Abstract:
A relay includes a first terminal, a second terminal, a third terminal, a fourth terminal, separable contacts electrically connected between the first and second terminals, an actuator coil comprising a first winding and a second winding, the first winding electrically connected between the third and fourth terminals, the second winding electrically connected between the third and fourth terminals, a processor, an output, a first voltage sensing circuit cooperating with the processor to determine a first voltage between the first and second terminals, and a second voltage sensing circuit cooperating with the processor to determine a second voltage between the third and fourth terminals. The processor determines that the separable contacts are closed when the first voltage does not exceed a first predetermined value and the second voltage exceeds a second predetermined value and responsively outputs a corresponding status to the output.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Patent Application Ser. No. 61/609,532, filed Mar. 12, 2012, which is incorporated by reference herein. 
    
    
     BACKGROUND 
     Field 
     The disclosed concept pertains generally to electrical switching apparatus and, more particularly, to relays, such as, for example, aircraft relays. 
     Background Information 
       FIG. 1  shows a conventional electrical relay  2  including a movable contact  4 , which makes or breaks a conductive path between main terminals A 1  and A 2 . Terminals X 1  and X 2  electrically connect to solenoid actuator coil windings  6 , 8 . On many relays, the actuator coil has two separate windings or a partitioned winding used to actuate closure of separable main contacts, such as  10 , and to hold the separable main contacts  10  together in a relay closed or on state. The need for the two coil windings  6 , 8  is the result of the desire to minimize the amount of electrical coil power needed to maintain the relay  2  in the closed state. 
     A typical normally open relay has a spring (not shown) on its armature mechanism (not shown) that holds the separable main contacts  10  open. In order to initiate movement of the armature mechanism for closure, a relatively large magnetic field is generated to provide sufficient force to overcome the inertia of the armature mechanism and, also, to build up enough flux in the open air gap of its solenoid (not shown) to create the desired force. During closure motion of the armature mechanism, both coil windings  6 , 8  are energized to produce a sufficient magnetic field. After the main contacts  10  close, the reluctance of the magnetic path in the solenoid is relatively small, and a relatively smaller coil current is needed to sustain the force needed to hold the main contacts  10  together. At this point, an “economizer” or “cut-throat” circuit (not shown) can be employed to de-energize one of the two coil windings  6 , 8  to conserve power and to minimize heating in the solenoid. 
     The economizer circuit (not shown) is often implemented via an auxiliary relay contact  12  (E 1 -E 2 ) that is physically driven by the same solenoid mechanism (not shown) as the main contacts  10 . The auxiliary relay contact  12  simultaneously opens as the main contacts  10  close, thereby confirming complete motion of the armature mechanism. The added complexity of the auxiliary contact  12  and the calibration needed for the simultaneous operation makes this configuration relatively difficult and costly to manufacture. 
     Alternatively, the economizer circuit (not shown) can be implemented by a timing circuit (not shown) which pulses a second coil winding, such as  8 , only for a predetermined period of time, proportional to the nominal armature mechanism operating duration, in response to a command for relay closure (i.e., a suitable voltage applied between terminals X 1 -X 2 ). While this eliminates the need for an auxiliary switch, it does not provide confirmation that the armature mechanism has closed fully and is operating properly. 
     There is room for improvement in relays. 
     SUMMARY 
