JPH0339258B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital thermistor thermometer that converts a change in the resistance value of a thermistor into a change in the oscillation frequency of a CR oscillation circuit.

The purpose of the present invention is to inexpensively produce a thermometer with constant sensitivity and high accuracy over a wide temperature range, using a thermistor whose resistance value changes exponentially with temperature. An object of the present invention is to realize a thermistor digital thermometer that can easily switch between display and Fahrenheit temperature display.

Traditionally, the most commonly used thermometers are glass thermometers that use the thermal expansion of mercury or colored alcohol sealed in a glass tube, and mechanical deformation due to the difference in thermal expansion coefficient of two metals bonded together. It was a pointer thermometer that used a bimetal that produced . These were convenient and relatively inexpensive, and had the advantage of being able to easily display Celsius and Fahrenheit temperatures using dual scales. However, since these thermometers have an analog display, there are restrictions on the minimum display unit, and they have the drawback of poor accuracy, especially when miniaturized. On the other hand, electric thermometers with digital displays have traditionally been used for scientific and technical measurements and industrial applications. However, although this type of thermometer is characterized by high accuracy, it has the disadvantage that the device is large and expensive.
It was not widely used as a general household thermometer.

The present invention combines the convenience and low cost of glass thermometers and pointer thermometers with the ability to easily display both Celsius and Fahrenheit temperatures. The display type thermometer is realized by using a thermistor as a temperature sensor.

A thermistor is a general term for a resistor whose resistance value changes sensitively depending on temperature.
Coefficient Thermistor refers to a composite sintered body of metal oxide with electrodes attached. Thermistors exhibit resistance changes that are extremely sensitive to temperature, the resistance value can be selected relatively freely, the shape is simple and small, and thermistors have a small thermal time constant and can be used for rapid temperature measurement. be suitable,
It has many advantages such as being able to be industrially mass-produced. However, since the change in resistance value is exponential, it has the disadvantage that its characteristics must be linearly corrected. Conventionally, the following two methods have been used for this linear correction. The first method is to combine a thermistor with series-parallel resistances and approximate the temperature characteristics of the combined resistance to a straight line, but this method requires a large number of high-precision resistors and can be corrected. The temperature range is narrow and the accuracy of linear correction is not good. Therefore, thermometers using this method are relatively poor in terms of accuracy, and have only been used in indoor air conditioning equipment, etc., which have a narrow operating temperature range. The second method of linear correction is to accurately measure the resistance value of the thermistor, perform AD conversion to convert it into a digital quantity, and perform linear correction using calculation means, but this method requires a large and expensive device. The scope of application was limited to scientific and technological thermometers. For this reason, the thermistor has been used more often as a sensor for detecting a fixed point of temperature than as a conventional thermometer. The present invention proposes a method for easily and accurately linearly correcting the resistance characteristics of a thermistor, and at the same time easily performing conversion calculations for switching between Celsius temperature display and Fahrenheit temperature display. FIG. 2 is a circuit diagram showing an embodiment of a CR oscillation circuit used in the present invention.
In this embodiment, thermistor 1, capacitor 2,
C-MOS inverters 3 and 4, and C-MOS inverters 3 and 4;
It consists of MOSNAND gate 5 and NAND
The output terminal of the gate 5 is connected to the input terminal of the inverter 4, and the output terminal of the inverter 4 is connected to the input terminal of the inverter 3. The inverter 3 is configured to output a pulse signal _F1 , which is an output signal of the CR oscillation circuit, from the output terminal _P2 .

A control signal G is input to the first input terminal _P1 of the NAND gate 5. NAND
One end of the thermistor 1 and a capacitor 2 are connected to the second input terminal of the gate 5 at the same time, and the other end of the thermistor 1 is connected to the output terminal P ₂ of the inverter 3.
Further, the other end of the capacitor 2 is connected to the output terminal of the inverter 4, respectively.

In such a circuit configuration, when the control signal G applied to the input terminal P ₁ is logic 'L' (hereinafter simply referred to as 'L'), the CR oscillation circuit stops operating, and the signal F at the output terminal P _{2 1} maintains logic 'H' (hereinafter simply referred to as 'H') and consumes almost no power. control signal G
When becomes 'H', the CR oscillation circuit starts operating, and the frequency f ₁ of the output pulse signal F ₁ at that time is expressed as follows, where R is the resistance value of thermistor 1 and C is the capacitance value of the capacitor. .

f ₁ = 1/2.2CR...Equation (1) The resistance value R of the thermistor at the absolute temperature T [K] is as follows, where R ₀ is the resistance value of the thermistor at the reference temperature T ₀ [K], and B is the thermistor constant. can be determined.

