JPH04109132A - Temperature sensor sensitivity-variable circuit - Google Patents

Abstract

PURPOSE:To realize the maximum sensitivity and precision in the subject temperature range by controlling a variable resistor means so that the divided voltage value divided by the resistance value of the variable resistor means and the equivalent resistance value of a thermistor is approximated to the preset voltage value. CONSTITUTION:An A/D conversion section 3 samples the divided voltage AN divided by the equivalent resistance value RS of a switch and a capacitor 1 by pulses from a pulse controller 5 and the equivalent resistance value RT of an NTC type thermistor 2 by the temperature at that time, the sampling value is digitally converted by VREF and VSS and sent to the controller 5. The controller 5 generates pulses to the capacitor 1 and the frequency so that the resistance values RS and RT are made equal based on the digital value and the data from a table memory section 4. The resistance value RS when the change of the pointer P of the pulse frequency (f) - resistance value RS table 4a is converged is read out from the table 4a, it is judged that the values RS = RT, and the temperature T corresponding to the resistance value RT is read out from the temperature T - resistance value RT table 4b to complete the processing.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a temperature sensor sensitivity variable circuit, and more particularly to a temperature sensing method using an NTC (negative characteristic) type thermistor whose equivalent resistance value changes logarithmically in accordance with the measured temperature.

Prior Art Conventionally, in this type of temperature sensing method, the temperature sensing sensitivity is fixed within the temperature range of the measurement target, and the upper limit of accuracy is uniformly determined by the circuit.

In such conventional temperature sensing methods, the temperature range to be measured is fixed, and depending on the circuit, the sensitivity and accuracy are also fixed. The disadvantage is that it is not possible to change the temperature range.

Purpose of the Invention The present invention was made in order to eliminate the drawbacks of the conventional ones as described above, and the purpose of the present invention is to provide a temperature sensor sensitivity variable circuit that can obtain maximum sensitivity and accuracy in the temperature range to be measured. shall be.

Structure of the Invention The temperature sensor sensitivity variable circuit according to the present invention is a temperature sensor sensitivity variable circuit for a temperature sensor that uses a thermistor whose equivalent resistance value changes depending on the measured temperature, and which changes the resistance value depending on an input control signal. storage means for storing the control signal and the resistance value corresponding to the control signal; and control means for variably controlling the variable resistance means using the control signal stored in the storage means. ,
a comparison means for comparing a predetermined voltage value with a divided voltage value divided by the resistance value of the variable resistance means variably controlled by the control means and the equivalent resistance value of the thermistor; and the comparison means calculation means for calculating the temperature sensed by the thermistor based on the resistance value corresponding to the control signal to the variable resistance means when it is detected that the divided voltage value and the predetermined voltage value are approximate; It is characterized by having the following.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, a switched capacitor (SC) 1 has a property that the equivalent resistance value R5 decreases in inverse proportion to the frequency of the human pulse, and an NTC (negative characteristic) type thermistor 2 has an equivalent resistance value RT that decreases logarithmically depending on the temperature. It has the property of decreasing.

An analog/digital converter section (ADC) 3 samples an analog voltage (hereinafter referred to as a divided voltage) AN divided by the equivalent resistance value R3 of the switched capacitor 1 and the equivalent resistance value R3 of the NTC type thermistor 2, It has a function of digitally converting the sampled value using V REF and VSS and encoding it.

The table storage unit 4 is a pulse frequency-equivalent resistance value (f-Rs) table (hereinafter f
-R, table) 4a, and a temperature-thermistor resistance value (TRt) table (hereinafter referred to as T-RT) that stores information indicating the characteristics of the equivalent resistance value RT of the NTC type thermistor 2 used and the temperature T. Table 4b).

The pulse controller section (CNT) 5 converts the equivalent resistance value R8 of the switched capacitor 1 into the equivalent resistance value R of the NTC type thermistor 2 based on the sampling value digitally converted by the analog/digital converter section 3 and the data from the table storage section 4. The pulse to the switched capacitor 1 and its frequency are generated to be equal to the frequency.

