The smoke sensor for the alarm system about a fire

From a fire the damage can be even more, than from thieves, and in time the submitted alarm signal will allow though something to rescue.

Fig. 3.21. An electric circuit of the sensor of a smoke

On industrial facilities are generally used by font for the alarm system about a fire thermal sensors (they are cheapest). Feature of their device such is that they submit an alarm signal when the protected room already burned down.

are Most reliable, according to firefighters, the sensors working on a smoke, however they on a pocket are considered as not all.

One of options of performance of the sensor of a smoke is given by font on fig. 3.21. Cхема consists of the generator (on elements of a chip of DD1.1, DD1.2, С1, R1, R2), the shaper of short impulses (on DD1.3 and С2, R3), the amplifier

the Fig. 3.22. A type of a design of the sensor

(VT1) and a radiator (HL1) IK-impulsov, and also the comparator (DD2) and a key on the transistor (VT2). At reception IK-impulsov by the HL2 photo diode works the comparator and the exit discharges the C4 condenser. As soon as passing of impulses will be broken, the condenser will be charged via the R9 resistor within 1 second to supply voltage, and the element D1.4 will start to work. It passes generator impulses on the switchboard of a current of VT2. Application of a light-emitting diode of HL3 is not necessary, but at its existence it is convenient to supervise the moment of operation of the sensor.

a sensor Design (fig. 3.22) has a working zone, at hit in which smoke passing IK-impulsov and if could not pass some impulses in a row is weakened — works the sensor (that provides a circuit noise stability). Thus in the connecting line there are impulses of a current which are allocated by the circuit of control provided on fig. 3.23.

Fig. 3.23. The control circuit

smoke Sensors can be connected font to one security loop (in parallel) much. At control of the circuit of control • the R14 resistor we establish transistors so that VT3 and VT4 were in the locked condition (the light-emitting diode of HL4 is not shone).

One sensor of a smoke in the PROTECTION mode consumes a current no more than 3 мА and is checked at work in a range of temperatures from-40 to +50 °C.

the Exit of the circuit of control (VT4 collector) can be connected by font to protection system directly instead of the sensor.

When using several sensors which have been at the same time established in different places, the circuit it is possible to add font with the indicator of number of the worked sensor of a smoke. For this purpose it is necessary, that frequencies of generators (depends from С1 and R2) differed from each other, and having used the digital indicator of frequency for example offered by M. Nazarov ("Radio", N 3, 1984, p. 29 — 30), will be easy to define an ignition place. Need of a message security loops separately to each sensor thus disappears that considerably will simplify distributing of wires and will lower their expense.

VT1 and VT2 Transistors can be replaced with font on КТ814. IK-diody will approach many other types, but selection of face value of the R6 resistor thus can be demanded.

Condensers are used by font С1, С2, С4, С5 the K10-17a type, SZ — К53 - 18-16B, С6 - К50 - 6-16B. SP5-2 type R14 resistor, the others of the C2-23 type. the Sensor of a smoke it is expedient to font to establish p to

in rooms where хра нятся easily flammable subjects, and to place in places where passes an air stream, for example near a ventilating opening, - in this case ignition will be revealed earlier.