
                 — 
                 — 
               
               
                 206 
                 Common 
                 Blue 
               
               
                 207 
                 Aux J1 
                 Grey/Pink 
               
               
                 208 
                 Aux J3 
                 White/Green 
               
               
                 209 
                 Aux J5 
                 White/Yellow 
               
               
                 210 
                 Aux J7 
                 White/Grey 
               
               
                 211 
                 Lock Command 
                 Black 
               
               
                 212 
                 Ground 
                 Green/Yellow 
               
               
                 213 
                 Aux J6 
                 Yellow/Brown 
               
               
                 214 
                 Aux J4 
                 Brown/Green 
               
               
                 215 
                 — 
                 — 
               
               
                 216 
                 Safety B+ (OSSD) 
                 Yellow 
               
               
                 217 
                 Safety A (OSSD) 
                 Pink 
               
               
                 218 
                 Aux J8 
                 Grey/Brown 
               
               
                 219 
                 +24 V DC 
                 Brown 
               
               
                   
               
             
          
         
       
     
     The power signal conductors  62  may include the Common signal at connector pin  206 , the Ground signal at connector pin  212 , and the +24V DC signal at connector pin  219 . 
     The safety signal conductors  64  may include an input Safety A+(output signal switching device (“OSSD”)) signal at connector pin  202 , serially routed through the safety sensors (or shorting plugs) via the distribution box  12 , with a corresponding output Safety A (OSSD) signal at connector pin  217 , and another input Safety B+(OSSD) signal at connector pin  216 , also serially routed through safety sensors (or shorting plugs) via the distribution box  12 , with another corresponding output Safety B (OSSD) signal at connector pin  203 . If a loss of electrical continuity is detected in either serially routed path, the system may trigger an alert and put the system and/or machine into a safe state accordingly. 
     The status signal conductors may include the Aux J1 signal at connector pin  207 , the Aux J2 signal at connector pin  204 , the Aux J3 signal at connector pin  208 , the Aux J4 signal at connector pin  214 , the Aux J5 signal at connector pin  209 , the Aux J6 signal at connector pin  213 , the Aux J7 signal at connector pin  210  and the Aux J8 signal at connector pin  218 . If, for example, the distribution box  12  has only four secondary electrical connector halves, then only four status signal conductors, such as Aux J144, may be used. However, if, for example, the distribution box  12  has eight secondary electrical connector halves, then all eight status signal conductors, Aux J1-J8, would be used. Alternative embodiments may provide additional conductor signals, connector pins and/or arrangements for further variations. 
     The Lock Command signal at connector pin  211  may be used by the safety PLC  42 , the general PLC  44  and/or any other remote device for locking the configuration. The connector pins  201 ,  205  and  215  in this embodiment are reserved for future use. 
     Referring now to  FIG. 5  and to Table 2 below, a logical pin out drawing and related description for the secondary electrical connector half  16  is shown in accordance with an embodiment of the present invention. The exemplar secondary electrical connector half  14  here has eight connector pins  231 - 238 , an electrical shrouding  242  and a notch  244  for facilitating a keyed insertion. 
     
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Connector Pin 
                 Description 
               
               
                   
               
             
             
               
                 231 
                 Aux 
               
               
                 232 
                 +24 V DC 
               
               
                 233 
                 Lock Command 
               
               
                 234 
                 Safety B+ (OSSD) 
               
               
                 235 
                 Safety A (OSSD) 
               
               
                 236 
                 Safety B (OSSD) 
               
               
                 237 
                 Common 
               
               
                 238 
                 Safety A+ (OSSD) 
               
               
                   
               
             
          
         
       
     
