MXPA99008077A - Method of driving zero cross relay and system that implems it - Google Patents

Abstract

The present invention relates to an electromechanical developer traction system that extends the life of the relay by ensuring operation of the developer in a manner that makes and breaks contact between the contact electrodes at a zero crossing point of the switched waveform. The aging of the developer and the environmental variations are dynamically compensated upon the occurrence of each actuation of the electromechanical developer to ensure proper timing of energization and de-energization of the developer to ensure commutation at the point of grows to zero. Additionally, the described traction system compensates for variations in the actual operation of contacts during actuation for the positive and negative half cycle of the switched waveform.Further, the system of the present invention alternately energizes and de-energizes the developer electromechanical during half positive and negative cycles of the switched waveform to prevent metal deposition from one contact electrode to the other. This system calculates the appropriate delays in a dynamic historical perspective by detecting changes in the voltage slope and the bobi current

Description

METHOD OF DRIVING ZERO CROSS RELAY AND SYSTEM THAT IMPLEMENTS IT Field of the Invention The present invention relates to relay switching circuits, and more particularly to timing and control circuits to ensure switching at the zero crossing of a relay. BACKGROUND OF THE INVENTION The switching of electric power has long been a requirement for the operation and control of several systems. These systems include everything from the simple tilting of a light switch to turn on a light or the resetting of a circuit breaker switch that has been automatically disconnected due to an overload of circuits, to the very complex and sophisticated computer controlled switching and spills of charging electrical energy in the space transporter. Although manually operated electrical switches are suitable for many of these applications, electronic control is increasingly being used to effect the switching of electrical power. Even modern room lighting systems use electronic motion sensors to control electrically operated switches to turn lights on and off within a room. Although small control electronics are well suited to process the required inputs and perform the logic required to control the switching of electrical power, many of these electronic components operate at digital voltages and currents and are not suitable for switching larger quantities. of electrical energy necessary to operate most of the electrical equipment. Although there have been many advances in the development and manufacture of high-power electronic switching circuits, the cost and cooling requirements of these devices, such as IGBT, MCT, and MOSFET, hamper their application in many electrical power switching applications. . In many of these applications, which vary anywhere from the From consumer devices, to electronic wall-mounted hand dryers, to large computer-controlled factory equipment, the use of electronically controlled electromechanical relay provides the required function at a cost and with a reliability that is acceptable. , A typical electronic relay, such as that illustrated in Figure 5, typically comprises at least one, and possibly two, impeller coils 10. In the case of a single coil relay, coil 10 is energized to create a magnetic field. which attracts a movable contact electrode 12 towards the * 25 physical contact with a stationary contact electrode 14 to complete the electrical circuit between the two power terminals 16, 18 for a normally open relay. If the relay is of the normally closed type, the energization of the impulse coil 10 will create a magnetic field that separates the - 5 physical contact of the two contact electrodes 12, 22 thereby interrupting the electrical circuit between the two energy terminals 18, 20. These single-coil relays typically also include a spring force (not shown) to maintain the electrode of movable contact in its still state, ie, away from the stationary contact electrode 14 for a normally open relay, and in contact with the stationary electrode 22 in the normally closed type relay. Several other designs are available for relays depending on the requirements of the application particular. The most sophisticated electromechanical relay designs include both an open pulse coil and a closed impulse coil, requiring the application of an electrical impulse signal to both open and close the relay. Other designs include circuit type relays Retention that allows the coil current to be interrupted as soon as the relay has changed, as well as elimination competition coil mechanisms that ensure that both the open and closed control coils are not energized at the same time. Other relay designs provide contacts both normally open and normally closed, and many provide auxiliary contacts to capture the position of the relay for control of the feedback. Regardless of the particular construction of the actual relay switching element, its reliability will be determined by the number of cycles it will endure in its half-life. As will be recognized by one skilled in the art, the mechanical simplicity and robustness of a typical relay design does not provide the limiting factor that determines the life of the relay. Instead, the typical limiting factor in the life of the relay is a purely electrical phenomenon that occurs in most relays over the opening and lock of the contact electrodes. Specifically, the opening and lock of the contact electrodes results in an electric arc that is formed through the contacts during a small period of time. The period of time during which an arc flows is determined by many factors including the mechanical rebound of the contacts after the lock, the distance between the contact electrodes, the magnitude of the current flow, as well as the level of ionization of the air at ? • 2.0 gap between the contact electrodes. This electric arc will also be extinguished, in the case when an alternating current is being switched, when the voltage between the contacts goes through zero and the cycle changes from positive to negative or from negative to positive. 