R=R ₀ exp {B1/T-1/T ₀ )}...Equation (2) Substitute equation (2) into equation (1) to obtain the following equation.

f ₁ = 1/2.2CR ₀ exp {B (1/T-1/T ₀ )} = exp (B
/T ₀ )/2.2CR ₀ exp(B/T)=ke ^-B/T …Equation (3) However, k=1/2.2CR ₀ e ^B/T ₀ …Equation (4) From expression (3), frequency f ₁ , the formula for finding the temperature T at that time is as follows.

T=Bloge/logk−logf ₁ (5) Formula On the other hand, the number N of pulses included in the pulse signal F ₁ during the fixed time t ₀ is as follows.

N=f ₁ t ₀ ...(6) From equations (5) and (6), the following equation is obtained.

T=Bloge/logk−log ^N /t ₀ =Bloge/logkt ₀ −logN…(7
) Equation (7) is expressed as Celsius temperature T°C and Fahrenheit temperature T〓 as shown in Equations (8) and (9), respectively.

T℃≒Bloge/logkt ₀ −logN−273 …Equation (8) T〓≒9Bloge/5(logkt ₀ −logN)−459.4 …Equation (9) Equations (8) and (9) are for constant time t _0. In the meantime, the number of pulses N output from the CR oscillation circuit as shown in Figure 1.
This is the formula to find the temperature by knowing . However, in order to obtain the temperature using this calculation formula, a counter circuit for counting the number of pulses N and a sophisticated calculation circuit for executing the calculation are required. This makes the circuit large-scale and expensive, making it unsuitable as a thermometer for general household use.
The thermometer according to the present invention uses a counter circuit that counts the number of pulses N instead of being equipped with a complicated and expensive calculation circuit, so that the thermometer calculates the equation (8) and
Equation (9) was calculated approximately.
The counter circuit will be explained below.

FIG. 2 is a graph representing equation (8), in which the horizontal axis shows the number of pulses N, and the vertical axis shows the temperature in degrees Celsius, T°C. This graph is a monotonically increasing curve whose slope gradually decreases as the number of pulses N increases, but the relationship between the number of pulses N and the temperature T°C is determined by the number of pulses N and the counting result S of the counter circuit that counts the pulses. It can be used as a reminder. That is, a counter is provided whose counting speed gradually slows down as the cumulative number of input pulses increases, and the relationship between the number of pulses N and the counting result S of the counter is expressed by the equation (8) between the number of pulses N and the temperature in degrees Celsius. The counting result S is displayed as a substitute value for the temperature T° C. so as to approximate the relationship of T° C. The line graph shown in Figure 3 shows the number of pulses N and the counting result S of the counter.
This is an example showing the relationship between N and N. As the number of pulses N increases, the slope of the straight line gradually decreases, and the curve approximates the curve of the graph in FIG. In this example, the slope of the straight line changes depending on the count result S of the counter,
The configuration is such that the slope, that is, the counting speed of the counter, gradually decreases each time the value of the counting result S increases by a constant value a. The smaller the value of the constant value a, the better the approximation accuracy of the line graph can be made, but if the accuracy of a general household thermometer is allowed to be ±0.5℃, the value of the constant value a should be about 5℃. . On the other hand, the approximation accuracy in a range where the value of the number of pulses N is close to 0 does not pose a major problem for the following reasons. That is, as is clear from equation (8), the range in which the value of the number of pulses N is close to 0 is an extremely low temperature range and is outside the measurement range of the thermometer of the present invention, so the approximation accuracy does not matter how bad it is. Therefore, the content value of the counter when the number of pulses N is 0 may be determined conveniently, and the most convenient value for configuring the counter circuit is preset in the counter as an initial value. In the following explanation, when measuring the temperature in degrees Celsius, the initial value will be Ti°C.

Next, the case of determining the Fahrenheit temperature T〓 will be described. Figure 4 is a graph representing equation (9), but the slope is larger than that of the graph in Figure 2, which represents equation (8), and the number of pulses that indicate 0°C is lower. It shows 32〓. This is Fahrenheit temperature T
This is because the relationship between T and Celsius temperature is expressed by the following equation.

