JP4254270B2 - Thermal sensing circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat sensing circuit that senses temperature using a temperature sensing element such as a thermistor.
[0002]
[Prior art]
Conventionally, in a heat detection circuit used as a fire alarm or the like, a temperature associated with a fire or the like is measured using a temperature detection element such as a thermistor, and the measured temperature exceeds a predetermined temperature or the measured temperature is a predetermined temperature. There are known devices that detect the occurrence of a fire, the temperature of a measurement object having reached a predetermined temperature, and the like by detecting that the temperature has risen beyond the rate of increase. In such a heat sensing circuit, a temperature sensing element such as a thermistor has a non-linear temperature characteristic. Therefore, it is necessary to correct a measurement signal obtained by the temperature sensing element in order to perform temperature measurement.
[0003]
For example, the resistance value of a thermistor decreases exponentially with increasing temperature. For this reason, a heat sensing circuit is known in which a voltage generated by passing a current through a thermistor is converted into digital data by an A / D converter, and temperature information is obtained from the digital data by an arithmetic process using an exponential function. It has been. In such a heat sensing circuit, it is necessary to perform complicated arithmetic processing such as exponential function calculation in order to correct the temperature characteristics of the temperature detection element, and a microcomputer is used for the arithmetic processing (for example, , See Patent Document 1).
[0004]
[Patent Document 1]
JP-A-10-49773
[0005]
[Problems to be solved by the invention]
However, when the temperature characteristic of the temperature detection element is corrected using the microcomputer as described above, there is an inconvenience that it is difficult to reduce the cost.
[0006]
An object of the present invention is to provide a heat sensing circuit capable of correcting the temperature characteristics of the temperature sensing element using a simple circuit and reducing the cost.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 is a heat sensing circuit including a temperature detection unit that generates a detection voltage corresponding to a characteristic value using a temperature detection element whose electrical characteristic value changes according to temperature. The detection voltage generated by the temperature detection means is converted from analog to digital. Digital AD conversion means for generating detection voltage data as data, and the AD conversion means Digital data Detection voltage data Used as an address The address corresponds to the detected voltage data And the temperature characteristics of the temperature sensing element were corrected. Table storage means for storing temperature data and generated by the AD conversion means Digital data The detection voltage data is acquired as an address by the table storage unit, and based on the temperature data output from the table storage unit, a determination unit that detects that a predetermined determination condition is satisfied, and the determination unit And a notifying means for notifying of heat detection when it is detected that the determination condition is satisfied.
[0008]
According to the first aspect of the present invention, the detection voltage corresponding to the temperature is generated by the temperature detection means, the detection voltage is analog-digital converted by the AD conversion means, and detection voltage data is generated. By obtaining the address of the table storage means, the table storage means outputs temperature data corresponding to the detected voltage data. Then, based on the temperature data output from the table storage unit, when the determination unit detects that a predetermined determination condition is satisfied, the notification unit notifies the heat detection.
[0009]
According to a second aspect of the present invention, in the heat sensing circuit according to the first aspect, a power supply stabilizing means for stabilizing a power supply voltage taken from outside and generating a reference voltage for the AD conversion means to perform analog-digital conversion. Is further provided.
[0010]
According to the second aspect of the present invention, the reference voltage for the analog-to-digital conversion by the AD conversion means is stabilized. In this case, the temperature data corresponding to the detected voltage data is directly output from the table storage means using the detected voltage data generated by the analog-digital conversion of the AD converting means as an address. Affects data accuracy. Accordingly, the accuracy of the temperature data is improved by stabilizing the reference voltage.
[0011]
According to a third aspect of the present invention, in the heat sensing circuit according to the first or second aspect, the AD conversion unit and a first and a second for switching the connection between the AD conversion unit and the temperature detection unit. An integrated circuit having second, third, and fourth switching means, and a resistance mode switching means for controlling on / off of the first, second, third, and fourth switching means, and the temperature detecting element is A temperature-sensitive resistor whose resistance value changes according to temperature, and the temperature detecting means divides the power supply voltage taken from the outside of the temperature detecting means between the heat-sensitive resistors connected in series. Between the first resistor and the thermal resistor that is connected to the connection point between the thermal resistor and the first resistor and that is connected in series with the power supply voltage taken from the outside of the temperature detecting means. A second resistor for voltage division The integrated circuit includes a first connection terminal connected to the thermal resistor via the first resistor, and a second connection terminal connected to the thermal resistor via the second resistor. The first switching means is connected to the first resistor via the first connection terminal and turns on and off the current flowing through the first resistor. The second switching means The third switching means is led to the first connection terminal, connected to the second resistance via the second connection terminal and turns on and off the current flowing through the second resistance. The voltage is guided to the AD conversion means as the detection voltage and turned on / off, and the fourth switching means guides the voltage led to the second connection terminal to the AD conversion means as the detection voltage and is turned on / off. And The resistance mode switching means is a first resistor for turning on the first and fourth switching means and turning off the second and third switching means in accordance with a detection voltage guided to the AD conversion means. The mode is switched between the second resistance mode in which the second and third switching means are turned on and the first and fourth switching means are turned off.
[0012]
According to the third aspect of the present invention, in the first resistance mode, when the first switching means is turned on, the current flowing through the thermal resistor and the first resistor through the first connection terminal A detection voltage generated between the thermal resistor and the first resistor is guided to the AD conversion means via the second connection terminal and the fourth switching means. Further, in the second resistance mode, when the second switching means is turned on, the current flowing through the thermal resistor and the second resistor via the second connection terminal causes the thermal resistor and the second resistor to be The detection voltage generated between the first and second switching means is led to the AD conversion means via the first connection terminal and the third switching means.
[0013]
In this case, in the first resistance mode, the first connection terminal is used for the purpose of flowing current to the thermal resistor and the first resistor, and the second connection terminal is used for the purpose of guiding the detection voltage to the AD conversion means. Used. On the other hand, in the second resistance mode, the second connection terminal is used for the purpose of flowing a current to the thermal resistor and the second resistance, and the first connection terminal is used for the purpose of guiding the detection voltage to the AD conversion means. It is done. Thereby, each of the first and second connection terminals can be used for two different applications.
[0014]
According to a fourth aspect of the present invention, in the heat sensing circuit according to any one of the first to third aspects, the determination means is temperature data output from the table storage means at a sampling timing for each predetermined sampling time interval. And second storage means for storing the temperature data output from the table storage means at the sampling timing immediately before the sampling timing at which the first storage means stores the temperature data. The difference between the temperature data stored by the first storage means and the temperature data stored by the second storage means is compared with predetermined differential reference data, and the difference is the differential A differential determination means for detecting a differential establishment state that is larger than the value of the reference data, and a power supply voltage taken from outside is a predetermined reset power. Power monitoring means for initializing the first and second storage means when the following conditions are met, and the determination condition is satisfied based on whether or not the differential determination state is detected by the differential determination means It is characterized by detecting this.
[0015]
According to the fourth aspect of the present invention, the temperature data output from the table storage means is stored in the first storage means, and the temperature data before a predetermined sampling time is stored in the first storage means. 2 storage means. When the difference between the temperature data stored by the first storage unit and the temperature data stored by the second storage unit is larger than the value of the predetermined differential reference data, that is, at a predetermined sampling time. When the temperature rise is larger than the value of the predetermined differential reference data, it is possible to detect that the determination condition is satisfied. Further, the determination means includes power supply monitoring means for initializing the first and second storage means when the power supply voltage becomes equal to or lower than a predetermined reset voltage. First and second storage means are initialized.
