FAST RESPONSE THERMOMETER

Abstract: A quick response digital thermometer includes a thermistor (10) mounted at the end of a flexible silicone probe (6). The thermistor (10) reaches a stable temperature in a very short time and enables accurate temperature measurement in a few seconds without the use of prediction or extrapolation.

Description: FAST RESPONSE THERMOMETER Background of the Invention Long measurement time is one of the great disadvantages of digital thermometers that measure by contact (contact thermometers). Typically a contact thermometer takes more than a minute to reach thermal equilibrium in order to perform an accurate measurement. This disadvantage was the main drive in the development of the infrared (IR) ear thermometers. The IR ear thermometer completes the measurement in a few seconds but suffers from many problems. Problems are caused mostly by the misuse of the device by the user, such as a wrong positioning in the ear. Another problem is the influence of the thermometer probe as it is brought into contact with the ear. Other methods have been developed for contact thermometers that perform prediction or extrapolation based on several measurements in a short period of time, but these methods do not yield the same results in different ambient conditions. The long measurement time of contact digital thermometers is caused by two main factors. The first factor is the large thermal mass of the thermometer probe. The probe is typically a chrome coated aluminum tube or a stainless steel tube with a thermistor inside it. The thermistor is fixed within the probe by an epoxy glue with a low thermal conductivity. The second factor is a plastic housing to which the metal probe is typically connected. The plastic housing also has a large thermal mass that, upon contact, reduces the temperature of the measured area. Furthermore, in an oral thermometer, this plastic housing presents an obstacle to the natural position of the tongue and thus prevents the forming of a homogenous environment around the measurement probe. Summary of the Invention A thermometer has a measurement probe with a small thermal mass that can reach a stable measurement in a few seconds. The measurement probe is connected to the body of the thermometer with a flexible sleeve that also has a small thermal mass. The sleeve avoids a significant change in the temperature of the area being measured upon contact. For oral measurements, the flexible connection between the thermometer sensor head and the plastic housing enables the tongue to maintain its natural position and to create a homogenous environment around the measurement probe. The thermometer preferably samples the temperature several times in a short measurement time to provide an accurate result. The thermometer preferably operates at a very low power consumption and is comparable in cost to a regular digital thermometer. Brief Description of the Drawings Figure 1 A is an elevational view of the thermometer. Figure 1 B is a plan view of the thermometer. Figure 2 is a cross-sectional view of the thermometer probe and the flexible connection. Figure 3 is a graph of experimental data of temperature versus time for the thermometer. Figure 4 is a block diagram of the electronic components of the thermometer. Figure 5 illustrates a preferred method of calibrating the thermometer. Detailed Description of the Preferred Embodiment Figures IA and 1 B show the general structure of the thermometer 1 in accordance with the preferred embodiment. A thermistor 10 is connected to the plastic housing 7 by a flexible part or flexible probe 6. The thermistor 10 and the plastic housing 7 are installed as an "insert" in a silicone mold during the molding of the silicone part 6. The silicone creates a water resistant layer around the conductive wires of the thermistor all the way up to the plastic housing and protects the wires from a short circuit or a tear. The hardness of the silicone, around 30-40 shor, is selected so that the silicone will be soft enough longitudinally so that it can be bent under the tongue. This allows the tongue to stay in its natural position and cover the thermistor in order to create a homogenous environment around it. The silicone part 6 should also be hard enough widthwise, so that a rectal measurement can be performed. In one embodiment, the flexible silicone part 6 also serves as an insulator to thermally isolate the thermistor 10 from the plastic housing 7. The thermometer 1 preferably has a liquid crystal display (LCD) 14 upon which temperature is displayed either in degrees Fahrenheit or Celsius. The thermometer 1 preferably incorporates two momentary push buttons 15 and 16. The button 15 is used to turn the thermometer 1 on. When turned on, the thermometer 1 will perform an automatic measurement each time it senses temperature above 32.0°C (89.6°F). When ambient room temperature is above 32.0°C (89.6°F) the automatic measurement function is preferably disabled and manual operation is effected by pushing the button 15. The button 16 has two functions. While the thermometer 1 is on, the button 16 scrolls through four memories, which include the last four temperature measurements and the time these measurements were taken. While the thermometer 1 is off, the button 16 changes the display from Fahrenheit to Celsius and vice versa. Pushing the buttons 15 and 16 simultaneously will reset the thermometer 1. Figure 2 illustrates a cross section of the tip and of the base of the thermometer probe 6 in accordance with a preferred embodiment of the present invention. The thermistor 10 is preferably very small. One applicable thermistor is a 23226339000A produced by Philips Netherlands, which includes a temperature sensitive resistor 3 that is connected to two long thin conductive wires 5. The resistor 3 and the wires are protected by a tiny molding of approximately 1 millimeter in diameter of a ceramic substance 2 with a good thermal conductivity. The stabilization time Tc of this thermistor is approximately 3 seconds. The thermistor 10 is preferably protected by a coating 4, approximately 10 μm thick, made of Chrome or Titanium, which can be applied during a process of vacuum coating or other electroless coating. Figure 3 shows an experimental stabilization graph of the thermistor temperature vs. time after the thermometer 1 is inserted into water bath with a temperature of 37.00°C (98.60°F). The graph shows that the thermometer 1 reaches stabilization after 6 to 7 seconds within an accuracy window of 0.05°F ( " 0.028°C). The thermometer 1 preferably checks the readings repeatedly for stability within the above tolerance for 1 second before it displays temperature and sounds an indicating beep. Figure 4 shows the electrical circuit that is used in the preferred embodiment of the thermometer 1. A microprocessor 41, such as an E0C60L05 produced by EPSON, Japan is used to measure the resistance of the thermistor 10, preferably through a resistance to frequency circuit, which is included in the microprocessor 41. The microprocessor 41 calculates the temperature based on the resistance of the thermistor 10 and displays the calculated temperature on the LCD 14. The microprocessor 41 preferably includes memory 43 for storing previously measured temperatures. The electrical circuit preferably has a low power consumption. Figure 5 illustrates a preferred method 500 of calibrating the thermometer. At a step 502, a thermometer bias is calculated at a first temperature. The bias is preferably calibrated by two resistors 44 (Figure 4). At a step 504, a thermometer slope is calibrated at a second temperature. The slope is preferably calibrated by a digital four-bit calibration 45, which is provided by four switches (Figure 4). The two calibrations give an accuracy of 0.05°F (0.028°C) in the temperature range from 32.0° (89.6°F) to 42.6°C (108.7°F). This accuracy is four times better than the accuracy of a regular medical digital thermometer. Although the invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments which do not provide all of the features and advantages set forth herein, are also within the scope of this invention. Accordingly, the scope of the invention is defined by the claims that follow.

