JPH09115074A - Fire alarm - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the disconnection of a thermistor as a thermosensitive element when a check test is performed for checking whether or not a fire alarm operates normally. SOLUTION: At the time of a fire, surrounding temperature is elevated and resistance value Rth of a thermistor 1 as a fire detection circuit is decreased. When the temperature gets higher than an operating temperature, an input voltage VS to the comparator of a fire judge circuit 2 gets lower than a reference voltage VR of the comparator, and the output of the comparator is turned into L state. Namely, the comparator outputs an alarm signal to a buzzer driving circuit 3, and a buzzer 4 is driven by a buzzer driving signal from a buzzer driving circuit and issues an alarm. Besides, when a check switch 10 is depressed and turned on, since a substitutive fire resistor serially connected with the check switch is parallelly connected to a sensitivity regulating resistor, the comparator outputs the alarm signal to the buzzer driving circuit 3, and the buzzer can perform the check corresponding to the buzzer driving signal from the buzzer driving circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fire alarm, and more particularly to a fire alarm for homes and homes.

[0002]

2. Description of the Related Art Conventionally, there is a thermal fire alarm device using a thermistor whose electric resistance changes due to heat as a heat sensitive element. In this method, a resistance is provided in series with a thermistor, and a change in voltage between them is monitored by using a comparator or the like, and if it is determined that the value exceeds a predetermined reference value, it is detected as a fire. In addition, in home fire alarm,
The fire alarm has a function to check and test whether the fire alarm operates normally. Therefore, in a fire alarm device that uses a thermistor, connect a switch and a resistor that are always open in parallel to the thermistor, and turn on the switch to artificially create the same state as a fire and perform an inspection test. Was there.

[0003]

In the conventional thermal fire alarm as described above, even if the thermistor is broken, it operates normally during inspection. Therefore, the break of the thermistor can be detected. There was a problem that I could not.

The present invention has been made in order to solve such a problem, and detects a disconnection of a thermistor which is a heat-sensitive element when an inspection test is performed to see if the fire alarm operates normally. The purpose is to obtain a fire alarm that can also be operated.

[0005]

A fire alarm device according to the present invention detects a fire due to heat and outputs an electric signal, and an electric signal output from the fire detection circuit is a predetermined reference value or more. When a fire judgment circuit outputs an alarm signal, an alarm drive circuit that receives an alarm signal from the fire judgment circuit and outputs an alarm drive signal, and an alarm drive driven by the alarm drive signal from the alarm drive circuit And a fire detection circuit,
In a fire alarm device comprising a fire determination circuit, an alarm drive circuit, and a power supply for driving the alarm, the fire detection circuit is a thermistor, and the fire determination circuit is between the positive side and the negative side of the power source. And a current limiting resistor connected in series with the thermistor, and two sensitivity adjusting resistors connected in series for setting a reference value between the positive side and the negative side of the power source. A comparator connected to a connection point of the thermistor and the current limiting resistor and a connection point of the two sensitivity adjustment resistors, a switching element that outputs the alarm signal based on the output of the comparator, and a positive side of the power supply. It consists of an inspection switch and an inspection resistor that are connected in series between the connection points of the above two sensitivity adjustment resistors, and the resistance value of the inspection resistor is a point. It is configured to include a set inspection means so as to vary the output of the comparator during the switch-on operation.

