JP2623779B2 - Temperature measuring device - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to a temperature measuring device using a temperature measuring resistor whose resistance value changes with a temperature change.

[Prior art and its problems] Conventionally, there is provided a CR oscillation circuit having a thermistor and a capacitor whose resistance value changes according to temperature, and a temperature measuring device that obtains a temperature by utilizing the fact that the oscillation cycle of the CR oscillation circuit changes according to temperature. There is. In such an apparatus, a reference oscillator that includes a crystal oscillator and sends out a reference pulse having a constant cycle is used for measuring the oscillation cycle of the CR oscillation circuit. That is, the number of pulses transmitted from the reference oscillator during the oscillation cycle of the CR oscillator (or a fixed multiple of the cycle, for example, three cycles) is counted.

By the way, the pulse width and period of the reference pulse are CR
A smaller one is preferable in terms of accurate measurement of the oscillation period of the oscillation circuit, but there is a limit due to various circumstances. Therefore, as the oscillation cycle of the CR oscillation circuit, that is, the cycle to be measured, becomes smaller due to the temperature, the count number of the reference pulse for measuring the cycle becomes smaller, and an odd reference pulse at the start and end of counting is counted or not counted. The error due to the loss can no longer be ignored. That is,
In such a conventional temperature measuring device, depending on the temperature range,
There was a problem that the measurement accuracy was different.

[Object of the Invention] The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a temperature measurement device in which measurement accuracy does not change irrespective of low temperature and high temperature.

[Summary of the Invention] In order to achieve the above object, the present invention is required to obtain an approximate temperature or a value corresponding thereto in the first stage, and to measure the temperature with a certain accuracy in the temperature range in the second stage. The gist is that a suitable measurement condition is selected and the temperature is measured under the selected condition.

Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings.

FIG. 1 shows a circuit configuration of the present embodiment, in which a reference oscillator 1 is a circuit for transmitting a 32 KHz reference pulse signal φ, and a timing pulse generation circuit 2 is a circuit for transmitting a reference pulse signal φ.
Is a circuit that generates a two-minute signal M and other timing pulse signals transmitted every two minutes based on the above, and transmits them to the CPU 3. CPU3 has various registers M _A , M _B , M _C , MS
1, a circuit having MS1, ST, and exchanging data and signals with each circuit unit based on a program in the ROM 4 and controlling each circuit unit. The ROM 4 fixedly stores a microprogram for controlling the operation of the CPU 3, a table described later, and the like. The display unit 5 is a circuit unit that displays the temperature based on the temperature data from the CPU 3. The NAND gate 6 receives the operation command signal ON from the CPU 3 and the reference pulse signal φ from the reference oscillator 1, and sends out a logical product of these. Inverter 7
Inverts the signal transmitted from the NAND gate 6 and supplies the inverted signal to the reference pulse counter 8. When the operation command signal ON is at the H level, the reference pulse counter 8 counts the reference pulse signal φ sent through the NAND gate 6 and the inverter 7 and constantly outputs the count data to the CPU 3.
A 1/32 second signal a is sent to the CPU 3 after the elapse of 1/32 second from the start of the temperature measurement, and the count data is cleared by receiving a reset signal RE described later. The latch circuit 9 is a circuit in which the measurement pulse number data sent from the CPL 3 is set.

The inverter 10 inverts the operation command signal ON, and the NOR gate 11 gives the OR of the signal from the inverter 10 and the stop command signal STO from the coincidence detection circuit 14 to the CR transmission circuit 12 as an oscillation command signal AC. The CR oscillation circuit 12 has a circuit configuration according to the thermistor selection signal SE from the CPU 3, receives the oscillation command signal AC, and sends out a pulse wave f having a frequency corresponding to the temperature at that time. The CR counter 13 is an n-digit counter for counting the number of pulses of the pulse wave f, and each digit data is sent to the coincidence detection circuit 14 and the CPU 3. The coincidence detection circuit 14 starts operation in response to the operation command signal b from the CPU 3, compares the number of measured pulses set in the latch circuit 9 with the number of pulses counted by the CR counter 13, and stops when the two coincide. This is a circuit for sending a command signal STO to the NOR gate 11 and the CPU 3.

