Patent Publication Number: US-2009232184-A1

Title: Digital food thermometer with fast response probe

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/344,531 filed Oct. 5, 2006, which is in turn a continuation-in-part of U.S. patent application Ser. No. 11/239,636 filed Sep. 30, 2005, which in turn is a continuation of PCT/US2004/010178 filed Apr. 2, 2004 which claims the benefit of U.S. Patent Application Ser. No. 60/459,256 filed Apr. 2, 2003. This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/648,409 filed Feb. 1, 2005, which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to temperature probes and, more particularly, to a temperature probe for use in with digital food thermometers. 
     BACKGROUND 
     Accurate, reliable and instantaneous sensing and measuring of temperature of food items is critically important. The most accurate and expedient manner in which to measure the temperature of a food item is by inserting a temperature-sensing device into the food item. A commonly used device is a digital thermometer. 
     It is very important to thoroughly clean the thermometer probe after each use. If food particles become lodged in the probe, food borne bacteria may develop. If the probe is not cleaned prior to its next use, those food borne bacteria could be transmitted to the food item. 
     Conventional digital thermometers include probes that are designed for insertion into food items. These probes are frequently fabricated from a metal such as stainless steel. An exemplary probe is disclosed in U.S. Pat. No. 3,975,720. There, probe  38  having a thermistor  42  disposed therein near distal end  4  is illustrated in  FIG. 1 . This style probe is satisfactory for some applications, but it tends to have a response time that is undesirably slow for many applications due to the separation between the thermistor and the food item. 
     There are known probe designs that exhibit increased response times. Exemplary probes are described in U.S. Pat. Nos. 4,133,208 and 6,000,845. The probe of the &#39;208 patent is illustrated in  FIG. 2 . The probe includes a shank  24   b  having an open distal end. A semi-conductor temperature sensing element  41   b  is disposed in and protrudes through the open distal end. The ends  51  of shank  24   b  are swedged around semi-conductor temperature sensing element  41   b  and the interior of shank  24   b  is filled with epoxy  49   b.  The probe of the &#39;845 patent is shown in  FIG. 3 . That probe is constructed from stainless steel and has a sensing end  28  that is inwardly tapered and has an opening  281 . The probe encloses a temperature sensor  32 . A temperature sensing point  324  of temperature sensor  32  protrudes partially from opening  281 . 
     The response times of the probe of the &#39;208 patent and the probe of the &#39;845 patent are more rapid than those of the traditional closed end probes because, as used, the temperature sensing element makes direct contact with the food item. However, in making direct contact, food is likely to become lodged or wedged in the crevices between end portions of the probe and the temperature-sensing element making it difficult to clean the probe. Food build-up can be dangerous as it can be a haven for food borne bacteria. In addition, it is believed to be unhealthy to directly contact the food item with the temperature-sensing element. 
     Accordingly, there remains a need for a probe for a digital thermometer that is both food safe and has a rapid response time. 
     SUMMARY 
     It is an object of this invention to provide a thermometer probe that has a rapid response time. 
     It is a further object of the invention to provide a thermometer probe that is easy to clean. 
     It is still another object of the invention to provide a thermometer probe that minimizes transmission of food borne bacteria. 
     In accordance with an aspect of the invention, a thermometer probe includes a probe housing having a distal end and a proximal end and the proximal end includes an opening or cavity an opening. A temperature sensing element, preferably a thermistor, is disposed in the probe housing close to the cavity. The cavity is covered by a thermally conductive, food safe coating. 
     Given the following enabling description of the drawings, the apparatus should become evident to a person of ordinary skill in the art. 
     These aspects of the invention are not meant to be exclusive. Furthermore, some features may apply to certain versions of the invention, but not others. Other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  illustrates a prior art food thermometer. 
         FIG. 2  depicts another prior art probe. 
         FIG. 3  shows still another prior art probes. 
         FIG. 4  illustrates a cross-sectional view of an embodiment of a probe in accordance with the invention. 
         FIG. 5  depicts another embodiment of the probe of the present invention. 
         FIG. 6  is a response time comparison between a prior art probe and the probe of the invention. 
     
