JPS6311824A - Electronic thermometer - Google Patents

Abstract

PURPOSE:To measure a wide range of temperature at a high accuracy, by providing a frequency measuring circuit for measuring oscillation frequency of a thermosensitive oscillation circuit to stratify the frequency-temperature characteristics in terms of frequency. CONSTITUTION:This apparatus comprises a thermosensitive oscillation circuit 12, equipped with a thermistor, in which the frequency varies exponentially according to changes in the temperature and a frequency measuring circuit 13 for measuring the oscillation frequency and a frequency data (f) from the circuit 13 is converted to a temperature data T with a temperature conversion circuit 9 to be displayed 10. Here, the frequency-temperature characteristic is divided in terms of a fixed frequency range and a linear approximation is applied to each range. Approximated straight lines are expressed by the respective inclinations and intersections with the temperature axis and the inclinations and the intersections present sensitivity values and offset values to be memorized into a sensitivity memory circuit 9a and an offset memory circuit 9c respectively. With such an arrangement, correspondingly to the data (f) inputted, the circuits 9a and 9c output a sensitivity value (a) and an offset value (c). A temperature data computing circuit 9d receives the input of the data (f) and the corresponding values (a) and (c) to obtain a data T on the approximate straight lines.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electronic thermometer that can measure with high precision over a wide temperature range.

[Conventional technology]

Conventionally, electronic thermometers have often used a thermistor as a temperature-sensitive element, and by using an oscillation circuit that can selectively connect a reference resistor and the thermistor, the frequencies are compared when each is switched, and the frequency ratio is calculated. Convert information to temperature. In this temperature conversion, the absolute temperature T is obtained by calculating equation (1).

However, B: Sensitivity constant of the thermistor R: Resistance value of the reference resistor Ro: Resistance value at temperature To of the thermistor Number of oscillation pulses when low resistance is selected Nx: Number of oscillation pulses when thermistor is selected B, R, Ro
, No are predetermined constants, so they can be converted to temperature T by finding Nx.

Here, if we pay attention to this temperature conversion method, we can see that
As shown in Japanese Patent No. 15134, there is a method in which a conversion code is stored in a ROM in advance and the temperature is directly converted to temperature using this conversion code.

Furthermore, as shown in Japanese Patent Application Laid-Open No. 58-19523, there is a method of calculating equation (1) using a computer system.

[Problem that the invention seeks to solve]

As mentioned above, the resistance value of a thermistor has non-linear characteristics with respect to temperature, so it is converted into temperature using various methods. , temperature can be easily converted, and it is also easy to make it into a 1-chip LSI. However, since the information on the B constant, which is the temperature sensitivity of the thermistor, is stored in the ROM in advance, it is impossible to provide a highly accurate electronic thermometer over a wide temperature range against variations in the B constant. was there.

In addition, the method of calculating equation (1) requires the support of a computer system to perform complex calculations such as natural logarithm calculations and division, and a thermometer-equipped calculator is effective because it can share calculation functions. be.

However, since portable thermometers that only measure temperature require calculators with more functions than necessary, it has not been possible to provide inexpensive thermometers.

Furthermore, even if a microcomputer that can only perform necessary processing operations is used instead of a calculator, a large number of ROM steps of the processing program are required to perform complex calculation processing.
This was difficult to achieve with an inexpensive 1-chip microcomputer.

In addition, in the above calculation method, the resistance values of thermistors R and T are (
2) It is assumed that it can be approximated by formula.

Rx = RoexpB (〒-ding) ・・・・・・・・・
(2) However, in general, it is impossible to approximate the temperature characteristics of the thermistor Rx with B as a constant over a wide temperature range, so by setting a certain limited temperature range, the following equation can be approximated: It is often said that In other words, since the approximation equation is insufficient, even if the temperature is calculated by calculation using equation (2), a thermometer with high accuracy over a wide temperature range cannot be realized.

The purpose of the present invention is to solve the above-mentioned conventional problems, to enable measurement of a wide temperature range with high precision, and to
An object of the present invention is to provide an electronic thermometer that can convert temperature using a simple calculation formula and can also adjust variations in the B constant of a thermistor.

[Means for solving problems]

In order to achieve the above object, the present invention provides the following □
It is structured like this. The configuration and operating principle will be explained below based on the principle diagram shown in FIG.