25 The electric arc between the contact electrodes of an electromechanical relay limits the life of the relay in essentially two ways. First, the electrical arching leaves carbon deposits on each of the contact electrodes which, over time, accumulate to form a high resistance contact between the contact electrodes. This high contact resistance results in increased heat dissipation within the electromechanical relay, as well as reduced voltage available at the relay output. Eventually, the accumulation of material on the surfaces of the contact electrodes will result in intermittent contacting of the contact electrodes. This intermittent contact results in the electrical circuit not being completed when the relay is energized due to insulating properties of the accumulation material that prevents physical contact of the conductive material of the contact electrodes. A second way in which the life of an electromechanical relay is shortened by the electric arc formed between the contacts during the opening and lock thereof is a result of the extreme heat of an electric arc. Specifically, since an electric arc extends between the two contact electrodes, a small portion of the contact electrode material will melt or vaporize from the surface. The amount of material burned in each cycle during which an arc is formed is a function of the voltage and current which the relay is trying to change. The greater the current flow between the electrodes of electrical contact, the hotter the electric arc, and thus the more contact material that burns. A second factor is the amount of contact material on the surface of the contact electrode. Although gold provides high fidelity electrical contact, its expense requires that it be plated on the surface of the contact electrode in relatively thin layers. These gold plate contacts are particularly susceptible to failure from the extended arcs during the switching operation due in part to the small amount of gold that is present and partly due to the softness of the gold itself. An alternative failure mode of electromechanical relays due to the generated arc, mainly during the lock of the contacts, is the welding of the contact electrodes. Specifically, as the contact electrodes come into contact, the force with which they typically join results in a slight mechanical rebound of the two contact electrodes, resulting in multiple contact and separation events in a very short period of time r20 . Each of these rebound events results in the generation of an electric arc which tends to greatly increase the temperature of the surfaces of the contact electrodes. This particular failure mode is generated when the surface material on the contact electrodes is '25 warms to a sufficient degree to liquefy to a certain degree, the surface material. If both surface materials of the electrical contacts liquefy and the contact electrodes come into physical contact, these two electrodes will be soldered. This event is a latent fault, the existence of which is not known until it is desired to break the electrical contact to de-energize the load to which the relay is connected. At this point it is noted that the relay has been welded in a closed configuration, and the circuit is no longer capable of being interrupted, resulting in the continued energization of the electrical load. Since this problem has existed since the invention of the first switch, many attempts have been made to overcome this problem. There is a family of solutions through which an electronic controller tries to control the opening and physical lock of the electromechanical relay to a point of minimum voltage difference between the electrodes. Specifically, it is desirable to open or close the contact electrodes when the voltage at the relay is zero volts (at the zero crossing of the alternating current waveform). However, since the activation of an electromechanical relay requires the physical movement of the contact electrodes, there will be some delay from the initial closing command issued by the electronic controller until the magnetic field accumulates at a sufficient level to begin the movement of the contact electrodes overcoming the force of the spring.

Additionally, there will also be a delay due to the amount of time it takes for the contacts to make the transition from their fully open to fully closed position. Previous attempts to measure the closing time and contact opening have involved measuring the voltage across the contacts or the load. However, this method has certain problems including those that result from contact rebound in the lock. It is a phenomenon of electromechanical relays that conform the contacts of the relay * U) age, tend to have more electric bounce. This bounce in turn provides false data for the measurement of contact time. Other methods to measure the closing and contact opening time include the determination of the nominal contact time at the time of manufacture of the relay electromechanical, and using this data in the electronic controller as an integrated delay. This method, however, presents problems as the relay ages and the opening and closing time changes, since there is no means to compensate for the fixed relays stored in the controller. There is an effect additional in the nominal time of the opening and lock with variations in the impulse voltage and the operating temperature of the environment in which the relay is located. Another problem exists with the previous controllers because they do not distinguish between switching during the positive cycle .25 or negative of the alternating current waveform, neither at the beginning nor at the end of the half cycle of the alternating current waveform. In the first situation, when the controllers do not distinguish between switching during the positive half cycle or negation of the alternating current waveform, metal plating can result from one contact electrode to the other. Although this process may be slowed down by the controller attempting to open and close the contacts near the zero crossing point of an alternating current waveform, the process will eventually result in the failure of the contacts. The second consideration that previous designs have not