外文翻譯---液位檢測(cè)

1、<p><b>　　附錄C</b></p><p>　　Liquid Level Measurement</p><p>　　Chemical industry with the progress of science and technology got rapid development, in order to make the equipment s

2、afe and reliable operation, and can be utmost to improve product quantity and quality, to effectively operate automatically and process adjustment, realize the scientific management for the enterprise to provide the nece

3、ssary material and energy of accurate data, must be in production in the process of pressure, flow, level, temperature, chemical composition of various parameters </p><p>　　Generally the process of container

4、s, tanks, towers, tank of liquid surface position level, slot bucket, cans, and warehouse ChuFa solid block, the accumulation of particles, powder height and surface position is called a material level; Two not fluid bou

5、ndary between the height and the liquid and solid separation height is called interface position, the position of assembly level, material level, liquid level interface.</p><p>　　Material level measurement t

6、o correctly measure the container storage capacity or quality, know container level of high and low and adjust at any time, in the material level to maintain the required height.</p><p>　　Material level meas

7、urement in chemical process, not only under normal temperature, atmospheric pressure and ordinary medium, material level, liquid level measurement of the interface, but also often meet high temperature, low temperature,

8、high pressure, inflammable and explosive (negative temperature). Viscosity and foam, boiling dielectric material level measurement problems.</p><p>　　In order to adapt to the characteristics of chemical obje

9、cts, to meet the requirements of the chemical process material level measurement, there are many material level measurement and instrumentation.</p><p>　　1. Ultrasonic liquid level meter and radar material l

10、evel meter</p><p>　　(1) ultrasonic liquid level meter</p><p>　　Material level measurement process, the ultrasonic signal, issued by the ultrasonic probe, the liquid or solid material surface aft

11、er launch back, by the same sensor receiving, ultrasonic measurement of the whole running time, so as to realize the measurement of material level, acoustic velocity transmission of the ultrasonic pulse, from transmittin

12、g to receiving to ultrasonic pulse need time interval and the transducer to the surface of the measured medium is proportional to the distance.</p><p>　　Emit ultrasonic level meter pulse, not the echo of det

13、ection at the same time. Due to the launch of the ultrasonic pulse width has a certain time, and after launch the ultrasonic sensor and aftershocks, during cannot detect the echo, so from the start down the surface of th

14、e probe a short distance can't normal inspection, this distance is called blind spots. Was the highest level such as into the blind area, detect instrument will not be able to correctly, there will be error, if neces

15、sary, heig</p><p>　　Ultrasonic liquid level meter also has shortcomings, the ultrasonic transmission by gas interference, level surface bubbles, corrugated, etc, the ultrasonic transmission by gas interferen

16、ce, level surface bubbles, corrugated, etc., the ultrasonic reflection effect. Material is volatile, liquid gas entrapment, the container by vibration (e.g., motors) are installed on the container can't use ultrasoni

17、c liquid level meter.</p><p>　　(2) radar material level meter</p><p>　　Radar level gauge USES launch - reflection - receive work mode. Radar level meter antenna emit electromagnetic wave, the wa

18、ve reflected by the measured object surface, again by the antenna, the electromagnetic wave from transmitting to receiving time is proportional to the distance to the liquid surface. In practice, there are two kinds of r

19、adar level gauge means the frequency modulation continuous wave and pulse wave. Liquid level meter adopts frequency modulation wave technology, power consump</p><p>　　Radar level gauge measuring the electrom

20、agnetic waves can pass through a vacuum, don't need a transmission medium, is not affected by air, steam, groove volatile fog effect, can be used for such as coarse benzene volatile medium level measurement.</p>

21、;<p>　　Radar level meter can be used for almost all of the liquid level measurement. Electromagnetic wave on the surface level when firing, signal attenuation, when the signal attenuation through the hours, can le

22、ad to radar level meter cannot detect enough electromagnetic wave signal, the conductive medium can be a very good reflection of electromagnetic wave, the dielectric constant is greater than 1.5 non conductive medium die