     The power signal conductors  62  may include coupling of the +24V DC signal at connector pin  232  and the Common signal at connector pin  237 , of the secondary electrical connector half  16 , from corresponding signals of the primary electrical connector half  14 . The safety signal conductors  64  may include coupling the input Safety A+(OSSD) signal at connector pin  238 , the output Safety A (OSSD) signal at connector pin  235 , the input Safety B+(OSSD) signal at connector pin  234  and the output Safety B (OSSD) signal at connector pin  236 , of the secondary electrical connector half  16 , from corresponding signals of the primary electrical connector half  14 . The status signal conductors  66  may include coupling the Aux signal at connector pin  231  of the secondary electrical connector half  16  from a particular one of the status signal conductors  66  from the primary electrical connector half  14 . A Lock Command signal may also be coupled to connector pin  233  of the secondary electrical connector half  16  from a corresponding signal of the primary electrical connector half  14 . 
     Referring now to  FIG. 6 , circuitry  300  for the distribution box  12 , which may accommodate, for example, eight potential safety sensors, shorting plugs or combinations thereof, is shown in accordance with an embodiment of the present invention. As described above with respect to  FIGS. 1, 4 and 5 , the power signal conductors  62  may comprise coupling of the +24V DC signal at connector pin  219  of the primary electrical connector half  14  to connector pin  232  at each of the secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 , and coupling the Common signal at connector pin  206  of the primary electrical connector half  214  to connector pin  237  at each of the secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 . The circuitry  300  may also include an LED  314  in series with a resistor  316 , coupled between the +24V DC signal and the Common signal, wherein the LED  314  illuminates upon receiving power. 
     The safety signal conductors  64  may comprise coupling the input Safety A+(OSSD) signal at connector pin  202  of the primary electrical connector half  14  to the input Safety A+(OSSD) signal at connector pin  238  of the first secondary electrical connector half  16 . Next, a safety sensor or shorting plug (not shown) allows coupling the input Safety A+(OSSD) signal at connector pin  238  of the first secondary electrical connector half  16  to the output Safety A (OSSD) signal at connector pin  235  of the first secondary electrical connector half  16 . Next, the output Safety A (OSSD) signal at connector pin  235  of the first secondary electrical connector half  16  couples to the input Safety A+(OSSD) signal at connector pin  238  of the next secondary electrical connector half  18 . Another safety sensor or shorting plug (not shown) then allows coupling the input Safety A+(OSSD) signal at connector pin  238  of the secondary electrical connector half  18  to the output Safety A (OSSD) signal at connector pin  235  of the secondary electrical connector half  18 . Next, the output Safety A (OSSD) signal at connector pin  235  of the secondary electrical connector half  18  couples to the input Safety A+(OSSD) signal at connector pin  238  of the next secondary electrical connector half  20 . This serial coupling continues from secondary electrical connector half to next secondary electrical connector half until reaching the last secondary electrical connector half  30 . At the last secondary electrical connector half  30 , the output Safety A (OSSD) signal at connector pin  235  couples to the output Safety A (OSSD) signal at connector pin  217  of the primary electrical connector half  14 . 
     In a similar, redundant fashion, the input Safety B+(OSSD) signal at connector pin  216  of the primary electrical connector half  14  couples to the input Safety B+(OSSD) signal at connector pin  234  of the first secondary electrical connector half  16 . Again, the safety sensor or shorting plug (not shown) allows coupling the input Safety B+(OSSD) signal at connector pin  234  of the first secondary electrical connector half  16  to the output Safety B (OSSD) signal at connector pin  236  of the first secondary electrical connector half  16 . Next, the output Safety B (OSSD) signal at connector pin  236  of the first secondary electrical connector half  16  couples to the input Safety B+ (OSSD) signal at connector pin  234  of the next secondary electrical connector half  18 . Another safety sensor or shorting plug (not shown) then allows coupling the input Safety B+(OSSD) signal at connector pin  234  of the secondary electrical connector half  18  to the output Safety B (OSSD) signal at connector pin  236  of the secondary electrical connector half  18 . Next, the output Safety B (OSSD) signal at connector pin  236  of the secondary electrical connector half  18  couples to the input Safety B+(OSSD) signal at connector pin  234  of the next secondary electrical connector half  20 . This serial coupling also continues from secondary electrical connector half to next secondary electrical connector half until reaching the last secondary electrical connector half  30 . At the last secondary electrical connector half  30 , the output Safety B (OSSD) signal at connector pin  236  couples to the output Safety B (OSSD) signal at connector pin  203  of the primary electrical connector half  14 . 
     The status signal conductors  66  may comprise individually coupling the Aux J1-J8 status signals from the primary electrical connector half  14  to each of the respective secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 . For example, the Aux J1 signal at connector pin  207  of the primary electrical connector half  14  individually couples to the Aux signal at connector pin  231  of the secondary electrical connector half  16 ; the Aux J2 signal at connector pin  204  of the primary electrical connector half  14  individually couples to the Aux signal at connector pin  231  of the next secondary electrical connector half  18 ; and so forth. 
     If a shorting plug (not shown) is attached to one of the secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 , the shorting plug couples together the Aux signal at connector pin  231  of that secondary electrical connector half to the +24V DC signal at connector pin  232  of that secondary electrical connector half. As such, a remote device monitoring the status signal conductors  66 , such as the general PLC  44 , may detect the +24V DC signal, which may be accordingly interpreted by the remote device as a shorting plug present at that secondary electrical connector half. The remote device may then execute software to read a table from memory which indicates the expected presence or absence of safety sensors for each secondary electrical connector half associated with a status signal, and then trigger an alert and/or put the system and/or machine into a safe state if the table indicates that a shorting plug should be present. 
     If, on the other hand, a safety sensor (not shown) is attached to the secondary electrical connector half, the safety sensor does not couple the Aux signal at connector pin  231  of the secondary electrical connector half to the +24V DC signal at connector pin  232  of the secondary electrical connector half. As such, the remote device may interpret the status signal in its default condition as indicating no shorting plug is present at that secondary electrical connector half Once again, the remote device may execute software to read the table from memory which indicates the expected presence or absence of safety sensors for each secondary electrical connector half associated with a status signal, and in this case, trigger an alert and/or put the system and/or machine into a safe state if the table indicates that a shorting plug should be present. 
