Abstract:
A method of encapsulating a liquid level sensor device within a protective monolithic block through over-molding a printed circuit board assembly supporting a plurality of electronic components and an external sensor that includes a pair of spaced apart sensor members extending from the protective monolithic block to sense the accumulation of condensate to a predetermined level within a collection reservoir from a condensate producing source within a polyamide adhesive.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    An encapsulated liquid level sensor device and a method of encapsulating the liquid level sensor device. 
         [0003]    2. Description of the Prior Art 
         [0004]    Sensors to monitor liquid levels are well known in the art. Such sensors often include a float member which rises and falls with the changing liquid level in a drain pipe, drain pan or tank. Float actuated switches are commonly used in equipment and systems to prevent overflow of liquid such as condensate in air conditioning and refrigeration systems. 
         [0005]    Often such float sensors and switches have been replaced by more reliable electronic probe switch devices. These devices eliminate moving parts generally using instead, a pair of probe sensors for detecting rising water levels. 
         [0006]    Further efforts have been undertaken to produce module structures to encapsulate electronic components on circuit boards to protect the components from the surrounding environment are represented by the patent documents discussed below. 
         [0007]    U.S. 2002/0189346 relates to a device for sensing a level of a fluid including a microcontroller disposed within a housing and a probe coupled to the microcontroller. The microcontroller applies a given DC potential to the probe for a first period of time, measures a voltage associated with the level of the fluid to be sensed after the first period of time and applies a reference DC potential to the probe for a second period of time. 
         [0008]    U.S. 2003/0173707 shows the use of polyamide based molding compositions for the production of moldings and for adhesive sealing or filling in the production of electrical or electronic devices, in particular of plugs, cables, switches, sensors, transponders and modules. 
         [0009]    U.S. 2006/0003137 discloses a method of encapsulating a component assembly comprising a first layer having a first set of physical properties and a second layer having a second set of physical properties to protectively surround the component assembly. A continuous transitory material is formed between the first layer and the second layer at associated first and second margin portions such that the first layer and the second layer are not prone to delamination. 
         [0010]    U.S. 2006/0171127 describes a control unit including a plurality of electronic parts sealed with a resin. 
         [0011]    U.S. 2006/0208915 discloses a liquid level control switch comprising a plurality of electronic components enclosed in a case including electrically conductive sensor-probe pins extend from a PC board and are positioned for detecting liquids at various levels within drains, drain pans, tanks, reservoirs and pipes of various dimensions. 
         [0012]    U.S. 2008/0179962 relates to a leak detector pad comprising a circuit board having a bottom surface and a top surface, spaced first and second electrically conductive traces located on the bottom surface, and an electronic circuit mounted on the top surface. 
         [0013]    U.S. 2009/0140866 shows a sensor for detecting the presence of a liquid comprising a housing having a concave upper surface, a concave lower surface, and a peripheral wall connecting the upper surface and the lower surface. A plurality of apertures are formed in the wall. A plurality of electrically conductive members extend above the upper surface and below the lower surface and are separated from one another by a gap in which a liquid can accumulate. The electrically conductive members are configured to generate an output signal when a conductive liquid comes into contact with the electrically conductive members and bridges the gap. An output connector is coupled to the plurality of electrically conductive members and is configured to carry the output signal. 
         [0014]    U.S. 2009/0268414 teaches an over-molded electronic module includes a frame, an electronic assembly and a polymeric body. The frame includes a sidewall that defines an opening to provide a position for the electronic assembly. The polymeric body is formed of a polymeric composition encapsulating both sides of the electronic assembly and a portion of the frame. 
         [0015]    U.S. 2009/0291288 relates to a molded part for bonding to metal or plastic substrates for use as a fastening element comprising a hot melt adhesive based on polyamide, polyolefins, polyesters, polyacrylates or polystyrene. 
         [0016]    U.S. 2009/0295027 discloses electrical components mounted on a circuit board sealed within a frame tray of a curable material that encapsulates the circuit board. The electrical components of the circuit board are positioned and sealed within the frame tray such that the cured material does not affect an airflow path which dissipates heat produced by the electrical components during use. The curing of the curable material shields the circuit board from moisture, dust and other environmental contaminates. 
         [0017]    U.S. 2010/0050756 shows a drain pan level monitoring system comprising a level sensor to generate a level sensor output signal related to a sensed level of condensation buildup within a drain pan. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention relates to a liquid level sensor device to selectively control the operation of an HVAC unit when condensate from the HVAC unit reaches a predetermined level within a condensate collector such as a primary or secondary drain pan. 
         [0019]    The liquid level sensor device comprising a protective monolithic block having a printed circuit board assembly and a pair of liquid level sensor pins or members coupled to the printed circuit board assembly projecting downwardly below the lower surface of the protective monolithic block to generate to signal to disable the HVAC when condensate reaches a predetermined level within a drain pan. 
         [0020]    The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    For a fuller understanding of the nature and object of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which: 
           [0022]      FIG. 1  is a top view of the encapsulated liquid sensor device of the present invention. 
           [0023]      FIG. 2  is a side view of the encapsulated liquid sensor device of the present invention. 
           [0024]      FIG. 3  is a top view of the printed circuit board assembly of the liquid level sensor device of the present invention. 
           [0025]      FIG. 4  is a side view of the printed circuit board assembly of the liquid level sensor device of the present invention. 