[0016]
According to a fifth aspect of the present invention, in the heat sensing circuit according to the fourth aspect, the determination unit compares the temperature data output from the table storage unit with predetermined constant temperature reference data, and calculates the temperature data. Is further provided with a constant temperature determination means for detecting a constant temperature establishment state in which the value is larger than the value of the constant temperature reference data, and the determination means is based on whether or not the differential determination state is detected by the differential determination means and the constant temperature determination means. It is characterized in that it is detected that the determination condition is satisfied according to whether or not the constant temperature establishment state is detected.
[0017]
According to the fifth aspect of the present invention, it is detected that the determination condition is satisfied depending on whether or not the differential establishment state is detected by the differential determination unit and whether or not the constant temperature establishment state is detected by the constant temperature determination unit. Therefore, when the temperature rise at the predetermined sampling time is larger than the value of the predetermined differential reference data, and when the temperature is higher than the value of the constant temperature reference data, it is detected that the determination condition is satisfied. It becomes possible to do.
[0018]
According to a sixth aspect of the present invention, in the heat sensing circuit according to the fifth aspect, a setting is made to a differential mode for detecting that the determination condition is satisfied according to presence / absence of detection of the differential establishment state; The thermosensitive resistor further includes a setting accepting unit that accepts a setting to be in a constant temperature mode for detecting that the determination condition is satisfied depending on whether or not the constant temperature establishment state is detected, and the thermal resistor has a resistance value as the temperature rises. The negative temperature characteristic resistor becomes smaller, and the determination unit detects that the determination condition is satisfied when the setting of the constant temperature mode is received by the setting reception unit when the constant temperature establishment state is detected. When the setting accepting means is accepted by the setting accepting means, a short-circuit judgment indicating that the differential establishment state is detected and that the negative temperature characteristic resistor is short-circuited. When the constant temperature determining means the temperature as the constant temperature reference data detects a constant temperature established state is characterized by that detects that the determination condition is satisfied.
[0019]
According to the sixth aspect of the present invention, when the setting receiving unit accepts the setting for setting the constant temperature mode, the determination unit establishes the determination condition when the constant temperature determination unit detects the constant temperature establishment state. Is detected. When the setting accepting unit accepts the setting for setting the differential mode, when the differential establishment state is detected by the differential determination unit, the determination unit detects that the determination condition is established, Even when the constant temperature establishment state is detected by the determination means using the short-circuit determination temperature as the constant temperature reference data, the determination means detects that the determination condition is satisfied.
[0020]
As a result, the user can switch between the constant temperature mode and the differential mode using the setting accepting means, and when the setting accepting setting is accepted by the setting accepting means, the constant temperature determining means is used. It becomes possible to detect a short circuit of the negative temperature characteristic resistor.
[0021]
The invention according to claim 7 is the thermal sensing circuit according to any one of claims 1 to 6, wherein the thermal resistor is a negative temperature characteristic resistor whose resistance value decreases as the temperature rises. When the temperature data falls below a predetermined disconnection determination temperature, it is provided with disconnection detection means for detecting disconnection of the negative temperature characteristic resistor, and the notification means detects the disconnection of the negative temperature characteristic resistor by the disconnection detection means. It is characterized by notifying heat detection.
[0022]
According to the seventh aspect of the present invention, when the temperature data falls below a predetermined disconnection determination temperature, the disconnection of the negative temperature characteristic resistor is detected by the disconnection detecting means, and the heat detection is notified. In this case, the disconnection detection means detects the disconnection of the negative temperature characteristic resistor when the temperature data falls below a predetermined disconnection determination temperature, so the disconnection detection means is configured using a temperature comparison circuit similar to the constant temperature determination means. Can do.
[0023]
The invention according to claim 8 is the heat sensing circuit according to any one of claims 1 to 7, wherein the heat sensitive resistor is a negative temperature characteristic resistor whose resistance value decreases as the temperature rises. Short circuit detection means for detecting a short circuit of the negative temperature characteristic resistor when temperature data exceeds a predetermined short circuit determination temperature, the short circuit detection means detects a short circuit of the negative temperature characteristic resistor. It is characterized by notifying heat detection.
[0024]
According to invention of Claim 8, when the said temperature data exceeds predetermined | prescribed short circuit determination temperature, the short circuit of a negative temperature characteristic resistor is detected by a short circuit detection means, and heat detection is alert | reported. In this case, since the short circuit detection means detects a short circuit of the negative temperature characteristic resistor when the temperature data exceeds a predetermined short circuit determination temperature, the short circuit detection means is configured using a temperature comparison circuit similar to the constant temperature determination means. Can do.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a block diagram showing an example of the configuration of the heat sensing circuit 10 according to the first embodiment of the present invention. A heat sensing circuit 10 shown in FIG. 1 is connected to a pair of sensor lines 11 for supplying power for operation of the heat sensing circuit 10 and transmitting a notification signal output from the heat sensing circuit 10 via a connection terminal 12. Connected. A surge absorber 13 that absorbs a surge voltage generated in the sensor line 11 and protects the internal circuit of the heat sensing circuit 10 is connected between both electrodes of the connection terminal 12. A diode bridge 14 is connected between both electrodes of the connection terminal 12, and the power supply voltage taken in from the sensor line 11 is rectified by the diode bridge 14 and then output to the constant voltage circuit 15. Power supply voltage V for operation from the power supply line 16 to each part in the heat sensing circuit 10 _OP Is output.
[0026]
The power line 16 includes, for example, a reset circuit 17 composed of a general-purpose reset IC (Integrated Circuit), a thermal circuit 18 that detects an ambient temperature and outputs a detection voltage corresponding to the detected temperature, and a thermal circuit 18. Based on the output detection voltage, for example, the connection terminal 109 of the integrated circuit 100 that detects that a predetermined temperature condition associated with the occurrence of a fire is established is connected, and the reset circuit is connected from the constant voltage circuit 15 via the power line 16. 17. Power supply voltage V to thermal circuit 18 and integrated circuit 100 _OP Is output.
[0027]
Between a pair of output lines of the diode bridge 14, a notification output circuit 19 made of, for example, a thyristor is connected. When the heat detection notification signal OUT indicating that the predetermined temperature condition is established is output from the integrated circuit 100 to the notification output circuit 19 at a high level, the notification output circuit 19 is turned on and the output line of the diode bridge 14 Is short-circuited.
[0028]
On the other hand, a receiver (not shown) that monitors the current flowing through the sensor line 11 is connected to the sensor line 11. This receiver is configured to detect that the current flowing through the sensor line 11 is increased as the notification output circuit 19 is turned on, for example, as a heat detection notification indicating a fire alarm or the like.
[0029]
The thermal sensing circuit 10 includes a thermistor 20 whose resistance value changes according to temperature, and a power supply voltage V output from the constant voltage circuit 15. _OP Is connected to a connection point between the thermistor 20 and the resistor 21 and the power supply voltage V _OP And a resistor 22 that divides the voltage between the thermistor 20 connected in series.