FIG. 2 shows the configuration of the CR oscillation circuit 12 in detail. That is, the output terminal of said oscillation command signal AC is input reference resistor to the other input terminal P ₂ R ₀ and NAND gate 23 to which one end of the capacitor C ₀ is connected from C-MOS to one input terminal P ₁ To the input terminal of the inverter 24. The output terminal of the inverter 24 is connected to the capacitor C _0.
And an input terminal of an inverter 25 made of CMOS. The output terminal P _OUT of the inverter 25 to which the pulse wave f is transmitted is connected to the switching transistor 20 and the switching transistor 21. The switching transistor 20 and the switching transistor 21 are opened by a signal obtained by inverting the thermistor selection signal SE by the inverter 22 and the thermistor selection signal SE, respectively, and a reference resistor R ₀ or a reference resistor R is provided between the output terminal P _OUT and the input terminal P _2.
Connect a series circuit of _R0 and thermistor _RTH . Thermistor R
_TH has a negative temperature coefficient, and the resistance value decreases as the temperature rises as shown in FIG. The reference resistor _R0 is a resistor whose resistance value does not change with temperature.

In the following description, the thermistor R _TH and the reference resistance R _0
Are R _TH and R ₀ , respectively, and the capacitance of the capacitor C ₀ is C ₀ .

In such a circuit configuration, the oscillation command signal AC is H
When it reaches the level, oscillation starts and the thermistor selection signal SE goes high.
Oscillation period MS when switching transistor 21 is open and switching transistor 20 is closed at the level
Is expressed as follows, where k is a constant proportional constant. MS = k C ₀ (R ₀ + R _TH ) Further, when the thermistor selection signal SE is at the L level, the switching transistor 20 is opened and the switching transistor 21 is opened.
The oscillation cycle ST when is closed is expressed as follows.

ST = k C ₀ , R ₀ ... The configuration of the CR oscillator is not limited to the thermistor R _TH alone, but the thermistor R _TH and the reference resistor R ₀ connected in series or only the reference resistor R _0. and, to obtain a pulse wave f of the oscillation cycle MS and ST, the reference resistance R ₀ is in this embodiment will be described below to remove the influence due to aging or the like of the dispersion or the capacitor C ₀ of the capacitor C ₀ temperature This is to take a measurement method.

Measurement Principle Next, the temperature measurement principle in this embodiment will be described.

The above reference resistor R ₀ , thermistor R _TH and capacitor C ₀
Is appropriately selected to constitute the CR oscillation circuit 12, and n obtained by the following equation is obtained from the oscillation periods MS and ST, and the relationship between the n and the temperature is experimentally obtained. For example, as shown in FIG. Become.

For this reason, the relationship as shown in FIG. 4, that is, each value of n and the temperature corresponding to it may be stored in advance in detail, and the temperature may be obtained from this and the obtained n. , N and the temperature, the storage capacity of the memory must be greatly increased. Further, a method of directly approximating the relationship shown in FIG. 4 to obtain a temporary function expression of n representing temperature, storing this, and calculating the temperature from this expression and n obtained as described above. However, in this case, the error due to the direct approximation becomes too large. Therefore, the present embodiment employs the following method.

First, a curve indicating the relationship between temperature and n as shown in FIG. 4 is linearly approximated at intervals of 5 ° C. to obtain a relationship with n by a plurality of straight lines as shown in FIG. Next, the equations of these straight lines are set as follows (where T is temperature and a and b are positive coefficients).

