Patent Publication Number: US-2015063421-A1

Title: Temperature measurement apparatus using negative temperature coefficient thermister

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Patent Application No. 10-2013-0104938, filed on Sep. 2, 2013, the contents of which are all hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     The present disclosure relates to a temperature measurement apparatus using a temperature coefficient (NTC) thermister. 
     The NTC thermister has an NTC and continuously changes in electric resistance, which is used as a temperature sensor due to such features. Particularly, in case of automobiles and electric automobiles stably operating within a range from about −45° C. to about 120° C., a temperature is measured using a temperature sensor using the NTC thermister. Also, components of automobiles and electric automobiles are protected by controlling charging a battery, etc. according to a measured temperature. 
     Merely, due to properties of the temperature sensor using the NTC, a range of fluctuation in voltage according to a temperature near a lower limit value or an upper limit value of a measurement range of the temperature sensor is not great. Accordingly, a temperature measured near the lower limit value or the upper limit value of the measurement range of the temperature sensor may be inaccurate. Accordingly, it is necessary to precisely measure a temperature near the lower limit value or the upper limit value of the measurement range of the NTC temperature sensor. 
     SUMMARY 
     Embodiments provide a temperature measurement apparatus capable of precisely measuring a temperature near a lower limit value or an upper limit value of a measurement range of a temperature sensor by using a negative temperature coefficient (NTC) thermister. 
     In one embodiment, a temperature measurement apparatus using a negative temperature coefficient (NTC) thermister includes a temperature sensor including the NTC thermister and a variable resistor part, in which a resistance value of the variable resistor part varies between a first resistance value for a first output voltage value and a second resistance value for a second output voltage value to allow a voltage value corresponding to a present temperature to be outputted and a voltage temperature matching unit outputting the present temperature based on the first output voltage value and the second output voltage value. 
     In another embodiment, a temperature measurement apparatus using an NTC thermister includes the NTC thermister including one end, to which a direct current (DC) voltage is applied, a variable resistor part including one end connected to another end of the NTC thermister and another grounded, having a first resistance value for a first output voltage value and a second resistance value for a second output voltage value, and a voltage temperature matching unit outputting a present temperature based on the first output voltage value and the second output voltage value. 
     A temperature near a lower limit value and an upper limit value of a temperature measurable range of the temperature sensor using the NTC thermister may be precisely measured. According thereto, a reliability of controlling a charging operation according to a temperature in an automobile and an electric automobile using the temperature sensor using the NTC thermister may increase. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a temperature measurement apparatus according to an embodiment; 
         FIG. 2  is a circuit diagram of the temperature measurement apparatus of  FIG. 1 ; 
         FIG. 3  is a flowchart illustrating operations of the temperature measurement apparatus of  FIG. 1 ; 
         FIG. 4  illustrates changes of a temperature-voltage curve of a temperature sensor using a negative temperature coefficient (NTC) according to a fixed resistance value included in the temperature sensor; 
         FIG. 5  illustrates changes of a temperature-voltage curve of a temperature sensor using an NTC according to another embodiment according to a variable resistance value included in the temperature sensor; 
         FIG. 6  is a block diagram of a temperature measurement apparatus according to another embodiment; 
         FIG. 7  is a circuit diagram of the temperature measurement apparatus of  FIG. 6 ; and 
         FIG. 8  is a flowchart illustrating operations of the temperature measurement apparatus of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, with reference to the attached drawings, exemplary embodiments will be described in detail to allow those skilled in the art to easily execute the same. However, the embodiments may be provided as various different forms and are not limited thereto. Also, in the drawings, in order to definitely describe the embodiments, an irrelevant part will be omitted. Throughout the specification, like reference numerals refer to like elements. 
     Also, it will be further understood that the terms “comprises” and/or “comprising” used herein, unless the context clearly indicates otherwise, specify the further presence of other components, but do not preclude the presence or addition of one or more other components. 
