Multi-channel protection for remote objects. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling

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It is often necessary to protect premises remote from the main security unit from intruders. At the same time, a two-wire line (loop) is laid from each object to the security console. For reliable operation of the security system, the circuit must have an indication of any violation of the security loop circuit: an open or short circuit, as well as a sensor operation at the facility.

Unlike many other security systems described in the literature, this scheme allows you to distinguish all these three states, as well as reliably control the operation of the security loop not only from the central security console, but also directly on the object (premises) itself. In addition, the circuit consumes little and provides for mixed power supply from the 220 V network and the battery - when the mains voltage fails, the power goes to the battery.

Rice. 2.33. Electrical diagram of the unit installed in the protected area (click to enlarge)

The principle of operation of the device is based on the detection of current changes in the security loop circuit. Unlike the most common bridge circuits, this one operates in a pulsed mode, which is more economical. An active device is installed on each protected object, assembled according to the scheme of fig. 2.33. It can be connected to many serially connected sensors F1 ... Fn, triggered by a break. In this case, all of them are connected to the circuit so that the operation of any of them breaks the entire circuit.

Any security devices having a relay output can be used as sensors.

The electrical circuit consists of an oscillator based on the elements of the D1.2 and D1.3 microcircuits with a frequency of approximately 2 Hz (its operation is described in detail in the first section). The HL1 LED flashes at the same frequency. If one of the sensors connected in series is triggered, a log will appear at the input of element D1.1/6. "1" - the key will close and the oscillator will stop working.

Rice. 2.34. Scheme of the central security alarm panel (click to enlarge)

In a protected area, the indicator of the normal state of the alarm loop is the blinking of the HL1 LED (when the loop of this channel is on on the central console). Diode VD2 prevents damage to the circuit from erroneous connection of the polarity of the security loop during the initial connection of the system.

The use of a circuit with an autogenerator at each protected object makes it possible to make the central console quite simple, with wider system capabilities. The control panel scheme is shown for two channels of protection of remote objects, fig. 2.34. All nodes of additional channels are identical, and therefore we will consider the operation of the entire system using the example of the first channel.

The activation of the security mode of the desired object (channel) is made by the corresponding toggle switch 1SA1...nSA1. In this case, if all sensors on the protected object are closed, the LEDs 1HL1...nHL1 will blink. These pulses are fed through the capacitor 1C1 to the base of the transistor 1VT2. It periodically opens and discharges the 1C2 capacitor (more precisely, it does not allow it to charge). The presence of a capacitor eliminates the accidental operation of the anti-interference protection system in the loop circuit. In the event of the disappearance of pulses, 1C2 is gradually charged to the supply voltage and trigger D1.1 is activated, which makes it possible to record the fact of a violation, even if it was short-lived.

The indicator of violation of the security loop is the continuous glow of the 1HL2 LED and the operation of the sound signaling device. At the same time, the state of the 1HL1 LED can be used to judge the nature of the security chain violation, which is very convenient. So, if the loop breaks, there will be no glow, and in the case of a continuous glow of the LED, there will be a short circuit in the line.

The notification mode is reset by the 1SA1 toggle switch - when it is turned off by its group of contacts, it resets the trigger by applying a high level to the input R.

Rice. 2.35. Power supply

Power supply for security system, fig. 2.35, assembled according to the classical scheme and does not need special explanations. For its manufacture, any transformer with a power of 20 ... 30 W is suitable, providing a voltage of 10 ... 12 V and a current of up to 1 A in the secondary winding (in standby mode, the system consumes a current of no more than 1 mA for each enabled channel). The maximum current of the transformer must correspond to that consumed by the buzzer. Transistor VTXNUMX is mounted on a radiator.

Setting up the remote control circuit consists in adjusting the sensitivity of the operation of the transistor 1VT1 (resistor 1R2) to pulses from a remote generator under a real loop line (similarly in other channels).

The topology of the printed circuit board for the oscillator circuit installed at the protected facility is shown in fig. 2.36 (it has two jumpers).

The circuits use fixed resistors MLT, tuning (1R2 ... nR2) multi-turn C5-2. Non-polar capacitors of the K10-17 type, electrolytic 1C2 ... pS2 of the K53-1 type for 20 V, and in the power supply K50-35 for 25 V. Any of those intended for car alarms can be used as an audible signaling device HA1. For sound notification, you can also use the usual speaker, connected according to the circuit with the generator shown in Fig. 2.37. In this case, the sound will be intermittent and it will be possible to adjust the volume of the speaker with a tuning resistor.

Rice. 2.36. PCB topology and element layout

Rice. 2.37. Wiring diagram

If desired, this scheme, in addition to security functions, can also be used as a fire alarm. To do this, a thermistor from the ST2-2 series (19 kOhm) is added in series to the circuit of the frequency-setting resistor R15, and the value of the elements (R2, C2, R3 and R5) is changed so as to obtain a frequency of 2 Hz at a nominal value of R2=10... 15 kOhm The methodology for calculating the values ​​of these elements is given in the first section.

In this case, the frequency of the autogenerator will depend on the temperature in the room, and by supplementing the central console circuit with a frequency analyzer, you can have a fire alarm in addition to the usual security one.

Publication: cxem.net

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