23、lectric constant was 1.0 (air) will also be able to guarantee sufficient r</p><p>　　(3) radar level gauge, ultrasonic liquid level meter</p><p>　　Ultrasound and radar is the main measuring princ

24、iple is different, lead to their different application occasions, radar is given that the dielectric constant of the measured substance, which is given that the density of the material being measured, so the low dielectr

25、ic constant material radar measurements will be effect to sell at a discount greatly, the solid matter in general, push harder, another wave of different means of transmission components, such as ultrasonic wave was laun

26、ched by the </p><p>　　Level two categories, including liquid level and material level. Liquid level and liquid level indicator and two continuous level measurement. Liquid level indicator is the level of sev

27、eral fixed position measuring, used in liquid level of upper and lower limit alarm, etc. Continuous level measurement is to measure liquid level continuously, it is widely used in many fields such as petroleum, chemical

28、industry, food processing, have very important significance. For more than 20 kinds of continuo</p><p>　　Manual gauging glass tube method: this method is using the principle of communicating vessels, level s

29、cale read directly from the instructions. Glass plate method: glass which can be installed through connectors can also be installed in the container wall openings, and series a few piece of glass to increase the range. N

30、umerical scale read directly from the glass plate level.</p><p>　　Double color gauge method: this method using the optical principle, make water shows green, and make the water vapor shows red, which indicat

31、e the water level.</p><p>　　Artificial gauging method: the method is used for measuring oil tank liquid level. When measuring, the surveyor gauge Surveyor to volume of the oil dipstick into oil, and filed wh

32、en feet lead contact with the tank bottom oil dipstick. According to the quantity of oil traces on the oil dipstick, read out the oil level height; End according to the quantity of oil dipstick test cream color change to

33、 determine the height of the water cushion layer, to determine high oil and high water above 4 method</p><p>　　Blowing method, differential method, HTG blowing method: because of the blow pipe approximation

34、is equal to the fluid column pressure in the static pressure, thus P = rho gH type of rho - liquid density; H - level. So the liquid level is measured by the static pressure P can be H. Strong method suitable for measuri

35、ng the corrosive gas blowing, have suspended material content in the liquid, and is mainly used in the measurement accuracy is not high.</p><p>　　Differential pressure method: the open container or atmospher

36、ic vessels, valves and gas phase pressure pipeline saves. Based on the relationship between differential pressure and liquid level Δ P = P2 - P1 = rho gH type: Δ P - positive and negative pressure chamber pressure transm

37、itter; P2 and P1 - led tube pressure; H - level. Differential pressure transmitter will pressure difference transformation for 4 ~ 20 mA dc signal. If the pressure in the measuring range lower limit of the corresponding&

38、lt;/p><p>　　Buoy method: this method USES the middle maglev barrel with holes as liquid level sensor. Stainless steel casing from buoy hole through the middle, between fixed to the roof and bottom. Liquid level

39、 change driven maglev hollow tube (permanent magnet) hides inside can move up and down the casing, and attract the casing of magnet can move up and down the casing wall, secondary instrument | instrument according to the

40、 moving magnet volume to calculate the liquid level.</p><p>　　Floating ball method: this method is using the lever principle of work. Floating ball with liquid level change and around the axis of rotation, t

41、he pointer on the drive shaft rotation, and at the other end of the lever balance weight balance, at the same time indicates the level value on the dial. Floating ball method have ball float within and outside the floati

42、ng ball type two kinds. Floating ball method is mainly used for high temperature measurement, the viscosity of the liquid level, but th</p><p>　　Servo method: this method USES volatile integral circuit, elim

43、inate jitter, prolong life, improve the precision of level measurement. The modern servo liquid meter measuring accuracy is higher, has 40 m range less than the accuracy of 1 mm, and generally has the function of measuri

44、ng density distribution and average density.</p><p>　　Sinking method: the location of the sinking as the change of liquid level change, but the variation is not equal and level variation. Torque tube sinking

45、 method: the torque tube core shaft torsional Angle changes, secondary instrument according to the torsional Angle variation to calculate the liquid level above five kinds of methods are using the buoyancy principle to w

