PORTABLE ELECTRONIC THERMOMETER AND METHOD OF TEMPERATURE MEASUREMENT
BACKGROUND OF THE INVENTION
This invention relates to electronic thermometers and more particularly to portable, probe-type electronic thermometers for clinical measurement of human body temperature.
In recent years there has been considerable interest in the development of electronic thermometers for clinical use as a means of overcoming numerous disadvantages of conventional glass mercury-bulb thermometers. Such disadvantages include difficulty in effectively sterilizing them to prevent cross-contamination; high cost resulting from frequent breakage and the large number required; inaccurate temperature measurement characterized by errors both as to reproducibility of measurement and as between measurements of different thermometers; and slow response time requiring a relatively long time for temperature measurement. Much of the art in this field is disclosed by the following representative U.S. Pat. Nos.: 2,919,580; 3,139,753; 3,187,576; 3,254,533; 3,348,415; 3,367,186; 3,377,862; 3,379,063; 3,402,378; 3,431,781; 3,530,718.
Despite many interesting approaches, prior art efforts in the growing electronic thermometer art have typically enjoyed only limited success, and have themselves been plagued with the above-described problems of difficulty in sterilization, inaccuracy, and slow response. To overcome the sterilization problem, it has been proposed to utilize disposable probe covers or sheaths as disclosed in U.S. Pat. Nos. 3,372,862; 3,367,186; 3,254,533; and others. However, some covers tend to slow temperature response and thus if there is already slow response, this problem may be worsened.
Other electronic thermometer approaches have sought to overcome the accuracy problem through use of conventional impedance bridge circuitry which is supplied by a regulated voltage, as through use of a zener diode or the like. The disclosures of U.S. Pat. Nos. 3,217,544 and 3,413,853 are exemplary. However, even this has not guaranteed accuracy, since in a portable battery-powered circuit, the battery voltage may fall after a time to a level below which the supply voltage can no longer be regulated. Inaccurate temperature measurement may, therefore, still occur.
To overcome the problem of slow response, it has been proposed to utilize a field-effect transistor (FET) as a probe sensing element, together with means for heating the FET to a temperature from which it can more quickly rise to body temperature. Such an arrangement is disclosed in U.S. Pat. Nos, 3,491,596 and 3,540,283. However, the clinical utility of this approach may be limited by its peculiar nature to measurement of temperature by insertion of the probe in the ear or by placement of the probe at the axilla. Such an FET probe is not readily adapted to measurement by oral or rectal insertion or to the use of disposable probe covers.
Regardless of these several important advances in the art, there continues to remain a problem in the art of inaccurate temperature measurement resulting from various error-producing thermal factors occurring during use of the temperature probe. As a practical matter, the sensing element cannot be completely thermally
isolated from the remaining portions of the probe assembly. Hence, the element's temperature is affected by factors thermally influencing the probe. For example, the probe is influenced not only by variations in ambient temperature but also by such factors as heating by the hand of the user, e.g., a nurse who is holding the probe, as well as the frequency of use, et cetera.
SUMMARY OF THE INVENTION
Among the several objects of the invention may be noted the provision of an electronic thermometer which is adapted for clinical measurement of body temperature; the provision of such an electronic thermometer and methods of temperature measurement permitting rapid i.e., accelerated determination of body temperature, requiring only a fraction of the time required for a mercury thermometer; the provision of such an electronic thermometer which is portable and is battery powered; the provision of such a thermometer which is accurate and dependable and automatically prevents inaccurate temperature indications due to insufficient battery voltage; the provision of such a thermometer which is conveniently carried and used, having small size and light weight; the provision of such a thermometer which provides a sustained indication of the measured temperature after initial indication thereof; the provision of such a thermometer which provides both an initial measured temperature indication and also a verified temperature indication; the provision of a thermometer which does not require manual off-on actuation in use; the provision of such a thermometer which can be used for oral, rectal and axillary temperature measurements; the provision of such a thermometer which includes a temperature probe permitting the use of low-cost and disposable probe covers which prevent cross-infection or re-infection of patients; the provision of such a thermometer having a probe and which provides accurate temperature measurement in having relative immunity to error-producing thermal factors influencing the probe; the provision of such a thermometer which is rugged and reliable, utilizing solid-state integrated circuit components, and which is economically manufactured. Other objects and features will be in part apparent and in part pointed out hereinafter.
Briefly, an electronic, battery-powered, probe-type thermometer of the invention for accelerated indication of temperatures includes a probe for introduction into a region having a temperature which is to be measured. The probe has a temperature sensitive element having a heat sensing relationship with the region when the probe is so introduced. Timing means initiates a predetermined timing interval in response to the temperature of the element exceeding a preselected level following said introduction of the probe. Means is provided for measuring the temperature of the element at the completion of the timing interval and before the element reaches the actual region temperature. A meter or other means indicates a temperature which is a function of the measured temperature of the element at the completion of the timing interval, the indicated temperature being a substantially accurate extrapolation of the temperature in the region. The temperature indication is thereby provided in substantially less time than would be required for the temperature of the element to reach the actual region temperature.
In a commercially preferred embodiment, the probe includes an elongate quill, a portion of which is adapted