[0030]
The integrated circuit 100 includes an AD converter 101, an AD input selector 102, an address decoder 103, a table memory 104, an EEPROM (Electrically Erasable Programmable Read Only Memory) 105, an oscillation circuit 106, a model setting circuit 107, and a determination circuit 108. The block includes a switch SW1, a switch SW2, and connection terminals 109, 110, 111, 112, 113, 114, 115, 116, and 117, and the switch 24 is connected to the outside of the integrated circuit 100 via the connection terminal 114. A switch 25 is connected via a terminal 115.
[0031]
A power supply line 16 is connected to the connection terminal 109, and the power supply voltage V output from the constant voltage circuit 15. _OP Is supplied to each circuit block in the integrated circuit 100 through the connection terminal 109. A ground line 23 is connected to the connection terminal 113, and a ground potential is supplied to each circuit block in the integrated circuit 100 via the connection terminal 113.
[0032]
For example, analog switches are used as the switches SW1 and SW2. The switch SW1 is interposed between the connection terminal 110 and the connection terminal 113, and the switch SW2 is interposed between the connection terminal 111 and the connection terminal 113. The switch SW1 is turned on and the switch SW2 is turned off by a control signal corresponding to a low temperature mode (first resistance mode) from the AD input selector 102 described later, and the power supply voltage V _OP Is divided by the thermistor 20 and the resistor 21, and the voltage generated at the connection point between the thermistor 20 and the resistor 21 is guided to the AD converter 101 and the AD input selector 102 via the connection terminal 112 as the detection voltage Vs.
[0033]
Further, the switch SW1 is turned off and the switch SW2 is turned on by the control signal corresponding to the high temperature mode (second resistance mode) from the AD input selector 102 described later, and the power supply voltage V _OP Is divided by the thermistor 20 and the resistor 22, and the voltage generated at the connection point between the thermistor 20 and the resistor 22 is led to the AD converter 101 and the AD input selector 102 through the connection terminal 112 as the detection voltage Vs.
[0034]
The AD converter 101 is, for example, an 8-bit A / D converter. The AD converter 101 performs analog-to-digital conversion on the detection voltage Vs guided through the connection terminal 112 to generate detection voltage data Dvs having a length of 8 bits and an address decoder 103. Output to. Further, the reference voltage V when the AD converter 101 performs analog-digital conversion. _ref As the power supply voltage V _OP Is used.
[0035]
Reference voltage V _ref For example, the power supply voltage V _OP A voltage generated by, for example, voltage dividing by resistance may be used. Also, the power supply voltage V _OP 2 types of reference voltage V _ref1 And reference voltage V _ref2 And the reference voltage V _ref1 And reference voltage V _ref2 For example, in the low temperature mode, the reference voltage V _ref As reference voltage V _ref1 And in the high temperature mode, the reference voltage V _ref As reference voltage V _ref2 It is good also as a structure using.
[0036]
The AD input selector 102 switches between a resistance mode having a low temperature mode for performing temperature correction suitable for the temperature characteristics of the thermistor 20 at a low temperature and a high temperature mode for performing temperature correction suitable for a high temperature. Specifically, the AD input selector 102 is configured using, for example, a comparator, and the detection voltage Vs guided through the connection terminal 112 and a predetermined mode switching voltage V _m Are compared using a comparator.
[0037]
For example, the AD input selector 102 detects that the detection voltage Vs is the mode switching voltage Vs. _m When the temperature is less than, the switch SW1 is turned on and the switch SW2 is turned off as the low temperature mode, and a temperature select signal is output to the address decoder 103 at a low level to indicate the low temperature mode. Further, the AD input selector 102 is configured such that the detection voltage Vs is, for example, the mode switching voltage Vs. _m At this time, the switch SW1 is turned off and the switch SW2 is turned on as the high temperature mode, and the temperature select signal is output to the address decoder 103 at a high level to indicate the high temperature mode.
[0038]
Note that the AD input selector 102 has a mode switching voltage V _m Lower lower mode switching voltage V _mL And upper mode switching voltage V higher than mode switching voltage _mH When switching from the low temperature mode to the high temperature mode, the detection voltage Vs rises and the lower mode switching voltage V _mL When switching from high temperature mode to low temperature mode, the detection voltage Vs decreases and the upper mode switching voltage V _mH It is good also as a structure which switches when it reaches | attains. As a result, a voltage difference can be made between the detection voltage Vs for switching from the low temperature mode to the high temperature mode and the detection voltage Vs for switching from the high temperature mode to the low temperature mode. _m Even if the vicinity fluctuates due to the influence of noise or the like, it is possible to prevent the resistance mode from being switched by mistake.
[0039]
The address decoder 103 makes the temperature select signal output from the AD input selector 102 correspond to 1 bit of the address, and adds it to the 8-bit detection voltage data Dvs output from the AD converter 101 to generate a 9-bit address. To the table memory 104.
[0040]
The table memory 104 is configured by using, for example, a ROM (Read Only Memory), and corrects the temperature characteristic of the thermistor 20 to the detected voltage data output from the AD converter 101 to obtain temperature data Dt representing the temperature. A temperature conversion table for conversion is stored in advance. FIG. 2 is an explanatory diagram for explaining the configuration of the temperature conversion table stored in the table memory 104.
[0041]
In FIG. 2, the address column 41 describes the 9-bit address of the table memory 104 in hexadecimal, and the data column 42 represents the 8-bit data stored in the address in hexadecimal. The Sel column 43 indicates the most significant bit of the address corresponding to the temperature select signal output from the AD input selector 102, and is set to “0” when the temperature select signal is low level, that is, in the low temperature mode, and the temperature select signal is high. It is set to “1” in the level, that is, in the high temperature mode. The Dvs column 44 is detection voltage data Dvs and corresponds to the lower 8 bits of the address of the table memory 104.
[0042]
Further, the temperature code column 45 is data stored in the table memory 104, and the address in which the Sel column 43 is “0” includes the low temperature mode, that is, the power supply voltage V _OP Is stored with a temperature code representing a temperature corresponding to the detected voltage data Dvs obtained by dividing the voltage by the thermistor 20 and the resistor 21. In addition, an address whose Sel column 43 is “1” has a high temperature mode, that is, a power supply voltage V _OP Is stored with a temperature code representing a temperature corresponding to the detected voltage data Dvs obtained by dividing the voltage by the thermistor 20 and the resistor 22. In this case, as the temperature code, for example, 8-bit data in which 0.5 ° C. is represented by 1 of the temperature code is used. The temperature value column 46 indicates a temperature value corresponding to the temperature code column 45.
[0043]
Accordingly, the table memory 104 outputs temperature data Dt obtained by correcting the temperature characteristics of the thermistor 20 to the determination circuit 108 in accordance with the address output from the address decoder 103.
[0044]
Returning to FIG. 1, the EEPROM 105 and the oscillation circuit 106 constitute a programmable oscillator, and the setting data is stored in the EEPROM 105, whereby the frequency of the clock signal CK output from the oscillation circuit 106 is changed or the frequency is adjusted. It is possible to do. Instead of using the EEPROM 105 and the oscillation circuit 106, a general-purpose programmable oscillator may be used. Further, the oscillation circuit 106 may be configured by a fixed frequency oscillator. The oscillation circuit 106 may be configured to output a plurality of clock signals having different frequencies.