     This need and others are met by embodiments of the disclosed concept in which a relay comprises: a first terminal; a second terminal; a third terminal; a fourth terminal; separable contacts electrically connected between the first and second terminals; an actuator coil comprising a first winding and a second winding, the first winding electrically connected between the third and fourth terminals, the second winding electrically connected between the third and fourth terminals; a processor; an output; a first voltage sensing circuit cooperating with the processor to determine a first voltage between the first and second terminals; and a second voltage sensing circuit cooperating with the processor to determine a second voltage between the third and fourth terminals, wherein the processor is structured to determine that the separable contacts are closed when the first voltage does not exceed a first predetermined value and the second voltage exceeds a second predetermined value and to responsively output a corresponding status to the output. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG. 1  is a block diagram of a conventional electrical relay. 
         FIG. 2  is a block diagram in schematic form of a circuit for sensing a direct current (DC) voltage on relay terminals in accordance with an embodiment of the disclosed concept. 
         FIGS. 3A and 3B  are block diagrams in schematic form of other current limiting circuits for the DC voltage sensing circuit of  FIG. 2 . 
         FIG. 4  is a block diagram in schematic form of a circuit for sensing alternating current (AC) or an inverted voltage on relay terminals in accordance with another embodiment of the disclosed concept. 
         FIG. 5  is a block diagram in schematic form of a circuit for sensing a direct differential terminal voltage in accordance with another embodiment of the disclosed concept. 
         FIG. 6  is a block diagram in schematic form of a circuit for indirect differential DC terminal voltage sensing in accordance with another embodiment of the disclosed concept. 
         FIG. 7  is a block diagram in schematic form of a circuit for indirect differential AC or inverted terminal voltage sensing in accordance with another embodiment of the disclosed concept. 
         FIG. 8  is a block diagram in schematic form of a relay including two terminal voltage sensing circuits for the main contacts (or load terminals) and the coil control terminals in accordance with another embodiment of the disclosed concept. 
         FIG. 9  is a block diagram in schematic form of a relay including two ground referenced terminal voltage sensing circuits for the main contacts (or load terminals) and the coil control terminals in accordance with another embodiment of the disclosed concept. 
         FIG. 10  is a block diagram in schematic form of a relay including two dual input/dual output terminal voltage sensing circuits for the main contacts (or load terminals) and the coil control terminals in accordance with another embodiment of the disclosed concept. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 
     As employed herein, the term “processor” shall mean a programmable analog and/or digital device that can store, retrieve, and process data; a controller; a computer; a workstation; a personal computer; a microprocessor; a microcontroller; a microcomputer; a central processing unit; a mainframe computer; a mini-computer; a server; a networked processor, or any suitable processing device or apparatus. 
     As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly. 
     The disclosed concept is described in association with aircraft relays, although the disclosed concept is applicable to a wide range of electrical relays. 
     Referring to  FIG. 2 , by providing voltage sensors, such as  20 , in order that the voltages at the main contacts  10  or load terminals (A 1 -A 2 ) and the coil control terminals (X 1 -X 2 ) of  FIG. 1  are known, control of the relay  2  can be optimized and diagnostic information can be obtained. Specifically, if the voltages at the load terminals (A 1 -A 2 ) are monitored, then the timing of contact closure can be determined and, hence, could be employed by an alternative mechanism to energize the two coil windings  6 , 8 . For example and without limitation, a suitable processor, such as an embedded microcontroller or an analog control circuit, can be employed as a main controller to switch off a second coil winding (e.g., without limitation, employing a solid state power transistor; a switch; a signal relay). Furthermore, if the main controller knows the two sets of terminal voltages, then by employing suitable deductive logic, basic diagnostics and/or health monitoring of the relay  2  can be performed on a continuous basis. For example, if there is no voltage applied to the coil control terminals (X 1 -X 2 ) (i.e., an open command), yet the load terminals (A 1 -A 2 ) both have equal, but non-zero voltages on them, then this could indicate that the main contacts  10  are welded and are incapable of opening. 