46、ork.</p><p>　　Such as R, R, l, is a fixed value, as long as the use of epsilon 1, epsilon 2, CH can calculate the liquid level H. Measurement of conductive liquid capacitance method principle, the formula is

47、 slightly. Capacitive liquid level meter price is low, easy to install and can be applied to occasions of high temperature and high pressure. Capacitive liquid level instrument measurements but repetitive accuracy is low

48、, need regular maintenance and calibration again, working life is not very long.</p><p>　　This method is especially suitable for the measurement of conductive liquid, sensitive device resistance characterist

49、ics, its resistance along with the change of liquid level change, so the resistance value is transmitted to the secondary circuit level. Electrical parameters of the liquid level sensor method to measure the liquid level

50、 changes.</p><p>　　Magnetostrictive method, ultrasonic method, modulating optical method, microwave method Magnetostrictive method: the method is used for measuring oil tank liquid level has two float, respe

51、ctively used to detect oil and gas and oil/water interface. Each float in possession of a set of permanent magnets, used to generate a fixed magnetic field. Measurement, level gauge head emit low "enquiry" puls

52、e current, the magnetic field generated from the current conduction down the waveguide. When electric </p><p>　　Ultrasonic method: antenna (mostly aperture antenna, also has a planar antenna) radiation, afte

53、r liquid surface reflection is the antenna, and then calculated by the secondary circuit, transmitting and receiving signals of liquid level difference. The liquid level meter adopts triangle wave form of frequency modul

54、ation, and through to the transmitting and receiving signal mixing after get the difference between the signal analysis, microwave transmission time, thus calculate the liquid level. Mi</p><p>　　Radar level

55、gauge is particularly suited to high pollution and high viscosity of the product, such as asphalt, etc. Repeat accuracy of radar level gauge measuring is higher, need regular maintenance and calibration, measurement accu

56、racy is higher, but the price is higher, difficult measurement of oil-water interface.</p><p>　　Modulating optical method and microwave method is similar, only by phase or frequency modulation of optical sig

57、nal instead of microwave signal. But light signals are greatly influenced by steam, oil, steam, and the liquid level fluctuation is very sensitive。</p><p>　　All three methods above is through testing to dete

58、rmine the level of the signal propagation time. Sets the time of transmitting and receiving signals to t, h = n / 2 is empty, v for wave propagation speed.</p><p>　　6 magnetic flap method, the vibration meth

59、od, radiation method, optical fiber sensors method</p><p>　　Magnetic flap method principle: float is equipped with a set of permanent magnets, with the liquid level change and move up and down, flip through

60、magnetic coupling driving magnetic flap components. When the liquid level goes up, the magnetic flap of red face outwards; When liquid level drops, white facing out. Therefore, according to the color of the magnetic flap

61、 determined level. Within the float magnet with magnetic flap magnetic structure is 10 mm, the distance between each frame. Adopt sev</p><p>　　Servo control vibration hammer to climb up and down motion and v

62、ibration, vibration free vibration after vibration sensor detection, the detection signal after FET transform to get the frequency of the maximum power point, finally by the empty cans inherent frequency/liquid level of

63、the liquid level relation. This method of level measurement need to shock hammer, servo mechanical moving parts, such as its working life is not too long, should be regular maintenance and calibration, installation i<

64、/p><p>　　Radiation method: radioactive isotope in the process of decay radiation, common rays are alpha, beta, and gamma rays. Among them, the gamma rays of the strong penetrating power, range far, therefore, w

65、idely used in the radiation level measurement. Gamma-ray intensity before and after the experiment, through the material change.</p><p><b>　　液位檢測(cè)</b></p><p>　　化學(xué)工業(yè)隨著科學(xué)技術(shù)的進(jìn)步得到了迅速發(fā)展，為了