In the fire alarm device according to the present invention, the reference voltage VR of the comparator of the fire determination circuit does not change at the time of fire, but the ambient temperature rises and the resistance value RTH of the thermistor which is the fire detection circuit decreases. Above the operating temperature,
The input voltage VS of the comparator becomes equal to or lower than the reference voltage VR of the comparator, the output of the comparator becomes the L state,
The switching element becomes conductive and an alarm signal is input to the alarm drive circuit, and the alarm device is driven by the alarm drive signal from the alarm drive circuit and issues an alarm. Also, when the inspection switch is pressed and turned on, the fire substitute resistor connected in series with the inspection switch is connected in parallel with the sensitivity adjustment resistor, and the input voltage of the comparator does not change, but the reference voltage of the comparator is As a result, the input voltage VS of the comparator becomes equal to or lower than the reference voltage VR of the comparator, the output of the comparator becomes the L state as in the case of a fire, the switching element becomes conductive, and the alarm signal is input to the alarm drive circuit. The alarm device is driven by an alarm drive signal from the alarm drive circuit to issue an alarm, and inspection can be performed. Even if the inspection switch is pressed and turned on, if the thermistor is disconnected, the resistance value of the thermistor becomes infinite, and even if the reference voltage of the comparator rises, the input voltage of the comparator rises further. As a result, the input voltage VS of the comparator becomes equal to or higher than the reference voltage VR of the comparator, the output of the comparator becomes the H state as in the monitoring, the switching element becomes non-conductive, and the alarm signal is not input to the alarm drive circuit. Since the alarm device is not driven, it is possible to detect disconnection of the thermistor when inspecting the inspection switch.

Another fire alarm device according to the present invention is a fire detection circuit for detecting a fire and outputting an electric signal, and an alarm signal when the electric signal output from the fire detection circuit is above a predetermined reference value. A fire judgment circuit that outputs a warning signal, a warning device drive circuit that outputs a warning driving signal in response to a warning signal from the fire judgment circuit, a warning device that is driven by a warning driving signal from the warning device driving circuit, and a fire detection circuit , Fire decision circuit,
In a fire alarm device comprising an alarm device driving circuit and a power supply for driving the alarm device, the fire determination circuit is provided between the plus side and the minus side of the power source and is connected in series with the fire detection circuit. A current limiting resistor, two sensitivity adjusting resistors connected in series between the positive side and the negative side of the power source, for setting a reference value;
A comparator whose input side is connected to the connection point of the thermistor and the current limiting resistor, and a second input side is connected to the connection point of the two sensitivity adjustment resistors; and a switching element which outputs an alarm signal based on the output of the comparator. Further, a transistor whose emitter is connected to the positive side of the power source, one end of which is connected to the collector of the transistor and the other end of which is connected to the first or second input side of the comparator, and whose resistance value is An inspection resistor set to change the output of the comparator when the transistor is turned on, a delay capacitor having one end connected to the positive side of the power supply, and the other end connected to the other end of the delay capacitor. It is connected in series with the delay resistor and the inspection switch connected between the other end of the delay resistor and the negative side of the power supply. One end is connected to the positive side of the power source, the other end is connected to the connection of the delay capacitor and the delay resistor, and the connection point of the series connection is two voltage dividing resistors connected to the transistor base. It is equipped with an inspection means.

Further, in another fire alarm device according to the present invention, when the ignition switch is continuously pressed, the capacitor immediately starts charging, and after a short delay, the voltage generated in the voltage dividing resistor gradually increases, Along with that, the base current flowing through the base of the transistor also increases, the voltage between the emitter and collector of the transistor also begins to gradually decrease, and the capacitor is charged when the ignition switch turns on for a predetermined time, and the voltage dividing resistor is generated. Voltage becomes maximum and the base current flowing through the base of the transistor also becomes maximum, the transistor is fully turned on and becomes conductive, the alarm signal is input to the alarm drive circuit, and the alarm device outputs from the alarm drive circuit. It is driven by an alarm drive signal and an alarm can be issued for inspection, so keep pressing the ignition switch for a predetermined time. Kere If not can also perform inspection for driving the alarm, and turned on by momentarily touching the ignition switch, therewith preventing malfunctions that simultaneously alarm is driven.

Further, the delay resistor of the checking means is a variable resistor whose resistance value changes with heat, and the resistance value of the variable resistor is set to be long at a low operating time and short at a high operating time. , The time from pressing the inspection switch to operating is within a normal range, for example, 5 seconds to 10 seconds. If longer than that, the fire alarm is installed in a cold environment or shorter than that. If this is the case, it will be possible for the user to judge that it is a warm environment, and it will be possible to install the fire alarm in a suitable place.

