Patent Publication Number: US-2015063401-A1

Title: Temperature measurement apparatus using negative temperature coefficient thermistor

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. 10-2013-0104932, 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 negative temperature coefficient (NTC) thermistor. 
     The NTC thermistor has a negative temperature coefficient and 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 thermistor. Also, components of automobiles and electric automobiles are protected by controlling charging a battery 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. Accordingly, it is impossible to definitely check whether the temperature sensor using the NTC normally operates and whether a short circuit or a disconnection of an NTC thermistor occurs. Accordingly, it is necessary to provide a temperature measurement apparatus capable of definitely determining a disconnection and a short circuit near a lower limit value or an upper limit value of a measurement range of a temperature sensor using an NTC. 
     SUMMARY 
     Embodiments provide Embodiments provide a temperature measurement apparatus capable of definitely determining whether a disorder such as a disconnection and a short circuit occurs near a lower limit value or an upper limit value of a measurement range of a temperature sensor using an NTC. 
     In one embodiment, a temperature measurement apparatus using a negative temperature coefficient (NTC) thermistor includes a temperature sensor including the NTC thermistor and a variable resistor part, in which a resistance value of the variable resistor part varies between a default resistance value for measuring a temperature and a temporary resistance value for determining a disconnection and an abnormal operation determination unit determining whether the NTC thermistor is disconnected, based on an output voltage of the temperature sensor when the variable resistor part has the temporary resistance value. 
     It is possible to definitely check whether a disorder such as a disconnection and a short circuit occurs near a lower limit value and an upper limit value of a temperature measurable range of the temperature sensor using an NTC. Accordingly, in automobiles and electric automobiles using the temperature sensor using the NTC thermistor, it is possible to increase the reliability of a controlling operation while controlling operations such as charging according to a temperature. Also, it is early checked whether the temperature sensor using the NTC thermistor breaks down, thereby allowing a component to be replaced at the beginning of an failure. 
     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 illustrating a temperature measurement apparatus according to an embodiment; 
         FIG. 2  is a circuit diagram illustrating the temperature measurement apparatus of  FIG. 1 ; 
         FIG. 3  is a flowchart illustrating operations of the temperature measurement apparatus according to an embodiment; 
         FIG. 4  illustrates changes of a temperature-voltage curve of a temperature sensor according to a fixed resistance value included in a temperature sensor using a negative temperature coefficient (NTC); 
         FIG. 5  is a block diagram illustrating a temperature measurement apparatus according to another embodiment; 
         FIG. 6  is a circuit diagram illustrating the temperature measurement apparatus of  FIG. 5 ; and 
         FIG. 7  is a flowchart illustrating operations of the temperature measurement apparatus of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, with reference to the attached drawings, various embodiments will be described in detail to allow those skilled in the art to easily execute. The embodiments may be provided as various different forms and are not limited to the embodiments. Also, 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 specify the presence of stated features or components, but do not preclude the presence or addition of one or more other features or 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 illustrating 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 , an abnormal operation determination unit  160 , a charge control unit  170 , and a battery  180 . 
     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  170  controls a charging operation related to the battery  180  of an electric automobile according to a disconnection sensing signal and a short-circuit sensing signal outputted by the abnormal operation determination unit  160 . 
     Other components of the temperature measurement apparatus  100  will be described in detail with reference to  FIG. 2 . 
       FIG. 2  is a circuit diagram illustrating the temperature measurement apparatus  100 . 
     The temperature sensor  120  includes a negative temperature coefficient (NTC) thermistor Rn 1  and a fixed resistor R 1 . The NTC thermistor 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 thermistor 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 a value obtained by multiplying an input voltage by intensity of the fixed resistor R 1 /(a resistance value of the NTC thermistor Rn 1 +the intensity of the fixed resistor R 1 ). The resistance value of the NTC thermistor 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 thermistor 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 the output of the temperature sensor  120  is applied, and the other end of the NTC thermistor 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 a present temperature by using a resistance value of the NTC thermistor 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 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  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 a 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 . 