T = b−an..., And the specific value of b for each straight line, that is, b ₁ ,
b ₂ , b ₃ ... and specific values of a, ie, a ₁ , a ₂ , a ₃
Are obtained and stored in the ROM 4 (see FIG. 1) in the form of a table corresponding to n as shown in FIG. 6, for example. Then, at the time of temperature measurement, specific values of a and b to be used are obtained from the above table from the value of n obtained as described above, and the temperature is obtained from these, n and the above equation.

Operation Next, the specific operation of the present embodiment configured as described above and measuring the temperature by the above-described method will be described with reference to the flowchart of FIG. 7 and the time chart of FIG.

When the power is turned on, a reference pulse signal φ of 32 KHz is transmitted from the reference oscillator 1 as shown in FIG. Then, as shown in FIG. 7B, when a two-minute signal M transmitted every two minutes is transmitted from the timing pulse generation circuit 2 (see FIG. 1) and the measurement timing is reached, the timing shown in FIG. This is detected in step S1, and then in step S2, the thermistor selection signal SE is set to H level and sent to the CR oscillation circuit 12 (first
See figure). As a result, the switching transistor 21 shown in FIG. 2 is turned on, and the resistance in the CR oscillation circuit 12 is the one obtained by connecting the reference resistances _R0 and _RTH in series. Thereafter, the operation command signal ON is transmitted at the H level as shown in FIG. 8 (c) (step S3).
Is inverted to an L level by an inverter 10 (see FIG. 1), which is given to a CR counter 13 and a reference pulse counter 8 as a reset signal RE. That is, as shown in FIG. 8 (d), at this time, the reset signal RE goes to the L level, and the CR counter 13 and the reference pulse counter 8 are released from the reset state and enter the countable state. Further, the reset signal RE is the NOR gate 1 to which the stop command signal STO at L level (see FIG. 8 (f)) is input.
It is inverted by 1 and becomes H level.
The signal is supplied to the oscillation circuit 12. That As shown in Figure 8 (e), the oscillation command signal AC at this point becomes the H level, which is input to the NAND gate 23 is applied to the input terminal P ₁ of the CR oscillation circuit 12 shown in Figure 2. H level oscillation command signal AC
There CR oscillation circuit 12 by input to the NAND gate 23 begins to sends such pulses wave f shown in Figure 8 (g) from the output terminal P _OUT starts oscillating. In this case, since the resistance value of the resistor in the CR oscillation circuit 12 is (R ₀ + R _TH ), the oscillation cycle MS ₁ becomes kC ₀ (R ₀ + R _TH ) as described above, and R _TH depends on temperature. since the value of which is assumed to oscillation cycle MS ₁ also reflects the temperature.

The pulse wave f is sent to the CR counter 13 (see FIG. 1), and the CR counter 13 counts it (see FIG. 8 (h)).

On the other hand, the reference pulse counter 8 whose reset state is released by the aforementioned reset signal RE counts the reference pulse signal φ from the reference oscillator 1 sent via the NAND gate 6 and the inverter 7 and reaches the above measurement timing. The elapsed time from the occurrence of this is measured (see FIG. 8 (R)).

The above operation is continued, and when 1/32 second has elapsed from the time when the measurement timing has been reached, a 1/32 second signal a is transmitted from the reference pulse counter 8 (see FIG. 8 (N)). This is detected in step S4, and the process proceeds to step S5.
Then, in step S5, the count number of the CR counter 13, that is, the number of oscillations of the CR oscillation circuit 12 in 1/32 second is read,
This is set in the register M _A which is incorporated in the CPU 3 (see FIG. 1). Then it obtains the highest bit of the digit a that is the first case of displaying number of oscillations that have been set in the register M _A 2 binary (step S6), and was added to 2 to the a (a + 2) th bit of the digit There Searching for the digits following data for each bit 0 at 1, and sets it in the register M _C that are incorporated in the latch circuit 9 and the CPU 3 (step S7). That is, when the oscillation number set in the register M _A is, for example, 111101 to binary representation, the latch circuit 9
And the register M _C is the binary representation the number 10000000 is set.

