RU37250U1 - SMOKE DETECTOR - Google Patents

Description

"MUSHCHEY

111ШИ1ШШ «1« Р1, G 08 в 17/10

Smoke detector

The proposed solution relates to fire alarm devices for detecting smoke at an early stage of ignition, and can be used to detect the presence of suspended particles (dust, fog, etc.) in the environment.

A known smoke detector (patent 660244, Switzerland, G 08 B 17/10, 29/00 from 03/31/87), containing an optical camera, a generator that controls the radiation source, amplifier, signal processing circuit. The optical signal reflected from the smoke particles enters the photodetector, amplified and fed to the signal processing circuit. When the optical channel is dusty, smoke detection at an early stage of ignition is difficult, and sometimes impossible. The lack of dust control reduces the reliability of this device and is its disadvantage.

A known smoke detector (RF patent 2125739, O 08 V 17/10 from 01/27/99), selected as a prototype, containing a generator connected to an optical radiation source, a photo detector connected to a photocurrent amplifier, which is connected to an amplifier through a high-pass filter a shaper whose output is connected to the input of the RS-trigger. The trigger output is connected to the first input of the And element and to the C input of the counter, and the second driver with the control input of the amplifier-former. The optical signal reflected from the smoke particles enters the photodetector, is amplified by a photocurrent amplifier, is synchronously filtered and fed to the signal processing circuit.

Known smoke detectors work on the principle of periodically emitting light pulses and then receiving an optical signal reflected from smoke particles by the photosensor. Further him

amplification, using various analog amplification devices (transistor stages, operational amplifiers, etc.), comparison with the reference voltage, and issuing a signal about the presence or absence of smoke. The disadvantages of the prototype should include

-use of analog devices;

- Lack of control of the operability of the optical channel during operation. When the prototype is working, the failure of the optical channel (emitter, photodetector, amplifiers) is adequate to give a signal that there is no alarm in the presence of smoke, or to give a false alarm to a fire;

- lack of control of dustiness of the optical channel.

The objective of the technical solution is to create a reliable smoke detector that allows, in particular, monitoring the operability and dustiness of the optical channel, eliminating analog devices and making a complete transition to digital circuitry.

The task in a smoke detector containing a control circuit connected to the detector, a light pulse source connected to another output of the control circuit and optically coupled to the photodetector, is achieved by the fact that the photodetector is directly connected to a bi-directional logic port that is connected to the control circuit.

Pa figure 1 shows a block diagram of a smoke detector. Pa figure 2 shows a block diagram of a smoke detector, in which a bi-directional logic port and control circuit are made in the form of a controller. Pa fig.Z shows the equivalent model of the photodetector. Pa figure 4 shows the timing diagram of the discharge of the photodetector. Pa fig.Z shows a schematic diagram of the smoke detector of figure 2.

M J / jl f

The smoke detector (figure 1) contains a light pulse source 1, optically coupled to a photodetector 2, which is connected to a bi-directional logic port 3, an alarm 4, the input of which is connected to the output of the control circuit 5, the other output of which is connected to the input of the light pulse 1, bidirectional logical port 3, connected to control circuit 5.

The smoke detector (Fig. 2) contains a light pulse source 1, optically coupled to a photodetector 2, which is connected to the logical port of the controller 6, which acts as a bi-directional logical port 3 and control circuit 5, the signaling device 4, the input of which is connected to the output of the controller 6, input the source of light pulses 1 is connected to the output of the controller 6.

The smoke detector (Fig. 5) contains, in principle, a controller 6 - AT90S1200 (DD1), a light source 1 infrared diode of the AL164B1 (VD1) type with a current limiting resistor Ohm, a photodetector 2 of the type ФД115, and the signaling device 4 made in the form of an audio element ZP1 type PPA1 and LED VD3 type AL307 with current-limiting resistance Ohm, C - storage capacity type K-50-35 -100 microfarads. The smoke detector is connected to a + U power supply with a voltage of 4.5-6 V.

Consider the principle of operation of the proposed smoke detector. Let photodetector 2 be an element of the RC circuit (Fig. 3), in which one or both elements are simultaneously sensitive to the luminous flux F. ((O) or. (O.)). Thus, the duration of the charge (discharge) cycle will also depend on the light flux r RC P (Ф) (Fig. 4). The optical signal emitted by the source of light pulses 1 is reflected from the smoke particles, enters the photodetector 2 and changes the duration of the charge (discharge) cycle.

in a smoke detector, there is an optical connection between the light pulse source 1 and the photodetector 2 even without smoke. This optical coupling can be used to determine the dustiness and serviceability of the optical channel.