[0045]
The switches 24 and 25 are setting switches for selecting a determination method for determining heat detection, and are switchable by the user. The switch 24 is switchable between a contact 26 side connected to the power supply line 16 and a contact 27 side connected to the ground line 23, and the switch 25 is switched to the contact 28 side connected to the power supply line 16 and the ground line 23. It is possible to switch to the contact 29 side connected to. Thereby, when the switch 24 is switched to the contact 26 side, the connection terminal 114 is set to the high level, and when the switch 24 is switched to the contact 27 side, the connection terminal 114 is set to the low level. When the switch 25 is switched to the contact 28 side, the connection terminal 115 is set to the high level, and when the switch 25 is switched to the contact 29 side, the connection terminal 115 is set to the low level.
[0046]
The model setting circuit 107 sets a determination method according to the voltage levels of the connection terminals 114 and 115. For example, if the signal name of the connection terminal 114 is MODE1 and the signal name of the connection terminal 115 is MODE2, the differential type (one type) is selected when MODE1 is low level and MODE2 is high level, and MODE1 and MODE2 are high level. A differential type (two types) is used, a compensation type is set when MODE1 and MODE2 are at a low level, and a constant temperature type is set when MODE1 is at a high level and MODE2 is at a low level. Then, a method setting signal indicating the set determination method is output to the determination circuit 108. Thereby, when the user switches the switches 24 and 25, the determination method of the differential type (1 type), the differential type (2 types), the compensation type, and the constant temperature type can be selected and set. Has been made possible.
[0047]
The determination circuit 108 detects the satisfaction of the determination condition according to the determination condition according to the determination method set by the model setting circuit 107. FIG. 3 is a block diagram for explaining an example of the configuration of the determination circuit 108. The determination circuit 108 shown in FIG. 3 forms a shift register between the register 120 and the register 120 that stores the temperature data Dt output from the table memory 104 in synchronization with the rising edge of the clock signal CK. In synchronization with the rising edge of the signal CK, a register 121 that stores the temperature data Dt stored in the register 120 at the preceding rising edge of the clock signal CK as the temperature data Dtm one clock earlier is provided.
[0048]
Further, the determination circuit 108 subtracts the temperature data Dtm output from the register 121 from the temperature data Dt output from the register 120, and outputs a subtraction value Ddt to the temperature difference determination circuit 123; A differential value register 124 that stores differential reference data Ddiff1 in advance and a differential value register 125 that stores predetermined differential reference data Ddiff2 different from the differential reference data Ddiff1 are provided.
[0049]
The temperature difference determination circuit 123 compares the differential reference data Ddiff2 output from the differential value register 125 when the method setting signal from the model setting circuit 107 is, for example, a signal indicating a differential type (two types). If the method setting signal is a signal indicating a determination method other than the differential type (two types), the differential reference data Ddiff1 output from the differential value register 124 is used as the differential reference data Ddiff. Capture as.
[0050]
Then, the temperature difference determination circuit 123 compares the subtraction value Ddt with the differential reference data Ddiff using a comparison circuit. If the subtraction value Ddt is equal to or less than the differential reference data Ddiff, the temperature difference determination signal Is output to the up / down counter 126 at a low level. On the other hand, when the subtraction value Ddt is larger than the differential reference data Ddiff, the temperature difference determination signal is output to the up / down counter 126 at a high level.
[0051]
Thereby, for example, when the cycle of the clock signal CK is 1 second, a temperature rise of 1 second is generated as the subtraction value Ddt, and when the temperature rise value is larger than the differential reference data Ddiff, Since the difference determination signal is output at a high level, it is possible to detect that the temperature rise per unit time, that is, the rate of temperature rise exceeds a predetermined value. In addition, when the user sets the determination method to the differential type (1 type) and the differential type (2 types) using the switches 24 and 25, the temperature increase rate to be detected is changed. It becomes possible to do.
[0052]
The up / down counter 126 adds 1 to the count value when the temperature difference determination signal output from the temperature difference determination circuit 123 is high level and the clock signal CK rises, and the clock difference signal rises when the temperature difference determination signal is low level. It is an up / down counter that subtracts 1 from the count value. When the count value reaches a predetermined threshold, for example, “10” or more, the differential detection signal OUTd is output to the output selector 134 at a high level.
[0053]
In this case, the differential detection signal OUTd is set to the high level when the predetermined temperature increase rate continues for a predetermined time or longer, for example, when the cycle of the clock signal CK is 1 second and the threshold value is 10 for 10 seconds or longer.
[0054]
Further, the determination circuit 108 includes a constant temperature value register 127 that stores predetermined constant temperature reference data Dconst in advance, and a short circuit value register 128 that stores in advance short circuit reference data Dshort indicating temperature data detected when the thermistor 20 is short-circuited. The constant temperature short circuit determination circuit 129 is provided.
[0055]
For example, when the method setting signal from the model setting circuit 107 is a signal indicating a constant temperature equation or a compensation equation, the constant temperature short circuit determination circuit 129 uses the constant temperature reference data Dconst output from the constant temperature value register 127 as the constant temperature short circuit reference data. On the other hand, if the system setting signal is a signal indicating a differential type (1 type) or a differential type (2 types), the short-circuit reference data Dshort output from the short-circuit value register 128 is used as the constant temperature short-circuit reference data. Import as Dcs.
[0056]
The constant temperature short circuit determination circuit 129 uses the comparison circuit to compare the temperature data Dt output from the register 120 with the constant temperature short circuit reference data Dcs, and when the temperature data Dt is equal to or less than the constant temperature short circuit reference data Dcs. Outputs a constant temperature short circuit determination signal to the up / down counter 130 at a low level. On the other hand, if the temperature data Dt is larger than the constant temperature short circuit reference data Dcs, the constant temperature short circuit determination signal is output at a high level. To 130.
[0057]
Thereby, the constant temperature short circuit determination circuit 129 is used to detect the short circuit of the thermistor 20 when the determination method is set to the differential type (1 type) or the differential type (2 types). When it is set to the constant temperature type or the compensation type, it is used to detect that the temperature detected by the thermistor 20 exceeds the predetermined constant temperature reference data Dconst. In order to detect that the predetermined constant temperature reference data Dconst has been exceeded, it is not necessary to provide a determination circuit for each, and the circuit is simplified.
[0058]
The up / down counter 130 is an up / down counter similar to the up / down counter 126. When the constant temperature short circuit determination signal output from the constant temperature short circuit determination circuit 129 is at a high level and the clock signal CK rises, the count value is incremented by one. When the short circuit determination signal is at low level and the clock signal CK rises, 1 is subtracted from the count value. When the count value reaches a predetermined threshold, for example, “10” or more, the constant temperature short circuit detection signal OUTcs is output to the output selector 134 at a high level.
[0059]
The determination circuit 108 includes a disconnection value register 131 that stores in advance disconnection reference data Dopen indicating temperature data detected when the thermistor 20 is disconnected, and a disconnection determination circuit 132. The disconnection determination circuit 132 compares the temperature data Dt output from the register 120 with the disconnection reference data Dopen output from the disconnection value register 131 using a comparison circuit, and the temperature data Dt is a value equal to or higher than the disconnection reference data Dopen. If there is, the disconnection determination signal is output at a low level to the up / down counter 133. On the other hand, if the temperature data Dt is smaller than the disconnection reference data Dopen, the disconnection determination signal is output at a high level. To 133.