There is a temperature-sensitive oscillation circuit 12 equipped with a micrometer and whose frequency changes exponentially with temperature changes, and a frequency measurement circuit 13 that measures the oscillation frequency of the temperature-sensitive oscillation circuit 12. Here, the frequency measurement circuit 13 includes a clock oscillation circuit 14 that generates a reference time, an AND gate 15 that passes only the output pulse of the temperature-sensitive oscillation circuit 12 within the reference time, and
It consists of a counter circuit 16 that counts the number of pulses that have passed through the gate 15. Then, the number of pulses of the temperature-sensitive oscillation circuit 12 generated within the reference time is counted.

That is, the frequency measurement circuit 13 obtains frequency data f of the temperature-sensitive oscillation circuit 12.

The frequency data f from the frequency measurement circuit 13 is converted into temperature data T by the temperature conversion circuit 9 and displayed on the display device 10. Here, the temperature conversion circuit 9 includes a temperature data calculation circuit 9d, a sensitivity storage circuit 9a, and an offset storage circuit 9c.

In the present invention, as shown in the frequency-temperature characteristic in FIG. 2, the frequency-temperature characteristic is divided into fixed frequency ranges and linearly approximated for each frequency range. Each approximated straight line can be represented by the slope and the intersection with the temperature axis. In other words, in Fig. 2, the horizontal axis shows frequency data f.
, temperature data T is plotted on the vertical axis, and the frequency-temperature characteristic of oscillation by the thermistor is linearly approximated. Hereinafter, the vertical axis will be referred to as the temperature axis. The polygon lines are straight lines Lo, L+, and L2.
, Ls, and each straight line has a frequency fo, f+,
f2) This is a straight line approximated in each range of f3 and f4. For example, the slope ao of the straight line Lo is a value obtained by dividing the difference between the upper limit value and the lower limit value of the frequency range (f+-fo) by the difference between the upper limit value and the lower limit value of the temperature data T (Tr-To). Also,
The straight line LO passes through the origin, and the intersection point Co with the temperature axis is T.
It is equal to o. Also, regarding the straight line L1, its slope al is the value obtained by dividing (f2-f+) by (T2TI), and the intersection point C1 with the temperature axis is the point Ci where the straight line L1 is extended and intersects with the temperature axis. . The slope of each straight line calculated in the same way and the intersection with the temperature axis are stored as sensitivity values and offset values in the sensitivity storage circuit 9a and the offset storage circuit 9C, as shown in Table 1. In other words, the sensitivity value a and the offset value C stored in correspondence to the frequency data r are outputted for each stratified frequency range. In other words, a constant representing an approximate straight line is output.

The temperature data calculation circuit 9d inputs the temperature sensing value a and the offset value C corresponding to the frequency data f and frequency data r from the frequency measurement circuit 16, and calculates the temperature data T on the approximated straight line. I have to.

[Effect]

The temperature of the thermistor can be determined with the above configuration, but how it works will be explained.

First, the thermistor is oscillated by the temperature-sensitive oscillation circuit 12. The temperature 1y for this oscillation frequency is nonlinear, but
In a narrow range, it can be approximated by a straight line, and the frequency-temperature characteristic is approximated by a plurality of broken lines. The intersection point C between the slope a, which is a constant of each straight line, and the temperature axis is stored in Table 1 as described above, and when the frequency data f is measured, a straight line is selected, and the straight line is determined by the two constants of that straight line. The above temperature T can be determined by calculation.

The calculation formula can be expressed as equation (3).

T2a (f − fo ) + c ・・・・・・・・・
(3) In general, the frequency-temperature characteristic shown in Figure 2 holds true even when the horizontal axis is the calculated value F(f) of the frequency data f, so the general formula is Equation (4). .

T = a −F (f) +c −−(4)
However, F(f): the calculated value of frequency data f, and on the other hand,
If the B constant of the thermistor used for temperature measurement is different and the stored sensitivity value a and offset value C are not appropriate, use the B constant correction value as a variable in the temperature T calculation formula in equation (5). Can be approximated.

T = ab-F (f) +c =------
--(5) As mentioned above, even if there are variations in the B constant of the thermistor, the temperature can be calculated by simple calculation.

〔Example〕

An example in which the present invention is applied to an electronic thermometer will be described below.

FIG. 3 is a block diagram showing the configuration of the electronic thermometer, and the differences from FIG. 1 are as follows. First, the temperature-sensitive oscillation circuit including the thermistor is constituted by a switching oscillation circuit that switches the thermistor and the reference resistance in a time-sharing manner. Next, the frequency measurement circuit becomes a frequency ratio measurement circuit that measures the oscillation frequency ratio when the thermistor and the reference resistor are respectively connected.

