消防报警和安全检测(外文文献翻译)

1、Fire Alarms and Security DetectionA fire alarm circuit, as its name implies, sounds an alarm in the event of a fire. There can be one or several alarms throughout a building, and there can be several alarm points, which activate the warming. The alarm points can be operated manually or automatically

2、; in the latter case they may be sensitive to heat, smoke or ionization. There are clearly many combinations possible, and this chapter gives some systematic account of the way they are built up.Several alarm points are connected in parallel, and whenever one of them is actuated the circuit is compl

3、eted and the alarm sounds. This is described as an open circuit, and it will be seen that it is not fail safe, because if there is a failure of supply, the fire alarm cannot work. Another characteristic of this circuit is that every alarm point must be capable of carrying the full current taken by a

4、ll the bells or hooters working together.The alarm points are connected in series with each other and with a relay coil. The relay is normally closed when de-energized, and opens when the coil is energized. Thus when an alarm point is activated the relay coil is de- energized, the relay closes and t

5、he alarm sounds. This system fails safe to the extent that if the coil circuit fails the main circuit operates the alarm. It is not of course safe against total failure of the supply because in that event there is no supply available to work the bells. The alarm points do not have to carry the opera

6、ting current of the bells or hooters. This arrangement is called a closed circuit in contrast to the open circuit. We can notice that in an open circuit the alarm points are wired in parallel and are normally open, whilst in a closed circuit they wired in series and are normally closed.A typical man

7、ually operated fire alarm point is contained in a robust red plastic case with a glass cover. The material is chosen for its fire resisting properties. The case has knock out for conduit entries at top and bottom but the material can be sufficiently easily cut for the site electrician to make himsel

8、f an entry in the back if he needs it. Alternative terminals are provided for circuits in which the contacts have to close when the glass is smashed and for circuits in which the contacts have to open when the glass is smashed. In the former case, there is a test switch which can be reached when the

9、 whole front is opened with an Allen Key. In the latter case, the test push is omitted because the circuit is in any case of the fail safe type. The alarm point illustrated is suitable for surface mounting. Similar ones are available for flush fixing and in weatherproof versions. The current carryin

10、g capacity of the contacts should always be checked with the maker's catalogue.A thermally operated alarm point consists of a bi-metal strip that deflects when the temperature rises, and thereby tilts a tube half full of mercury. When the tube tilts the mercury flows into the other half of the t

11、ube where it completes the circuit between two contacts previously separated by air. Alternatively, the arrangement within the tube can be such that the mercury breaks the circuit when the tube is tilted. The casing of the alarm is of stainless steel. Heat detectors of this type are usually set to o

12、perate at 6E . They are frequently used in boiler houses.A smoke operated alarm point would be used only in special circumstances which make it necessary to detect smoke rather than heat. This type can cause nuisance operation of the alarm by reacting to small quantities of smoke which have not been

13、 caused by a fire; they have for example been known to sound the alarm as a result of cigarette smoke in an office. Modern ones have adjustable sensitivity so that they can be set to avoid nuisance operation.An ionization detector contains a chamber which houses some low strength radioactive materia

14、l and a pair of electrodes. The radioactive material makes the air in the chamber conductive so that a small current flows between the electrodes. The size of the current varies with the nature of the gas in the chamber and as soon as any combustion. Products are added to the air there is a sudden c

15、hange in the current flowing. The detector also has a second chamber which is permanently sealed so that the current through it never changes. As long as the currents through the two chambers are equal there is no output, as soon as they become unbalanced there is a net output which is used to opera

16、te a transistor switch in the main circuit through the detector.The human being is the most efficient fire detector, provided that he is actually there at the time. The combination of his eyes, ears and nose allows him to differentiate between various phenomena. He can smell the difference between c

17、igarette smoke, burning toast and something more sinister such as burning paper. He can see smoke and flames and will often hear a fire before he has noticed either the flames or the smoke. Sometimes, the first thing he notices is heat, for example, a hot partition wall. It is these phenomena that f

