【 Weak current College 】 fire detectors of misreporting and improvement method

With economic development, a large number of buildings constructed and used for the protection of personal and property safety of automatic fire alarm system is becoming more and more necessary. Now the automatic fire alarm system has been widely used in various small unit, but there are still some problems, such as system of false positives, false negatives, and frequently is also more common Jet phenomenon, this article from the fire detector works, analysis of fire detectors and major sources of interference, and to make some improvements. Keywords: improvement of fire detector

First, fire detector works

Fire detectors are building fire alarm system, an important part, also called a probe or sensitive headers. Its mission is to detect the occurrence of fire, send to the alarm system, fire alarm signal to the people. Detector is how detect fires? fire occurs, will inevitably produce smoke, flame or high temperature, the detector is sensitive to these, because of their exposure to change the normal state, usually caused by the current, voltage or mechanical part of the change or shift, and then by zooming in, transfer, process, issued to fire a fire signal in the control room, and displays the fire location, location. Based on this we will fire detectors can be divided into three categories: smoke, heat and light radiation.

1 smoke detector

An ion sensing smoke detectors, smoke into outer ionization chamber, interferes with the normal operation of charged particles, so that the current, voltage, destroyed the inner and outer balance between ionization chamber, the detector will this produce induction, a beep signal, photoelectric sensing probes, it has a light emitting element and a photosensitive element, usually by the light emitting element, through the lens to photosensitive components, circuit maintain normal, such as a smoke barrier from, arriving at the light-sensitive components will be significantly reduced, so the photosensitive components put light intensity changes to current changes, by amplifying circuit alarm signal; there is also a pipeline pumping smoke detector, smoke of reflection or scattering effect produces light perception current, mainly used in the ship. The detector used Semiconductor components, small size, low price, high-resistance, long life, is very promising.

2. heat detector

One is the use of metal enamel characteristics: under normal circumstances, the detector circuit is in a disconnected state, when the ambient temperature rises to a certain value, the extension of metal expansion, so that the circuit is switched on, the signal; the other is to use the characteristics of the fusible metal detector circuit in the fixed a low melting point alloy, when the temperature rises to its melting point, metal melting, with spring force, make contact with, the circuit is switched on, the alarm signal. There is also a difference in type, when warming faster than a specific value when the sensor alarm.

3. optical radiation detector

One is the infrared radiation detectors. Substances in combustion, producing infrared radiation, blink detector PBS infrared sensors to the induction, and produces electrical signals, with enlarged alarm; another is ultraviolet radiation detector, it is the use of organic compounds produced by the combustion, the ultraviolet UV-sensitive pipe electrodes stimulate ion, relay, close the circuit alarm

2. fire detection system status and development of technology

1, technology

Since reform and opening up, accompanied by the economic construction and the rapid development of the cause of the fire, the fire protection industry to flourish. China fire safety electronics industry is part of the Chinese fire industry, and who is a technical part of the gold is higher, and is part of the fastest growing, international General Universal's fire alarm devices are capable of producing. In the face of high-tech development opportunity and the internationalization of competition in the domestic market challenges, fire products to a more reliable, intelligent, networked early fire detection and alarm technology development. Traditional automatic fire alarm system and a modern fire alarm system, the first difference between lies detector performance itself. The switch quantity probe into analog sensor on a qualitative leap, smoke concentration, increased rate or other feelings parameter to simulate the value passed to the controller, the system determines the fire data processing power and intelligent level increased, decreasing the probability of false alarms. Difference between the two lies in the signal processing methods to do a thorough improvement of the detector in the analog signal continuously sent to the controller assess or determine the controller with the appropriate algorithms to identify false or true fire, it development and detection of contaminated State. The high quality of the signal processing technology, means that the system has a high "smart". Increased system reliability is a modern fire detection and alarm technology direction of development. Smart fire detection and alarm system by its intelligent allocation can be divided into three system a is an intelligent detection, monitoring and intelligent, the third is to detect intelligent and control and intelligence. The latter is more intelligent system, its reliability, but the disadvantage is the high cost.

