Abstract:
A temperature sensing device enclosed in a housing having at least one thermally isolative wall and machined slot for isolating the temperature sensing device to ensure accurate reading of ambient temperature in room.

Description:
CROSS REFERENCE OF RELATED APPLICATIONS 
       [0001]    This patent claims the priority benefit under 35 U.S.C. §119(e) of U.S. provisional patent application Ser. No. 61/078,881 (2008P12615US), submitted on Jul. 8, 2008; the content of which is hereby incorporated by reference for all purposes. 
     
    
     FIELD 
       [0002]    The present invention generally relates to temperature sensing devices used to measure the temperature of the ambient air in a room or particular space. More specifically, the present invention relates to a method and apparatus to accurately read such ambient temperature for monitoring room temperature for building automation climate control systems. 
       BACKGROUND 
       [0003]    Building automation climate control systems which include heating, ventilating, and air conditioning (HVAC) systems, have at least one thermostat to monitor the ambient air temperature within a room of a building to provide feedback as to whether the air temperature of the room needs to be altered to satisfy a pre-set point. The thermostat is arranged so that a temperature sensing element is housed within an enclosure to sense the temperature of the air passing over, through, or in contact with the enclosure. The building automation climate control system may then compare this air temperature to the pre-set point to determine if the air temperature of the room needs to be changed to satisfy the pre-set point. In general, the temperature sensing element is interconnected with a processor circuit to accomplish this function. The temperature sensing element can be either indirectly coupled or directly secured to the processor circuit which includes a plurality of interconnecting members (or conductive wires). The processor circuit is coupled to the housing and is enclosed therein. 
         [0004]    In addition to the temperature sensing device, there are other components within the mounting enclosure that generate heat. Due to the heat transfer of these components, the thermal readings made at the sensing element may not be accurate of the ambient room temperature. Therefore, there may be substantial differences between the air temperature measured by the thermostat and the actual ambient air temperature of the room. In this situation, the climate control system may perform inefficiently because the temperature measured by the thermostat may not be the accurate ambient air temperature of the room. Therefore, a need exists for a device and method to accurately read the ambient temperature of a room by a temperature sensing device. 
       SUMMARY OF INVENTION 
       [0005]    It is one object of the present invention to provide, a temperature sensing device for measuring ambient temperature in a room, comprising: a temperature sensing element affixed to a printed circuit board; an enclosure surrounding the temperature sensing element; and a plurality of venting slots to allow ambient temperature air to flow through a sensor channel to the temperature sensing element. 
         [0006]    It is another object of the invention to provide, a method to accurately read temperature for a room sensor apparatus comprising the steps of: providing a temperature sensing element affixed to a printed circuit board; providing an enclosure housing the temperature sensing element; isolating the temperature sensing element from the heat producing components with at least one thermally isolative wall; and allowing ambient air to flow freely in the enclosure using venting slots. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1   a ) shows a perspective view from the top looking down of the room sensor housing with its external and internal components. 
           [0008]      FIG. 1   b ) shows a perspective view from the bottom looking up of the room sensor housing with its external and internal components 
           [0009]      FIG. 2  shows side view of top cover of housing with vent slots. 
           [0010]      FIG. 3  shows another side view of top cover of housing with vent slots. 
           [0011]      FIG. 4  shows a cross section view of the sensor channel of which the ambient air flows through to reach the temperature sensing element. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    In  FIGS. 1   a ) and  1   b ), enclosure  10  comprises top cover  20  and base  30 . Printed circuit board  40  is housed within enclosure  10 . Printed circuit board  40  also comprises display panel  50 , connector header  60  for wiring to other devices in the building, phone jack  70  to connect to a field device (i.e., laptop) for immediate information, up to four tactile switches  75  and temperature sensor  90 . The active components of the printed circuit board  40  generate nearly 1 watt of heat, therefore it is important to separate that heat from the temperature sensor  90 . Typically this is achieved through distance; the further away the temperature sensor  90  is from the internal heat of the printed circuit board  40 , the less affected the temperature reading will be from the internal heat given off by the printed circuit board  40 . 
         [0013]    In the present invention, distance is also employed; however conductive and convective barriers are included to further increase the accuracy of temperature sensor  90 . Top cover  20  comprises top thermally isolating wall  100  and base  30  comprises bottom thermally isolating wall  200  each molded into both the top cover  20  and base  30  respectively to prevent the convective heat transfer from the components of the printed circuit board  40  through the air to the temperature sensor  90 . The printed circuit board  40  also includes a machined slot  80  that essentially locates the temperature sensor  90  on an island. The machined slot  80  forces the heat given off by the components of the printed circuit board  40  to flow around machined slot  80  which increases the distance that the heat must conduct along, thereby limiting the heat transferred to the sensor. This limits the false thermal readings due to the conductive heat transfer of the components of the printed circuit board  40  through the copper on the printed circuit board  40 . The heat is easily transferred through the copper and printed circuit board  40  itself, however, in the present invention, the isolation described above does not allow the heat to conduct too close to the temperature sensor  90 . 
         [0014]    After the top cover  20  and base  30  are fastened together, the top thermally isolating wall  100  and bottom thermally isolating wall  200  touch both the top and bottom surfaces of the printed circuit board  40  so that the air surrounding the temperature sensor  90  is completely isolated from the air surrounding the rest of the printed circuit board  40 . The machined slot  80  is just inside of this isolated space so there is no tolerance issue of having the top cover  20 , base  30  and machined slot  80  all having to meet at the exact same location. It should also be noted, that a wide assortment of temperature sensor  90  may be used in the present invention. 
         [0015]      FIGS. 2 and 3  show venting slots  300  located around the top cover  30 . The venting slots comprise inlet slots  400  and outlet slots  500  to allow ambient air to flow through enclosure  10  and across temperature sensor  90 . The sensor channel  600  (shown in  FIG. 4 ) includes the path of the ambient air entering the inlet slots  400  and exiting through the outlet slots  500 . The air moves in and out of the sensor channel  600  by means of natural convection. Natural convection is the movement of air due to the temperature gradient caused by the internal components that generate heat. Hot air rises, therefore, the heat generated by the components causes an upward flow of air across the components and also up and along the wall of the room. This air flow will draw the unheated, room ambient air from below the enclosure  10  to enter the top cover  20  at the inlet slots  400  and naturally flow upward. The 45° degree angled top thermally isolating wall  100  and bottom thermally isolating wall  200  direct the air to flow up and out the side of top cover  20 . Although the temperature sensor  90  is completely isolated from the other internal components within the enclosure  10 , it is heavily vented to allow room ambient air to freely pass through the sensor channel. The 45° angle of the machined slot  80  and top and bottom thermally isolating walls  100  and  200  respectively allow the room air to more easily flow through the sensor channel. The venting slots  300  require a large enough cumulative opening to allow the naturally convective air to move freely in and out of the sensor channel  600 . 
         [0016]      FIG. 4  shows a cross section view of the sensor channel  600 . As mentioned above, sensor channel  600  represents the path of air that enters through inlet slots  400  and then exits through outlet slots  500  flowing over temperature sensor  90 . 
         [0017]    While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the present invention.