    
    
     DETAILED DESCRIPTION  
       FIG. 4   a  shows a cross-sectional view of a probe  460  according to an embodiment of the invention. The probe  400  includes a probe housing  405  having a proximal end  410  and a distal end  415 . As best shown in  FIG. 4   b,  proximal end  410  includes an opening  420 . A temperature-sensing device  425  is preferably disposed within housing  405  proximate to an opening or cavity  420 . Temperature sensing device  425  includes a proximal surface and a distal surface. In addition, temperature sensor  425  may include lead wires  430 , or other coupling mechanisms, that extend through probe housing  405  to couple temperature sensing device  425  to thermometer circuitry (not shown) for displaying the measured temperature. A preferred temperature-sensing device is a GT thermistor such as the 104GT thermistor available from Ishizuka Electronics Corporation (Semitec) of Tokyo, Japan. 
     In accordance with an aspect of the invention, a thermally conductive food safe coating is applied over opening  420  to promote heat transfer from the food item and to minimize the potential of unwanted food build-up in proximal end  410 . As illustrated in  FIG. 4   a,  the opening  420  is preferably filled with coating  435 . However, in some embodiments the coating may not fill the entire opening and there may be a small gap between the proximal surface of temperature sensing device  425  and coating. Alternatively, as illustrated in  FIG. 5 , temperature-sensing device  425  may be disposed such that it protrudes through opening  420 . In this embodiment, coating  435  may cover the entire exposed surface of temperature sensing device  425  as well as the seam between temperature sensing device  425  and probe housing  405 , or the entire exposed surface of temperature sensing device  425  and some or all of proximal end  410 . Preferred coatings include TEFLON®, particularly polytetrafluoroethylene and fluorinated ethylene propylene copolymer, and thermoset powder coatings such as ER05-3D9 available from Pioneer Powder Products of Melrose, Park Ill. 
     In accordance with another aspect of the invention, proximal end  410  is preferably tapered as depicted in  FIGS. 4 and 5 . However, proximal end  410  may be, flat, rounded or otherwise configured to suit the user&#39;s application. 
       FIG. 6  illustrates a graph comparing response time of a conventional digital thermometer having a closed end probe to that of a digital thermometer having a probe according to the present invention. The response time was measured from room temperature, approximately 76° F., or 24° C., to the boiling point of water, 212° F., or 100° C. The conventional closed end probe of  FIG. 6  (probe a) is comprised of SUS 304 stainless steel housing that is about 80 mm long with a diameter d of about 3.4 mm. Probe a includes a tapered proximal end having a taper angle α of about 26°. A Semitec 104GT thermistor is disposed in probe a proximate to the proximal end. Probe b of  FIG. 6  is similar to probe a but further includes an opening having an inner radius of about 4 mm and an outer radius of about 5 mm. The thermistor is placed in the proximal end as close to the opening as possible. The opening was coated with TEFLON®. The response time for probe a was 20 seconds and the response time for probe b was 8 seconds. Accordingly, probe b has a response time that is reduced by about 60% from the response time of probe a. 
     In keeping with the invention, the probe may be connected to a housing containing thermometer circuitry. The housing may also contain, for example, a temperature display, and a variety of user actuated controls. Thermometer circuitry preferably includes microprocessor that receives input signals from the temperature-sensing device  425  and converts those signals to a temperature reading for display. In accordance with a preferred aspect of the invention, the microprocessor is appropriately programmed to provide a stabilized (+/−0.3° F.) reading in 8 seconds or less measured from room temperature to boiling water. The microprocessor may also be programmed to provide enhanced accuracy in the important food safety temperature range. For example, the microprocessor of the present embodiment is programmed to be accurate within +/−0.5° F. in the temperature range of 130° F. to 180° F. 
     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions would be readily apparent to those of ordinary skill in the art. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.