Abstract:
A pump control system incorporates one or more solid state level sensors as well as solid state pump control switches. Elimination of mechanical or electrode-mechanical parts by using ultrasonically based fluid level sensors as well as solid state switches for motor control enhances reliability and results in reduced power consumption and dissipation.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/641,532 filed Jan. 5, 2005 and entitled “Density Sensing, Solid State, Sump Pump Switching System”. 
   FIELD OF THE INVENTION 
   The invention pertains to pump control systems. More particularly, the invention pertains to such control systems which incorporate solid state level sensors in combination with solid state motor drive circuits. 

   BACKGROUND 
   A variety of pump control systems are known in the prior art. Many of these systems can be used to control fluid levels in tanks or sumps. 
   Representative prior art systems include those disclosed in U.S. Pat. No. 6,565,325 entitled “Sensor Based Control System”, and in U.S. Pat. No. 5,707,211 entitled “Variable Speed Pump System with a Hydropneumatic Buffer/Pressure Tank”. Each of the noted patents is assigned to the Assignee hereof and is incorporated herein by reference. 
   In various of the known pump control systems levels are sensed by switch carrying floats. Others use electromechanical components for switching electrical energy to the respective pump motor or motors. 
   It has been recognized that it would be desirable to eliminate electromechanical or mechanical components from such systems to improve reliability thereof. There is thus an ongoing need for more reliable pump control systems. Preferably such improved reliability can be achieved without substantially increasing either the manufacturing costs or the complexity of such systems. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of a system in accordance with the invention; 
       FIG. 2  is a schematic block diagram illustrating current flow in one portion of an alternating current cycle; and 
       FIG. 3  is a schematic/block diagram circuit illustrating current flow in another portion of an alternating current cycle. 
   

   DETAILED DESCRIPTION 
   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. 
   In accordance with the invention, solid state circuitry is provided both for liquid level management as well as for motor power switching. Level detection can be accomplished by detecting the strength of sonic/ultrasonic wave conduction between a sonic/ultrasonic transmitter(s) and a separately located sonic/ultrasonic receiver(s). 
   A differential in the strength of the received sonic/ultrasonic signal(s) is experienced between the presence of air between the transmitter and receiver(s), and when there is a body of liquid between the transmitter and receiver. A method in accordance with the invention detects the density differential between air and a liquid (water). 
   In one aspect of the invention, operation of a pump&#39;s electric motor produces sound waves that potentially interfere with detection of received sonic/ultrasonic waves used for level detection. An electronic circuit can be employed to discriminate between transmitted waves that have been received and spurious waves that have been received. A method in accordance with the invention reduces sonic/ultrasonic interference and provides more reliable operation. 
   In another aspect of the invention; the detected presence of liquid or air at specific elevations in a tank or sump is processed and connected to power switching components to operate the pump(s) motor(s) as needed. 
   Solid state, semiconductor power switching devices configured in accordance with the invention provide reliability that is superior to mechanical switches with moving parts. 
   In a disclosed embodiment solid state switches such as IGBT&#39;s (insulated gate bipolar transistors) or MOSFET (metal oxide semiconductor field effect transistor) and associated standard or fast recovery diodes can be used to control energy for pump motor(s). By configuring the devices as described below, it is possible to switch line voltage and associated AC alternating currents into a resistive or inductive load with minimal dissipative losses. 
   Semiconductor switch devices can be enabled by applying a gate-to-source voltage across the device terminals. In this state current flows through a respective diode/switch pair to the load. 
   When the AC cycle is in the positive region relative to one diode and switch combination, current flows therethrough into a load. Current through the other diode and switch combination leg is impeded due to the blocking action of that diode. The reverse voltage across a non-conducting switch is restricted to the voltage drop across its intrinsic body diode thereby protecting the device. 
   During the negative portion of the AC cycle current flows through the other diode/switch pair and into the load. Current fails to enter the one diode and switch combination due to the blocking action of the respective diode. As described above, the reverse voltage applied to that switch is restricted to the voltage drop across the switch&#39;s intrinsic body diode. 
   By removing the gate-to-source voltage from the individual switches, current flow can be disabled because of the high impedance of the switches, such as Collector-to-Emitter (IGBT) or Drain-to-Source (MOSFET) in the off state. 
   In another aspect of the invention, the switching speed of the switch current can be controlled through selected gate drive techniques. As a result, no snubbers are required to keep the switching devices from failing. Further, the switching devices can be formed on a singular silicon substrate. This results in low interconnect losses, low electrical noise, and ease of product assembly. Because only a small voltage signal is required to enable any of the switches, low power consumption as well as relatively low dissipation are obtainable. 
   In another aspect of the invention, a tank can be controlled using one or more sonic/ultrasonic transmitters. The transmitters transmit, through the fluid in the tank to one or more receivers. Control circuits coupled to transmitters and receivers provide the necessary processing. 
   A pump switching system can be used to control pump(s) which in turn raise or lower the level of fluid. The present system can be used in the storage of fluids, such as in a water storage tank or to control fluid level in a sump all without limitation. 