1 chip microcomputer (l chip MPU
) 6 is the above analog/digital converter section 3,
It has a built-in table storage section 4 and a pulse controller section 5.

FIG. 2 shows the fRs table 4 in the table storage section 4 of FIG.
It is a figure showing a and T-RT table 4b. FIG. 2(a) is a diagram showing the f-RS table 4a of the table storage unit 4, and the f-RS table 4a includes the pulse frequency f to the switched capacitor 1 and the pulse frequency f when the pulse frequency f is supplied. 2N equivalent resistance values R5 of the switched capacitor 1 are stored.

That is, in the f-RS table 4a, as the pulse frequency f increases, the equivalent resistance value R5 of the switched capacitor 1 decreases, or as the pulse frequency f decreases, the equivalent resistance value R5 of the switched capacitor 1 increases. The pulse frequency f and the equivalent resistance value R5 are stored in association with each other.

FIG. 2(b) shows the TRT table 4b in the table storage section 4.
2N temperatures T corresponding to the equivalent resistance value RT of the NTC type thermistor 2 which is equivalent to the equivalent resistance value R5 of the switched capacitor 1 are stored in the TR table 4b.

FIG. 3 is a diagram for explaining the principle of one embodiment of the present invention. In the figure, when the equivalent resistance value R5 of the switched capacitor 1 and the equivalent resistance value R of the NTC type thermistor 2 are equal (Rs - R,), the amount of fluctuation in the divided voltage AN (hereinafter referred to as the amount of divided voltage fluctuation) ) ΔAN becomes maximum.

That is, as the equivalent resistance value R8 of the switched capacitor 1 becomes larger than the equivalent resistance value RT of the NTC type thermistor 2 (R5>RT), or the switched capacitor 1
The smaller the equivalent resistance value R3 of the NTC type thermistor 2 is than the equivalent resistance value RT of the NTC type thermistor 2 (R5 - RT), the smaller the divided voltage fluctuation amount ΔAN becomes.

As this divided voltage fluctuation amount ΔAN increases, the temperature at the center of the temperature range to be measured by the NTC type thermistor 2 can be measured with better sensitivity and accuracy. The pulse frequency f to the switched capacitor 1 may be generated by the pulse controller section 5 so as to be equal to the equivalent resistance value R7 of 2.

Therefore, the pulse controller section 5 sets the digital output of the analog/digital converter section 3 obtained by sampling the divided voltage AN to be VCC/2.
The pulse frequency f to the switched capacitor 1 may be generated by sequentially reading the values of the f-Rs child table a.

FIG. 4 is a flowchart showing the operation of one embodiment of the present invention. The operation of one embodiment of the present invention will be explained using these FIGS. 1 to 4.

First, in order to initialize the equivalent resistance value R8 of the switched capacitor 1, the pulse controller section 5
Set the address of pointer P in table 4a to N/2 (step 11 in FIG. 4), read out the pulse frequency f from f-R specified by this pointer P, the address in table 4a, that is, address N/2, and switch. Generate a pulse to capacitor 1 (step 12 in Fig. 4)
゜13).

At this time, in the analog/digital converter section 3, the voltage is divided by the equivalent resistance value R5 of the switched capacitor 1 due to the pulse from the pulse controller section 5 and the equivalent resistance value R7 of the NTC type thermistor 2 due to the temperature at that time. The divided voltage AN is sampled, and the sampled value is digitally converted by VREF and V55 and sent to the pulse controller section 5 (Step 1 in Fig. 4).
4).

The pulse controller section 5 receives sampling data D converted into digital data by the analog/digital converter section 3.
and VCo/2 previously held. If the sampling data D is larger than Vcc/2 (D>Vcc/2) (Step 16 in FIG. 4),
It is determined that the equivalent resistance value R3 of the switched capacitor 1 is smaller than the equivalent resistance value RT of the NTC type thermistor 2, and f-
R, adds 1- to the address of pointer P in table 4a (step 17 in FIG. 4).

