Abstract:
A controller and method for controlling the temperature of a steam room. The controller comprises a backing plate and a housing that serves as a moisture barrier. The housing comprises an overlay portion and mounts to the backing plate. A circuit board is mounted to the backing plate. One or more primary temperature sensors are mounted to the circuit board and located within the housing, are spaced above the circuit board, and are biased against the overlay portion. One or more secondary temperature sensors are located within the housing to sense a temperature of a backside of the respective one of more primary temperature sensors wherein an estimation of a temperature of the steam room is obtained.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application 61/722,428 filed on Nov. 5, 2012. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    The present invention was not developed with the use of any Federal Funds, but was developed independently by the inventor. 
     
    
     BACKGROUND 
       [0003]    1. Field 
         [0004]    The invention relates to a more accurate and faster responding method of measuring the temperature inside a steam bath. 
         [0005]    2. Background 
         [0006]    Steam baths, due to their wet environment and rapidly changing temperatures, have a unique difficulty in sensing the ambient temperature of the steam room. The wet environment of the steam room requires that the temperature sensor be sealed inside a housing. This housing protects the sensor from the moisture but also prevents the sensor from quickly and accurately sensing the temperature of the steam room. As a steam room heats up, the sensor reads a much lower temperature than that of the actual steam room. This problem is most evident during the initial heat up and tends to diminish as the room temperature is being maintained. As a result, the room temperature tends to have a very large overshoot and then slowly drops toward the intended setting after an extended lapse of time. 
         [0007]    The chart depicted in  FIG. 1  shows the performance of an existing control with a single sensor located behind the overlay or front surface of the housing cover. The line  102  depicts the actual temperature reading of the control sensor. In this case, the set point of the controller has been set to 105° F. (40.5° C.) as shown along the Y-axis. The control sensor reaches 105° F. (40.5° C.) set point and the control throttles back the heater to maintain that temperature. The control sensor appears to control the room temperature quite well. The line  104 , however, shows the temperature of the steam room as measured by an independent thermocouple located approximately 6″ off the wall in front of the controller. The temperature sensed by the independent thermocouple is what the steam bather actually feels. 
         [0008]    The result is that the temperature of the steam room significantly overshoots the set-point temperature by approximately 10° F. (5.6° C.) and even though the steam room actually reaches the set point temperature after only 5 minutes has elapsed, the controller does not register this temperature until nearly an additional eleven minutes has passed, as shown in  FIG. 1 . 
         [0009]    In contrast, if the steam generator is controlled by the thermocouple hanging 6″ (15.24) off the wall the bather would have a more enjoyable experience since the controller would not overshoot the set point. As a result, there is a need for a controller that is capable of controlling a steam generator would to save energy by not overheating the room and increase comfort as the desired programmed temperature is reached much sooner with less overshoot. 
         [0010]    Having a sensor protrude into the steam room far enough to accurately measure the room&#39;s temperature, however, is not considered aesthetically pleasing in a steam room or shower environment. Manufacturers typically have sacrificed performance for aesthetics. Thus, there is a need to for a controller that is capable of sensing and measuring the ambient temperature in the steam room from a location that is actually at a different temperature and that is capable of satisfying both aesthetic and performance considerations. 
         [0011]    The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background. 
       SUMMARY 
       [0012]    A controller and method for controlling the temperature of a steam room. The controller comprises a backing plate and a housing that serves as a moisture barrier. The housing comprises an overlay portion and mounts to the backing plate. A circuit board is mounted to the backing plate. One or more primary temperature sensors are mounted to the circuit board and located within the housing, are spaced above the circuit board, and are biased against the overlay portion. One or more secondary temperature sensors are located within the housing to sense a temperature of a backside of the respective one of more primary temperature sensors wherein an estimation of a temperature of the steam room is obtained. The one or more primary sensors and the one or more secondary sensors establish a temperature differential therebetween. The sensors may be thermistors. In one form of the invention the circuit board is a flexible circuit board, the one or more primary sensors are mounted to the flexible circuit board, the flexible circuit board biases the primary sensor in compression against the overlay. The one or more primary sensors may be in direct contact with the overlay and the one or more primary sensors have a cuboidal shape that contacts the overlay on one side thereof and the temperature is sensed from all sides thereof. 
         [0013]    In one form of the invention, at least one of the one or more secondary sensors are mounted to the circuit board behind one of the primary sensors to read the ambient temperature surrounding the backside of the primary sensor. 
         [0014]    A microprocessor may be provided to take the temperature reading from one of the primary sensors and subtracts the temperature reading from one of the secondary sensors to determine a differential which is added to the primary sensor temperature to get a more accurate estimation of the actual steam room temperature. The differential may be further multiplied by a constant before being added to the primary temperature reading, the constant is derived from a compensation sensor formula: ((PS−SS)/K)+PS, wherein 
         [0015]    PS=primary sensor temperature 
         [0016]    SS=secondary sensor temperature 
         [0017]    K=constant based on the characteristics of the control. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
           [0019]      FIG. 1  is a graph showing the performance of an existing control with a single sensor behind the overlay; 
           [0020]      FIG. 2  depicts the controller of the present invention located in a steam room having a steam generator; 
           [0021]      FIG. 3  is a cut away partial isometric view of the controller of  FIG. 2 ; and 
           [0022]      FIG. 4  is a graph of the effective performance of the controller of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    To overcome these and other problems of existing controllers, the controller  10  of the present invention uses multiple temperature sensors within the housing. In addition, an algorithm that more quickly and accurately predicts the temperature of the actual steam room may be employed by the controller  10 . 
