JP2004226348A - Thermal sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal fire alarm for home use which detects a break in a temperature-sensitive element under fire testing. <P>SOLUTION: The thermal sensor 10 detects a fire by comparing an output signal from a temperature detection circuit 1 comprising the temperature-sensitive element Rth and a resistive element Rc to a reference signal from a reference circuit 2 comprising resistive elements Ra, Rb. The temperature detection circuit 1 is configured such that a test switching circuit 3 comprising a normally-closed test switch SW and an auxiliary resistance Rd in series is connected to the resistive element Rc in parallel. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat detector that detects a fire using a temperature-sensitive element such as a thermistor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been a heat sensor that uses a temperature-sensitive element such as a thermistor and determines a temperature based on a change in resistance to detect a fire.
[0003]
FIG. 4 shows a block diagram of a residential fire alarm employing this type of heat detector.
[0004]
The fire alarm for a house is configured to detect heat by a fire detection circuit, drive the alarm circuit when a certain temperature is exceeded, and output an alarm. Also, by operating the switch SW, a fire test signal is output to the fire detection circuit, the fire detection circuit determines a false fire condition, activates the alarm circuit, and confirms that the operation is normal. I have to.
[0005]
FIG. 5 shows a circuit diagram of this type of heat detector (fire detection circuit).
[0006]
This circuit compares the threshold voltage at the point A defined by the resistors Ra and Rb with the output voltage at the point B (shared voltage to Rx) divided by the thermistor Rth and the voltage dividing resistor Rx, When the voltage at point B becomes higher than the threshold voltage at point A, it is determined that a fire has occurred, a Low signal is sent to the alarm circuit, and the alarm circuit is driven.
[0007]
That is, when the temperature detected by the thermistor Rth increases, the resistance value of the thermistor Rth decreases, the output voltage at the point B increases, and when the voltage exceeds the threshold voltage at the point A, it is determined that a fire has occurred. .
[0008]
In FIG. 5, the switch SW is for performing a fire test operation. When the switch SW is turned on, the resistor Ry is connected in parallel with the thermistor Rth, and the voltage at the point B increases. I try to make it.
[0009]
However, according to this configuration, depending on the resistance value of the resistor Ry, a fire may be determined even if the thermistor Rth is disconnected, and there is an insufficient point as a circuit for performing a fire test.
[0010]
Patent Document 1 discloses a heat detector that detects the occurrence of a fire using a thermistor.
[0011]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 7-333074
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention has been proposed to solve the above problems, and has as its object to provide a heat detector capable of detecting disconnection of a thermistor even during a fire test.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the heat detector according to claim 1 outputs an output signal from a temperature detection circuit composed of a temperature sensitive element and a resistance element to a reference signal from a reference circuit composed of a resistance element. Compared with, a heat detector for detecting a fire, the temperature detection circuit is connected to a test switch circuit in which a normally closed test switch and an auxiliary resistor are connected in series to a resistance element in parallel. It is configured.
[0014]
Here, a thermistor having a negative temperature characteristic or the like is used as the temperature sensing element.
[0015]
According to such a configuration, at the time of fire, the environmental temperature rises and the resistance of the thermistor decreases, so that the output voltage of the temperature detection circuit exceeds the threshold voltage of the reference circuit, and a fire can be determined. In addition, during the test, the auxiliary resistor is disconnected and the output voltage of the temperature detection circuit rises, so that the fire is simulated as in the case of a real fire, and the alarm output can be easily confirmed.
[0016]
In addition, if the thermistor is disconnected, even if the test switch is opened, a voltage exceeding the threshold voltage is not output from the temperature detection circuit, so that the alarm output operation is not performed during the test.
[0017]
According to the second aspect, the test switch is a pull-string switch that opens and closes its contact each time the pull operation is repeated.
[0018]
According to the third aspect, the test switch is a push-button switch that opens and closes its contact each time the push button is pressed.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0020]
FIG. 1 is a circuit block diagram showing a configuration example of a main part of a heat detector (fire detection circuit unit) 10 of the present invention.
[0021]
In FIG. 1, reference numeral 2 denotes a reference circuit including resistance elements Ra and Rb for setting a threshold voltage for fire determination, and reference numeral 1 denotes a temperature detection including a thermistor Rth as a temperature sensing element and a resistance element Rc. Circuit.
[0022]
Further, a test switch circuit 3 in which a normally-closed test switch SW and an auxiliary resistor Rd are connected in series is connected in parallel to the resistance element Rc of the temperature detection circuit 1.
[0023]
Reference numeral 4 denotes a comparator that compares an output signal (voltage) from the point A of the reference circuit 2 with a reference signal (threshold voltage) from the point B of the temperature detection circuit 1 to determine a fire.