     Hereinafter, referring to  FIGS. 1 to 3 , a temperature measurement apparatus  100  according to an embodiment will be described. 
       FIG. 1  is a block diagram of the temperature measurement apparatus  100 . 
     Referring to  FIG. 1 , the temperature measurement apparatus  100  includes a direct current (DC) current generation unit  110 , a temperature sensor  120 , a buffer  130 , a voltage temperature matching unit  140 , a voltage temperature table storage unit  150 , a charge control unit  160 , and a battery  170 . 
     The DC voltage generation unit  110  generates a DC voltage. 
     The voltage temperature table storage unit  150  stores a voltage temperature table. The voltage temperature table includes a plurality of temperature values corresponding to a plurality of output voltages of the temperature sensor  120 , respectively. 
     The charge control unit  160  controls a charging operation related to the battery  170  of an electric automobile according to a present temperature. 
     Other components of the temperature measurement apparatus  100  will be described in detail with reference to  FIG. 2 . 
       FIG. 2  is a circuit diagram of the temperature measurement apparatus  100 . 
     The temperature sensor  120  includes a negative temperature coefficient (NTC) thermister Rn 1  and a fixed resistor R 1 . The NTC thermister Rn 1  has one end, to which a DC voltage generated by the DC voltage generation unit  110  is applied. The fixed resistor R 1  has one end connected to another end of the NTC thermister Rn 1  and another end grounded. 
     A voltage applied to the fixed resistor R 1  is allowed to be an output voltage of the temperature sensor  120 . The output voltage of the temperature sensor  120  is the intensity of the fixed resistor R 1 /(a resistance value of the NTC thermister Rn 1 +the intensity of the fixed resistor R 1 ). The resistance value of the NTC thermister Rn 1  becomes smaller as a temperature increases. Accordingly, an output voltage becomes greater as the temperature increases. On the contrary, the resistance value of the NTC thermister Rn 1  becomes greater as the temperature decreases. Accordingly, the output voltage becomes smaller as the temperature decreases. 
     The buffer  130  includes an operational amplifier Op and a fixed resistor R 2 . An input end of the operational amplifier Op is connected to the one end of the fixed resistor R 1 , to which an output of the temperature sensor  120  is applied, and the other end of the NTC thermister Rn 1 . The fixed resistor R 2  has one end connected to an output end of the operational amplifier Op and another end grounded. Since the buffer  130  includes the operational amplifier Op, which is an active element, the output voltage of the temperature sensor  120  may be buffered without a load effect and a buffered voltage may be outputted. 
     An input end of the voltage temperature matching unit  140  is connected to the output end of the operational amplifier Op and the one end of the fixed resistor R 2 . 
       FIG. 3  is a flowchart illustrating operations of the temperature measurement apparatus  100 . 
     The temperature  120  outputs a voltage value corresponding to the present temperature by using the resistance value of the NTC thermister Rn 1 , varying with a temperature (S 101 ). 
     The buffer  130  buffers the output voltage of the temperature sensor  120  and outputs a buffered voltage (S 103 ). When the temperature sensor  120  and the voltage temperature matching unit  140  are directly connected to each other without the buffer  130 , since the load effect occurs and drops a voltage, it is impossible to transmit an accurate voltage value. Accordingly, the output voltage of the temperature sensor  120  may be accurately transmitted to the voltage temperature matching unit  140  through the buffer  130 . 
     The voltage temperature matching unit  140  matches the buffered voltage with a voltage on the voltage temperature table stored in the voltage temperature table storage unit  150  and outputs a present temperature corresponding to the buffered voltage value (S 105 ). The voltage temperature table varies with properties of the temperature sensor  120 . On the other hand, the buffer  130  may be omitted. In this case, the voltage temperature matching unit  140  may output a present temperature corresponding to the output voltage of the temperature sensor  120 . 
     Hereinafter, referring to  FIGS. 4 to 8 , a temperature measurement apparatus using an NTC temperature sensor according to another embodiment will be described. 
