Abstract:
A low cost, tilt switch of simple construction facilitates tamper detection or provides notice of equipment tipping for safety applications. In one example embodiment, a tilt sensor includes an electrically insulative housing, a conductive ball, and two opposing electrical contacts. The switch further includes an arrangement for aligning the two opposing electrical contacts when the tilt sensor housing is formed. The sensor is mountable in a device being monitored for tilt or excessive movement. In one example application, the tilt switch or sensor effects an electrical connection that signals meter tampering when a meter is moved or inverted.

Description:
FIELD OF THE INVENTION 
     The present invention relates to electrical switches that are responsive to being oriented at an angle to close an electrical circuit. In addition, the present invention relates to manufacturing electrical switches that are environmentally friendly. 
     BACKGROUND OF THE INVENTION 
     Electrical tilt switches can operate to open or close electrical circuits as a function of the angle of inclination of the switch. Such switches normally include a free moving electrically conductive element that contacts at least two terminals when the conductive element moves to an operating position by gravity. A well-known form of the electrical tilt switch is the mercury switch. In a typical mercury switch, a glob of mercury moves freely within a sealed housing. As the housing is inclined, gravity pulls the glob of mercury to one end of the housing where it completes an electrical circuit. Mercury tilt switches are fairly easy to manufacture, however, due to environmental concerns, it is becoming increasingly difficult to manufacture any product that includes mercury because of its toxicity and disposal difficulty. 
     A common substitute for mercury in a tilt switch is free moving conductive element, such as a single metal ball. Tilt switches utilizing metal balls in place of globs of mercury are exemplified in U.S. Pat. No. 4,628,160 to Canevari and U.S. Pat. No. 3,763,484 to Byers. The use of a metal ball to complete an electric circuit is a simple and inexpensive way to create a tilt switch. Tilt switches have been used in connection with various applications, including electrical appliances to disconnect the power to the appliance where the appliance is accidentally tipped over. Tilt switches have also been used in connection with watt-hour meters to preserve the life of a battery in the unit during shipping, as exemplified in U.S. Pat. No. 5,107,203 to Timko, by disconnecting the battery when the meter is in the vertical (storage) position. A movable member (e.g., a metallic ball) within a tilt switch moves off of the internal contacts connecting the battery and the electronic circuitry when the meter is moved from the horizontal orientation. 
     The use of induction type watt-hour meters installed in meter sockets at customers&#39; sites has led to wide-spread tampering of watt-hour meters in an effort to reduce the indicated consumption and thereby defraud the utility company through indication of less-than-actual power consumption. A large share of the meter tampering is done by residential and commercial customers with single-phase induction watt-hour meters. Of the more than twenty-five commonly detected methods of meter tampering, more than two-thirds of these require either removal of the meter from its socket or removal of the cover glass. One well-known method of meter tampering involves removal of the meter from its socket and reinstallation of the meter in an upside down position. Since the terminals are reversed and the meter registers are caused to run in reverse, thereby reducing the total indicated power consumption without interruption of the power supply to the user. 
     Although U.S. Pat. No. 4,039,943 to Tapscott and U.S. Pat. No. 4,542,337 to Rausch disclose watt-hour meters using a ball switch device to detect meter tampering, both use rather complex electromechanical devices to accomplish their goals. On one hand, Tapscott uses a gravity (ball) switch with an auxiliary magnet scheme to not only cause the meter to operate in the forward direction when installed upside down, but also to cause it to run at a greater rate than indicated by the actual power consumed, thereby penalizing the defrauder. Rausch, on the other hand, discloses an electromechanically complex hall switch having an enclosed race (circular track) with a plurality of spaced outer contacts, where a metallic ball moves around the enclosed race from one outer contact to another. Both devices are parts-intensive and costly to manufacture. 
     Accordingly, there is a need for a low-cost and highly reliable device that can be adapted to both new and existing meters to readily detect the most common types of meter tampering. A switching device or tilt sensor that addresses the aforementioned problems, as well as other related problems, is therefore desirable. 
     SUMMARY OF THE INVENTION 
     Various embodiments of the present invention are directed to addressing various needs in connection with tamper detection and tilt sensing of electrical/electromechanical devices. Some watt-hour meters are equipped with a tilt switch that operates with the switch in a normally closed position. The closed tilt switch is sensitive to external disturbances of the meter, that cause the switch to temporarily open. However, in the present invention the tilt switch operates in the normally open circuit position and detects meter tampering when the switch closes. 