[0024]
Here, the resistance element Rc has a resistance value of about several MΩ, and the auxiliary resistance Rd has a resistance value of several tens kΩ which is sufficiently smaller than the resistance value of the resistance element Rc. That is, the resistance value of the resistance circuit 5 composed of the resistance element Rc and the test switch circuit 3 is set to be several tens kΩ, which is almost the same as that of the auxiliary resistance Rd when the test switch SW is closed and not tested. I have. That is, at the time of the non-test, the auxiliary resistance Rd functions as a fire determination resistance.
[0025]
The heat detector 10 is employed, for example, in a fire alarm for a house or the like, and its external configuration is shown in FIG.
[0026]
This residential fire alarm is designed to perform a fire test by operating a push button or a drawstring. That is, each time the pressing operation of the push button or the pulling operation of the drawstring is repeated, the contact of the test switch SW is opened and closed.
[0027]
Hereinafter, description will be made with reference to the shared voltage transition diagram of FIG.
[0028]
In a normal (non-test) state, the test switch SW is in a closed state, and the fire determination is made by determining the output voltage at the point A of the reference circuit 2, that is, the shared voltage (fire determination threshold voltage) Vab for the resistor Rb, This is performed by comparing the output voltage at the point B of the temperature detection circuit 1, that is, the shared voltage Vcd for the resistance circuit 5.
[0029]
In a normal monitoring state in which no fire has occurred, since the shared voltage Vcd is smaller than the threshold voltage Vab from the relationship between the shared voltage for the thermistor Rth and the shared voltage Vcd for the resistor circuit 5, the fire is not determined. (FIG. 3 (a)).
[0030]
If a fire occurs, the environmental temperature rises, the resistance value of the thermistor Rth decreases based on the negative temperature characteristic, and the shared voltage Vcd becomes larger than the threshold voltage Vab. )).
[0031]
On the other hand, during the fire test, the test switch SW is turned on, so that the auxiliary resistance Rd is disconnected, and the resistance value of the resistance circuit 5 is the resistance Rc. Voltage. That is, since the resistance value of the resistor Rc is about several MΩ, the shared voltage Vcd becomes larger than the threshold voltage Vab, and it is determined that the fire is simulated (FIG. 3C).
[0032]
Next, when the thermistor Rth is in a disconnected state, the resistance value of the thermistor Rth becomes several tens MΩ and the shared voltage Vcd is almost at the ground level, so that disconnection can be detected regardless of non-test and test. That is, even if the test switch SW is pressed, it is not determined that the fire is a simulated fire.
[0033]
In the configuration example of the heat detector 10 described above, a thermistor having a negative temperature characteristic is used as a temperature-sensitive element. However, a PTC thermistor having a positive temperature characteristic may be used as a temperature-sensitive element. .
[0034]
【The invention's effect】
As can be understood from the above description, the heat detector according to any one of claims 1 to 3 includes a resistance element and a test switch circuit that disconnects an auxiliary resistance during a fire test. The output voltage of the circuit can be sufficiently increased to exceed the threshold voltage, enabling a fire determination operation, and, when the temperature sensing element is in a disconnected state, disconnection without determining that a fire has occurred. Can be detected.
[0035]
In particular, in claim 2, the heat switch is used as a fire alarm for a house because the test switch is a pull string switch that opens and closes contacts by pulling operation, and in claim 3, the test switch is a push button switch. can do.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a configuration example of a main part of a heat detector (fire detection circuit unit) of the present invention.
FIG. 2 is a view showing an external configuration of a fire alarm for a house adopting the heat detector of the present invention.
FIGS. 3A and 3B are shared voltage transition diagrams showing the relationship between the shared voltage and the threshold voltage, where FIG. 3A shows a normal monitoring when no fire occurs, FIG. 3B shows a fire occurrence, and FIG. 3C shows a fire test. , (D) shows the magnitude of the shared voltage when the thermistor is disconnected.
FIG. 4 is a block diagram of a conventional residential fire alarm.
FIG. 5 shows a circuit diagram of a conventional heat detector (fire detection circuit unit).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Heat detector 1 Temperature detection circuit Rth Thermistor Rc Resistance element 3 Test switch circuit Rd Auxiliary resistance SW Test switch 2 Reference circuits Ra, Rb Resistance elements 4 constituting reference circuit 4 Comparator

Claims (3)

In a heat detector that detects a fire by comparing an output signal from a temperature detection circuit configured with a temperature sensitive element and a resistance element with a reference signal from a reference circuit configured with a resistance element,
A heat sensor, wherein the temperature detection circuit is configured by connecting a test switch circuit in which a normally closed test switch and an auxiliary resistor are connected in series to the resistance element in parallel. In claim 1,
The heat sensor is characterized in that the test switch is a pull string type switch that opens and closes its contact each time the pull operation is repeated. In claim 1,
The heat sensor is characterized in that the test switch is a push-button switch that opens and closes its contact each time the push button is pressed.

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