     FIG. 1  illustrates an overall view of system  10  in accordance with the invention. A tank T contains a liquid or fluid F which can have a variety of levels such as L 1 , L 2 . An ultrasonic density sensing system  12 , which includes at least one ultrasonic transmitter  12   a  and a plurality of ultrasonic receivers  12   b ,  12   c  . . .  12   n , is coupled to the tank T. It will be understood that the exact arrangement and/or coupling mechanism of the elements  12   a ,  12   b ,  12   c  . . .  12   n  would be understood by those of skill in the art and are not limitations of the present invention. The sensors  12   b ,  12   c  . . .  12   n  can be used to sense and/or control a liquid level, such as L 1 , L 2  in the tank T. 
   System  10  can also incorporate control circuitry  18  which can include processing circuitry  18   a . The circuitry  18   a  might be implemented with a variety of configurations such as programmable controllers, programmable logic arrays, programmable processors and associated software  18   a - 1  or the like all without limitation. 
   Circuitry  18   a  is in turn coupled to an output oscillator  18   b  and receiving circuitry  18   c  which can include filters  18   c - 1  as well as detection circuitry  18   c - 2 . Filters  18   c - 1  can discern signals being emitted from respective ultrasonic transducers such as  18   b, c  . . . n. Filters  18   c - 1  reject or minimize spurious noise and signals received from receiving transducers  12   b ,  12   c  . . .  12   n.    
   Oscillator circuitry  18   b  emits electrical signals of a predetermined ultrasonic frequency which in turn drive ultrasonic output transducer  12   a . Detectors  18   c - 2  can be implemented as hardware or software or combinations thereof for purposes of processing signals received from receiving transducers  12   b ,  12   c  . . .  12   n . For example, and without limitation, detectors  18   c - 2  can incorporate circuitry and/or software for determining when the filtered signal from receiving ultrasonic transducer  12   b  is above or below a signal level that is associated with a level such as L 1  which might be above or below the transducer  12   b.    
   In the event that the level L 1  is above the transducer  12   b , signals received from the transducer  12   b  will be dependent on the density characteristics of the fluid F in the tank T. Where the level L 1  is below the level of the transducer  12   b  output signals received therefrom will reflect the density of the ambient air in the tank T between the level L 1  and the transducer  12   b.    
   Similarly signals from the receiver  12   c  will be indicative of the level L 2  of the fluid F in the tank. Where the level L 2  is higher in the tank than is the location of the receiver  12   c  the received signals on the line of  14   c  will reflect the presence of the fluid F and its associated density in the entirety of the space between the emitter  12   a  and the receiver  12   c . Where the level L 2  is below the level of the receiver  12   c  the differing density of the air above the level L 2  will alter the characteristics of the received signals from the transducer  12   a  which travel in part through the fluid F and in part through the ambient air. 
   Output signals from the detectors  18   c - 2 , which could be binary signals, can in turn be coupled to processing circuitry  18   a , which could incorporate any necessary timing circuitry or timing software, to detect the level or presence of fluid F relative to the receivers  12   b ,  12   c  . . .  12   n . Processing circuitry  18   a  can in turn emit output control signals  22  to a variety of circuits including switching circuitry  26  and/or alarm circuitry  28  all without limitation. Switching circuitry  26  can in turn provide signals to the alarm system  28  and/or actuate one or more pumps  32  for purposes of adjusting the level of fluid F in tank T. 
     FIGS. 2 and 3  illustrate exemplary switching circuitry  26  in two different conditions. In  FIG. 2 , circuitry  26  is illustrated with a current flow to a load such as pump(s)  32  during a first or positive portion of an AC cycle, primarily into a resistive load.  FIG. 3  illustrates the switching circuitry  26  where the alternating current flow is exhibiting a second or negative portion of the cycle. It will be understood that the switching circuitry  26  of  FIGS. 2 and 3  is exemplary only. Other alternates come within the spirit and scope of the present invention. 
   As illustrated in  FIG. 2 , during a first or positive portion of an AC cycle, current I+ can flow through input ports P 1 , P 2  through a diode D 1  and switch Q 1 . Where the drive circuitry  26   a  provides appropriate gate-to-source of voltage to the switch Q 1  the switch Q 1  will conduct and current can then flow from the output port P 3  through the load, such as pump  32 . During this portion of the cycle, current flow through the D 2 /Q 2  branch is impeded due to the blocking action of diode D 2 . The reverse voltage across switch Q 2  should be restricted to the voltage drop across its intrinsic body diode thereby protecting device Q 2 . 
   As illustrated in  FIG. 3 , in a second or negative portion of the alternating current cycle a current I− can flow in the indicated direction through the load, such as the pump  32  through diode D 2 , conducting switch Q 2  and outport P 1  to the source. Current I− in  FIG. 3  is blocked from flowing into the D 1 /Q 1  by the reverse biased diode D 1 . As noted above, the reverse voltage applied across the switch Q 1  should be restricted to the voltage drop across its intrinsic body diode. 
   As would be understood by those of skill in the art, the presence of an appropriate gate-to-source voltage across the respective switches Q 1 , Q 2  can produce a current flow in the appropriate direction to the respective switch. Current flow can be disabled by removal of the gate-to-source voltage in view of a high impedance between the respective collector emitter. Representative switches can included insulated gate bipolar transistors or metal oxide semiconductor field effect transistors. In the former a high impedance can be present across the collector-to-emitter junction in the absence of appropriate gate drive. In the latter case a high impedance will be present across the drain-to-source junction in the absence of an appropriate drive voltage. 
   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.