[0060]
The up / down counter 133 is an up / down counter similar to the up / down counter 126. When the disconnection determination signal output from the disconnection determination circuit 132 is at a high level and the clock signal CK rises, the count value is incremented by one. When the clock signal CK rises at low level, 1 is subtracted from the count value. When the count value becomes a predetermined threshold, for example, “10” or more, the disconnection detection signal OUTo is output to the output selector 134 at a high level.
[0061]
The output selector 134 outputs the heat detection notification signal OUT to the notification output circuit 19 through the connection terminal 116 at a high level based on the disconnection detection signal OUTo, the constant temperature short circuit detection signal OUTcs, the differential detection signal OUTd, and the method setting signal. Then, the notification output circuit 19 is turned on. Then, a receiver (not shown) connected to the sensor line 11 detects the heat detection notification.
[0062]
Returning to FIG. 1, the reset circuit 17 _OP When the voltage drops, a reset signal is output to the integrated circuit 100 via the connection terminal 117, and the registers 120 and 121 and the up / down counters 126, 130, and 133 of the determination circuit 108 are initialized. As a result, the power supply voltage V _OP When the operation of the integrated circuit 100 becomes unstable due to a decrease in the temperature of the integrated circuit 100, it is possible to suppress erroneous notification of heat detection due to a malfunction of the determination circuit 108.
[0063]
Next, the operation of the heat sensing circuit 10 shown in FIG. 1 will be described. First, in a state where the switch SW1 is turned on and the switch SW2 is turned off in the low temperature mode, the ambient temperature is conducted to the thermistor 20, and the temperature of the thermistor 20 becomes substantially equal to the ambient temperature. A resistance corresponding to the temperature of the thermistor 20 is generated in the thermistor 20. Then, the power supply voltage V output from the constant voltage circuit 15 _OP Is divided by the thermistor 20 and the resistor 21, and the voltage generated at the connection point between the thermistor 20 and the resistor 21 is guided to the AD converter 101 and the AD input selector 102 via the connection terminal 112 as the detection voltage Vs. Thereby, the detection voltage Vs according to the ambient temperature is generated.
[0064]
Next, the AD input selector 102 controls the detection voltage Vs and the lower mode switching voltage V. _mL For example, the detection voltage Vs is the lower mode switching voltage V _mL If it is less than this, the low temperature mode is maintained, and the temperature select signal is output to the address decoder 103 at a low level. On the other hand, the detection voltage Vs is the lower mode switching voltage V _mL In the above case, the low temperature mode is switched to the high temperature mode, the switch SW1 is turned off and the switch SW2 is turned on, and the temperature select signal is output to the address decoder 103 at a high level.
[0065]
Next, the AD converter 101 converts the detection voltage Vs from analog to digital to generate detection voltage data Dvs having a length of 8 bits and outputs the detection voltage data Dvs to the address decoder 103.
[0066]
FIG. 4 is a diagram showing the relationship between the temperature of the thermistor 20 and the detected voltage data Dvs. In FIG. 4, the horizontal axis represents the temperature of the thermistor 20, and the vertical axis represents the output value of the AD converter 101, that is, the value representing the detected voltage data Dvs in decimal. The graph 47 shows a low temperature mode, that is, the switch SW1 is on, the switch SW2 is off, and the reference voltage V of the AD converter 101. _ref As reference voltage V _ref1 It is a graph at the time of using. The graph 48 shows a high-temperature mode, that is, the switch SW1 is turned off, the switch SW2 is turned on, and the reference voltage V of the AD converter 101 _ref As reference voltage V _ref2 It is a graph at the time of using.
[0067]
The graph 47 shows a curve that is almost a straight line below 46 ° C. (the temperature indicated by the broken line 49 in FIG. 4), but if it exceeds 46 ° C., the linearity deteriorates. On the other hand, the graph 48 shows a curve that is almost linear above 40 ° C. (the temperature indicated by the broken line 50 in FIG. 4), but the linearity is poor at temperatures below 40 ° C. In this case, for example, the detection voltage Vs when the temperature of the thermistor 20 is 43 ° C. (the temperature indicated by the one-dot chain line 51 in FIG. 4) is the mode switching voltage V _m The detection voltage Vs when the temperature of the thermistor 20 is 40 ° C. is the lower mode switching voltage V _mL The detection voltage Vs when the temperature of the thermistor 20 is 46 ° C. is the upper mode switching voltage V _mH Is set as
[0068]
For example, when the ambient temperature rises from 20 ° C. in the low temperature mode, the temperature of the thermistor 20 also rises, and detection voltage data Dvs corresponding to the temperature of the thermistor 20 is output from the AD converter 101 along the graph 47. . When the temperature further rises and the temperature reaches 40 ° C., the detection voltage Vs becomes the lower mode switching voltage V _mL The switch SW1 is turned off by the AD input selector 102, the switch SW2 is turned on, and the temperature select signal is output to the address decoder 103 at a high level to switch to the high temperature mode.
[0069]
As a result, when the temperature rises to 40 ° C. or higher, as a result of switching to the high temperature mode, detected voltage data Dvs corresponding to the temperature of the thermistor 20 is output from the AD converter 101 along the graph 48. Therefore, it is avoided that the temperature detection accuracy is lowered due to the poor linearity indicated by the broken line portion 52 of the graph 47.
[0070]
Further, when the temperature of the thermistor 20 rises above 40 ° C., detected voltage data Dvs corresponding to the temperature of the thermistor 20 is output from the AD converter 101 along the graph 48. In this case, since the graph 48 shows a curve that is almost a straight line at a portion that exceeds 40 ° C., the temperature detection accuracy is not lowered due to the poor linearity portion of the graph 48.
[0071]
Since the AD converter 101 is an 8-bit AD converter, the detection voltage data Dvs is output in the range of 0 to 255 in decimal. Therefore, the reference voltage V of the AD converter 101 in the low temperature mode and the high temperature mode. _ref And switch to the reference voltage V in the low-temperature mode. _ref1 In the high temperature mode, the reference voltage V _ref2 By doing so, the detected voltage data Dvs in the portion showing the curve that is almost a straight line in the graph 47 and the graph 48 is adjusted to fall within the range of 0 to 255 in decimal.
[0072]
Next, the address decoder 103 outputs a 9-bit address based on the detected voltage data Dvs and the temperature select signal to the table memory 104. The temperature data Dt corresponding to the address is output from the table memory 104 to the determination circuit 108. As a result, the temperature characteristic of the thermistor 20 is corrected with high accuracy, and highly accurate temperature data Dt is output to the determination circuit 108.
[0073]
Referring to FIG. 3, temperature data Dt output from table memory 104 is stored in register 120 in synchronization with the rising edge of clock signal CK, and the temperature data Dt stored in register 120 is stored in the next clock. In synchronization with the rising edge of the signal CK, it is stored in the register 121 as temperature data Dtm. At this time, new temperature data Dt is stored in the register 120. Thereby, for example, when the cycle of the clock signal CK is 1 second, the register 121 stores the temperature data Dtm one second before the temperature data Dt.