     The abnormal operation determination unit  160  determines whether the present temperature is out of a preset normal operation temperature range (S 107 ). The normal operation temperature range is formed by setting a range of a temperature corresponding to an output voltage that is not a disconnection or a short circuit in a temperature range measurable by the temperature sensor  120 . When the present temperature is out of the normal operation temperature range, there is a probability of a disconnection or a short circuit. 
     When the present temperature is out of the normal operation temperature range, the abnormal operation determination unit  160  determines whether the present temperature maintains a value out of the normal operation temperature range for more than a preset abnormal operation reference time (S 109 ). When it is not more than an abnormal operation reference time, the abnormal operation determination unit  160  determines it as a normal operation state. 
     When the present temperature maintains the value out of the normal operation temperature range for more than the abnormal operation reference time, the abnormal operation determination unit  160  determines whether the present temperature is lower than a lower limit value of the normal operation temperature range (S 111 ). 
     When the present temperature is not lower than the lower limit of the normal operation temperature range, the abnormal operation determination unit  160  outputs a short-circuit sensing signal for indicating a short circuit of the NTC thermistor Rn 1  (S 113 ). When the present temperature is higher than an upper limit value of the normal operation temperature range and the NTC thermistor Rn 1  is short-circuited, a voltage supplied by the DC voltage generation unit  110  is all applied to the fixed resistor R 2  and the voltage temperature matching unit  140  outputs a very high present temperature. 
     When the present temperature is lower than the lower limit of the normal operation temperature range, the abnormal operation determination unit  160  outputs a disconnection sensing signal indicating a disconnection of the NTC thermistor (S 113 ). When the NTC thermistor Rn 1  is disconnected, the voltage supplied by the DC voltage generation unit  110  is absolutely not applied to the fixed resistor R 1  and the temperature matching unit  140  outputs a very low present temperature. 
     Hereinafter, referring to  FIGS. 4 to 7 , a temperature measurement apparatus according to another embodiment will be described. 
       FIG. 4  illustrates changes of a temperature-voltage curve of the temperature sensor  120  according to a resistance value included in the temperature sensor  120  using an NTC. 
     The output voltage of the temperature sensor  120  is the intensity of the fixed resistor R 1 /(the resistance value of the NTC thermistor Rn 1 +the intensity of the fixed resistor R 1 ). Accordingly, at a high temperature, in which the resistance value of the NTC thermistor 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 thermistor 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 thermistor 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 thermistor 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 a low temperature or a high temperature according to the intensity of the fixed resistor R 1  included in the temperature sensor  120 . 
     Accordingly, when the abnormal operation determination unit  160  determines a disconnection or a short circuit according to whether the present temperature maintains being out of the normal operation temperature range for the abnormal operation reference time or more, a state that is neither a disconnection nor a short circuit may be determined as a disconnection or a short circuit. 
     Accordingly, in the embodiment, in order to increase the linearity of temperature-voltage properties at an intermediate temperature or more of the temperature measurement range, a value of the fixed resistor R 1  included in the temperature sensor  120  is adjusted to allow an inclination at the intermediate temperature or more of the temperature measurement range to be greater than an inclination of a temperature-voltage curve at the intermediate temperature or less of the temperature measurement range. In  FIG. 4 , the curve is forced to move toward the B curve. According thereto, temperature of the intermediate temperature or more of the temperature measurement range is allowed to be precisely measured. 
     Determining whether the NTC thermistor is short-circuited is determined according to whether an output temperature of the voltage temperature matching unit  140  maintains being higher than the upper limit value of the normal operation temperature range for exceeding an abnormal operation reference time. Since a degree of precision of temperature measurement relatively decreases at the intermediate temperature or less of the temperature measurement range, it is determined by adding an additional switch and an additional fixed resistor whether being disconnected. An operation of determining whether being disconnected will be described in detail with reference to  FIGS. 5 to 7 . 
