JPS586994B2 - Photoelectric smoke detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric smoke sensing method that can prevent malfunctions of photoelectric smoke detectors due to strong external light and the like.

In a photoelectric smoke detector, the light emitting element emits light intermittently, and the light receiving element receives light in synchronization with this, and when the pulsed light from the light emitting element is scattered by smoke, the scattered light enters the light receiving element. and is detected by the light receiving element.

However, this type of smoke detector can sometimes issue false alarms in response to strong external light, such as from a photo flash.

This is because the smoke detection chamber of a photoelectric smoke detector is designed to allow smoke to enter and block outside light, but it is impossible to completely seal it because it is necessary to allow smoke to enter. Generally speaking, it is simply a zigzag path that allows smoke to enter but does not allow light to enter.

Therefore, even if normal light can be sufficiently blocked, extremely intense flash light from a strobe or the like will diffusely reflect along the zigzag path, and a portion of it will enter the smoke detection chamber, where the light receiving element will sense this and radiate it out.

In order to be insensitive to such external light or noise, it is recommended to use a storage type photoelectric smoke detector.

In other words, this type of sensor accumulates the power of multiple detections in an attenuation accumulation circuit such as a capacitor with a discharge resistor, and issues an alarm when it exceeds a certain value. do not respond to

However, as is clear from the above principle of operation, this type of sensor has the disadvantage that the alarm is delayed.

The present invention aims to improve these points and provide a photoelectric smoke detector that does not malfunction due to strong instantaneous external light such as a flash or noise, and does not delay its alarm operation. .

Next, the present invention will be explained in detail with reference to Examples.

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows output waveforms for explaining its operation.

In FIG. 1, C and CL are sensor lines, which serve as power and signal lines.

These lines C and CL include a switching circuit SWC for alarm,
A constant voltage circuit CVC is connected, and an oscillation circuit OSC and other subsequent circuits are connected between constant voltage power supply lines L1 and L2 drawn out from the circuit CVC.

This subsequent circuit includes a light emitting circuit made up of transistors Tr1 to Tr3, a comparator COMP, resistors R1 to R5, a capacitor C1, and a light emitting element LED, and a light receiving amplification circuit made up of a photoreceiver PC, an amplifier A, and resistors R7 and R8. A differentiation circuit consisting of a capacitor C3 and a resistor R9, and a transistor T
r4~Tr9, FET, capacitor C2, resistor R10~
It is composed of a discrimination circuit consisting of R13.

As the light receiver PC, a photoconductive element, a photodiode, a photovoltaic cell, or other appropriate device can be used.

Next, the operation of this sensor will be explained with reference to the waveform diagram in FIG.

The oscillation circuit OSC operates for 200 μsec as shown in FIG.
A pulse with a width of is generated at a period of 4 seconds and is applied to transistors Tr1, Tr2, and Tr5 to turn on these transistors.

When the transistor Tr2 is turned on, the light emitting element LED, in this example a light emitting diode, is energized to emit light, and when the transistor Tr1 is turned on, the capacitor C1 is charged through the resistor R1.

The comparator COMP receives the terminal voltage of this capacitor C1 at one input terminal, and has resistors R3 and R3 at the other input terminal.
A divided voltage (set voltage) of the power supply voltage by R4 is applied, and when the former exceeds the latter, an output is generated.

The output of this comparator is the transistor Tr3, Tr6, Tr
9 and turn it on.

The output of the comparator and therefore the turn on of these transistors is the second
As shown in Figure 3, after the output of the oscillation circuit OSC disappears, 200μ
sec and also lasts for 200 μsec.

The light emitting element LE is turned on again by turning on the transistor Tr3.
D emits light, and therefore the light emitting element lights up twice in each cycle, as shown in FIG. 2.

On the light receiving side, if no smoke enters the sensor, the light emitting element LED
No light from the smoke enters the receiver PC; on the other hand, if smoke enters, the scattered light from the smoke enters the receiver PC.

When light exceeding the set level enters the receiver PC, amplifier A
produces an output, and light below that level produces no output.

When smoke does not enter the sensor, there is therefore no output from amplifier A, but as described above, the oscillator OSC and comparator C
Transistors Tr5, Tr6, Tr
9 is turned on.