[0074]
Next, the subtracter 122 subtracts the temperature data Dtm from the temperature data Dt, and outputs the subtraction value Ddt to the temperature difference determination circuit 123. When the differential method (two types) is set as the determination method, the differential reference data Ddiff2 is set as the differential reference data Ddiff, and when a determination method other than the differential method (two types) is set, The differential reference data Ddiff1 is set as differential reference data Ddiff. Then, the subtraction value Ddt is compared with the differential reference data Ddiff by the temperature difference determination circuit 123. If the subtraction value Ddt is equal to or less than the differential reference data Ddiff, the temperature difference determination signal is increased and decreased at a low level. On the other hand, when the subtraction value Ddt is larger than the differential reference data Ddiff, that is, when it is detected that the temperature increase rate exceeds a predetermined value, the temperature difference determination signal is high. The level is output to the up / down counter 126.
[0075]
Next, when the temperature difference determination signal is in the high level state for 10 seconds or longer, that is, when the predetermined temperature increase rate continues for 10 seconds or longer, the differential selector signal OUTd is output from the up / down counter 126 at the high level. It is output to 134. Thereby, when the heat sensing circuit 10 is used as, for example, a fire alarm, it is possible to suppress accidental notification of the occurrence of a fire due to a temporary temperature rise.
[0076]
On the other hand, in the constant temperature short circuit determination circuit 129, when the constant temperature type or the compensation type is set as the determination method, the constant temperature reference data Dconst is set as the constant temperature short circuit reference data Dcs, and the differential method (one type) or the differential type is used as the determination method. When (2 types) is set, the short circuit reference data Dshort is set as the constant temperature short circuit reference data Dcs. Then, the constant temperature short circuit determination circuit 129 compares the temperature data Dt output from the register 120 with the constant temperature short circuit reference data Dcs. When the temperature data Dt is equal to or less than the constant temperature short circuit reference data Dcs, the constant temperature short circuit determination signal Is output to the up / down counter 130 at a low level. On the other hand, when the temperature data Dt is larger than the constant temperature short circuit reference data Dcs, a constant temperature short circuit determination signal is output to the up / down counter 130 at a high level.
[0077]
Next, when the constant temperature short circuit determination signal is in the high level state for 10 seconds or longer, that is, when the constant temperature type or compensation type is set as the determination method, the temperature above the predetermined temperature is continuously detected for 10 seconds or longer. When the differential type (1 type) or the differential type (2 types) is set as the determination method, the up / down counter 130 is detected when the short circuit of the thermistor 20 is continuously detected for 10 seconds or more. The constant temperature short circuit detection signal OUTcs is output to the output selector 134 at a high level.
[0078]
Further, the disconnection determination circuit 132 compares the temperature data Dt output from the register 120 with the disconnection reference data Dopen. When the temperature data Dt is equal to or higher than the disconnection reference data Dopen, the disconnection determination signal is at a low level. On the other hand, when the temperature data Dt is smaller than the disconnection reference data Dopen, the disconnection determination signal is output to the up / down counter 133 at a high level.
[0079]
Next, when the disconnection determination signal is in the high level state for 10 seconds or longer, that is, when the disconnection of the thermistor 20 is continuously detected for 10 seconds or longer, the disconnection detection signal OUTo is output from the up / down counter 133 at the high level. It is output to the selector 134.
[0080]
Next, based on the disconnection detection signal OUTo, the constant temperature short circuit detection signal OUTcs, the differential detection signal OUTd, and the method setting signal, the output selector 134 causes the heat detection notification signal OUT to be high level via the connection terminal 116 based on the notification output circuit. 19 and the notification output circuit 19 is turned on. Specifically, the output selector 134 generates and outputs the heat detection notification signal OUT by, for example, the following logical sum operation.
[0081]
For example, when the method setting signal is a signal indicating a differential type (1 type) and a differential type (2 types), the heat detection notification signal OUT is generated as OUT = OUTo + OUTcs + OUTd. Thereby, when the rate of temperature increase of the thermistor 20 exceeds a predetermined rate of increase, when the thermistor 20 is short-circuited or when the thermistor 20 is disconnected, the heat detection notification signal OUT is output at a high level, and a notification output circuit 19 is turned on, and a heat detection notification is detected by a receiver (not shown) connected to the sensor line 11.
[0082]
Further, when the method setting signal is a signal indicating a compensation formula, for example, the heat detection notification signal OUT is generated as OUT = OUTo + OUTcs + OUTd. As a result, when the rate of increase in the temperature of the thermistor 20 exceeds a predetermined rate, when the temperature of the thermistor 20 exceeds a predetermined temperature, and when the thermistor 20 is disconnected, the heat detection notification signal OUT is at a high level. Is output, the notification output circuit 19 is turned on, and a notification of heat detection is detected by a receiver (not shown) connected to the sensor line 11.
[0083]
When the method setting signal is a signal indicating a constant temperature type, for example, the heat detection notification signal OUT is generated as OUT = OUTo + OUTcs. As a result, when the temperature of the thermistor 20 exceeds a predetermined temperature and when the thermistor 20 is disconnected, the heat detection notification signal OUT is output at a high level, the notification output circuit 19 is turned on, and the sensor line 11 is connected. The notification of heat detection is detected by the receiver (not shown). Thereby, as shown in FIG. 5, the determination content is switched according to the setting content of the determination method.
[0084]
Since the thermistor 20 indicates that the temperature is higher as the resistance value is smaller, the temperature data Dt indicates a higher temperature when the thermistor 20 is short-circuited. Therefore, when the thermistor 20 is short-circuited when the determination method is set to the compensation method and the constant temperature method, the temperature data Dt becomes a value larger than the constant temperature reference data Dconst, so that the heat detection notification signal OUT is at a high level. Is output, the notification output circuit 19 is turned on, and a notification of heat detection is detected by a receiver (not shown) connected to the sensor line 11.
[0085]
(Second Embodiment)
Next, a heat sensing circuit 10a according to a second embodiment of the present invention will be described. FIG. 6 is a block diagram showing an example of the configuration of the heat sensing circuit 10a according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the part similar to the heat sensing circuit 10 shown in FIG.
[0086]
The heat sensing circuit 10a shown in FIG. 6 differs from the heat sensing circuit 10 shown in FIG. 1 in the following points. That is, the thermal circuit 18a in the thermal sensing circuit 10a shown in FIG. 6 does not include the signal line 30 included in the thermal circuit 18 in the thermal sensing circuit 10 in order to guide the detection voltage Vs to the connection terminal 112. Further, the integrated circuit 100a in the heat sensing circuit 10a does not include the connection terminal 112.
[0087]
The integrated circuit 100a is interposed between the connection terminal 110 and the AD converter 101 and the AD input selector 102a, and between the connection terminal 111 and the AD converter 101 and the AD input selector 102a. Switch SW4.
[0088]
The AD input selector 102a turns on the switches SW1 and SW4 and turns off the switches SW2 and SW3 in the low temperature mode, and outputs a temperature select signal to the address decoder 103 at a low level to indicate the low temperature mode. In the mode, the switches SW1 and SW4 are turned off, the switches SW2 and SW3 are turned on, and a temperature select signal is output to the address decoder 103 at a high level to indicate the high temperature mode.
