JPS5888642A - Smoke detector - 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 A photoreceiver disposed outside a direct radiation area of the invention for receiving scattered radiation and generating an output signal when smoke is present in the radiation area; and an output signal of the photoreceiver. and an evaluation circuit which generates an alarm signal when a predetermined threshold value is exceeded.

Such a smoke detector is, for example, WO-PAgθ//3
．． Already known from IA and KP/PA/RI779. In these known devices, light #. It is controlled by a hapulse generator to deliver short duration light pulses. The light receiver (radiation receiver) receives the light scattered by the smoke of the scattering field, but also receives the light reflected by the walls. To compensate for aging and temperature-dependent changes in the transmitter and receiver, a scattered light detector driven by the same light with a second identical receiver cell is used to transmit the light emitted from the transmitter. It has already been proposed to measure and control light (e.g. US Patent No. DA/gθ
(See specification No. 792). However, this structure is not sufficient to compensate for all possible changes due to contamination.

It is an object of the present invention to provide a smoke detector which generates a fault signal when the radiation source becomes contaminated or aged to such an extent that the function or performance of the smoke detector is affected.

This object of the invention is solved by the configuration described in claim 1. Advantageous embodiments and further developments of the invention are described in the patent claims.

In an advantageous embodiment of the smoke detector according to the invention, the light source arranged below emits the light in the form of a cone from the bottom upwards. The main receiver is arranged centrally symmetrically above, while the reference cell is arranged above, slightly to the side of the direct optical path or radiation path of the light or radiation source. In such an arrangement, dust accumulates only on the light source or the artificial radiation source. In contrast, gaseous condensate deposits uniformly on the main receiver and the reference cell. Therefore, measuring the light output of the light source by measuring the signal of the reference cell results in a signal that is proportional to the received signal of the optical receiver. In this case, it is important that the reference cell is placed close to the receiver, so that both cells are contaminated to the same extent.

According to another advantageous embodiment of the smoke detector according to the invention:
The light source or radiation source is arranged above and the receiver and reference cell below.

In this case as well, it is important that the lower cells be located close to each other and covered by windows as horizontal as possible. This means that surfaces with different slopes are
This is because they will be contaminated to different degrees by the settling dust.

The signal of the reference cell can be directly used to generate a fault signal as soon as it falls below a certain threshold.

According to other embodiments, the reference cell signal is used to control the current of the light source or the artificial radiation source. In this way, the received light scattered by the smoke will not be affected by contamination and aging of the light transmitter. A fault signal is generated when the transmitter current exceeds a threshold value at which control is no longer possible.

Hereinafter, embodiments of a smoke detector according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows, in cross section, the structure of a smoke detector according to the invention. A light source / with an optical system /7 emits a hollow cone of light radiation into the space surrounding the detector. Center aperture 7g
prevents direct irradiation of the receiver/B. On the contrary,
The reference cells 7, 2 are arranged within the light cone. With such a configuration, the photoreceiver/6 and the reference cell/6 will be equally contaminated. In particular, dust is mainly caused by light sources/
In the circuit of one embodiment of a smoke detector according to the invention shown in FIG. L1 and 52
A monitoring circuit with a light transmitter 8 and a switching stage U is connected in between.

An evaluation processing circuit, such as that described in KP-FA/F779, can be connected afterwards.

The light transmitter consists of an oscillator that supplies a current of about 1 ampere to the light source with a duration of approximately 10 .theta..mu.s at time intervals of about -seconds. The light source consists of an infrared light emitting diode. The oscillator has a control circuit consisting of a voltage quadrant sister with an associated limiting resistor 3 and a transistor gate with an associated limiting resistor S, a resistor 7 and a capacitor 6.
and a feedback circuit consisting of. The above current pulse is generated for a large capacitor/θ power supply/.

This current pulse is applied to the power supply via a resistor //. This current pulse is generated when resistors G and D apply voltage across the transistor gate, making it conductive.

