JPH047456B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to an electronic thermometer, and particularly to an electronic thermometer that can measure the body temperature of a subject at an early stage after starting measurement.

(b) Prior art and its problems Generally, electronic thermometers using temperature sensors such as mercury thermometers and thermistors are used to measure body temperature. These thermometers usually have the detection part inserted under the armpit or under the tongue when taking measurements, but since it takes time for the detection part to reach thermal equilibrium with body temperature, there is a problem in that it takes a long time to complete the measurement. be. Therefore, in order to solve this problem and measure body temperature early, conventional electronic thermometers insert the sensor part into the armpit, etc., and add a certain temperature (for example, 0.5 degrees Celsius) after a certain period of time after starting the measurement. A method was used to predict body temperature. However, the degree of increase in detected temperature during body temperature measurement varies depending on the individual (for example, the time constant for reaching an equilibrium state differs). The above-mentioned conventional electronic thermometer completely ignores such individual variations, and therefore has the disadvantage that the obtained measurement results are low in accuracy.

(c) Purpose of the Invention The purpose of the present invention is to eliminate the drawbacks of the conventional electronic thermometers described above and to provide an electronic thermometer that is capable of performing early and highly accurate measurements.

(d) Structure and Effects of the Invention In order to achieve the above object, the electronic thermometer of the present invention has a linear relationship between the logarithm T _L of the time differential of the body temperature to be measured and time t, and T _L = Focusing on the fact that it can be expressed as A-τ't, the constants A and τ' are determined by a regression method, and the convergence body temperature is predicted from these constants. That is, the electronic thermometer of the present invention includes a sensor that detects body temperature, samples the output of this sensor, and samples the output of this sensor at each of n sampling times.
In addition, means for calculating the logarithmic value T _Li of the time differential of each detection output, and the calculated sample times t1, t
Based on the logarithm value T _L of the time differential of the detection output for each _{2 ,} ... _ti ... _tn and τ' by a regression method, and means for predicting and calculating the body temperature Ts after thermal equilibrium based on the calculated constants A and τ' and the detected initial temperature To.

According to the electronic thermometer of this invention, constants that differ for each individual are calculated by regression method to predict convergence body temperature, so body temperature can be measured quickly and accurately without being influenced by individual variations. I can do it.

Here, in order to facilitate understanding of the electronic thermometer of the present invention, the principle of its adoption will be explained.

Generally, when time is plotted on the horizontal axis and temperature is plotted on the vertical axis, the passage of time when body temperature is measured by a temperature sensor changes exponentially as shown in FIG. 1.

In the figure, the temperature value required for body temperature measurement is the convergence temperature Ts, but it takes time to reach this temperature using normal methods. This is a phenomenon that occurs due to the physiological reason that the human body loses heat due to the thermometer itself, and it takes time for the body to return to its original state.

The present invention attempts to estimate the convergence value by predicting the characteristic curve as soon as the measurement starts.

It is known that the following thermal equilibrium equation d(Ts-T)/dt=-1/τ(Ts-T) (1) holds between the temperature Ts in equilibrium and the temperature T at time t. .

From this formula (1), Ts−T=(Ts−To)e ^-1/ 〓 ^tFrom this formula, T=Ts−(Ts−To)e ^-1/ 〓 ^t (2) Where, τ: time constant, T _S : Initial value (value of T when t=0). The time constant τ is a constant representing the speed at which thermal equilibrium is reached, and is thought to vary from person to person.

Now, if we set τ′=1/τ and differentiate the above equation (2) with time, we get T′=dT/dt=τ′(Ts−To)e ⁻ 〓′ ^t (3). Furthermore, if we take the logarithm of both sides of equation (3), we get logT′=logτ′(Ts−To)−τ′t (4). Here, by setting T _L = logT' and A = logτ' (Ts - To), equation (4) can be expressed as T _L = A - τ't (5).

As shown in Figure 2, this equation (5) has a slope of -
At τ', it becomes a straight line that intersects the vertical axis at A.