66、能使設(shè)備安全可靠的運(yùn)行，并能最大限度的提高產(chǎn)品的數(shù)量和質(zhì)量，對(duì)生產(chǎn)過(guò)程有效的進(jìn)行操作會(huì)和自動(dòng)調(diào)節(jié)，為企業(yè)實(shí)現(xiàn)科學(xué)管理提供必要的物料和能量的準(zhǔn)確數(shù)據(jù)，就必須對(duì)生產(chǎn)過(guò)程中的壓力、流量、物位、溫度、化學(xué)成分得等各種參數(shù)進(jìn)行及時(shí)、準(zhǔn)確的測(cè)量。</p><p>　　一般把工藝過(guò)程中的罐、塔、槽等容器存在的液體表面位置叫液位，槽斗、罐、倉(cāng)庫(kù)等所儲(chǔ)發(fā)固體塊、顆粒、粉料的堆積高度和表面位置叫做料位；二種不容液體的分界高度以及液體

67、與固體間的分界高度叫做界面位置，液位、料位、界面位置總成物位。</p><p>　　物位測(cè)量的目的在于正確地測(cè)知容器中儲(chǔ)藏物質(zhì)的容量或質(zhì)量，隨時(shí)知道容器物位的高低和調(diào)節(jié)，在物位保持在所要求的高度。</p><p>　　在化工過(guò)程的物位測(cè)量中，不僅有常溫、常壓，一般性介質(zhì)的液位、料位、界面的測(cè)量，而且還常常會(huì)遇到高溫、低溫（負(fù)溫）、高壓、易燃易爆。粘性及多泡沫、沸騰狀介質(zhì)的物位測(cè)量問(wèn)題。&l

68、t;/p><p>　　為適應(yīng)化工對(duì)象的特點(diǎn)，滿足化工過(guò)程物位測(cè)量的要求，目前已有許多測(cè)量物位的方法和儀表。</p><p>　　超聲波液位計(jì)、雷達(dá)物位計(jì)</p><p><b>　　超聲波液位計(jì)</b></p><p>　　物位測(cè)量過(guò)程中，超聲波信號(hào)，由超聲波探頭發(fā)出，經(jīng)液體或固體物料表面發(fā)射后折回，由同一個(gè)探頭接收，測(cè)量超

69、聲波的整個(gè)運(yùn)行時(shí)間，從而實(shí)現(xiàn)物位的測(cè)量，超聲波脈沖以聲波速度傳播，從發(fā)射到接收到超聲波脈沖所需要時(shí)間間隔與換能器到被測(cè)介質(zhì)表面的距離成正比。</p><p>　　物位計(jì)發(fā)射超聲波脈沖時(shí)，不能同時(shí)檢測(cè)反射回波。由于發(fā)射的超聲波脈沖具有一定的時(shí)間寬度，同時(shí)發(fā)射完超聲波后傳感器還有余震，期間不能檢測(cè)反射回波，因此從探頭表面向下開(kāi)始的一小段距離無(wú)法正常檢測(cè)，這段距離稱為盲區(qū)。被測(cè)的最高物位如進(jìn)入盲區(qū)，儀表將不能正確檢測(cè)，

70、會(huì)出現(xiàn)誤差，如有需要，可以將物位計(jì)加高安裝。</p><p>　　超聲波液位計(jì)也有不足之處，超聲波的傳輸受氣體干擾，物位表面有氣泡，波紋等不平，超聲波的傳輸受氣體干擾，物位表面有氣泡、波紋等不平，超聲波的反射效果大打折扣。物料有揮發(fā)、液夾氣時(shí)，容器上由震動(dòng)（如容器上安裝有電機(jī)）不能選用超聲波液位計(jì)。</p><p><b>　　雷達(dá)物位計(jì)</b></p>

71、<p>　　雷達(dá)液位計(jì)采用發(fā)射-反射-接收的工作模式。雷達(dá)液位計(jì)的天線發(fā)射出電磁波，這些波經(jīng)被測(cè)對(duì)象表面反射后，再被天線接收，電磁波從發(fā)射到接收的時(shí)間與到液面的距離成正比。在實(shí)際運(yùn)用中，雷達(dá)液位計(jì)有兩種方式即調(diào)頻連續(xù)波式和脈沖波式。采用調(diào)頻波技術(shù)的液位計(jì)，功耗大，須采用四線制，電子電路復(fù)雜。而采用雷達(dá)脈沖波技術(shù)的液位計(jì)，功耗低，容易實(shí)現(xiàn)本質(zhì)安全，精確度高，適用范圍更廣。</p><p>　　雷達(dá)液位計(jì)

