EA007638B1 - Fire alarm device - Google Patents

Abstract

A smoke fire detector relates to devices for smoke indication and embodied for use in fire alarm systems for detecting fire break with smoke.The inventive task is to develop smoke signaling device providing higher performance properties such as power consumption, sensitivity, stability, reliability, interference immunity and life time.The smoke fire detector comprises a set point integrating unit, a controlled pulsed oscillator, a smoke sensor, an amplifier, a controlled integrating device, a low-pass filter, a reset circuit, an alarm signal-conditioning box. An electric pulse generator is powered via a first-level comparator from the set point integrating unit connected to the power network via a stabilized current generator and the integrating device. A radiator and an optical radiation receiver and a light-diffusing space formed by their angular diagrams are positioned meeting the requirements of the axial symmetry or symmetry relative two planes crossing on the radiator-receiver axis. A detector smoke chamber is provided with a light-forming plate and sinusoidal peripheral guides for leading out straight-passing light beams and easing smoke approach. The sensor output via the amplifier, as well as the controlled pulse generator output are connected to the controlled integrating device. The latter is connected to the set point integrating unit input via the low-pass filter and the reset circuit. The set point integrating unit is connected to the input of the alarm signal-conditioning box via the integrator and the second level comparator. The performance ability of the detector is tested using an optical radiator calibrator (by pressing a knob on the housing), while the sensibility is checked by using a light-diffusing simulator.Fig.1 shows a complete circuit diagram, fig 2 gives timing sheets reflecting the optical smoke density in the detector chamber and pulses at stages corresponding to the standby state, procedure of smoke formation dynamics analysis and fire alarm procedure, fig 3 provides design features of the smoke fire detector manufactured according to the invention.

Description

The invention relates to opto-electronic devices for indicating smoke aerosol and is intended for use as a detector in fire alarm systems when an area of ignition appears, accompanied by the formation of smoke.

Known linear fire detectors [1], are used to detect fires in large premises. The detector’s smoke sensor consists of an emitter and a receiver of infrared optical radiation separated by a distance of 10 to 100 m. The detector’s principle of operation is based on the use of an optical effect caused by a smoke spray. The appearance of smoke on the route between the emitter and the receiver leads to a change in the magnitude of the signal recorded by the receiver. When the change reaches the threshold set in the receiver, a fire alarm is generated. The disadvantage of this detector is its low sensitivity to the concentration of smoke particles in the air and, as a consequence, the impossibility of its use for fire detection in the early stages of fire.

Also known fire detector [2], consisting of the emitter and receiver of optical radiation, oriented relative to each other in such a way that the receiver records the optical radiation coming from the source and scattered by the smoke aerosol particles in the transverse direction, i.e., when scattered at an angle γ = 90 ° relative to the direction of the incident beam. The appearance of smoke causes a change in the scattered radiation signal. When the scattered signal reaches a set threshold, the electrical circuit generates a fire alarm. The disadvantages of such a device are the small value of the signal-to-light ratio and the insufficiently high quality indicators in terms of reliability, noise immunity, and service frequency. This is explained by the low value of the light scattering indicatrix for smoke particles in the direction of the angle γ = 90 °.

