JPH0477356B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention is directed to a so-called fire detection system in which a detection section is driven intermittently in synchronization with the oscillation cycle of an oscillation circuit, and a fire is detected based on the signal output of the detection section. Concerning an intermittent drive type fire detector.

(Prior Art) Conventionally, so-called intermittent drive type fire detectors have been used, in which a detection unit is driven intermittently in synchronization with the oscillation cycle of an oscillation circuit, and fire is detected based on the signal output of the detection unit. is equipped with an internal comparator, and compares the fire level, which is the threshold value of the comparator set in advance, with the detection output from the detection unit, for example, the detection level from the temperature detection unit that detects a temperature rise due to a fire, Fire was determined based on the signal output of the comparator.

In order to reduce current consumption, such conventional fire detectors are equipped with an oscillation circuit that outputs oscillation pulses with a pulse voltage equal to the power supply voltage at a predetermined period, and the temperature detection unit and the The comparator was driven intermittently.
One input terminal of the comparator is given a predetermined reference voltage that is a fire level, and the other input terminal is given a signal voltage corresponding to the temperature rise from the temperature detection section, and the reference voltage and signal When the signal voltage reaches the reference voltage, a detection operation is performed and a fire signal is output.

(Problems to be Solved by the Invention) However, a constant voltage circuit is provided before the oscillation circuit, and a constant power supply voltage is supplied to the oscillation circuit to cause the oscillation circuit to perform stable oscillation. Therefore, immediately after power is supplied to the fire detector, the voltage supplied to the oscillation circuit gradually increases due to the effect of the smoothing capacitor installed in the constant voltage circuit, and before reaching the specified power supply voltage, that is, at a low power supply voltage. The oscillation circuit will start oscillating operation, and when the oscillation circuit starts oscillating operation,
A drive voltage corresponding to the pulse voltage of the oscillation pulse from the oscillation circuit, that is, a voltage lower than the specified voltage, was supplied for comparison. Therefore, in the comparator,
A fire level is set according to the low drive voltage.
In other words, a reference voltage with a value lower than the predetermined reference voltage will be applied to one input terminal of the comparator, and if the value of this reference voltage is lower than the signal voltage input to the other input terminal of the comparator, it will be as if there is a fire. The situation would be the same as that at the time of detection, and the comparator would detect the fire and output a fire signal, potentially causing a false alarm.

(Means for Solving the Problems) The present invention has been made in view of the above problems, and aims to prevent malfunctions in an unstable state such as after power is turned on, that is, in a state where the power supply voltage has not reached a specified voltage. In addition, in order to reduce excessive current consumption, speed up power supply startup, and provide a highly reliable fire detector with a simple circuit configuration, a detection section that detects changes in physical phenomena caused by fire, and a predetermined cycle The detection unit is intermittently driven in synchronization with the oscillation pulse output using the oscillation pulse output of the oscillation circuit as a power source, and determines a fire based on the detection output of the detection unit. The fire detector is characterized in that the oscillation circuit includes a voltage detection element that stops the oscillation operation when the power supply voltage of the oscillation circuit becomes lower than a predetermined voltage.

(Example) The figure is a circuit diagram showing one embodiment of the present invention.

First, the configuration will be described. Reference numeral 1 denotes a power supply that outputs a predetermined power supply voltage, and a thyristor SCR is connected between the power supply and signal lines drawn out from the power supply 1. In addition, transistors Q3 and Q4 and a resistor R are connected between the power supply and signal line drawn out from power supply 1.
A constant voltage circuit consisting of 5, R6, a Zener diode ZD2, and a smoothing capacitor C2 is connected, and a constant voltage E ₀ determined by the Zener voltage of the Zener diode ZD2 is shaped to supply driving power. Reference numeral 2 denotes an oscillation circuit that oscillates at a predetermined period, and intermittently supplies driving power E ₀ to the detection section 4 in synchronization with the oscillation period of the oscillation circuit 2, thereby intermittently driving the comparator 5 and the sensor 6. The sensor 6 outputs a signal voltage corresponding to the temperature change due to the fire to one input terminal of the comparator 5. The other input terminal of the comparator 5 is given the divided voltage of the resistors R7 and R8 as a reference voltage, and when the signal voltage from the sensor 6 becomes larger than the reference voltage, a signal is output to the counter 3. The counter 3 calculates, for example, 10 oscillation pulses based on the oscillation pulses from the oscillation circuit 2.
The signal output from the comparator 5 is counted within a predetermined time, and when the count value within the predetermined time reaches a predetermined number 3, the thyristor SCR is made conductive and a detection signal is sent out.

Next, the internal configuration of the oscillation circuit 2 will be explained. A first resistor R1, a Zener diode ZD1 set to a predetermined Zener voltage, a second resistor R2, and a first transistor Q1 are connected in series between the power supply line L2 and the common line L3. A third resistor R3 has one end connected to the power supply line L2, and the other end of the third resistor R3 has its base connected to the first transistor Q1. A second transistor Q2, a fourth resistor R4, and a capacitor C1 are connected in series between a connection point between the third resistor R3 and the base of the first transistor Q1 and the power supply line L2. From the connection point of the first resistor R1 and Zener diode ZD1 to the second transistor Q
It is connected to the base of 2. Here, the Zener voltage of the Zener diode ZD1 is set to provide a base voltage that turns on the second transistor Q2 when the drive power supply voltage reaches the specified voltage _E0 . Transistor Q2 and resistor R
A resistor R9 is connected between the connection point of No. 4 and the common line L3, and a voltage change across the resistor R9, that is, an oscillation pulse, is output to the counter 3, and at the same time, this oscillation pulse is supplied to the detection unit 4 as a driving power source. .