T〓=9/5T℃+32...Equation (10) The graph in Figure 4 showing the relationship between the Fahrenheit temperature T〓 and the number of pulses N is approximated to a line graph using the same method and under the same conditions as for the Celsius temperature. is shown in FIG. 5, the initial value Ti of the counter is as follows.

Ti = 9/5 Ti°C + 32 (11) Equation (11) Further, the change range b of the content value of the counter whose slope should change is expressed by the change range a in the case of Celsius temperature as follows.

b=9/5a...Equation (12) As stated above, the temperature T in Celsius and the temperature T in Fahrenheit are pulsed by a counter circuit having the characteristics shown by the line graphs in Figures 3 and 4, respectively. It can be determined by counting the number N. However, since it is uneconomical to simultaneously provide a counter circuit dedicated to Celsius temperature and a counter circuit dedicated to Fahrenheit temperature in one thermometer, it is desirable to realize a common counter circuit for both. FIG. 6 is a block diagram showing a specific embodiment of the present invention that meets this requirement. The block diagram of FIG. 6 will be explained below.

In the drawing, 6 is the CR oscillation circuit shown in FIG. 1, to which a control signal G is applied to an input terminal P ₁ and a pulse signal F ₁ is output from an output terminal P ₂ . Reference numeral 7 denotes a variable frequency dividing circuit, which divides the frequency of the pulse signal F ₁ by a frequency division ratio Kf determined by receiving the frequency division ratio designation signal x, and outputs the pulse signal F ₂ . Here, the frequency division ratio Kf is the frequency f ₁ of the input pulse signal F ₁ and the output pulse signal
It is the ratio of the frequency f ₂ of F ₂ and is defined by the following formula.

Kf=f ₂ /f ₁ (13) Equation 8 is a read-only memory (hereinafter referred to as ROM), which receives address data A and outputs the frequency division ratio designation data x. Reference numeral 9 denotes an address frequency divider, which divides the frequency of the pulse signal _F2 and outputs a pulse signal _F3 . The pulse signal _F3 is a signal that is output every time the counting result of the counter circuit of this embodiment changes by a certain value, and corresponds to the constant values a and b mentioned in the explanation of FIGS. 3 and 5. One pulse is output for each change. 10 is an address counter which counts the pulse signal _F3 and outputs the counting result as the address data A. Reference numeral 11 denotes a sensitivity switching frequency divider, which divides the pulse signal F ₂ by one of two frequency division ratios K _C and K _F determined by the unit selection signal U to generate the pulse signal F ₄ . Output.

One pulse of the pulse signal _F4 corresponds to the minimum unit of temperature measurement, and the temperature is quantified by counting the number of pulses of the pulse signal _F4 . 12 is a temperature counter, and the pulse signal
Count the number of _F4 pulses and output the counting result S.
In addition, the temperature counter 12 is designed to be able to preset an initial value Si;
Si is supplied from the data selection circuit 13. The data selection circuit 13 selects either of the two numerical values Ti° C. and Ti〓 shown in equation (11) using the unit selection signal U, and outputs it as the initial value Si of the counter 12. 14 is a data latch, and temperature counter 1
2 is received and stored, and the counting result S, which is the stored content, is displayed on the display device 15.
Communicate. The display device 15 is composed of a numeric display using a liquid crystal, a light emitting diode, etc., its driving circuit, and a signal decoder, and digitally displays the counting result S of the temperature counter 12, as well as a unit selection signal U.
Change the display unit, decimal point position, etc.

Reference numeral 16 denotes a unit switching circuit which manually determines whether to measure in degrees Celsius or degrees Fahrenheit and outputs the unit selection signal U mentioned above.

Reference numeral 17 denotes a measurement temperature out-of-range detection (over-detection) circuit, which detects a temperature outside the measurement range of this thermometer based on address data A and outputs an overscale signal Over. The overscale signal
Over is stored in the data latch 14 and further transmitted to the display device 15 to display on the display screen that the temperature is outside the measurement range.

