Fire alarm connection diagram and principle of its operation. Fire alarm sensor Connection of fire sensors

During installation, we use a specific connection scheme for fire detectors. This article will discuss exactly this. Fire detectors have different connection schemes. It is worth remembering when planning the circuit that the alarm loop is limited in the number of fire detectors connected to it. The number of connected sensors per loop can be found in the description of the control device. Manual and smoke detectors contain four terminals. 3 and 4 are closed in the diagram. This design makes it possible to control the fire alarm system. More specifically, by connecting a smoke detector using pins 3 and 4, a “Fault” signal will be generated on the control device if the detector is removed.

When connecting, it is worth remembering that the fire sensor terminals have different polarities. Pin two is often a plus, and pins three and four are minus; the first pin is used when connecting a final or control LED. But often it is not used.

If you look at the connection diagram, you can see three resistances, Rok, Rbal. and Radd. The resistor values ​​can be read in the manual of the control device and are usually supplied with it. Rbal. according to its functions, it is needed for the same purpose as Radditional; it is used in smoke detectors and manual ones. The control device is usually not included in the kit. Sold separately.

During normal operation, thermal sensors are usually short-circuited, therefore our resistance Rbal does not participate in the circuit until a trigger occurs. Only after this will our resistance be added to the chain. This is necessary in order to create an “Alarm” signal after one or two sensors are triggered. When we use a connection in which the “Alarm” signal is generated from two sensors, then when one is triggered, the control device receives an “Attention” signal. These connections are used for both smoke and heat sensors.

By connecting smoke sensors and using Radditional in the circuit, an “Alarm” will be sent to the control device only after two sensors are triggered. When the first sensor is triggered, the control device will display an “Attention” signal.

If the resistor Radd is not used in the circuit, the “Alarm” signal will be sent to the control device as soon as the sensor is triggered.

Manual call points are connected only in one mode, that is, so that when one device is triggered, an “Alarm” signal immediately appears in the system. This is necessary for immediate notification of a fire.

At industrial facilities, thermal sensors are mainly used for fire alarm (they are the cheapest). The peculiarity of their device is that they sound an alarm when the protected premises have already burned down.

According to firefighters, smoke detectors are considered the most reliable, but not everyone can afford them.

Fig 1. Schematic diagram of a fire smoke detector

One of the options for making a smoke sensor is shown in Fig. 1. The circuit consists of a generator (on microcircuit elements DD1.1, DD1.2, C1, R1, R2), a short pulse former (on DD1.3 and C2, R3), an amplifier (VT1) and an IR emitter (HL1) pulses, as well as a comparator (DD2) and a transistor switch (VT2). When IR pulses are received by photodiode HL2, the comparator is triggered and its output discharges capacitor C4. As soon as the passage of the pulses is disrupted, the capacitor will charge through resistor R9 within 1 second to the supply voltage, and element D1.4 will begin to operate. It passes generator pulses to the current switch VT2. The use of the HL3 LED is not necessary, but if it is present it is convenient to control the moment the sensor is triggered.

Fig 2. Smoke sensor design

The design of the sensor (Fig. 2) has a working zone, when smoke enters it, the passage of IR pulses is weakened, and if several pulses fail to pass in a row, the sensor is triggered (which ensures noise immunity of the circuit). In this case, current pulses appear in the connecting line, which are highlighted by the control circuit shown in Fig. 3.

Figure 3. Control circuit

You can connect many smoke detectors to one security loop (in parallel). When setting up the control circuit with resistor R14, we install the transistors so that VT3 and VT4 are in a locked state (LED HL4 does not light).

One smoke sensor in SECURITY mode consumes a current of no more than 3 mA and is tested when operating in the temperature range from -40 to +50 °C.

The output of the control circuit (VT4 collector) can be connected to the security system directly instead of the sensor.

When using several sensors installed simultaneously in different places, the circuit can be supplemented with an indicator of the number of the activated smoke sensor. To do this, it is necessary that the frequencies of the generators (depending on C1 and R2) differ from each other, and using a digital frequency indicator, for example, proposed by M. Nazarov ("Radio", N 3, 1984, pp. 29-30), it will be easy to determine place of fire. At the same time, there is no need to run security loops separately to each sensor, which will significantly simplify the wiring and reduce their consumption.

Transistors VT1 and VT2 can be replaced with KT814. IR diodes will suit many other types, but this may require selecting the value of resistor R6.

Capacitors used are C1, C2, C4, C5 of type K10-17a, SZ - K53-18-16V, C6 - K50-6-16V. Resistor R14 is type SP5-2, the rest are type C2-23.