72、測(cè)量時(shí)發(fā)出的電磁波能夠穿過(guò)真空，不需要傳輸媒介，具有不受大氣，蒸汽、槽內(nèi)揮發(fā)霧影響的特點(diǎn)，能用于揮發(fā)的介質(zhì)如粗苯的液位測(cè)量。</p><p>　　雷達(dá)液位計(jì)幾乎能用于所有的液體的液位測(cè)量。電磁波在液位表面發(fā)射時(shí)，信號(hào)會(huì)衰減，當(dāng)信號(hào)衰減過(guò)小時(shí)，會(huì)導(dǎo)致雷達(dá)液位計(jì)無(wú)法測(cè)到足夠的電磁波信號(hào)，導(dǎo)電介質(zhì)能很好的反射電磁波，介電常數(shù)大于1.5的非導(dǎo)電介質(zhì)（空氣的介電常數(shù)為1.0）也能夠保證足夠的反射波，介電常數(shù)越大，反射信號(hào)越

73、強(qiáng)。在實(shí)際應(yīng)用中，幾乎所有的介質(zhì)都能反射足夠的反射波。</p><p>　　雷達(dá)液位計(jì)和超聲波液位計(jì)比較</p><p>　　超聲波和雷達(dá)主要的是測(cè)量原理的不同，而導(dǎo)致他們的不同的運(yùn)用場(chǎng)合，雷達(dá)是鑒于被測(cè)物質(zhì)的介電常數(shù)的，而超聲波是鑒于被測(cè)物質(zhì)的密度的，所以介電常數(shù)很低的物質(zhì)雷達(dá)的測(cè)量效果就要打折扣，對(duì)于固體物質(zhì)一般也推難，另外波的發(fā)射方式元件不同，如超聲波是通過(guò)壓電物質(zhì)的震動(dòng)來(lái)發(fā)射的，所

74、以它不可能用在壓力比較高或負(fù)壓的場(chǎng)合，一般只用在常壓容器。而雷達(dá)可以用在高壓的過(guò)程罐。雷達(dá)的發(fā)射角度比超聲波大，小容器或瘦長(zhǎng)的容器不推薦用非接觸式雷達(dá)，一般推薦導(dǎo)播雷達(dá)。最后就是精度上的溫度，當(dāng)然了，雷達(dá)肯定比超聲波高，在儲(chǔ)罐上肯定用高精度雷達(dá)的，而不會(huì)選超聲波。至于價(jià)格方面，一般情況下超聲波比雷達(dá)低，當(dāng)然一些大量程的超聲波價(jià)格也是很高的。如6-70米的量程，首選超聲波液位計(jì)。注意槽內(nèi)的攪拌，槽壁的粘附物會(huì)產(chǎn)生干擾的反射波，影響液位測(cè)量

75、，在安裝是要選擇合適的安裝位置，以避免這些因素的干擾。</p><p>　　物位包括液位和料位兩類。液位又包括液位信號(hào)器和連續(xù)液位測(cè)量?jī)煞N。液位信號(hào)器是對(duì)幾個(gè)固定位置的液位進(jìn)行測(cè)量，用于液位的上、下限報(bào)警等。連續(xù)液位測(cè)量是對(duì)液位連續(xù)地進(jìn)行測(cè)量，它廣泛地應(yīng)用于石油、化工、食品加工等諸多領(lǐng)域，具有非常重要的意義。對(duì)20余種連續(xù)液位測(cè)量方法進(jìn)行比較分析。玻璃管法、玻璃板法、雙色水位法。</p><p

