Abstract:
Assemblies, systems, and methods which prolong relay life by dynamically compensating the make and break contact timing between the contact points of the relay and a zero crossing point of the power supply&#39;s waveform are provided according to the present disclosure. The life cycle of the relay components are dramatically increased through the use of these assemblies, systems, and methods due to a decrease in arcing and other physically damaging phenomena between the contacts of the relay. The present disclosure also provides for assemblies, systems, and methods whereby a processor analyzes the inductive kickback effect in the relay load voltage signal and dynamically adjust the relay open time such that the inductive kickback effect is minimized. In exemplary embodiments, the systems/methods provided herein advantageously adjust the relay open time such that the relay switching time corresponds with current zero cross and do so without requiring complicated current monitoring components.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 10/934,776 filed Sep. 3, 2004 now abandoned, entitled “Zero Cross Switching Relay Module,” which claims priority to provisional application Ser. No. 60/500,147, filed Sep. 3, 2003, both of which are hereby incorporated in their entireties, including but not limited to those portions that specifically appear hereinafter. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to electrical relays, and more particularly, but not necessarily entirely, relays that switch at specified instances. 
     2. Background Art 
     Relays are used as switches to control power to electrical devices. A relay may be defined as an electromechanical switch operated by a flow of electricity in one circuit and controlling the flow of electricity in another circuit. A relay may consist basically of an electromagnet with a soft iron bar, called an armature, held close to it. A movable contact is connected to the armature in such a way that the contact is held in its normal position by a spring. When the electromagnet is energized, it exerts a force on the armature that overcomes the pull of the spring and moves the contact so as to either complete or break a circuit. When the electromagnet is de-energized, the contact returns to its original position. Variations on this mechanism are possible: some relays have multiple contacts; some are encapsulated; some have built-in circuits that delay contact closure after actuation; some, as in early telephone circuits, advance through a series of positions step by step as they are energized and de-energized. 
     Since the actuation of a relay requires the physical movement of one of the contact electrodes, there may be some delay from the issuance of a close command until the magnetic field has build to a sufficient level to begin movement of the contact electrodes by overcoming the spring force. This delay makes it difficult to precisely time the actual opening or closing of the electrodes. 
     Relays are often used to switch alternating current (AC). AC occurs when charge carriers in a conductor or semiconductor periodically reverse their direction of movement. Household utility current in the U.S. and some other countries is AC with a frequency of 60 hertz (60 complete cycles per second), although in other countries it is 50 Hz. 
     An AC waveform may be sinusoidal, square, or sawtooth-shaped. Some AC waveforms are irregular or complicated. An example of sine-wave AC is common household utility current (in the ideal case). One characteristic of the AC waveform is that it crosses zero when reversing directions. At this zero crossing point, there is no current flowing. 
     The voltage of an AC power source also changes from instant to instant in time. The AC voltage changes is also a sinusoidal wave that over time starts at zero, increases to a maximum value, then decreases to a minimum value, and repeats. 
     In applications where relays are repeatedly switched, the life of the relay may be cut short by arcs (a luminous bridge of ionized gas) that form across the relay contacts when switched. The time period in which the arc flows is determined by many factors including the mechanical bounce of the contracts upon closure, the distance between the contact electrodes, the magnitude of the current flowing, as well as the level of ionization of the air in the gap between contact electrodes. 
     These arcs may cause pits and welds to accumulate on the contact surface which diminish the useful life of the relay. The pits are formed through a small portion of the contact electrode melting or vaporizing due to the extreme heat of the arc. The extreme heat may also weld the contacts together, thereby making the relay unusable. In addition, these arcs may cause a build up of carbon deposit on the contacts, which, over time, accumulate to form a high resistance contact between the contacts, thus reducing the current flow to the load and making the relay less efficient. 
     Such arcs can generally, be suppressed by eliminating the voltage difference or current flow across relay contacts while switching the relay. This has been accomplished in the past by turning the load on with a triac while switching the relay on or off. Unfortunately, these triacs provide a path bypassing the high level of isolation offered by electromechanical relays. Moreover, triacs will also often fuse from the high inrush currents characteristic of certain loads. 
     In recent years some attempts have been made to control the physical opening and closing of an electromechanical relay at a point as close as possible to zero voltage in the sine waveform. For example, one technique is based on an assumption that zero voltage points correspond with zero current points. A complicating factor, however, is that in AC circuits, inductors and capacitors generally introduce phase shifts between voltage and current across a given component. Thus, in some instances, voltage zero cross is out of phase with current zero cross. In such instances, opening the relay at a zero voltage would not effectively prevent arcing. 
     Furthermore, other methods of determining current zero cross generally involve using an expensive current transformer with associated circuitry in order to dynamically measure the load current for a relay. The use of such current monitors, however, is generally both complicated and expensive. 
     These and other disadvantages and/or limitations are addressed and/or overcome by the assemblies, systems, and methods of the present disclosure. 
     SUMMARY 