recognized, that of closing at the beginning or end of a half cycle of the AC waveform, also reduces the life of the relay on an optimized design. Specifically, since the variations in the opening and closing time of the relay can not be measured before they occur, electronic activation with an integrated delay will probably result in a lock of the contacts (or an opening of the contacts) to a point slightly displaced from * 20 moment of actual zero crossing of the alternating current waveform. If the contact makes the transition so that the opening or lock with rebound occurs at the beginning of a half cycle of the AC waveform to be switched, a small arc can be formed which will increase in * 25 intensity as the voltage difference between the electrodes increases at the beginning of the half cycle, and may last the entire length of that half cycle (8,333 milliseconds for an AC waveform of 60 Hertz). On the other hand, if the contact transition is made to make or break the physical contact slightly before the crossing point to zero, the arc that can be generated, besides being small to begin with, will be extinguished according to the difference of The voltage between the electrodes continues to decrease as the zero crossing point approaches. Therefore, there is a need in the art for an electronic controller that overcomes these and other known problems in the art that decrease the reliability and half-life of electromechanical relays. SUMMARY OF THE INVENTION In view of the above problems in the art, and the failure of previous attempts to overcome these problems, it is a primary object of the present invention to overcome these and other known problems in the art. Specifically, it is an object of the present invention -20 provide an electromechanical relay impulse control circuit which minimizes the arcing between the contact electrodes during the cycling of the electromechanical relay. More particularly, it is an object of the present invention to provide a control circuit which dynamically determines the actual opening and closing time of the contact electrodes to ensure that the delay used in the control circuit is accurate under the changing circumstances. of the operation of the electromechanical relay. It is another object of the present invention to provide this electromechanical relay control that is cost efficient and very reliable. Thus, it is an object of the present invention to increase the service life of the electromechanical relays without prohibitively increasing the cost of their associated control or reducing the reliability of the overall system of the electromechanical control / relay system. In view of these objects, it is a feature of the present invention that the opening and physical lock time of the contact electrodes is measured during each cycle of turning on and off the electromechanical relay. It is another feature of the present invention that this dynamic time measurement is carried out by monitoring the electrical feedback of the relay coil during contact closure. It is another feature of the present invention that the opening of the contact electrodes is measured by the voltage produced by the collapsing magnetic field around the coil. Specifically, it is a feature of the present invention that this time is identified by a pattern of the changing slope corresponding to the field of decay of the coil followed by a rise / fall of the slope representing the opening of the contacts / armature. It is a further feature of the present invention that the on and off of the relay alternates between the positive and negative half cycles of the switched waveform to avoid the metal plate of one contact in the other. Furthermore, it is a feature of the present invention that the control institutes different timing when the contacts are opened in the half positive cycle of the switched waveform than when the contacts are opened in the negative half cycle to ensure proper operation over life. whole operation half of the electromechanical relay, it is an additional feature of the present invention that the alternating current cycle is measured from the limit of ascent to the limit of ascent (from top to top), and of limit of descent until limit of descent (chasm to chasm) to compensate any variation of hardware circuits in the detection of the chronometraje of the cycle of alternating current. In view of the above objects and features, a preferred embodiment of the present invention utilizes an AC voltage waveform sensing circuit to detect the zero voltage crossover thereof. In addition, a slope detector is coupled to both the positive and negative side of the relay coil with a current sensing resistor in series and in parallel with the relay coil itself. In a preferred embodiment, logic control is included to calculate the opening time and relay lock to dynamically set the control delay for the relay coil pulse. Preferably, the control logic monitors a history of the activation time of the relay after each activation to allow dynamic prediction of the activation of the relay coil over the half-life and the relay. In a preferred embodiment of the present invention, a method for controlling the activation of an electrical relay having a coil and at least two electrical contacts, one of which is coupled to an electrical source, comprises the steps of activating the relay, monitoring a first electrical parameter of the coil during the activation of the relay, calculate a time of activation of the relay based on the first electrical parameter of the coil, monitor a second and a third electrical parameter of the electrical source, calculate a .15 activation command delay based on the activation time of the relay and the second parameter of the electrical source, and delay the activation of the relay for the activation command delay based on the third electrical parameter. Preferably, the step of monitoring the first parameter .20 electrical coil comprises the step of detecting the slope of the first electrical parameter. This method preferably further comprises the step of determining the actual activation of the contacts based on a transition to a positive slope of the first electrical parameter that follows a negative slope • 25 of the first electrical parameter.