After that, in step 8, the operation command signal b is sent out as shown in FIG. As a result, the coincidence detecting circuit 14 takes in the set value of the latch circuit 9 and the count value of the CR counter 13 and compares them.

Thereafter, the CR counter 13 outputs the pulse wave f from the CR oscillation circuit 12.
, The reference pulse counter 8 continues counting the reference pulse signal φ sent from the reference oscillator 1 via the NAND gate 6 and the inverter 7. Then, the count number of the CR counter 13 increases, and the latch circuit 9
When the set value is equal to the set value set in, a stop command signal STO is sent from the coincidence detecting circuit. The stop command signal STO is sent to the NOR gate 11, whereby the oscillation command signal AC becomes L level, and the oscillation of the CR oscillation circuit 12 stops. The stop command signal STO is also sent to CPU3 and
3 detects this in step S9, and proceeds to step S10. In this step, the current reference pulse counter 8
Set the count value (i.e., a value proportional to time since reached the measurement timing) to read the register M _B,
Then dividing the value of the register M _B by the value of the register M _C (i.e. also the number of oscillations of the count value, that is the CR oscillation circuit 12 of it and CR counter 13 is latched value of the latch circuit 9), as a result, that CR oscillator A value proportional to the oscillation cycle of the circuit 12 is set in the register MS1 (step S11). Next, as shown in FIG. 8 (c), the operation command signal ON is set to L (step S12), the reset signal RB is set to H level as shown in FIG. 8 (d), and the CR counter 13 and the reference pulse counter 8 are reset. And Further, as shown in FIG. 8 (L), the operation command signal b is set to the L level to stop the operation of the coincidence detecting circuit 14 (step S13). By the above operation, a value proportional to the above-described oscillation cycle MS is set in the register MS1.

Next, at step 20, the thermistor selection signal SE is set to L level, and the resistance of the CR oscillation circuit 12 is set to only the reference resistance _R0 . Then, the operation command signal ON is set to the H level again, the oscillation command signal AC is set to the H level (step S21), the reset state of the CR counter 13 and the reference pulse counter 8 is released, and the reference pulse counter 8 starts counting, and The oscillation circuit 12 restarts oscillation. In this case, the oscillation cycle is different from the previous one and becomes kC ₀ R _{0 as} described above, and the pulse wave f is sent to the CR counter 13 as in the previous case, and the CR counter 13 starts counting the pulse wave f of the above oscillation cycle. When the count value of the CR counter 13 reaches the set value of the latch circuit 9, a stop command signal STO is sent from the coincidence detecting circuit 14, whereby the oscillation command signal AC becomes L level and the CR oscillation circuit 12 Oscillation stops. In step S22, the CPU 3 detects the stop command signal STO and determines a value proportional to the count value of the reference pulse counter 8, that is, the time during which the oscillation is performed in the oscillation cycle (the proportional constant in this case is kC ₀ (R ₀ +
Last time value proportional to R _TH) period in outgoing ropes time of the same as the proportional constant of the value set in the register M _B. ) It was set in the register M _B (step S23), dividing this value by value or number of oscillations of the register M _C, and sets a value proportional to the result i.e. oscillation cycle in the register ST (step S24). Thereafter, the operation command signal ON is set to L level (step S25), the CR counter 13 and the reference pulse counter 8 are reset, and the operation command signal b is set to L level to stop the operation of the coincidence detection circuit 14 (step S25).
S26).

By the above operation, a value proportional to the above-described oscillation cycle ST (the proportionality constant is the same as the value set in the register MS1) is set in the stop command signal ST.

Next, in order to obtain an accurate value of the value set in the register MS1, that is, a value proportional to the oscillation period kC ₀ (R ₀ + R _TH ), the same value is obtained again, and the average of two measured values is obtained. That is, in steps S30 and S31, steps T2 and
The CR oscillation circuit 12 sends out a pulse wave f having an oscillation cycle kC ₀ (R ₀ + R _TH ) again, and the CR counter 13
Starts counting, and the reference pulse counter 8 counts the signal φ to measure the elapse of time. And steps S32 to S36
In a generally similar operation as the step S9~S13 is performed again, after a value proportional to the oscillation period when the resistance of the CR oscillation circuit _{12 (R 0 + R TH)} , and sets it in the register MS2.