The timing circuit 18 is a circuit that outputs three types of timing signals that control the temperature measurement operation of this thermometer. The first is a control signal G for the CR oscillation circuit 6, which controls the ON/OFF of the CR oscillation circuit 6 and also defines the above-mentioned fixed time _t0 . The second signal I is the counter 1 used in this thermometer.
This is an initialization signal for initializing the frequency dividers 7, 9, and 11, and is output prior to the temperature measurement operation. The third signal is a latch sampling signal L, which updates the contents of the data latch 14 and is output at the end of the temperature measurement operation to save the measured data. These three types of signals I,
The waveforms of G and L are waveforms A and A in Fig. 7, respectively.
They are shown as B and C. A time reference circuit 19 is composed of an oscillation circuit with high frequency accuracy and a frequency divider, and generates an accurate time reference signal and supplies it to the timing circuit 8.

How the temperature measurement operation is performed in the thermometer having the above-described configuration will be described below. First, before temperature measurement, the unit switching circuit 16
A unit of measurement is selected by a unit selection signal U output from. Next, the initialization signal I is output from the timing circuit 18, and resets the variable frequency divider circuit 7, the address frequency divider 9, the address counter 10, and the sensitivity switching frequency divider 11. At the same time, an initial value Si is preset in the temperature counter 12 by the initialization signal I, and a value suitable for the temperature unit is selected for the initial value Si by the data selection circuit 13. That is, when measuring the temperature in degrees Celsius, the numerical value Ti°C is used as the initial value Si, and when measuring the temperature in degrees Fahrenheit, the numerical value Ti〓 is used. After the circuit initialization is completed,
When the control signal G becomes 'H', the CR oscillation circuit 6 starts operating and the pulse signal _F1 is output. At this time, the address data A that is the output of the address counter 10 specifies address 0 of the ROM 8, so that the initial value of the frequency division ratio specification data x is transferred from the ROM 8.
x ₁ is output. The value of the frequency division ratio Kf at this time is
If K ₁ , the pulse signal is output from the variable frequency divider circuit 7.
A pulse signal F ₂ having a frequency that is K ₁ (K ₁ <1) times the frequency of F ₁ is output. The pulse signal F ₂ is frequency-divided by the address frequency divider 9 to become the pulse signal F ₃ , whose frequency f ₃ is determined by the division ratio of the address frequency divider 9.
Assuming K _A , it becomes as follows.

f ₃ = K _A f ₂ = K _A K ₁ f ₁ …(14) From equation (14), the first pulse of pulse signal F ₃ is 1
It can be seen that the number N ₁ of pulses included in the pulse signal F ₁ until the number of pulses is output is 1/K ₁ ×K _A. When one pulse is output from the address frequency divider 9, the address counter 10 counts the pulse and changes the address data A from address 0 to address 1.

As a result, the second frequency division ratio designation data _x2 is output from the ROM8. If the division ratio at this time is K ₂ , then the division ratio specification data changes to x ₃ , and the number of pulses N ₂ included in the pulse signal F ₁ is 1/K until the division ratio changes to K ₃ . ₂ ×K _A. Similarly, the pulse signal F ₁ is input when the n-th frequency division ratio Kn.
The number of pulses Nn is expressed as 1/Kn×K _A. At this time, the number of pulses of pulse signal F ₂ is always 1/K _A from equation (14), so the relationship between the cumulative number of pulses N of pulse signal F ₁ and the cumulative number of pulses M of pulse signal F ₂ is shown in Figure 8. It will look like the line graph shown in . The slope of each straight line segment in this graph is determined by the division ratio K ₁ , K ₂ ,
. . . Kn . . . The rate of change in slope must be equal to the rate of change in the line graphs of FIGS. 3 and 5.

On the other hand, the pulse signal F ₂ is frequency-divided by the sensitivity switching frequency divider 11 and output as a pulse signal F ₄ .

The frequency division ratio of _the sensitivity switching frequency divider 11 is K _C when measuring temperature in Celsius, and _{K F} when measuring temperature in Fahrenheit. ₄ outputs K _C /K _A and K _F /K _A pulses, respectively.

Further, the cumulative number of pulses M _C and M _F of the pulse signal F ₄ are K _C ×M and K _F ×M, respectively. The changes in the cumulative number of pulses M _C and M _F can be expressed as the graphs of graphs Graph 1 and C of FIG. 8, respectively. The changes in the number of pulses for one line segment of the line graph are K _C /K _A and K _F /K _A , but these values are constant values a and b shown in the line graphs of Figures 3 and 5, respectively. The frequency division ratios K _C and K _F must be determined so that they are equal.

Therefore, by substituting a=K _C /K _A and b=K _F /K _A into equation (12), the following relational expression is obtained.