In a preferred additional mode the step of activating the relay comprises the step of activating the relay to make the electrical contact between the two electrical contacts. In this mode, the step of monitoring the first electrical parameter of the coil comprises the steps of monitoring the current flow to the coil and detecting a slope of the monitored current flow. Additionally, the step of monitoring the first electrical parameter further comprises the step of determining the actual lock of the contacts based on a transition to a positive slope of the current flow flowing through • negative slope of the current flow. In an alternative preferred embodiment, the step of activating the relay comprises the step of activating the relay to interrupt the electrical contact between the two contacts • 15 electric. In this mode, the step of monitoring the first electrical parameter of the coil comprises the steps of monitoring the voltage across the coil and detecting a slope of the monitored voltage. Preferably, the step of monitoring the first electrical parameter further comprises the passage of * 20 to determine the actual opening of the contacts based on a transition to a positive slope of the voltage after a negative slope of the voltage. In a preferred embodiment of the method of the present invention, the step of monitoring a second and a third parameter The electric power source comprises the steps of monitoring the frequency of the electric source and monitoring a zero crossing of the electric source respectively. In addition, the step of retarding is preferably started after detection of a zero crossing. Additionally, in a preferred method the step of calculating an activation command delay comprises the steps of calculating a first activation command delay to activate the relay during a positive half cycle of the electrical source, and calculating a second command delay of activation for the activation of the relay during a medium ^ negative cycle of the electric source. In addition, the step of delaying activation preferably comprises the step of alternating between the first activation command delay and the second activation command delay. In a very preferred embodiment, the steps of monitoring a first electrical parameter 5 of the coil and calculating a time of activation of the relay are performed after each activation of the relay. An alternative embodiment of the present invention contemplates a method of calculating the activation time of the relay contact, the relay having at least one coil and at least one set of contacts. This method comprises the steps of monitoring a coil energization command, monitoring a slope of an electrical parameter of the coil during the energization of the coil, determining a contact activation point based on a change of the slope of the electrical parameter of the coil, and time a period from the energization command of the coil to the contact activation point. Preferably, the step of monitoring a slope of an electrical parameter comprises the step of monitoring the slope of the current flow through the coil. Alternatively, the step of monitoring a slope of an electrical parameter comprises the step of monitoring the voltage slope across the coil. In this mode, the step of monitoring the voltage slope through the coil is performed during the opening of the relay. In a preferred embodiment of the present invention, wherein an AC electric power source is coupled to one of at least one set of contacts, the method further comprises the step of monitoring a second electrical parameter of the electrical power source. In addition, the step of timing comprises the steps of timing a period of the energizing command of the coil to the point of activation of the contact after energizing the relay during a half positive cycle of the alternating current electrical source, and timing a period from the energizing command of the coil to the point of activation of the contact after energizing the relay during a half negative cycle of the alternating current electric power source. In a preferred embodiment the step of timing comprises the steps of timing a first period from the energizing command of the coil to the contact activation point after energizing the relay to close the at least one set of contacts, and timing a second period from the energization command of the coil to the contact activation point after energizing the relay to open the at least one set of contacts. In addition, the step of monitoring a slope of an electrical parameter of the coil during energization thereof preferably comprises the steps of monitoring a slope of current flowing through at least one coil during the lock of the relay, and monitoring a slope of voltage through at least one coil during the opening of the relay. In an alternative preferred embodiment, the step of determining a contact activation point based on a change in the slope of the electrical parameter of the coil comprises the step of determining the contact activation point upon detecting a positive slope after the occurrence of a negative slope after a positive initial slope during energization. A relay activation circuit for use with a relay having at least one coil and at least one set of contacts, when at least one of the contacts is coupled to an AC electric power source in accordance with the teachings of the present invention comprises a slope detector circuit coupled with the coil and monitoring a slope of a parameter of electrical energy during the energization of the coil, a driver's circuit of the relay, and a logic processor circuit in sensory communication with the slope detector circuit, and in contact * 5 controllable with the relay driver circuit. Preferably, the logic processor circuit includes a timing circuit and determines a delay time of activating the relay as a period from the start of the relay driver circuit to a positive change in the slope of the parameter following a negative slope after a positive initial slope. In a preferred embodiment, the circuit further comprises a source voltage zero crossing sensor circuit having an input in sensory communication with the source of AC electric power and an output coupled to the logic processor. In this mode, the logic processor monitors the zero crossing information and calculates a frequency of the source voltage. In addition, the logic processor circuit calculates an activation command delay time of relay based on the time delay of the relay activation and the frequency of the voltage source to minimize a voltage difference between each of the relay contacts in the activation. The logic processor circuit initiates the operation of the relay driver circuit in the -25 expiration of the relay activation command delay time. The delay time of the relay activation command preferably begins after detection of a zero crossing of the source voltage. In an alternative preferred embodiment, the logic processor circuit calculates a first relay activation delay time for the activation of the relay during a positive half cycle of the source voltage and a second delay time for activating the relay for the activation of the relay during a half negative cycle of the source voltage. In addition, the logic processor circuit alternates the activation of the relay between the positive and negative half cycles of the source voltage. Alternatively, the logic processor circuit calculates a first relay activation delay time to open the relay contacts, and a second relay activation delay time to close the relay contacts. As an additional alternative, the logic processor circuit calculates a first relay activation delay time to open the relay contacts during a half positive cycle, a second relay activation delay time to open the relay contacts for a half cycle negative, a third relay activation delay time to close the relay contacts during a positive half cycle, and a fourth relay activation delay time to close the relay contacts during a half negative cycle.