Of the known devices, the closest to the claimed invention is a fire detector [3], the optical scheme of which includes an emitter and an optical receiver, recording the radiation in the smoke chamber, scattered in the direction of the angle γ equal to 45 °. In the absence of smoke in the chamber, the pulses detected by the radiation receiver after amplification turn out to be below the threshold level. The comparison circuit prohibits the passage of such pulses to the counter, forming a reset pulse. The appearance of smoke in the smoke chamber causes an increase in the recorded signal and, when the latter reaches the threshold level, the electrical comparison circuit allows the passage of pulses to the counter, blocking the passage of pulses to a reset. If, during the passage of four clock pulses, the concentration of smoke does not drop to a critical level, the circuit will record a fire condition. Such a device has several disadvantages that reduce the effectiveness of its use in fire alarm systems. First of all, it is a weak signal of scattered radiation, since the light-scattering volume formed in the smoke chamber at the intersection of the cones, which determine the angular apertures of the radiator and receiver, has rather small geometrical dimensions. Therefore, although the indicatrix of scattering at an angle of γ of 45 ° is slightly higher than at 90 °, the scattered radiation signal detected by the receiver is limited in magnitude, as in the case of the previous analogue, which makes it difficult to achieve a sufficient sensitivity of the detector to the smoke in the chamber. With such an optical-geometric scheme of the mutual arrangement of the optical pair (emitter and receiver), there is practically no possibility of increasing the sensitivity of the device by increasing the size of the light-scattering volume. The disadvantages of the prototype, due to the chosen orientation of the axes of the emitter and receiver, should include a large variation in sensitivity values for black and light smoke. Existing device does not provide equal conditions for smoke inlet in different radial directions due to the lack of symmetry of the optical-geometrical scheme, since the optical pair in the smoke chamber does not have axial symmetry. Due to the features of the device in the prototype, it is structurally difficult to fine-tune the elements that form the angular aperture of the emitter and receiver, which significantly reduces the reproducibility of the output values of the smoke sensor and requires additional configuration. In addition, the channels of access of smoke into the smoke chamber in the prototype are made in a form that has kinks, which contribute to increased turbulence and impede free smoke passage. The protection scheme of the existing device against possible instability (or short-term power supply failures) of the power supply in the line is not effective enough. With such changes in the supply voltage, the stability of maintaining the threshold level is not maintained. The circuit of amplitude comparison of signals in the prototype is very sensitive to the effects on the detector of short-term optical pulses caused by accidental entry into the area of the light-scattering volume of individual particles of non-smoke nature, as well as caused by electrostatic discharges, impulse noise in the power supply network and radio interference. The standby mode of operation of the prototype requires significant power consumption, since it implies the continuous functioning of the smoke sensor at a high clock frequency specified by the electric pulse generator, i.e. the operation of the electric pulse generator is not adapted to the temporal features of the smoke conditions. This leads to a more rapid development of a given LED resource. The prototype does not provide the ability to assess the level of sensitivity

- 1 007638 device when changing the dusting of the inner surfaces of the chamber. In terms of the asymmetric geometry of the optical pair, the signal-to-light ratio is practically unattainable (high enough) and therefore reliable control of the causes of the detector malfunctioning, manifested in possible false alarms caused by excessive dusting of the structural elements inside the smoke chamber, is difficult. This leads to the need to reduce the maintenance period for removing dust from the sensor.

The objective of the invention is the creation of a fire smoke detector - a reliable, highly sensitive, noise-free device, free from the indicated disadvantages.

The problem is solved as follows.

A fire detector containing an electric pulse generator, an amplifier, a fire alarm driver, a smoke sensor including an emitter and receiver of optical radiation, additionally includes a controlled integrator, a low-pass filter (LPF), a reset circuit and a master oscillator with two outputs that includes a stabilized generator current, integrator, first level comparator and second level comparator. The smoke sensor further includes a light absorbing screen, light-forming plates and sine-like guides. The input of the controlled generator of electrical pulses is connected to the first output of the master integrator through a first-level comparator with an integrator connected to the network via a stabilized current generator. The emitter, the receiver of optical radiation and the light-scattering volume formed by their angular diagrams are located in the smoke chamber of the sensor, subject to the condition of axial symmetry or symmetry with respect to two planes intersecting on the axis of the emitter-receiver. In the modes of checking the efficiency and sensitivity assessment, the smoke sensor contains an optical radiation calibrator and a light scattering simulator. The output of the receiver of the smoke sensor through the amplifier, as well as the output of the controlled generator of electric pulses, is connected to a controlled integrator, which is connected to the input of the master integrator through a low-pass filter and a reset circuit. On the second output, the master integrator is connected via an integrator and a second level comparator to the fire alarm driver.