76、>　　人工檢尺法玻璃管法：該方法利用連通器原理工作，液位直接從指示標(biāo)度尺讀出。玻璃板法：玻璃板可通過(guò)連通器安裝，也可在容器壁上開(kāi)孔安裝，并可串聯(lián)幾段玻璃板以增大量程。液位數(shù)值直接從玻璃板刻度尺讀出。</p><p>　　雙色水位計(jì)法：該方法利用光學(xué)原理，使水顯示綠色，而使水蒸汽顯示紅色，從而指示出水位。</p><p>　　人工檢尺法：該方法用于測(cè)量油罐液位。測(cè)量時(shí)，測(cè)量員把量油尺投

77、入油品中，并在尺砣與罐底接觸時(shí)提起量油尺。根據(jù)量油尺上的油品痕跡，讀出油面高度；根據(jù)量油尺末端試水膏顏色的變化確定水墊層的高度，從而確定油高和水高以上4種方法都是人工測(cè)量方法，具有測(cè)量簡(jiǎn)單、可靠性高、直觀、成本低的優(yōu)點(diǎn)。</p><p>　　吹氣法、差壓法、HTG法吹氣法：因吹氣管內(nèi)壓力近似等于液柱的靜壓力，故P＝ρgH  式中，ρ－液體密度；H－液位。故由靜壓力P即可測(cè)量液位H。吹氣法適用于測(cè)量腐蝕性

78、強(qiáng)、有懸濁物的液體，主要應(yīng)用在測(cè)量精度要求不高的場(chǎng)合。</p><p>　　差壓法：對(duì)于開(kāi)口容器或常壓容器，閥門(mén)及氣相引壓管道可以省掉。壓力差與液位的關(guān)系為ΔP＝P2－P1＝ρgH  式中：ΔP－變送器正、負(fù)壓室壓力差；P2、P1－引壓管壓力；H－液位。差壓變送器將壓力差變換為4～20 mA的直流信號(hào)。如果壓力處于測(cè)量范圍下限時(shí)對(duì)應(yīng)的輸出信號(hào)大于或小于4 mA，則都需要采用調(diào)整遷移彈

79、簧等零點(diǎn)遷移技術(shù)，使之等于4 mA。HTG法：該方法應(yīng)用于油罐差壓液位測(cè)量中。</p><p>　　浮筒法：該方法采用中間帶孔的磁浮筒作為液位敏感元件。不銹鋼套管從浮筒中間孔穿過(guò)，固定在罐頂和罐底之間。液位變化帶動(dòng)空心磁浮筒（內(nèi)藏永久磁鐵）沿套管上下移動(dòng)，并吸引套管內(nèi)的磁鐵沿套管內(nèi)壁上下移動(dòng)，二次儀器|儀表根據(jù)磁鐵的移動(dòng)量計(jì)算出液位。</p><p>　　浮球法：該方法利用杠桿原

80、理工作。浮球跟隨液位變化而繞轉(zhuǎn)軸旋轉(zhuǎn)，帶動(dòng)轉(zhuǎn)軸上的指針轉(zhuǎn)動(dòng)，并與杠桿另一端的平衡重平衡，同時(shí)在刻度盤(pán)上指示出液位數(shù)值。浮球法有內(nèi)浮球式和外浮球式兩種。浮球法主要用于測(cè)量溫度高、粘度大的液位，但量程較小。</p><p>　　伺服法：該方法采用波動(dòng)積分電路，消除抖動(dòng)、延長(zhǎng)壽命、提高液位測(cè)量精度?，F(xiàn)代伺服液位儀的測(cè)量精度較高，已達(dá)到40 m量程內(nèi)小于1 mm的精度，且一般都具有測(cè)量密度分布和平均密

81、度的功能。</p><p>　　沉筒法：沉筒的位置隨著液位的變化而變化，但其變化量并不與液位變化量相等。扭力管式沉筒法：扭力管芯軸的扭角發(fā)生變化，二次儀表根據(jù)扭角的變化量計(jì)算出液位　以上5種方法都是利用浮力原理來(lái)工作的。 電容法、電容傳感器浸入液體的深度（m）；l－電容傳感器垂直高度（m）；R－內(nèi)極板圓柱底面半徑（m）；r－外極板圓柱底面半徑（m）。由于R、r、l等都是固定值，只要利用ε1、ε2、CH就