In a preferred embodiment of the circuit of the present invention, the slope detector circuit comprises a current sensing circuit coupled in series with the coil to monitor the current through the coil during energization of the coil. Alternatively, the slope detector circuit comprises a voltage monitor circuit coupled in parallel with the coil for monitoring the voltage across the coil during energization of the coil. Still further, the slope detecting circuit preferably comprises a current sensing circuit coupled in series with the coil for monitoring the current through the coil during energization of the coil to close the contacts, and a voltage monitor circuit coupled in parallel with the coil to monitor the voltage across the coil during energizing the coil to open the contacts. These and other objects, features, and aspects of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. , 20 Brief Description of the Drawings Figure 1 is a graphic illustration of an electromechanical coil current characteristic during energization of the coil during contact lock; Figure 2 is a graphic representation of a -25 relay coil voltage characteristic during contact opening; Figure 3 is a simplified block diagram of one embodiment of the present invention; Figure 4 is a simplified schematic diagram of an embodiment of the present invention illustrating elements in the embodiment of Figure 3 in greater detail; and Figure 5 is a schematic illustration of an electromechanical relay illustrating general concepts of these devices. Although the invention is susceptible to various modifications and alternative constructions, certain embodiments illustrating them have been shown in the drawings and will be described later in detail. However, it should be understood that there is no intention to limit the invention to the specific forms described, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents that fall within the spirit and scope of the invention as defined. by the appended claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As described above, in order to operate an electromechanical relay controller in a manner that allows the opening and closing of the contact electrodes at zero crossing of the alternating current waveform that is is going to switch, the actual timing of this opening and lock event needs to be known. Also, as described above, the above methods of measuring these opening and closing events have been affected by the aging of the relay, the electric bounce, the driven voltage, and the temperature. Therefore, one embodiment of the present invention measures the opening and contact lock times dynamically to ensure that the delay used by the electronic controller is compensated for the various parameters that affect this time. Although it is impossible to anticipate the actual relay activation time, these dynamic readings of previous activations are used to approximate the anticipation of the activation time for each subsequent operation of the relay. This historical information of the actual activation time of the relay is updated every time the relay is physically operated. The opening and lock of the contact electrodes can be measured electrically by monitoring the electrical feedback of the relay coil. As illustrated in Figure 1, the electromechanical relay coil current 100 exhibits a short and small amount of current change 102 during the lock of the relay contact electrodes. This change is thought to occur due to a change in the inductance of the electromagnet as the relay contact electrodes close. This coil current 100 can be captured in any known manner, and is preferably captured by placing a current sensing resistor in series with the electromagnetic relay coil and monitoring the resulting voltage therethrough. As can be seen from Figure 1, the current of the electromagnet relay coil 100 initially increases with a positive slope, which then becomes negative as the contact electrodes close. After this, the coil current 100 again exhibits a positive slope until its steady state current level is reached. The change in slope from positive to negative and back to positive is case 102 which can be used to determine the actual contact lock period for the electromagnet relay. Specifically, the contact lock time is timed from the initial coil enable signal 104 that is being initiated to the coil current event 102. As soon as the contact electrodes have come into physical contact, the voltage seen in the load 106 goes up. The opening of the electromagnetic relay contact electrodes provides a different scenario than the phenomenon of the coil current illustrated in Figure 1 during the contact lock. Specifically, during the opening of the contact electrodes, the voltage produced by the collapsing magnetic field around the driving coil can be monitored, as opposed to the coil current, to determine the contact opening point. In typical coil pulse circuits, a diode or diode / protective zener network is coupled across the coil to prevent the rear EMF that is generated when the coil shuts down from destroying the driving transistor. However, if the common protective network is removed and a high-voltage transistor with a resistor is placed across the coil, then the voltage across the coil has a unique voltage pattern representing the opening of the contacts as shown. illustrated in Figure 2 by voltage trace 108. As can be seen, this unique pattern is identified by a changing slope corresponding to the field of the decaying coil followed by a rise / fall in the slope representing the contact opening. When this pattern of coil voltage 108 is compared to the voltage delivered to load 110 it can be seen that the change in slope from negative to positive voltage 108 indicates the point of contact opening. The actual contact opening time is calculated from the enable signal of the coil 104 going down until the slope of the coil voltage 108 changes from negative to positive as illustrated in Figure 2. Having established an understanding of these two phenomena, attention is drawn to Figure 3, which illustrates one embodiment of the present invention in the form of a block diagram. As can be seen from this Figure 3, the electromagnetic relay pulse and the control