JPS5931759B2 - optical fire detector - Google Patents

Description

[Detailed description of the invention] This invention relates to an optical fire detector.

Optical fire detectors that detect smoke using scattered light or transmitted light have the problem of malfunctioning due to external light or electrical noise.

For this reason, conventionally, as shown in FIG. 1, a pulse signal output from a rectangular wave oscillator 1 is modulated by a modulator 11 with an alternating current signal of frequency fl output from a fixed frequency oscillator 2, and this modulated pulse A light emitting element 4 such as a light emitting diode is driven by a signal to emit modulated light in pulses, and of the light received by the light receiving element 5, only the received light output with a frequency f due to the modulated light is selectively amplified by a selective amplifier 8. When the output of 8 reaches a predetermined value, the switching circuit 9 operates to output a fire signal to a receiver (not shown),
Optical fire detectors are known that are designed to prevent malfunctions caused by external light or electrical noise. However, in such an optical fire detector, in order to prevent malfunction, the oscillation frequency of the fixed frequency oscillator 2 and the tuning frequency of the selection amplifier 8 must be made the same, and the adjustment is troublesome and time-consuming. . Further, the oscillation frequency of the fixed frequency oscillator 2 and the tuning frequency of the selective amplifier 8 each fluctuate due to temperature changes, resulting in a difference. For this reason, if the selectivity of the selection amplifier 8 is lowered to widen the selection frequency range, signals other than the modulation signal will also be detected and amplified, resulting in malfunction. In view of the above points, this invention eliminates the influence of temperature changes on the frequency and eliminates the effects of external light and electrical The present invention provides an optical fire detector that prevents malfunctions caused by noise.

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, 1 is a rectangular wave oscillator that outputs a pulse signal, and 2 is a fixed frequency oscillator that is operated by the output of the rectangular wave oscillator 1.
One set of electrode plates of a mechanical oscillator 3, such as a crystal, piezoelectric ceramic, or tuning fork, having a set of electrode plates is connected, and the frequency f1 is set by controlling the mechanical oscillator 3.
Outputs an AC signal. 4 is driven by a pulse signal modulated with an alternating current signal of frequency f1 output from the fixed frequency oscillator 2, and emits modulated pulse light into the smoke detection chamber (not shown). A light emitting element such as a light emitting diode that emits light; 5 a light receiving element such as a solar cell that detects scattered or transmitted light of the light emitted from the light emitting element 4; 6 a preamplifier that amplifies the light receiving output of the light receiving element 5; 7 is a magnetostrictive delay line, a bucket, which delays the output of the preamplifier 6 by the Mars output time of the rectangular wave oscillator 1 so that the subsequent selection amplifier 8 is not influenced by the fixed frequency oscillator 2 that shares the mechanical oscillator 3. Brigade Device (BucketBrigadeDevic)
8 is a selection amplifier that amplifies the output of the delay circuit 7, and this selection amplifier 8 has a tuning circuit connected to the other set of electrode plates of the mechanical vibrator 3, and 8 is a selection amplifier that amplifies the output of the delay circuit 7. By controlling the vibrator 3, only the signal of frequency f1 is selectively amplified.

Reference numeral 9 denotes a switching circuit, which operates when the output of the selection amplifier 8 reaches a predetermined value and switches the receiver (
(not shown) outputs a fire signal.

Next, the operation of this optical fire detector will be explained in the case of a scattered light type with reference to FIG.

In FIG. 3, 1 represents the output of the rectangular wave oscillator 1, 2 represents the output of the fixed frequency oscillator 2 and the light emitting output of the light emitting element 4, and 3 represents the output of the fixed frequency oscillator 2.
is the light receiving output of the light receiving element 5, 4 is the output of the delay circuit 7,
Reference numeral 5 indicates the output of the selection amplifier 8, and reference numeral 6 indicates the fire signal output of the switching circuit 9. When the rectangular wave oscillator 1 outputs the pulse signal shown in FIG. 31, the fixed frequency oscillator 2 operates under the control of this pulse signal to generate a modulated pulse signal with a frequency f1 shown in FIG. 32 determined by the mechanical oscillator 3. The light emitting element 4 is operated by this modulated pulse signal and emits the modulated pulsed light shown in FIG. 32. If there is no smoke in the smoke sensing chamber, the light receiving element 5 will not produce an output, and therefore the preamplifier 6, delay circuit 7, selection amplifier 8, and switching circuit 9 will not produce any output. However, when smoke enters the smoke detection chamber due to a fire outbreak, the light emitted from the light emitting element 4 is scattered by the smoke, and this scattered light causes the light receiving element 5 to receive a pulse modulated at the frequency f1 shown in FIG. The light receiving output of the light receiving element 5 is amplified by a preamplifier 6 and input to a delay circuit 7.