       FIG. 4  illustrates changes of a temperature-voltage curve of the temperature sensor  120  using a negative temperature coefficient (NTC) according to a fixed resistance value included in the temperature sensor  120 . 
     The output voltage of the temperature sensor  120  is the intensity of the fixed resistor R 1 /(the resistance value of the NTC thermister Rn 1 +the intensity of the fixed resistor R 1 ). Accordingly, at a high temperature, in which the resistance value of the NTC thermister Rn 1  is relatively small as the intensity of the fixed resistor R 1  increases, an effect of changes in the resistance value of the NTC thermister Rn 1  becomes insignificant in such a way that the curve of  FIG. 4  moves toward an A curve. On the contrary, at a low temperature, in which the resistance value of the NTC thermister Rn 1  is relatively great as the intensity of the fixed resistor R 1  decreases, the effect of changes in the resistance value of the NTC thermister Rn 1  becomes insignificant in such a way that the curve of  FIG. 4  moves toward a B curve. Due to such properties of the temperature sensor  120 , it becomes inaccurate to measure a temperature at the low temperature or the high temperature according to the intensity of the fixed resistor R 1  included in the temperature sensor  120 . 
       FIG. 5  illustrates changes of a temperature-voltage curve of a temperature sensor using an NTC according to another embodiment according to a variable resistance value included in the temperature sensor. 
     In case of the embodiment of  FIG. 4 , as described above, according to the intensity of the fixed resistor R 1  included in the temperature sensor  120 , there is a limitation in measuring an accurate temperature at the low temperature or the high temperature. Accordingly, in another embodiment, to overcome the limitation, a variable resistor is included in the temperature sensor  120  instead of the fixed resistor R 1 . After the variable resistor is allowed to have a plurality of values, the temperature sensor  120  outputs voltage values corresponding to respective variable resistance values and matches mean values of the outputted voltage values with temperatures. 
     A linearity of temperature-voltage properties is allowed to increase at an intermediate temperature or more of a temperature measurement range. That is, to allow an inclination of a temperature-voltage curve at the intermediate temperature or more of the temperature measurement range to be greater than an inclination thereof at less than the intermediate temperature of the temperature measurement range, a first output voltage value is outputted by adjusting a value of the variable resistor included in the temperature sensor  120 . In this case, in  FIG. 5 , the curve shows as the B curve. According thereto, a temperature at the intermediate temperature or more of the temperature measurement range is allowed to be precisely measured. 
     Also, the linearity of temperature-voltage properties is allowed to increase at less than the intermediate temperature of the temperature measurement range. That is, to allow the inclination of a temperature-voltage curve at the intermediate temperature or more of the temperature measurement range to be smaller than the inclination thereof at less than the intermediate temperature of the temperature measurement range, a second output voltage value is outputted by adjusting the variable resistance value. In this case, in  FIG. 5 , the curve shows as the A curve. According thereto, a temperature at less than the intermediate temperature of the temperature measurement range is allowed to be precisely measured. 
     After the plurality of voltage values are outputted while allowing variable resistance values to be different one another, a mean voltage value of the voltage values is matched with a temperature, thereby showing temperature-voltage properties as an AVR curve of  FIG. 5 . Accordingly, the linearity may be shown throughout the entire section of the temperature measurement range and it is possible to precisely measure a temperature in the entire section of the temperature measurement range. Through this, in another embodiment, it is allowed to be performed to precisely measure the temperature. 
       FIG. 6  is a block diagram of a temperature measurement apparatus  200  according to another embodiment. 
     Referring to  FIG. 6 , the temperature measurement apparatus  200  may include a DC current generation unit  210 , a temperature sensor  220 , a buffer  230 , a voltage value storage unit  240 , a temperature sensor control signal generation unit  250 , a voltage value operation unit  260 , a voltage temperature matching unit  270 , a voltage temperature table storage unit  280 , a charge control unit  290 , and a battery  295 . 
