Temperature measuring device

Abstract

To provide a temperature measuring device capable of precisely measuring a temperature by using a thermistor.SOLUTION: A temperature measuring device includes: a thermistor 5 for measuring a temperature by a resistance value that changes in accordance with a change in a temperature; a reference resistor 3 that has less change in a resistance value because of a change in a temperature with resistance having the same resistance value as a resistance value prescribed in the thermistor 5; a voltage dividing resistor 4 for dividing an input voltage from a power supply with the reference resistor 3 or the thermistor 5; switches 2 each of which is connected to one / the other of the reference resistor 3 and the thermistor 5, and selects one of the reference resistor 3 and the thermistor 5 and allows a current from the power supply to flow; an A / D converter 6 for converting a divided analog voltage into digital data; and a control section 7 for correcting the measurement result of the thermistor 5 with a deviation from a fixed temperature of a temperature calculated from a divided voltage value when the current is allowed to flow to the reference resistor 3 as a correction value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a temperature measuring device using a thermistor, which is a temperature measuring element that utilizes the temperature characteristics of a semiconductor. [Background technology]

[0002] Patent Document 1 describes a method in which a thermistor for reference junction compensation is used in a temperature measuring device using a thermocouple to correct the temperature drift of a measurement circuit using only the reference junction compensation.

[0003] In Patent Document 1, a resistance-temperature table for a thermistor is created, the analog voltage generated in the thermistor by a constant current source is converted into a digital count value, and a correction coefficient is determined based on the temperature difference between the temperature obtained from the resistance-temperature table and a reference temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-009611 A Summary of the Invention [Problem to be solved by the invention]

[0005] Because the resistance value of a thermistor fluctuates due to changes in the surrounding temperature and hardware characteristics such as the circuit configuration, the measured temperature contains an error and needs to be corrected.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a temperature measuring device that can measure temperature with high accuracy using a thermistor. [Means for solving the problem]

[0007] The temperature measuring device of the present invention comprises a thermistor that measures temperature based on a resistance value that changes in response to temperature change, a voltage dividing resistor connected in series with the thermistor and dividing the voltage from a power source, a reference resistor connected in parallel with the thermistor and having the same resistance value as a predetermined resistance value of the thermistor and whose resistance value changes little with temperature change, a switch that selects either the thermistor or the reference resistor and passes current from a power source through it, and a control unit that corrects the measurement result of the thermistor by using as a correction value the amount by which the temperature calculated from the divided voltage value when current is passed through the reference resistor and the temperature deviates from the predetermined temperature.

[0008] With this configuration, the deviation of the temperature calculated from the divided voltage value when a current flows through the reference resistor from the predetermined temperature is used as a correction value, and the measurement result of the thermistor is corrected, thereby enabling accurate temperature measurement.

[0009] In addition, in the temperature measuring device of the present invention, a plurality of thermistors are provided in parallel with the reference resistor, the switch selects one of the plurality of thermistors or the reference resistor and passes a current from a power source through it, and the control unit corrects the measurement results of the plurality of thermistors by using as a correction value the deviation of a temperature calculated from a divided voltage value when a current is passed through the reference resistor from a predetermined temperature.

[0010] With this configuration, the measurement results of the multiple thermistors are corrected by a correction value calculated by passing a current through the reference resistor, making it possible to measure the temperatures at multiple locations with high accuracy.

[0011] In the temperature measuring device of the present invention, the control unit repeats, at a predetermined time interval, calculation of the correction value using the reference resistor and temperature measurement using the thermistor.

[0012] With this configuration, a correction value is calculated using the reference resistor at a predetermined time interval, and the temperature measurement by the thermistor is corrected. Therefore, the correction value is applied at the appropriate time, and the temperature can be measured with high accuracy. Effect of the Invention

[0013] The present invention can provide a temperature measuring device that can measure temperature with high accuracy by using a thermistor. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of a temperature measuring device according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing an example of a circuit configuration for measuring the resistance value of a thermistor. [Diagram 3] FIG. 3 is a diagram showing the relationship between the voltage and temperature of a thermistor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a temperature measuring device according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0016] In FIG. 1, a temperature measuring device 1 according to one embodiment of the present invention includes a switch 2, a reference resistor 3, a voltage dividing resistor 4, a thermistor 5, an A / D converter 6, and a control unit .