     The example electronic circuit  20  of  FIG. 2  can be employed to sense voltages across two input terminals  22 , 24 . This circuit  20  can sense both AC and DC voltages, although only a positive voltage is acknowledged. If a difference in properly polarized voltage is present across the input terminals  22 , 24 , then the series combination of rectifier diode  26 , zener diode  28 , current limiting diode  30  and input light emitting diode (LED)  32  of opto-isolator  34  begin to conduct. The diode  26  protects the opto-isolator LED  32  from reverse voltages and may be omitted if reverse voltages are not expected. The zener diode  28  sets a minimum voltage needed for detection. This can be employed to avoid false detection of a stray voltage or noise on the input terminals  22 , 24 . The current limiting diode  30  controls the current such that a suitable current flows regardless of the input terminal voltage. The diode  30  can be replaced by a plurality of series-connected diodes (not shown) if terminal voltages are expected to exceed the diode&#39;s rated reverse voltage. In that case, as is conventional, a suitable voltage balancing resistor network (not shown) can be employed parallel to the series-connected diodes. The photo-transistor detector  36  of the opto-isolator  34  outputs a suitable logic output  38  to a processor (e.g., microprocessor) (not shown) to determine the state of the system operatively associated with the two input terminals  22 , 24 . If the logic output  38  is employed to sense an alternating current (AC) voltage, the logic output  38  can be suitably filtered or time averaged since, otherwise, it is only active (i.e., logic low in this example) during the positive half cycle of an input AC voltage. 
       FIGS. 3A and 3B  show a suitable combination of a resistor  40  and a JFET  42 , and a resistor  44  and a depletion-mode MOSFET  46 , respectively, that can be substituted for the current limiting diode  30  of  FIG. 2 . 
       FIG. 4  shows a bi-polar circuit  50  corresponding to the circuit  20  of  FIG. 2 . The bi-polar circuit  50  operates in the same manner, except that both positive and negative terminal voltages can generate an output logic signal  52 . This allows detection of both positive and negative half-cycles of an AC signal at input terminals  54 , 56 . Some suitable processing of the output logic signal  52  is employed by a monitoring circuit (not shown), in order to account for output interruptions near the AC waveform zero-crossings. 
       FIG. 5  shows another circuit  60  for sensing differential AC or DC voltages across two input terminals  62 , 64 . The example circuit  60  has an advantage over the circuits  20 , 50  of  FIGS. 2 and 4  and provides a relatively high input impedance with relatively less loading of the input terminals  62 , 64  (i.e., there are relatively very low leakage currents). The operational amplifier  66  is configured as a common differential amplifier. Resistors  68 , 70 , 72 , 74  are selected to provide an overall gain (or attenuation) of the amplifier stage, such that an appropriate voltage is presented at the op-amp output  76  for driving the opto-isolator input LEDs  78 , 80 . The op-amp output signal  82  is proportional to the differential voltage on the input terminals  62 , 64 . Since a minimum voltage is needed to bias the input LEDs  78 , 80  on, this circuit  60  provides no logic output with near zero input voltages. This circuit  60  also can avoid false detection of a stray voltage or noise on the input terminals  62 , 64 . Diodes  84  and  86  clamp the input voltage protect the op-amp  66  from relatively high input voltage transients. The op-amp  66  employs an independent, isolated power supply (not shown) for power; however, if a plurality of circuits, such as  60 , are employed to sense a plurality of other terminal pairs (not shown) at similar voltage levels, then a common power supply (not shown) can be employed for these circuits. 
       FIG. 6  shows a circuit  90  including two voltage comparators  92 , 94  to detect the presence of voltage on the main relay terminals (A 1 -A 2 ). This circuit  90  senses the presence of voltage with respect to a common ground reference  96 , such as for example and without limitation, the chassis of an aircraft (not shown) in which a corresponding relay (not shown) is installed. The example circuit  90  employs two resistor divider networks,  98 , 100  and  102 , 104 , to indirectly present proportionately scaled voltages at the non-inverting (+) inputs of the two comparators  92 , 94 . By comparing these voltages to a predetermined voltage reference, Vref, each of the two comparator outputs  106 , 108  represents the corresponding terminal input voltage and provides a high-level logic signal if the corresponding terminal input voltage is above a predetermined value as determined by the ratio of the corresponding resistor divider network resistances and the predetermined voltage reference Vref voltage. The example circuit  90  senses positive DC voltages. 