18、ire detector designers measure to detect the onset of fire. It is the onset of fire that is crucial; very small fires can be put out quickly and safely with portable fire extinguishers, or even a cup of coffee if detected soon enough. Obviously, the smaller the fire, the less it may be observed. Fir

19、e detectors must, therefore, be designed without the risk of false alarms. So what technology is used today to detect these phenomena?Two techniques are used for the detection of smoke: photoelectric smoke detectors and ionization smoke detectors. Photoelectric detectors are arranged so that, althou

20、gh visible light cannot enter, smoke can enter freely. This type of detector is based on a matt black chamber about the size of a coffee cup. A dividing wall is placed in the middle of the chamber on either side of which is located a light transmitter and a light receiver. Under normal circumstances

21、, light from the transmitter is not received by the receiver, as the chamber is not reflective. When smoke particles enter the chamber, light bounces off these particles which results in a signal being received. A similar effect can be observed when sunshine enters a smoky room. These photo-electric

22、 detectors are highly sensitive and reliable, so long as the smoke particles are visible.Certain classes of fire, however, emit invisible smoke particles long before the fire is actually alight and in these cases an ionization smoke detector must be present. Although the design of these detectors is

23、 slightly more complicated than in the case of photo-electric detectors, the basic principle is very simple. Two metal plates are separated by several millimeters and a voltage is applied across them. Since air does not conduct electricity, no current flows. If an ionizing radioactive source is brou

24、ght close to the plates then the air itself is ionized, that is, electrically charges particles are present between the plates and these allow a tiny current to flow. Any particles entering the chamber, either visible or invisible, tend to neutralize the ions, thus decreasing the current flow. It is

25、 this reduction in current which is monitored in measuring the amount of smoke that is present.Fire detection and its corresponding safety systems are crucial parts of an intelligent building. This paper reviews the current state of development of fire detection and alarm systems in the intelligent

26、building. New technologies and concepts developed in intelligent buildings, such as advanced multi-function sensors, computer vision systems and wireless sensors, real-time control via the Internet, and integrated building service systems, have also been reviewed and discussed. These new technologie

27、s and concepts will improve the capability of fire detection systems to discriminate between fire and non-fire threats and will increase the time available for property and life protection. However, much effort is still needed to remove barriers to the further development of these new technologies.N

28、ew sensor technologies will be key components in the next generation of intelligent buildings. Current intelligent buildings often have embedded processors and dedicated information networks. The new generation is expected to add the capability to learn about the buildings circumstances and its occu

29、pants needs and change the behavior of its control systems accordingly. The employment of a large number of sensors within the building will allow it to operate in a responsive manner, rather than using pre-programmed control models as are employed in the first two generations of intelligent buildin

30、g. The information provided by sensors includes changes in both internal and external environments of a building, such as smoke, temperature and humidity, air quality, air movement, and the number of building occupants as well as a host of other properties. The system will use sensors to identify ho

31、w a particular person tends to react to particular circumstances and to learn different behaviors for different people. The number of sensors required to obtain this type of functionality is quite high, especially since one of the major goals of intelligent buildings is to allow individualized contr

32、ol of an environment. This need will increase the cost of intelligent buildings and make it difficult to manage the resulting large amount of data. Development of cost-effective sensors has consequently been identified as a key need for intelligent buildings. Fortunately, many of the properties that

33、 need to be monitored can be used for multiple purposes. Security systems that can track the entry and exit of occupants from an office building can also be used to ensure complete evacuation of a building during a fire or even, in more advanced forms, determine where occupants may be trapped and un

34、able to escape. Similarly, parameters such as temperature and air movement are as relevant to fire detection as the maintenance of the indoor working environment. Dual use sensorsand sensor systems that are flexible enough to interpret data from different events will be key to making cost efficient

35、intelligent buildings. Efforts are being made to develop multi-function sensors for simultaneously detecting fire and monitoring indoor air quality (IAQ). Multi-function sensors that combine inputs from several different chemicals or physical processes would be expected to reduce the rate of false a

36、larms and increase the speed of detection of real problems. They should therefore enhance fire safety while at the same time lowering total system costs. The chemical gas sensor has potential for this type of application. Chemical sensor techniques are now available for measuring almost any stable g