K _F /K _C =9/5...Equation (15) For example, if K _C = 1/9 and K _F = 1/5, Equation (15) is satisfied.

The temperature counter 12 counts the cumulative number of pulses M _C and M _F of the pulse signal F ₄ , and it is necessary to preset the temperature counter 12 with initial values Ti°C and Ti 〓 corresponding to the unit of temperature measurement. Therefore, the counting results S show changes as shown in the line graphs of FIGS. 3 and 5, respectively.

After a certain period of time t ₀ has elapsed, the control signal G of the CR oscillation circuit 6 becomes 'L', so that the CR oscillation circuit 6 stops operating, and no new pulses are supplied to the variable frequency divider circuit 7 and below. . Temperature counter 1 at this time
The counting result S in 2 means the measured value of temperature,
The measured value is stored in the data latch 14 by the output of the latch signal L from the timing circuit 18, and simultaneously displayed numerically on the display device 15.

The series of operations described above is repeated at regular intervals, so that the latest measured values are always displayed.

Next, the specific configuration of the variable frequency divider circuit 7 will be briefly explained. There are three methods of implementing the variable frequency divider circuit as described below. The first one is composed of a presettable down counter and a 0 detection circuit, and after presetting the division ratio specification data x to the presettable down counter, it performs a down count until the content value becomes 0. When this is detected, the data x is preset again and this operation is repeated. In this method, the frequency division ratio Kf is as shown in the following equation.

Kf=1/x (16) The second implementation method of the variable frequency divider circuit 7 is composed of a counter and a numerical match detection circuit, which detects the match between the content value of the counter and the frequency division ratio specification data x. However, this method resets the counter, starts counting again from 0, and repeats this operation. In this method as well, the frequency division ratio Kf is given by equation (16).

The third implementation method is to perform frequency division using a rate multiplier. The operating principle of rate multiplier is "TTL Application Manual"
(Published by Texas Instruments Asia Limited) A detailed explanation is given on page 31 and is well known, so it will be omitted here. A rate multiplier with a binary 8-bit configuration is appropriate as a rate multiplier used in a household thermometer, but the frequency division ratio Kf is an 8-bit binary number transmitted to the rate data input terminal. It is expressed by the following equation using the frequency ratio designation data x.

Kf=x/256...Equation (17) As is clear from Equation (17), the variable frequency divider circuit using the rate multiplier is advantageous in that the frequency division ratio Kf can be set linearly, and the embodiment of the present invention Ideal for use as a variable frequency divider.

Next, the configuration of the sensitivity switching frequency divider 11 will be specifically explained. In the embodiment shown in FIG. 6, if the measurement unit of both Celsius temperature and Fahrenheit temperature is 1 degree or 0.1 degree, two types of frequency division ratios of the sensitivity switching frequency divider 11 are obtained.
There is a relationship between K _C and K _F as shown in equation (15). An embodiment of the sensitivity switching frequency divider 11 that satisfies this relationship is shown in the circuit diagram of FIG. The example circuit uses signals output from two frequency dividers 11a and 11b having division ratios given by K _C and K _F , respectively.
It is configured such that one of F _4C and F _4F is selected by an AND-OR gate 11c controlled by a unit selection signal U to produce an output pulse signal F ₄ . When the measurement unit is 0.1℃ and 0.1〓,
The circuit configuration will be the simplest if the frequency division ratios K _C and K _F are set to 1/9 and 1/5, respectively. In addition, in the same example, if the frequency division ratios K _C and K _F are 1/9 and 1/50, respectively, the thermometer shown in Figure 6 has a measurement unit of 0.1°C for Celsius temperature and 1〓 for Fahrenheit temperature. be able to.

FIG. 10 is a circuit diagram showing another embodiment of the sensitivity switching frequency divider. In this circuit, K _C /
A frequency divider 11d having a frequency division ratio of K _F is provided, and the output signal of the frequency divider 11d is F _4C when measuring temperature in degrees Celsius.
, and when measuring the Fahrenheit temperature, the pulse signal _F2 is selected by the AND-OR gate 11c controlled by the unit selection signal U, and the pulse signal is output.
Output F ₄ . When the measurement units of Celsius temperature and Fahrenheit temperature are both 1 degree or 0.1 degree, the frequency division ratio K _C /K _F of frequency divider 11d is 5/9, and such frequency divider 1
1d is easily achieved by using a 9-base rate multiplier and making its rate input the number 5.