     The DC voltage generation unit  210  generates a DC voltage. 
     The temperature sensor  220  includes an NTC thermister  223  and a variable resistor part  221 . The variable resistor part  221  has one of a plurality of resistance values under the control of the voltage value operation unit  260 . In this case, the plurality of resistance values includes a first resistance value for a first output voltage value and a second resistance value for a second output voltage value. 
     The voltage temperature table storage unit  270  stores a voltage temperature table. The voltage temperature table includes a plurality of temperature values corresponding to a plurality of values, which are the mean of the first output voltage value and the second output voltage value. 
     The charge control unit  290  controls a charging operation related to the battery  295  of an electric automobile according to a present temperature. 
     Other components of the temperature measurement apparatus  200  will be described in detail with reference to  FIG. 7 . 
       FIG. 7  is a circuit diagram of the temperature measurement apparatus  200 . 
     The temperature sensor  220  includes an NTC thermister Rn 2 , a resistor R 3 , a resistor R 4 , and a switch SW. The NTC thermister Rn 2  has one end, to which a DC voltage generated by the DC voltage generation unit  210  is applied. The resistor R 3  has one end connected to another end of the NTC thermister Rn 2  and another end grounded. 
     The fixed resistor R 4  and the switch SW are connected in series between the NTC thermister Rn 2  and a ground. In the embodiment, one end of the fixed resistor R 4  is connected to the NTC thermister Rn 2  and one end of the switch SW is connected to another end of the resistor R 4  and another end thereof grounded. In another example, one end of the switch SW is connected to the NTC thermister Rn 2  and one end of the resistor R 4  is connected to another end of the switch SW and another end thereof is grounded. 
     In the embodiment of  FIG. 7 , when the switch SW is turned on, a combined resistance value of the fixed resistor R 3  and the fixed resistor R 4  may be the first resistance value for the first output voltage value. When the switch SW is turned off, the combined resistance value of the fixed resistor R 3  and the fixed resistor R 4  may be the second resistance value for the second output voltage value. 
     In a graph of  FIG. 5 , to allow temperature-voltage properties of the temperature sensor  220  to correspond to the B curve rather than the A curve, the first resistance value of the variable resistor part  221  may be smaller than a resistance value of the NTC thermister Rn 2  at the intermediate temperature of the temperature measurement range. The first resistance value of the variable resistor part  221  may be smaller than ⅕ of the resistance value of the NTC thermister Rn 2  at the intermediate temperature of the temperature measurement range. 
     In the graph of  FIG. 5 , to allow the temperature-voltage properties of the temperature sensor  220  to correspond to the B curve rather than the A curve, the second resistance value of the variable resistor part  221  may be greater than the resistance value of the NTC thermister Rn 2  at the intermediate temperature of the temperature measurement range. To improve the linearity of the temperature-voltage properties of the temperature sensor  220  between an upper limit temperature and an intermediate temperature of the temperature measurement range, the second resistance value of the variable resistor part  221  may be greater than five times the resistance value of the NTC thermister Rn 2  at the intermediate temperature of the temperature measurement range. 
     The switch SW may be turned on or off according to a temperature sensor control signal. Particularly, the switch SW may be a transistor such as metal-oxide semiconductor field effect transistor (MOSFET). 
     The buffer  230  includes an operational amplifier Op and a fixed resistor R 5 . An input end of the operational amplifier Op is connected to the one end of the fixed resistor R 3 , to which an output of the temperature sensor  220  is applied, and the other end of the NTC thermister Rn 2 . The fixed resistor R 5  has one end connected to an output end of the operational amplifier Op and another end grounded. Since the buffer  230  includes the operational amplifier Op, which is an active element, the output voltage of the temperature sensor  220  may be buffered without a load effect and a buffered voltage may be outputted. 
       FIG. 8  is a flowchart illustrating operations of the temperature measurement apparatus  200 . 