     Alternatively, AC voltages can be detected if diodes (not shown) are added at the inputs in series with the resistors  98  and  102 , and processing of the output signals is provided as was discussed, above, in connection with the circuit  20  of  FIG. 2 . As with that circuit  20 , only the positive half-cycle voltage is detected. If the monitoring circuit (not shown) is powered from a chassis-referenced power supply (not shown), then the same power supply can power the two comparators  92 , 94 . 
       FIG. 7  shows a window comparator-based sensing circuit  110 , which can sense AC voltages. This circuit  110  works similar to the circuit  90  of  FIG. 6 , except that the comparators  112 , 114 , 116 , 118  are configured in pairs to produce logic-high outputs  120 , 122  when each corresponding input terminal voltage is near zero. The near zero range is determined by the ratios of the resistor divider networks,  124 , 126  and  128 , 130 , and the voltage reference levels, Vref_1&gt;0 and Vref_2&lt;0. The example comparators  112 , 114 , 116 , 118  have open collector outputs in order to logic-OR their outputs to implement the window comparator function. Alternatively, the two outputs of each window comparator pair can employ an exclusive-OR discrete electronic logic gate (not shown) or the main controller circuit (not shown) can generate a single output signal that switches states only if both sensed input terminal voltages are unequal, as would be the case if the corresponding relay contacts (not shown) were open. As with the circuit  90  of  FIG. 6 , the power supply (not shown) of the main controller circuit (not shown) is referenced to the chassis ground  96 . 
     The voltage sensing circuits  20 , 50 , 60 , 90 , 110  of  FIGS. 2 and 4-7  are non-limiting examples of circuits to sense relay terminal voltages, although a wide range of suitable voltage sensing circuits may be employed.  FIG. 8-10  show examples of relay systems  140 , 240 , 340  including these voltage sensing circuits. In  FIG. 8 , both of the load terminals (A 1 -A 2 ) and the coil control terminals (X 1 -X 2 ) of relay  141  are monitored by one of these voltage sensing circuits, such as the direct differential terminal voltage sensing circuit  60  of  FIG. 5 . A relay controller module  142  receives the logic outputs  144 , 146  of the voltage sensing circuits  20 , 50  or  60  and uses suitable logic (e.g. without limitation, as shown in Table 1, below, which shows diagnostics with only voltage sensing) to determine the state of the relay main contacts  10 . The term “V High” means that the input terminal voltage is above a corresponding suitable predetermined threshold voltage for that terminal, and the term “V Low” means that the input terminal voltage is below a corresponding suitable predetermined threshold voltage for that terminal. These corresponding suitable predetermined threshold voltages can be the same, although upper and lower thresholds for each signal preferably allow for out-of-range parameter detection. 
     The controller module  142  can be any suitable processor, such as for example and without limitation, an embedded microcontroller circuit, digital logic circuitry and/or discrete analog components. The controller module  142  implements an economizer circuit function by direct control from output  143  of a suitable switch  148  electrically connected in series with the second pull-in solenoid coil winding  150 . The switch  148  can be, for example and without limitation, a suitable signal electro-mechanical relay or a suitable semiconductor device, such as a transistor. The controller module  142  sends relay status information  152  by a suitable communication interface  154  to a power distribution unit (PDU), a main controller or a load management controller  156  (e.g., for a vehicle). 
     Example 1 
     A load terminal (A 1 -A 2 ) differential voltage can be about 50 mV to about 175 mV when the separable contacts are closed in the presence of a suitable load current, while the load terminal A 2  can be at about 0 mV when the separable contacts are open. 
     