2. development prospects

People expect automatic fire alarm system is first of all requires a system of early discovery of fire, followed by eliminating false positives and reducing system costs. Intelligent fire alarm system may end up developing robots and intelligent alarm system. Modern fire alarm system for the rapid development on the other hand is a composite detector and a variety of novel detectors are emerging, more and more sophisticated detection performance. In a lot of new technology and new products, a will is typically used for ion sensing smoke sensor with improved as the combination of composite CO detector, air concentrations of CO in earlier than smoke and flame generation, therefore, its speed of response, development prospects are good. Another point-type laser smoke detector, its sensitivity is higher than the current photoelectric smoke detector 50 times, use it instead of air-breathing smoke alarm system provides very early fire detection, and a much lower cost, the prospects are very good.

In recent years infrared beam smoke detection, cable-style fixed temperature detector, combustible gas detector, etc in fire protection engineering increasing and has the appropriate product standards and design specifications. The detector works similar with photoelectric smoke detector,Just smoke do not have to enter the point type photoelectric smoke detector sample room. Linear beam detectors in a long path to 100m instead of several points of the type smoke detectors, a protected area, the location of the installation is relatively high, in relative humidity is high and strong electric field environment reflects the advantages of speed, suitable for the protection of large indoor and outdoor facilities, especially suitable for protecting hard-to-use point detector or even impossible to use the dot detector.

Intelligent fire protection systems as part of a building automation system, intelligent building as both can be used with other building security systems, fire protection system of intelligent, networked communication and to upper management system alerts and delivery information for municipal fire dispatching system, urban fire prevention management system and integrated information management network of interconnected to provide fire and building effective fire protection system status and other information and the city center to share data and information. Fire fighting automation system integrated into the building automation system, control the width and depth varies greatly and abroad. Generally speaking, the intelligent building automation system mostly in fire is an independent, self-contained, this sui generis system of fire protection systems and building, security and system independent of each other, connectivity, and when a global event, will not form other system coordinated and focused solutions event.

3. fire detectors cause interference and improve methods

1, several fire detector works

With economic development, a large number of buildings constructed and used for the protection of personal and property safety of automatic fire alarm system is becoming more and more necessary. But the automatic fire alarm system setting, often find that some of the system is not satisfactory. Such as: fire detectors often failure or damage, increased maintenance cost; detector are often misused, making fire alarm watch troubled. Excludes equipment quality does not cross the border and other circumstances, we find that these situations are often due to the disruption of detection equipment. The following is from the fire detector works, step by step analysis of probes of parts and the main source of interference, and to make some improvements.

Fire detectors in general working principles as shown in Figure 1: sensors detect fires or fire occurs in the values, transmitting circuit will detect components of the original signal is converted to current/voltage signal or pulse, switch data, into the automatic fire alarm controller, controller received signal to calculate analysis, and determine if there is fire is occurring, is an alarm signal. Some systems to mitigate fire auto-alarm controller burden in fire detectors installed in the CPU, the controller of data analysis tasks.

Now, let me briefly introduce two detector works:

A photoelectric smoke detector

Photoelectric smoke detector has a labyrinth smoke detection room, inside there is a light and a PC components. As is the labyrinth design, light rays usually does exposure to the PC component, but when there is smoke enters the light scattering in the smoke generation, thus some rays to the PC component, smoke more dense, scattering to the PC component of light on the more sensitive components and optical signal is converted to an electrical signal is output.

B ion sensing smoke detector

Ion sensing smoke detector consists of a radioactive source, an external sample room and a built-in ion reference sample room. When radioactive irradiation of substances in the air, some substances become positively charged ions, with other substances become negatively charged ions. With the positive ions and negatively charged ions in the electric field of the role of an electric field. When the smoke into the sample Chamber later and charged ions, reduction in the number of charged ions makes electric voltage change, smog, the more concentrated the greater the voltage changes.

