Abstract:
A thermometer configured to measure the temperature of a medium. The thermometer typically includes a temperature sensor positioned within a sealed sensor chamber. The sensor chamber, in turn, is positioned within a heat storage chamber. The heat storage chamber contains a thermal insulator. Heat energy thus is exchanged between the medium and the temperature sensor through the thermal insulator contained within the heat storage chamber so as to slow reaction of the temperature sensor.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates generally to thermometers, and more particularly to thermometers for use in temperature-controlled environments.  
         BACKGROUND OF THE INVENTION  
         [0002]    Thermometers often are used to measure the ambient temperature within refrigerators, ovens, and other devices with temperature-controlled compartments. Typically, these thermometers are small devices with a temperature probe and readout, and are designed to be placed entirely within the temperature-controlled compartment to measure the operating temperature of the compartment. On certain devices equipped with access doors and glass windows, it may be possible to position such a thermometer near the glass window, such that the readout may be viewed by a user without opening the door. On many other devices, however, the access door does not have a window, and the thermometer can be read only by opening the access door, and looking at the thermometer inside the compartment.  
           [0003]    One problem with current oven and refrigerator thermometers is that air currents caused by opening the door of the oven or refrigerator often change the temperature of the air adjacent the thermometer, affecting the temperature measurement by the thermometer. For example, when a refrigerator is opened, warm air may enter and travel to the thermometer, causing the thermometer to indicate a temperature higher than the actual temperature of the refrigerator prior to opening the door. Similarly, cool air may enter through an oven door and cause an oven thermometer to indicate a lower temperature than the actual operating temperature of the oven before the door was opened. Erroneous temperature readings can cause users to set their refrigerators to unnecessarily cool levels, thereby wasting electricity and/or inadvertently freezing the contents of the refrigerator. Likewise, an oven user may set the heat of the oven too high based on an erroneous temperature reading and bum or overcook the oven contents.  
           [0004]    It would be desirable to provide a thermometer capable of providing a stable, accurate reading of the temperature of an oven, refrigerator, or other device, without significant interference from air currents caused by opening the door of such a device.  
         SUMMARY OF THE INVENTION  
         [0005]    A thermometer configured to measure the temperature of a medium is provided. The thermometer typically includes a sensor chamber and a temperature sensor positioned within the sensor chamber. The thermometer may also include a heat storage chamber positioned adjacent the sensor chamber. The temperature sensor is typically thermally coupled to the medium through the sensor chamber and the heat storage chamber such that heat energy may be exchanged between the medium and the temperature sensor. The heat storage chamber may be bounded by an outer wall and an inner wall, and may contain a liquid such as hydraulic fluid.  
           [0006]    The thermometer also may be used to measure the operating temperature of a compartment having a door, where opening the door of the compartment alters the temperature of the compartment. The thermometer may include a temperature sensor and an indicator coupled to the temperature sensor. Typically, the indicator is configured to indicate a temperature value measured by the temperature sensor. The thermometer also may include a double-walled probe with an inner wall and an outer wall substantially surrounding the inner wall. A space between the outer wall and the inner wall may define a heat storage chamber filled with a liquid (e.g., an oil such as hydraulic fluid), and a space within the inner wall may define a sensor chamber filled with air. The temperature sensor typically is positioned within the sensor chamber, the heat storage chamber typically being configured to insulate the sensor chamber and temperature sensor from intermittent temperature fluctuations caused by opening the door of the compartment.  
           [0007]    In addition, the compartment may include a rack, and the thermometer may employ a clip. The clip typically includes a probe-receiving bore at one end, and a rack-receiving bore at an opposite end. The probe-receiving bore may be configured to mount to the probe. The rack-receiving bore is configured to mount to the rack to selectively secure the thermometer to the rack. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a front cross-sectional view of a thermometer according to one embodiment of the present invention.  
         [0009]    [0009]FIG. 2 is an isometric view of a temperature-controlled device which contains a pair of thermometers variously attached to an internal rack.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]    Referring initially to FIG. 1, a thermometer according to one embodiment of the present invention is shown generally at  10 . Thermometer  10  typically includes an indicator  12  coupled to a temperature probe  14 . Indicator  12  is configured to display a temperature value corresponding to a temperature sensed by temperature probe  14 .  