[0010]

1 is a block diagram showing a configuration of a fire alarm device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a configuration of a fire detection circuit and a fire determination circuit of the fire alarm device, FIG. 3 is a circuit diagram showing a configuration of a buzzer drive circuit of the fire alarm device. In FIG. 1, 1 is a fire detection circuit composed of a thermistor which is a heat-sensitive element, 2 is a change in the voltage of the resistance value of the thermistor 1, and outputs an alarm signal when the voltage exceeds a predetermined reference value. The fire determination circuit 3 is a buzzer drive circuit that is an alarm drive circuit that receives a warning signal from the fire determination circuit 2 and outputs a buzzer drive signal. Reference numeral 4 is an alarm device that is driven by the buzzer drive signal of the buzzer drive circuit 3. A certain buzzer 5 is a battery that is a power source for driving various circuits and devices such as the fire detection circuit 1 and the fire determination circuit 2, and 6 is a power switch connected in series to the battery 5.

Reference numeral 7 is a voltage drop alarm circuit for detecting the voltage of the battery 5 and outputting an alarm signal to the buzzer drive circuit 3 when the detected value is below a predetermined value of 5.1 V, for example. A time limit timer that cuts energization during sleep time, for example, 6 hours, during operation provided between the circuit 7 and 9 according to the voltage of the battery 5 in each circuit except the buzzer 4, the buzzer drive circuit 3, and the low voltage warning circuit 7. A constant voltage circuit for supplying a constant voltage that does not fluctuate, 10 is an inspection switch, 11 is an inspection circuit that outputs a fire pseudo signal to the fire detection circuit 1 when the inspection switch 10 is on, and 12 is a string alarm stop switch 13. A timer circuit that is activated when turned on and outputs an alarm stop signal for a predetermined time. The inspection switch 10
And the inspection opening circuit 11 is put together and an inspection means is comprised.

In FIG. 2, reference numeral 21 is a current limiting resistor provided between the positive side and the negative side of the constant voltage circuit 9 and connected in series with the thermistor 1, and 22 and 23 are constant voltage circuits 9.
Of two reference voltage dividing resistors (sensitivity adjusting resistors) that are provided between the positive side and the negative side and are connected in series for setting a reference value, and 24 is a comparator, the first input side 24a of which is a thermistor. 1 and the current limiting resistor 21 are connected to each other, the second input side 24b thereof is connected to the connection point of the two sensitivity adjusting resistors 22 and 23, and one of the power supply terminals 24c is the positive side of the constant voltage circuit 9. The other power source terminal 24d is connected to the negative side of the constant voltage circuit 9 through the resistor 26. 27 is a comparator 24
Is a transistor which is a switching element whose base is connected to the output side 24e of the constant voltage circuit 9 through the resistor 25, the emitter of which is connected to the positive side of the constant voltage circuit 9 and the collector of which is the negative side of the constant voltage circuit 9 through the resistor 30. Is connected to the input side of the buzzer drive circuit 3, and the emitter and the base thereof are connected via a resistor 28 and a capacitor 29 which are connected in parallel. Current limiting resistor 2
The fire judging circuit 2 is composed of the resistors 1 to 30.

Reference numeral 31 is a switching transistor of the inspection circuit 11, the emitter of which is connected to the positive side of the constant voltage circuit 9 and the collector of which is connected to the second input side 24b of the comparator 24 through the fire substitute resistor 32. There is.
33 and 34 are two bias resistors (voltage dividing resistors) connected in series, one bias resistor 33 is connected to the positive side of the constant voltage circuit 9, and the other bias resistor 34 is checked via the delay resistor 35. It is connected to one end of the switch 10. The other end of the inspection switch 10 is connected to the negative side of the constant voltage circuit 9. A delay capacitor 36 is connected between the positive side of the constant voltage circuit 9 and the connection point of the bias resistor 34 and the delay resistor 35. Inspection circuit 1 with switching transistor 31 to delay capacitor 36
1 is configured. The resistance value of the fire surrogate resistor 32 is set to such a value that the second input voltage of the comparator 24 becomes larger than the terminal voltage of the thermistor 1 at room temperature when the switching transistor 31 is turned on.