     One embodiment of the invention is directed to a tilt sensor that includes a first insulative housing member having therein a first electrical conductive member having a first contact portion and a first lead portion extending through and outwardly from the first housing. The tilt sensor also includes a second insulative housing member having therein a second electrically conductive member having a second contact portion and a second lead portion extending through and outwardly from the housing. The second insulative housing is adapted to fit with the first insulative housing to form a tilt sensor housing, the tilt sensor housing having a cavity defined therein by the first and second conductive members. The tilt sensor also includes means, integral with the first and second insulative housing members, for aligning the first and second contact portions to each other and includes an electrically conductive spherical member disposed within the cavity. The first and second contact portions are spaced apart within the housing cavity so as to form a gap, the gap being electrically closed with the conductive spherical member as the spherical members rolls into the gap when the tilt sensor is within a predefined angle of inclination. 
     In a related embodiment, the tilt sensor also includes an inversion detection feature. The gap between the conductive members is electrically closed with the conductive spherical member (or ball) when the tilt sensor exceeds a predefined angle of inclination and a convex configuration of one of the housing halves protrudes into the housing cavity to push the ball into the gap. 
    
    
     
       The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures in the detailed description that follow more particularly exemplify these embodiments. 
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1A  is a cut away side view of the tilt sensor according to the present invention. 
         FIG. 1B  is a cut away view of tilt sensor of  FIG. 1A  along section B—B. 
         FIG. 1C  is one embodiment of conductive member used in the present invention. 
         FIG. 1D  illustrates a top half of the housing of the tilt sensor of the present invention. 
         FIG. 1E  illustrates a top view of the top half of the tilt sensor housing with a conductive member. 
         FIG. 1F  illustrates a side cut away view of  FIG. 1E  of the top half of the sensor housing. 
         FIG. 2A  is a cut away side view of another embodiment of a tilt sensor according to the present invention. 
         FIG. 2B  is a cut away view of the tilt sensor of  FIG. 2A  along section B—B. 
         FIG. 2C  is another embodiment of a conductive member used in a tilt sensor of the present invention. 
         FIG. 2D  illustrates a side view of the top half of the housing of the tilt sensor of the present invention. 
         FIG. 2E  illustrates a top view of the bottom half of the tilt sensor housing with a conductive member. 
         FIG. 2F  illustrates an end, cut away view of  FIG. 2E  of the bottom half of the sensor housing. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is generally directed to a tilt sensor or a switch of a simple construction and having an inversion detection capability. While the present invention is not necessarily limited to such an application, the invention will be better appreciated using a discussion of example embodiments in such a specific context. 
     In one example embodiment, a tilt sensor includes an electrically insulative housing, a conductive ball, a center conductor and a non-conductive cap. The center conductor is captivated by the non-conductive cap, which is press fit onto the housing after the metallic ball has been placed inside the cavity of the housing. The center conductor can be formed in a configuration to give a desired angle of activation, depending on the application. The sensor is mountable in a device being monitored for tilt or excessive movement. In one example application, a tilt switch or sensor effects an electrical connection that signals meter tampering. During normal meter operation, the tilt switch (or sensor) is in the open circuit position and indicates a tamper when the switch (or sensor) closes. The metallic ball switch indicates a tamper when the circuit within the switch closes (the metallic ball makes contact with the internal contacts). 
     Referring to  FIGS. 1A-1F , a tilt sensor  10  is illustrated that includes an insulative (e.g. polymer) sensor housing  20  that is comprised of two housing members, a top housing member  20 A, and a bottom housing member  20 B that are configured to fit together to form a single sensor housing  20 . Housings  20 A and  20 B are sonic welded together, in this example, but the means for joining the housing is not so limited. The housing can be adhered together with an adhesive or an outside clip (or band) or can be placed inside of a metal canister for surface mounting on a printed circuit board. Sensor  10  further includes a top housing aperture  22 A and a top housing pin  24 A that correspond to a bottom housing aperture  22 B and a bottom housing pin  24 B that fit together to align the housings with each other (center-line to center-line). The fitted housings together also form a cavity  30  within housing  20 . Top housing member  20 A includes an insert molded, top conductive member  40  that is comprised of a contact portion  42  and a lead portion  44 . 
