Patent Publication Number: US-7212090-B2

Title: Relay with core conductor and current sensing

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to electromagnetic relays and contactors, and is more specifically related to the structure of an electromagnetic or electromechanical relay of the type that has a winding or coil that is energized to move an armature such that a load current may be applied to a load device. Relays and contactors may be considered as devices in which the appearance of a pilot current or voltage causes the opening or closing of a controlled switching device to apply or discontinue application of load current. The invention is particularly concerned with a combination of a relay and a current sensor for measuring the amount of load current, or the quality thereof, that is being applied to the load device. 
   Electromagnetic or electromechanical relays or contactors are devices in which current that flows through an actuator coil closes or opens a pair of electrical contacts. This may occur in a number of well-known ways, but usually an iron armature is magnetically deflected towards the core of the coil to make (or break) the controlled circuit. In electromechanical relays, the voltage drop across the switching or output contacts is low, i.e., on the order of millivolts, so any power loss through the relay contacts is kept low in comparison with solid state relays, where the forward voltage drop may be one volt or sometimes higher. 
   Electromagnetic or electromechanical relays are commonly used to control the application of power to a load, for example, to control the application power to a blower or fan in a ventilation, heating, or air conditioning system. These devices are inexpensive and in general have good reliability over a reasonable life span. Wear of the contacts may occur in time due to arcing if the relay acts to break the circuit at a time when there is significant current load flowing. This may also produce switching noise, which may disturb electronic devices located near the relay. 
   If it is desired to monitor the load current to the associated load device, a separate current sensor is employed. This may involve a hall-type solid-state device or other current detector device. This adds circuit complexity and cost to the control circuitry for the load device. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an improvement to a relay or contactor that overcomes the above-mentioned drawback(s) of the prior art. 
   It is another object to provide a combination of an electromagnetic relay and load current sensor in which the coil or winding of the device plays a dual role. 
   It is a more specific object to provide a relay or contactor which permits monitoring of the quality of the load current that is being applied to the load device. 
   In accordance with one aspect of the present invention, an electromechanical relay may be situated in series with a source of AC line power and an AC load. Actuator current, i.e., pilot current, is applied to an actuator coil for closing and releasing a contactor arm of the relay, e.g., an armature. Normally a spring or similar means biases the armature away from the actuator coil. A first, or moving, electrical contact carried on the armature; a second, or fixed electrical contact is adapted to make contact with the first contact when the actuator coil closes the armature. The second contact is connected to a core conductor that passes through an axial bore of the actuator coil. The coil picks up voltage that is induced by load current carried on the core conductor going to the AC load during the time that the actuator coil pulls in the armature. A load current sensor has input terminals connected to a winding of said actuator coil for picking up this induced voltage. This induced voltage is representative of the load current carried on the core conductor. The output from the sensor can be employed for controlling timing of opening or breaking of the load circuit so that the contacts are opened at a time when the applied current crosses through zero amperes. Also, the output of the sensor may be used to alert to high load conditions, i.e., lock rotor or stall; to very low load conditions, which may be indicative of blockage of air duct or filter, or to extremely low load conditions, which may be indicative of a drive belt failure or open circuit to the fan or blower motor. Comparison of the phase of the applied AC voltage and the AC load current can also be used to measure power factor or power phase angle, i.e., phase difference between voltage and load current. 
   Alternatively, an electromechanical relay (or contactor) is adapted to be situated in series with a source of polyphase AC line power (e.g., three-phase power) and the AC load. In this case, the contactor armature carries a plurality (e.g., three) of moving electrical contacts, each of which is coupled to a respective phase conductor. There are a respective plurality (e.g., two or three) of fixed electrical contacts adapted to make contact with the movable contacts when the actuator coil closes, i.e., pulls in the contactor armature. These fixed contacts are connected to respective core conductors that pass through the axial bore of the actuator coil, so that the three core conductors carry respective phase portions of the load current to the AC load. In this case, the load current sensor, whose input terminals are connected to a winding of the actuator coil, detects an induced voltage representative of the net of the respective phases of the load current. In a balanced system, the induced voltages from the three phases would cancel one another out, resulting in a zero reading. However, if there is a phase imbalance, an output level will appear, which can be used both to indicate the presence of an imbalance and to identify its phase. 