       FIG. 5  is a block diagram illustrating a temperature measurement apparatus  200  according to another embodiment. 
     Referring to  FIG. 5 , the temperature measurement apparatus  200  may include a DC current generation unit  210 , a temperature sensor  220 , a buffer  230 , a voltage temperature matching unit  240 , a voltage temperature table storage unit  250 , an abnormal operation determination unit  260 , a charge control unit  270 , and a battery  280 . 
     The DC voltage generation unit  210  generates a DC voltage. 
     The temperature sensor  220  includes an NTC thermistor  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 abnormal operation determination unit  260 . In this case, the plurality of resistance values includes a default resistance value for measuring a temperature and a temporary resistance value for determining whether being disconnected. 
     The voltage temperature table storage unit  250  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  220 , respectively. 
     The charge control unit  270  controls a charging operation related to the battery  280  of an electric automobile according to a disconnection sensing signal and a short-circuit sensing signal outputted by the abnormal operation determination unit  260 . 
       FIG. 6  is a circuit diagram of the temperature measurement apparatus  200 . 
     The variable resistor part  221  of the temperature sensor  220  includes a fixed resistor R 3 , a fixed resistor R 4 , and a switch SW. The NTC thermistor 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 thermistor Rn 2  and another end grounded. 
     The fixed resistor R 4  and the switch SW are connected in series between the NTC thermistor Rn 2  and a ground. In the embodiment, one end of the fixed resistor R 4  is connected to the NTC thermistor Rn 2  and one end of the switch SW is connected to another end of the resistor R 4  and another end thereof is grounded. In another example, one end of the switch SW is connected to the NTC thermistor 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. 6 , 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 default resistance value for measuring the temperature. 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 temporary resistance value for determining the disconnection. 
     In a graph of  FIG. 4 , to allow temperature-voltage properties of the temperature sensor  220  to correspond to the B curve rather than the A curve, the default resistance value of the variable resistor part  221  may be smaller than a resistance value of the NTC thermistor Rn 2  at the intermediate temperature of the temperature measurement range. To increase the linearity of the temperature-voltage properties of the temperature sensor  220  between the upper limit temperature and the intermediate temperature of the temperature measurement range, the default resistance value of the variable resistor part  221  may be smaller than ⅕ of the resistance value of the NTC thermistor Rn 2  at the intermediate temperature of the temperature measurement range. 
     On the other hand, to allow determining whether being disconnected to be easily performed within a low temperature range of the temperature measurement range, the temporary resistance value of the variable resistor part  221  may be greater than the default resistance value of the variable resistor part  221 . When there is shown a noticeable difference between output voltages of the temperature sensor  220  having the temporary resistance value and having the default resistance value, it is clearly determined whether being disconnected. 
     To allow the determining whether being disconnected to be easily performed within the low temperature range of the temperature measurement range, the temporary resistance value of the variable resistor part  221  may be greater than ten times the default resistance value of the variable resistor part  221 . For this, the resistance value of the fixed resistor R 3  may be greater than ten times the resistance value of the fixed resistor R 4 . 
     The switch SW may be turned on or off by the abnormal operation determination unit  260 . 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 thermistor 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. 
     An input end of the voltage temperature matching unit  240  is connected to the output end of the operational amplifier Op and the one end of the fixed resistor R 5 . 
     Other components of the temperature measurement apparatus  200  will be described in detail with reference to  FIG. 7 . 
       FIG. 7  is a flowchart illustrating operations of a method of detecting a disorder of the temperature sensor  220 . 
     The temperature  220  outputs a voltage value corresponding to a present temperature by using the resistance value of the NTC thermistor Rn 2 , varying with a temperature and the default 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 temperature matching 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 temperature matching unit  240  through the buffer  230 . 
