US 3849622 A
A non-ionic fluid thermometer for sensing the temperature of substances such as meat during cooking by microwave radiation, including a non-ionic fluid such as diphenyl, toluene, etc., used as a heat indicator which is subjected to heating by conduction and is substantially non-responsive to microwave radiation, the non-ionic fluid expanding and indicating the meat temperature in connection with calibrated indicia.
Description (OCR text may contain errors)
O Umted States Patent 1 1 [111 3,849,622
Merriam Nov. 19, 1974 NON-IONIC FLUID THERMOMETER FOR 3,185,809 5/1965 Bohm et al. 219/1055 MICROWAVE OVEN 3,469,452 9/1969 Ayres 73/371 3,731,037 5/1973 Levinson 219/1055 Inventor: Charles J. Merriam, 305 Lake Point Tower, Chicago, Il]. 60611 Filed: Apr. 19, 1971 Appl. No.: 135,344
Related U.S. Application Data Division of Ser. No. 833,323, June abandoned,
Primary Examiner-J. V. Truhe Assistant Examiner-Hugh D. Jaeger Attorney, Agent, or Firm-Merriam, Marshall, Shapiro & Klose [5 7 ABSTRACT A non-ionic fluid thermometer for sensing the temperature of substances such as meat during cooking by microwave radiation, including a non-ionic fluid such as diphenyl, toluene, etc., used as a heat indicator which is subjected to heating by conduction and is substantially non-responsive to microwave radiation, the non-ionic fluid expanding and indicating the meat temperature in connection with calibrated indicia.
4 Claims, 2 Drawing Figures Ml CROW/1 V5 6 E It 5 RA TOR PATENTEL 1 3.849.622
MICROV/A VE GENE/M TOR NON-IONIC FLUID THERMOMETER FOR MICROWAVE OVEN This is a divisional application of a co-pending application, Non-Ionic Fluid Thermometer for Microwave Heating U.S. Ser. No. 833,323, filed June 16, 1969,
BACKGROUND OF THE INVENTION This invention relates to heat sensing and indicating apparatus, and more particularly to devices for sensing the temperature of articles or food substances subjected to heating by microwave radiation.
Microwave ovens have been commercially available for several years, however, several difficulties in the use of such ovens for cooking food substances have prevented their wide spread acceptance. In particular, it is known that due to the highly penetrative nature of the high frequency radiant energy utilized in such ovens, food substances are heated much more quickly than in conventional gas or electric ovens. Since the wellknown meat thermometers for conventional ovens are overly responsive to microwave radiation heating and burst or break, the cooking time must be estimated from the oven manufacturer's recommendations on the basis of the type of food, the size, composition, etc. However, this is a haphazard procedure at best, and it is only after several months of experience in using microwave ovens that one can consistently avoid overcooking food.
SUMMARY OF THE INVENTION Therefore, in accordance with the principles of the present invention, there is provided a heat sensing and indicating device for use in microwave radiation heating which is not responsive to microwaves. More particularly, a non-ionic fluid is used as a heat indicator in an organic solvent, such as diphenyl, toluene, or other high boiling point liquids. The non-ionic fluid may be confined in a conventional non-dielectric thermometer stem and bulb (such as glass) for insertion into the center of the article being cooked. As the microwave radiant heat penetrates deeper into the article, the nonionic fluid is subjected to heating by contact with the food and not by the microwaves, and therefore expands within the tube. The fluid expansion is coupled to indicating means, in terms of degrees or it may be calibrated to indicate rare, medium, and well-done and/or food temperatures for a variety of foods which can be cooked by microwave radiation.
BRIEF DESCRIPTION OF THE DRAWINGS This invention will be better understood from the following detailed description thereof taken in conjunction with the accompanying drawings in which:
FIG. 1 is a thermometer constructed in accordance with the principles of the present invention as utilized for indicating the temperature of a food article being cooked by microwave radiation in an oven; and
FIG. 2 is an elevational view illustrating the construction of a preferred embodiment of the invention illustrating a thermometer incorporating an expandable LII non-ionic fluid in a confined glass tube, use of which is illustrated in FIG. 1.
Referring now to FIG. 1, there is illustrated a microwave oven defined by walls 12 and a front door 14 for cooking a food substance 16 mounted within a pan 18 on oven shelf 20 for being subjected to microwave radiation generated through a suitable microwave radiation source 22. The construction details of microwave ovens, including the microwave sources are well known in the art.
A thermometer constructed in accordance with the present invention is inserted into the center of the article 16 so as to indicate the temperature and thereby the cooking status of the article. As illustrated in FIG. 2, the thermometer 30 includes an elongated, glass tubular probe section 32 incorporating a thin, hermetically sealed channel 34 extending from a cavity 36 at the pointed head end 38. An indicia-bearing member 40 containing temperature indicating numerals 42 and- /or rare, medium, well-done indications 44 for beef, pork, etc. is mounted with suitable clip means 46 to the tube 32.
In accordance with the principles of the present invention, the cavity 36 communicating with channel 34 is filled with a non-ionic fluid 47 such as an organic liquid-diphenyl, toluene, etc., or any other non-ionic liquid. The non-ionic fluid does not respond to the microwave energy source 22 which has penetrated to the center of food article 16, but is heated by conduction as the article is heated. As in a conventional thermometer, the fluid within tube 32 begins to expand and thereby rise within channel 34 towards the bulb end 48 of the tube. This provides a precise heat indication and the actual cooking status of food substance 16, thereby eliminating the guesswork involved in prior art microwave food cooking. It is understood that during calibration of the thermometer 30, the indicia-bearing member 40 is marked with the temperature references 42 or references 44 for the various foods.
As indicated, the non-ionic fluid is provided to respond to the heating of the meat, but is substantially non-responsive to the microwave radiation. One factor for this non-responsiveness to microwaves may be that such radiation does not appreciably affect the spin orbits of electrons in the non-ionic fluid. Another factor may be that as opposed to meat which readily absorbs microwave energy since it has a relatively high dielectric constant, non-ionic fluids absorb microwave energy very poorly due to their relatively low dielectric constant. The actual interaction or lack thereof between the microwave radiation and the non-ionic fluid may be due to either one or both of the above factors or to other factors not presently understood.
The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.
What is claimed is: l. A method determining the temperature of food being heated in a microwave oven through microwave energy comprising the steps of:
providing a heat responsive thermometer being nonresponsive to microwave energy and having a hollow portion containing an expandable fluid also being nonresponsive to said microwave energy;
inserting the termometer into the food to be heated in a heat transferring relationship;
placing the food and thermometer into the microwave oven and heating the food by microwave ener y.
2. T e method of claim 1 in which-said expandable fluid is a non-ionic liquid.
3. The method of claim 2 in which said-non-ionic liquid is an organic liquid.
4. The method of claim 2 in which said non-ionic liquid is diphenyl.