In FIG. 3, reference numeral 40 is an AND gate of the buzzer driving circuit 3, the first input terminal of which is the fire judging circuit 2.
Of the timer circuit 12 and the second input terminal thereof is connected to the output side of the timer circuit 12. Reference numeral 41 denotes a transistor for driving the buzzer 4, the collector of which is connected to the positive side of the battery 5 via the buzzer 4, the emitter of which is connected to the negative side of the battery 5 and the base of which is for blocking backflow through the resistor 42. Are connected to the cathodes of the first and second diodes 43 and 44. The anode of the first diode 43 is connected to the output terminal of the AND gate 40, and the anode of the second diode 44 is connected to the output side of the voltage drop warning circuit 7. As described above, the buzzer driving circuit 3 is composed of the AND gate 40 to the second diode 44.

Next, the operation of the fire alarm device according to the embodiment of the present invention will be described. First, the operation during fire monitoring will be described. At the time of fire monitoring, the output voltage of the constant voltage circuit 9 is applied to the thermistor 1 and the current limiting resistor 21, and the comparator 24 compares the voltage VS generated in the thermistor 1 with the reference voltage VR generated across the sensitivity adjusting resistor 23. There is. The reference voltage VR is determined by the output voltage of the constant voltage circuit 9 and the sensitivity adjusting resistors 22 and 23. Also,
When the resistance value of the thermistor 1 is RTH and the output voltage of the constant voltage circuit 9 is E, the input voltage VS on the first input side of the comparator 24 is obtained by the following equation. VS = RTH / [R21 + RTH] × E Further, the reference voltage VR is also the same, and is calculated by the following equation. VR = R23 / [R22 + R23] × E When the voltage on the second input side which is the inverting input terminal is smaller than the voltage on the first input side which is the non-inverting input terminal, that is, when VS> VR Comparator 2
The output of 4 is in the H state.

When monitoring the ambient temperature below the operating temperature,
The relationship between the reference voltage VR of the comparator 24 and the input voltage VS is VS> VR, and the output of the comparator 24 is H.
Remains. When the output of the comparator 24 is H,
No current flows through the resistor 25, the transistor 27 is non-conductive, the L state is input to the first input terminal of the AND gate 40 of the buzzer drive circuit 3, and the second input terminal of the AND gate 40 is input. Since the signal in the H state, which is always output when it is not operating, is input from the timer circuit 12, the output terminal of the AND gate 40 outputs the signal in the L state. The signal is the first diode 43 and the resistor 42.
To the base of transistor 41 via. At this time, the transistor 41 is off, the collector and the emitter are non-conductive, no voltage is applied to the buzzer 4, and the buzzer 4 does not ring. Normally, when the room temperature is, for example, 60 degrees or less, the buzzer 4 is not sounded and the resistance values of the sensitivity adjustment resistors 22 and 23 are adjusted so that the reference voltage VR of the comparator 24 is set.

Next, the operation at the time of fire will be described.
When the ambient temperature rises during a fire, for example, the thermistor 1 which is a fire detection circuit of a fire alarm installed on the ceiling of a room
Senses the heat in the room, and the resistance value RTH of the thermistor 1 decreases. Since the voltage applied to the fire judgment circuit 2 is constant,
Although there is no change in the reference voltage VR of the comparator 24 of the fire judgment circuit 2, the input voltage VS of the comparator 24, that is, the voltage across the thermistor 1 changes according to the resistance value RTH of the thermistor 1, and the ambient temperature rises, and the operating temperature rises. As described above, the relationship between the reference voltage VR of the comparator 24 and the input voltage VS is VS <VR, and the output of the comparator 24 is in the L state. When the output of the comparator 24 is in the L state, a current flows through the resistor 25 and the transistor 27 becomes conductive. Then, the H state is input to the first input terminal of the AND gate 40 of the buzzer drive circuit 3, and is always output from the timer circuit 12 to the second input terminal of the AND gate 40 when it is inactive. Since the signal in the H state is input, the output terminal of the AND gate 40 outputs the signal in the H state. The signal is the first diode 43
And the resistor 42, the transistor 41 is turned on, the transistor 41 is turned on, the collector and the emitter are conducted, and a voltage is applied to the buzzer 4, and the buzzer 4 continuously sounds to warn of a fire.