       
         
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 V A1-GND   
                 V A2-GND   
                 V A1-A2   
                 V X1-GND   
                 V X2-GND   
                 V X1-X2   
                 Information Deduced 
                 Status 
               
               
                   
               
             
             
               
                 Low 
                 Low 
                 Low 
                 Low 
                 Low 
                 Low 
                 No power on input; Relay commanded open; 
                 No Fault 
               
               
                   
                   
                   
                   
                   
                   
                 Relay contact status: undetermined 
                   
               
               
                 High 
                 Low 
                 High 
                 Low 
                 Low 
                 Low 
                 Power present at input; Relay commanded open;  
                 No Fault 
               
               
                   
                   
                   
                   
                   
                   
                 Relay contact status: open 
                   
               
               
                 High 
                 High 
                 Low 
                 Low 
                 Low 
                 Low 
                 Power present at input and output; Relay  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                 commanded open; Relay contact status: possibly  
                   
               
               
                   
                   
                   
                   
                   
                   
                 closed (failed or welded) 
                   
               
               
                 High 
                 High 
                 Low 
                 Low 
                 High 
                 High 
                 Power present at input and output; Relay  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                 command undefined (possible loss of connection  
                   
               
               
                   
                   
                   
                   
                   
                   
                 at input); Relay contact status; possibly closed 
                   
               
               
                 Low 
                 Low 
                 Low 
                 High 
                 Low 
                 High 
                 No power on input; Relay commanded closed;  
                 No Fault 
               
               
                   
                   
                   
                   
                   
                   
                 Relay contact status: undetermined 
                   
               
               
                 High 
                 Low 
                 High 
                 High 
                 Low 
                 High 
                 Power present at input; Relay commanded closed;  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                 Relay contact status: open (failed to close) 
                   
               
               
                 High 
                 High 
                 Low 
                 High 
                 Low 
                 High 
                 Power present at input and output (normal power  
                 No Fault 
               
               
                   
                   
                   
                   
                   
                   
                 to load); Relay commanded closed; Relay contact  
                   
               
               
                   
                   
                   
                   
                   
                   
                 status: closed 
                   
               
               
                 High 
                 High 
                 Low 
                 High 
                 High 
                 Low 
                 Power present at input and output; Relay  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                 commanded open (possible loss of connection  
                   
               
               
                   
                   
                   
                   
                   
                   
                 at input); Relay contact status: closed 
               
               
                   
               
             
          
         
       
     
     In Tables 1 and 2:
         V A1-GND  is voltage at terminal A 1  with respect to ground (e.g. chassis ground);   V A2-GND  is voltage at terminal A 2  with respect to ground (e.g., chassis ground);   V A1-A2  is differential voltage between terminals A 1  and A 2 ;   V X1-GND  is voltage at terminal X 1  with respect to ground (e.g., chassis ground);   V X2-GND  is voltage at terminal X 2  with respect to ground (e.g., chassis ground);   V X1-X2  is differential voltage between terminals X 1  and X 2 ;   Current (Table 2 only) is current flowing between terminals A 1  and A 2 ;   Low means that voltage (or current) is below an expected minimum threshold; and   High means that voltage (or current) is above an expected minimum threshold.       