Claims: WHAT IS CLAIMED IS: 1. A thermometer for measuring body temperature, the thermometer comprising: a thermistor with a time constant of less than 5 seconds, wherein the thermistor is coated with a hard, thin, thermally conductive layer; and an electrical circuit configured to measure the resistance of the thermistor and to determine the body temperature based at least upon the resistance of the thermistor, the circuit configured to display the body temperature upon a display. 2. The thermometer of Claim 1, wherein the electrical circuit comprises a microprocessor. 3. The thermometer of Claim 1 configured for oral, rectal, and underarm use. 4. The thermometer of Claim 1, further comprising a flexible part to which the thermistor is attached. 5. The thermometer of Claim 4, wherein the flexible part comprises silicone. 6. The thermometer of Claim 4, further comprising a plurality of leads extending from the thermistor, wherein the leads are embedded in the flexible part. 7. The thermometer of Claim 4, wherein the flexible part is formed by placing the thermistor in a mold and filling the mold with a flexible material. 8. The thermometer of Claim 1, wherein the thermally conductive layer is formed by vacuum coating. 9. The thermometer of Claim 1, wherein the electrical circuit comprises a plurality of memories, wherein the memories are configured to store temperatures measured. 10. The thermometer of Claim 9, wherein the memories are additionally configured to store times of temperature measurements. 11. The thermometer of Claim 9, further comprising a push button, wherein the push button is configured to cause the contents of the memories to be displayed on the display. 12. The thermometer of Claim 11, wherein the push button has a first function when the thermometer is on and a second function when the thermometer is off. 13. The thermometer of Claim 1, wherein the thermometer can be configured by a user to display temperature in one of Fahrenheit and Celsius. 14. The thermometer of Claim 1, further comprising at least two push buttons. 15. The thermometer of Claim 14, wherein all of the functions of the thermometer can be accessed through the push buttons. 16. A method of calibrating a digital medical thermometer, the method comprising: calibrating a bias of the thermometer at a first temperature; and calibrating a slope of the thermometer at a second temperature. 17. The method of Claim 16, wherein the bias is calibrated by at least setting a resistance. 18. The method of Claim 17, wherein the slope is adjusted by at least setting a plurality of switches. 19. A thermometer for measuring human body temperature, the thermometer comprising: a temperature sensor, the temperature sensor having a surface with an exposed portion and an embedded portion, wherein the exposed portion forms a portion of an external surface of the thermometer, the temperature sensor comprising: a temperature sensitive resistor, a thermally conductive molding in which the temperature sensitive resistor is encased, two leads extending from the resistor through the thermally conductive molding and through the embedded portion, and a protective thermally conductive coating, wherein at least a portion of the coating forms the exposed portion; a display configured to display temperature in a digital format; a temperature determining circuit configured to determine temperature based at least upon the resistance of the temperature sensitive resistor, the circuit connected to the leads and to the display; and a probe having an elongated portion and a tip at an end of the elongated portion, wherein the embedded portion of the temperature sensor is embedded in the probe at the tip, and wherein the leads extend through the elongated portion. 20. The thermometer of Claim 19, further comprising a housing attached to a base of the probe, wherein the temperature determining circuit and the display are disposed in the housing. 21. The thermometer of Claim 19, wherein the probe comprises a flexible material. 22. The thermometer of Claim 21, wherein the probe is solid. 23. The thermometer of Claim 23, wherein the probe comprises silicone. 24. The thermometer of Claim 19, wherein the coating comprises chrome. 25. The thermometer of Claim 19, wherein the coating comprises titanium. 26. The thermometer of Claim 19, wherein the coating is less than 50 microns in thickness. 27. The thermometer of Claim 19, wherein the coating is about 10 microns in thickness. 28. The thermometer of Claim 19, wherein the temperature sensor has a time constant of less than 5 seconds. 29. The thermometer of Claim 19 having a stabilization time of less than 10 seconds to within an accuracy window of 0.05 degrees Fahrenheit when immersed in a 98.6 degree Fahrenheit water bath from an initial temperature of 72 degrees Fahrenheit.

Inventors: RUBINSTEIN ELIAHU, RUBINSTEIN, ELIAHU
Applicants: RUBINSTEIN ELIAHU, RUBINSTEIN, ELIAHU
Application year: 2000
Main classification: G01K13
IPC codes: G01K7, G01K13