As described above, the buzzer 4 sounds when a fire is detected, but the buzzer 4 also operates when the inspection switch 10 is turned on during maintenance and a fire pseudo signal is output from the inspection circuit 11 to the fire detection circuit 1. You can ring and perform an inspection. The operation of the inspection circuit 11 when the inspection switch 10 is turned on will be described in detail.
When the inspection switch 10 is turned on, the voltage generated in the resistor 33 is applied to the base of the switching transistor 31, and the switching transistor 31 is turned on. Then, since the fire substitute resistor 32 is connected in parallel to the sensitivity adjusting resistor 22, the value of the reference voltage VR 'of the comparator 24 is determined by the following equation. VR ′ = R23 / [{R22 // R32} + R23] × E Therefore, the connection of R32 causes the reference voltage VR ′ of the comparator 24 to rise.

Therefore, at the time of inspection within the operating temperature range of this fire alarm device, the reference voltage VR of the comparator 24 is used.
The relation between'and the input voltage VS is VS <VR ', and the output of the comparator 24 is in the L state. Then, as in the case of a fire, the buzzer 4 continuously sounds to check whether the function of the fire alarm is normal. After that, when the inspection switch 10 is turned off, the switching transistor 31 is turned off and the monitoring state is restored, and the fire alarm is restored.

The above is the description of the inspection operation when the inspection switch 10 is turned on.
Unless you keep pressing for a predetermined time, the buzzer 4 will ring and you cannot perform inspection. This is because even if the inspection switch 10 is turned on, the voltage necessary for turning on the switching transistor 31 is not generated in the resistor 33 immediately. That is, when the inspection switch 10 is turned on, the capacitor 36 immediately starts charging, the voltage generated in the resistor 33 gradually rises after a short delay, and the base current flowing through the base of the switching transistor 31 also increases accordingly. The voltage between the emitter and collector of the switching transistor 31 also begins to gradually decrease.

After a lapse of a predetermined time of, for example, 10 seconds, the capacitor 36 is charged, the voltage generated in the resistor 33 reaches its maximum value, and the base current flowing through the base of the switching transistor 31 also reaches its maximum value. Turns on completely and becomes conductive. Therefore, if the inspection switch 10 is not pressed for 10 seconds, the buzzer 4 cannot be sounded and the inspection cannot be performed. In this way, the inspection switch 10 can be inspected for the first time by pressing and holding the inspection switch 10 for a certain period of time. For example, the inspection switch 10 can be used when a child accidentally hits a ball while playing indoors or when cleaning. The broom accidentally touches and the inspection switch 10 turns on,
At the same time, if the buzzer 4 sounds, it will be confusingly confusing with a fire alarm.

When the inspection switch 10 is turned on to start the inspection operation and the thermistor 1 is disconnected, the resistance value RTH of the thermistor 1 becomes infinite and the reference voltage VR 'of the comparator 24 becomes The relationship with the input voltage VS is VS> VR ', and the output of the comparator 24 is H.
State. That is, the state becomes the same as the monitoring state, the buzzer 4 does not ring, and the disconnection of the thermistor 1 can be detected. Even if the fire alarm is installed in an extremely cold environment, the buzzer will not sound during inspection. This is because the resistance value of the thermistor is such that the resistance value becomes higher as the temperature becomes lower, so the resistance value of the thermistor becomes close to infinity at the time of very low temperature as in the case of disconnection. .