         [0011]    As shown in FIG. 2, indicator  12  typically is a dial indicator, and includes a needle  16  configured to rotate and point to a temperature value depicted on temperature scale  18  of face  20 . The temperature scale may include numerals and scoring marks and typically is configured to indicate temperature values on a Fahrenheit temperature scale. Alternatively, the temperature scale may be a Celsius temperature scale, or another predetermined temperature scale. In addition, colored bands or other indicia may be used instead of numerals and/or scoring marks to indicate temperature ranges.  
         [0012]    Referring again to FIG. 1, it will be appreciated that indicator  12  also typically includes a frame portion  22  partially surrounding needle  16 , and a glass portion  24  through which needle  16  and temperature scale  18  may be read by a user. Alternatively, indicator  12  may be another type of analog indicator, such as a linear scale, or may be a digital indicator (e.g., digits on an LCD screen), or may be some other type of device capable of indicating a temperature value to a user.  
         [0013]    Probe  14  typically includes a heat storage chamber  26 , a sensor chamber  28 , and a temperature sensor  30  disposed within the sensor chamber. Accordingly, probe  14  is typically of a double-walled construction, including an outer wall  32  and an inner wall  34 . The walls are constructed from a rigid heat-conductive material, typically stainless steel. Outer wall  32  and inner wall  34  typically are attached to frame  22  of indicator  12  via a collar  23  adjacent respective top ends  32   a ,  34   a.    
         [0014]    As indicated, outer wall  32  substantially encloses and surrounds inner wall  34 . The space between outer wall  32  and inner wall  34  defines the heat storage chamber  26 . The space within, and bounded by, inner wall  34  defines sensor chamber  28 . Heat storage chamber  26  thus at least partially surrounds sensor chamber  28  and temperature sensor  30 . In one embodiment of the invention, heat storage chamber  26 , in combination with frame  22  of indicator  12 , completely surrounds sensor chamber  28  and temperature sensor  30 . For example, in the present embodiment, the heat storage chamber and sensor chamber form concentric cylinders wherein the interior, cylindrical sensor chamber  28  is completely encased within the exterior, cylindrical heat storage chamber  26 . Alternatively, heat storage chamber  26  and sensor chamber  28  may be formed in another shape.  
         [0015]    Heat storage chamber  26  is positioned adjacent sensor chamber  28  intermediate temperature sensor  30  and a medium  36  to be measured. Typically, medium  36  is an environment or atmosphere within an oven, refrigerator, or other device. Alternatively, medium  36  may be a material, such as a roast, stew, frozen food, or other heated or cooled object.  
         [0016]    Typically, temperature sensor  30  is a bimetallic strip, formed in a helical shape. Those skilled in the art will recognize that bimetallic strips are formed of joined metal halves  30   a ,  30   b . The metal halves each are formed of a different metal composition, and have different rates of thermal expansion, which causes the strip to wind and unwind in response to temperature changes at a predetermined rate. One example of a suitable bimetallic strip is disclosed in U.S. Pat. No. 4,211,114 to Hood, the disclosure of which is herein incorporated by reference.  
         [0017]    Typically, bimetallic strip  30  is joined to inner wall  34  at a first coupling  37 , and to shaft  17  at a second coupling  39 . Shaft  17  is rotatably mounted within collar  23  and cavity  35 . As bimetallic strip  30  winds and unwinds in response to temperature changes, shaft  17  is caused to rotate. Needle  16 , it will be noted, is mounted to shaft  17 , and also rotates as the bimetallic strip winds and unwinds, thereby indicating a temperature value on the temperature scale  18  of face  20 .  