The current flowing through the light emitting diode (light source /) is connected to the reference cell (with measuring resistor /3 and feedback coupling resistor /ll).
controlled via a phototransistor/2). Resistor/
As soon as the pressure on 3 becomes high enough, transistor /S becomes conductive and reduces the base current of the quadratic sister. It goes without saying that photocells can be used instead of phototransistors.

The monitoring circuit or monitor circuit U consists of resistors /6 and /6.
7 and a thyristor 36. A resistor 3 measures the current flowing through the light source. light source/
If this current becomes too large as a result of contamination or aging, the thyristor 36 will switch to conduction, indicating a fault.

FIG. 3 shows one embodiment of circuitry that may be used when the reference cell 12 monitors, rather than controls, the transmitter.

The light source / is driven by an oscillator /9 as in FIG. Note that in the oscillator /9, elements 7.2 to /left are not used. As an example of the reference cell/, 2,
A photodiode 20 with a measuring resistor 2/ is shown. With each pulse, the switching transistor, 2-, switches into conduction as soon as the reference pulse becomes sufficiently strong.

As a result, the capacitor 2, which is gradually charged via the resistor 23, is discharged. With a very small reference pulse, this capacitor 2'l no longer discharges, but charges via the measuring resistors 2S and 2B to a high potential at which the thyristor 27 switches into conduction. When thyristor 27 switches to conduction, this is a fault indication.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing the structure of a smoke detector with a reference cell; FIG. 1 is a circuit diagram showing a circuit according to a preferred embodiment of the invention; and FIG. 3 is a circuit diagram showing another circuit example. It is. /...Light source, S...Power transistor, 3. S...Limiting resistor, G, 15...Transistor, l/θ λda
...Capacitor, 7. Zapa, //, /, 3゜/'I, /
A, /7. /9123...Resistor, /2...Phototransistor 1.2o...Photodiode, u/, 2!
r,, 2A...Measuring resistance, Koniken switching transistor 1.27. ．． 3A...thyristor, A...light receiver, S...light transmitter, L...conductor, [engineering]...monitor circuit. 1・21j

Claims (1)

[Claims] /) a pulse-driven light source (11) disposed outside the direct emission area of the light source (1) and receiving scattered light in the presence of smoke in the external emission area; A smoke detector comprising: a light receiver (/6) that generates an output pulse; and an evaluation circuit that generates an alarm signal when the output signal of the light receiver (/6) exceeds a predetermined threshold. A reference cell (/) is provided near the light receiver (/6) in the direct radiation path of the light source (fl), and in the reference cell, when smoke is present, the light receiver (1)
6) A smoke detector characterized in that it monitors scattered incident light. (2) The smoke detector according to claim 1, wherein the distance between the reference cell (/) and the light receiver (/6) is smaller than 2 crrL. 3) The smoke detector according to claim 1 or 2, wherein the light source (1) is arranged above and the light receiver (/6) and the reference cell (/2) are arranged below. q) Claim 1 in which the light source (1) is arranged below and the light receiver (/6) and the reference cell (/) are arranged above.
The smoke detector according to item 1 or 2. S) A smoke detector according to any one of claims 1 to 7, comprising means for generating a fault signal when the output pulse of the reference cell falls below a predetermined threshold. . B) Light source (1) based on the output signal of the reference cell (7, 2)
) to a constant reference signal and providing means for generating a fault signal when the current of the light source exceeds a predetermined threshold. Smoke detector as described in. W) The smoke detector according to claim jJIJ or claim 6, which generates a disturbance signal when the signal transmitted from the light source (1) to the reference cell (/, 2) changes by a predetermined coefficient. . g) A smoke detector according to claim 7, wherein the coefficient is between 8S and 5. 9), conductor at time intervals of 2θ to roo seconds. 7. The smoke detector according to claim 5, further comprising a disturbance signal generating oscillator which short-circuits and for 10 seconds.