The fire alarm is from -10 ° C to 50 ° C.
If it is installed in an environment in the temperature range of ° C, it can operate. However, since the landlord sets the installation location of the home-use fire alarm device, the fire alarm device may be installed at an unsuitable place such as directly above the gas stove. Therefore, by using the following configuration,
It is possible for the inspector to check whether the fire alarm is installed in the optimum place as an alarm by the time until the buzzer sounds during inspection. In this case, the resistance 35 of the check circuit 11 in FIG. 2 may be a thermistor having a negative characteristic, the resistance value of which greatly changes depending on the temperature. Then, the time for which the capacitor 36 is charged is determined by the time constant of the capacitor 36 and the resistor 35, the voltage applied to the capacitor 36 and the resistor 35 is constant, and the capacitance of the capacitor 36 does not change much with temperature. Then, it is changed by the change of the resistance value of the resistor 35. In this way, if the time from when the inspection switch 10 is pressed to when it is activated is 5 to 10 seconds, it is assumed that the normal range, that is, the fire alarm is installed at a suitable position, and if it is longer than that, the fire alarm is activated. It is possible to let the user judge that the installation location of the alarm device is a cold environment, and if it is shorter than that, it is a warm environment, and the fire alarm device can be installed in a suitable place. In addition, although the thermal type using a thermistor was used as the fire alarm, it was confirmed whether the installation location is suitable if the inspection circuit as described above is provided even for a smoke type fire alarm, for example. Can be discriminated during inspection. The thermistor used for the resistor 35 may have either a negative characteristic or a positive characteristic, but if the characteristic is positive, the time until the buzzer sounds is shorter as the installation environment is lower and longer as the installation environment is higher.

It is not necessary to keep the buzzer 4 ringing forever when a fire is detected or in the case of a pseudo fire as described above, and because it is necessary to set it in the monitoring state, the ringing of the buzzer 4 is stopped. Then, the timer is operated so as to return to the monitoring state after a predetermined time.
In the operation of the timer, when the alarm stop switch 13 is turned on, the timer circuit 12 is activated and outputs the alarm stop signal in the L state to the buzzer drive circuit 3 for 5 minutes, for example. Then, since the alarm stop signal in the L state is input to the second input terminal of the AND gate 40 of the buzzer drive circuit 3, the output terminal of the AND gate 40 outputs the signal in the L state and the transistor 41 is turned off. The collector and the emitter are non-conductive, and even if the alarm signal is input to the buzzer drive circuit 3 from the fire determination circuit 2, the buzzer drive circuit 3 stops the buzzer 4 from ringing for 5 minutes, and 5 minutes elapses. After that, it returns to the original monitoring state. The timer operating time is set to 5 minutes because, for example, when the thermistor is warmed by a rapid heating operation, this is sufficient time to return to normal temperature.

Next, the operation of the low voltage warning circuit 7 in the monitoring state of the fire alarm will be described. The voltage monitoring circuit of the low voltage warning circuit 7 constantly monitors and detects the voltage of the battery 5, and the built-in alarm signal oscillating circuit operates only when the detected value is below a predetermined value of 5.1 V, for example. The buzzer drive circuit 3 to periodically generate an H-state alarm signal.
Output to The H state alarm signal input to the buzzer drive circuit 3 is applied to the base of the transistor 41 via the second diode 44 and the resistor 42. Then, the transistor 41 is turned on, the collector and the emitter are electrically connected, and the buzzer 4 sounds to warn of the battery voltage drop. The buzzer beeping time for the low voltage alarm of the battery 5 is, for example, about
It is 20 ms, and the cycle is, for example, about 10 to 15 seconds.
As described above, the alarm signal oscillating circuit of the voltage drop alarm circuit 7 is operated by being applied only when the voltage of the battery 5 is equal to or lower than the predetermined value of 5.1 V, for example, to generate the alarm signal in the H state, and the buzzer drive circuit 3 In addition, the alarm signal generated is periodically output, so that the current consumption can be greatly reduced and the life of the battery 5 can be extended.