[0017] The switches 2 are connected to the reference resistors 3 and thermistors 5, respectively, and select one of the reference resistors 3 or thermistors 5 through which current from the power supply flows, turning it on and turning the other reference resistors 3 or thermistors 5 off.

[0018] The reference resistor 3 is a high-precision resistor that has the same resistance as the specified resistance of the thermistor 5 and that has little change in resistance due to temperature changes. The reference resistor 3 and thermistor 5 are connected in parallel.

[0019] The voltage dividing resistor 4 divides the input voltage from the power supply between the reference resistor 3 and the thermistor 5. The divided voltage is output to an A / D converter 6. The voltage dividing resistor 4 is connected in series to the parallel circuit of the reference resistor 3 and thermistor 5.

[0020] The thermistor 5 is a temperature measuring element that uses the temperature characteristics of a semiconductor. The specified resistance of the thermistor 5 is generally the resistance value at 25°C. As the temperature increases, the resistance value of the thermistor 5 decreases, and as the temperature decreases, the resistance value increases. The rate of change in resistance value due to temperature change is represented by a parameter called B constant, and the resistance value at T°C is expressed by the following formula. Note that B constant is a value in absolute temperature.

[0021]

number

[0022] The A / D converter 6 converts the input analog voltage into digital data. When the resistance value of thermistor 5 changes, the voltage input to the A / D converter 6 changes, causing a change in the digital data output from the A / D converter 6. As shown in the figure, if the positive reference voltage of A / D converter 6 (indicated by "+REF" in the figure) is input to the A / D converter 6, which is the same as the reference resistor 3 and thermistor 5, and the negative reference voltage (indicated by "-REF" in the figure) is grounded, no measurement error will occur even if the 3.3V power supply fluctuates.

[0023] The control unit 7 controls the switch 2 to pass a current through one of the thermistors 5, and the divided voltage is converted by the A / D converter 6 into digital data, from which the temperature of the thermistor 5 is detected.

[0024] The A / D converter 6 and the control unit 7 are configured, for example, by a field-programmable gate array (FPGA), etc. The switch 2 is configured, for example, by an enhancement type P-channel metal-oxide-semiconductor field-effect transistor (MOSFET).

[0025] To measure temperature using the thermistor 5, it is necessary to detect the change in the resistance value of the thermistor 5 due to a change in temperature. To detect the change in the resistance value of the thermistor 5, as shown in Figure 2, the power supply voltage is divided by the thermistor 5 and voltage dividing resistor 4, and the resistance value of the thermistor 5 is detected from the divided voltage (the voltage at the terminal indicated by A in the figure).

[0026] FIG. 3 shows the relationship between the divided voltage and the temperature of thermistor 5 when the resistance value of thermistor 5 and voltage dividing resistor 4 is 10 KΩ using the 5V power supply shown in FIG.

[0027] The curve indicated by B in Figure 3 shows the relationship between the voltage and the temperature of thermistor 5. The curve showing the characteristics of this thermistor 5 approaches the straight line indicated by C in the vicinity of 25°C, which means that the voltage and temperature are in a proportional relationship, making it suitable for measuring temperature.

[0028] In this embodiment, the control unit 7 corrects the measurement result of the thermistor 5 by using as a correction value the deviation of the temperature calculated from the divided voltage value when a current is passed through the reference resistor 3 from a predetermined temperature, for example 25°C.

