Electronic thermometer

The electronic thermometer comprises a temperature sensor which senses the temperature of an object, a prediction temperature computing apparatus for deriving a converged temperature according to the temperature sensed by the temperature sensor, apparatus for providing a range of error associated with the predicted converged temperature computed by the prediction temperature computing apparatus, and a display for displaying the range of error.

BACKGROUND OF THE INVENTION 
The present invention relates to an electronic thermometer such as an 
electronic clinical thermometer, and in particular to an electronic 
thermometer which can measure the temperature of an object at an early 
time after the beginning of measuring. 
Generally in an electronic thermometer, for instance in an electronic 
clinical thermometer, the sensing portion is placed under the armpit or 
under the tongue of a patient for temperature measurement, but it normally 
takes time before this sensing portion comes into a thermal equilibrium 
with the patient's body temperature. According to a conventional 
electronic thermometer, either (a) the temperature as it transits from a 
changing state to a stable state is continually displayed, or (b) after 
the lapse of a certain time period after the beginning of the measurement 
process a converged body temperature is predicted and is then displayed 
once and for all. However, simply displaying the changing value of the 
body temperature as in case (a) does not give a stable converged or final 
temperature value at an early time, while on the other hand just 
performing body temperature prediction once as in case (b) may give a 
seemingly definite body temperature at an early time but cannot provide a 
high quality body temperature measurement at this time point. Thus, the 
sooner a body temperature prediction is made the more the predicted 
temperature value contains error, and conversely the later a body 
temperature prediction is made the more the predicted temperature value 
approaches the actual body temperature value but the longer it takes to 
make the prediction, so the more the benefit of making the prediction at 
all becomes irrelevant. Furthermore, the user cannot readily know how much 
error a temperature value prediction actually contains. 
SUMMARY OF THE INVENTION 
Accordingly, it is the primary object of the present invention to provide 
an electronic thermometer which can show a converged temperature at an 
early time and can measure more accurately the converged temperature with 
the passage of time. 
According to the most general aspect of the present invention, these and 
other objects are accomplished by an electronic thermometer, comprising a 
temperature sensor which senses the temperature of an object, a prediction 
temperature computing means for deriving a converged temperature according 
to the temperature sensed by the temperature sensor, a means for providing 
a range of error associated with the predicted converged temperature 
computed by the prediction temperature computing means, and a display 
means for displaying the range of error. 
According to the electronic thermometer of this invention, since the 
converged temperature is predicted at a plurality of predicted time points 
after different passages of time after the beginning of measurement and 
the ranges of error at these time points as well as these predicted 
temperatures are displayed, not only measurement can be made at an early 
time but also a converged temperature which has a greater accuracy 
corresponding to the longer passage of time can be produced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to the preferred 
embodiments thereof, and with reference to the appended drawings. FIG. 1 
shows a block diagram of the electronic thermometer according to the third 
embodiment of this invention. In this drawing, 1 denotes a sensor such as 
a thermistor for sensing body temperature, 2 is an A/D converter for 
converting an output analog signal of the sensor 1 into a digital signal, 
and 3 is a CPU which predicts a converged temperature at predetermined 
time points by receiving the sensed temperature signal from the A/D 
converter 2, according to a program stored in a ROM 4, and which performs 
a calculation for determining the range of error. 5 is a RAM for storing 
various data during the calculation process. 6 is a body temperature 
display for displaying a predicted converged body temperature, and 7 is an 
error display for displaying the range of error of the converged 
temperature displayed on the body temperature display 6. Digital displays 
are used for the body temperature display 6 and error display 7, and per 
se known display elements such as liquid crystal, light emitting diode, or 
fluorescent tube types are used. 8 is a start switch for commanding the 
start of measurement. 
The RAM 5 is provided with an error table 41 as shown in FIG. 4. In this 
error table 41 is stored data of the predicted range of error associated 
with the passage of time after the beginning of measurement. 
In the drawing it is shown as an example that the range of error is 
.+-.0.5.degree. C. after the passage of 20 seconds, .+-.0.4.degree. C. 
after the passage of 40 seconds, and .+-.0.1.degree. C. after the passage 
of 10 minutes. These error ranges relative to time periods may be set in 
advance according to experiment, but may alternatively be computed from 
actual measured temperatures. 