Embodiments of the present invention will be described below based on the drawings. In this example, the present invention is applied to an electronic thermometer, and the origin is set at a frequency ratio of 1 and a temperature of 37°C.

1 is a switching oscillator circuit, and a reference resistor R1 thermistor Rx
, a capacitor C, and a semiconductor switch SW are configured to selectively connect the reference resistor R and thermistor Rx to perform full CR oscillation. 2 is a counter circuit that counts the number of output pulses output from the switching excavation circuit 1 to a predetermined value N.

When counted, an overflow signal is output. 6 is a clock oscillation circuit, which outputs a clock signal. 4 is a timer circuit that counts clock signals and outputs the counting result, that is, time information.

A latch circuit 5 stores and outputs time information when the overflow signal is output from the counter circuit 2. Further, the counter circuit 2 and the timer circuit 4 are reset immediately after the overflow signal is output.

A coincidence circuit 6 detects coincidence between the time information output from the latch circuit 5 and the time information output from the timer circuit 4, and outputs a coincidence signal.

A latch circuit 7 stores and outputs the count value Nx of the counter circuit 2 when the coincidence signal is output as a frequency ratio signal.

11 is a frequency ratio measuring circuit, and the counter circuit 2)
A clock excavation circuit 6, a timer circuit 4, launch circuits 5 and 7, and a -number circuit 6 are also configured.

8 is a B constant input means, which outputs B constant information set according to the B constant variation of the thermistor Rx.

Reference numeral 9 denotes a temperature conversion circuit, which is composed of a B constant correction storage circuit 9b, a sensitivity storage circuit 9a, an offset storage circuit 9c, and a temperature data calculation circuit 9d. The B constant correction storage circuit 9b receives the B constant information set by the B constant input means 8 and outputs a B constant correction value. The sensitivity storage circuit 9a and the offset storage circuit 9c receive the frequency ratio signal Njc outputted from the frequency ratio measurement circuit 11 as input, and as described later (corresponding to the stratified values of the frequency ratio signal Nx) The temperature data calculation circuit 9d outputs the offset value C, respectively.The temperature data calculation circuit 9d outputs the frequency ratio signals Nx and B.
Using the constant correction value, sensitivity value a, and offset value C as input, the temperature difference Tc is calculated. 10 is a display device;
Display temperature data Tc.

The operation of the electronic thermometer having the above configuration will be explained.

First, the oscillation frequencies of the switching excavation circuit 1 when the reference resistor R and thermistor Rx force are selected are fo and f, respectively.
-T, the following equation is obtained.

,=f−・・・・・・・・・・・・・・・ (7
)CRx where K: oscillation constant First, the counter circuit 2 and the timer circuit 4 have been reset by the coincidence signal from the coincidence circuit 6 at the end of the previous measurement. The switching oscillation circuit 1 selects the reference resistor R, the counter circuit 2 counts the output pulses of the switching oscillation circuit 1, and the timer circuit 4 counts the output pulses of the clock oscillation circuit B.

When the count value of the counter circuit 2 reaches a predetermined value No, time information of the timer circuit 40 is stored in the latch circuit 5 by an overflow signal. After that, the counter circuit 2) and the timer circuit 4 are reset, and the switching oscillation circuit 1
selects thermistor Rx.

Again, the counter circuit 2 counts the output pulses of the switching excavation circuit 1, and the timer circuit 4 counts the output pulses of the clock generation circuit B. When a match between the timer circuit 40 time information and the time information stored in the latch circuit 5 is detected, a match signal is generated and the count value N of the counter circuit 2 is detected.
x is stored by the latch circuit 7. Thereafter, the counter circuit 2 and timer circuit 4 are reset.

That is, the selection time of the reference resistor R and the thermistor Rx is the same, and the number of pulses output from the switching oscillation circuit 1 during that time is No and Nx, respectively.

From the above, solving for the absolute temperature T yields equation (1). Furthermore, if the reference resistance R is set equal to the resistance value Ro at the temperature To of the thermistor, (8)
It becomes like the formula.

Therefore, once N, r and B are determined, other To and N.

Since is a predetermined constant, the temperature can be determined.

Here, the characteristics of the thermistor resistance value with respect to temperature are (2)
Although it has a nonlinear characteristic as shown in the equation, it can be considered linear in a narrow temperature range, so the temperature T in degrees Celsius
c can be expressed as in equation (9).