2. main sources of interference

By fire detector composition, structure and working principle, we can easily figure out which parts of the fire detectors are vulnerable to outside interference, but these outside interference factors is the source of interference. We believe that fire detectors are most vulnerable to interference of the following sections:

A sensing element

Sensing element is fire detector "eyes", but it's "vision" limited. For example: when smoke some characteristics of similar substances (such as dust, water spray) was it "sees", considered to be smoke, resulting in false alarms. On the other hand, because the sensing element is exposed to the outside world in General, the more susceptible to outside influence of dust, moisture and reduce sensitivity.

B detection circuit

Detection circuit is including the sensing element, a set of circuit, the main function is to transfer the sensing element of the "information" is converted to our required voltage or current signals. When subjected to external electromagnetic interference, it will produce false alarm or alarm, or even cause damage to the device.

C communication circuits and communication lines

Communication circuits and communication line is responsible for the detection of the "information" to the fire alarm control unit, but in this process are likely to be affected by interference from false alarms. For example: detection circuit routing information from the a/d conversion into a digital signal, and then the communication circuits and communication lines to the fire alarm control unit, but may be subject to interference and signal "0" to "1" signal or low level to high level, so that the fire alarm controller receives a false information and false alarms.

3, jamming detector working interference factors, we believe there are the following:

A dust

The natural environment of destruction, chaos, factories, etc. all exhaust misplaces causing dust content in the air, and dust on fire detectors (especially the smoke detector) is a "killer". Excessive dust room stay in sampling will result in a large number of scattering of light, so that the PC components receive too many false alarms cause detector light.

B moisture

> Moisture, especially in the South of the rainy weather, humidity is usually greater than 95 per cent, which will probe the electronic panels and detection components have a great impact. First of all, will cause a short circuit electronic panels moisture damage, and secondly, when moisture into the detector detection room, on the probing components cause interference. Especially on the smoke detector, when moisture enters the detection room, a large number of scattering detector light sources emit light, resulting in false alarm detectors.

C electromagnetic fields

Fluorescent lamp ballasts, high-voltage motors, communication transmitters and other devices emit electromagnetic interference, when the detector is installed in the vicinity of these devices, more or less will be electromagnetic interference.

D high-speed airflow

When the detector is installed in a high-speed air flow position, such as ventilation and air conditioning of air near the, wind room, duct, etc; gas will smoke blown off probe detector alarm slowly.

4. improved method

In most cases, the source of interference is not excluded, therefore, we can only reduce interference point of view.

A reasonable specification for the wiring installed,

According to incomplete statistics, 70 per cent of the false alarm of fire detectors are installed because it is not reasonable. Therefore, the correct selection of the type of fire detectors, as well as in accordance with the relevant technical descriptions and specifications for proper installation and wiring is the key to reducing interference effects. For example, in the relative humidity greater than 95% RH for long-term, large amounts of dust, the usual case where there's smoke, and vapor stranded, kitchen, boiler room and generator room, tea boiler room, garage and other places is not appropriate to set the heat fire detectors, etc. In a real application that we are not difficult to find some examples of the error, such as: smoke detectors installed in electric water heater or above installed in indoor air duct, the wind. These conditions caused by false alarm rate is very high, so according to the actual location of the correct choice of fire detectors are very important.

Then there is the installation location. For example: the detector to the wall the horizontal distance beam edges should not be less than 0.5m; detector around 0.5m there should not be screened from within, and so on. If the detector is installed in an air supply and return air ducts in the room, the detector should be installed in a outlet air flow back through the path. Conduct smoke test will help determine the location of the detector is installed correctly, you need to pay special attention to the flow of smoke and the traffic path (Figure 4). When the probe must be installed near the diffuser, there will be a need to keep a certain distance. These provisions will not only ensure that probes can effectively and quickly detect fires occur, but is also an effective way to avoid interference.