     In exemplary embodiments, the present disclosure provides for assemblies, systems, and methods for dynamically adjusting relay switching times to correspond with current zero cross using a voltage monitor or the like coupled with a processor. Thus, the assemblies, systems, and methods provided herein advantageously determine the relay open time for the relay wherein the relay open time corresponds to the time delay between when an open control signal is sent and current zero cross. In exemplary embodiments, the assemblies, systems, and methods advantageously determine the relay open time by utilizing a low-cost voltage monitor or the like to measure the voltage at the load side of the relay, without a need for transformers or similarly complex/expensive current monitoring components, thereby providing a significant commercial advantage as a result. Typically, the voltage signal is continuously analyzed by the processor in order to dynamically determine the relay open time, as later discussed herein. In exemplary embodiments, additional circuitry may be included to modify the voltage signal prior to and for the benefit of facilitating analysis by the processor; e.g., the voltage signal may be filtered, normalized, and/or scaled. 
     According to the present disclosure, a novel correlation technique is used to determine the relay open time such that switching corresponds with the current zero-cross. In general, when current is interrupted to an inductive load the magnetic field of the load will cause the voltage on the load side of the relay to spike until an arc is formed whereby the energy in the load&#39;s magnetic field is dissipated. This sudden change of voltage is sometimes referred to as inductive kickback. In exemplary embodiments of the present disclosure, a processor analyzes the inductive kickback effect to the load voltage signal in order to dynamically adjust relay open times such that inductive kickback is minimized. Thus, the processor analyzes the load voltage signal data, e.g., for time subsequent to the last line voltage zero cross, amplitude, etc., and the processor also adjusts the relay open time such that the next relay open more accurately approximates relay switching at a zero current point. Each time the relay is opened the resulting kickback is analyzed and the timing is adjusted. By checking the inductive kickback each time the relay is opened the circuit can dynamically adjust for changes in the operation of the relay and load. In general, minimal inductive kickback indicates that the relay open time is optimally configured to correspond with current zero cross. As such, a complex and/or expensive current monitor is not necessary since inductive kickback can be monitored and measured using a voltage monitor, thereby providing a significant commercial advantage as a result. 
     Additional features, functions and benefits of the disclosed apparatus, systems and methods will be apparent from the description which follows, particularly when read in conjunction with the appended figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To assist those of ordinary skill in the art in making and using the disclosed assemblies, systems, and methods, reference is made to the appended figures, wherein: 
         FIG. 1  is a block diagram showing an exemplary system for zero cross switching according to the present disclosure. 
         FIG. 2  is a diagram showing several output signals over time for the system of  FIG. 1 . 
         FIGS. 3-5  are schematics of a first exemplary embodiment of the system in  FIG. 1 . 
         FIGS. 6-8  are schematics of a second exemplary embodiment of the system in  FIG. 1 . 
         FIG. 9  is a flow chart showing illustrative steps taken in carrying out an exemplary method for adjusting relay actuation delay for a relay system such as the system in  FIG. 1 . 
         FIG. 10  is a block diagram of an exemplary embodiment of the system in  FIG. 1 , wherein the sensor circuit is a voltage detector or monitor or the like, and wherein the inductive kickback effect on the load voltage signal is analyzed to effect current zero cross switching. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENT(S) 
     According to the present disclosure, advantageous assemblies, systems, and methods are provided for dynamically adjusting switching times in order to reduce arcing. More particularly, the disclosed assemblies, systems, and methods generally involve monitoring component waveforms, e.g., voltage on the load side of a relay, and opening/closing the relay at or near a zero crossing, e.g., zero current. In general, dynamic readings of prior actuations are used to anticipate the actuation time for each subsequent operation of the relay. In exemplary embodiments, the dynamic readings are continuously updated each time the relay is actuated to thereby optimize the characteristic switching time for each individual relay and adjust for any variations in switching time over the life of the relay. 
     Referring now to  FIG. 1  there is shown generally an exemplary system  100  for zero cross switching in block diagram format. The system  100  typically comprises a relay  110 , an input line  112 , a reference circuit  114 , a microprocessor  116 , a sensor circuit  118 , and a load  120 . The input line  112  typically comprises an alternating current (AC) which may be at any selected frequency. The input line  112  is the source of power controlled by the relay  110 . 
     The relay  110  may be any type as is commonly used in the art to provide an electromechanical switch between an input line  112  and a load  120 . Typically, a relay  110  may comprise a drive coil, a movable contact electrode, and a stationary contact electrode (not explicitly shown in the figure). The drive coil is energized to create a magnetic field which moves the movable contact electrode into contact with the stationary contact electrode to complete an electrical circuit between the input line  112  and the load  120 . When the drive coil is switched off or on, the movable contact electrode may take several milliseconds to open or close. The exact switching time varies from relay to relay and can change for a particular relay over time. More sophisticated relays designs include both a drive open and a drive close coil, requiring the application of an electrical drive signal to both open and close the relay. Other relays have both normal open and normal closed contacts. Other designs as are known in the art and all have application within the scope of the present disclosure. 
     In order to switch the relay  110  at the zero cross, an independent sensor circuit  118  is used for the relay  110  to time the characteristic delay that the relay  110  experiences to open or close its contacts. The sensor circuit  118  provides the microprocessor  116  with an output signal. From the output signal, it can be determined the difference in time from the zero cross of the monitored waveform (either voltage or current) and the opening and closing of the relay  110 . The output signal may comprise a pulsed signal component. The sensor circuit  118  may selectively monitor either voltage or current, or a combination of both. 
     The reference circuit  114  is also connected to the input line  112 . The reference circuit  114  provides the microprocessor  116  a reference signal for timing the start of a switch. 
     The microprocessor  116  provides timing/control and adjustment to ensure that the relay  110  switches during a zero crossing or as close thereto as possible. In addition, the microprocessor  116  may be any logic circuit such as a programmable logic array, custom circuit, or other appropriate circuitry known in the art for processing logic and timing signals. In the microprocessor  116  are the appropriate input/output circuitry required for the described implementation of the present disclosure. 