Now, the action of this first embodiment of the electronic thermometer of 
this invention will be described, with reference to the flow chart of FIG. 
5. 
When the start switch 8 is turned on, action begins, and a timer is 
activated at step ST1. This timer is for counting the passage of time from 
the beginning of measurement, and is incorporated in the CPU 3 although 
not specifically shown in the drawing. Then the sensed output of the 
sensor 1 is inputted at step ST2 and a predicted body temperature Ts is 
computed in this step. An example of the method of computing this 
predicted body temperature Ts will be given later. Then the time count 
value in the timer is read out and the time of computing the predicted 
body temperature is obtained, in ST3. Then in ST4 an error table 41 is 
referred to. Then in ST5 the error .DELTA.t at that time is read out from 
the RAM 5 and the predicted body temperature data Ts and the error data 
.+-..DELTA.T is obtained. And in step ST6 both these data are displayed in 
the respective displays. In other words, the predicted body temperature Ts 
is displayed on the body temperature display 6 and the error data .DELTA.T 
is displayed on the error display 7. Then in step ST7 it is determined 
whether the measurement is complete or not, and, if the start switch 8 is 
not turned off, in the case of a NO answer the process returns to step ST2 
and the processing in steps ST2 to ST6 is repeated as time passes and the 
computations of the predicted temperature and the derivation of the error 
associated with the passage of time are continually performed and the 
predicted body temperature and its range of error are displayed each time 
as a pair. 
For instance, if the predicted body temperature after the passage of 1 
minute is 36.4.degree. C., then the range of error after the passage of 1 
minute may be found to be .+-.0.3.degree. C. from the error table 41. As 
shown in FIG. 2, on the temperature display 6 is displayed 36.4.degree. 
C., and .+-.0.3.degree. C. is displayed on the error display 7. Therefore, 
after the passage of 1 minute, the user can see that the range of error is 
.+-.0.3.degree. C. and the body temperature is 36.4.degree. C., by looking 
at the displays. If he wants to have a more accurate reading, he may 
continue the measurement. For instance, if he continues the measurement 
for ten minutes in all, and an indication of 36.6.degree. C. is obtained 
on the body temperature display 6, then .+-.0.1.degree. C. will be 
displayed on the error display 7 and the user can know that the body 
temperature is 36.6.degree. C. with an error range of .+-.0.1.degree. C., 
and can perform more reliable body temperature measurement than after the 
passage of only one minute. Thus, this electronic thermometer can show the 
converged body temperature and its range of error, for each particular 
time point from an early time to an almost steady point after the passage 
of a substantially long time. Therefore since the user can take into 
account the range of error at each point he can make a body temperature 
measurement with an accuracy which suits his particular purpose. 
Although in the above embodiment the error display 7 displays both the 
positive and negative error ranges, or .+-..DELTA.T, this display may be 
replaced by a pair of error displays 7a and 7b as shown in FIG. 3 for 
showing a body temperature Ta+.DELTA.T (36.7.degree. C.) including an 
upper error limit on the one and a body temperature Ta-.DELTA.T 
(36.1.degree. C.) including a lower error limit on the other. By having 
such a display, the user can know at a glance what range the converged 
temperature will fall in just by looking at the display. 
Now a concrete example of the method of computing the predicted body 
temperature Ts in step ST2 shown in FIG. 5 will be described in the 
following, with reference to the flow chart of FIG. 6. The method of 
computing the predicted body temperature shown here was invented by the 
inventor, and according to it, noting that there is a linear relation 
between the logarithm T.sub.L of the time derivative of the temperature T 
of an object and the time t, and that this relation can be expressed as: 
EQU T.sub.L =A-.tau.'t 
the constants A and .tau.' are obtained by a recursion method and the 
converged body temperature Ts is predicted from these constants. 