     Bottom housing member  20 B includes insert molded bottom conductive member  50  that includes a contact portion  52  and a lead portion  54  that partially protrudes outside of housing  20 . Contact portion  52  includes a concave portion  56  (in the form of a spoon or ladle). Inside of cavity  30  and bounded by conductive members  40  and  50  is a conductive spherical member  60  (e.g. metallic ball) that rolls within cavity  30  of sensor  10  as the sensor is tipped. 
       FIG. 1B  illustrates a cut away side view of sensor  10  along section B—B of FIG.  1 A. In this example embodiment, spherical member  60  rests on bottom conductive member  50 . A gap  70  is formed between conductive member  40  and conductive member  50  (members  40  and  50  are spaced apart) so as to have a degree of electrical isolation or separation between the two conductive members. When tilt sensor  10  is tipped (or an angle of inclination is imparted), conductive spherical member  60  moves towards gap  70  and eventually spherical member  60  electrically connects conductive member  40  and conductive member  50  to close an electrical circuit. In this example embodiment, closing the electrical circuit constitutes a tamper signal that the sensor  10  (and metering device) has been tipped to such an angle of inclination so as to close the circuit. In one example embodiment, tilt sensor  10  is used in connection with a watt hour meter as a means for signaling and detecting tampering with the meter, such as when the meter is removed from its socket, is tilted or is turned upside down to interfere with its normal operation. 
       FIG. 1C  illustrates one example embodiment of a conductive member  50  which is configured in the form of spoon having a concave portion  56  (of contact portion  52 ) and a lead portion  54  that extends partially outside of housing  20 . Concave portion  56  is configured to hold conductive spherical member  60  (or metallic ball) in the steady state/default condition. 
       FIGS. 1D-1F  illustrate separate portions of sensor  10 . In particular,  FIG. 1D  illustrates a side view of the top half of sensor  10  with conductive member  40  embedded in the housing.  FIG. 1E  illustrates a top view of top housing  20 A with pin  24 A protruding from the housing and an aperture  22 A formed in housing  20 A.  FIG. 1F  illustrates a side, cut away view of top housing portion  20 A with contact portion  42  embedded or molded into housing  20 A. 
     In the above embodiment, concave portion  56  is sub-mounted (recessed) into the housing so as to aid retention as well as create, when assembled, a larger contact area for the ball to fall into. The degree of tilt needed to actuate the switch can be adjusted by increasing or decreasing the diameter of the free moving metallic ball. Due to the nature of the assembled geometry, the switch can actuate in any direction or combination of angles. The polymer housing of the switch can also incorporate assembly aids to assist in final placement onto a circuit board. 
     Referring to  FIGS. 2A-2F , a tilt sensor  110  is illustrated that includes an insulative (e.g. polymer) sensor housing  120  that is comprised of two housing members, a top housing member  120   a , and a bottom housing member  120   b  that are configured to fit together to form a single sensor housing  120 . Sensor  110  further includes a top housing aperture  122   a  and a top housing pin  124   a  that correspond to a bottom housing aperture  122   b  and a bottom housing pin  124   b  that fit together to align the housings (and conductive members  140  and  150 ) with each other. The fitted housings together also form a cavity  130  within housing  120 . Top housing member  120   a  includes an insert molded, top conductive member  140  that is comprised of a contact portion  142  and a lead portion  144 . 
     Bottom housing member  120   b  includes an insert molded bottom conductive member  150  that includes a contact portion  152  and a lead portion  154  that partially protrudes outside of housing  120 . Inside of cavity  130  and bounded by conductive members  140  and  150  is a conductive spherical member  160  (e.g. metallic ball) that rolls within cavity  130  of sensor  110  as the sensor is tipped. Contact portion  152  includes a concave portion  156  (in the form of a spoon or ladle) that can easily capture ball  160 . 