     Referring now to  FIG. 2  a composite timing diagram is depicted showing graph  122  illustrating the input line  112  reference waveform  128 , graph  124  illustrating the sensor circuitry  118  output  136  for zero cross switching when energizing the relay, and graph  126  illustrating the sensor circuitry  118  output  138  for zero cross switching when de-energizing the relay. All of the graphs show how its respective signal changes (vertical axis) over time (horizontal axis). Both  FIGS. 1 and 2  will be referred to as the waveforms shown in  FIG. 2  are described. 
     Graph  122  illustrates a reference waveform  128  for the input line  112 . For zero voltage switching (when closing the relay contacts, graph  124 , the reference waveform  128  may represent the voltage of the power supply  112 . For zero current switching (when opening the relay contacts), graph  126 , the reference waveform  128  may represent the current of the power supply  112 . 
     The reference waveform graph  122  shows a plurality of zero crossing points  132 . This is when the reference waveform  128  crosses the neutral (or zero) line  130 . The zero crossing points  132  are when the voltage or current is zero, as the case may be. A series of vertical lines, one of which is indicated at  134 , allows the zero crossing points  132  to be identified on the other two graphs  124  and  126 . The reference waveform graph  114  may represent the output from the reference circuit  114  to the microprocessor  116 . 
     When the load  120  is being switched on or off, the microprocessor  116  will wait for a zero crossing point  132 , and preferably, but not necessarily, for the next zero crossing point  132 , to begin the switching process. From this zero cross crossing point  132 , the microprocessor  116  will wait an additional delay time before turning the coil on or off to switch the relay  110 . This delay time is characteristic of the relay  110  it is switching and is measured to ensure that the relay  110  will make or break contact at exactly the zero crossing point  132  of the input line  112 . 
     For zero voltage switching (that is the relay contacts are closed at or near a zero voltage cross point), graph  124 , the output  136  from the sensor circuitry  118  to the microprocessor  116  begins at a low state. This may imply that the relay  110  is open and that no power is being supplied to the load  120 . When the relay  110  is closed, the output  136  switches to a high state as can be seen with the rising edge marked with reference numeral  140 . In addition, the sensor circuitry  118  is such that the output  136  also drops to a low state momentarily when the reference waveform  128  has a zero crossing point  132  as can be seen with the pulse marked with reference numeral  142 . 
     Relay turn on delay time  144  represents the time it takes for the relay  110  to close after the microprocessor  116  energizes the coil. Turn on delay time  146  represents the time the microprocessor delays energizing the coil from a zero crossing point  132 . Turn on error time  148  represents the time from when the relay  110  actually closes to the next zero crossing point  132 . 
     The microprocessor  116  is programmed to begin the switching process at a zero cross point  132 . Since it is desired that the relay  110  actually closes on a subsequent zero crossing point  132 , the microprocessor  116  delays energizing the coil of the relay  110  for the turn on delay time  146 . The turn on delay time  146  is adjusted by the microprocessor  116  dynamically pursuant to the turn on error time  148 , generally after each time the relay  110  is actuated. 
     When the turn on error time  148  is equal to zero or as close to there as possible, then the microprocessor  116  knows that the coil on the relay  110  is actually closing on a zero crossing point  132 . This is when the time duration of the first high state will be equal to the one half of the cycle length of the input line. 
     For zero current switching (that is the relay contacts are opened at or near a zero current cross point), shown in graph  126 , the sensor circuitry  118  output  138  is at a high state, except that at every zero crossing point  132  the output  138  momentarily switches to a low state, as is shown at  150 . The microprocessor  116  is programmed to begin the switching off process on a zero crossing point  132 . Because it is desired to have the relay  110  open on a zero crossing point  132 , the microprocessor  116  delays de-energizing the coil of the relay  110  for a turn off delay time  154 . Once the microprocessor  116  actually turns the coil off, the relay turn off time  152  is the time it actually takes the relay  110  to open. The turn off error time  156  is the time from a zero crossing point  132  until the relay  110  actually opens. The turn off delay time  154  is adjusted dynamically by the microprocessor  116  pursuant to the turn off. error time  156  after each time the relay  110  is actuated. 
     When the turn off error time  156  is equal to zero or as close to there as possible, then the microprocessor  116  knows that the coil on the relay  110  is actually opening on a zero crossing point  132 . This is when the time duration of the last high state will be equal to the one half of the cycle length of the input line. Most advantageously, various implementations of the present disclosure can be arrived at using the information provided herein to greatly increase the useful life of a relay. 
       FIGS. 3-5  are schematics for one illustrative embodiment of the present disclosure for up to eight loads using zero voltage switching. Referring now to  FIG. 3 , a microprocessor  160  is the central logic circuit controlling the switching. Inputs  160 A from the reference circuitry  162  and sensor circuitry  166  are shown. The reference circuitry  162  is shown in the upper left hand corner. The reference circuitry  162  is connected to an input line  163  from a power supply (not explicitly shown on  FIG. 3 ). 
     Referring now to  FIG. 4 , a relay  164  is also connected to the input line  163 . An output line  168  from the relay  164  is connected to a load (not shown). An optocoupler  166 A and trimming comparator  166 B, forming the sensor circuitry  166 , are also connected to the output line  168 . The optocoupler  166 A sources the zero cross signals, in that whenever the output line  168  voltage is not equal to neutral, a current will flow from the optocoupler  166 A to produce a signal to the microprocessor  160 . The trimming comparator  166 B trims the curved output signal from the optocoupler  166 A into a sharp rising and falling edge for providing a consistent timing trigger. The threshold can be adjusted to provide a narrower or wider signal around the zero cross as needed for better precision. Table 1 provides a parts list for  FIGS. 3-5 : 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 REFER- 
                   