37、aseous species emitted from materials and prior to or during combustion. Chemical species can be sensed through a multitude of interactions, including catalytic, electrochemical, mechanic-chemical, and optical processes. In one square inch, several hundred individual sensors can be placed in an arra

38、y. By coating each sensor with a different semi-conducting material, several hundred different readings for gas signatures can be made by an expert system. Recently, one olfactory sensor array system has been developed for environmental monitoring and for fire and smoke detection.Heat detectorsTwo t

39、ypes of technology are used. First, mechanical heat detectors rely on expanding solids, liquids and gases to close a switch; secondly, electronic detectors use a thermistor to measure the actual temperature. Furthermore, there are two variants: fixed temperature detectors which simply produce an out

40、put when the temperature exceeds a predetermined level and rate of rise detectors that provide an output when the rate of rise in temperature exceeds a pre-defined limit. However, rate of rise detectors invariably have an upper temperature limit at which they will provide output regardless of the ra

41、te of rise function.Flame detectorsFlame detectors look for characteristic emissions of either infrared or ultra-violet light from the flames. This type of detection is particularly useful for fires caused by volatile fuels, for example, gas and petroleum spirit. With the aid of these detectors the

42、fire detection industry is able to move some way towards simulating the ability of the human to detect a fire. It may not be as good as the human, but it is available 24 hours a day and 365 days a year, at a very reasonable cost.Intruder detectionThere is a far wider range of intruder detectors avai

43、lable than is the case for fire detectors. It is necessary to thwart the intelligent criminal whose ingenuity knows no bounds: if they can get round it, they will. The simplest intruder detectors are basically switches operated from such disturbances as opening doors, walking on pressure mats, cutti

44、ng essential wires etc. In these detectors, the skill is in the mechanical design. For obvious reasons, it is not possible to discuss the operation of intruder detectors in great detail here.In addition to simple contacts a wide range of movement/presence detectors are available. The most common of

45、these is the passive infra-red (PIR) detector which can detect the heat of a human body against the natural ambient temperature. This is no mean heat considering the human body is at 37 degrees centigrade and that is the internal body temperature, let alone skin temperature. With outdoors clothing t

46、he target may not only be some 0.5-1 degrees above the ambient. Other active systems are available, such as microwave and ultrasonic. Both of these techniques depend upon the transmission of a signal which is reflected from any moving object in range. Movement alters the frequency of the received si

47、gnal (the Doppler Effect) and it is the difference between the transmitted and received signals which indicates the speed of movement.火灾报警和平安检测火灾报警电路，顾名思义，在火灾发生时发出警报。在建筑物中可以有一个 或几个警报，并且可以有几个报警点，激活变暖。报警点可以手动或自动操作， 在后者的情况下，他们可能是敏感的热量，烟雾或电离。显然有许多组合可能， 本章给出了一些系统的帐户，他们建立了。几个报警点并联连接，当其中一个被驱动电路完成和报警声音。这被描述

48、为 一个开路，它会被看到，它不是故障平安，因为如果有供应失败， 火警不能工作。 该电路的另一个特点是， 每一个报警点必须能够承载电流全被所有的钟声和汽笛 一起工作。报警点串联连接，继电器线圈。断电时继电器通常闭合，线圈通电时翻开。 因此，当一个报警点被激活的继电器线圈被解除电， 继电器关闭和报警声音。 该 系统失败的平安程度， 如果线圈电路故障的主电路运行报警。 这不是当然平安的 供应完全失败， 因为在这种情况下， 没有可用的工作铃。 报警点不必携带的钟声 或警报器的工作电流。 这种排列被称为闭合电路， 与开断电路相反。 我们可以注 意到，在一个开放的电路中，报警点并联在一起，通常是翻开的，而