In the proposed device, unlike the prototype, the emitter and the receiver of optical radiation are located in the smoke chamber coaxially, and on their axis in the center of the chamber there is a light absorbing screen of the smallest possible size, shielding the photodetector from direct rays from the source. According to the selected values of the angular apertures of the emitter and receiver, light-shaping plates are installed in the smoke chamber so that they, together with the light-absorbing screen, determine the easily adjustable and reliably controlled external and internal radial dimensions of the axially symmetric light-scattering volume of the smoke aerosol. The geometrical dimensions of the light-scattering volume with such a geometry significantly exceed the corresponding dimensions for the prototype. The indicatrix of scattering for light and dark fumes in the claimed device for selected small angles of scattering of light in the forward direction is more than an order of magnitude higher than at an angle of 45 ° in the prototype. Due to these factors, the claimed device achieves an increased signal-to-light ratio, which significantly increases the level of reliability of the device. To output the light rays that directly passed through the scattering volume, channels of a sinusoidal shape are located along its perimeter outside the smoke chamber, through which smoke input into the smoke chamber area is also made and smoke output is made. To receive the optical signal scattered by smoke particles, an electrical circuit is mounted in the detector case, which ensures the registration of scattered radiation, switching operating modes, sending a fire alarm signal, checking the operation in standby mode and evaluating the sensitivity of the device during adjustment. Reducing the energy consumption of the detector and the corresponding extension of its service life compared to the prototype is achieved through the use of a controlled generator of electrical pulses in the circuit operating in standby mode at a reduced (10 times relative to the clock) generation frequency. Such an economical mode of operation of the signal generator is realized due to the switching action of the controlled integrator, the low-pass filter and the reset circuit for the master integrator, which manifests itself in maintaining the standby mode at a lower pulse repetition rate. The increased reliability of operation under external conditions of different nature and the stability of the threshold level of signals are ensured by a number of built-in stabilized current generators, which directly feed the main functional blocks of the circuit. The effect of increasing noise immunity and protection against false positives has been achieved thanks to the principle of signal integration, implemented in the claimed device. When exposed to short-duration pulses of a non-smoke nature with an amplitude even much higher than the threshold, the principle of integration protects the circuit from false triggering.

FIG. 1 shows the structural scheme of the proposed fire detector. FIG. 2 contains timing diagrams of signals at the output of the main functional blocks of the detector. FIG. 3 shows the construction of a practically realized detector.

The practical implementation of the invention is made as follows. The smoke smoke detector contains a two-way master integrator 1 (including stabilized gene

- 2 007638 current controller 2, integrator 3, first level comparator 4 and second level comparator 5), controlled electric pulse generator 6, smoke sensor 7 (including emitter 8, optical radiation receiver 9, light scattering volume 10 formed by their angular diagrams, light absorbing screen 11, light-shaping plates 12, sine-shaped guides 13, optical radiation calibrator 14, light scattering simulator 15), amplifier 16, controlled integrator 17, low-pass filter 18, reset circuit 19, fire signal generator t evogi 20.

The input of the controlled electric pulse generator 6 is connected to the first output of the master integrator 1 via a first level comparator 4 with an integrator 3 connected to the network via a stabilized current generator 2. The emitter 8, the optical radiation receiver 9, formed by their angular diagrams of the light scattering volume 10 and the light absorbing screen 11 located in the smoke chamber of the sensor in compliance with the conditions of axial symmetry. In another implementation of the detector, they are arranged in symmetry with respect to two perpendicular planes intersecting on the emitter-receiver axis. The outer dimensions of the light-scattering volume 10 are limited by the light-forming plates 12. Sine-shaped guides 13 are located along the perimeter of the smoke chamber. In the detector test mode, an optical radiation calibrator is placed in the axial zone. In the detector sensitivity evaluation mode, a light scattering simulator 15 is placed in the zone of the light-scattering volume. The output of receiver 9 of smoke sensor 7 through amplifier 16 and the output of controlled electric pulse generator 6 are connected to controlled the integrator 17. Managed integrator 17, through the low-pass filter 18 and the reset circuit 19 is connected to the input of the integrator 3, and the integrator 3 through the second level comparator 5 on the second output of the master integrator 1 is connected to the fire alarm shaper 20.

Timing diagrams of signals (for smoke density, as well as electric current and voltage) at the output of the main blocks of the proposed device give an idea of the functions they perform (Fig. 2):

a) the optical density of the smoke in the chamber of the smoke sensor 7;

b) voltage of master integrator 1;

c) voltage of the first level comparator 4;

d) signals of a controlled generator of electric pulses 6;

d) current pulses at the output of the amplifier 16;

e) the signals of the controlled integrator 17;

g) signals at the output of the low-pass filter 18;

h) the signals of the reset circuit 19;

K) the voltage at the output of the fire alarm shaper 20.