   The above and many other objects, features, and advantages of this invention will be more fully appreciated from the ensuing description of certain preferred embodiments, which are to be read in conjunction with the accompanying Drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is an basic schematic view of a relay with load current sensing according to one embodiment of the present invention. 
       FIG. 1A  shows an alternative relay arrangement. 
       FIG. 2  is a schematic view of an alternative embodiment. 
       FIG. 3  is a chart for showing application of pilot current and sensing of induced voltage for explaining embodiments of this invention. 
       FIG. 4  is a schematic view of a three-phase embodiment of the present invention. 
       FIG. 5  is an applications chart for explaining various embodiments of embodiments of this invention. 
       FIG. 6  is a sectional view of a linear action relay according to another embodiment of the invention. 
       FIG. 7  is an end elevation thereof. 
       FIG. 8  is a perspective back view of a spring contactor member of this embodiment. 
       FIG. 9  is a perspective front view of the contactor member. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference now to the Drawing,  FIG. 1  shows schematically a relay arrangement according to one embodiment of the invention. Here, an electromagnetic or electromechanical relay  10  has an electromagnet or actuator  12  formed of a wire coil or winding  14  wound upon a bobbin  16 . A core conductor  18  is made of a conductive material, which may in some cases be ferromagnetic, that passes along the axis of the actuator  12  through an axial bore or passageway in the bobbin  16 . A yoke  20  of ferromagnetic material supports the actuator coil and also supports a leaf spring  22  or other equivalent spring on which an iron armature  24  is mounted. The leaf spring  22  can be non-conductive or can be mounted on insulation so that the leaf spring  22  is electrically isolated from the yoke. The armature  24  pivots at the location of the spring  22 , and is biased away from the actuator. A movable contact  26  is mounted on the armature and a fixed contact  28  is mounted on the core conductor. This contact  28  is the normally open or N.O. contact. Alternatively, the normally closed or N.C. contact could be used. There can be a permanent magnet or other means used for latching the relay upon actuation, in which case a reverse pulse may be employed to open the relay. Also, a manual reset provision, i.e., a relay reset button (momentary contact switch) can be used in some embodiments to open the relay after it has been actuated. 
   An AC power source  30 , i.e., which may be standard household AC main line power or may be a synthetically generated power, is connected in a circuit that includes the core conductor  18 , the contacts  26 ,  28  and an AC load  32 , such that power is applied to the load  32  when the armature  24  is pulled in or closed, and power is cut off when the armature  24  is released. 
   A source circuit  34  for actuator current provides the pilot current or actuator current to the coil  14  of the relay, and this is controlled by a switch device or circuit, represented here by ON/OFF circuit  36 . A voltage sensor circuit  38  is also connected to the leads to the coil or winding  14 , and is sensitive to the voltage that is induced onto the coil by the AC load current that flows through the core conductor  18 . This voltage is generally proportional to the magnitude of the load current, and provides a measure of the amount of current flowing through the AC load device  32 . The phase of the AC load current is also available. An output of the sensor circuit  38  goes to an input of a control circuit  40 , which may be operative to supply control signals to the ON/OFF circuit  36 . In a heating, ventilation, or air conditioning environment, the control circuit  40  may be a portion of a furnace control board or air conditioning control board. In that case, it is useful for the control circuit to be sensitive to motor load current conditions on the blower motor, inducer motor, compressor motor, or other devices so as to assist in controlling the power or in some cases in adjusting the voltage and waveforms of the power flowing to those load devices. In addition, it is possible to generate an alarm if a fail condition is detected, such as lock rotor (high level) load current, or if an unusually low load current or absence of current is detected. 
   The fixed contact  28  may be positioned directly in line with the core conductor, or may be positioned elsewhere with a conductor leading to the core conductor, as design requirements may dictate. 
   An alternative relay arrangement shown in  FIG. 1A  includes a relay  10 ′ in which its normally closed (NC) fixed contact is connected with the core conductor  18 ′. Here the elements that are correspond to the same element in  FIG. 1  are identified with the same reference number but primed. The remainder of the circuit is omitted in this view. 