         [0018]    Heat storage chamber  26  typically contains a liquid, such as hydraulic oil or hydraulic fluid, and thus also is referred to as liquid chamber  26 . Alternatively, virtually any other liquid configured to withstand the temperatures being measured may be used. For example, an oil such as food-grade cooking oil, bean oil, mineral oil, or another suitable oil may be used. Alternatively, heat storage chamber  26  may be filled with a non-liquid material capable of storing heat energy, such as a powder. In one embodiment of the invention, a graphite power is used. As indicated, heat storage chamber  26  typically is filled to a level which will accommodate expansion of the liquid or non-liquid with expected variations in temperature. Temperature sensor  30  typically is contained entirely within such liquid or non-liquid.  
         [0019]    In accordance with the invention, it will be appreciated that the liquid increases the thermal mass of heat storage chamber  26 , as compared to an air-filled chamber. The heat storage chamber thus is configured to absorb heat energy from medium  36 . Accordingly, the thermal mass of the liquid slows the speed at which heat is transferred from environment  36  to temperature sensor  30 . Therefore, heat storage chamber  26  acts as a stabilizer, causing thermometer  10  to indicate a substantially stable temperature reading when exposed to brief fluctuations in temperature, such as occurs when a refrigerator or oven door is opened by a user to read the thermometer.  
         [0020]    The heat storage chamber has a heat capacity sufficient to maintain the temperature of the temperature sensor substantially at the temperature of the medium for a predetermined period of time when the temperature of the medium fluctuates. Typically, the predetermined period of time is less than about 3 minutes. In one preferred embodiment of the invention, the predetermined period of time is between about 30 and 90 seconds.  
         [0021]    As shown in FIG. 2, the thermometer of the present invention also may include an elongate clip  50  configured to attach, at one end, to probe  14  and, at an opposite end, to a rack  52  within compartment  54  of temperature-controlled device  56 . Typically, temperature-controlled device  56  is an oven. Alternatively, temperature-controlled device  56  may be a refrigerator, or other device configured to heat or cool a compartment or to keep a compartment within a predetermined temperature range. Typically, temperature-controlled device  56  includes a door  58  allowing a user access to compartment  54 . Door  58  may be opened to read thermometer  10  and check the temperature of compartment  54 . Opening the door to check the temperature often takes between about 30 and 90 seconds. However, the door may remain open for as long as 3 minutes, or longer, such as when other cooking-related operations are performed while checking the temperature. During these periods in which the door is open, heat storage chamber  26  insulates the sensor chamber and temperature sensor therein from substantial heat exchange with medium  36  due to convection currents entering compartment  54 .  
         [0022]    Clip  50  typically includes a probe-receiving portion  60  configured to grip probe  14  and a rack-receiving portion  62  configured to grip an elongate bar  52   a  of rack  52 . Clip  50  typically is stamped from a single sheet of metal, and includes split segments  64 ,  66 . Probe-receiving portion  60  typically defines a probe-receiving opening formed between split segments  64 ,  66 . Likewise, rack-receiving portion  62  typically defines a rack-receiving opening formed between split segments  64 ,  66 . A fastener  68  is configured to draw each of split segments  64 ,  66  together to secure elongate bar  52   a  within the rack-receiving portion  62  and simultaneously to secure probe  14  within probe-receiving portion  60 . Alternatively, clip  50  may be of an alternate suitable shape and form, and need not be stamped.  
         [0023]    Thermometer  10 ′ is shown in FIG. 2 attached to elongate bar  52   b  by clip  50 ′ in an above-the-bar orientation. The thermometer is configured to rotate within clip  50 ′ until the temperature scale  18 ′ is right-side-up, or in some other predetermined orientation desired by the user. Once properly oriented, the user may tighten fastener  68 ′ to secure the thermometer  10 ′ within the clip and to secure the clip to elongate bar  52   b , as described above. Therefore, the thermometer of the present invention may be mounted either above or below the rack, or at virtually any angle to the rack, with the temperature scale right-side-up and easily readable by the user. Once installed, the thermometer provides a stable temperature reading for the temperature within compartment  54 .  
         [0024]    While the invention has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the invention includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. No single feature, function, element or property of the disclosed embodiments is essential. The following claims define certain combinations and subcombinations which are regarded as novel and non-obvious. Other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such claims are also regarded as included within the subject matter of the present invention irrespective of whether they are broader, narrower, or equal in scope to the original claims.