JPS6012678B2 - Signal processing circuit for photoelectric smoke detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal processing circuit for an optical fin type smoke detector that utilizes light scattered by smoke.

Conventionally, a circuit as shown in FIG. 1 has been used as this type of signal processing circuit.

That is, 1 is an oscillation circuit that oscillates a pulse with a predetermined period, and its output is given to one of the input terminals of the light emitting element 2 and the AND circuit 3. The other input terminal of the AND circuit 3 is connected to the output terminal of an amplifier 5 that amplifies the signal from the light receiving element 4. Therefore, in the normal monitoring state, the light A from the light emitting element 2 that emits light in response to the pulse train from the oscillation circuit 1 does not enter the light receiving element 4, and no output signal appears at the output terminal of the amplifier 5. Therefore, AND circuit 3
No smoke detection signal is output.

On the other hand, when dust B is generated due to a fire or the like, the light A from the light emitting element 2 is scattered by the bonito B, and the scattered light A' enters the light receiving element 4, is amplified by the amplifier 5, and is input to the AND circuit 3. .

In addition, since the synchronization signal is directly given to the other input terminal of the AND circuit 3 from the oscillation circuit 1, the bonito detection signal is output from the AND circuit 3, and the presence or absence of smoke is monitored through an alarm etc. using this world power signal. was configured to do so.
Figure 2 is a time chart showing this operation, where a is the output from the light emitting element 2, b is the output from the amplifier 5, and c is the output from the AND circuit 3. It shows.

By the way, in the conventional example configured as above,
Since the amplifier 5 detects the scattered light A' with a light receiving element, it is required to have a high gain gain and is susceptible to noise, and as can be seen from Figure 2, it is particularly susceptible to the effects of the spike 6 of the oscillation circuit 1. , and the SN ratio was low, and it was difficult to lower the detection level 7, so it had the disadvantage that a highly sensitive one could not be manufactured. The present invention aims to eliminate the above-mentioned drawbacks and provide a highly sensitive rattan sensor.

Hereinafter, the present invention will be explained along with the drawings.

FIG. 3 shows an embodiment of the invention.

In this case, the same reference numerals will be used for parts corresponding to those in FIG. 1 to avoid duplication of explanation, and detailed explanation will be omitted. 8 is a one-shot circuit whose input terminal receives the output from the oscillation circuit 1, and whose output terminal is connected to one input terminal of an AND circuit 9. Also, the oscillation circuit 1
The output from the NOT circuit 10 is also given to the NOT circuit 10, and the output from the NOT circuit 10 is given to the other input terminal of the AND circuit 9. On the other hand, the output of this AND circuit 9 is given to the input terminal of the AND circuit 3, and the other input terminal of the AND circuit 3 is connected to the output terminal of the amplifier 5, and the bonito sensing signal is output from the output terminal. is configured to do so. Next, the operation of the embodiment of the present invention shown in FIG. 3 will be explained with reference to the time chart shown in FIG.

The output from the oscillation circuit 1 is applied to the light emitting element 2, as well as to the one-shot circuit 8 and the knot circuit 10', as shown in FIG. 4d.

This one-shot circuit 8 receives a pulse from the oscillation circuit 1 and outputs a pulse longer than the pulse from the oscillation circuit 1 as shown in FIG. 4e. On the other hand, the NOT circuit 10 inverts the pulse train from the oscillation circuit 1 as shown in FIG. 4f. When the one-shot circuit 8 and the not circuit 10 are ANDed by the AND circuit 9, as shown in FIG. A synchronization signal having a difference in pulses from the oscillator circuit 1 is obtained. Incidentally, the spike 6 from the oscillation circuit 1 appearing in the output of the amplifier 5 is synchronized with the rise of the pulse train output from the oscillation circuit 1, as shown in FIG. There is no overlap. Therefore, using this synchronization signal, the amplifier 5
If the output is detected, it will not be affected by spike 6 at all. Furthermore, when smoke is generated, the light A from the light emitting element 2 is scattered by the bonito B as in the conventional example, and the scattered light A' enters the light receiving element 4.
A sensing signal is sent to the amplifier 5.

The amplifier 5 amplifies the signal from the light-receiving element 4 and provides an output to the other terminal of the AND circuit 3, which has one terminal supplied with the synchronizing signal from the AND circuit 9. AND circuit 3
Now, take the logical product of these and from its output terminal,
Send out a smoke detection signal as shown in . At this time, since the AND circuit 3 is not affected by the spike 6 from the oscillation circuit 1 as described above, the detection level 7 can be sufficiently lowered. Note that in the above, an example using two AND circuits 3 and 9 was described for ease of explanation.
It goes without saying that the present invention can be implemented in exactly the same way using a single three-input AND circuit instead of these. According to the present invention configured as described above, since it is possible to prevent the influence of spikes from the oscillation circuit, the detection level can be sufficiently lowered, and a highly sensitive and stable smoke detector can be realized. There are advantages.

[Brief explanation of the drawing]

Figure 1 is a signal processing circuit of a conventional photoelectric smoke detector, Figures 2 a to c are time charts of various parts, Figure 3 is a signal processing circuit of a photoelectric smoke detector according to the present invention, and Figure 4 is a signal processing circuit of a conventional photoelectric smoke detector. In the time chart of each part, d is the oscillation circuit, e is the one-shot circuit,
f represents a NOT circuit, g represents an AND circuit, h represents an amplifier, and i represents each output from the AND circuit. 1...Oscillation circuit, 2...Light emitting element, 3...
...AND circuit, 4... Light receiving element, 5...
...Amplifier, 6...Spike, 7...Detection level, 8...One-shot circuit, 9...And circuit,
10... knot circuit, A... light, A'...
...Scattered light, B...Smoke. Spear 1 Figure O 2 Figure O 3 Figure Sai〈Figure

Claims (1)

[Claims] 1 An oscillation circuit that oscillates pulses with a predetermined period, a light emitting element that emits light in synchronization with the pulses from this oscillation circuit, a light receiving element that receives light from this light emitting element, and a signal that increases the signal received by this light receiving element. In the photoelectric smoke detector, a one-shot circuit and a knot circuit are connected to the output terminal of the oscillation circuit, and the outputs from the one-shot circuit and the knot circuit are connected to the output terminal of the amplifier. A signal processing circuit for a photoelectric smoke detector, characterized in that an AND circuit is connected to perform a logical product, and a smoke detection signal is detected through the AND circuit.