     Each of the status signal conductors  66  may also couple to an LED that illuminates upon a shorting plug coupling together the Aux signal at connector pin  231  of a secondary electrical connector half to the +24V DC signal at connector pin  232  of the secondary electrical connector half. For example, the Aux signal at connector pin  231  of the secondary electrical connector half  16  may also couple to an LED  302  in series with a resistor  304  to the Common signal at connector pin  237  of the secondary electrical connector half  16 ; the Aux signal at connector pin  231  of the secondary electrical connector half  18  may also couple to an LED  306  in series with a resistor  308  to the Common signal at connector pin  237  of the secondary electrical connector half  18 ; and so forth. 
     The Lock Command signal at connector pin  211  of the primary electrical connector half  14  also couples to the Lock Command signal at connector pin  233  for each of the respective secondary electrical connector halves  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 . 
     Referring now to  FIG. 7 , a safety distribution system  400  is shown. The safety distribution system  400  may comprise an enclosure  402  in proximity to a warning light tower, or other alarm indicating device, and may contain a remote monitoring device  404 , such as a safety PLC. A group of safety signal conductors  406 , which may include a Safety A+(OSSD) signal  408 , a Safety B+(OSSD) signal  410 , a Safety A (OSSD) signal  412  and a Safety B (OSSD) signal  414 , as described with respect to  FIGS. 1 and 4-6  above, are coupled to the device  404  for monitoring electrical continuity of the safety signal conductors  406 , which provide redundant loop back paths through safety sensors in the system. 
     The safety signal conductors  406  are coupled to a first electrical cable  420  having cable endings  422  and  424  of the same type, such as female cable end  422  and female cable end  424 . The first electrical cable  420 , in turn, couples to a first adapter port  426  via a first connector half  428  of the opposite type as the cable end  424 . The first adapter port  426 , in turn, couples the safety signal conductors  406 , via a second connector half  430 , to a safety sensor cable  432  and safety sensor  434 . The first adapter port  426  receives the safety signal conductors  406  back from the safety sensor cable  434  via the safety sensor cable  432 , and, in turn, couples the safety signal conductors  406  to a third connector half  436 . 
     A second electrical cable  440  having cable endings  442  and  444  of the same type, and similar to the first electrical cable  420  and cable endings  422  and  424 , couples between the first adapter port  426 , via the third connector half  436 , and a second adapter port  446 , via a first connector half  448  on the second adapter port  446  of the opposite type as the cable end  444 . Similar to as described above, the second adapter port  448 , in turn, couples the safety signal conductors  406 , via a second connector half  450 , to a safety sensor cable  452  and safety sensor  454 . The second adapter port  446  receives the safety signal conductors  406  back from the safety sensor cable  454  via the safety sensor cable  452 , and in turn, couples the safety signal conductors  406  to a third connector half  456 . This coupling may repeat multiple times via multiple cables and adapter ports until reaching a last adapter port  466 . At the last adapter port  466 , a shorting plug  480  may be coupled to a third connector half  476  of the last adapter port  476  to loop back the safety signal conductors  406  through each cable and adapter port to the device  404 . The device  404  may then monitor the safety signal conductors  406  for electrical continuity, and may trigger an alert and/or put the system and/or machine into a safe state if electrical continuity on any of the safety signal conductors  406  is lost. 
     Accordingly, the safety sensor  434  may not be bypassed simply by coupling the first electrical cable  420  to the second electrical cable  440  as the cable ends  424  and  442  are of the same type. Similarly, the safety sensor  454  may not be bypassed simply by coupling the second electrical cable  440  to the third electrical cable  460  as the cable ends  444  and  462  are of the same type. Also, the safety sensor  474  may not be bypassed simply by coupling the third electrical cable  460  to the shorting plug  480  as the cable end  464  and the connector half on the shorting plug  480  are of the same type. 
     In an alternative embodiment, male cable endings of the same type may be used. In addition, in alternative embodiments, another safety sensor instead of a shorting plug may be used, or one or more adapter port having differing numbers of connector halves, and subsequently attached safety sensors and/or shorting plugs, may also be used. 
     One or more specific embodiments of the present invention have been described above. It is specifically intended that the present invention not be limited to the embodiments and/or illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the present invention unless explicitly indicated as being “critical” or “essential.” 
     Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper,” “lower,” “above,” and “below” refer to directions in the drawings to which reference is made. Terms such as “front,” “back,” “rear,” “bottom,” “side,” “left” and “right” describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first,” “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
     When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a,” “an,” “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising,” “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     References to “a microprocessor” and “a processor” or “the microprocessor” and “the processor” can be understood to include one or more microprocessors that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices. Furthermore, references to memory, unless otherwise specified, can include one or more processor-readable and accessible memory elements and/or components that can be internal to the processor-controlled device, external to the processor-controlled device, and can be accessed via a wired or wireless network. 
     The present invention may be part of a “safety system” used to protect human life and limb in a field, warehouse, factory or industrial environment. Nevertheless, the term “safety,” “safely” or “safe” as used herein is not a representation that the present invention will make the environment safe or that other systems will produce unsafe operation. Safety in an industrial process depends on a wide variety of factors outside of the scope of the present invention including: design of the safety system, installation and maintenance of the components of the safety system, and the cooperation and training of individuals using the safety system. Although the present invention is intended to be highly reliable, all physical systems are susceptible to failure and provision must be made for such failure.