The inventive fire smoke detector (Fig. 1) works as follows. In the absence of smoke particles inside the smoke chamber (Fig. 2, a), the detector is in standby mode of operation with low energy consumption, cyclically repeated at relatively long intervals of time equal to the T1 period (about 5 s, Fig 2, d). The beginning of the period is characterized by the absence of electric charge (Fig. 2, b) in the master integrator 1). With the passage of time from the current generator 2, linear accumulation of charge occurs in integrator 3. When the voltage reaches a set threshold level and _then .1, the first level comparator is triggered (Fig. 2, c) and turns on a controlled pulse generator 6, which generates a short (about 30 μs a) electric impulse (Fig. 2, d), which serves to power the emitter 8. Simultaneously from the output of the generator 6, as a result of integration, the impulse integrates a controlled integrator 17, the voltage from which (Fig. 2, e) with a time delay (f of 2, x), given by the low pass filter 18 is input to the reset circuit 19. When reaching levels _{and pO} b sa (Fig. 2, g) a reset circuit 19 is activated (FIG. 2, s), discharging capacitor integrator 3 to the zero level (Fig. 2b). In this case, the first level comparator 4 turns off the generator 6, stopping (for the duration of the cycle) the supply of optical pulses (Fig. 2, d). This ends one of the work cycles of T1 duration in standby mode. At the end of the reset pulse, the charge on the capacitor of integrator 3 rises again during the on-duty cycle, ensuring continuous cyclic operation with a period T1 set by the stabilized current generator 2. The energy-saving cyclic standby mode of the detector is constantly maintained until the smoke aerosol appears (FIG. 2, a) with a concentration that exceeds the set threshold value. With some delay in time with respect to the generator pulse, an electric pulse appears at the output of the controlled integrator 17, reflecting the discharge of the capacitor (Fig. 2, e), taking into account the integral effect of the scattered radiation pulse. Since the delay time is selected longer the reaction time of the photodetector 9, the voltage at the input of reset circuit 19 (FIG. 2, w) can not reach the level of _{dew and} b. Therefore, the reset circuit 19 does not work (Fig. 2, h) and the integrator 3 over time will continue the accumulation of electric charge (Fig. 2, b) from the stabilized current generator 2, which manifests itself in a further increase in voltage (higher than and _p . ₁ ). The generator 6 will remain in the on state, generating pulses at the clock frequency (Fig. 2, d) with a characteristic repetition period of T2 << T1. In this case, the circuit goes into the mode of analyzing the dynamics of the smoke level (in Fig. 2, d) there is a case of smoke growth)

- 3 007638 T2 period. If at this stage the smoke level falls below the threshold, then the first level comparator 4 will work, switching the controlled electric pulse generator 6 to the standby mode of generating signals at a lower frequency. If at this stage of the analysis the level of smoke in the chamber does not subside (figure 2, a), then in the integrator 3 the accumulation of charge will continue even after the time T1 has elapsed when the voltage of the second level and _then reaches ₂ (Fig. 2, b) the second-level comparator 5 set on this voltage will work, turning on the fire alarm driver 20. The appearance of the fire alarm (Fig. 2, k) indicates the presence of smoke aerosol with a concentration above the threshold value in the detector chamber. .

In the proposed device, in accordance with the selected angular diagrams of the emitter and receiver in the smoke chamber, the light-shaping plates 12 are installed so that they, together with the light-absorbing screen, determine the simply adjustable and reliably controlled external and internal radial dimensions of the light-scattering volume of the smoke aerosol. This easily achieves the repeatability of the parameters of the optical circuit during adjustments.

The optoelectronic circuit ensures reliable functioning of the detector with almost complete elimination of false positives due to dusting of the internal surfaces of the smoke chamber. The maintenance period for removing dust from the chamber is significantly extended. This result was obtained due to the fact that, in particular, the intensely dusty surfaces in the proposed device were removed from the zone of the receiver’s aperture.