                   
               
               
                 QTY 
                 ENCE 
                 DESCRIPTION 
                 VALUE 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 U20 
                 HEX SCHMITT-TRIGGER  
                 74HC14 
               
               
                   
                   
                 INVERTER 
                   
               
               
                 2 
                 U14-15 
                 OCTAL BUS TRANSCEIVER 3  
                 74HC244 
               
               
                   
                   
                 STATE 
                   
               
               
                 1 
                 U11 
                 16-BIT MICROPROCESSOR 
                 MSP430 
               
               
                 2 
                 U8-9 
                 QUAD COMPARATOR 
                 LM339 
               
               
                 1 
                 U13 
                 2.7 V RESET W/WATCHDOG  
                 X5043 
               
               
                   
                   
                 AND EEPROM 
                   
               
               
                 8 
                 U4 U7  
                 AC INPUT OPTO-ISOLATED  
                 H11AA4 
               
               
                   
                 U10 U12  
                 TRANSISTOR 
                   
               
               
                   
                 U16 U19 
                   
                   
               
               
                   
                 U21 U23 
                   
                   
               
               
                 1 
                 U2 
                 Darlington output 1 us/7 us 
                 6N139 
               
               
                 1 
                 Q1 
                 NPN, PNP TRANSISTOR PAIR 
                 MBT3946 
               
               
                 1 
                 U3 
                 OPTO-TRANSISTOR, 4-PIN, SMT 
                 H11A817B 
               
               
                 2 
                 U17-18 
                 TRANSISTOR ARRAY 
                 ULN2803LW 
               
               
                 1 
                 U1 
                 LOW POWER OFF-LINE SWITCHER 
                 TNY264 
               
               
                 1 
                 U5 
                 3.3 V REGULATOR SOIC-8 
                 78L33 
               
               
                 1 
                 U6 
                 12 V REGULATOR DPAK 
                 78M12 
               
               
                 1 
                 U22 
                 DIFFERENTIAL TRANSCEIVER 
                 MAX3486 
               
               
                 4 
                 TVS2-5 
                 MOV SURGE ABSORBER  
                 150 VAC 
               
               
                   
                   
                 V14D241/V14D621 
                   
               
               
                 2 
                 TVS6-7 
                 BIDIRECTIONAL TVS 
                 5.6 V 
               
               
                 1 
                 TVS1 
                 TRANSIENT VOLTAGE  
                 220 V 
               
               
                   
                   
                 SUPPRESSOR 
                   
               
               
                 1 
                 C5 
                 CAPACITOR, TANTALUM, 25 V 
                 10 uF 
               
               
                 2 
                 C6-7 
                 1206 CAPACITOR 1 UF 
                 1 uF 
               
               
                 11 
                 C2 C4  
                 0603 CAPACITOR .1 UF 
                 .1 uF 
               
               
                   
                 C8-16 
                   
                   
               
               
                 1 
                 C1 
                 HOLDING CAPACITOR 
                 2.2 uF 
               
               
                 1 
                 C3 
                 Y1 SAFETY CAPACITOR 
                 2200 pF 
               
               
                 4 
                 R1-2  
                 RESISTOR, SM 2010 
                 56K 
               
               
                   
                 R18-19 
                   
                   
               
               
                 5 
                 R3 R5  
                 0603 RESISTOR 5% 10K 
                 10K 
               
               
                   
                 R12 R17  
                   
                   
               
               
                   
                 R24 
                   
                   
               
               
                 1 
                 R4 
                 0805 RESISTOR 51 OHM 
                 51 
               
               
                 7 
                 RN10 
                 4 DISCRETE RESISTOR  
                 10K 
               
               
                   
                 RN4-9 
                 NETWORK 0603 
                 10K 
               
               
                 4 
                 RN1-3  
                 4 DISCRETE RESISTOR  
                 3.0K 
               
               
                   
                 RN11 
                 NETWORK 0603 
                   
               
               
                 16 
                 R7-10 
                 RESISTOR, SM 2512 
                 10K/47K 
               
               
                   
                 R13-16 
                   
                   
               
               
                   
                 R20-23 
                   
                   
               
               
                   
                 R25-28 
                   
                   
               
               
                 1 
                 R11 
                 0603 RESISTOR 5% 2.2K 
                 2.2K 
               
               
                 1 
                 R6 
                 0603 RESISTOR 5% 3.3K 
                 3.3K 
               
               
                 1 
                 T2 
                 TRANSFORMER 
                 EFD-15 
               
               
                 8 
                 RL1-8 
                 DOUBLE COIL LATCHING RELAY 
                 12 V Coil 
               
               
                 1 
                 SW1 
                 8 SWITCH DIP SWITCH 
                   
               
               
                 1 
                 Y1 
                 CERAMIC RESONATOR WITH CAPS 
                 7.3728 MHz 
               
               
                 6 
                 D1-5 D7 
                 Diode - MELF, 600 V 
                 DL4937 
               
               
                 1 
                 Z1 
                 ZENER DIODE, 15 V SMB 
                 15 V 
               
               
                 1 
                 CR1 
                 DUAL HEAD-TO-TAIL DIODE  
                 DAN217 
               
               
                   
                   
                 PACKAGE 
                   
               
               
                 14 
                 LED1-14 
                 LED, SURFACE MOUNT 1206 PKG 
                   
               
               
                 1 
                 D6 
                 RECTIFIER 1 AMP SM 
                 DF08S 
               
               
                 1 
                 J6 
                 CONNECTOR, 14 PIN MINIFIT 
                   
               
               