     The temperature  220  outputs a first output voltage value corresponding to a present temperature by using the resistance value of the NTC thermister Rn 2 , varying with a temperature, and the first resistance value of the variable resistor part  211  (S 201 ). 
     The buffer  230  buffers the output voltage of the temperature sensor  220  and outputs a buffered voltage (S 203 ). When the temperature sensor  220  and the voltage value storage unit  240  are directly connected to each other without the buffer  230 , since a load effect may occur and a voltage may be dropped, it is impossible to transmit an accurate voltage value. Accordingly, the output voltage of the temperature sensor  220  may be accurately transmitted to the voltage value storage unit  240  through the buffer  230 . 
     The voltage value storage unit  240  stores a value of the buffered voltage (S 205 ). On the other hand, the buffer  230  may be omitted, in which the voltage value storage unit  240  stores an output voltage value of the temperature sensor  220 . 
     The temperature sensor control signal generation unit  250  determines whether the output voltage value of the temperature sensor  220  is the second output voltage value (S 207 ). 
     When the output voltage value of the temperature sensor  220  is not the second output voltage value, the temperature sensor control signal generation unit  250  generates a control signal to allow the variable resistor part  221  to have the second resistance value (S 209 ). Particularly, in the embodiment of  FIG. 7 , the temperature sensor control signal generation unit  250  generates the control signal and turns off the switch SW connected to the fixed resistor R 4 . Only the fixed resistor R 3  is connected to the NTC thermister Rn 2 , thereby allowing the variable resistor part  221  to have the second resistance value for the second output voltage value. 
     When the output voltage value of the temperature sensor  220  is the second output voltage value, the temperature sensor control signal generation unit  250  generates a control signal to allow the variable resistor part  221  to have the first resistance value (S 211 ). Particularly, in the embodiment of  FIG. 7 , the temperature sensor control signal generation unit  250  generates the control signal and turns on the switch SW connected to the fixed resistor R 4 . Both the fixed resistor R 3  and the fixed resistor R 4  are connected to the NTC thermister Rn 2 , thereby allowing the variable resistor part  221  to have the first resistance value for the first output voltage value. 
     The voltage value operation unit  260  outputs a mean of the first output voltage and the second output voltage value stored in the voltage value storage unit  240  (S 213 ). 
     The voltage value operation unit  260 , after performing operation, initializes the number of outputting voltages and the output voltage values stored in the voltage value storage unit  240  (S 215 ). 
     The voltage temperature matching unit  270  matches the mean buffered voltages with a voltage on the voltage temperature table stored in the voltage temperature table storage unit  280  and outputs a present temperature corresponding to the mean buffered voltage value (S 217 ). The voltage temperature table may vary with the first resistance value of the variable resistor part  221 , the second resistance value of the variable resistor part  221 , and properties of the NTC thermister Rn 2  of the temperature sensor  220 . The voltage temperature table may store a temperature corresponding to a voltage value that is a mean of the output voltage values according to the first output voltage value and the second output voltage value. 
     Since the temperature is measured using the operations as described above, all the first output voltage value and the second output voltage value are outputted, thereby outputting the temperature. One of consuming largest times till the first output voltage value and the second voltage value are measured is turning on and off the switch. Accordingly, as the switch operates at a higher speed, the temperature may be more rapidly measured. When an MOSFET operating at a high speed, whose general open short-circuit operation time is less than 20 ms, is used as the switch, the temperature may be rapidly measured. 
     Features, structures, effects, etc. described in the above embodiments, are included in at least one embodiment and but are not limited to one embodiment. In addition, features, structures, effects, etc. described in the respective embodiments may be executed by a person of ordinary skill in the art while being combined or modified with respect to other embodiments. Accordingly, it will be understood that contents related the combination and modification will be included in the scope of the embodiments. 
     It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the embodiments. For example, respective components shown in detail in the embodiments may be executed while being modified. Also, it will be understood that differences related to the modification and application are included in the scope of the embodiments as defined by the following claims. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.