It is advisable to install a smoke detector in rooms where flammable items are stored, and to place it in places where air flow passes, for example near a ventilation opening - in this case, a fire will be detected earlier.

The circuit can find other applications, for example, as a contactless sensor for security alarms or automation devices.

A smoke detector is one of the most common devices in fire alarm and fire extinguishing systems. The device reacts to combustion products, their ability to change the optical environment, infrared radiation of an object and other signs by which a fire can be detected. Due to the fact that smoke, even in small quantities, greatly changes the optical transparency of the atmosphere and immediately rises upward, it is quite easy to detect. This makes it possible to determine the source of a fire at an early stage, which explains the proliferation of these detectors. But to use them effectively, you need to know how it works, how it works, and take this into account when choosing the installation location.

Smoke sensor design

The point smoke detector consists of two parts. The first looks like a flat cylinder with a four-pin pad (called a socket), it is mounted on the ceiling or wall. The second working part looks like a two-stage truncated cone. At its base there is an electronic unit, and at the top there is a smoke chamber. The parts open easily because the sensor has to be removed periodically. This is done in order to clean it from dust and carry out routine maintenance or quick replacement. The smoke detector is connected by simply turning the socket. To control the presence of a detector in the socket, there are two contacts that close after installing the device. Sometimes it is necessary to turn off the smoke detector, as in the case of dusty work in a room. To do this, it simply unscrews from the socket.

An optical fire detector uses the scattering effect of the emitter. It is installed so that its light does not fall on the photodetector. If there is smoke in the sensor, the transparency of the air changes and the light is reflected onto the photodiode, which triggers the sensor. The smoke chamber has a complex shape. It provides free air movement, minimizes dust ingress and protects against electromagnetic interference. In addition, due to the black curved plates located around the perimeter of the camera, it prevents external light sources and radiation from the LED from entering due to multiple reflections on the photodiode. Almost all radiation falling on the plates is absorbed by them.

The connection diagram for fire alarm smoke detectors is traditional, using a four-wire cable. Two wires supply power, the third sends an alarm if smoke is detected, and the fourth monitors the presence of a detector in the socket.

How the smoke detector works

According to the principle of operation, fire smoke detectors are divided into two types: optical and ionization. The first ones are:

• point;
• linear;
• aspiration.

The second devices are divided into two groups: radioisotope and electrical induction, used in especially critical premises.

Point smoke detectors use the property of gray smoke to scatter infrared radiation. The emitter and receiver are located in the same housing. Smoke entering the device causes a change in the optical medium, which leads to reflection of the LED radiation onto the photodiode. If the power of radiation hitting the photodetector is greater than a certain threshold value, then the device will work.

Linear smoke detectors consist of two parts: an emitter and a receiver. They are installed under the ceiling on walls opposite each other in direct line of sight. The principle of operation of the smoke sensor is as follows. The emitter (LED) is constantly on. The receiver (photodiode) constantly monitors the power of the received signal. When the radiation changes beyond a certain limit, the sensor is triggered. The connection diagram for fire smoke detectors of this type differs from conventional single-case ones in that there is an additional power cable to the emitter.

The principle of operation of an aspiration smoke sensor is to forcefully extract air from the atmosphere of a protected premises and subsequently monitor its condition using ultra-sensitive laser smoke sensors. Used in “clean” production areas, server rooms, operating rooms and other places where early fire detection is especially required. It has a high cost.

The radioisotope sensor irradiates the chamber atmosphere, ionizing it. A voltage is applied to the electrodes inserted into the ionization region, and an ionization current occurs. When smog enters, air ions begin to stick to large and less mobile smoke particles. This leads to a decrease in the ionization current, which signals the presence of a fire. The sensor is effective in detecting black smoke that absorbs infrared radiation. Due to radioactive radiation, it is not used in residential buildings.

The electro-induction sensor has an electric pump that sucks air into a gas tube, where it is charged under the influence of a corona discharge. Moving further and entering the chamber with the measuring electrode, it induces a potential proportional to the volume of charged particles. The electronic unit processes the amplitude, the rate of its increase and issues an alarm if the threshold values ​​are exceeded. Used on the Mir international space station.

Is it possible to make a smoke detector yourself?

The easiest way to make an optical linear smoke detector. The circuit consists of two LEDs, a phototransistor, an operational amplifier, a variable resistance and a piezoceramic emitter. The entire design is carried out on one board. Light from the first LED opens the phototransistor, and the voltage from the emitter goes to the inverting input of the operational amplifier. A potential is supplied to the other input of the amplifier through a variable resistor, which regulates the sensitivity of the device. If the balance between the amplifier inputs is disturbed due to the presence of smoke, a signal appears at the output, turning on a second indicator LED and a piezo siren. The device can even be connected as a smoke detector to a fire alarm.

