Abstract:
A control switch incorporates a solid state transducer, a strain gauge. The transducer responds to a local environmental condition, such as fluid level, or pressure and exhibits a parameter change which can be detected as an electrical output. Control circuits coupled to the transducer can sense the parameter change and switch a source of electrical energy to a load in response thereto.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/123,850 filed May 20, 2008 and entitled “Strain Gauge Pump Switch” which claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/939,453 filed May 22, 2007 and entitled “Strain Gauge Pump Switch”. The disclosures of these applications are fully incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The invention pertains to solid state pump control switches. More particularly, the invention pertains to such switches which incorporate a strain gauge as a transducer to convert an environment condition, such as a level of a fluid, to an electrical signal. 
       BACKGROUND 
       [0003]    Various types of switches have been developed for use in turning pumps on and off in response to an external ambient condition, such as water level. Such switches tend to be used in relative harsh environments such as in tanks of water, or, sump pits which are used to collect foundation water. Other environments include industrial fluids which might be caustic or acidic, as well as high or low temperatures. 
         [0004]    While known switches can be useful and function properly over a period of time, they are always subject to failure. Switch failures in turn translate into non-running pumps which can result in flooded commercial, industrial and residential locations. Alternately, non-running pumps can result in water supply deficiencies, or failures to supply commercial or industrial fluids for various applications. 
         [0005]    One switch configuration has been disclosed in U.S. Pat. No. 7,307,538, issued Dec. 11, 2007, and entitled “Pump Connector System”. The &#39;538 Patent is assigned to the assignee hereof and is incorporated herein by reference. 
         [0006]    There is an on-going need for control switches usable in such environments which exhibit greater reliability and longer lifetimes than do known switches. Preferably, such improved switches would be price competitive with known switches and readily substitutable therefore. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a diagram of a switch assemblage in accordance with the invention; 
           [0008]      FIG. 2  is a side sectional view of an exemplary switch housing as in  FIG. 1 ; 
           [0009]      FIG. 3  is an end view of an embodiment of a transducer in accordance with the invention; and 
           [0010]      FIG. 4  is a block diagram of control circuits in accordance with an embodiment of the invention.  FIG. 4A  is a perspective view of an electrical cable and AC connector in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, as well as the best mode of practicing same, and is not intended to limit the invention to the specific embodiment illustrated. 
         [0012]    Embodiments of the invention incorporate a strain gauge as a transducer to sense the presence of a fluid either through displacement, buoyancy of a structure or by fluid pressure deforming a strain gauge platform. Such embodiments can be implemented as solid state structures which can be digitally calibrated for various settings or pressure. 
         [0013]    In one aspect of the invention, such transducers can be coupled to electronic control and switching circuitry which can switch electrical energy to activate a load, such as an electric motor for a pump. Advantageously, motor starting inrush currents are diverted away from the transducers in such embodiments. Further, such transducers can accurately respond to changing conditions, such as level or pressure, resist vibration and can withstand harsh operating environments. 
         [0014]    The control and switching circuitry can include relatively high power semiconductor switches which are controlled by one or more programmable processors which in turn are coupled to one or more solid state transducers, preferable strain gauges. The processor(s) can digitally calibrate one or more strain gauges. 
         [0015]    In another aspect of the invention, a solid state switch, such as a triac, can be coupled in parallel with a relay to a pump motor connector. The switch and relay can be independently controlled by control circuits in the unit. In response to signals from the strain gauge, the control circuits can bias the switch to a low impedance state to couple electrical energy to the pump connector. In this state, the switch can couple the motor start up, inrush, current without arcing or the like to the pump connector to start the motor. Once the inrush currents have subsided, for example after a time interval such as two or three seconds, the control circuits can activate the relay which changes state and provides a closed contact pair to carry the motor current as an alternate to the solid state switch. The relay contacts shunt the motor current away from the switch enabling it to cool off as needed. 
         [0016]    When the strain gauge indicates that the lower water level has been reached, the control circuits de-energize, turn off, the relay which open circuits the motor current circuit through those contacts. Subsequently, after another time interval, such as two or three seconds, the solid state switch is biased off, or placed in a high impedance state by the control circuits. When the switch turns off it, and not the relay contacts, absorbs any turn off current or voltage transients which might otherwise cause arcing at the relay contacts. Those contacts are thus protected from electro-ablation, contact burning. 
         [0017]    With respect to  FIGS. 1-4 , a pump control system  10  includes a water tight housing  12  with an open end  12   a  closed by a retaining ring  14  which carries an axially movable pressure sensing plate  16 . Sensing plate  16  carries a connector prong  30 , best seen in  FIG. 3 . Housing  12  is placed in the sump along with a pump to be switched on and off. 
         [0018]    An electrical cable  20  couples housing  12  to a double sided AC connector  22 . Connector  22  carries a pump AC receptacle  22   a  at one end and AC outlet prongs  22   b  at the other end. In operation, a pump AC connector is plugged into receptacle  22   a.  Prongs  22   b  are plugged into a local utility supplied AC outlet. 
         [0019]    Ring  14  has an annular shape with molded radial members  14 - 1 , - 2 , - 3 , and - 4 . Radial member  14 - 4  carries an elongated, deflectable, metal plate  32  which supports a strain gauge  34 . A centered perforation  36  in a free end of plate  32  receives the connector prong  30  with a friction fit and supports pressure plate  16  for axial motion in response to applied fluid pressure. 
         [0020]    A printed circuit board  40  carries sensing and control circuits  42 . Surge suppressing circuits  44  are coupled to a DC supply  46 . A digital circuit regulator  48  and analog circuit regulator  50  feed digital circuits  56  and differential amplifier  52  respectively. 
         [0021]    The differential amplifier  52  is coupled to strain gauge  34  via connectors  34   a.  Movement of the plate  16  in a first direction in response to increasing fluid pressure generates a signal of a first polarity at amplifier  52 . Movement of plate  16  in the opposite direction, in response to decreasing fluid pressure generates a signal of the oppose polarity at amplifier  52 . 
         [0022]    Digital control circuits  56  include a programmable processor or computer  58   a,  and associated storage, random access memory, EEPROM and Flash memory indicated generally at  58   b.  Software, or, control programs stored in EEPROM or Flash memory can be executed by processor  58   a  in carrying out the above described switching process. 
         [0023]    Circuits  56  can be accessed via a programming interface  58   e.  A factory calibration port  58   f  is also provided. 
         [0024]    Digital output circuits  58   c  are respectively coupled to Triac driver  62   a  and Triac  62   b,  and relay driver  64   a  and relay  64   b.  As described above, electrical energy from connector  22  is switched by Triac  62   b  and relay  64   b  to provide a switched AC output  20   c  which can be coupled to pump motor  24  via pump receptacle end  22   a.    
         [0025]    A vent tube  20   d  extends from within housing  12 , via cable  20  and terminates at connector  22 . Tube  20   d  maintains pressure in the housing  12  at local atmospheric pressure. 
         [0026]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.