When the voltage of the battery 5 drops in the operating state of the timer circuit 12 of the fire alarm, the voltage drop warning circuit 7 operates to output an alarm signal to the buzzer drive circuit 3 to make the buzzer 4 ring. When the alarm signal of the voltage drop alarm circuit 7 uses an OR gate composed of, for example, two backflow preventing diodes 43 and 44 for the transistor 41 that drives the buzzer 4 in the buzzer drive circuit 3, Is input via a different route, the timer circuit 12 operates to output an alarm stop signal and the AND gate 40 of the buzzer drive circuit 3 does not output an alarm signal. A low battery voltage warning can be activated.

Further, since the power switch 6 is provided, it is sufficient to turn off the power switch 6 when the user goes out for a long period of time and the alarm of the voltage drop of the battery 5 is unnecessary. Further, for example, when the alarm of the low voltage is not required during sleep, the power switch 6 is turned on and the time limit timer 8 is operated, for example, for 6 hours from 12:00 in the evening to 6 in the morning.
If the battery 5 and the low voltage warning circuit 7 are cut off,
Even if the battery 5 drops below a predetermined voltage value, the voltage drop warning circuit 7 does not operate, the consumption current can be further reduced, and the life of the battery 5 can be further extended. The capacitor 36 and the transistor 31 are provided so that the buzzer does not sound when an object is hit. However, by omitting these, a normally open switch is provided instead of the transistor 31, and a direct resistance is provided. You may make it connect with 32. The first input side of the comparator 24 is a non-inverting input terminal, the second input side is an inverting input terminal, the second input side is a non-inverting input terminal, and the first input side is an inverting input terminal. Good. Although the output of the comparator 24 changes from the H state to the L state, it may change from the L state to the H state.

[0028]

As described above, according to the present invention, the reference voltage VR of the comparator of the fire judging circuit does not change at the time of fire, but the ambient temperature rises and the resistance value Rth of the thermistor which is the fire detecting circuit decreases. However, when the operating temperature is exceeded, the input voltage VS of the comparator becomes the reference voltage VR of the comparator.
Below, the output of the comparator becomes the L state, the switching element becomes conductive, the alarm signal is input to the alarm drive circuit, and the alarm device is driven by the alarm drive signal from the alarm drive circuit and issues an alarm. Also, when the inspection switch is pressed and turned on, the fire substitute resistor connected in series with the inspection switch is connected in parallel with the sensitivity adjustment resistor, and the input voltage of the comparator does not change,
The reference voltage of the comparator rises, resulting in the input voltage VS of the comparator becoming equal to or lower than the reference voltage VR of the comparator, the output of the comparator is in the L state as in the case of a fire, the switching element is in the conductive state, and the alarm drive circuit is activated. An alarm signal is input, and the alarm device is driven by the alarm drive signal from the alarm drive circuit to issue an alarm,
Can be inspected. Even if the inspection switch is pressed and turned on, if the thermistor is disconnected, the resistance value of the thermistor becomes infinite, and even if the reference voltage of the comparator rises, the input voltage of the comparator rises further. As a result, the input voltage VS of the comparator becomes equal to or higher than the reference voltage VR of the comparator, the output of the comparator becomes the H state as in the case of monitoring, the switching element becomes non-conductive, and the alarm signal is not input to the alarm drive circuit. Since the alarm device is not driven, it is possible to detect the disconnection of the thermistor when the inspection switch is inspected.

When the check switch is kept pressed, the capacitor immediately starts charging, and after a short delay, the voltage generated in the voltage dividing resistor gradually rises, and the base current flowing through the base of the transistor also increases accordingly. The voltage between the emitter and collector of the transistor also begins to drop gradually, and when a predetermined time has passed since the inspection switch was turned on,
The capacitor is charged, the voltage generated in the voltage dividing resistor becomes the maximum value, the base current flowing in the base of the transistor also becomes the maximum value, the transistor is fully turned on and becomes conductive, and the alarm signal is input to the alarm drive circuit. The alarm device is driven by the alarm drive signal from the alarm drive circuit to issue an alarm for inspection, so if the inspection switch is not pressed for a predetermined time, the alarm device may be inspected. This has the effect of preventing an erroneous operation in which the inspection switch is momentarily touched and turned on, and at the same time the alarm device is driven.