   Another embodiment of this invention is shown in  FIG. 2 , in which elements that are common also to the previous embodiment are identified with the same reference numbers as in  FIG. 1 , and do not need to be discussed in great detail. In this embodiment, in addition to the load current sensor  38 , which is coupled to the leads of the coil  14 , there is also a line voltage sensor  42  which measures the level of the main AC voltage that is applied from the AC source  30  to the load  32 . The sensor may provide an integrated level that indicates the magnitude of the AC applied voltage, or in some cases it may provide the instantaneous voltage level, which may be useful in detecting the power factor or the phase difference ΔΦ between the applied AC voltage and the AC current that flows through the core conductor  18  and the load  32 . In such case, a power factor circuit  44 , which may be of analog or digital design has inputs coupled respectively to the load current sensor  38  and to the voltage sensor  42 , and its output may be provided to the control circuit  40 . 
     FIG. 3  is a wave chart showing the relation of the actuator current that is applied to the coil or winding  14  and the timing of the sensor  38  that detects the main load current flowing through the core conductor  18 . This is one of many possible schemes that enables the same coil or winding  14  to be used both to pull in the armature  24  and also to provide an induced voltage to the sensor  38 , without the two interfering with one another. This scheme may be employed when  24  volt AC thermostat power is used for actuation of the relay, and where the main AC source  30  provides 110 volt or 220 volt AC household power to the load device  32 . Here, only a portion A of the AC wave (from the thermostat power) is employed for closing the relay  10 , e.g., for a time of about one millisecond for each half cycle. This is rectified, e.g., in the actuator current source circuit  34 , and may be integrated so as to maintain latch of the relay. The sensor  38  is turned off for this portion A, but may be turned on for any or all of a remaining sensor portion S, which is up to about 7 milliseconds for each half-cycle. 
   The core  18  may incorporate a permanent magnet. Then when the relay is to be actuated, the coil  14  is pulsed to actuate the load relay ON and then latches in the ON state. This allows the current sensor to read the entire line cycle. The relay can then be pulsed OFF by reversing the coil bias. 
   In the event that the actuator current is provided from a steady DC source, e.g., “battery”, then the induced voltage that appears on the coil  14  and represents the load current would be superimposed on the DC voltage, and can be easily separated from it in the sensor  38 . As another alternative, a separate, additional winding may be placed on the bobbin  16  of the relay  10  to be used for detecting the load current. A latching relay arrangement is also possible, employing a permanent magnet at the core, as is well known. 
   A polyphase version of the relay arrangement of this invention is illustrated in  FIG. 4 , in which elements that are similar to those in the previous embodiments are identified with similar reference numbers, but raised by  100 . Here the relay  110  is configured as a three-phase relay or contactor, with a relay actuator coil  114  and with three separate core conductors  118   a ,  118   b , and  118   c , each carrying one phase of the three phase load power. There are three respective movable contacts  126   a ,  126   b , and  126   c , and three fixed contacts  128   a ,  128   b , and  128   c . The load and the source of AC power are omitted from this view. A load current sensor  138  is connected to the leads of the winding or coil  114 , as in the previous embodiments. However, in this case, because the three phase conductors  118   a ,  118   b , and  118   c  will be carrying currents that are mutually separated by 120 degrees, the effect of the voltage induced by the three phases of the load current will be to cancel one another out, provided the load is in balance. In this embodiment, a logic circuit  140  is connected with an output of the sensor  138 , and indicates phase balance as long as the induced voltage is zero, but indicates an unbalanced condition if the induced voltage is different from zero, i.e, if there is a significant net load current. The threshold for this logic circuit  140  may be selected depending on the type of load. 
   Of course, by feeding only one of the three phases through a single core conductor, as with the embodiments of  FIG. 1  and  FIG. 2 , it is possible to measure the magnitude of the load current for that phase, and also the phase angle thereof. 
     FIG. 5  is a chart for explaining some of the capabilities and advantages of the various embodiments of this invention. 
   First, for a two-wire (e.g., single phase) embodiment such as that of  FIG. 2 , the line voltage detection facility of detector  42  can be used to measure the quality of the line voltage, i.e., whether there is an overvoltage problem or an undervoltage (brown-out) problem, and this information may be used to determine whether the device should be disabled. The timings of the zero-crossings of the applied line voltage are also available, and these may be used to control the timing of the actuator power, i.e., pilot current that is applied to the relay coil  14 , so that the armature is pulled in and contact is made at a time when the line voltage is at or near zero. 