circuit comprises a logic circuit 112 which can be a general purpose microprocessor, programmable logic array (PLA), customer specific application integrated circuit (ASIC) ), or other suitable circuits known in the art for processing logic and stopwatch signals. Included in this logic circuit 112 are the appropriate input / output conditioning circuits required for the particular implementation chosen. The logic circuit 112 uses an alternating current voltage sensor 114 to detect the zero crossing point of the alternating current voltage waveform applied to the load. This system also includes both a coil current slope detector 116 and a coil voltage slope detector 118 to enable adequate capture of the coil phenomena described above. Although various types of detectors can be used to detect the current and voltage of the coil, one embodiment of the present invention uses a series load resistor 120 and a parallel load resistor 122, although other more expensive sensing devices can be used. , and are considered to be within the scope of the present invention. The system of the present invention energizes the relay coil 124 by driving a high voltage transistor 126. This high voltage transistor can be of any suitable technology, including a MOSFETt, IGBT, MCT, and so on. The logic circuit 112 uses the slope detectors ll, 118 and the relay pulse signal 128 to determine the activation time of the relay for both the opening and the lock of the contact electrodes at each activation. This timing is then used by the logic circuit 112 to calculate a delay time to be used to generate the relay pulse signal 128. Specifically, this timing is used to determine the exact point in time relative to the form of AC wave when the pulse signal of relay 128 should be initiated to ensure activation of the relay contact at the zero crossing point of the AC waveform. The logic circuit 112 also determines in which half cycle of the alternating current waveform the relay pulse signal 128 is initiated. The logic 112 then alternates which half cycle of the alternating current waveform during which the signal of Relay pulse 128 will be initiated. As described above, the switching on and off of the relay between positive and negative half cycles prevents the metal plate from one contact electrode to the other. During the development of this feature of the present invention, it was discovered that the timing for the opening of the contacts varies depending on the polarity of the current flowing through the contact electrodes. That is, the timing is different when the contact electrodes are opened in the positive half cycle than when the contact electrodes are opened in the negative half cycle of the alternating current waveform. It is believed that this difference in timing is a result of the alternating current either helping or preventing the opening of the contacts after activation. Therefore, a preferred embodiment of the present invention measures the timing for both situations, ie the opening during the positive half cycle and the opening during the negative half cycle, and uses different delay times depending on whether the opening will occur in the middle positive or negative cycle. As a result, the preferred embodiment of the present invention stores four time delay values, a positive on delay, a negative on delay, a positive off delay, and a negative off delay. Since the relay will be turned on during both a negative and a positive half cycle of the alternating current waveform, this waveform is preferably measured for the timing of the limit of rise to the limit of rise, and of the limit of descent to the limit of down to compensate for any variation due to variations in hardware circuits of the timing of the alternating current cycle detected by it. During the operation of the present invention, the alternating current energy used to drive the load attached to the relay is sampled for a cycle time (from zero to zero crossing). Having determined the cycle time of the alternating current waveform to be switched by the relay, the zero crossing point is detected again. As soon as the zero point has been detected, a delay is initiated followed by, at the end of the delay, the generation of the relay pulse signal 128. As soon as the relay pulse signal has been initiated, the slope detector 116 which monitors the coil current is sampled to determine the contact lock time from the phenomenon 102 illustrated in Figure 1. The time period from the energization or energization of the relay coil by generating the pulse signal of relay 128 to the detection of the current slope transition 102 (see Figure 1) is measured to determine the time required for the relay contact electrodes to close. This period is subtracted from the period of the alternating current cycle, resulting in a time delay to be used for the delay period for the next ignition of the relay. The method for measuring the shutdown delay is the same as that described above, with the exception that the slope detector 118 is used. This slope detector 118, however, will detect two slope changes. The first slope change is the rear EMF slope resulting from the opening of transistor 126, while the second slope change results from the relay contact opening. It is this second slope change that is used to measure the delay required to compensate the opening and contact time. The delay measurements for the opening and closing time during the opposite half cycles are measured and calculated in the same way, and stored separately within the logic circuit 112. The measurement of these delay times is presented each time it is activated the electromagnet relay. This provides a measurement of actual delay current of the relay in its changing environment and its current age. These measured delays are used for each successive cycling of the relay to ensure that the timing of the delay is as close as possible to the opening and closing time of the anticipated relay. In this way a constant history is being recorded so that the long-term changes in the relay caused by both age and environment will be compensated over time. This will allow the relay contacts to open or close consistently at the voltage crossing point to zero of the AC voltage