                 4 
                 J2-5 
                 CONNECTOR, MALE POSITRONIC 
                   
               
               
                 1 
                 J1 
                 14 PIN 2-ROW HEADER  
                   
               
               
                   
                   
                 .100 SPACING 
               
               
                   
               
             
          
         
       
     
       FIGS. 6-8  are schematics of one illustrative embodiment of the present disclosure for up to eight loads using zero current switching. Referring to  FIG. 6 , a microprocessor  170  is the central logic circuit controlling the switching. Inputs  170 A from the reference circuitry  172  and sensor circuitry  176  are shown. The reference circuitry  172  is shown in the upper right hand corner. The reference circuitry  172  is connected to an input line  173  from a power supply (not explicitly shown in  FIG. 6 ). 
     Referring now to  FIG. 7 , a relay  174  is also connected to the input line  173 . An output line  178  from the relay  174  is connected to a load (not explicitly shown in  FIG. 7 ). A current sense transformer  176 A and trimming comparator  176 B, forming the sensor circuitry  176 , are also connected to the output line  168 , The current sense transformer  176 A sources the zero cross signals, in that whenever the output line  168  current is not equal to neutral, a current will flow from the current sense transformer  176 A to produce a signal to the microprocessor  170 . The trimming comparator  176 B trims the curved output signal from the current sense transformer  176 A into a sharp rising and falling edge for providing a consistent timing trigger. The threshold can be adjusted to provide a narrower or wider signal around the zero cross as needed for better precision. Table 2 provides a parts list for  FIGS. 6-8 : 
     
       
         
               
               
               
               
               
             
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                   
                   
                 REFER- 
                   
                   
               
               
                 QTY 
                 PART NO 
                 ENCE 
                 DESCRIPTION 
                 VALUE 
               
               
                   
               
               
                 1 
                 VAA-0010 
                 U14 
                 HEX SCHMITT-  
                 74HC14 
               
               
                   
                   
                   
                 TRIGGER 
                   
               
               
                   
                   
                   
                 INVERTER 
                   
               
               
                 1 
                 VAA-0015 
                 U15 
                 QUAD 2-INPUT  
                 74VHC00 
               
               
                   
                   
                   
                 POS-NAND GATE 
                   
               
               
                 2 
                 VAA-0024 
                 U10-11 
                 OCTAL BUS  
                 74HC244 
               
               
                   
                   
                   
                 TRANSCEIVER 3  
                   
               
               
                   
                   
                   
                 STATE 
                   
               
               
                 1 
                 VAB-0033 
                 U8 
                 16-BIT  
                 MSP430 
               
               
                   
                   
                   
                 MICROPROCESSOR 
                   
               
               
                 2 
                 VAZ-0006 
                 U6-7 
                 QUAD  
                 LM339 
               
               
                   
                   
                   
                 COMPARATOR 
                   
               
               
                 1 
                 VAZ-0009 
                 U9 
                 RESET  
                 X5043 
               
               
                   
                   
                   
                 W/WATCHDOG 
                   
               
               
                   
                   
                   
                 AND EEPROM 
                   
               
               
                 1 
                 VBF-0021 
                 U2 
                 Darlington output  
                 6N139 
               
               
                   
                   
                   
                 1 us/7 us 
                   
               
               
                 1 
                 VBF-0040 
                 Q1 
                 PNP, NPN DUAL  
                 MBT3946 
               
               
                   
                   
                   
                 TRANSISTOR 
                   
               
               
                 1 
                 VBF-0041 
                 U3 
                 OPTO- 
                 H11A817B 
               
               
                   
                   
                   
                 TRANSISTOR,  
                   
               
               
                   
                   
                   
                 4-PIN, SMT 
                   
               
               
                 2 
                 VBF-0044 
                 U12-13 
                 TRANSISTOR  
                 ULN2803LW 
               
               
                   
                   
                   
                 ARRAY 
                   
               
               
                 1 
                 VBF-0049 
                 U1 
                 LOW POWER  
                 TNY264 
               
               
                   
                   
                   
                 OFF-LINE  
                   
               
               
                   
                   
                   
                 SWITCHER 
                   
               
               
                 1 
                 VBH-0016 
                 U4 
                 3.3 V REGULATOR  
                 78L33 
               
               
                   
                   
                   
                 SOIC-8 
                   
               
               
                 1 
                 VBH-0017 
                 U5 
                 12 V REGULATOR  
                 78M12 
               
               
                   
                   
                   
                 DPAK 
                   
               
               
                 1 
                 VBI-0010 
                 U16 
                 DIFFERENTIAL  
                 MAX3486 
               
               
                   
                   
                   
                 TRANSCEIVER 
                   
               
               
                 2 
                 VBZ-0003 
                 TVS2-3 
                 BIDIRECTIONAL  
                 5.6 V 
               
               
                   
                   
                   
                 TVS 
                   
               
               
                 1 
                 VBZ-0018 
                 TVS1 
                 TRANSIENT  
                 220 V 
               
               
                   
                   
                   
                 VOLTAGE  
                   
               
               
                   
                   
                   
                 SUPPRESSOR 
                   
               
               
                 1 
                 VBZ-0020 
                 TVS4 
                 MOV SURGE  
                 385 VAC 
               
               
                   
                   
                   
                 ABSORBER 
                   
               
               
                 1 
                 VCA-0002 
                 C5 
                 CAPACITOR,  
                 10 uF 
               
               
                   
                   
                   
                 TANTALUM, 25 V 
                   
               
               
                 2 
                 VCA-0013 
                 C6-7 
                 1206 CAPACITOR  
                 1 uF 
               
               
                   