Nx Tc=ab(imaginary--1)+c ・・・・・・・・・・・・
(9) However, a: Sensitivity value B constant correction value C: Offset value Here, the case where No=10000 and B24000 (K) will be explained.

The sensitivity storage circuit 9a and the offset storage circuit 90 classify the frequency ratio signal Nx into layers, and convert the corresponding sensitivity values a and offset values C as shown in Table 2.

In addition, B of the thermistor Rx incorporated in the switching oscillation circuit 1
The constant is measured in advance, and by setting it according to the result, the B constant input means 8 is set to the thermistor R.
B constant information specific to x is output. The B constant correction storage circuit 9b includes the B constant input means 8 as shown in Table 3.
The B constant information set by is converted into a B constant correction value.

Table 3 In other words, the frequency ratio signal Nx is held in the frequency ratio measuring circuit 11, and the frequency ratio signal Nx is converted into a sensitivity value a and an offset value C by the sensitivity storage circuit 9a and the offset storage circuit 9C. Further, the B constant information is converted into a B constant correction value by the B constant correction storage circuit 9b.

The temperature data calculation circuit 9d then generates a frequency ratio signal Nx
In addition, the B constant correction value outputted from the B constant correction storage circuit 9b includes the sensitivity storage circuit 9a and the offset storage circuit 9.
Each time C is supplied with a frequency ratio signal Nx car, respectively,
Input the sensitivity value a and offset value C to be output according to Table 2, and calculate the temperature data T in degrees Celsius using the calculation formula shown in formula 00).
c is calculated and displayed on the display device 10.

That is, in the present invention, the sensitivity value a and the offset value C are stratified as shown in Table 2 in response to the frequency ratio signal Nx output from the frequency ratio measurement circuit 11, and are stored in the sensitivity storage circuit 9a and the offset storage circuit 9C. By setting the sensitivity value a and the offset value C, the sensitivity value a and the offset value C are output every time the temperature is measured. Further, a B constant correction value S is outputted from the B constant correction storage circuit 9b. Then, the sensitivity value a, the offset value C, and the B constant correction value S are calculated by substituting them into the linear equation regarding the frequency ratio signal Nx shown in equation (10). That is, the temperature is calculated by approximating the temperature characteristic of the frequency ratio signal Nx to a straight line for each layer of the frequency ratio signal Nx0 shown in Table 2.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, even if the thermistor has nonlinear resistance-temperature characteristics, the temperature can be digitally displayed with high accuracy.

In addition, in a wide temperature range, the resistance value of the thermistor (
2) In a narrow temperature range that cannot be approximated by equation (
9) Highly accurate temperature measurement can be performed by approximating the straight line shown in equation 9.

Furthermore, even if there is an apparent decrease in sensitivity of the thermistor due to the on-resistance of the inverter in the switching oscillator circuit 1, (
9) Highly accurate temperature measurement can be performed by approximating the straight line shown in equation 9.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the principle of the present invention, Fig. 2 is a frequency-temperature characteristic diagram, and Fig. 3 is a block diagram of an electronic thermometer showing an embodiment of the present invention. It is. 1...Switching oscillation circuit, 9...Temperature conversion circuit, 9a...Sensitivity memory circuit, 9b...B constant correction memory circuit, 9c...・・・
- Offset storage circuit, 9d...Temperature data calculation circuit. Man 1 Figure L J Figure 2 1 F;) N 1 (4-y in ξ ↑ W, 3 Figure

Claims (2)

[Claims] (1) A temperature-sensitive oscillator circuit equipped with a thermistor whose frequency changes exponentially with temperature changes, a frequency measurement circuit that measures the oscillation frequency of the temperature-sensor oscillation circuit, and a frequency data of the frequency measurement circuit. In an electronic thermometer equipped with a temperature data calculation circuit that generates temperature data according to frequency-temperature characteristics, the frequency-temperature characteristics are stratified by frequency, each stratified range is approximated by a straight line, and each straight line is The temperature data calculation circuit includes a sensitivity storage circuit and an offset storage circuit that store a sensitivity value, which is the slope of the line, and an offset value, which is the intersection of the straight line and the temperature axis, in a table, respectively. data and
An electronic thermometer characterized in that the sensitivity value and offset value corresponding to the frequency data are input, and temperature data on a straight line including the frequency data is calculated. (2) In the electronic thermometer according to claim 1,
An electronic thermometer comprising: a B constant correction storage circuit that stores a constant correction value determined by the B constant of the thermistor; and the temperature data calculation circuit calculates temperature data as one of the B constant correction value input data. .