FIG. 11 is also a circuit diagram showing another embodiment of the sensitivity switching frequency divider, in which a frequency divider 11e having a frequency division ratio of K _F /K _C and an AND controlled by a unit selection signal U are shown.
-OR gate 11c. In this circuit, the pulse signal F ₂ directly becomes the pulse signal F ₄ when measuring the temperature in degrees Celsius, and the output signal F _4F of the frequency divider 11e becomes the pulse signal F ₄ when measuring the temperature in degrees Fahrenheit. In this embodiment, if the frequency division ratio K _F /K _C is 9/50, the units of measurement for Celsius temperature and Fahrenheit temperature can be 0.1° C. and 1〓, respectively. Also, such a frequency divider 11e is easily achieved by using a 50-decimal rate multiplier and fixing its rate input to the value 9.

FIG. 12 is also a circuit diagram showing another embodiment of the sensitivity switching frequency divider, in which the rate input data y of the hexadecimal rate multiplier 11f is sent to the data selection circuit 11g controlled by the unit selection signal U. This is a method that allows you to set the settings accordingly. Data selection circuit 11
The rate input data y selected by g has a value of 5 when measuring Celsius temperature and a value of 9 when measuring Fahrenheit temperature. This allows both Celsius and Fahrenheit temperatures to be measured in units of 1 degree or 0.1 degree.

Next, the configuration of the address frequency divider 9 will be specifically explained. The address frequency divider 9 shown in the block diagram of FIG. 6 uses the pulse signal F ₂ as an input signal, and the function of the frequency divider 9 is always the number of pulses of the pulse signal F ₂ corresponding to a constant temperature range. Therefore, any pulse signal may be used as the input signal as long as it is always proportional to the frequency of the pulse signal _F2 . For example, an addressing frequency divider can be considered in which the output signal F _4C or F _4F of the two frequency dividers 11a or 11b of the sensitivity switching frequency divider shown in the circuit diagram of FIG. 9 is used as an input signal. If one pulse of the signal F _4C corresponds to 1°C, one pulse of the output signal of the address frequency divider with the frequency division ratio K _A using the signal F _4C as an input signal is 1/
K _A corresponds to ℃. Therefore, the value of the frequency division ratio K _A is 1/
5, the approximation steps of the line graph shown in FIG. 8 are at intervals of 5°C. Similarly, if one pulse of the signal F _4F corresponds to 1〓, then the output pulse of an address frequency divider with the frequency division ratio K _A using the signal F _4F as an input signal corresponds to 1/K _A 〓, When the value of the frequency division ratio K _A is 1/5, the approximation steps are at intervals of 5〓. Similarly, output signals F _4C and F _4F of frequency dividers 11d and 11e included in the sensitivity switching frequency divider shown in the circuit diagrams of FIGS. 10 and 11 are used as input signals of the address frequency divider. can do. or,
When a signal is extracted from the intermediate frequency dividing stage of the frequency dividers 11a, 11b, 11d, and 11e and used as an input signal of an address frequency divider, or when such frequency dividers are configured with a rate multiplier. It is also possible to use a carry signal from a rate multiplier.

Figure 13 shows the address frequency divider 9 shown in Figure 6.
This is a circuit diagram showing a multi-purpose frequency dividing circuit that can serve as both the frequency divider 11 and the sensitivity switching frequency divider 11, which is extremely convenient in realizing the thermometer of the present invention that can switch between Celsius temperature display and Fahrenheit temperature display. It is a circuit.
In the drawing, the variable frequency divider circuit 7, ROM 8, address counter 10, temperature counter 12, and unit switching circuit 16 are the same as those shown in FIG. 6, so a detailed explanation of each will be omitted. Furthermore, the CR oscillation circuit 6, data selection circuit 13, data latch 14, display device 15, over detection circuit 17, timing circuit 18, and time reference circuit 19 in FIG. 6 are not shown because they are not directly related to the explanation of this circuit diagram. do not have.