                   
                   
                 1 UF 
                   
               
               
                 12  
                 VCA-0043 
                 C1 C4  
                 0605 CAPACITOR 
                 .1 uF 
               
               
                   
                   
                 C16-25 
                 .1 UF 
                   
               
               
                 8 
                 VCA-0061 
                 C8-15 
                 0603 CAPACITOR  
                 .01 uF 
               
               
                   
                   
                   
                 .01 UF 
                   
               
               
                 1 
                 VCA-0109 
                 C2 
                 HOLDING  
                 2.2 uF 
               
               
                   
                   
                   
                 CAPACITOR 
                   
               
               
                 1 
                 VCA-0093 
                 C3 
                 Y1 SAFETY  
                 2200 pF 
               
               
                   
                   
                   
                 CAPACITOR 
                   
               
               
                 1 
                 VCB-0050 
                 R8 
                 RESISTOR, ½ W  
                 130K 
               
               
                   
                   
                   
                 SURFACE MOUNT 
                   
               
               
                 5 
                 VCB-0134 
                 R1 R3  
                 0603 RESISTOR  
                 10K 
               
               
                   
                   
                 R5-7 
                 5% 10K 
                   
               
               
                 1 
                 VCB-0162 
                 R2 
                 0805 RESISTOR  
                 51 
               
               
                   
                   
                   
                 51 OHM 
                   
               
               
                 1 
                 VCB-0165 
                 RN12 
                 4 RESISTOR SM  
                 1.0K 
               
               
                   
                   
                   
                 NETWORK 0603 
                   
               
               
                 4 
                 VCB-0167 
                 RN8-11 
                 4 RESISTOR SM  
                 10K 
               
               
                   
                   
                   
                 NETWORK 0603 
                   
               
               
                 6 
                 VCB-0169 
                 RN1-5  
                 4 RESISTOR SM  
                 3.0K 
               
               
                   
                   
                 RN13 
                 NETWORK 0603 
                   
               
               
                 1 
                 VCB-0187 
                 R4 
                 0805 RESISTOR  
                 2.2K 
               
               
                   
                   
                   
                 2.2K 
                   
               
               
                 2 
                 VCB-0205 
                 RN6-7 
                 4 RESISTOR SM  
                 47 
               
               
                   
                   
                   
                 NETWORK 0603 
                   
               
               
                 1 
                 VCC-0014 
                 T2 
                 FLYBACK  
                 EFD-15 
               
               
                   
                   
                   
                 TRANSFORMER 
                   
               
               
                 8 
                 VCC-0024 
                 T1 T3-9 
                 CURRENT SENSE  
                 FIS125 
               
               
                   
                   
                   
                 TRANSFORMER 
                   
               
               
                 8 
                 VCF-0005 
                 RL1-8 
                 DOUBLE COIL  
                 12 V Coil 
               
               
                   
                   
                   
                 LATCHING RELAY 
                   
               
               
                 1 
                 VCG-0007 
                 SW1 
                 8 SWITCH DIP  
                   
               
               
                   
                   
                   
                 SWITCH 
                   
               
               
                 1 
                 VCK-0012 
                 Y1 
                 CERAMIC  
                 7.3728  
               
               
                   
                   
                   
                 RESONATOR  
                 MHz 
               
               
                   
                   
                   
                 WITH CAPS 
                   
               
               
                 3 
                 VCL-0002 
                 D1-3 
                 Diode - MELF, 600 V 
                 DL4937 
               
               
                 1 
                 VCL-0004 
                 Z1 
                 ZENER DIODE,  
                 15 V 
               
               
                   
                   
                   
                 15 V SMB 
                   
               
               
                 17 
                 VCL-0007 
                 CR1-2  
                 DUAL HEAD-TO-  
                 DAN217 
               
               
                   
                   
                 CR5-8 
                 TAIL 
                   
               
               
                   
                   
                 CR12-15 
                 DIODE 
                   
               
               
                   
                   
                 CR18-21 
                 PACKAGE 
                   
               
               
                   
                   
                 CR23-25 
                   
                   
               
               
                 11  
                 VCL-0008 
                 LED1-11 
                 LED, SURFACE  
                   
               
               
                   
                   
                   
                 MOUNT 1206 PKG 
                   
               
               
                 9 
                 VCL-0019 
                 CR3-4  
                 DOIDE, SM  
                 BAS16 
               
               
                   
                   
                 CR9-11 
                 SOD123 
                   
               
               
                   
                   
                 CR16-17  
                   
                   
               
               
                   
                   
                 CR22 
                   
                   
               
               
                   
                   
                 CR26 
                   
                   
               
               
                 1 
                 VCL-0027 
                 D4 
                 RECTIFIER 1  
                 DF06S 
               
               
                   
                   
                   
                 AMP SM 
                   
               
               
                 1 
                 VDC-0004 
                 J10 
                 CONNECTOR,  
                   
               
               
                   
                   
                   
                 14 PIN MINIFIT 
                   
               
               
                 1 
                 VDC-0023 
                 J1 
                 14 PIN 2-ROW  
                   
               
               
                   
                   
                   
                 HEADER .100 
                   
               
               
                 7 
                 VDC-0039 
                 J2-8 
                 CONNECTOR,  
                   
               
               
                   
                   
                   
                 3 PIN 
                   
               
               
                 1 
                 VDC-0147 
                 J9 
                 CONNECTOR, 
                   
               
               
                   
                   
                   
                 POSITRONIC 
               
               
                   
               
             
          
           
               
                 (8-LINE RELAY MODULE) 
               