The smoke detector operation algorithm consists of the following steps. The duration of the cycle ti (Fig. 4) of the charge (discharge) of the photodetector 2 is measured to a certain threshold level Un, in the absence of a light flux from the source of light pulses 1, then the source of light pulses 1 is turned on and the duration of the charge (discharge) cycle ti of the photodetector 2 is measured , then find At | ti-t2 |. In this case, the influence of destabilizing factors (such as background illumination, temperature, etc.) is subtracted and only the change in the charge (discharge) time At remains due to the action of the optical emitter. Then At is compared with the threshold settings Ati, At2 ... Atn. For example, if, then this may correspond to the absence of smoke and the integrity of the optical channel, if At2 the optical channel is dusty, if At Ati the optical channel is defective, if - the presence of smoke.

In a practical implementation, it is convenient to use the time - number of pulses conversion for measuring ti and t2 (similar to the principle of operation of an analog-to-digital converter with a time-pulse

by transformation) N1 tifr, N2 t2fr, where fr is the clock frequency of the pulse generator. In this case, the difference At | ti-t2 | - is proportional to the difference in the number of pulses N1 - N2 | frjti-t2 |.

Reaching the threshold level Un is controlled by a threshold device, which can be performed on logic elements. In this case, the photodetector 2 is directly connected to the logical port. Gates with high input

resistance (CMOS - series) switching threshold from a logical unit to a logical zero, as a rule, is equal to half the supply voltage of the microcircuits. In this case, the number of pulses is measured, during which the voltage at the photodetector 2 from a logical unit reaches a logical zero.

The use of controller 6, with the proposed time-pulse conversion, reduces the number of elements, makes it possible to carry out multiple measurements with averaging their results, eliminate systematic errors, automatically control the correct operation of the device, and correct errors caused by the dustiness of the optical camera.

The smoke detector of figure 2 operates as follows. In the memory of the controller 6, pre-set threshold values kl, k2, k3 are recorded. The port of the controller 6, to which the photodetector 2 is connected, is set to a high state (the photodetector capacitance is charging), then this port of the controller 6 is switched as the input with a high resistance, and the internal counter (timer) of the controller 6 is turned on, the count of which stops when the controller input 6, to which the photodetector 2 is connected, is discharged to the level corresponding to a logical zero, while the logical ports of the controller 6 play the role of a threshold device. This state of the counter (N1) is remembered by the controller 6. Then, the controller port 6, to which the photodetector 2 is connected, is again set to a high state (the capacity of the photodetector 2 is charged), then the controller 6 turns on the light source 1, sets the controller port 6 to which photodetector 2 is connected as an input with high resistance; at the same time, the internal counter (timer) of controller 6 is turned on, the count of which is stopped when the input of controller 6, to which photodetector 2 is connected, is discharged to a level

corresponding to logical zero, this counter state (N2) is stored by controller 6. Controller 6 turns off the light pulse source 1. There is a difference k N2-N1, which is compared with threshold values kl, k2, k3 by controller 6. If, then the smoke detector is operational, optical the channel is dustless, there is no smoke. If, then the controller 6 includes a signaling device 4, which generates a signal characterizing the dustiness of the optical channel. If, then the controller 6 includes a signaling device 4, which generates a signal indicating a malfunction of the optical channel. If, then the controller 6 turns on the alarm 4, which gives an alarm indicating the presence of smoke. The signals for each type of alarm are different from each other.

The threshold values kl, k2, kS can be determined as follows.

Measure the smoke detector, in the absence of smoke, and the dustless optical channel (intrinsic state of the optical channel of the smoke detector), and determine .7kO. Place the smoke detector in a smoke chamber with bright smoke, the optical density of which is, for example, 0.1 dB / m, measure. Then determine .1kO.

Consider the influence of destabilizing factors. Assume that the RC circuit (FIG. 4) is charged to voltage UQ. Such a circuit is discharged according to the well-known law U Uoexp (-t / T), where t is RC. The discharge time will be measured to a certain threshold level Un. It is assumed that the time constant is sufficiently small and the measurement of time intervals tl and t2 is carried out directly one after another, therefore, the change in the threshold level Un, the background illumination Φ, and the temperature per measurement cycle can be neglected. When the supply voltage and temperature change, both UQ and linearly change

the associated Un (UH / Uo-const). Consider how this affects the operation of devices. The time intervals tl and t2 are determined from the expressions

Un Uoexp (-tl / Tl), Un Uoexp (-t2 / T2),

where T1 and T2 R2 "C2 are the time constants of the circuit in the absence and presence of a light flux pulse. Using logarithm and a simple transformation, we determine the time intervals tl, t2: Find At

At - | ti- t2h | т1 ln (Un / Uo) - т2 ln (Un / Uo) h 1 1-т2 | ln (Un / UQ). Therefore, At | ti-12 | independent of voltage UQ.