waveform. Nevertheless, since no system is able to perfectly anticipate the real time lock or opening of any particular cycle, optimal performance is achieved by minimizing variation in control parameters such as, for example, using a regulated voltage supply for the relay coil. As will be recognized by one skilled in the art, the load reference in the above discussions is assumed to be a resistive load. However, if an inductive load is to be controlled via the system of the present invention, the zero crossing detection must be a load current measurement, not a voltage measurement. Although one skilled in the art will recognize that the detection of the slope of the current voltage produced by the relay can be implemented in several ways including the use of an amplifier and differentiator, an exemplary implementation of one embodiment of the present invention is illustrated in FIG. Figure 4. However, this implementation is included by way of example and not by way of limitation, and does not mean that it excludes other implementations of the circuit the system described above. With this in mind, and returning specifically to Figure 4, each slope detector 116, 118 comprises a capacitor 130, 132, a diode 134, 136, a resistor 138, 140 and a transistor 142, 144, respectively. In this embodiment, the two detectors 116, 118 are physically wired in "O" [or disjunctive] together on line 146. It is possible to separate these two circuits from each other and that each slope measurement occurs at different times. This is done to reduce the number of logical ports per relay required for slope detection, resulting in cost minimization and reliability maximization. Preferably the slope signal is greater than 1.2 volts to drive the detector. In operation a captured positive slope charges the capacitor (130, 132) through the base emitter of the transistor (142, 144), and turns on the collector of the transistor. A negative slope picked up turns off the transistor and discharges the capacitor through the diode. The detector output is high for a negative slope and low for a positive slope in this implementation. The control logic 112 captures this change to calculate the delay times as described above. Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the visa art of the foregoing description. In accordance with the foregoing, this description is to be considered as illustrative only and is for the purpose of teaching those skilled in the art the best mode for carrying out the invention. The details of the structure and implementation of the various components described above can vary substantially without departing from the spirit of the invention, and exclusive use is reserved for all modifications that come within the scope of the appended claims.

Claims (29)

1. CLAIMS 1. A method of controlling the actuation of an electrical relay having a coil and at least two electrical contacts, one of which is coupled to an electrical source, comprising the steps of: operating the relay; supervising a first electrical parameter of the coil during the activation of the relay; calculate a time of actuation of the relay based on the first electrical parameter supervised of the coil; supervise a second and third electrical parameters of the electrical source; calculate a command command delay based on the time of actuation of the relay and the second parameter of the electric source; and delaying the actuation of the relay for the command command delay based on the third electrical parameter. The method of claim 1, wherein the step of monitoring the first electrical parameter of the coil comprises the step of detecting the slope of the first electrical parameter. The method of claim 2, further comprising the step of determining the actual actuation of the contacts based on a transition to a positive slope of the first electrical parameter after a negative slope of the first electrical parameter. The method of claim 1, wherein the step of actuating the relay comprises the step of actuating the relay to make electrical contact between the two electrical contacts, and wherein the step of monitoring the first electrical parameter of the coil comprises the steps of : monitor the flow of current to the coil; detect a slope of the monitored current flow. The method of claim 4, wherein the step of monitoring the first electrical parameter further comprises the step of determining the actual closure of the contacts based on a transition to a positive slope of the current flow after a negative slope of the flow of current. The method of claim 1, wherein the step of actuating the relay comprises the step of actuating the relay to break the electrical contact between the two electrical contacts, and where the step of monitoring the first electrical parameter of the coil comprises the steps of: monitor the voltage across the coil; detect a slope of the monitored voltage. The method of claim 6, wherein the step of monitoring the first electrical parameter further comprises the step of determining the actual opening of the contacts based on a transition to a positive slope of the voltage after a negative slope of the voltage. The method of claim 1, wherein the step of monitoring a second and a third electrical parameters of the electrical source comprises the steps of monitoring the frequency of the electrical source and monitoring a zero crossing of the electrical source, respectively, and where the delay step is initiated when a zero crossing is detected. The method of claim 1, wherein the step of calculating a command command delay comprises the steps of calculating a first command command delay for actuation of the relay during a positive half cycle of the electrical source, and calculating a second drive command delay to activate the relay during a half negative cycle of the electrical source. The method of claim 9, wherein the step of delaying the drive comprises the step of alternating between the first drive command delay and the second drive command delay. The method of claim 1, wherein the steps of monitoring a first electrical parameter of the coil and calculating a time of actuation of the relay are carried out at the occurrence of each actuation of the relay. 