Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
1999-10-12
2001-06-26
Bennett, G. Bradley (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
Reexamination Certificate
active
06250802
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to electronic thermometers, and particularly to electronic thermometers having preheating devices to shorten the measuring time.
Thermistors have been widely used in electronic thermometer probes for measuring temperature. As described, for example, in U.S. Pat. No. 3,025,706, the thermistors generally used in such applications are those having a high negative temperature coefficient (NTC), i.e., having an electrical resistance which varies greatly in the negative direction with changes in temperature, as distinguished from ordinary resistors which have relatively small temperature coefficients. However, when using NTC thermistors for temperature measurement, long time intervals are generally required to make precise measurements because of the time needed for raising the temperature of the probe to that of the body whose temperature is being measured.
It is also known to shorten this time interval by preheating the probe to the approximate temperature of the body whose temperature is being measured. For example, U.S. Pat. No. 4,158,965 does this by applying auxiliary current to the thermistor to cause it to act as a heating element for raising the temperature of the probe, before the thermistor is used for making the precise temperature measurement. However, since the same thermistor is used for two functions, preheating and precise temperature measurement, its characteristics making it optimum for one function (e.g., preheating) may detrimentally affect its performance with respect to the other function (e.g., temperature measurement).
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide an electronic thermometer having advantages in the above respects.
According to one aspect of the present invention, there is provided an electronic thermometer for measuring the temperature of a body, including a probe having a heating element for preheating the probe to the approximate temperature of the body, and a temperature measuring element for measuring the precise temperature the body; characterized in that the heating element is a low-resistance thermistor having a positive temperature coefficient (PTC) for rapidly preheating the probe, and the temperature measuring element is a relatively high-resistance thermistor having a negative temperature coefficient (NTC) for precisely measuring the temperature of the body.
As will be described more particularly below, since a separate thermistor (of the PTC type) having a relatively low resistance is provided for the preheating function, such an electronic thermometer is inherently capable of performing the preheating function more efficiently, e.g., by reducing the time interval for preheating the probe to the body temperature; and since a separate thermistor (of the NTC type) having a high resistance is provided for its measuring function, the thermometer is also inherently capable of performing the temperature measuring function more efficiently than when both functions are performed by a single thermistor.
According to further features in the described preferred embodiment, the PTC thermistor and NTC thermistor are embedded in a heat-conductive plastic, preferably an epoxy resin having conductive particles. In addition, the heat-conductive plastic embedding the two thermistors is covered by an outer layer of an inert metal. Such an outer layer is preferably in the form of a thin coating applied directly onto the heat-conductive plastic.
According to still further features in the described preferred embodiment, the resistance at ambient temperature of the NTC thermistor is at least two orders of magnitude larger than that of the PTC thermistor. Preferably, the resistance at ambient temperature of the PTC thermistor is from 10 to 100 ohms, and that of the NTC thermistor is from 10 to 100 Kohms.
According to additional features in the described preferred embodiment, the probe is attached to a housing including a display and electrical circuitry connecting the PTC and NTC thermistors to the display for displaying the measured temperature. The electronic circuitry includes a manual control adapted to be selectively operated to selectively actuate the electrical circuitry to a Standby Mode wherein the PTC thermistor is effective to preheat the probe to the approximate temperature of the body, and to a Measuring Mode wherein the NTC thermistor is effective to measure the precise temperature of the body. In the described preferred embodiment, the manual control includes a first key manually depressible to actuate the electrical circuitry to the Standby Mode and a second key manually depressible to actuate the electrical circuitry to the Measuring Mode.
The foregoing features enable the time interval required for measuring temperature to be minimized, and/or the temperature measurement itself to be enhanced.
Further features and advantages of the invention will be apparent from the description below.
REFERENCES:
patent: 3025706 (1962-03-01), Oppenheim
patent: 3540283 (1970-11-01), Dean
patent: 4158965 (1979-06-01), Prosky
patent: 4183248 (1980-01-01), West
patent: 4790324 (1988-12-01), O'Hara et al.
patent: 5035514 (1991-07-01), Newman
patent: 5923258 (1999-07-01), Tseng
patent: 6036361 (2000-03-01), Gregory et al.
patent: 6048094 (2000-04-01), Tornare
patent: 03272475 (1991-12-01), None
Barish Benjamin J.
Bennett G. Bradley
HomeCare Technologies Ltd
Verbitsky Gail
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