Further, the delay resistance of the above-mentioned inspection means is a resistance whose resistance value changes by heat, and the resistance value of the resistance is set to be long at a low operating time and short at a high operating time so that the inspection can be performed. The time from when the switch is pressed to when it is activated is within a normal range, for example, 5 seconds to 10 seconds. If it is longer than that, the fire alarm is installed in a cold environment, and if it is shorter than that, it is warm. It is possible to let the user judge that it is an environment,
This has the effect of enabling the fire alarm to be installed in a suitable location.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a fire alarm device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a fire detection circuit and a fire determination circuit of the fire alarm device.

FIG. 3 is a circuit diagram showing a configuration of a buzzer drive circuit of the fire alarm device.

[Explanation of symbols]

1 fire detection circuit, 2 fire judgment circuit, 3 buzzer drive circuit (alarm drive circuit), 4 buzzer (alarm), 7
Low voltage alarm circuit, 10 inspection switch, 11 inspection circuit.

Claims (3)

[Claims] 1. A fire detection circuit that detects a fire by heat and outputs an electric signal, and a fire determination circuit that outputs an alarm signal when the electric signal output from the fire detection circuit is equal to or greater than a predetermined reference value. Alarm device drive circuit that outputs an alarm drive signal in response to an alarm signal from the fire judgment circuit, an alarm device that is driven by the alarm drive signal from the alarm device drive circuit, a fire detection circuit, a fire judgment circuit, and an alarm device drive In a fire alarm device comprising a circuit and a power supply for driving an alarm device, the fire detection circuit is a thermistor, and the fire determination circuit is provided between the plus side and the minus side of the power source, and the thermistor and A current limiting resistor connected in series, two sensitivity adjusting resistors connected in series for setting a reference value, provided between the positive side and the negative side of the power source, and the thermistor. And a comparator connected to the connection point of the current limiting resistance and the connection point of the two sensitivity adjustment resistances, and a switching element that outputs the alarm signal based on the output of the comparator. It consists of an inspection switch and an inspection resistor connected in series between the connection points of two sensitivity adjustment resistors, and the resistance value of the inspection resistor is set so as to change the output of the comparator when the inspection switch is turned on. A fire alarm that is equipped with an inspection means. 2. A fire detection circuit that detects a fire and outputs an electrical signal, a fire determination circuit that outputs an alarm signal when the electrical signal output from the fire detection circuit is equal to or greater than a predetermined reference value, and a fire determination circuit. An alarm device drive circuit that receives an alarm signal from the circuit and outputs an alarm drive signal, an alarm device that is driven by an alarm drive signal from the alarm device drive circuit, a fire detection circuit, a fire determination circuit, an alarm device drive circuit, and In a fire alarm device comprising a power supply for driving an alarm device, the fire determination circuit is provided between the positive side and the negative side of the power source, and a current limiting resistor connected in series with the fire detection circuit, It is provided between the positive side and the negative side of the power source and is connected in series for setting a reference value.
Based on the output of the comparator, one sensitivity adjustment resistor, the first input side is connected to the connection point of the thermistor and the current limiting resistor, and the second input side is connected to the connection point of the two sensitivity adjustment resistors A transistor having an emitter connected to the positive side of the power supply, and a collector connected to the transistor at one end, and the other end connected to the first or second input to the comparator. Of the delay capacitor connected to the positive side of the power source and the positive side of the power source connected to the positive side of the power source, and the delay resistor connected to the positive side of the power source. Check that the delay resistor is connected between the other end and one end, and that is connected between the other end of the delay resistor and the minus side of the power supply. A switch connected in series, one end connected to the positive side of the power source, the other end connected to the connection of the delay capacitor and the delay resistor, and the connection point of the series connection connected to the transistor base. A fire alarm characterized by comprising an inspection means consisting of two voltage dividing resistors. 3. The fire alarm device according to claim 2, wherein the delay resistor of the inspection means is a variable resistor whose resistance value changes due to heat.