JPS6356595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dimming type smoke sensor that issues an alarm by detecting attenuation of light due to smoke entering between a light source and a light receiving element.

A conventional dimming type smoke detector is constructed as shown in the block diagram of FIG. That is, an oscillation circuit 1 that generates a pulse, a light source L such as a light emitting diode that is driven by the pulse and projects light into the smoke monitoring space, and a light receiving element P such as a photodiode that receives the light from the light source L. An amplifier circuit 2 that amplifies the signal of the light receiving element P, a first voltage holding circuit 3 that holds the output voltage of the amplifier circuit 2 for a short time, and a second voltage holding circuit 4 that holds the output voltage for a long time; It consists of a comparison circuit 5 for comparing two output voltage levels, and a switching circuit 6 such as an SCR triggered by the output of the comparison circuit 5.

In the above configuration, if smoke enters,
The transmitted light from the light source L to the light receiving element P is attenuated, the signal level of the light receiving element P is reduced, and as a result, the output voltage of the amplifier circuit 2 is reduced. When the smoke concentration increases in a relatively short period of time, the output voltage of the first voltage holding circuit 3 becomes lower than the output voltage of the second voltage holding circuit 4, and at this time, the comparison circuit 5 An output signal is generated based on the voltage difference, and the switching circuit 6 is activated. In addition, light source L
Slow light changes due to deterioration of the lens, reflector, light receiving element P, etc.
Since the output of the second voltage holding circuit 4 changes in the same way as the output of the second voltage holding circuit 4, the voltage difference is small.
produces no output signal.

In the dimming type smoke detector configured as described above, among the two voltage holding circuits 3 and 4, the voltage stored in the capacitor constituting the time constant circuit of the voltage holding circuit 4, which holds the voltage for a particularly long time. The accumulated charge is retained even after the power is turned off, so when the power is turned off for a short time, such as after a short power outage or during a sensor operation test, when the power is turned on again. Since the light source does not immediately reach a predetermined amount of light, there is a problem in that a difference occurs between the voltage levels of the two voltage holding circuits 3 and 4, resulting in an alarm output.

This invention was devised to solve the above problem, and will be described in detail below based on an embodiment shown in FIGS. 2 and 3.

As shown in the block diagram of FIG. 2, the dimming type smoke detector of the present invention includes an oscillation circuit 1 that generates pulses, a light source L, a light receiving element P, an amplifier circuit 2, and an output voltage of the amplifier circuit 2. A conventional circuit consisting of a first voltage holding circuit 3 that holds the output voltage for a long time, a second voltage holding circuit 4 that holds the output voltage for a long time, a first comparison circuit 5 that compares these two output voltage levels, and a switching circuit 6, A circuit for detecting a drop in the voltage supplied to the light source L is provided. That is, a reference voltage circuit 7 and a second comparison circuit 8 are provided, and the voltage generated in the resistor 9 connected in series with the light source L, which depends on the forward current during light emission of the light source L, is compared with the voltage of the reference voltage circuit 7. , when the voltage of the resistor 9 is higher than the reference voltage, the second
The comparator circuit 8 is configured to generate an output. A gate circuit 10 is provided between the first comparison circuit 5 and the switching circuit 6, and the second comparison circuit 8 is connected to this gate circuit 10, so that the output of the second comparison circuit 8 and the output of the first comparison circuit 5 are simultaneously output. The configuration is such that the output of the gate circuit 10 is output and the switching circuit 6 is operated only when the output is on. Note that the reference voltage circuit 7 includes a Zener diode 11 and a resistor 12, as shown in FIG. 3 as an example.

According to the dimming type smoke detector of the present invention configured as described above, when the power is cut off for a short time,
The voltage of the oscillation circuit 1 decreases, and the amount of light emitted from the light source L decreases. At this time, the voltage applied to the resistor 9 is lower than the voltage of the reference voltage circuit 7, and when the power is turned on again and current supply to the sensor is started, even if the first comparison circuit 5 outputs, 2. Since the output of the comparison circuit 8 is not output, the output of the gate circuit 10 is not output, so the switching circuit 6 is not activated, and no false alarm occurs.

In addition, as a place to detect a decrease in the light intensity of the light source,
The resistor 9 in the embodiment shown in FIG. 2 may be used, for example, in the vicinity of the power supply section of the oscillation circuit 1 or the transistor (not shown) of the oscillation circuit 1. In other words, when the power supply voltage drops, the Any location where the voltage of the light source drops may be used.

As explained above, the dimming type smoke detector of the present invention has a structure in which the signal output of the light receiving element is input to a circuit that holds it for a short time and a circuit that holds it for a long time, and an alarm signal is generated based on the voltage difference between them. In the sensor,
By simply adding a simple circuit, false alarms can be eliminated when power is resupplied after a temporary power outage or when power is cut off during a sensor operation test, which is an excellent disaster prevention effect.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional dimming type smoke detector, Fig. 2 is a block diagram showing an embodiment of the dimming type smoke detector of the present invention, and Fig. 3 is an embodiment of a reference voltage circuit. FIG. 1...Oscillation circuit, 2...Amplification circuit, 3...Electronic circuit 1
Voltage holding circuit, 4... Second voltage holding circuit, 5...
First comparison circuit, 6...Switching circuit, 7...
Reference voltage circuit, 8... second comparison circuit, 10... gate circuit, L... light source, P... light receiving element.

Claims (1)

[Claims] 1. An oscillation circuit, a light source that emits pulsed light by the oscillation circuit, a light receiving element that receives light from the light source after passing through a smoke monitoring space, an amplifier circuit that amplifies the output signal of the light receiving element, and the amplifier circuit. a first voltage holding circuit that holds the output for a short time, a second voltage holding circuit that holds the output for a long time, a comparison circuit that compares the outputs of the two voltage holding circuits, and is activated by the output of the comparison circuit. In a dimming type smoke detector, a detection circuit for detecting a drop in the voltage supplied to the light source, and a gate circuit are provided between the comparison circuit and the switching circuit, and the output of the detection circuit is A dimming type smoke detector characterized in that the gate circuit is controlled by the following.