The delay circuit 7 delays the input modulated pulse signal while the rectangular wave oscillator 1 outputs the pulse signal as shown in FIG. 3 and outputs the delayed signal. Since the signal of frequency f1 outputted from this delay circuit 7 matches the tuning frequency of the tuning circuit controlled by the mechanical oscillator 3 of the selection amplifier 8, it is amplified by the selection amplifier 8 as shown in FIG. When the output of the amplifier 8 reaches a predetermined value, the switching circuit 9 operates and outputs the fire signal shown in FIG. 36. By the way, when the light receiving element 5 receives external light such as a flash or a lighting device with a frequency different from the oscillation frequency f1 of the fixed frequency oscillator 2 and generates an output, the output of the light receiving element 5 is delayed by the delay circuit 7 and then selected. Input to amplifier 8.

However, the selection amplifier 8 does not produce an output because the frequency of the input signal is different from the tuning frequency f1. Similarly, the light receiving element 5
The selection amplifier 8 does not produce an output even when the signal receiving device 8 receives an electric signal having a frequency other than f1. Therefore, the switching circuit 9 does not operate and does not output a fire signal. Furthermore, when the ambient temperature of this optical fire detector changes, the oscillation frequency of the fixed frequency oscillator 2 and the tuning frequency of the selection amplifier 8 change, but the oscillation circuit of the fixed frequency oscillator 2 and the tuning circuit of the selection amplifier 8 Since they are controlled by the same mechanical vibrator 3, they always show the same frequency fluctuations, and there is no difference between the oscillation frequency and the tuning frequency.

As shown by the dotted line in FIG. 2, a gate circuit 10 controlled by the output of the rectangular wave oscillator 1 is provided between the selection amplifier 8 and the switching circuit 9, so that the gate circuit 10 is controlled by the output of the rectangular wave oscillator 1. Alternatively, the gate circuit 10 may be closed to prohibit the output of the selection amplifier 8 from being input to the switching circuit 9.

According to this invention, the oscillation circuit of the fixed frequency oscillator 2 that modulates the light emitted from the light emitting element 4 and the tuning circuit of the selective amplifier 8 that amplifies the received light output by the modulated light of the light receiving element 5 are integrated into the same mechanical oscillator 3. Since they are both controlled, the oscillation frequency of oscillator 2 and the tuning frequency of amplifier 8 can be easily set to the same frequency.

Furthermore, even if the ambient temperature changes, the oscillation frequency and tuning frequency will not deviate. Therefore, since the selectivity of the selection amplifier 8 can be increased, an optical fire detector that does not malfunction can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional optical fire detector, Fig. 2 is a block diagram of an embodiment of the optical fire detector according to the present invention, and Fig. 3 is an operation of the optical fire detector shown in Fig. 2. It is a figure explaining a state. 1... Square wave oscillator, 2... Fixed frequency oscillator, 3... Mechanical resonator, 4... Light emitting element, 5... Light receiving element, 7... Delay circuit, 8... Selection amplifier, 9... Switching circuit, 10... Gate circuit.

Claims (1)

[Claims] 1. A square wave oscillator, a fixed frequency oscillator that modulates the pulse output of the square wave oscillator at a specific frequency, and a light emitting element that is driven by the modulated pulse signal and emits modulated light intermittently. a light-receiving element that detects scattered light or transmitted light from the light-emitting element; a delay circuit that delays the output of the light-receiving element while the rectangular wave oscillator outputs a pulse signal; It consists of a selective amplifier that amplifies only the output of the modulated pulsed light, a switching circuit that operates to output a fire signal when the output of the selective amplifier reaches a predetermined value, and a mechanical oscillator that has two sets of electrodes. An optical fire detector comprising a mechanical oscillator, one set of electrodes being connected to the oscillation circuit of the fixed frequency oscillator and the other set of electrodes being connected to the tuning circuit of the selection amplifier. 2. The optical fire detector according to claim 1, wherein the output of the selection amplifier is configured not to be input to the switching circuit while the rectangular wave resonator is producing an output.