       FIG. 9  shows another relay system  240  in which the four terminal voltages for (A 1 , A 2 , X 1  and X 2 ) of relay  241  are sensed with respect to the vehicle chassis ground  96 . The four discrete logic outputs  242 , 244 , 246 , 248  from the voltage sensing circuits  20 , 50  or  60  of  FIG. 2, 4 or 5  are processed by the relay controller module  142  to determine the relay state in a similar manner as that of the relay system  140  of  FIG. 8 . It will be understood, however, that any suitable combination of direct differential sensing and/or ground referenced sensing may be employed, depending on the needs of the particular application. 
       FIG. 10  shows another relay system  340  including a relay  341  in which the dual input/dual output indirect or direct differential terminal voltage sensing circuits  90  or  110  of  FIG. 6 or 7  are employed. The dual input differential terminal voltage sensing circuits  90  or  110  detect differential voltage with respect to ground  96  and the dual outputs  342 , 344  and  346 , 348  of each of the sensing circuits  90  or  110  are processed by the relay controller module  142 . 
     Example 2 
     The disclosed concept replaces a relay auxiliary circuit with voltage sensing electronics. A suitably low voltage between the load terminals (A 1 -A 2 ) of the relay allows the elimination of a conventional relay auxiliary circuit and provides a status to a PDU, a main controller or a load management controller, such as  156 , which needs to know which relays of a power distribution system are on. Further, if the terminal set X 1 -X 2  is high and the terminal set A 1 -A 2  is low, then suitable electronics can be employed to transfer from the pull-in coil to the hold coil. This combines “coil control electronics” or a “cut-throat circuit” function with auxiliary switch functions. This eliminates various mechanical adjustments of the relay, and reduces the cost of the auxiliary switch and the cost of the coil control electronics. 
     Relays often use the circuit of  FIG. 1  to switch between the pull-in and hold coils. The disclosed concept determines when there is a suitable high voltage (e.g., without limitation, 28 V) between the coil terminals and a suitable low voltage between the load terminals. Hence, the auxiliary circuit of the relay can be eliminated, which provides a significant cost and mechanical adjustment savings. Furthermore, if that is done, then these two signals can be used to “replace” the circuit of  FIG. 1  that controls the coil. For example, if the relay has closed (as determined by the low voltage between the load terminals A 1 -A 2 ) and the coil voltage shows that it had closed (as determined by the high voltage between the coil terminals X 1 -X 2 ), then the relay controller module  142  ( FIGS. 8-10 ) can switch to the “hold coil”. 
     Example 3 
     Additionally, the disclosed voltage sensing circuits  20 , 50 , 60 , 90 , 110  and relay systems  140 , 240 , 340  can employ a current sensor  400  (shown in phantom line drawing in  FIGS. 8-10 ) structured to sense current flowing through the load terminals (A 1 -A 2 ), then the relay can provide detailed load management information as shown in Table 2, which shows diagnostics with both voltage and current sensing. The term “I High” means that the sensed current is above a corresponding suitable predetermined threshold current, and the term “I Low” means that the sensed current is below a corresponding suitable predetermined threshold current. These corresponding suitable predetermined threshold currents can be the same, although upper and lower thresholds for each signal preferably allow for out-of-range parameter detection. 
     Suitable unique current and voltage thresholds can be employed to establish functional health limits for load current and voltage based upon insulation and/or contamination across the separable contacts. 
     
       
         
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 V A1-GND   
                 V A2-GND   
                 V A1-A2   
                 V X1-GND   
                 V X2-GND   
                 V X1-X2   
                 Current 
                 Information Deduced 
                 Status 
               
               
                   
               
             
             
               
                 Low 
                 Low 
                 Low 
                 Low 
                 Low 
                 Low 
                 Low 
                 No power on input; Relay commanded open;  
                 No Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 Relay contact status: undetermined 
                   
               
               
                 Low 
                 Low 
                 Low 
                 Low 
                 Low 
                 Low 
                 High 
                 Relay commanded open; Possible sensor failure;  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 Relay contact status: closed (possible failure or welded) 
                   
               
               
                 High 
                 Low 
                 High 
                 Low 
                 Low 
                 Low 
                 Low 
                 Power present at input; Relay commanded open;  
                 No Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 Relay contact status: open 
                   
               
               
                 High 
                 Low 
                 High 
                 Low 
                 Low 
                 Low 
                 High 
                 Power present at input; Relay commanded open;  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 Possible sensor failure; Relay contact status:  
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 undetermined 
                   
               
               
                 High 
                 High 
                 Low 
                 Low 
                 Low 
                 Low 
                 Low 
                 Power present at input and output; Relay commanded  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 open; Relay contact status: possibly closed (failed  
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 or welded) 
                   
               
               
                 High 
                 High 
                 Low 
                 Low 
                 Low 
                 Low 
                 High 
                 Power present at input and output; Relay commanded  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 open; Relay contact status: closed (failed or welded) 
                   
               
               
                 Low 
                 Low 
                 Low 
                 High 
                 Low 
                 High 
                 Low 
                 No Power on input; Relay commanded closed;  
                 No Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 Relay contact status: undetermined 
                   
               
               
                 Low 
                 Low 
                 Low 
                 High 
                 Low 
                 High 
                 High 
                 Relay commanded closed; Possible sensor failure or  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 source voltage collapse; Relay contact status:  
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 undetermined 
                   