12. A method for calculating the time of contacting the relay contacts, the relay having at least one coil and at least one set of contacts, comprising the steps of: monitoring a coil energizing command; monitor a slope of an electrical parameter of the coil during its energization; determining a contact drive point based on a change in the slope of the electrical parameter of the coil; timing a period of the coil energize command to the contact actuation point. The method of claim 12, wherein the step of monitoring a slope of an electrical parameter comprises the step of monitoring the slope of the current flow through the coil. The method of claim 12, wherein the step of monitoring a slope of an electrical parameter comprises the step of monitoring the voltage slope across the coil. The method of claim 14, wherein the step of monitoring the voltage slope across the coil is carried out during the opening of the relay. The method of claim 12, wherein a source of AC electric power is coupled to one of at least one set of contacts, further comprising the step of monitoring a second electrical parameter of the electrical power source, and wherein the step of timing comprises the steps of: timing a period of the coil energizing command to the contact actuation point upon energization of the relay during a positive half cycle of the AC electric power source; and timing a period of the coil energizing command to the contact drive point when energizing the relay during a half negative cycle of the alternating current electrical power source. i or 17. The method of claim 12, wherein the step 10 of timing comprises the steps of: timing a first period of the coil energizing command to the contact actuation point upon energization of the relay to close the at least one set of 15 contacts; and timing a second period of the coil energizing command to the contact driving point when relay energization occurs to open the at least one set of contacts. 18. The method of claim 17, wherein the step of monitoring a slope of an electrical parameter of the coil during energization comprises the steps of: monitoring a slope of current flowing through the at least one coil during closure of the relay; 25 and monitor a voltage slope across the at least one coil during the opening of the relay. The method of claim 12, wherein the step of determining a contact drive point based on a change in the slope of the electrical parameter of the coil comprises the step of determining the contact point of contact when detecting a slope occurs positive after the occurrence of a negative slope after an initial positive slope when energization occurs. 20. A relay drive circuit for use with a relay having at least one coil and at least one set of contacts, at least one of the contacts being coupled to a source of AC electric power, comprising: a circuit slope detector coupled to the coil and monitoring a slope of a parameter of electrical energy during the energization of the coil; a relay exciter circuit; and a logic processor circuit in sensor communication with said slope detector circuit, and in controllable contact with said relay driver circuit, said logic processor circuit including a timing circuit; and wherein said logic processor circuit determines a relay drive delay time as a period from the start of said relay driver circuit to a positive change in the slope of said parameter after a negative slope after an initial positive slope. The circuit of claim 20, further comprising a zero-crossing sensor circuit of the source voltage having an input in sensor communication with the AC electric power source and an output coupled to said logic processor, and where said logic processor monitors said zero crossing information and calculates a voltage frequency of the source. 22. The circuit of claim 21, wherein said logic processor circuit calculates a relay drive command delay time based on said relay drive delay time and said source voltage frequency to minimize a voltage difference between each one of the contacts of the relay at the time of its actuation, said logic processor circuit initiating the operation of said relay driver circuit upon the expiration of said relay drive command delay time, said command command delay time of relay being initiated after detection of a zero crossing of the source voltage. The circuit of claim 21, wherein said logic processor circuit calculates a first relay drive delay time for driving said relay during a positive half cycle of the source voltage and a second relay drive delay time for actuation of said relay during a half negative cycle of the voltage of the source. 24. The circuit of claim 23, wherein said logic processor circuit alternates the actuation of the relay between positive and negative half cycles of the source voltage. 25. The circuit of claim 21, wherein said logic processor circuit calculates a first relay drive delay time to open the relay contacts, and a second relay actuation delay time for closing the relay contacts. 26. The circuit of claim 21, wherein said logic processor circuit calculates a first relay actuation delay time to open the relay contacts during a positive half cycle, a second relay actuation delay time to open the relay contacts. relay during a negative half cycle, a third relay activation delay time for closing the relay contacts during a positive half cycle, and a fourth delay time for activating the relay for closing the relay contacts during a half negative cycle. The circuit of claim 20, wherein said slope detector circuit comprises a current sensing circuit coupled in series with the coil for monitoring the current through the coil during energization of the coil. The circuit of claim 20, wherein said slope detector circuit comprises a voltage monitor circuit coupled in parallel with the coil for monitoring the voltage across the coil during energization of the coil. 29. The circuit of claim 20, wherein said slope detector circuit comprises a current sensing circuit coupled in series with the coil to monitor the current through the coil during energization of the coil to close the contacts, and a circuit voltage monitor coupled in parallel with the coil to monitor the voltage across the coil during energization of the coil to open the contacts.