A fire alarm sensor is a device that gives a signal in case of fire and heavy smoke. Let's consider several options for homemade circuits

The sensor is assembled on two microcircuits DA1 K157UD2, DD1 K561KTZ. DA1 are operational amplifiers connected in a comparator circuit. DA1.1 has a temperature sensor; almost any thermistor R6 can be used with a resistance from 1 to 100 kOhm. Resistance R2 sets the operating threshold of the comparator.

As the temperature rises, the resistance of the thermistor decreases and the voltage at the non-inverting input of the second output of the comparator increases. As soon as it becomes higher than the voltage level at the inverting third input, the output voltage will increase to the level of the supply voltage.
The comparator DA1.2 has a smoke sensor. Resistance R3 sets the current flowing through the LED VD1. The light flux affects the photodiode VD2, which, together with the resistance R8, constitutes a divider, the voltage from which goes to the inverting input of the comparator DA1.2. The voltage divider on resistors R4, R5 sets the voltage at the non-inverting input of the comparator. When smoke appears in the event of a fire, the photodiode will be illuminated with a weaker light flux, its resistance increases, the voltage at the inverting input decreases and becomes lower than the voltage at the non-inverting input. Therefore, the potential difference at the output of DA1.2 will change almost abruptly to the level of the supply voltage.
Chains R9, R10, C1 and R11, R12, C2 are used to protect against interference that may appear at the input of the comparator and switch it. Capacitance C4 filters the power supply so that IC DA1 is not excited. The outputs of the comparators DA1.1 and DA1.2 through diodes VD3, VD4 are connected to load resistance R15. To connect the sensor with the main alarm unit, there is an isolation on the key IC DD1. All four keys are connected in parallel. When the supply voltage appears at the output of any of the comparators, capacitor C3 will begin to charge, which protects the circuit from short-term interference at the input or along the power circuit. When C3 is charged to a given level, the DD1 keys will begin to pass current, and at the contact<тревога>a potential difference will appear. It will indicate a critical situation at the protected facility.
The temperature sensor is configured as follows. Heat the thermistor to 45 °C and adjust resistance R2 until VD5 lights up; when the temperature drops, the LED should go out. The smoke sensor is configured by adjusting resistance R5 so that it is triggered only when smoke appears. If the sensor operates unclearly, it is necessary to more accurately select resistor R8 for a specific photodiode.

A feature of this circuit is that, in its internal composition, it is a ready-made temperature sensor.

The sensor output is an open-drain output that is designed to carry a current of up to 4 mA. When the programmed temperature of any of the three DS1821 sensors reaches the TH level, a voltage drop will appear across resistance R1, which will unlock the thyristor and turn on relay K1. Relay contacts switch any signaling device, for example.

The circuit reacts to a sudden drop in sensor illumination due to smoke by emitting an alarm. The circuit will not work on gradual changes in brightness, which allows you to avoid false alarms. The buzzer sounds for about 10 seconds, but this time can be changed by adjusting the resistance of resistor R5.

Natural light must also be used as a light source, but it will be better if a bright beam of light from a Chinese laser pointer is applied to the light sensor. The required sensitivity is regulated by resistor R1. The sensor itself plays the role of a photoresistor, the resistance of which is low when illuminated and high when darkened.

Even in ancient times, people used the transmission of information about the beginning of some events over a distance in the form of light signals or clearly audible sounds, when bonfires were lit on hills or bells were rung.

The life of a modern person is associated with the operation of a large number of various equipment, the operation of which is often monitored remotely using various types of alarms. Among them, information about the start of a fire at critical industrial facilities and inside multi-storey buildings with a large number of people is given the utmost importance.

Purpose of fire alarm

Its main task is to promptly transmit information at the first signs of fire to the duty service, which can quickly arrive at the scene of the incident and take emergency measures to extinguish the fire that has arisen and prevent its spread.

Additional tasks of fire alarm systems (FAS) can be:

remote activation of pre-positioned fire extinguishing means - various types of fire extinguishers created in relation to specific conditions of production or facility;

ensuring the unlocking of access control systems to facilitate the mass evacuation of people from a dangerous place;

transfer of information to additional dispatch control points;

other functions.

Fire alarm composition

The fire alarm system is considered as a specific electrical control system, the circuit of which consists of various parts:

special sensors - detectors that indicate the start of a fire;

channels for transmitting signals about sensor activation;

control panels, reception (RCP) and display of information for operating personnel;

public warning systems.