82、能計(jì)算出液位H。測(cè)量導(dǎo)電液體的電容法原理，其公式推導(dǎo)略。電容式液位儀價(jià)格較低，安裝容易，且可以應(yīng)用于高溫、高壓的場(chǎng)合。但電容液位儀測(cè)量重復(fù)精度較低，需定期維修和重新標(biāo)定，工作壽命也不是很長(zhǎng)。</p><p>　　電阻法：該方法特別適用于導(dǎo)電液體的測(cè)量，敏感器件具有電阻特性，其電阻值隨液位的變化而變化，故將電阻變化值傳送給二次電路即得到液位。液位傳感器的電參數(shù)產(chǎn)生變化的方法來(lái)測(cè)量液位的。 磁致伸縮法、超聲

83、波法、調(diào)制型光學(xué)法、微波法　　磁致伸縮法：該方法用于測(cè)量油罐液位中有兩個(gè)浮子，分別用來(lái)檢測(cè)油氣界面和油水界面。各浮子內(nèi)都藏有一組永久磁鐵，用來(lái)產(chǎn)生固定磁場(chǎng)。測(cè)量時(shí)，液位計(jì)頭部發(fā)出低電流“詢問(wèn)”脈沖，該電流產(chǎn)生的磁場(chǎng)沿波導(dǎo)管向下傳導(dǎo)。當(dāng)電流磁場(chǎng)與浮子磁場(chǎng)相遇時(shí)，產(chǎn)生“返回”脈沖（也稱“波導(dǎo)扭曲”脈沖）。詢問(wèn)脈沖與返回脈沖之間的時(shí)間差即對(duì)應(yīng)油水界面和油氣界面的高度。磁致伸縮液位計(jì)安裝容易，測(cè)量精度很高，但液體密度變化和溫度變化會(huì)帶來(lái)測(cè)量誤

84、差，浮子沿著波導(dǎo)管外的護(hù)導(dǎo)管上下移動(dòng)，容易被卡死。</p><p>　　超聲波法：天線（大多為口徑天線，也有平面天線）輻射出去，經(jīng)液面反射后被天線接收，然后由二次電路計(jì)算發(fā)射信號(hào)與接收信號(hào)的時(shí)間差得液位。該液位儀采用三角波頻率調(diào)制形式，并通過(guò)對(duì)發(fā)射信號(hào)與接收信號(hào)混頻后得到的差額信號(hào)的分析，得到微波傳輸時(shí)間，從而計(jì)算出液位。微波速度受傳播介質(zhì)、溫度、壓力、液體介電常數(shù)的影響很小，但液體界面的波動(dòng)、液體表面的泡沫、液

85、體介質(zhì)的介電常數(shù)對(duì)微波反射信號(hào)強(qiáng)弱有很大影響。當(dāng)壓力超過(guò)規(guī)定數(shù)值時(shí)，壓力對(duì)液位測(cè)量精度將產(chǎn)生顯著影響。對(duì)于介電常數(shù)小于規(guī)定數(shù)值的液體，大部分雷達(dá)液位儀都需要采用波導(dǎo)管，但波導(dǎo)管的銹蝕、彎曲和傾斜都會(huì)影響測(cè)量精度。例如：當(dāng)空高h(yuǎn)為20 m，導(dǎo)波管與垂直方向傾斜角度α只要超過(guò)0．573°，則引起的液位誤差Δh將超過(guò)1 mm，由此證明，在傾斜角度α（單位為度）較小時(shí)，Δh滿足：</p><p>　　雷達(dá)液位儀