The transistors Tr5 and Tr9 are turned on by the transistor Tr.
4. Since Tr8 is off, it has no meaning, but turning on transistor Tr6 turns on transistor Tr7 through the path of Tr7-R12, and these transistors and resistor R
11 through capacitor C2. Charge.

Thus, the capacitor C2 is always in a charged state and this capacitor voltage is applied to the gate of the P-channel depletion type field effect transistor FET, turning it off.

When the oscillator circuit OSC produces a pulse output, if a flash happens to occur, the photoreceiver PC senses this and the amplifier A produces an output.

The output of the amplifier A is differentiated by a differentiating circuit consisting of C3 and R9, and is made into a narrow pulse of 200 μsec or less as shown in FIG. 2, and then applied to the transistors Tr4 and Tr8 to turn them on.

Of course, the transistor Tr5 is also turned on by the output from the light emitting side, and as a result, the capacitor C2 is discharged.

However, at this time, since the transistor Tr9 is off, the transistor FET is not turned on.

Subsequently, the comparator COMP produces an output and turns on the transistors Tr6 and Tr9, but at this time, since the output of the differentiating circuit has disappeared, the transistor Tr8 is off, so the transistor FET is not turned on either.

In addition, when using a flash bulb, the flash duration is several tens of milliseconds.
ec continues, but the detection power from amplifier A is differentiator C.
3. It is differentiated by R9 and becomes a narrow pulse as described above, and at this time positive and negative half waves are generated, but the negative half wave has the opposite polarity to transistor Tr4 etc., so these transistors must be turned on again. There isn't.

In this way, false alarms due to flash will not occur.

Note that the time point at which the subsequent pulsed light is generated may be delayed by several tens of milliseconds or more, and in this case, although the alarm is delayed a little, there is an advantage that the differentiating circuit R9C3 can be omitted.

When smoke enters the sensor, transistors Tr4 and Tr5 are turned on by the output of the oscillator circuit OSC and the output of the amplifier A including the photoreceiver PC, discharging the capacitor C2, but at this time, the transistor Tr9 is off, so Although the transistor FET is not turned on, the subsequent output of the comparator COMP and the light emission of the light emitting element LED,
The output of amplifier A turns on transistors Tr8 and Tr9, which turns on transistor FET, and the voltage generated across resistor R13 inputs to switching circuit SWC to operate it.

As is well known, this switching circuit SWC short-circuits the lines C and CL using a switching element such as a thyristor.
This will alert you.

Note that when the comparator COMP produces an output, the transistor Tr6 is turned on, which causes the transistor Tr7 to turn on.
However, when amplifier A produces an output at the same time, transistor Tr8 turns on, so the circuit of transistors Tr6 and Tr7 is short-circuited, and transistor T
r7 won't turn on.

Therefore, in this case, capacitor C2 is not charged,
Also, no positive voltage is applied to the gate of the transistor FET to turn it off.

Furthermore, even if the flash happens to be activated in synchronization with the output of the comparison COMP, no alarm will be issued in this case since the capacitor C2 is not discharged.

After all, in this circuit, even if the amplifier A on the detection side generates an output in synchronization with the output of the oscillation circuit OSC, if this occurs only once as shown in Fig. 2, no alarm will be issued, and the output will be output twice in a row. An alarm is issued when this occurs.

As explained in detail above, according to the present invention, the photoelectric smoke detector does not malfunction due to photographic strobes, etc., and has a very small alarm delay, for example, only 200 μsec as in the above embodiment. is obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIGS. 2, 1 to 5 are waveform diagrams for explaining the operation. In the drawing, LED is a light emitting element, PC is a light receiving element, C3, R9
is a differential circuit.

Claims (1)

[Scope of Claims] 1. In a photoelectric smoke detector that emits pulsed light intermittently from a light emitting element and issues an alarm when a light receiving element receives the pulsed light while emitting the pulsed light, the pulsed light is emitted from the light emitting part each cycle. A photoelectric smoke sensing system characterized in that a plurality of pulsed lights are emitted in succession at each pulse, and an alarm is issued when a light receiving output is received from the light receiving element corresponding to each of the plurality of pulsed lights. 2. The photoelectric smoke sensing system according to claim 1, wherein the output of each pulsed light from the light emitting section and the output of external light are differentiated by differentiating the output of the light receiving element.