[0089]
Since the other configuration is almost the same as that of the heat sensing circuit 10 shown in FIG. 1, the operation of characteristic points of the present embodiment will be described below. In the thermal sensing circuit 10a shown in FIG. 6, in the low temperature mode, the switches SW1 and SW4 are turned on and the switches SW2 and SW3 are turned off by the AD input selector 102a. And the power supply voltage V _OP Is divided by the thermistor 20 and the resistor 21, and the voltage generated at the connection point between the thermistor 20 and the resistor 21 is detected voltage Vs through the resistor 22, the connection terminal 111, and the SW4, and the AD converter 101 and the AD input selector. 102.
[0090]
On the other hand, in the high temperature mode, the switches SW1 and SW4 are turned off and the switches SW2 and SW3 are turned on by the AD input selector 102a. And the power supply voltage V _OP Is divided by the thermistor 20 and the resistor 22, and the voltage generated at the connection point between the thermistor 20 and the resistor 22 is detected as a detection voltage Vs through the resistor 21, the connection terminal 110, and the SW3, and the AD converter 101 and the AD input selector. 102.
[0091]
Thereby, in the integrated circuit 100a, the connection terminal 111 is used for inputting the detection voltage Vs in the low temperature mode, and the connection terminal 110 is used for inputting the detection voltage Vs in the high temperature mode. Unlike the integrated circuit 100, it is not necessary to provide the dedicated connection terminal 112 for inputting the detection voltage Vs, and the number of connection terminals can be reduced by one.
[0092]
(Third embodiment)
Next, a heat sensing circuit 10b according to a third embodiment of the present invention will be described. FIG. 7 is a block diagram showing an example of the configuration of the heat sensing circuit 10b according to the third embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the part similar to the heat sensing circuit 10a shown in FIG.
[0093]
The heat sensing circuit 10b shown in FIG. 7 differs from the heat sensing circuit 10a shown in FIG. 6 in the following points. That is, the heat sensing circuit 10b does not include the reset circuit 17. Further, the integrated circuit 100b in the heat sensing circuit 10b does not include the connection terminal 117 but includes the power supply monitoring circuit 135, the voltage regulator 136, and the connection terminal 137.
[0094]
Since the other configuration is substantially the same as that of the heat sensing circuit 10a shown in FIG. 6, the operation of characteristic points of the present embodiment will be described below.
[0095]
The power supply monitoring circuit 135 has a power supply voltage V _OP When the voltage drops below a predetermined voltage, a reset signal is output to the determination circuit 108, and the registers 120 and 121 and the up / down counters 126, 130, and 133 of the determination circuit 108 are initialized. As a result, the power supply voltage V _OP When the operation of the integrated circuit 100b becomes unstable due to a decrease in the temperature of the integrated circuit 100b, it is possible to suppress erroneous notification of heat detection due to a malfunction of the determination circuit 108. Further, since it is not necessary to receive a reset signal from the outside of the integrated circuit 100, it is not necessary to provide the connection terminal 117, and the number of connection terminals can be reduced by one.
[0096]
The voltage regulator 136 has a power supply voltage V _OP Is output to each part in the integrated circuit 100b as an operating power supply voltage, and the reference voltage V _ref1 And reference voltage V _ref2 Is generated with higher accuracy and output to the AD converter 101. As a result, the power supply voltage V _OP Therefore, the operation of the integrated circuit 100b is stabilized. Further, a reference voltage V that is a reference voltage for analog-digital conversion of the AD converter 101 _ref1 And reference voltage V _ref2 Therefore, the accuracy of the analog-digital conversion of the AD converter 101 can be improved, the accuracy of the detection voltage data Dvs can be improved, and the temperature detection accuracy of the heat sensing circuit 10b is improved.
[0097]
The operating power supply voltage generated by the voltage regulator 136 is output to the thermal circuit 18 a via the connection terminal 137. As a result, the detection voltage Vs is generated using the operation power supply voltage stabilized by the voltage regulator 136, so that the accuracy of the detection voltage Vs is improved and the temperature detection accuracy of the heat sensing circuit 10b is improved.
[0098]
Note that the temperature detection element is not limited to the thermistor, and a temperature detection element such as a posistor or a platinum resistance temperature detector, or a thermocouple may be used. Further, the heat sensing circuits 10, 10a, 10b are not limited to fire alarms, and may be, for example, a heat sensing circuit used for detecting heat of a heat treatment apparatus in a production process of a factory. Further, the notifying means is not limited to outputting a signal indicating the notification of heat detection to the receiver connected via the sensor line 11, but for notifying the heat detection by, for example, a buzzer or a lamp. May be.
[0099]
【The invention's effect】
According to the first aspect of the present invention, since the detection voltage data is acquired as an address of the table storage means, temperature data corresponding to the detection voltage data is output from the table storage means. The temperature characteristic can be corrected using a simple circuit.
[0100]
According to the second aspect of the present invention, it is possible to improve the accuracy of the temperature data used for detecting that the predetermined determination condition is satisfied, and thus it is possible to improve the accuracy of reporting the heat detection. .
[0101]
According to the third aspect of the present invention, each of the first and second connection terminals can be used for two different applications, so that the number of connection terminals of the integrated circuit can be reduced, and low Cost can be increased.
[0102]
According to the fourth aspect of the present invention, when the temperature rise at the predetermined sampling time is larger than the value of the predetermined differential reference data, that is, when the temperature increase rate exceeds the predetermined increase rate, the heat detection is performed. Can be notified. In addition, since the determination means includes power supply monitoring means for initializing the first and second storage means when the power supply voltage becomes equal to or lower than a predetermined reset voltage, when the determination means is integrated, the first and second It is not necessary to provide the integrated circuit with a connection terminal for receiving a signal for initializing the second storage means from the outside. Therefore, the number of connection terminals of the integrated circuit can be reduced and the cost can be reduced.
[0103]
According to the fifth aspect of the present invention, it is possible to notify heat detection when the rate of temperature increase exceeds a predetermined rate of increase and when the temperature is higher than the predetermined temperature.
[0104]
According to the sixth aspect of the present invention, when the setting accepting unit accepts the setting for setting the differential mode, it is possible to detect a short circuit of the negative temperature characteristic resistor using the constant temperature determining unit. There is no need to separately provide a circuit for detecting a short circuit of the characteristic resistor, and an increase in circuit scale for detecting a short circuit of the negative temperature characteristic resistor can be suppressed.
[0105]
According to the seventh aspect of the present invention, the disconnection detection means can be configured using a temperature comparison circuit similar to the constant temperature determination means, so that AD conversion means and a disconnection of the negative temperature characteristic resistor are detected A table storage means can be used, and an increase in circuit scale for detecting disconnection of the negative temperature characteristic resistor can be suppressed.
[0106]
According to the invention described in claim 8, since the short-circuit detection means can be configured by using a temperature comparison circuit similar to the constant temperature determination means, the AD conversion means and the disconnection of the negative temperature characteristic resistor are detected. A table storage means can be used, and an increase in circuit scale for detecting a short circuit of the negative temperature characteristic resistor can be suppressed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of a configuration of a heat sensing circuit according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram for explaining a configuration of a temperature conversion table stored in a table memory.