86、特別適合于高污染度或高粘度的產(chǎn)品，如瀝青等。雷達(dá)液位儀測(cè)量的重復(fù)精度較高，無(wú)須定期維修和重新標(biāo)定，測(cè)量精度也較高，但價(jià)格較高，測(cè)量油水界面困難?！　≌{(diào)制型光學(xué)法與微波法類似，只是采用相位或頻率調(diào)制的光信號(hào)代替微波信號(hào)。但光信號(hào)受水蒸汽、油蒸汽影響較大，并對(duì)液面波動(dòng)很敏感，且必須采用易受污染的光學(xué)鏡頭。</p><p>　　以上3種方法都是通過(guò)檢測(cè)信號(hào)傳播的時(shí)間來(lái)確定液位的。設(shè)發(fā)射信號(hào)與接收信號(hào)的時(shí)間差為t，則空

87、高h(yuǎn)＝vt／2，v為波的傳播速度。 6　磁翻板法、振動(dòng)法、核輻射法、光纖傳感器法　　磁翻板法原理：浮子裝有一組永久磁鐵，隨液位變化而上下移動(dòng)，通過(guò)磁耦合作用帶動(dòng)磁翻板組件翻轉(zhuǎn)。當(dāng)液位上升時(shí)，磁翻板的紅色面朝外；液位下降時(shí)，白色面朝外。故根據(jù)磁翻板的顏色即可確定液位。浮子內(nèi)磁鐵與磁翻板磁性結(jié)構(gòu)中每片翻板間的距離為10 mm。采用幾臺(tái)磁翻板裝置串聯(lián)可增大量程。</p><p>　　振動(dòng)法的原理中振動(dòng)液位儀由導(dǎo)軌、

88、測(cè)試架、激錘、振動(dòng)傳感器、伺服機(jī)構(gòu)等組成。伺服機(jī)構(gòu)控制振錘上下爬動(dòng)并激振，激振后的自由振動(dòng)被振動(dòng)傳感器檢測(cè)，該檢測(cè)信號(hào)經(jīng)FET變換后得到最大功率處的頻率，最后由空罐時(shí)固有頻率／液位關(guān)系得到液位。這種液位測(cè)量方法需要激錘、伺服機(jī)構(gòu)等機(jī)械運(yùn)動(dòng)部件，其工作壽命不是很長(zhǎng)，須定期維修和重新標(biāo)定，安裝也較復(fù)雜?！　≥椛浞ǎ悍派湫酝凰卦谒プ冞^(guò)程中會(huì)輻射射線，常見(jiàn)的射線有α、β、γ射線。其中，γ射線的穿透力強(qiáng)，射程遠(yuǎn)，故在核輻射液位測(cè)量中廣泛采用。

89、實(shí)驗(yàn)證明，穿過(guò)物質(zhì)前后γ射線強(qiáng)度會(huì)發(fā)生變化?！　『溯椛涫揭何粌x由放射源、探測(cè)器及處理電路組成。放射源大都采用鈷－60或銫－137。探測(cè)器有電離室、記數(shù)管、閃爍計(jì)數(shù)器等幾種，其作用是探測(cè)射線穿透物質(zhì)后的強(qiáng)度。核輻射液位儀采用非接觸式安裝采用點(diǎn)式放射源、探測(cè)器，測(cè)量范圍較小；采用點(diǎn)式放射源、線狀探測(cè)器，測(cè)量范圍較大；采用線狀放射源、探測(cè)器，測(cè)量范圍最大。除γ射線外，中子射線也可用來(lái)測(cè)量液位。中子射線的穿透能力極強(qiáng)，比γ射線強(qiáng)10倍以上，可

90、穿透壁厚達(dá)9英寸的鋼質(zhì)容器。射線液位儀安裝方便，測(cè)量精度能滿足大罐測(cè)量的需要，有一定的應(yīng)</p><p>　　光纖傳感法：文獻(xiàn)提出了一種光纖液位傳感器，當(dāng)液位變化時(shí)，壓力傳感器的敏感彈性膜片產(chǎn)生位移，帶動(dòng)反光膜移動(dòng)，使探頭感受的光強(qiáng)發(fā)生變化，從而計(jì)算出液位。文獻(xiàn)提出了又一種光纖液位傳感器，根據(jù)探頭在氣相和液相介質(zhì)中感受到光強(qiáng)的差異，判斷探頭的位置，并控制探頭跟蹤液位的變化，從而得到液位數(shù)值。</p>