In the drawing, 20 and 21 are both frequency dividers, and their respective frequency division ratios are 1/9 and 1/5. The two frequency dividers 20 and 21 correspond to the two frequency dividers 11a and 11b shown in the circuit diagram of FIG. 9, and their output signals are called F _4C and F _4K , respectively. 22, 23, 24, and 25 are signal switching circuits, each of which selects one of the two signals under the control of the unit selection signal U output from the unit switching circuit 16. Such signal switching circuits 22 to 25 are used in practical circuits.
This is normally accomplished with an AND-OR gate, but for the sake of explanation, it is expressed here as a switch with two contacts, P _C and P _F. The switch is closed to the contact P _C side when the unit selection signal U specifies the Celsius temperature, and the contact is closed when the Fahrenheit temperature is selected.
It operates as if it were closed to the P _F side.

Next, the circuit configuration of this example circuit will be explained. CR
The pulse signal F ₁ output from the oscillation circuit 6 is frequency-divided by the variable frequency divider circuit 7 to become the pulse signal F ₂ . The pulse signal F ₂ is guided to a contact P _C of the signal switching circuit 22 and a contact P _F of the signal switching circuit 23 . The output signal F _4F of the frequency divider 21 and the output signal F _4C of the frequency divider 20 are led to the contact P _F of the signal switching circuit 22 and the contact P _C of the signal switching circuit 23, respectively. signal switching circuits 22 and 23
The output signals of are input signals of frequency dividers 20 and 21, respectively. The output signal F _4C of the frequency divider 20 is guided to the contact P _C of the signal switching circuit 23, and
Contact P _C of the signal switching circuit 24 and the signal switching circuit 25
is guided by the contact point P _F. Further, the output signal F _4F of the frequency divider 21 is guided to the contact P _F of the signal switching circuit 22 , as well as to the contact P _F of the signal switching circuit 24 and the contact P _C of the signal switching circuit 25 . The output signal of the signal switching circuit 24 becomes a pulse signal _F4 ,
It is led to a temperature counter 12. Further, the output signal of the signal switching circuit 25 becomes a pulse signal _F3 and is guided to the address counter 10, and by incrementing the address counter 10, the address data A is updated and new frequency division ratio designation data x is sent from the ROM 8.
is now read out.

When measuring the temperature in degrees Celsius with such a configuration, four signal switching circuits 2 are selected by the unit selection signal U.
2, 23, 24, and 25 are all closed to the contact P _C side. As a result, the pulse signal F ₂ is applied to the frequency divider 20 via the signal switching circuit 22, and is frequency-divided by 1/9 to become the signal F _4C . One pulse of the signal F _4C is 1
℃ and is transmitted to the temperature counter 12 as a pulse signal _F4 via the signal switching circuit 24,
The signal is transmitted to the frequency divider 21 via the signal switching circuit 23 and divided into 1/5. As a result, one pulse of the output signal of the frequency divider 21 corresponds to 5°C, and this signal is converted to the pulse signal F ₃ via the signal switching circuit 25.
This is then transmitted to the address counter 10. In this way, the temperature counter 12 can be incremented in 1°C increments, and the address counter 10 can be incremented in 5°C increments.

On the other hand, when measuring Fahrenheit temperature, four signal switching circuits 22, 23, 2 are selected by the unit selection signal U.
4 and 25 are all closed to the contact P _F side. As a result, the pulse signal F ₂ is applied to the frequency divider 21 via the signal switching circuit 23, and the frequency is divided by 1/5 and the signal F _4F
becomes. One pulse of the signal F _4F corresponds to 1〓,
The pulse signal _F4 is transmitted to the temperature counter 12 via the signal switching circuit 24, and is also transmitted to the frequency divider 20 via the signal switching circuit 22, where the frequency is divided by 1/9. As a result, one pulse of the output signal of the frequency divider 20 corresponds to 9〓 (=5℃),
The signal is converted into a pulse signal via the signal switching circuit 25.
F ₃ and is transmitted to the address counter 10.
In this way, the temperature counter 12 can be made to increment in units of 1〓, and the address counter 10 can be made to be incremented in units of 9〓, that is, in units of 5°C.

The operation in the case of Celsius temperature measurement and Fahrenheit measurement has been explained above using the circuit diagram of FIG.
This can be done in units, and at the same time, there is no need to provide the address frequency divider 9 shown in FIG. 6 exclusively.

The operating principle of the thermistor thermometer of the present invention has been described in detail above with reference to the drawings.