               
               
                 High 
                 Low 
                 High 
                 High 
                 Low 
                 High 
                 Low 
                 Power present at input; Relay commanded closed;  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 Relay contact status: open (failed to close) 
                   
               
               
                 High 
                 Low 
                 High 
                 High 
                 Low 
                 High 
                 High 
                 Relay commanded closed; Possible sensor failure;  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 Relay contact status: undetermined (possible high  
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 resistance) 
                   
               
               
                 High 
                 High 
                 Low 
                 High 
                 Low 
                 High 
                 Low 
                 Power present at input and output (normal power to  
                 Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 load); Relay commanded closed; Relay contact status:  
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 closed; Load no drawing current (possible load fault) 
                   
               
               
                 High 
                 High 
                 Low 
                 High 
                 Low 
                 High 
                 High 
                 Power present at input and output (normal power to  
                 No Fault 
               
               
                   
                   
                   
                   
                   
                   
                   
                 load); Relay commanded closed; Relay contact status:  
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 closed 
               
               
                   
               
             
          
         
       
     
     Example 4 
     Non-limiting examples of current sensors, such as  400 , include Hall effect sensors for DC applications; current transformers for AC load imbalance and ground fault detection; and shunts on, for example, a 270 VDC contactor with corresponding thermal measurement for linear compensation. Current sensors can be placed, for example and without limitation, on terminals or lugs, around conductors, or within contactor buss bars (e.g., Hall effect: shunt). 
     Example 5 
     The disclosed concept can be employed in connection with the following features: (1) determination of contactor “open/close” state and communication of the same to remote systems, such as  156  of  FIGS. 8-10  (e.g., without limitation, electronic or solid state auxiliary contacts; coil and plunger sealing redundancy (e.g., the current profile of the coil can be monitored to ensure that the plunger seals the magnetic path)); (2) determination of contactor “on/off” response time (e.g., without limitation, this time can be employed to indicate contactor health; coil performance; change in response time over the life of the product; change in performance as compared to other indicators, such as on resistance); (3) contactor “on resistance” (e.g., without limitation, this resistance can be saved and/or used to evaluate initial factory build performance; heat generation versus wear; performance versus number of electrical cycles (e.g., without limitation, typical relays are rated for 50,000 or 100,000 cycles; depending upon the application, the wear versus number of electrical cycles may need to be de-rated, load de-rated, or the contactor size may need to be increased if the device does not meet failure/quality criteria); impact on contactor performance when subjected to in-rush loads, capacitive loads, or a rupture fault current; also, this resistance can be employed to alert the user of potential reliability concerns, advice for contactor replacement, and/or re-torque of the contactor mounting mechanism); (4) contactor “in-rush current limit” (e.g., without limitation, this value can be used to indicate a potential issue with a downstream load, such as a three-phase motor wearing out and causing a much higher than expected starting in-rush current; this value can be used as a warning only for early diagnostics, such as a warning only for early diagnostics, such as a pump load wearing out or being in need of service); (5) contactor “over current” (e.g., this value (I 2 T) can be used to provide protection and replace in-line fuses in power distribution units; protection against relatively large feeder short circuit faults); (6) contactor “over temperature” (e.g., without limitation, this temperature can be used to provide a nearly linear I 2 T trip curve on a contactor by compensating for changes in resistance with changes in temperature and current; can be used as an input to a processor (e.g., a microcontroller) when sensing current using a shunt: can be taken on the contactor coil to provide a health measurement (e.g., checking for shorted coil windings; checking for a pull-in coil staying on as a result of, for example, a bad cut-throat circuit)); (7) contactor “power factors” (e.g., without limitation, the values can be employed to monitor power conditions on an aircraft and regulate the power within the power distribution unit delivering clean power to other aircraft systems/loads); (8) contactor “bounce” (e.g., without limitation, this parameter can be used to indicate contact wear; contamination; spring wear; misadjusted wear allowance; contactor nearing the end of useful life); (9) relay pull-in voltage; and (10) relay drop-out voltage. 