     The voltage temperature matching unit  240  matches the buffered voltage with a voltage on a voltage temperature table stored in the voltage temperature table storage unit  250  and outputs a present temperature corresponding to the buffered voltage value (S 205 ). The voltage temperature table varies with properties of the temperature sensor  220 . On the other hand, the buffer  230  may be omitted. In this case, the voltage temperature matching unit  240  may output a present temperature corresponding to the output voltage of the temperature sensor  220 . 
     The abnormal operation determination unit  260  determines whether the present temperature is out of a preset normal operation temperature range (S 207 ). When it is not more than an abnormal operation reference time, the abnormal operation determination unit  160  determines it as a normal operation state. 
     When the present temperature is out of the normal operation temperature range, the abnormal operation determination unit  260  determines whether the present temperature maintains a value out of the normal operation temperature range for more than the preset abnormal operation reference time (S 209 ). When it is not more than the abnormal operation reference time, the abnormal operation determination unit  160  determines it as a normal operation state. 
     When the present temperature maintains the value out of the normal operation temperature range for more than an abnormal operation reference time, the abnormal operation determination unit  260  determines whether the present temperature is lower than a lower limit value of the normal operation temperature range (S 211 ). 
     When the present temperature is not lower than the lower limit of the normal operation temperature range, the abnormal operation determination unit  260  outputs a short-circuit sensing signal indicating a short circuit of the NTC thermistor (S 213 ). 
     When the present temperature is lower than the lower limit of the normal operation temperature range, the abnormal operation determination unit  260  controls the variable resistor part  221  in the temperature sensor  220  to have the temporary resistance value (S 215 ). Particularly, in the embodiment of  FIG. 6 , the abnormal operation determination unit  260  turns off the switch SW in the temperature sensor  220 . When the switch SW is turned off, intensity of a combined resistance of the fixed resistor R 3  and the fixed resistor R 4  of the temperature sensor  220  is changed. Accordingly, when the NTC thermistor Rn 2  is not disconnected, the output voltage of the temperature sensor  220  becomes different from before turning off the switch. 
     In this case, since the switch is turned off, it is impossible to allow the voltage temperature matching unit  240  to match the output voltage of the temperature  220  with the voltage temperature table and to output a present temperature. Accordingly, before the switch is short-circuited or a disconnection signal is outputted, a gap in the temperature measurement occurs. During the gap, the abnormal operation determination unit  260  outputs a temperature before turning the switch on and inputs the temperature to the charge control unit  270 . Accordingly, as the switch operates at the higher speed, the gap in the temperature measurement may be more reduced. 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 gap in the temperature measurement may be reduced. 
     The abnormal operation determination unit  260  determines whether a voltage outputted by the temperature sensor  20  according to the temporary resistance value of the variable resistance unit  221  is greater than a disconnection determination reference voltage (S 217 ). Particularly, in the embodiment of  FIG. 6 , the abnormal operation determination unit  260  determines whether the output voltage of the temperature sensor  220  after turning off the switch is greater than the disconnection determination reference voltage. In the embodiment, the intensity of a disconnection determination reference voltage of the fixed resistor R 3  may be set as a half or ⅔ of the intensity of a voltage of the DC voltage generation unit  210 . 
     The abnormal operation determination unit  260 , when the output voltage of the temperature sensor  220  is smaller than the disconnection determination reference voltage, determines the temperature sensor  220  as being in a normal operation state and turns on the switch SW in the temperature sensor  220  (S 219 ). 
     The abnormal operation determination unit  260  outputs an NTC thermistor disconnection sensing signal when the output voltage is smaller than the disconnection determination reference voltage (S 221 ). When the NTC thermistor Rn 2  is disconnected, since the voltage is not supplied from the DC voltage generation unit  210  to the variable resistor part  221 , a voltage lower than the disconnection determination reference voltage is outputted. 
     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 present invention as defined by the following claims.