FIG. 3 is a block diagram for explaining an example of a configuration of a determination circuit.
FIG. 4 is a diagram showing the relationship between the temperature of the thermistor and detected voltage data.
FIG. 5 is a diagram showing a list of determination contents according to determination methods.
FIG. 6 is a block diagram showing an example of a configuration of a heat sensing circuit according to a second embodiment of the present invention.
FIG. 7 is a block diagram showing an example of a configuration of a heat sensing circuit according to a third embodiment of the present invention.
[Explanation of symbols]
10, 10a, 10b Thermal sensing circuit
11 Sensor line
16 Power line
18, 18a Thermal circuit (temperature detection means)
19 Notification output circuit (notification means)
20 Thermistor (Negative temperature characteristic resistor)
21 Resistance (first resistance)
22 Resistance (second resistance)
23 Ground line
24, 25 switches
30 signal lines
100, 100a, 100b integrated circuit
101 AD converter (AD conversion means)
102,102a AD input selector (resistance mode switching means)
103 Address decoder
104 Table memory (table storage means)
106 Oscillator circuit
107 Model setting circuit (setting accepting means)
108 determination circuit (determination means)
110 connection terminal (first connection terminal)
111 connection terminal (second connection terminal)
112 Connection terminal
120 registers (first storage means)
121 register (second storage means)
122 Subtractor
123 Temperature difference judgment circuit (differential judgment means)
124,125 differential value register
126, 130, 133 Up / down counter
127 Constant temperature register
128 Short-circuit value register
129 Constant temperature short circuit judgment circuit (constant temperature judgment means, short circuit detection means)
131 Disconnection value register
132 Disconnection determination circuit (disconnection detection means)
134 Output selector
135 Power supply monitoring circuit (Power supply monitoring means)
136 Voltage regulator (power stabilization means)
SW1 switch (first switching means)
SW2 switch (second switching means)
SW3 switch (third switching means)
SW4 switch (fourth switching means)

Claims (8)

In a heat sensing circuit comprising a temperature detecting means for generating a detection voltage corresponding to a characteristic value using a temperature detection element whose electrical characteristic value changes according to temperature,
AD conversion means for generating detection voltage data which is digital data obtained by analog-digital conversion of the detection voltage generated by the temperature detection means;
Table storage storing temperature data corresponding to the detected voltage data and corrected temperature characteristics of the temperature detecting element at the address using the detected voltage data which is digital data generated by the AD conversion means as an address Means,
Detection voltage data, which is digital data generated by the AD conversion means , is acquired as an address by the table storage means, and a predetermined determination condition is established based on temperature data output from the table storage means. A determination means for detecting this,
A heat sensing circuit comprising: notifying means for notifying heat detection when the determination means detects that the determination condition is satisfied.   2. The heat sensing circuit according to claim 1, further comprising power supply stabilization means for stabilizing a power supply voltage taken from outside and generating a reference voltage for the AD conversion means to perform analog-digital conversion. An integrated circuit comprising: the determination means; the AD conversion means; and first, second, third, and fourth switching means for switching the connection between the AD conversion means and the temperature detection means;
A resistance mode switching means for controlling on / off of the first, second, third, and fourth switching means;
The temperature sensing element is a thermal resistor whose resistance value changes according to temperature,
The temperature detection means includes a first resistor that divides a power supply voltage taken from outside the temperature detection means with the thermal resistor connected in series, the thermal resistor, and the first resistor. And a second resistor that divides the power supply voltage taken in from the outside of the temperature detecting means with the thermal resistor connected in series,
The integrated circuit includes a first connection terminal connected to the thermal resistor via the first resistor, and a second connection terminal connected to the thermal resistor via the second resistor. Further comprising
The first switching means is connected to the first resistor via the first connection terminal and turns on and off a current flowing through the first resistor.
The second switching means is connected to the second resistor via the second connection terminal and turns on and off a current flowing through the second resistor.
The third switching unit guides the voltage guided to the first connection terminal to the AD conversion unit as the detection voltage, and turns on and off.
The fourth switching means guides the voltage guided to the second connection terminal to the AD conversion means as the detection voltage and turns on and off.
The resistance mode switching means turns on the first and fourth switching means and turns off the second and third switching means in accordance with a detection voltage guided to the AD conversion means. 3. The thermal sensing according to claim 1, wherein the mode is switched between a second resistance mode in which the second and third switching means are turned on and the first and fourth switching means are turned off. circuit. The determination means includes a first storage means for storing temperature data output from the table storage means at a sampling timing for each predetermined sampling time interval;
Second storage means for storing the temperature data output from the table storage means at the sampling timing immediately before the sampling timing at which the first storage means stores the temperature data;
The difference between the temperature data stored by the first storage means and the temperature data stored by the second storage means is compared with predetermined differential reference data, and the difference is the differential reference Differential determination means for detecting a differential establishment state that is greater than the data value;
Power supply monitoring means for initializing the first and second storage means when the power supply voltage taken from outside becomes a predetermined reset voltage or less,
The heat sensing circuit according to any one of claims 1 to 3, wherein it is detected that the determination condition is satisfied based on whether or not the differential determination state is detected by the differential determination unit. The determination unit compares the temperature data output from the table storage unit with predetermined constant temperature reference data, and detects a constant temperature determination unit that detects a constant temperature establishment state in which the temperature data is larger than the value of the constant temperature reference data. Further comprising
The determination unit detects that the determination condition is satisfied according to presence / absence of detection of a differential establishment state by the differential determination unit and presence / absence of detection of a constant temperature establishment state by the constant temperature determination unit. The heat sensing circuit according to claim 4. The differential mode is set to detect that the determination condition is satisfied depending on whether the differential establishment state is detected, and the determination condition is detected based on the detection of the constant temperature establishment state. Further comprising setting accepting means for accepting the setting to be in the constant temperature mode,
The thermal resistor is a negative temperature characteristic resistor whose resistance value decreases with increasing temperature,
The determination means detects that the determination condition is satisfied when the constant temperature establishment state is detected when the setting acceptance means accepts the setting for setting the constant temperature mode, and the setting acceptance means detects the differential mode. When the setting to be received is accepted, the constant temperature determination means is in the constant temperature establishment state when the differential establishment state is detected and the short temperature determination temperature indicating that the negative temperature characteristic resistor is short-circuited is the constant temperature reference data 6. The heat sensing circuit according to claim 5, wherein when the signal is detected, it is detected that the determination condition is satisfied. The thermal resistor is a negative temperature characteristic resistor whose resistance value decreases with increasing temperature,
A disconnection detecting means for detecting disconnection of the negative temperature characteristic resistor when the temperature data falls below a predetermined disconnection determination temperature;
The heat sensing circuit according to any one of claims 1 to 6, wherein the notification means notifies the detection of heat when the disconnection of the negative temperature characteristic resistor is detected by the disconnection detection means. The thermal resistor is a negative temperature characteristic resistor whose resistance value decreases with increasing temperature,
Short circuit detecting means for detecting a short circuit of the negative temperature characteristic resistor when the temperature data exceeds a predetermined short circuit determination temperature,
The heat sensing circuit according to any one of claims 1 to 7, wherein when the short circuit detecting unit detects a short circuit of the negative temperature characteristic resistor, the notification unit reports heat detection.

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