SU439006A1 - Smoke detector - Google Patents

Description

one

The invention relates to alarm systems and can be widely used as a sensor signaling the presence of a certain concentration of smoke in a controlled environment (air, gas), for example, in the event of a fire. A smoke detector containing optical lenses, a light flux modulator located between lenses located in front of the light source and an air intake chamber, in which a lens optically coupled to a photodiode connected to an amplifier, a generator, a detector and a controllable unit are located, is known power supply with a light source connected to the yom.

The proposed smoke detector differs from the known one in that it introduces a delay unit, a multiplier, an integrator, additional amplifiers, and a photodiode. Moreover, the output of the amplifier is connected through a serially connected multiplier, and integrator. PREVIOUS Amplifier to the input of the detector. The other INPUT of the multiplier is connected via successively connected delay unit and generator, to the control input of the luminous flux modulator. An additional photodiode is optically coupled to a corresponding lens placed at the exit of the air intake chamber, and through a corresponding additional amplifier is connected to the input of the controlled power supply unit.

This makes it possible to reduce the number of false positives and increase the speed of the device, i.e., to increase the reliability of its operation.

The drawing shows a smoke detector. It contains optical lenses 1-4, a light flux modulator 5, a light source 6, an air intake chamber 7, a photodiode 8, an additional photodiode 9, an amplifier 10, additional amplifiers 11 (threshold) and 12, an oscillator 13, a signaling device 14, a controlled unit power supply 15, delay unit 16, multiplier 17, and integrator 18.

Smoke detector works as follows.

The light flux from the light source 6 passes through the optical system of the lenses G and 2 and is modulated by a modulator 5 (modulation frequency 400 Hz and above). A modulated parallel beam of light passes through the camera 7 and the lens 4 is focused on the photodiode 9, a pulsating voltage appears in the load of which. This voltage is amplified by the amplifier 12 and is fed to the control input of the power supply unit 15 of the light source 6.

In the absence of smoke in a controlled environment, the light source 6 is in the under-exposure mode. In the absence of a useful signal

the fluctuation interference arrives at one of the inputs of the multiplier 17, to the second input of which a delayed reference oscillation is fed from the generator 13. As a result of multiplying the interference and the reference oscillation, an alternating oscillation is obtained, which after integration has a voltage level lower than the threshold set in the threshold amplifier 11. In this case, the detector 14 does not work.

When smoke enters the inlet of the chamber 7 through the filter 19 coarse particles, the light flux falling on the photodiode 9 is attenuated. At the output of the additional amplifier 12, the control voltage of the power supply unit 15 of the light source 6 appears. As a result, the brightness of its luminescence increases to a value that provides radiation to the spectrum of the spectrum of the upper visible region (blue — l; 0.49 μm, blue — X l; 0.46 μm, violet — i 0.4 μm). This ensures the optimal operation of the detector in an emergency situation, since the scattering of light by smoke particles is most intense in the region. "0.51-t-0.4 μm. Smoke-scattered rays are focused by lens 3 onto a photodiode 8, which converts a variable fluctuating scattered light flux into an electrical signal amplified by a selective narrow-band amplifier 10 (tuned to the frequency of light flux modulation). The output signal of amplifier 10 is fed to one of the inputs of multiplier 17, the second input of which receives a reference oscillation delayed by a certain amount (delay block 16) from one of the outputs of generator 13. The result of multiplying the signal carrying information about the presence of smoke in chamber 7 is on the reference the oscillation is averaged in integrator 18.

Since the input of the multiplier 17 receives not only the useful signal, but also the noise signal, there are alternating sign, noise and quadratic signal components at its output. The latter, after integration, will give a significant excess voltage over the voltage resulting from the integration of the alternating noise component. If the averaged voltage exceeds the threshold set in the AND amplifier, the alarm system 14 (or control) is triggered, including either the appropriate signal devices (light, sound, etc.), or (if necessary, simultaneously) equipment or urgent mechanisms measures for emergency response.

The proposed smoke detector makes it possible to reduce the likelihood of false alarms to a predetermined value.

which is determined by the threshold set in the final amplifier. This is achieved by reducing the noise interference in the signal processing circuit and increasing the weight of the useful signal after integration. The detector has an order of magnitude faster response than the known device, which is determined by the integration time and at a sufficiently high modulus frequency of the light flux (400 rd and above) is tens of milliseconds.

Sensitivity of smoke photoelectric detectors based on the principle of receiving and processing scattered aerosols

5 light is determined by the fluctuations of the received signal and the intrinsic noise of the photodetectors. The proposed smoke detector makes it possible to isolate a signal that is spun in noise, which increases the potential for the sensitivity of the photoelectric method to low smoke concentrations.

In the circuit of the proposed detector there are no explosive elements (relays, contactors, etc.), so it can be widely used as a sensor of emergency situations in explosive rooms. In addition, the detector can be used in dusty rooms with high levels of radiation.

Subject invention

A smoke detector containing optical lenses, a light beam modulator, located between the lenses placed in front of the light source and the air intake chamber, in which the light is parallel to

The lens is optically coupled to a photodiode connected to an amplifier, a generator, a detector, and a controllable power supply unit with a light source connected to it, characterized in that

increase the reliability of the device; a delay block, a multiplier, an integrator, additional amplifiers and a photodiode are introduced into it; the output of the amplifier is connected via a serially connected multiplier, an integrator, a threshold amplifier to the input of the detector, another input of the multiplier is connected via a serially connected delay unit and a generator, to the control input of the light flux modulator;

an additional photodiode is optically coupled to a corresponding lens placed at the exit of the air intake chamber, and through a corresponding additional amplifier connected to the input of the controlled power supply unit.