     Example 6 
     Relay separable contacts, such as  10 , usually start with a contact voltage drop (CVD) of about 50 mV to about 60 mV between A 1  and A 2  when fully closed at rated current. Typical relay specifications allow a change of CVD over life to about 100 mV, 125 mV or 150 mV. Loading on the separable contacts during use is usually about 50% of rating up to about 100% continuous; this concerns how relays or contactors are designed into systems and how they are typically loaded with current as compared to the maximum device rating. A relatively lower contact force corresponds to a relatively higher CVD. The load terminal voltage is essentially zero when the contacts are open. By monitoring the relay timing, when the A 1 -A 2  voltage changes state to the CVD, resulting from the X 1 -X 2  voltage, the voltage for pick-up and drop out and the relay timing can be determined. The ability to compare the A 1 -A 2  voltage versus the X 1 -X 2  voltage and timing allows the relay manufacturer to optimize the coil size, permits determining when to transfer from the pick-up coil to the hold coil, and permits determining the contact open or closed status. 
     As a result, a mechanical switch and/or a resistor-capacitor circuit are not needed for timing from the X 1 -X 2  input to the state change of the relay separable contacts. The mechanical link from the main separable contacts to the auxiliary switch is one of various error-prone adjustments along with switching from the pull-in coil to the hold (or “release”) coil. For example, the mechanical switch is usually spring actuated, which provides another force that the coil must “overcome”. Because of the lack of “precision” across broad environmental and voltage constraints, the “hold” timing is much broader than it “needs” to be and the coil has to be able to withstand the longer times. 
     In the disclosed concept, “coil control” electronics or timing circuits are used instead of mechanical adjustments. Mechanical wear would indicate/create a need for a relatively higher pick-up voltage to close the relay. As a result, a threshold can be set for when the pick-up voltage change is outside an acceptable range or trending to show wear. 
     Similarly, the drop-out voltage can be monitored. If more friction occurs, then this can be observed since the relay will hold closed at a relatively lower voltage. Also, the relay timing will change. As a result, a threshold can be set for when the drop-out voltage change is outside an acceptable range or trending to show wear. 
     While the example terminal voltage sensing circuits of  FIGS. 2 and 4-7  include comparators and other similar circuits to generate a logic output indicative of the presence (or absence) of voltage with respect to a predetermined threshold, they do not provide an analog value that a processor may utilize to measure actual coil pick-up, drop-out or contact drop voltage levels. However, this functionality could be easily employed by providing selected analog signals generated internally in some of the circuits presented directly to the processor. For example, if the processor were implemented using a microprocessor, the microprocessor could employ an integral analog-to-digital (A/D) converter which could sample the analog signals from the sensing circuit to determine the actual terminal voltages for use in performing diagnostic functions. In the circuit of  FIG. 5 , an analog voltage of the output signal  82  at the output of operational amplifier  66  is essentially a voltage proportional to the differential voltages sensed at the input terminals  62 , 64 . In the circuit of  FIG. 6 , the analog voltages present at the non-inverting inputs of comparators  92 , 94  are also proportional to sensed terminal voltages and could be sampled by an A/D converter. A similar approach could be employed with the circuit of  FIG. 7 . 
     In addition to determining wear by monitoring changes in operational voltages over a relay&#39;s life, changes in timing of the logic signals may also be used as indication of mechanism wear. For example, if the time period between detection of voltage application to the coil control terminals X 1 ,X 2  and the detection of appropriate voltages at relay terminals A 1 ,A 2  indicating contact closure increases, then this may be indicative of jamming or drag in the relay mechanism. A suitable predetermined maximum duration for this period may be determined for allowable relay performance, beyond which the relay may need to be inspected, serviced or replaced. 
     A thermistor or other suitable temperature sensor can be added to account for temperature effects. For example, the resistance of copper changes with temperature. The thermistor measures the temperature of the copper as an input to provide a linear signal when measuring current for over-current protection. 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.