How fire detectors are designed and work

The occurrence of the first signs of fire can be assessed by the appearance of smoke, rapid heating of the environment, or a strong flash of light. These three factors are incorporated into the operating principle of various technical devices.

In the industrial and residential sectors, four types of sensors operating on different principles are most widespread:

1. detecting the beginning of smoke spread - smoke detectors;

2. the appearance of sudden heating indoors - thermal;

3. separation of electromagnetic waves in the optical range of the visible, ultraviolet or infrared spectrum - flame;

4. simultaneous exposure to heat and smoke, and often in combination with the appearance of bright light - combined.

Fire alarm sensors can only monitor the state of the monitored parameter or respond to its change by issuing a signal to an external system. According to this principle, they apply not only to passive, but also to active devices. Detectors can be created to monitor a specific local area or an extended, elongated area. The latter constructions are called linear.

How smoke detectors work

The sensor is placed on the ceiling in the place where smoke rises and begins to concentrate when a fire starts.

Structurally, the smoke detector consists of:

1. split housing;

2. electronic board;

3. optical system.

These parts are individually assembled on automated production lines and, after passing various tests and inspections, are assembled manually into a single module.

The operation of the sensor is based on recording the moment of smoke appearance in its housing due to the activation of an optical system, which includes:

Emitting a strictly directed beam of light;

Which converts the light flux incident on it into an electrical signal.

Structurally, the light beam from the source is directed slightly away from the photocell. Under normal operating conditions with normal indoor air conditions, light cannot reach the surface of the photocell, as shown in picture No. 1.

If smoke appears in the sensor housing, light rays begin to be reflected in all directions. They hit the photocell and it fires. This moment is controlled by an electronic circuit. It generates an information command and transmits it via communication channels to the fire alarm receiving device.

If water vapor or gases that deflect the light flux begin to penetrate into the sensor cavity, the photocell will also work, and the logic circuit will provide false information about the occurrence of a fire.

For this reason, smoke detectors are not installed in areas where they are likely to operate incorrectly. These include kitchens, bathrooms, showers. Installing smoke detectors in places where smokers gather will also cause them to operate frequently and falsely.

Such a fire detector will not respond to an increase in temperature and a flash of light from an open fire. Therefore, such modules are installed in those rooms where a fire is associated with smoke in the environment due to temperature damage to the insulation of electrical wires, fabrics, and other similar materials.

They are installed in places with a large number of operating electrical equipment in industrial production, material storage warehouses, electrical substations and laboratories.

Operating principle of heat detectors

They are also placed on the ceiling, where the heat generated by an open fire rises. They can work according to the factor:

1. achieving the maximum permissible heating value;

2. rate of temperature increase.

Threshold devices

Sensors of this type were the very first to be created. At first they worked due to the flow of an easily molten alloy from a fuse installed at the point of contact of two conductors. Due to this, when the environment heated to 60–70 degrees, the electrical circuit broke and a signal was issued about the start of a fire.

The operating principle of one of these designs of a disposable, non-renewable heat detector type IP-104 is shown in the picture.

Inside the housing there are spring contacts, which are retracted from each other by mechanical tension forces, and are held in place by Wood's alloy, consisting of low-melting metals. The sensor is triggered when heated to 68 degrees, and the circuit is broken by charged springs.

Such designs are constantly being improved. Now they are produced with replaceable fuse inserts or elements controlled from a distance. The logic circuit can be made using different principles and electronic components.

Integral detectors

The sensor's operation is based on measuring the rate of change in the electrical resistance of metals when they are heated.

A stabilized voltage is supplied to the terminals of the thermal control element from the power source. Under its action, a current determined by Ohm's law flows in an electrical circuit through a wire resistor and a measuring device. Its value strictly depends on the resistance.

When exposed to normal room temperature, its value remains virtually unchanged. When the voltage is stabilized, the current does not change either.

When the control element begins to be affected by the temperature of the open fire from the emerging flame, the resistance of the sensor begins to quickly increase and the current begins to change according to the same law. The rate of its deviation from the previously established value is fixed by an electronic circuit, which is usually set to increase by 5 degrees per second.

When a critical heating rate is reached, the sensor’s logic circuit sends a signal to the receiving module via communication channels.

This circuit does not have devices that react to smoke, and it will not work on it.

Such structures work most effectively in fires caused by the ignition of flammable liquids from petroleum products, carbon fuels, and flammable solid materials. They are installed in storage areas for containers with flammable liquids, warehouses for building materials and in similar industrial buildings.