     In one example, switch  110  is comprised of 2 distinct concave inductive (metallic) members  140 ,  150 ) that are insert molded into each polymer housing half. Both inserts are sub-mounted (recessed) so as to aid retention as well as create, when assembled, a larger contact area for spherical member  160  (or ball) to fall into. Top housing member  120   a  differs from the lower by using a continuous radial saddle (.200 R.) polymer crown which, upon inversion, forces the ball into the contact position. The free-floating metallic ball is dropped into one half prior to assembly. The degree of tilt sensitivity can be adjusted by increasing or decreasing the diameter of the metallic ball, varying the size of the gap between the contacts or varying the shape or radius of the contact portions. Due to the nature of the assembled geometry, the tilt switch can actuate in any direction or combination of angles in any direction. The polymer housing members can also incorporate assembly aids to assist in final placement onto a circuit board. Polymer plating in the housing members could also be used as a substitute for the metallic (inserts) conductive members. 
       FIG. 2B  illustrates a cut away, side view of sensor  110  along section B—B of FIG.  2 A. In this example embodiment, spherical member (or ball)  160  rests on bottom conductive member  150 . A gap  170  between top conductive member  140  and bottom conductive member  150  (members  140  and  150  are spaced apart) is formed so as to have a degree of electrical isolation or separation between the two conductive members. When tilt sensor  110  is tipped (or angle of inclination is imparted) conductive spherical member  160  moves towards gap  170  and eventually spherical member  160  electrically connects top conductive member  140  and bottom conductive member  150  to close an electrical circuit (see shadow of ball  160 ). In this example embodiment, closing the electrical circuit constitutes a signal that tilt sensor  110  has been tipped to such an angle of inclination so as to close the circuit. In one example embodiment, tilt sensor  110  is used in connection with a watt-hour meter as a means for signaling and detecting tampering with the meter, such as when the meter is removed from its socket, is tilted or is turned upside down to interfere with its normal operation. 
       FIG. 2C  illustrates one example embodiment of a top contact member  140  which is configured in the form of a hollowed-out spoon having a concave portion  146 , an aperture  147 , and a lead portion  144  that partially extends outside of housing  120 . As will be discussed later, contact portion  142  and housing  120   a  are configured to reject metallic ball  160  in the sensor inverted position. 
       FIGS. 2D-2F  illustrate partial views of sensor  110 . In particular,  FIG. 2D  illustrates a side view of the top half of sensor  110  with top conductive member  140  embedded in housing  120   a .  FIG. 2E  illustrates a top view of top housing member  120   a  with pin  124   a  protruding from the housing and an aperture  122   a  formed in housing  120   a .  FIG. 2F  illustrates an end, cut away view of top housing portion  120   a  with contact portion  142  embedded or molded into housing  120   a . Top half  120   a  is illustrated as including aperture  122   a  and pin  124   a  with a portion of cavity  130  shown in invisible lines formed in top housing member  120   a . Note that the bottom of cavity  130  is in a convex configuration  130   a  in order to prevent the spherical member from resting on cavity  130 , thereby forcing it to move back towards gap  170  or to its steady state position on the bottom of housing  120   b . In this example, conductive member  140  includes an aperture  147 . However, conductive member  140  can also be configured to have a convex portion instead of aperture  147  so that the housing need not be convex and pushes spherical member  160  back to the bottom of housing  120   b  and contact portion  152 . 
     In the various embodiments disclosed the conductive members are illustrated as having a spoon-like configuration. However, the invention is not necessarily limited to this configuration in the conductive member since the conductive member can be configured in the form of a square, a rectangle, or a pyramid/cone for holding or cupping spherical member  60 . The conductive members are adapted to be configured into different shapes for facilitating mounting on a printed circuit board or another apparatus. In a related embodiment, the conductive members are functionally substitutable with a polymer plating on both housings and cavity. The plated conductive members extend beyond the inside of the polymer housing and are formed as tracks on the outside of the polymer housing to facilitate electrical contact with other electrical components. Although the primary advantage of the present invention (for environmental purposes) would be to use a metallic ball, a glob of mercury could also be utilized where the housing is hermetically sealed and the tilt switch application requires a more stable contact between the conductive members (e.g., conductive members  40  and  50 ). It has been discovered that the present invention is less susceptible to false tamper signals (that may be caused by vibration or inadvertent jarring of the sensor) because the metallic spherical member is less likely to fall into the gap (e.g., gaps  70  or  170 ) and contact both conductive members simultaneously. 
     Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the present specification. The claims are intended to cover such modifications and devices.