JPS62224890A - Photoelectric type analog smoke sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to improvements in photoelectric analog smoke detectors used in automatic fire alarm systems and the like.

[Background Art] A photoelectric smoke detector, which detects smoke by arranging a light-emitting element such as an LED and a light-receiving element such as a photodiode in a chamber and detecting smoke by receiving scattered light from smoke that has flowed into the chamber, is an automatic fire detector. It is frequently used in alarm systems (hereinafter abbreviated as "self-fire alarm systems").

Such conventional photoelectric smoke detectors are of the so-called ON/OFF type, and when the output value of the light receiving element exceeds a certain threshold, a smoke detection signal is sent to, for example, a receiver of a self-fire alarm system. However, recently, in order to detect fires early and improve reliability, intelligent self-fire alarm systems have been developed in which fire judgment is made on the receiver side. Information is considered essential.

Although such photoelectric analog smoke detectors require high-speed response, ambient light (hereinafter referred to as "
This is called "disturbance light." ) would cause a malfunction, so the smoke entrance and exit of the chamber has a complex labyrinth structure to prevent ambient light from entering. As a result, the speed at which smoke flows into the chamber is limited, resulting in a slow response, leaving problems such as the inability to handle the high-speed response required of an intelligence fire alarm system.

[Object of the Invention] An object of the present invention is to provide a photoelectric analog smoke detector that is not affected by ambient light (has improved responsiveness).

[Disclosure of the Invention] In order to achieve the above object, the photoelectric analog smoke detector according to the present invention uses a light receiving element to detect light scattered by smoke from luminescent pulses that are intermittently output from a light emitting element. In a photoelectric analog smoke detector configured to convert into an electrical signal and output an electrical signal according to smoke density, the gain near the frequency of the disturbance light is greater than the gain near the light emission frequency of the light emitting element. A received light signal amplification section that has a small frequency characteristic and amplifies the electrical signal photoelectrically converted by the light receiving element; an integrating circuit section that integrates the output from the received light signal amplification circuit; and an output from the integrating circuit section. and a timing control section that generates a signal for driving the integrating circuit section in synchronization with the lighting timing of the light emitting element.

Embodiment An embodiment of the present invention is shown in FIG. In the figure, 3 is an LED forming a light emitting element arranged in the chamber 2 of the photoelectric analog smoke detector 1, and 4 is a photodiode (hereinafter referred to as "photo diode") forming a light receiving element arranged in the chamber 2. , "PD"). The LED 3 is driven by the light emitting element drive circuit 5 to intermittently output light emitting pulses, and the PD 4 detects smoke by photoelectrically converting scattered light caused by smoke that has entered the chamber 2. The signal photoelectrically converted by the light-receiving element 4 is amplified by the light-receiving signal amplifying section 6 and sent to the integrating circuit section 7. The output of the integrating circuit section 7 is amplified to a necessary level by a DC amplifier section 8 and transmitted to a receiver (not shown).

In this embodiment, the light emitting element driving circuit section 5 and the integrating circuit section 7
is the control signal a% output from the timing control section 9
b. The control signals at and b are shown in FIGS. 2(a) and 2(b). Here, the control signal a is a rectangular pulse signal emitted from the oscillation circuit 91 in the control section 9, and is input to the light emitting element drive circuit section 5 to cause the LED 3 to emit light. That is, T1 shown in the figure is the light emission pulse width of LED2,
T2 is the light emission interval. The signal a is also input to an AND circuit 92 and its pulse width is adjusted. The signal a is directly input to one terminal of this circuit 92, and the resistor 93 is input to the other terminal.
and a capacitor 94, the width T3 (=T1-Td) is delayed from the signal a by the time Td by the AND circuit 92.
) is output in the form of a rectangular pulse control signal (see Figure 2 (
b)). This control signal is applied to the FET 71 of the integrating circuit section 7.
input into the gate.

FET71 outputs 0N10FFL according to this control signal.
, controls the integration timing of the CR integration circuit including the resistor 72 and the capacitor 73. That is, T3 defines the integration time of this integration circuit, and the circuit is operated for the time of T3 to integrate the output of the received light signal amplifying section 6, and at other times, the integrated value is held. It goes without saying that other suitable switching means, such as an analog switch, can be used in place of the FET 71.

In the light reception signal amplification section 6, three transistors 61 to 63
are connected as shown. The frequency characteristics of the amplifying section 6 are such that the values of the resistor 64 and the capacitor 65 are appropriately selected, and the gain in the band below 100 Hz is, for example, several kHz.
The gain is set to a significantly smaller value, for example, about one-tenth, than the gain in the band of several hundred kHz. Note that 66 is a capacitor for removing DC component.