Operating principle of flame detectors

A fairly large class of these sensors reacts to an open fire or a smoldering fire without producing smoke.

A sensitive photocell detects the appearance of one of the optical wave spectra or its full range. At the same time, the design turns out to be quite complex and expensive. For this reason, they are not used in residential buildings, but are used in the oil and gas industry.

The simplest models of this type are capable of being triggered by exposure to a welding arc, bright sunshine, fluorescent lamps, and electromagnetic interference in the optical spectrum. Various filters can be used to eliminate false operation.

Operating principle of combined detectors

All designs of fire detectors that operate based on one sign of fire may trigger falsely. To expand the reliability of transmitted information, devices are created that immediately combine the capabilities of smoke and thermal models, or are supplemented with a flame reaction function.

To do this, they immediately include an infrared, thermal and optical sensor. They can, in most cases, be configured to trigger from each input parameter separately or only when they appear simultaneously.

For critical industrial premises, there are four-channel combined detectors that additionally take into account the appearance of carbon monoxide.

Operating principle of manual fire call points

The simplest designs of an ordinary button with a self-resetting spring are used to manually notify operational workers about the start of a fire. To do this, personnel who notice the beginning of signs of fire need only open the protective cover and press the button.

This action closes the contacts of the circuit and turns on the “Fire Alarm” notification. When the button is released, the signal is not interrupted: its power supply chain is automatically set to self-locking. People will be warned about the fire hazard until the responsible employee uses a special key to unlock it.

Such hand-held sensors are installed in all rooms where masses of people gather (shops, hospitals, cinemas, industrial facilities) at a height of one and a half meters and at a distance between them of up to 50 m.

Brief conclusions on choosing fire detectors

The design and principle of operation of the sensor must comply as much as possible with the conditions ensuring fire safety of the controlled premises.

In large industrial buildings with different equipment, it is not always advisable to use the same types of detectors, and their number, even with limited financial resources, must cover all dangerous fire zones in accordance with the requirements of regulatory documents.

Channels for transmitting signals about detector activation

After the types and number of fire sensors have been determined for installation in the premises, they are connected by wires into loops, which are assembled into a control panel in the operational security service.

For loops, wires with copper cores are selected and laid with the ability to monitor the technical condition. SNIP and GOST impose requirements on them regarding methods of separate installation with other cable lines and to ensure protection from mechanical damage.

Instruments for receiving and monitoring signals

Control panel panels are created by manufacturers of varying degrees of complexity for professional, semi-professional or household use.

Professional devices are designed to solve not only fire safety issues, but also the protection of facilities. They:

monitor the state of multipath circuits and are capable of simultaneously processing analog and digital signals;

allow cascade combination into blocks to create a complex hierarchy of control circuits;

connect to the computer of the fire and security service;

record in time and transmit all information occurring at the controlled object;

are used only at critical industrial facilities.

Semi-professional devices work with digital signals. They are manufactured in a single building that combines:

power supply from a stationary electrical network;

backup power supply - a powerful battery capable of ensuring autonomous operation of the system from several hours to a day;

electronic control unit;

CPU.

At critical facilities, the processor is protected from unauthorized access by placing it in hard-to-reach places with complete shielding, preventing hacking attempts using a special remote scanner, and complex coding of processed and transmitted information.

Such models are capable of processing signals from two hundred and fifty sensors. They can already be used in the residential sector.

Multi-beam household control panels

They are designed to work in private households with various outbuildings.

Capable of processing signals from electrical contacts of reed switches or electronic circuits, as well as information received via wireless channels from two to eight different sources.

The simplest apartment control panels

They are represented by the simplest models, operating in single-channel mode, which is quite sufficient for the apartment owner. Even such a device is capable of transmitting information about sensor activation to the owner’s mobile phone in the form of SMS.

Control panel panels intended for domestic purposes are accompanied by detailed technical documentation from the manufacturer with instructions and connection diagrams. The European standard EN54 has been introduced for them.

Fire warning systems

In crowded buildings, a light and sound warning system is used to warn personnel and visitors using the “Alarm” command. At the same time, information is transferred to the management of the enterprise and duty services for taking emergency measures.

An example of the distribution of various fire alarm devices and the organization of a warning system is shown in the picture.

Like all technical devices, fire alarm systems require periodic monitoring and performance checks, a set of maintenance measures, settings, and adjustments. In this case, it is necessary to follow the rules of their operation.

I would like to express confidence that the initial information presented about the design of modern fire alarms will prompt the reader to think: in practice, create for yourself an optimal system that excludes fire in the event of an accidental fire or deliberate arson.