[0029] The reference resistor 3 is a high-precision resistor with little change in resistance value, so it can maintain its resistance value at the specified temperature by the thermistor 5, and the divided voltage value when a current flows through the reference resistor 3 contains errors in the circuit configuration through which the current flows from the power supply, including the voltage dividing resistor 4. Therefore, by using the deviation between the temperature calculated from this divided voltage value and the specified temperature as a correction value, it is possible to correct errors due to changes in the surrounding temperature and hardware characteristics such as the circuit configuration, thereby enabling accurate temperature measurement.

[0030] The control unit 7 sequentially passes a current from the reference resistor 3 to the thermistor 5 at predetermined time intervals to measure the temperature.

[0031] The control unit 7 determines a correction value based on the temperature calculated from the divided voltage value when a current is passed through the reference resistor 3, and corrects the temperature calculated from the divided voltage value when a current is passed through the thermistor 5 using the correction value.

[0032] If the temperature calculated when a current is passed through the reference resistor 3 is higher than a predetermined temperature, the control unit 7 corrects the temperature by subtracting the difference from the temperature calculated when a current is passed through the thermistor 5.

[0033] If the temperature calculated when a current is passed through the reference resistor 3 is lower than a predetermined temperature, the control unit 7 adds the difference to the temperature calculated when a current is passed through the thermistor 5 to correct the temperature.

[0034] Thus, in the above-described embodiment, the control unit 7 corrects the measurement result of the thermistor 5 by using the deviation of the temperature calculated from the divided voltage value when a current is passed through the reference resistor 3 from a predetermined temperature as a correction value.

[0035] As a result, the deviation of the temperature calculated from the divided voltage value when a current flows through the reference resistor 3 from the predetermined temperature is used as a correction value, and the measurement result of the thermistor 5 is corrected. This allows for accurate temperature measurement.

[0036] Moreover, the control unit 7 includes a plurality of thermistors 5 , and corrects the measurement results of the plurality of thermistors 5 with a correction value calculated by passing a current through the reference resistor 3 .

[0037] As a result, the measurement results of the multiple thermistors 5 are corrected by the correction value calculated by passing a current through the reference resistor 3. This makes it possible to measure the temperatures at multiple locations with high accuracy.

[0038] Furthermore, the control unit 7 repeats the calculation of the correction value using the reference resistor 3 and the temperature measurement using the thermistor 5 at predetermined time intervals.

[0039] As a result, a correction value is calculated by the reference resistor 3 at predetermined time intervals, and the temperature measurement by the thermistor 5 is corrected. Therefore, the correction value is applied at the appropriate time, and the temperature can be measured with high accuracy.

[0040] Although an embodiment of the present invention has been disclosed, it will be apparent to one of ordinary skill in the art that modifications may be made thereto without departing from the scope of the present invention, and all such modifications and equivalents are intended to be encompassed by the following claims. [Explanation of symbols]

[0041] 1 Temperature measuring device 2 Switch 3 Reference Resistance 4 Voltage divider resistor 5 Thermistor 6 A / D Converter 7 Control section

Claims

1. a thermistor that measures temperature by a resistance value that changes in response to temperature changes; a voltage dividing resistor connected in series with the thermistor to divide a voltage from a power supply; a reference resistor connected in parallel with the thermistor, the reference resistor having the same resistance as a predetermined resistance value of the thermistor and having a small change in resistance value with respect to a change in temperature; a switch for selecting either the thermistor or the reference resistor and allowing a current from a power source to flow; a control unit that corrects the measurement result of the thermistor by using a correction value that is the deviation of a temperature calculated from a divided voltage value when a current is passed through the reference resistor from a predetermined temperature.

2. A plurality of thermistors are provided in parallel with the reference resistor; the switch selects one of the plurality of thermistors and the reference resistor to pass a current from a power source; 2. The temperature measuring device according to claim 1, wherein the control unit corrects the measurement results of the multiple thermistors by using a correction value that is a deviation of a temperature calculated from a divided voltage value when a current is passed through the reference resistor from a predetermined temperature.

3. 3. The temperature measuring device according to claim 1, wherein the control unit repeats, at a predetermined time interval, calculation of the correction value using the reference resistor and temperature measurement using the thermistor.

Images