First, in step ST21 an initial temperature T.sub.0 is stored. Then, in step 
ST22, it is determined whether the sampling time has come or not, and when 
it has come in step ST23 a sensed temperature Ti which is taken in through 
the A/D converter 2 is stored in the RAM 5. Then the time derivative 
dTi/dt of the sensed temperature Ti is computed in step ST24, and the 
logarithm of this value T.sub.L i is taken in step ST25. Then in step ST26 
the computed T.sub.L i and the relevant sampling time t.sub.i are stored 
in the RAM 5. Then in step ST27 it is determined whether the number of 
sampling times i has reached an initially defined value n or not. If it 
has not, the flow of control returns to step ST22, and thereafter steps 
ST22 through ST26 are repeated upon arrival of each sampling time until 
the number of sampling times i reaches the value n. By this series of 
processing steps, the sampling times t.sub.1 to t.sub.n n and the 
logarithms T.sub.L 1 to T.sub.L n of the time derivative of the sensed 
temperature at each sampling time are stored in the RAM 5. When the 
sampling times i has reached the value n, according to the data t.sub.1 to 
t.sub.n and T.sub.L 1 to T.sub.L n obtained in the above described 
routine, the constants A and .tau.' are computed from the following 
formulae, based on the recursion method, in steps ST28 and ST29: 
##EQU1## 
From these formulae, the characteristic curve which is peculiar to the 
patient on which the measurement is being made is determined, and the 
converged temperature Ts is computed from the equation Ts=(e.sup.A 
/.tau.')+T.sub.o, in step ST30. 
Since the actual error of the converged temperature from the experimental 
result at each sampling time t.sub.i becomes smaller than the value 
expressed as: 
##EQU2## 
where s, b, e, and m are constants (see FIG. 7), there is displayed either 
Ts.+-..DELTA.T or else 
Ts-.vertline..DELTA.T.vertline..about.Ts+.vertline..DELTA.T.vertline. as 
the display of temperature at time t. The range of error at this time t 
may be averaged and stored in an error table 41 as shown in FIG. 4, but 
may also be computed from the above formula at each time so as to make an 
error table 41 anew every time. 
FIG. 8 is a block diagram showing the electronic thermometer of the second 
embodiment of this invention. 
The electronic thermometer of the second embodiment is similar to that of 
the first embodiment but is provided with displays 81 and 82 in place of 
the displays 6 and 7. 
The display 81 is a present sensed body temperature display, displaying the 
present sensed temperature. 
The display 82 is a prediction body temperature display which displays the 
predicted body temperature including the range of error of the body 
temperature. 
The display elements used in these displays 81 and 82 are digital display 
elements similar to those of the device of the first embodiment. 
Now, the action of the electronic thermometer of the second embodiment will 
be described according to the flow chart shown in FIG. 11. 
As in the first embodiment, action is started by turning on the start 
switch 8 and the timer is activated in step ST1. Then the sensed output of 
the sensor 1 is taken in and the predicted body temperature Ts is computed 
in step ST2, and the time count of the timer is read out in step ST3. The 
routines of these steps ST2 and ST3 are repeated until the passage of 
twenty seconds after the beginning of measurement, by the operation of 
step ST100. That is, the temperature is not displayed during this period, 
because the sensed temperature immediately after the beginning of 
measurement is not stable. 
The computation of the predicted body temperature Ts performed in step ST2 
is carried out according to the previously described procedure (see FIG. 
6), and an error table 41 is provided in the RAM 5. 
After the passage of twenty seconds after the beginning of the measurement, 
the flow of control proceeds to step ST7 through steps ST5 and ST6, and 
the predicted body temperature Ts including the range of error.+-..DELTA.T 
and the present sensed temperature T are displayed on the respective 
displays 82 and 81. Then the above operations are repeated until the start 
switch 8 is turned off, by the operation of step ST8. 
For instance, if the predicted body temperature after the passage of three 
minutes is 37.3.degree. C., the range of error after the passage of three 
minutes is .+-.0.2.degree. C. (see FIG. 4). If the present body 
temperature is 36.8.degree. C. at this time point, as shown in FIG. 2, the 
present sensed body temperature 36.8.degree. C. is displayed on the 
display 81, the predicted body temperature 37.3.degree. C. is displayed on 
the predicted body temperature display portion 82a of the predicted body 
temperature display 82, and the range of error .+-.0.2.degree. C. is 
displayed on the error range display portion 82b of the predicted body 
temperature display 82. 
By looking at these displays, the user can know that the predicted body 
temperature is 37.3.degree. C. and the error has diminished to 
.+-.0.2.degree. C., and further that the present body temperature has 
reached 36.8.degree. C., and may stop the measurement if a rough 
measurement is sufficient. 