Next, the operation will be explained. When the power is turned on, the smoothing capacitor C2 is charged immediately after the power is turned on, and the power supply voltage between the power line L2 and the common line L3 gradually increases. Power line L2 and common line L
A base current flows into the transistor Q1 through the resistor R3 in response to a rise in the power supply voltage between the two transistors. Even if the base current flows through the transistor Q1, the operation of the transistor Q1 is prohibited by the intervention of the blocking means, that is, the Zener diode ZD1, until the power supply voltage between the power supply line L2 and the common line L3 rises to a predetermined voltage. Furthermore, when the charging of the capacitor C2 progresses and the power supply voltage between the power supply line L2 and the common line L3 reaches the specified voltage _E0 , the Zener diode ZD1 becomes conductive, and the transistor Q1 becomes conductive through the resistor R1, the Zener diode ZD1, and the resistor R2. Collector current flows through. Transistor Q1
When the transistor Q2 is turned on, the base voltage is applied to the transistor Q2, and the transistor Q2 is turned on. When the transistor Q2 is turned on, a specified power supply voltage E ₀ is supplied to the detection unit 4, and the comparator 5 and sensor 6 are driven.
Also, when transistor Q2 is turned on, transistor Q
2. Charge the capacitor C1 through the resistor R4. After a predetermined time determined by the time constant of capacitor C1 and resistor R4 has elapsed, when the voltage across capacitor C1 is charged to a voltage approximately equal to the power supply voltage _E0 , the potential difference between the emitter and collector of transistor Q2 becomes approximately zero volts, and the transistor Q2 turns off. When transistor Q2 turns off, oscillation circuit 2
Since the output terminal of the transistor Q2, that is, the collector side of the transistor Q2, is at approximately zero volts, and both ends of the capacitor C1 are charged to approximately the power supply voltage _E0 , the base side of the transistor Q1 is reverse biased to approximately _-E0 , and the transistor Q2 is reverse biased. Q1 turns off. When the transistor Q1 is turned off, the charge stored in the capacitor C1 is discharged through the resistors R4, R9, the capacitor C2, and the resistor R3. When the discharge of the capacitor C1 progresses and the reverse bias of the transistor Q1 is released, the transistor Q1 is
A base current flows through the transistor Q1, turning on the transistor Q1. When the transistor Q1 is turned on, the transistor Q2 is turned on, and the oscillation operation continues in the same manner.
That is, the specified voltage is synchronized with the oscillation cycle of the oscillation circuit 2.
E ₀ is intermittently supplied to the detection unit 4, and the comparator 5 and sensor 6 are intermittently driven. Here, if the sensor 6 detects a temperature rise due to a fire,
When the signal voltage from the sensor 6 becomes higher than the reference voltage formed by the divided voltage of the resistors R7 and R8, the comparator 5 outputs a signal, drives the counter 3, makes the thyristor SCR conductive, and sends out a detection signal.

In the above embodiment, the Zener diode ZD1 that prohibits the oscillation operation of the oscillation circuit 2 until the predetermined power supply voltage is reached is inserted between the resistors R1 and R2, but the connection point between the resistors R1 and R2 and the transistor The Zener diode ZD1's anode side is connected to the base of the transistor Q2, that is, the anode side of the Zener diode ZD1 is connected to the connection point of the resistors R1 and R2, the cathode side of the Zener diode ZD1 is connected to the base of the transistor Q2, and the Zener voltage of the Zener diode ZD1 is adjusted as appropriate. It may be configured such that the base voltage is set to turn on the transistor Q2 when a predetermined power supply voltage is reached.

Furthermore, in the above embodiment, a temperature sensor that outputs a signal voltage corresponding to a temperature rise due to a fire is used as the sensor 6. A smoke sensor may be used which is provided facing each other with a smoke detection space in between and detects the amount of smoke based on the light reception output of the light receiving section which is attenuated or scattered by the smoke flowing into the smoke detection space.

(Effects of the Invention) As described above, according to the present invention, the present invention includes a detection unit that detects changes in physical phenomena caused by a fire, and an oscillation circuit that outputs oscillation pulses at a predetermined period.
The detection section is intermittently driven in synchronization with the oscillation pulse output using the oscillation pulse output of the oscillation circuit as a power source,
In the fire detector that discriminates fire based on the detection output of the detection unit, the oscillation circuit is provided with a voltage detection element that stops the oscillation operation when the power supply voltage of the oscillation circuit becomes lower than a predetermined voltage. This has the effect of preventing malfunctions due to power supply failures, reducing excessive current consumption, speeding up power supply startup, and further increasing the reliability of the fire detector.

[Brief explanation of the drawing]

The figure is a circuit diagram showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Constant voltage power supply, 2... Oscillation circuit, 3... Counter, 4... Detection part, 5... Comparator, 6
...Sensor, ZD1, ZD2...Zener diode, SCR...Thyristor, Q1, Q2, Q3...
...Transistor, C1, C2...Capacitor, R
1, R2, R3, R4, R5, R6, R7, R8
……resistance.

Claims (1)

[Scope of Claims] 1. A detection unit that detects changes in physical phenomena caused by a fire, and an oscillation circuit that outputs oscillation pulses at a predetermined period, the detection unit generating the oscillation using the oscillation pulse output of the oscillation circuit as a power source. In a fire detector that is intermittently driven in synchronization with a pulse output and determines a fire based on the detection output of the detection section, an oscillation operation is performed in the oscillation circuit when the power supply voltage of the oscillation circuit becomes lower than a predetermined voltage. A fire detector characterized by being equipped with a voltage detection element that stops the fire.