As described above, the resistance of the CR oscillation circuit 12 is set to (R ₀ + R _TH )
The value proportional to the oscillation cycle is calculated twice, and they are set in the registers MS1 and MS2, respectively.
A value proportional to the oscillation cycle when the resistance of the oscillation circuit 12 is set to the reference resistance _R0 is set in the register ST. Note that the register
The proportional constants between the values set in MS1, MS2, and ST and the corresponding oscillation periods are all the same.

Thereafter, the value of the register ST is subtracted from the arithmetic average of the set values of the registers MS1 and MS2, and the result is further divided by the value of the register ST and multiplied by 100 to calculate the aforementioned n (step S37). . Note that the value of each register is not the oscillation cycle itself, but is a value proportional to each oscillation cycle with the same proportionality constant, so that the operation is equivalent to the operation according to the above equation. Based on n obtained in this manner, the coefficients a and b of the approximate straight line to be used are read from the table of the ROM 4 (step S38), and the temperature T is calculated based on the following equation.
Is calculated (step S39).

T = b-an Then, in step S40, the obtained temperature T is displayed on the display unit 5, and the process returns to step S1 to wait for the next measurement timing.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the present invention.

[Effects of the Invention] As described in detail above, the present invention is required to obtain an approximate temperature or a value corresponding to the approximate temperature in the first stage and measure the temperature in the temperature range with constant accuracy in the second stage. Since the present invention relates to a temperature measuring device that selects a suitable measuring condition and measures the temperature under the selected condition, it is possible to provide a temperature measuring device in which the measurement accuracy does not change regardless of a low temperature or a high temperature.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration of an embodiment of the present invention, FIG. 2 is a diagram showing a detailed configuration of a CR oscillation circuit in FIG. 1,
FIG. 3 is a diagram showing a temperature characteristic of a thermistor used in the CR oscillation circuit, FIG. 4 is a diagram showing an embodiment of a relationship between n calculated from the oscillation cycle of the CR oscillation circuit and temperature, and FIG. FIG. 6 is a table showing a curve obtained by approximating the curve in FIG. 4 with a plurality of straight lines, and FIG. 6 is a table showing the coefficients a and b of the equation of each straight line in FIG. , FIG. 7 is a diagram showing the operation of the present embodiment, and FIG. 8 is a time chart of various signals. 1. Reference oscillator 2. Timing pulse generation circuit
3 CPU, 4 ROM, 5 Display section, 8 Reference pulse counter, 9 Latch circuit, 12 CR oscillation circuit, 13
…… CR counter, 14… Match detection circuit, 20, 21 …… Switching transistor, R ₀ …… Reference resistance, R _TH … Thermistor, C ₀ … Capacitor, P ₁ , P ₂ …… Input terminal, P _OUT
…… Output terminals, M _A , M _B , M _C , MS1, MS2, ST …… Register.

Claims (1)

(57) [Claims] An oscillator having a temperature measuring resistor whose resistance value changes with a temperature change, an oscillation frequency of which changes according to temperature, and a detecting means for detecting the number of pulses output from the oscillator within a predetermined time Measuring pulse calculating means for calculating the number of measuring pulses according to the number of pulses detected by the detecting means; reference pulse generating means for outputting a reference pulse having a constant frequency; and the measuring pulse number calculating means from the oscillator. A reference pulse counting means for counting the number of reference pulses output from the reference pulse generating means while the determined number of measurement pulses is output; and a reference pulse number obtained by the reference pulse counting means and the measurement pulse. A temperature measuring device, comprising: temperature calculating means for obtaining a temperature from the number of measurement pulses obtained by the number calculating means.