1. Field of the Invention
The present invention generally relates to a calibration system for recalibrating electronic thermometers. More specifically, the present invention relates to recalibration system comprising a tympanic thermometer, a blackbody calibration unit and a computer for recalibrating the infrared temperature sensor within the tympanic thermometer. In particular, the present invention relates to a recalibration system for recalibrating tympanic thermometers using the ambient temperature sensed by the tympanic thermometer as a primary control parameter in the recalibration process.
2. Background Art
The diagnosis and treatment of many body ailments depends upon an accurate reading of the internal or core temperature of a patient's body temperature reading, and in some instances, upon comparison to a previous body temperature. For many years, the most common way of taking a patient's temperature involved utilization of Mercury thermometers. However, such thermometers are susceptible to breaking and must be inserted and maintained in the rectum or mouth for several minutes, often causing discomfort to the patient.
Because of the drawbacks of conventional Mercury thermometers, electronic thermometers were developed and are now in widespread use. Although electronic thermometers provide relatively more accurate temperature readings than Mercury thermometers, they nevertheless share may of the same drawbacks. For example, even though electronic thermometers provide faster readings, a half a minute must still pass before an accurate reading can be taken. Finally, electronic thermometers must still be inserted into the patient's mouth, rectum or axilla.
Tympanic thermometers provide nearly instantaneous and accurate readings of core temperature without undue delay attendant with other thermometers. The tympanic thermometer is generally considered by the medical community to be superior to oral, rectal or axillary sites for taking a patient's temperature. This is because the tympanic membrane is more representative of the body's internal or core temperature and more responsive to changes in core temperature. Tympanic thermometers, those thermometers that sense the infrared emissions from the tympanic membrane, offer significant advantages over Mercury or conventional electronic thermometers.
Recent efforts to provide a method and apparatus for measuring temperature of the tympanic membrane have produced several excellent infrared tympanic thermometers. For example, U.S. Pat. No. 5,293,877 to O'Hara et al. provides for a tympanic thermometer that measures internal body temperature utilizing the infrared emissions from the tympanic membrane of the ear, and is herein incorporated by reference in its entirety. Typically, tympanic thermometers require calibration at the factory during manufacturing in order achieve the quick and accurate temperature reading capability noted above. Calibration of the tympanic thermometer at the factory requires individual calibration of each thermometer unit so that the proper calibration parameters can be written to the EEPROM of each thermometer's microprocessor. These calibration parameters involve determining the proper values for variables representing the sensors within each thermometer. Once these calibration parameters are determined and written to the memory of each thermometer, calibration is complete and the unit is shipped for sale.
However, responsivity of the infrared system and transmissivity of the optical system set during calibration can change over time, thereby bringing the tympanic thermometer out of calibration which results in inaccurate temperature readings being taken by the thermometer. Responsivity of the tympanic thermometer's infrared system involves changes in the response characteristics of the thermal radiation sensor of the thermometer over time. Similarly, transmissivity of the optical system deals with the transmission characteristics of the optical waveguide and other parts of the thermometer's optical system that may drift or change as a function of time or due to scratches and deformations that occur during use. During recalibration, the calibration parameters dealing with the thermometer's infrared and optical systems are adjusted.
Recalibration of the tympanic thermometer usually requires recalibrating the variables related to the infrared and optical subsystems of the thermometer incorporated in the calibration equations written to the EEPROM during factory calibration. A prior art recalibration device usually comprises a unit housing one or more blackbodies that permit the user to recalibrate the thermometer at one or more set temperatures designated for each blackbody. In operation, the sensor portion of the thermometer is inserted into a cavity containing a blackbody set at a predetermined temperature. Readings are then taken from each sensor and a set of calibration parameters are calculated and written over the original parameters set in the EEPROM.
Ambient temperature is another important calibration parameter that must be determined during the recalibration procedure because it provides an indication of temperature stability of the surrounding environment that the tympanic thermometer is experiencing prior to recalibration. Temperature stability permits accurate recalibration to take place as long as recalibration is within a specific range of ambient temperature conditions. For example, a tympanic thermometer experiencing an ambient temperature that is too high or otherwise outside the permissible range of ambient temperatures will adversely affect the recalibration process and result in an inaccurate calibration of the thermometer.
To sense the ambient conditions being experienced by the tympanic thermometer, prior art recalibration devices have utilized an ambient sensor that resides directly on the recalibration device itself for sensing the surrounding ambient temperature prior to recalibration. Although this method provides an easy means of determining ambient temperature, several disadvantages remain. For example, a more accurate ambient temperature reading of the tympanic thermometer is best taken from the thermometer itself rather than from the recalibration device since temperature stability of the tympanic thermometer is a far more critical factor than the temperature stability of the room containing the recalibration device. Further, instances may occur where a tympanic thermometer to be recalibrated might have just been stored in a high temperature area, such as a the compartment of a vehicle exposed to the sun or in a room having different environmental conditions than the room where recalibration is occurring. In this instance, the ambient temperature of the tympanic thermometer will be much higher than the surrounding cooler temperature of the room sensed by the calibration device's ambient sensor, thereby providing an inaccurate ambient temperature reading to the recalibration device since the thermometer has not stabilized to its surroundings. However, if the recalibration system takes into account the present ambient temperature experienced by the tympanic thermometer itself prior to recalibration, then a more accurate and reliable determination of the thermometer's temperature stability can be determined before recalibration occurs.
As of yet, nothing in the prior art has addressed the problem of developing an ambient sensor system that determines the temperature stability of the tympanic thermometer before recalibration of the thermometer occurs. Further, nothing in the prior art has addressed the problem of ensuring that recalibration takes place in an environment where ambient temperature is within a stable range of temperatures.
Therefore, there exists a need in the medical art for an ambient sensor system that takes an ambient temperature reading from within the thermometer itself without use of separate ambient sensors outside the thermometer and also incorporates a fail-safe routine whereby recalibration does not occur unless the ambient temperature of the thermometer is within a predetermined range and the thermometer is in a state of thermal equilibrium.