             
          
           
               
                 QTY 
                 PART NO 
                 DESCRIPTION 
               
               
                   
               
               
                 1 
                 VDB-0113 
                 8-LINE RELAY MODULE PC BOARD 
               
               
                 1 
                 VEC-0100 
                 COMMERCIAL RELAY MODULE 
               
               
                   
                   
                 CUSTOM LABEL 
               
               
                 1 
                 VEC-0101 
                 COMMERICAL RELAY RIGHT LED  
               
               
                   
                   
                 CUSTOM LABEL 
               
               
                 1 
                 VEC-0114 
                 COMMERICAL RELAY LEFT LED  
               
               
                   
                   
                 CUSTOM LABEL 
               
               
                 1 
                 VHA-0053 
                 RELAY MODULE TOP SHIELD 
               
               
                 1 
                 VHA-0054 
                 COMMERCIAL RELAY MODULE  
               
               
                   
                   
                 BOTTOM SHIELD 
               
               
                 1 
                 VHB-0007 
                 SHIELD SIDE INSULATOR 
               
               
                 8 
                 VHD-0015 
                 6-32 × ¼″ TORX PANHEAD STEEL ZINC 
               
               
                   
               
             
          
         
       
     
     In accordance with the features and combinations described above, a useful method, as shown in  FIG. 9 , of switching a relay includes the steps of monitoring a reference waveform from an input line from a source of AC electric power to determine zero crossing points of a monitored waveform {step  200 ). Next, the relay coil is energized after a first relay actuation delay time (step  202 ). An output line from one of the electrical contacts of the relay to a load is monitored to determine a turn on error time (step  204 ). 
     Based upon the results from the previous step, the first relay actuation delay time is adjusted based upon the turn on error time such that turn on error time is reduced for subsequent actuations of the relay (step  206 ). Upon a command to turn the load controlled by the relay off, the next step is de-energizing the relay coil after a second relay actuation delay time (step  208 ). Again, the next step is monitoring the output line to determine a turn off error time (step  210 ). The final step is adjusting the second relay actuation delay time based upon the turn off error time such that turn off error time is reduced for subsequent actuations of the relay (step  212 ). 
     Referring now to  FIG. 10 , an exemplary system  300  for current zero cross switching is depicted in block diagram format. The system  300  typically includes a relay  310 , an input line  312 , reference circuitry  314 , a processor  316 , sensor circuitry  318 , and a load  320 . The input line  312  typically comprises an alternating current (AC) which may be at any selected frequency. The input line  312  includes a line voltage power source that is controlled/switched by the relay  310 . 
     The relay  310  may be any type as is commonly used in the art to provide an electromechanical switch between an input line  312  and a load  320 . In one embodiment and as shown in  FIG. 10 , the relay  310  is coupled with a relay driver  310 A. During operation the relay driver  310 A receives a control signal from the processor  316  and switches the relay  310  on or off. 
     In exemplary embodiments, the load  320  is an inductive load whereby current zero cross and voltage zero cross may be out of phase. Thus, since zero voltage does not necessarily correspond with zero current across the relay  310 , line voltage zero cross may not effectively be used to determine relay open times. Rather, the system  300  analyzes the inductive kickback effect on the load voltage signal in order to effect current zero cross switching. 
     In order to switch the relay  310  at the current zero cross, independent sensor circuitry  318  is used to monitor the load voltage signal for the relay  310 . In exemplary embodiments, the sensor circuitry  318  is a voltage detector or voltage monitor or the like, although the present disclosure is not limited thereto. 
     In general, the voltage detector  318  includes a first capacitor  318 C 1  and a second capacitor  318 C 2 . In exemplary embodiments, the first capacitor  318 C 1  has a low value C 1  (typically around 100 pF) and high voltage capacity. The first capacitor  318 C 1  advantageously couples the high voltage load signal to the low operational voltage components of voltage detector. The first capacitor  318 C 1  should have sufficient voltage capacity to handle the maximum value of an inductive kickback in the load voltage signal. The second capacitor  318 C 2  is a low voltage capacitor with a value C 2 . Together with the first capacitor  318 C 1  the second capacitor  318 C 2  scales the voltage signal entering the analog-to-digital converter (A/D)  318 AD by a factor of C 2 /C 1 . The voltage detector may also include a first resistor  318 R 1  which is used to filter the load voltage signal and provide protection for the first capacitor  318 C 1 . The A/D reference  318 REF coupled through second resistor  318 R 2  is typically a DC bias to adjust the scaled voltage signal to the center of the A/D input range. 
     In general, the voltage detector  318  scales, filters, and normalizes the load voltage signal for the A/D, which then digitizes the modified signal. The digitized signal  318 D is then typically passed to the processor  316 . In exemplary embodiments, the processor  316 , memory  316 A, and the A/D  318 AD may be combined into a microprocessor, CPU or the like. In general, the processor analyzes the signal  318 D from the voltage detector and adjusts the subsequent relay open time for the relay  310  such that inductive kickback is minimized. In exemplary embodiments, the load voltage is continuously monitored allowing for dynamic adjustment to the relay open time. 
     An exemplary operational method for the system  300  is provided herein. Initially the processor  316  is loaded with an estimated relay open time for the relay  310 . The estimated relay open time may be determined by the time it takes an average relay to open after the control is set to open the relay. In one embodiment, the turnoff time is synchronized based off the line voltage zero cross as determined by the reference circuitry  314 . Each time the relay  310  is opened, the open control signal is sent “X” seconds prior to the desired switching time, where “X” equals the relay open time. 
     As previously discussed, the processor  316  analyzes the digitized load voltage signal  318 D in order to adjust the relay open time such that the switching time corresponds with current zero cross. For example, the processor  316  monitors elapsed time from the last voltage zero cross and the amplitude of the digitized signal  318 D. The processor  316  may also track whether the last relay open occurred during a positive or a negative AC lobe in the digitized signal  318 D. 
     In general, when the relay is opened and the current is not zero, an inductive kickback voltage is generated. The processor  316  detects this voltage spike and is able to determine when it occurred in relation to the voltage zero cross using the logic functions provided in TABLE 3: 
     