According to the present invention, not only can the exponential characteristic of the thermistor be linearly corrected using a purely digital method, but also switching between Celsius temperature display and Fahrenheit temperature display can be achieved with a simple additional circuit. As a result, we have created a digital thermometer that is as convenient as the conventionally widely used glass thermometers and pointer thermometers, but has high accuracy, an easy-to-read display, and can measure both Celsius and Fahrenheit temperatures. It became available at an extremely low price. Furthermore, it has become easy to incorporate various additional functions, as described below, into general household thermometers, which were previously only available in expensive special purpose thermometers. Additional functions include a maximum and minimum thermometer that memorizes the maximum and minimum temperatures and displays them as necessary, a timed thermometer that measures and records the temperature at a fixed time every day in combination with a clock device, and a thermometer that can set the upper or lower temperature limit. Convenient functions include a thermometer with an alarm that issues an alarm when the temperature is outside the temperature range, an average thermometer that calculates and displays the daily average temperature, and the like. Moreover, the measurement units of these thermometers can be easily and freely switched between Celsius and Fahrenheit as needed. This expands the sales channels for thermometers as a product and makes mass production possible, leading to lower prices.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the CR oscillation circuit used in the present invention, and FIGS. 2 and 4 show the number N of pulses output from the CR oscillation circuit in FIG. 1 during a unit time. Figures 3 and 5 are graphs showing examples of line graphs approximated to the graphs in Figures 2 and 4, respectively, and Figure 6 is a graph showing the relationship between Celsius temperature and Fahrenheit temperature. Block diagram showing a configuration example of a thermometer according to an embodiment of the invention, No. 7
Figures A, B, and C are signal waveform diagrams for explaining the operation of the block diagram in Figure 6. In Figure 8, the horizontal axis is the number of pulses N of the pulse signal _F1 , and the vertical axis is the number of pulses N of the pulse signal _F2 . This is a line graph for explaining the operation of the block diagram in FIG. 6, which is shown by the cumulative number of pulses M, and the cumulative number of pulses M _C and M _F of the pulse signal _F4 , and is a line graph for explaining the operation of the block diagram in FIG. 12 and 12 are circuit diagrams showing each embodiment of the sensitivity switching frequency divider shown in FIG. 6, and FIG. 13 shows the address frequency divider and sensitivity switching frequency divider shown in FIG. 6. FIG. 2 is a circuit diagram showing an embodiment in which the frequency divider is a common frequency divider. 1...Thermistor, 2...Capacitor, 6...
CR oscillation circuit, 11c...AND-OR gate, 1
1a, 11b, 11d, 11e, 20, 21...
Frequency divider, 11f... 4-bit binary rate multiplier, 22, 23, 24, 25... Signal switching circuit.

Claims (1)

[Claims] 1. A CR oscillation circuit including a thermistor as a specific number of resistors, a variable frequency division circuit whose frequency division ratio can be set and whose input signal is a signal output from the CR oscillation circuit, and the variable frequency division circuit. an address frequency divider that counts pulse signals output from the address frequency divider, an address counter that counts the output signal of the address frequency divider, and frequency division of the variable frequency divider circuit according to an increase in the count value of the address counter. A read-only memory that sets the ratio in a direction that decreases the frequency of the output signal of the variable frequency divider circuit, a temperature counter that counts the pulse signal output from the variable frequency divider circuit, and a temperature measurement device that measures the counted value of the temperature counter. A thermistor thermometer characterized by being equipped with a display device for displaying the value. 2. A CR oscillation circuit that includes a thermistor as a specific number of resistors, a variable frequency divider circuit whose frequency division ratio can be set and whose input signal is the signal output from the CR oscillation circuit, and a pulse signal output from the variable frequency divider circuit. an address frequency divider that counts output signals of the address frequency divider; and an address counter that counts output signals of the address frequency divider; a read-only memory that sets the frequency of the output signal of the circuit in a direction that decreases; a sensitivity switching frequency divider that counts the pulse signal output from the variable frequency divider circuit and whose frequency division ratio can be switched to two levels; , a unit switching circuit that supplies a switching signal for specifying switching between Celsius temperature and Fahrenheit temperature to the sensitivity switching frequency divider, and sets each initial value corresponding to Celsius temperature and Fahrenheit temperature in the address counter; a temperature counter that counts pulse signals output from the sensitivity switching frequency divider; and a temperature counter that converts the counted value of the temperature counter into degrees Celsius and Fahrenheit temperatures that respectively correspond to the two-stage division ratio of the sensitivity switching frequency divider. A thermistor thermometer characterized by comprising a display device for displaying each temperature measurement value.