         [0024]    In  FIGS. 2 and 3 , there is shown the controller  10  mounted to a wall  12  of a steam bath enclosure or shower  14 . The steam bath  14  includes a steam generator  16 , typically located in an inconspicuous location, such as a nearby vanity  18  or closet, or in a remote area, such as an attic or basement. The steam generator  16  includes a steam outlet  20  which introduces steam into the steam bath  14  via a steam head  22  by a typical piping connection (not shown). A control cable  24  or wireless communication may be provided between the controller  10  and the steam generator  16 . Also included are any necessary water lines, drain lines, and electrical power connections (all not shown for simplicity). 
         [0025]    Referring now to  FIG. 3 , the controller  10  includes an external housing  26 . The housing  26  is preferably fabricated from a durable moisture resistant material, such as metal or the like. The housing  26  serves as a moisture barrier. A backing plate  28  serves as the rear of the housing  26 . A display and user controls are typically located on the front face of the housing  26 . In the instant case, a touchscreen display and control  30  is located on the front face of the housing  26 . A power on/off control switch  32  is also located on the front face of the housing  26 . 
         [0026]    A circuit board (PCB)  34  is mounted to the interior face of the backing plate  28 . A strain relief  36  is located on the exterior surface of the backing plate  28  for accepting the control cable  24  therethrough. One or more primary sensors  38  and one or more secondary sensors are provided as discussed in greater detail below. 
         [0027]    The one or more primary temperature sensors  38  are placed behind the moisture barrier formed by the housing  26 . One side  44  of the barrier is in contact with the steam room  14  and the other side  46  of the barrier is in contact with the primary sensor  38  to form an overlay  42 . 
         [0028]    Even though the primary sensor(s)  38  are in close proximity to the surface or overlay  42  of the housing, the primary sensor(s)  38  are still mostly influenced by the temperature inside the housing  26 . 
         [0029]    As best seen in  FIG. 2 , typically, the housing  26  needs to heat up to the steam room temperature before the primary sensor  38  located within the housing  26  is capable of accurately reading the steam room temperature. Additionally, the housing  26  is mounted to the wall  12  of the steam room  14  which serves as a major heat sink, preventing the controller  10  from heating up more quickly. 
         [0030]    Referring now back again to  FIG. 3 , by adding an additional secondary sensor(s)  40  inside the housing  26  to measure the housing temperature behind the primary sensor a temperature differential is established between the primary sensor(s)  38  and the secondary sensor(s)  40 . This differential can be used to calculate the actual steam room  14  temperature far more accurately than existing designs. Through testing the relationship of this differential can be combined with the primary sensor  38  reading to eliminate any error. 
         [0031]    The sensors used in the present invention are preferably thermistors. Thermistors vary resistance with temperature and the ones selected for this design are very small to keep their thermal mass at a minimum. Although, the type of sensor is not critical to the design, the smaller physical mass of the sensor gives and added benefit of a rapid temperature response as compared to other larger sensors. The resistance value of the thermistor sensors are measured by analog inputs of the control&#39;s microprocessor. A microprocessor  46  then reads the sensors and calculates the actual steam room temperature. 
         [0032]    In the design shown, the primary sensor  38  is soldered to the flexible PCB  28 . The PCB  28  via a flex circuit bend  44  holds the sensor  38  in compression against the overlay  42 . This flexible design simplifies assembly and eliminates the otherwise needed precision tolerances required to maintain a substantially zero clearance between the sensor  38  and the overlay  42 . 
         [0033]    The primary sensor  38  is in direct contact with the overlay  42 . The sensor  38  is preferably a six sided, cuboidal device and contact the overlay  42  preferably on one side only. The sensor  38  senses temperature from all sides. The actual reading is an average of all its sides. This is why it is advantageous to read the temperature of the internal surrounding environment of the primary sensor  38 . 
         [0034]    The secondary sensor  40  is soldered to the PCB behind the primary sensor  38 . The location is less critical but should to be in a location that best reads the ambient temperature surrounding the backside of the primary sensor  38 . 
         [0035]    The microprocessor  46  uses the primary sensor  38  temperature reading and subtracts the secondary sensor  40  temperature reading to determine a differential. If that differential is added to the primary sensor  38  reading, a more accurate estimation of the actual room  14  temperature is obtained. 
         [0036]    In actual practice the differential should be multiplied by a constant before added to the primary temperature reading. That constant is unique to that housing/PCB design. A Compensation Sensor Formula is as follow. For the design shown, the constant is 0.8: 
         [0000]      Compensation Sensor Formula: (( PS−SS )/ K )+ PS    
         [0037]    PS=primary sensor temperature 
         [0038]    SS=secondary sensor temperature 
         [0039]    K=constant based on the characteristics of the control and determined through testing. 
         [0040]    The results shown in  FIG. 4  show the effective performance of the controller  10  of the present invention. The line  106  is the calculated temperature of the steam room as determined by the steam bath controller  10 . The line  108  is the actual temperature of the steam room  14 . The line  108  is the temperature the bather feels. A should be readily apparent, the controller  10  more accurately controls the temperature of the steam bath room  14  and more accurately reaches the desired set point temperature with less overshoot. 
         [0041]    The present design has an additional benefit of reacting to temperature changes more rapidly. The primary sensor(s) will react more quickly to the changes in temperature than the secondary sensor(s). Therefore, the difference between the primary and secondary sensor is much greater with a rapid temperature change and is smaller with slow temperature changes. The faster the temperature changes the more the compensation reacts, again helping to better follow the actual room temperature. 
         [0042]    Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” and the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
         [0043]    Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.