           [0026]      FIG. 5  is a side view of the printed circuit board assembly of the liquid level sensor device of the present invention with the protective relay. housing of the present invention. 
           [0027]      FIG. 6  is side view of the liquid level sensor device of the present invention and the encapsulating mold. 
       
    
    
       [0028]    Similar reference characters refer to similar parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    The present invention relates to a liquid level sensor device to selectively control the operation of an HVAC unit when condensate from the HVAC unit reaches a predetermined level within a condensate collector such as a primary or secondary drain pan. 
         [0030]    Specifically, as best shown in  FIGS. 1 through 5 , the present invention relates to an encapsulated liquid level sensor device generally indicated as  8  comprising a protective monolithic block  10  having a printed circuit board assembly generally indicated as  12  including a printed circuit board  14  supporting a plurality of electronic components generally indicated as  16  and a relay  18  enclosed within a relay cover or protective shroud  20  disposed therein. A lamp or visual indicator  22  including a lens  23  coupled to the electronic components  16  of the printed circuit board assembly  12  extends upwardly from the top of the protective monolithic block  10 ; while, a pair of liquid level sensor pins or members each indicated as  24  coupled to the electronic components  16  of the printed circuit board assembly  12  project downwardly below the lower surface  26  of the protective monolithic block  10  to generate a signal to disable the HVAC (not shown) and to illuminate the lamp or visual indicator  22  when condensate reaches a predetermined level with a drain pan (not shown) as described more fully hereinafter. 
         [0031]    The electronic components  16 , the relay  18 , the lamp or visual indicator  22  and the liquid level sensor pins or member  24  are operatively coupled between the HVAC (not shown) and a power supply (not shown) by a connector/conductor assembly generally indicated as  28  and a conductor/cable assembly generally indicated as  30 . 
         [0032]    The method of producing the encapsulated liquid level sensor  8  is best understood with references to  FIGS. 6 through 8 . 
         [0033]    The initial step in the over molding process is the application of adhesive to the edges  32  of the relay  18 . The relay cover or protective shroud  20  is then positioned over the relay  18  by aligning a pair of alignment pins each indicated as  34  disposed diagonally on the lower edge of opposite corners  36  and  38  of the relay cover or protective shroud  20  over a corresponding alignment aperture  40  ( FIG. 3 ) formed in the printed circuit board  14 . When so aligned, the relay cover or protective shroud  20  is snapped or press-fitted into the corresponding alignment aperture  40  and pressed onto the upper surface of the printed circuit board  14  engaging the adhesive on or adjacent the relay  18  to secure the relay cover or protective shroud  20  in place in surrounding relationship relative to the relay  18 . 
         [0034]    An upper modular block  44  including a lens aperture  46  formed therethrough and a lower modular block  48  including a pair of sensor pin or member apertures each indicated as  50  formed therethrough of a molding die are positioned in surrounding relationship relative to the printed circuit board assembly  12 , plurality of electronic components  16 , relay cover or protective shroud  20 , and lamp or visual indicator  22  with the lens  23  extending through the lens aperture  46  and each pair of liquid level sensor pins  24  extending through the corresponding sensor pin or member aperture  50 . The connector/conductor assembly  28  and the conductor/cable assembly  30  extend through a corresponding aperture each indicated as  51  ( FIG. 7 ) formed on opposite ends of the mold die. Each aperture may be cooperatively formed by correspondingly cutout portions in adjacent edges of the upper modular block  44  and the lower modular block  48  to fit tightly around the connector/conductor assembly  28  and the conductor/cable assembly  30 . 
         [0035]    A low pressure molding resin such as a polyamide based hot-melt adhesive with a melt range of from about 120° C. to about 180° C. and a viscosity of from about 2500 cP to about 5000 cP at about 210° C. is then injected through a gate  52  of the molding die. The injection pressure is at least 30 psig but preferably from about 60 psig to about 300 psig. The hot-melt adhesive, low pressure adhesive is allowed to set or solidify. 
         [0036]    Finally, the upper modular block  44  and the lower modular block  48  of the molding die are removed. 
         [0037]    The electronic components  16 , the relay  18  and the pair of liquid level sensor pins or members  24  comprise the control circuit coupled to the HVAC unit allowing HVAC unit to operate under normal conditions. So long as the liquid level with the HVAC condensate drain pan (not shown) is below a predetermined level the tips of the pair of liquid level sensor pins or members  24  remain above the liquid. However, in the event there is a blockage or other abnormality in the drainage system that prevents free flowing drainage of the liquid through the drainage system, the liquid level within the HVAC condensate drain pan will rise until the tips of the pair of liquid level sensor pins or members  24  are submerged in the condensate. When this occurs, a conductive path is created between the tips of the pair of liquid level sensor pins or members  24  causing the relay  18  to open to interrupt operation of the HVAC system. In addition, the lamp or visual indicator  22  will illuminate to indicate the open circuit condition. The circuit remains open, with the HVAC unit or system inoperable, until the condensate recedes below the tips of the pair of liquid level sensor pins or members  24  at which time the HVAC unit returns to normal operating condition. 
         [0038]    It will thus be seen that the objects set forth above, among those made apparent from the preceding description are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense. 
         [0039]    It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. 
         [0040]    Now that the invention has been described,