When he wants to have a measurement of a greater accuracy, he may continue 
the measurement until a permissible range of error is attained. 
Although in the second embodiment described above the predicted body 
temperature display 82 displays a predicted body temperature and the range 
of error in both plus and minus or .+-..DELTA.T, these displays may be 
displayed on a separate display. And in place of these displays two 
displays 82a and 82b as shown in FIG. 10 may be provided to display a body 
temperature t.sub.s +.DELTA.T (37.5.degree. C.) including an upper error 
limit on the one and a body temperature T.sub.s -.DELTA.T (37.1.degree. 
C.) including a lower error limit on the other. By having such a display, 
the user can know at a glance what range the converged temperature will 
fall in just by looking at the display. 
Further, FIG. 12 is a block diagram of the electronic thermometer of the 
third embodiment of this invention. 
The electronic thermometer of this third embodiment performs an action 
similar to that of the first embodiment (see FIGS. 5 and 6), but is 
adapted particularly to display the present sensed body temperature and 
the predicted body temperature including the range of error in analog 
form. 
Namely, the display 121 is comprised of a plurality of rectangular segments 
S.sub.1 to S.sub.n arranged either in a horizontal row (FIG. 13(a)) or in 
an arcuate row (FIG. 13(b)), and each segment consists for instance of a 
LCD and is driven by a decoder driver 122. 
This display 121 may be provided either as two separate displays, the one 
for displaying the present sensed body temperature and the other for 
diplaying the predicted body temperature including the range of error, as 
shown in FIG. 12 or as a single display as shown in FIGS. 13(a) and 13(b). 
For instance, if the predicted body temperature after the passage of 3 
minutes is 37.3.degree. C., since the range of error after the passage of 
three minutes is .+-.0.2.degree. C. (see error table 41), the range of the 
predicted body temperature is found to be from 37.1.degree. C. to 
37.5.degree. C. If the present body temperature is 36.8.degree. C. at this 
time point, these present body temperature and range of the expected body 
temperature are displayed as shown in FIG. 13. Namely, the present body 
temperature is displayed by lighting up the display segments of the 
leftmost end of the display 121 up to 36.8.degree. C. The predicted body 
temperature range is displayed by lighting up the display segments of from 
37.1.degree. to 37.5.degree. C. The display mode of this predicted body 
temperature range of from 37.1.degree. C. to 37.5.degree. C. is a blinking 
mode, to distinguish it from the display mode of the present body 
temperature. 
Lastly, FIGS. 14(a) and 14(b) show the external appearance of embodiments 
of the above described electronic thermometer. 
The electronic thermometer shown in FIG. 14(a) is comprised of a main body 
casing 141, a small diameter sensor arm 141a integrally formed on an end 
thereof, and a temperature sensor 141b provided at the free end of this 
sensor arm 141a. And the main body casing 141 is provided with a digital 
display 142a or 142b as relating to the second embodiment described above 
(shown on the side of the drawing as an alternative). And a slide type 
power switch 143 is provided in the other end of the main body casing 141. 
The electronic thermometer shown in FIG. 14(b) is comprised of a main body 
casing 145, a probe 147 connected to the main body casing 145 by way of a 
cable 146, and a temperature sensor 147a provided on the free end of the 
probe 147. An an analog display 148 similar to the one shown in the third 
embodiment described above and a slide type power switch 149 are provided 
in the main body casing 145. 
In the above described embodiments, the ranges of errors were set so as to 
correspond to the passage of time from the beginning of measurement, but 
this invention is not to be limited by this concept, but may be associated 
with the predicted converged temperature irrespective of the passage of 
time. For instance, by comparing the temperature differences of adjacent 
predicted converged temperatures, the range of error may be computed 
according to the difference of the temperature differences. Alternatively, 
for instance, by correcting the range of error associated with each 
predicted converged body temperature derived from the temperature 
difference of two adjacent predicted converged body temperatures, the 
corrected range of error may be selected as the final range of error. By 
doing so, even when the sensor and the body become separated from each 
other during measurement, no measurement error occurs. Other modifications 
are also possible. Therefore, the present invention is not to be 
considered as limited by any features of the shown embodiments, or of the 
drawings, but solely by the appended claims.