JP2569924B2 - Temperature sensor sensitivity variable circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature sensor sensitivity variable circuit, and more particularly, to a temperature sensor system using an NTC (negative characteristic) type thermistor whose equivalent resistance value changes logarithmically according to a measured temperature.

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

In such a conventional temperature sensing method, the temperature range to be measured is fixed, and the sensitivity and accuracy are fixed depending on the circuit. However, there is a disadvantage in that the temperature range in which

SUMMARY OF THE INVENTION The present invention has been made to eliminate the above-mentioned drawbacks of the prior art, and has as its object to provide a temperature sensor sensitivity variable circuit capable of obtaining maximum sensitivity and accuracy in a temperature range to be measured. And

A temperature sensor sensitivity variable circuit according to the present invention is a temperature sensor sensitivity variable circuit of a temperature sensor using a thermistor whose equivalent resistance value changes according to a measured temperature, and the resistance value varies according to an input control signal. Variable resistance means, 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 by the control signal stored in the storage means. Comparing means for comparing a resistance value of the variable resistance means variably controlled by the control means and a divided voltage value divided by an equivalent resistance value of the thermistor with a predetermined voltage value set in advance; When the divided voltage value and the predetermined voltage value are detected to be approximate by the means, the resistance value corresponding to the control signal to the variable resistance means is used. Calculating means for calculating the temperature sensed by the thermistor.

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 one embodiment of the present invention. In the figure, a switched capacitor (SC) 1 has a property that an equivalent resistance value R _S decreases in inverse proportion to the frequency of an input pulse, and an NTC (negative characteristic) type thermistor 2 has an equivalent resistance value R _T depending on temperature and a logarithmic function. It has the property of being reduced.

Analog / digital converter (ADC) 3 is (or less divided voltage) analog voltage divided by the equivalent resistance R _T of the equivalent resistance R _S and NTC thermistor 2 of the switched capacitor 1 sampling A _N It has a function of digitally converting the sampled value by V _REF and V _SS and encoding it.

The table storage unit 4 stores a pulse frequency-equivalent resistance (f−R _S ) table (hereinafter referred to as f−R _S ) in which the equivalent resistance value R _S of the switched capacitor 1 and the pulse frequency f are stored in correspondence with each other.
R and _S table) 4a and the temperature information indicating the characteristic of the equivalent resistance R _T and the temperature T of the NTC type thermistor 2 are using is stored - thermistor resistance (T-R _T) table (hereinafter T-R and _T table) is composed of a 4b.

The pulse controller unit (CNT) 5 determines the equivalent resistance value R _S of the switched capacitor 1 based on the sampling value digitally converted by the analog / digital converter unit 3 and the data from the table storage unit 4 to the NTC thermistor 2.
Of the switched capacitor 1 and the frequency thereof are generated so as to be equal to the equivalent resistance value _{RT of} .

The one-chip microcomputer (1 chip MPU) 6 includes the analog / digital converter 3, the table storage 4, and the pulse controller 5.

FIG. 2 is an f- _RS table of the table storage unit 4 of FIG.
It is a diagram showing 4a and T-R _T table 4b. Figure 2 (a) is a diagram showing an f-R _S Table 4a of the table storage unit 4, f-R _S the table 4a switched capacitor 1
And the equivalent resistance value R _S of the switched capacitor 1 when the pulse frequency f is supplied is 2 ^N
Are stored.

That is, the f- _RS table 4a indicates that the equivalent resistance value R _S of the switched capacitor 1 decreases as the pulse frequency f increases, or the equivalent resistance value R _S of the switched capacitor 1 decreases as the pulse frequency f decreases. _The pulse frequency f and the equivalent resistance value R _S are stored in association with each other so that _S increases.

FIG. 2 (b) shows the T- _RT table 4b of the table storage unit 4.
In the T- _RT table 4b, ^2N temperatures T corresponding to the equivalent resistance value _RT of the NTC type thermistor 2 equivalent to the equivalent resistance value _RS of the switched capacitor 1 are stored.

FIG. 3 is a diagram for explaining the principle of one embodiment of the present invention. In the figure, when the equivalent resistance R _T of the equivalent resistance R _S and NTC thermistor 2 of the switched capacitor 1 are equal (R _S = R _T), the amount of variation of the divided voltage A _N (hereinafter divided voltage fluctuation to) ΔA _N becomes the maximum.

That is, the equivalent resistance value R _S of the switched capacitor 1 becomes
As the equivalent resistance R _T of the NTC type thermistor 2 becomes larger (R _S > R _T ) or the equivalent resistance R _S of the switched capacitor 1 becomes smaller than the equivalent resistance R _T of the NTC type thermistor 2 (R _S <R _T), the divided voltage fluctuation .DELTA.A _N becomes smaller.

As the divided voltage variation ΔA _N increases, the temperature at the center of the temperature range to be measured by the NTC type thermistor 2 can be measured with high sensitivity and accuracy. Therefore, the equivalent resistance value R _S of the switched capacitor 1 becomes NTC. The pulse frequency f to the switched capacitor 1 by the pulse controller 5 so that the equivalent resistance value R _T of the thermistor 2 becomes equal.
Should be generated.