       
         
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 AC Lobe Sign Subsequent 
                 Voltage 
                 Resultant Change to Relay 
               
               
                 To Last Relay Open 
                 Kickback Sign 
                 Open Time 
               
               
                   
               
             
             
               
                 Positive 
                 Negative 
                 Increase relay open time by 
               
               
                 Negative 
                 Positive 
                 adding an error delay 
               
               
                 Positive 
                 Positive 
                 Decrease relay open time 
               
               
                 Negative 
                 Negative 
                 adding an error advance 
               
               
                   
               
             
          
         
       
     
     Typically, an error delay or error advance is added to the estimated relay open time to determine the subsequent relay open time. The processor  316  monitors the magnitude of the inductive kickback spikes in order to estimate the size of the error advance or delay. The closer the relay open time is to the optimal relay open time the smaller the resultant spike and, therefore, the smaller the error. By adjusting the relay open time for the last estimated error and comparing the resultant inductive kickback spike to previous kickback spikes the processor  316  is able to hone in on the optimal relay open time wherein the relay switching time corresponds to current zero cross. In exemplary embodiments, when the relay switching time corresponds to the current zero cross the inductive kickback spike will be reduced or eliminated, thus, indicating no error. The processor  316  may include any logic circuits, e.g., a programmable logic array, custom circuit, or other appropriate circuitry known in the art, for processing the relay open time adjustments as provided above. Furthermore, the processor  316  includes the appropriate input/output circuitry required for the described implementation of the present disclosure. Processor  316  may be, for example, a CPU, whereby factors such as the shape, slope, duration, etc., of each inductive kickback spike may be analyzed by the processor  316  to more precisely estimate the relay open time error. 
     It will be appreciated that the present disclosure includes a relay closed at a zero voltage cross and opened at a zero current cross. Alternatively, the relay could be opened just at zero current cross. The isolation circuitry allows full isolation between line and load afforded by the relay in the open position. The present disclosure may be utilized in home automation systems. 
     It will be appreciated that the structure and apparatus disclosed herein is merely one example of a means for sensing a zero point crossing of a reference waveform, and it should be appreciated that any structure, apparatus or system for sensing a zero point crossing of a reference waveform which performs functions the same as, or equivalent to, those disclosed herein are intended to fall within the scope of a means for sensing a zero point crossing of a reference waveform, including those structures, apparatus or systems for sensing a zero point crossing of a reference waveform which are presently known, or which may become available in the future. Anything which functions the same as, or equivalently to, a means for sensing a zero point crossing of a reference waveform falls within the scope of this element. 
     It will also be appreciated that the structure and apparatus disclosed herein is merely one example of a means for automatically adjusting the delay time, and it should be appreciated that any structure, apparatus or system for automatically adjusting the delay time which performs functions the same as, or equivalent to, those disclosed herein are intended to fall within the scope of a means for automatically adjusting the delay time, including those structures, apparatus or systems for automatically adjusting the delay time which are presently known, or which may become available in the future. Anything which functions the same as, or equivalently to, a means for automatically adjusting the delay time falls within the scope of this element. 
     It will further be appreciated that the structure and apparatus disclosed herein is merely one example of a means for sensing a zero current crossing point, and it should be appreciated that any structure, apparatus or system for sensing a zero current crossing point which performs functions the same as, or equivalent to, those disclosed herein are intended to fall within the scope of a means for sensing a zero current crossing point, including those structures, apparatus or systems for sensing a zero current crossing point which are presently known, or which may become available in the future. Anything which functions the same as, or equivalently to, a means for sensing a zero current crossing point falls within the scope of this element. 
     It will further be appreciated that the structure and apparatus disclosed herein is merely one example of a means for sensing a zero voltage crossing point, and it should be appreciated that any structure, apparatus or system for sensing a zero voltage crossing point which performs functions the same as, or equivalent to, those disclosed herein are intended to fall within the scope of a means for sensing a zero voltage crossing point, including those structures, apparatus or systems for sensing a zero voltage crossing point which are presently known, or which may become available in the future. Anything which functions the same as, or equivalently to, a means for sensing a zero voltage crossing point falls within the scope of this element. 
     Those having ordinary skill in the relevant art will appreciate the advantages provided by the features of the present disclosure. For example, it is a feature of the present disclosure to provide a relay switching circuitry capable of closing and opening the relay at zero crossings, or at least at substantially zero crossings. Another feature of the present disclosure is to provide relay switching circuitry that closes a relay at substantially zero voltage across the relay contacts and opens the same relay contacts at substantially zero current. 
     Although the present disclosure has been described with reference to exemplary embodiments and implementations thereof, the disclosed assemblies, systems, and methods are not limited to such exemplary embodiments/implementations. Rather, as will be readily apparent to persons skilled in the art from the description provided herein, the disclosed assemblies, systems, and methods are susceptible to modifications, alterations and enhancements without departing from the spirit or scope of the present disclosure. Accordingly, the present disclosure expressly encompasses such modification, alterations and enhancements within the scope hereof.