Also, the above comparison shows that the sampling data D is Vcc/
If smaller than 2, (D < V cc/2) (
Step 16) in FIG. 4, it is determined that the equivalent resistance value R5 of the switched capacitor 1 is larger than the equivalent resistance value RT of the NTC type thermistor 2, and the pointer P of the f-Rs child table a is
1 is subtracted from the address (step 18 in FIG. 4).

After that, the pulse controller unit 5 determines whether the change in the pointer P of the f-RS child table a has converged (step 19 in FIG. 4), and the change in the pointer P of the f-RS table 4a must have converged. For example, R3<RT or R
5> f determined to be RT and 1 above added or subtracted
- Read the pulse frequency f from the address in the R5 table 4a and generate a pulse to the switched capacitor 1 (
Figure 4 Step 12.13).

On the other hand, if the change in the pointer P of the f-Rs child table a converges, it is determined that R5#RT, and the equivalent resistance value R5 of the switched capacitor 1 is calculated from the address of the pointer P of the f-R5 table 4a at that time. Read (Step 20 in Figure 4)
).

The pulse controller unit 5 determines that the read equivalent resistance value R5 of the switched capacitor 1 is equal to the equivalent resistance value RT of the NTC type thermistor 2 (step 21 in FIG. 4).
, the temperature T corresponding to the equivalent resistance value RT of the NTC type thermistor 2 is read out from the T-R7 table 4b, and the process is completed (step 22 in FIG. 4).

In this way, by controlling the input pulse frequency of the switched capacitor 1 configured serially with the NTC type thermistor 2 by the pulse controller section 5, maximum sensitivity and accuracy can be obtained in the temperature range of the measurement target. I can do it.

In addition, the analog/digital converter section 3, table storage section 4, and pulse controller section 5, that is, the necessary hardware, are integrated into a single chip microcomputer 6.
The above effects can be easily achieved by incorporating it into the .

Although the switched capacitor 1 and the NTC type thermistor 2 have been described in one embodiment of the present invention, it is obvious that the present invention can be applied to other variable resistance elements and other thermistors, and is not limited thereto.

As described in detail, according to the present invention, a divided voltage value divided by the resistance value of the variable resistance means whose resistance value is variable according to the input control signal and the equivalent resistance value of the thermistor and a predetermined By variably controlling the variable resistance means using a control signal so that the set predetermined voltage value is approximate, maximum sensitivity and accuracy can be obtained in the temperature range to be measured. There is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 2(a) shows the pulse frequency of the table storage section in FIG.
FIG. 2(b) is a diagram showing an equivalent resistance value table, FIG. 2(b) is a diagram showing a temperature-thermistor resistance value table in the table storage section of FIG. 1, and FIG. 4 are flowcharts showing the operation of one embodiment of the present invention. Explanation of symbols of main parts 1...Switched capacitor 2...NTC type thermistor 3...Analog/digital converter section 4.
...Table storage section 4a...Pulse frequency-equivalent resistance value table 4
b...Temperature-thermistor resistance table 5...
...Pulse controller section

Claims (1)

[Claims] (1) A temperature sensor sensitivity variable circuit for a temperature sensor using a thermistor whose equivalent resistance value changes depending on the measured temperature, comprising variable resistance means whose resistance value changes according to an input control signal, and the control storage means for storing a signal and the resistance value corresponding to the control signal; control means for variably controlling the variable resistance means according to the control signal stored in the storage means; a comparison means for comparing the divided voltage value divided by the resistance value of the variable resistance means and the equivalent resistance value of the thermistor with a preset predetermined voltage value; and calculation means for calculating the temperature sensed by the thermistor based on the resistance value corresponding to the control signal to the variable resistance means when it is detected that the voltage value is approximate. Sensor sensitivity variable circuit.