Since the temperature T is actually measured at each time t,
T'=dT/dt can be determined, and T=logT' can also be determined. Therefore, (t1,
A and τ' can be calculated from the values of T _L1 ), (t2, T _L2 ), . . . (tn, T _Lo ) using a well-known regression method.
That is, A=Σti ² ΣT _L −ΣtiΣtiT _Li /nΣti ² −(Σti) ² (6) τ′=−nΣtiT _Li −ΣtiΣT _Li /nΣti ² −(Σti) ² (7
) On the other hand, as mentioned above, since logτ'(Ts-To)=A, the convergence temperature Ts becomes Ts=e ^A /τ'+To (8). In this equation (8), the initial value To is detected, and the constants A and τ′ are calculated using equations (6) and (7).
You can find Ts. Moreover, the constants A and τ′, which include individual variations, are lost early in the measurement (t1,
...tn), it is possible to predict the convergence temperature Ts quickly and accurately.

(E) Description of Embodiments FIG. 3 is a block diagram of an electronic thermometer in which the present invention is implemented. In the figure, 1 is a sensor such as a thermistor for detecting body temperature, 2 is an A/D converter that converts the output from sensor 1 from an analog signal to a digital signal, and 3 is a CPU, which is the A/D converter 2. After receiving the detected temperature signal from the ROM 4, it performs control for predicting the convergence temperature Ts, which will be described later, according to a program stored in the ROM 4. 5 is a RAM that stores various data during the control process. 6 is a display that displays the measured body temperature. This display 6
As the display body, well-known ones such as liquid crystal, light emitting diode, fluorescent display tube, etc. are used. 7 is a switch for instructing the start of measurement.

Next, the operation of the electronic thermometer of the above embodiment will be explained with reference to the flowchart shown in FIG.

When switch 7 is turned on and operation starts,
First, in step ST1, the initial temperature value To is taken into the CPU 3 via the A/D converter 2. continue,
Step to see if sample time has arrived
Determine in ST2. When sample time arrives,
The detected temperature T1 at that time taken in through the A/D converter 2 is stored in the RAM 5 (ST3). next,
Calculate the time differential value dT1/dt of the detected temperature T1 (ST4), and further calculate the logarithm value of this time differential value T _L1 =
Find logdT1/dt (ST5). Then, calculate T _L1 and the sample time t1 at that time in RAM 5.
(ST6). Next, the number of sample times i
It is determined whether or not n has reached a preset value (ST7). If it has not reached n, the process returns to step ST2. From then on, steps ST3 and ST are performed every time a sample time arrives until the number of samples i reaches n.
4,...Repeat the process of ST6. Through this processing, each sample time t1, t2,...tn and the logarithm of the time differential value of the detected temperature for each sample time are
T _L1 , T _L2 , . . . T _Lo are stored in the RAM 5.

When the sample time count i reaches n, step
When the judgment in ST7 is YES, the stored data t1, t2, ... tn and T _L1 , T _L2 , ... T _Lo
Calculate the constant A using equation (6) above based on (ST
In addition to 8), the constant τ' is further calculated using the above equation (7) (ST9). As a result, the characteristic curve unique to the person to be measured is specified, so the convergence temperature Ts is then calculated using the above equation (8) (ST10), and this temperature Ts is displayed as the body temperature on the display 6 ( ST11).

After the display, if the detected temperature is still changing (ST12), the process returns to step ST2 and the above process is repeated, but when the change in the detected temperature becomes 0, other required measurement completion processes are subsequently performed.

[Brief explanation of drawings]

Figure 1 shows the time course of body temperature in a thermometer, and Figure 2 shows the logarithm of the time differential of temperature versus time t.
_FIG . 3 is a block diagram of an electronic thermometer in which the present invention is implemented, and FIG. 4 is a flow diagram for explaining the operation of the electronic thermometer. 1...Sensor, 2...A/D converter, 3...
CPU, 4...ROM, 5...RAM, 6...Display, 7...Start switch.

Claims (1)

[Claims] 1. A sensor that detects body temperature, samples the output of this sensor, and samples the output of this sensor at each of n sample times.
ti, means for calculating the logarithm T _Li of the time differential of each detection output, and the calculated sample times t1,...
...logarithm of the time differential of the detection output for each tn T _L 1,...
...T _Lo and means for calculating the constants A and τ' of the linear equation T _L = A - τ't by a regression method, and the calculated constant A
An electronic thermometer comprising means for predicting and calculating body temperature Ts after thermal equilibrium based on τ' and detected initial temperature T ₀ .