Consider the effect of background illumination and temperature. Let the resistance (O) of the photosensor be sensitive to the light flux. This resistance can be represented in the form + AR (Oo) + AL (Phi) + AR (T), where RO is the resistance of the photodetector in the absence of light, AR (Oo) is the change in resistance caused by the influence of background illumination, AR (Phi) is the change resistance when the light flux from the source of light pulses hits the photodetector, AR (T) change in the photodetector resistance under the influence of temperature. Using the above calculations, we find At:

At ln (Un / oo) | m1-r2 | ln (Un / Uo) R2.CH ln (Un / Uo) | RO H - AR (Oo) + AR (T) + AR (Oo) + AR (T) + AR (OH) «Ch

 ln (Un / Uo) AR (

Thus. At | ti-til does not depend on background illumination and temperature, and, therefore, does not reduce the sensitivity of the smoke detector.

(Un / Uo), (Un / Uo).

The smoke detector is easily implemented on a modern element base (figure 5). In this case, as controller 6, we used an Atmel microcontroller - AT90S1200 (DD1), based on field-effect transistors, with an integrated clock generator that does not require external elements and has a frequency fp, an eight-bit timer-counter, bidirectional logic ports PD and PBs that can operate as input or output ports. Input impedance over 100 megohms. Light pulse source 1 infrared diode of type AL164V1 (VD1) with a current limiting resistor Ohm, photodetector 2 of type ФД115, type of signaling device 4 - sound element ЗП1 of type ППА1 and LED VD3 of type АЛ307 with current-limiting resistance Ohm, С - storage capacity of type K-50-35 -100 uf. The smoke detector is connected to a + U power supply with a voltage of 4.5-6 V.

The algorithm of the smoke detector (figure 5) is as follows. In the memory of the controller 6, pre-set threshold values kl, k2, k3 are recorded. The ports of the controller 6 PDO, PD5, PB4, PB1 are set as output to a high state, the remaining ports are disabled. When the PD5 port is set to high, the capacitance of photodetector 2 is charged. Then the PD5 port of controller 6 is initialized as an input with a high resistance, and the internal pulse counter of the internal clock of controller 6 is turned on, which stops when the voltage at the photodetector 2 is connected to the PD5 port of controller 6 will have a level equal to logical zero. This counter state is memorized (N1). Then, the PD5 port of controller 6 is again set to high and the capacitance of photodetector 2 VD2 is charged. The PD5 port of controller 6 is initialized as an input with a high resistance, the PDO port is turned on as an output in

a low state, while the current flows through the diode VD1, which is the source of light pulses 1, at the same time the internal pulse counter of the internal clock of controller 6 is turned on, which stops when the voltage at the photodetector 2 connected to the PD5 port of controller 6 has a level equal to the logical to zero. This counter state is again remembered (N2) by the controller 6, and the light pulse source 1 - VD1 is turned off. There is a proximity k N2-N1, which is compared with the threshold values kl, k2, k3 by the controller 6. If, then the smoke detector works normally, there is no smoke, the camera is dustless. The VD3 LED turns on briefly through the PB4 port, indicating that the fire detector is operating normally. Next, the cycle of operation of the controller 6 is repeated from the beginning. If, and this state is repeated many times over a long time (for example, within ten minutes), then the controller 6 through the port РВ1 gives short-term pulses in the audio range to control the signaling device 4 ЗП1, characterizing the dustiness of the optical channel. If, and there was no state, then the controller 6 through the FBI port gives short-term pulses in the audio range, indicating a malfunction of the optical channel. These sound impulses differ from those that show the dustiness of the optical channel. If, then through the FBI port a continuous alarm signal with a frequency of O is issued to signaling device 4 of ZP1, indicating the presence of smoke.

Thus, in comparison with the prototype, the proposed smoke detector is made entirely on digital circuitry, provides control over the operability and dustiness of the optical channel during operation, which increases the reliability of its operation.

Claims (1)

A smoke detector containing a control circuit connected to the detector, a light pulse source connected to another output of the control circuit and optically coupled to the photodetector, characterized in that the photodetector is directly connected to a bi-directional logical port that is connected to the control circuit.