Thus, as the digital output of the pulse controller unit 5 an analog / digital converter unit 3 obtained by sampling the divided voltage A _N is V _CC / 2, f-R
The pulse frequency f to the switched capacitor 1 may be generated by sequentially reading the values of the _S table 4a.

FIG. 4 is a flowchart showing the operation of one embodiment of the present invention. The operation of the embodiment of the present invention will be described with reference to FIGS.

First, the pulse controller 5 sets the address of the pointer P of the f- _RS table 4a to N / 2 in order to initialize the equivalent resistance value _RS of the switched capacitor 1 (step 11 in FIG. 4), F specified by this point P
-R _S Table 4a address, i.e. to generate a pulse from the address N / 2 reads the pulse frequency f to the switched capacitor 1 (Fig. 4 step 12, 13).

At this time, in the analog / digital converter section 3, the equivalent resistance value R _S of the switched capacitor 1 due to the pulse from the pulse controller section 5 and the temperature at that time are used.
The divided voltage A _N divided by the equivalent resistance value R _T of the NTC type thermistor 2 is sampled, and the sampled value is
It is digitally converted by V _REF and V _SS and sent to the pulse controller 5 (step 14 in FIG. 4).

The pulse controller 5 compares the sampling data D digitally converted by the analog / digital converter 3 with V _CC / 2 held in advance (step 15 in FIG. 4), and the sampling data D is compared with V _CC / 2. If it is larger (D> V _CC / 2) (Step 16 in FIG. 4), it is determined that the equivalent resistance value R _S of the switched capacitor 1 is smaller than the equivalent resistance value R _T of the NTC type thermistor 2, and the f- _RS table 4a Is added to the address of the pointer P (step 17 in FIG. 4).

Further, according to the above comparison, the sampling data D is V _CC / 2
If it is smaller (D <V _CC / 2) (FIG. 4, step 16),
It is determined that the equivalent resistance value R _S of the switched capacitor 1 is larger than the equivalent resistance value R _T of the NTC thermistor 2, and 1 is subtracted from the address of the point P in the f- _RS table 4a (fourth).
Figure Step 18).

After that, the pulse controller unit 5 sets the f- _RS table
It is determined whether or not the change of the pointer P in 4a has converged (4th
If the change of the pointer P in the f- _RS table 4a has not converged, it is determined that _RS < _RT or _RS > _RT, and the f- _{RS obtained} by adding or subtracting 1 is shown in FIG. Table 4a
The pulse frequency f is read from the address of FIG. 4 to generate a pulse to the switched capacitor 1 (steps 12, 1 in FIG. 4).
3).

On the other hand, if the change in the pointer P of the f- _RS table 4a converges, it is determined that R _S ≒ _RT, and the equivalent resistance value R _{S of the} switched capacitor 1 is determined from the address of the pointer P in the f- _RS table 4a at that time. _S is read (step 20 in FIG. 4).

The pulse controller 5 determines that the read equivalent resistance value _RS 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 from the T- _RT table 4b, and the processing is terminated (FIG. 4, step 22).

As described above, by controlling the input pulse frequency of the switched capacitor 1 formed serially with the NTC type thermistor 2 by the pulse controller unit 5, maximum sensitivity and accuracy can be obtained in the temperature range of the measurement object. Can be.

Further, by incorporating the analog / digital converter unit 3, the table storage unit 4, and the pulse controller unit 5, that is, the necessary hardware in the one-chip microcomputer 6, the above effects can be easily realized. it can.

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

Effect of the Invention As described above, according to the present invention, the resistance value of the variable resistance means whose resistance value varies in accordance with the input control signal and the divided voltage value divided by the equivalent resistance value of the thermistor are determined in advance. In order to approximate the set predetermined voltage value,
By variably controlling the variable resistance means with a control signal, there is an effect that the maximum sensitivity and accuracy can be obtained in the temperature range to be measured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG.
FIG. 2B is a diagram showing an equivalent resistance value table, FIG. 2B is a diagram showing a temperature-thermistor resistance value table in the table storage unit of FIG. 1, and FIG. 3 is a diagram for explaining the principle of an embodiment of the present invention. FIG. 4 is a flowchart showing the operation of one embodiment of the present invention. Description of Signs of Main Parts 1 ... Switched Capacitor 2 ... NTC Type Thermistor 3 ... Analog / Digital Converter Unit 4 ... Table Storage Unit 4a ... Pulse Frequency-Equivalent Resistance Table 4b ... Temperature-Thermistor Resistance Table 5 ... Pulse controller

Claims (1)

(57) [Claims] 1. A temperature sensor sensitivity variable circuit of a temperature sensor using a thermistor whose equivalent resistance value changes according to a measured temperature, wherein a variable resistance means whose resistance value changes according to an input control signal; Storage means for storing the control signal and the resistance value corresponding to the control signal; control means for variably controlling the variable resistance means by the control signal stored in the storage means; and variably controlled by the control means. A comparing means for comparing a divided voltage value divided by a resistance value of the variable resistance means and an equivalent resistance value of the thermistor with a predetermined voltage value set in advance; and Calculating a 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 predetermined voltage value is approximate. Temperature sensor sensitivity changing circuit, characterized in that a means.