The level of the electrical signal Ι (γ) at the output of the optical radiation receiver 9 at a given illumination, created by the emitter in the smoke chamber in the vicinity of the light-scattering volume, is linearly dependent on the optical density of the smoke, the value of the light-scattering volume of the medium \ (γ) for a scattering angle γ. The geometrical dimensions of the light-scattering volume with an axisymmetric geometry significantly (about 2π times) exceed the corresponding values for the prototype. The indicatrix of light scattering \ (γ) for different types of smoke at small scattering angles γ (on the order of several degrees for the claimed device) has a value significantly (10 or more times) greater than the corresponding values at scattering angles 45 and 90 °, implemented in the prototype and second analog. The choice of small values of the scattering angle γ and a significant increase in the scattering volume, implemented with a symmetric optical-geometrical scheme, manifest themselves in a significant increase in the sensitivity parameter and signal-to-noise ratio of the proposed device compared to the prototype.

The rays that directly pass the light-scattering volume are output outside the smoke chamber through sinus-shaped channels formed by peripheral guides 13. The latter, in addition to reducing illumination, impede the creation of turbulence areas and therefore facilitate free smoke passage to the smoke chamber area and unimpeded smoke output outside it.

The electrical circuit of the device provides registration of scattered radiation, analysis of smoke density dynamics, a fire alarm signal, standby test using the calibrator 14 (when a button is pressed on the detector housing) and an estimate of the sensitivity level of the device (when configured using a light scattering simulator 15) .

Increased reliability and noise immunity of the device from external influences of different nature and the necessary stability to maintain a given threshold level of signals is provided by a number of built-in stabilized current generators (for example, 3), which directly feed the main functional elements of the device.

The reduced power consumption of the detector compared to the prototype is achieved thanks to the use of a controlled electric pulse generator 6 in the circuit, switched by master integrator 1 to the standby mode at a low (10 times relatively clock) generation frequency.

Unlike the prototype with amplitude registration of signals, thanks to the principle of integration embedded in the circuits of master 1, controlled by 17 integrators and low-pass filter 18, the proposed device ensures reliable switching to various operating modes. Namely, the duty mode is maintained at a lower pulse repetition rate in the absence of smoke (Fig. 2, d). The circuit is switched from the standby mode to the intermediate mode of operation at the clock frequency (Fig. 2, d), which analyzes the smoke dynamics. The fire alarm mode is activated (Fig. 2, k) in the event of further increase and concentration of smoke or maintain concentration at the threshold level.

The functions performed by the main structural components determined the device of the invention as a whole (Fig. 3).

Thus, the proposed device has higher quality indicators in comparison with the prototype in terms of power consumption, sensitivity, reliability, noise immunity, stability and duration of good functioning.

Sources of information taken into account:

1. Linear smoke detectors: new technical solutions 2004. // Algorithm without

- 4 007638 pass. №1, 2004.

2. Or11ea ztoku be! Him1og. // Patent EP 00926646 A1 C 08B 17/107, 1999.

3. Fire-detector opto-electronic smoke detector IP-212-41M. // Collection of passports and recommendations for the installation of devices brand Rubezh, 2004, p. 4-9.

Claims (3)

CLAIM 1. Fire smoke detector, containing an electric pulse generator, an amplifier, a fire alarm driver, a smoke sensor including an emitter and an optical radiation receiver, characterized in that it also contains a controlled integrator, a low-pass filter, a reset circuit and a master integrator having two outputs comprising a stabilized current generator, an integrator, a first level comparator and a second level comparator, and the smoke sensor further comprises a light absorbing screen, with input An electric pulse generator is connected to the first output of the master integrator through a first level comparator with an integrator connected to the network via a stabilized current generator, and the radiator, optical radiation receiver and the scattering volume formed by their angular diagrams in the sensor smoke chamber, observing the condition of axial symmetry, output the receiver of the smoke sensor through the amplifier, as well as the output of a controlled generator of electric pulses are connected to a controlled integrate Ator, which, via the lowpass filter and a reset circuit coupled to the input of the integrator and the integrator through a second comparator the output level of the second integrator is connected to the master builder fire alarm. 2. Fire smoke detector according to claim 1, characterized in that the emitter, receiver of optical radiation and the light-scattering volume formed by their angular diagrams are located in the smoke chamber of the sensor observing the condition of symmetry with respect to two planes intersecting along the axis connecting the radiator, light-absorbing screen and receiver optical radiation, and the smoke chamber is equipped with light-forming plates and sinus-shaped peripheral guides. 3. Fire smoke detector according to claim 2, characterized in that the smoke sensor contains an optical radiation calibrator and a light scattering simulator.