消防報警和安全檢測(外文文獻翻譯)

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.火災(zāi)報警和平安檢測火災(zāi)報警電路，顧名思義，在火災(zāi)發(fā)生時發(fā)出警報。在建筑物中可以有一個 或幾個警報，并且可以有幾個報警點，激活變暖。報警點可以手動或自動操作， 在后者的情況下，他們可能是敏感的熱量，煙霧或電離。顯然有許多組合可能， 本章給出了一些系統(tǒng)的帳戶，他們建立了。幾個報警點并聯(lián)連接，當其中一個被驅(qū)動電路完成和報警聲音。這被描述

48、為 一個開路，它會被看到，它不是故障平安，因為如果有供應(yīng)失敗， 火警不能工作。 該電路的另一個特點是， 每一個報警點必須能夠承載電流全被所有的鐘聲和汽笛 一起工作。報警點串聯(lián)連接，繼電器線圈。斷電時繼電器通常閉合，線圈通電時翻開。 因此，當一個報警點被激活的繼電器線圈被解除電， 繼電器關(guān)閉和報警聲音。 該 系統(tǒng)失敗的平安程度， 如果線圈電路故障的主電路運行報警。 這不是當然平安的 供應(yīng)完全失敗， 因為在這種情況下， 沒有可用的工作鈴。 報警點不必攜帶的鐘聲 或警報器的工作電流。 這種排列被稱為閉合電路， 與開斷電路相反。 我們可以注 意到，在一個開放的電路中，報警點并聯(lián)在一起，通常是翻開的，而

49、在一個封閉 的電路，他們有線串聯(lián)，通常關(guān)閉。一個典型的手動操作火災(zāi)報警點包含在一個強大的紅色塑料外殼與玻璃蓋。 該材料選擇其耐火性能。 這種情況下， 在頂部和底部的管道條目敲出來， 但材料 可以很容易地切割為現(xiàn)場電工， 使自己在后面的入口， 如果他需要它。 當玻璃打 碎時，觸點必須在玻璃打碎時接觸， 電路必須在玻璃破裂時翻開。 在前者的情況 下，有一個測試開關(guān)，可以到達當整個前端翻開與 Allen Key 。在后者的情況下， 測試推被省略， 因為該電路是在任何情況下的故障平安型。 說明的報警點適用于 外表安裝。 類似的可用于沖洗固定和防水的版本。 觸點的電流承載能力應(yīng)始終與 制造商的目錄進行核

50、對。熱驅(qū)動報警點由一個雙金屬片偏轉(zhuǎn)，當溫度升高，從而傾斜管半滿的汞。當 管傾斜時， 水銀流入管的另一半， 在那里完成兩個先前空氣別離的觸點之間的電 路。另外，在管內(nèi)的安排可以這樣，汞打破電路時，管傾斜。報警器外殼為不銹 鋼。這種類型的熱檢測器通常設(shè)置在 65°C 工作。它們經(jīng)常用于鍋爐房。只有在特殊情況下才可使用煙霧報警器，這樣才有必要探測煙霧而不是熱 源。這種類型可以通過對少量未被火災(zāi)引起的煙霧的反響而引起警報的滋擾操 作；例如，他們知道在辦公室里由于香煙煙霧而發(fā)出警報?，F(xiàn)代的可調(diào)靈敏度， 使他們可以設(shè)置，以防止滋擾操作。電離檢測器包含一個容納一些低強度放射性材料和一對電極的腔室。

51、放射性 物質(zhì)使室中的空氣導電， 使小電流在電極間流動。 電流的大小隨氣體的性質(zhì)在腔 室中，并盡快任何燃燒。 產(chǎn)品被添加到空氣中有一個突然變化的電流流動。 探測 器也有第二個腔室， 它被永久密封， 使電流通過它永遠不會改變。 只要通過兩個 腔室的電流是相等的，沒有輸出，一旦它們變得不平衡，有一個凈輸出，這是用 來操作在主電路中的晶體管開關(guān)通過檢測器。人類是最有效的火災(zāi)探測器，只要他當時在那里。他的眼睛，耳朵和鼻子的 組合使他能夠區(qū)分各種現(xiàn)象。 他可以聞到香煙煙霧， 烤面包和一些更險惡的東西， 如燃燒紙的區(qū)別。 他可以看到煙霧和火焰， 經(jīng)常會聽到火之前， 他注意到無論是 火焰或煙霧。有時，他注意到

52、的第一件事是熱，例如，一個熱隔墻。正是這些現(xiàn) 象，火災(zāi)探測器設(shè)計者檢測火災(zāi)的發(fā)生。 這是火災(zāi)的發(fā)生是至關(guān)重要的， 非常小 的火災(zāi)可以迅速和平安地攜帶便攜式滅火器， 甚至一杯咖啡， 如果很快檢測到足 夠。顯然，火越小，觀察到的越少。因此，必須設(shè)計火災(zāi)探測器，無誤報危險。 那么今天使用什么技術(shù)來檢測這些現(xiàn)象呢？兩種技術(shù)用于檢測煙霧：光電煙霧探測器和電離煙霧探測器。光電探測器被 布置成，雖然可見光不能進入， 煙霧可以自由進入。 這種類型的探測器是基于一 個馬特黑商會大小的咖啡杯。 分隔壁放置在腔室的中間， 在其兩側(cè)位于光發(fā)射器 和光接收器上。 在正常情況下， 由于發(fā)射器不反射， 接收器的光不會被接收

53、器接 收到。當煙霧粒子進入電離室時，光會反射這些粒子，從而導致信號被接收。當 陽光進入煙霧彌漫的房間時， 也可以觀察到類似的效果。 這些光電探測器是高度 敏感和可靠的，只要煙霧顆粒是可見的。某些類別的火，但是，發(fā)射不可見的煙霧粒子早在火實際上是點燃，在這種 情況下，必須有一個電離煙霧探測器。 雖然這些探測器的設(shè)計比光電探測器的情 況稍微復(fù)雜一些， 但根本原理非常簡單。 兩個金屬板相隔幾毫米， 并在它們之間 施加電壓。由于空氣不導電，所以沒有電流。如果一個電離輻射源靠近板，那么 空氣本身被電離， 也就是說， 電荷粒子之間存在的板和這些允許一個微小的電流 流動。任何進入室內(nèi)的粒子，無論是可見的還是不可見的，都傾向于中和離子， 從而降低電流。這是電流的減少，在測量的煙霧量是目前監(jiān)測。火災(zāi)探測及其相應(yīng)的平安系統(tǒng)是智能大廈的重要組成局部。本文回憶了在智 能大廈的火災(zāi)檢測和報警