According to such a configuration, when the LED 3 emits light as shown in FIG.
The output waveform is as shown by the broken line in FIG. As mentioned above, the input to the integrating circuit section 7 is during time T3 (integration 08 o'clock).
At other times (when integration is OFF), the final value integrated at the previous integration time 08 is held, so the integration circuit section 7 performs further integration at the next integration time 08, and its output (the 2 (shown by the solid line in Fig. 2 (C)) is the received light signal amplification section 6.
gradually approaches the value of the output.

As actual disturbance light, for example, light from a fluorescent lamp (brightness changes according to a commercial frequency of 60 Hz or 50 Hz) can be considered. In order to deal with such disturbance light, for example, if the emission pulse width (Tl) of the LED 3 is set to about 4 to 10 μs, the frequency characteristics of the received light signal amplification section 6 will cause the L
The light reception signal based on the light emission of the ED 3 is amplified by the circuit section 6, but the light reception signal based on the disturbance light is not so much amplified.

Next, the response time τ of the integrating circuit section 7 is selected to be several tens of times T3. For example, T1 = 5μS N T 2 = 40m
5n If T3=4 μs and τ=100 μs, then the response time T of the sensor l is T=(τ/T3)XT2=(100μs/4μs)×40ms=1000ms. Therefore, by selecting each time in this way, the output of the integrating circuit section 7 will be the average value of the past 25 pulses of light scattered by smoke, and will be based on the noise signal due to disturbance light (for example, 60H2 fluorescent lamp light). (The output will no longer appear.

This will be further explained using FIG. To simplify the explanation, it is assumed that the light reception pulse signal (peak value VP) due to the light emission pulse of the LED 3 occurs eight times during one period of the noise signal (peak value VN), and the response time τ of the integrating circuit section 7 is 8 times of the received light pulse signal. In this case, the output of the received light signal amplifying section 6, that is, the input of the integrating circuit section 7 is as shown in FIG. 3(a).
It will look like the one shown below. The integrating circuit section 7 is shown in FIG. 3(b).
) Since the integration operation is performed only in the shaded portion, the output signal VO is as follows, and it can be seen that no noise signal appears in the output signal VO of the integrating circuit section 7. This is true in the case exemplified above (T1=5μs1T2=40m, sz T3=4
The same holds true for μsi r=100 μs).

The output signal VO of the integrating circuit section 7 is sent to the DC amplifier section 8.
The signal is then amplified to the required level and sent to the receiver of the intelligence fire alarm system.

That is, according to this embodiment, for example, by making the light emission time of the LED 3 short, approximately 10 μs or less, it is possible to provide an output that is not affected by ambient light such as fluorescent light and can respond at a high speed within 1 second. It becomes possible.

The frequency characteristics of the received light signal amplification section are determined as appropriate depending on the surrounding situation in which the smoke detector is installed, taking into account the type of ambient light, etc. Not limited. Further, the pulse width of the light emitting element is determined in accordance with the frequency characteristics of the amplifier circuit, but if the disturbance light is of low frequency, it is preferable to shorten the pulse width.

Further, in the above-mentioned embodiment, the driving pulse width of the integrating circuit section was made smaller than the driving pulse width of the light emitting element, but the embodiment is not limited to such an embodiment. Needless to say, it is sufficient if the drive is performed synchronously. [Effects of the Invention] As is clear from the above explanation, the photoelectric analog smoke detector of the present invention can generate an analog signal according to the smoke density. Further, since the output signal is not affected by ambient light, the labyrinth structure of the chamber can be simplified, and a photoelectric analog smoke detector with high high speed response can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIGS. 2(a) to (C)
) is a diagram showing the output waveform of each part, and FIGS. 3(a) and 3(b) are explanatory diagrams of the operating principle of the integrating circuit part. 1... Photoelectric analog smoke detector, 2... Chamber, 3... Light emitting element, 4... Light receiving element.

Claims (1)

[Claims] A light-receiving element detects light scattered by smoke from light emission pulses intermittently output from a light-emitting element, converts the light into an electrical signal, and outputs an electrical signal according to the smoke density. In the photoelectric analog smoke detector configured in a light reception signal amplification section that amplifies the light reception signal; an integration circuit section that integrates the output from the light reception signal amplification circuit; an output amplification section that amplifies the output from the integration circuit section; A photoelectric analog smoke detector comprising: a timing control section that generates a signal for driving the integration circuit section.