   When the relay switch is closed and current is flowing through the load  32  and through the center or core conductor  18 , measures of the quality of the load current can be provided by the load current sensor  38 , and the load current may be monitored for current overload and current no-load conditions, and for power factor or current-voltage phase difference AD. The timing of the load current zero crossings is also available, so that the timing of the release of the relay can be controlled so as to break contact when at the time that the AC load current is at or near zero amperes. 
   As discussed in respect to  FIG. 4 , the three-wire relay arrangement provides a simple and direct means to indicate phase balance and unbalance during the time that the switch is closed and the three-phase AC load current is flowing. 
   In a four-wire or five-wire arrangement, the detected load current value can be employed as a transducer input, for ground-fault isolation, arc interrupt, or for remote circuit breaker control. 
   Another embodiment is shown in  FIGS. 6 to 9 , in which the moving contact(s) are supported on a linear-action armature rather than a swing arm, so that the motion upon closure and release is along an axis of the actuator coil. This has the advantage of predictable alignment of the contacts when the relay is manufactured, for better, chatter-free closure. In addition, as the contacts wear over time, the contacts stay in alignment and avoid drift in alignment of the type that can occur in hinged or pivot action armatures. Here, similar parts to those of the previous embodiment are identified with the same reference numbers but raised by 200. 
   In this relay  210 , the actuator coil  214  has a core conductor  218  disposed along its axis with a fixed core contact  228  at one end. The ferromagnetic yoke  220  provides a magnetic return path from the back to the front of the coil  214 . A magnetic movable armature  224  is in the form of a generally rectangular plate (See  FIGS. 8 and 9 ) having a plurality of spring clips or leaf springs  122  disposed at its edges, here two sets of two leaf spring clips  222 ,  222 , one set along the left edge and one set along the right edge. In this embodiment, these spring clips  222  are of generally S-shaped profile to accommodate the axial motion of closure, and also to hold the armature by spring action against an associated support conductor  230 . The moving contact  226  is affixed into a central apertured recess  229  in the plate or armature  224 . The contact  226  can be in the form of a two-sided rivet type contact so as to be used in both normally open and normally closed operation. 
   The plate or armature  224  may be formed of spring steel, preferably a good conductor (e.g., Fe—Ni) of suitable springiness and magnetic permeability. Alternatively, the plate  224  can be formed of beryllium copper, and a ferromagnetic layer, e.g., Invar, can be mounted onto it. 
   A fixed contact  227  is mounted in axial alignment with the contact  226  on a conductive support member  231 . The support member has a contact blade  232  extending upward and a lower conductive foot  233  for penetrating an aperture in a printed circuit board. 
   In this embodiment, the contact  227  serves as normally closed contact, and the contact  228  serves as normally open contact. 
   The four S-shaped spring clips  222  provide balanced spring force so that the motion of the armature plate  224  is in the linear direction along the axis of the coil  214 . The clips  222  also provide electrical continuity between the contact  226  and the support conductor  230 , which serves as a common terminal. 
   As shown in  FIG. 6 , the spring action armature plate  224  is normally biased against the support conductor  230 , but is held about 0.006 inches away from the support conductor by engagement of the contacts  226  and  227 . This creates a spring bias holding the contacts in normal electrical engagement. Upon application of actuator current through the coil  214 , the armature plate  224  is pulled towards the coil  214 , and the contact  226  pushes against the normally open contact  228 . When the actuator current is terminated, the spring clips  222  return the actuator plate back away from the coil  214 . 
   In this embodiment, a smaller holding current can be employed once the relay has been actuated, e.g., the actuator can be reduced to about thirty percent of its initial level after actuation. The relay will hold in the closed or actuated condition until the actuator current is removed. A small momentary reverse current may be applied in some cases for faster opening action. 
   The current along the core conductor  218  can be sensed by the main winding or by an auxiliary winding in the coil  214  and used in a manner as described in respect to the prior embodiments. Also, relays of this construction could be employed in DC applications. 
   While the invention has been described with reference to specific preferred embodiments, the invention is certainly not limited to those precise embodiments. Rather, many modifications and variations will become apparent to persons of skill in the art without departure from the scope and spirit of this invention, as defined in the appended claims.