49、在一个封闭 的电路，他们有线串联，通常关闭。一个典型的手动操作火灾报警点包含在一个强大的红色塑料外壳与玻璃盖。 该材料选择其耐火性能。 这种情况下， 在顶部和底部的管道条目敲出来， 但材料 可以很容易地切割为现场电工， 使自己在后面的入口， 如果他需要它。 当玻璃打 碎时，触点必须在玻璃打碎时接触， 电路必须在玻璃破裂时翻开。 在前者的情况 下，有一个测试开关，可以到达当整个前端翻开与 Allen Key 。在后者的情况下， 测试推被省略， 因为该电路是在任何情况下的故障平安型。 说明的报警点适用于 外表安装。 类似的可用于冲洗固定和防水的版本。 触点的电流承载能力应始终与 制造商的目录进行核

50、对。热驱动报警点由一个双金属片偏转，当温度升高，从而倾斜管半满的汞。当 管倾斜时， 水银流入管的另一半， 在那里完成两个先前空气别离的触点之间的电 路。另外，在管内的安排可以这样，汞打破电路时，管倾斜。报警器外壳为不锈 钢。这种类型的热检测器通常设置在 65°C 工作。它们经常用于锅炉房。只有在特殊情况下才可使用烟雾报警器，这样才有必要探测烟雾而不是热 源。这种类型可以通过对少量未被火灾引起的烟雾的反响而引起警报的滋扰操 作；例如，他们知道在办公室里由于香烟烟雾而发出警报。现代的可调灵敏度， 使他们可以设置，以防止滋扰操作。电离检测器包含一个容纳一些低强度放射性材料和一对电极的腔室。

51、放射性 物质使室中的空气导电， 使小电流在电极间流动。 电流的大小随气体的性质在腔 室中，并尽快任何燃烧。 产品被添加到空气中有一个突然变化的电流流动。 探测 器也有第二个腔室， 它被永久密封， 使电流通过它永远不会改变。 只要通过两个 腔室的电流是相等的，没有输出，一旦它们变得不平衡，有一个净输出，这是用 来操作在主电路中的晶体管开关通过检测器。人类是最有效的火灾探测器，只要他当时在那里。他的眼睛，耳朵和鼻子的 组合使他能够区分各种现象。 他可以闻到香烟烟雾， 烤面包和一些更险恶的东西， 如燃烧纸的区别。 他可以看到烟雾和火焰， 经常会听到火之前， 他注意到无论是 火焰或烟雾。有时，他注意到

52、的第一件事是热，例如，一个热隔墙。正是这些现 象，火灾探测器设计者检测火灾的发生。 这是火灾的发生是至关重要的， 非常小 的火灾可以迅速和平安地携带便携式灭火器， 甚至一杯咖啡， 如果很快检测到足 够。显然，火越小，观察到的越少。因此，必须设计火灾探测器，无误报危险。 那么今天使用什么技术来检测这些现象呢？两种技术用于检测烟雾：光电烟雾探测器和电离烟雾探测器。光电探测器被 布置成，虽然可见光不能进入， 烟雾可以自由进入。 这种类型的探测器是基于一 个马特黑商会大小的咖啡杯。 分隔壁放置在腔室的中间， 在其两侧位于光发射器 和光接收器上。 在正常情况下， 由于发射器不反射， 接收器的光不会被接收

53、器接 收到。当烟雾粒子进入电离室时，光会反射这些粒子，从而导致信号被接收。当 阳光进入烟雾弥漫的房间时， 也可以观察到类似的效果。 这些光电探测器是高度 敏感和可靠的，只要烟雾颗粒是可见的。某些类别的火，但是，发射不可见的烟雾粒子早在火实际上是点燃，在这种 情况下，必须有一个电离烟雾探测器。 虽然这些探测器的设计比光电探测器的情 况稍微复杂一些， 但根本原理非常简单。 两个金属板相隔几毫米， 并在它们之间 施加电压。由于空气不导电，所以没有电流。如果一个电离辐射源靠近板，那么 空气本身被电离， 也就是说， 电荷粒子之间存在的板和这些允许一个微小的电流 流动。任何进入室内的粒子，无论是可见的还是不可见的，都倾向于中和离子， 从而降低电流。这是电流的减少，在测量的烟雾量是目前监测。火灾探测及其相应的平安系统是智能大厦的重要组成局部。本文回忆了在智 能大厦的火灾检测和报警