液壓氣動介紹外文文獻翻譯、中英文翻譯

液壓氣動介紹外文文獻翻譯、中英文翻譯,液壓,氣動,介紹,外文,文獻,翻譯,中英文 Url:http:/www.HydraulicsP hydraulic system isnt complete without the right type of pressure sensors.From sub-sea to aerospace applications,hydraulics can be found in benign laboratories or harsh operating conditions prone to extreme temperatures,shock,vibration,electromagnetic interference(EMI),radio frequency interference(RFI),and pulsations.As electronic controls started to appear in early 1970s,a new control system term,electrohydraulics entered the industrial world.These early control systems started the industrial automation revolution.Over time,better sensing technologies and the availability of low cost microprocessors and controllers accelerated the growth of hydraulic controls.Today,pressure measurements play an important role in determining the health of hydraulic systems by means of overall performance,safety,and feedback.Depending upon the application,most modern hydraulic systems operate from 1000 to 10,000 psi;however there are some that may go as high as 60,000 psi.Pressure measurements can be accomplished with a simple on-off pressure switch or an electronic pressure sensor that offers a linear electronic output signal.Electronic pressure sensors are replacing pressure switches,due to their flexibility and performance;however,there are topics that must be addressed for performance and reliability in hydraulic applications.Pressure sensing technologies,sensor packaging,hydraulics transient protection,and EMI/RFI protection must be considered carefully for each application.Figure 1.A typical capacitance sensor contains both a fixed and a moving plate.Pressure sensing technologies The two main technologies for pressure sensing are capacitive and piezoresistive.Capacitive technology employs gap sensing by means of a capacitance change between two plates;one fixed and other moving,as shown in Figure 1.This capacitor is normally connected to a complex electronic circuit that will covert the capacitance to an output signal such as 1-5 V or 4-20 mA.Because the change of capacitance is in the range of 1 pico Farad to 1 femto Farad,the electronic circuitry is placed closely to the sensing plates,to minimize stray capacitance.This tends to limit the operating temperature of the sensor,as there is a short distance between the media and capacitor.If a metal or doped semiconductor is stretched or compressed,its resistance changes because of dimensional changes(length and cross-sectional area)and resistivity change(this latter property is called piezoresistance).Strain gauge technology is used to measure the change in length from L to L and resistance change from R to R.The strain sensitivity or gauge factor,G,can be calculated by:(R R)(L L)For metal strain gauges,the typical gauge factor is 2.These strainmeasuring devices are normally called strain gauges and come in different sizes.Figure 2 shows an outline of a bonded foil strain gauge.Bonded foil strain gauges are made from nickel chromium or nickel constantin material and typically have a Mylar insulator backing.This allows one to glue the gauge to a metallic or ceramic substrate.Thin film gauges,fabricated by sputtering metal on an insulated substrate,do not require any glue for bonding.In the early 1960s,semiconductor gauges were developed to offer higher gauge factors(from 55 to 200)with a smaller package size.Semiconductor gauges can be fabricated in two ways:the use of bulk silicon or germanium material that has been doped in either P-type such as boron or N-type material such as phosphorus to provide the electrical and thermal performances;ion implanting using P and N types of material together to form a P-N junction.These strain gauges are normally connected in a Wheatstone bridge configuration as shown in Figure 3(four active arms are shown for maximum compensation)to provide a limited temperature compensation.For metal or thin film strain gauges,the output signal is 3mV/V with an operating strain of 1100 microstrain whereas semiconductor gauges will provide up to 50mV/V with 300 microstrain.Pressure sensor packaging Primary pressure sensor packaging is dependent upon the sensing technology and operating conditions of an application.Signal conditioning electronics and electrical interface can be considered as secondary issues as part of this discussion.Lets review some of these packages,benefits,and issues.Most low cost ceramic capacitive sensing elements employ a ceramic diaphragm made with an Alumina 96,machined pressure port,retainer ring,housing,and O-rings.The ceramic diaphragm is normally held to the pressure port by means of a primary O-ring.A secondary O-ring is used with the retaining ring on the opposite side to hold the ceramic diaphragm when pressure is applied.In this design,the media comes in contact with the ceramic diaphragm,primary Oring,and pressure port material.For low-pressure applications,the ceramic diaphragm tends to be large and thin.This has the potential for failure under high shock and vibration conditions.Ceramic sensors are used in industrial and off-road applications up to 1500 psi;however,the proof pressure(also known as the overload pressure)is restricted to 1.2 times the rated pressure.Today,this technology has limited use above 1500 psi,due to the availability of low cost strain gauge technologies with much better performance and longevity.In cyclic environments,the proof pressure rating must be reduced to same as operating pressure range to avoid failure of the O-ring seal.Since this design does not incorporate a hermetic seal,these sensors are not suitable for operation in ammonia,hydrogen,oil and gas production,hydraulics,oxygen service,and many other critical mild to harsh applications.The O-ring can be specified in a range of materials to deteragainst specific media attack that can cause system failure in certain abusive environments.Sensor manufacturers typically provide a list of O-ring materials such as Buna,Viton,and EPDM that can be specified by the customer.Since the metal foil strain gauges tend to be large,they are normally put on a beam or diaphragm prior to welding to a pressure port.Thin film sensors are smaller,but they also need to be welded to a pressure port.In both cases,the welds need to be deep enough so that they do not fail under normal and overload conditions operating above 2500 psi.Under high cyclic and pressure conditions,where the pressure pulsations can vary by 50%of the pressure sensor range,the sensor package design must incorporate a mechanism to make sure that the weld is under compression to avoid sensor failure.Because both metal foil and thin film technologies have low outputs at high operating strains(typically 1000 microstrain),the diaphragm material must be carefully selected so there is enough room for overpressure without sacrificing shift in sensor performance.Common diaphragm materials used in metal foil and thin film sensors tend to be 15-5,17-4 and 17-7 PH high strength stainless steels with yield strengths up to 190,000 psi and low thermal coefficient of expansion.The pressure ports must be of the same material as the diaphragm to avoid any separation of the welds under thermal conditions.Sensors employing semiconductor strain gauge technology can be broken into two categories;oil-filled sensors employing a thin isolation diaphragm and ion implantation technology and the emerging diffusion bonded bulk silicon Krystal Bond Technology.Oil-filled piezoresistive sensors mainly employ a small silicon chip with ion implanted strain gauges,isolated from the real world by means of a thin metallic membrane(typical thicknesses between 0.001 and 0.0015 in.,depending upon the pressure range).With bulk semiconductor strain gauge technology,the strain gauges are directly mounted onto a machined sensing element,where the diaphragm and pressure port are machined in the same process.This eliminates the problems associated with welds,oil filled cavities,and internal O-rings.The use of a direct inorganic diffusion process allows semiconductor gauges to be placed precisely on a metallic diaphragm efficiently and accurately on the side of the diaphragm that is not exposed to the media.The hermetic design is excellent for high cyclic environments associated with hydraulic pumps and motors.The high gauge factor,along with low operating strain,allows the diaphragm to be thick.This offers excellent proof and burst pressures.Figure 2.View of a typical bonded foil strain gauge.Figure 3.Semiconductor gauges use a Wheatstone bridge circuit.Pressure spikes and transient protection Rapid opening and closing of valves and solenoids in hydraulic systems tends to generate rapid,high frequency pressure spikes and transients that may last from a few microseconds to hundreds of milliseconds.The amplitude of these fast moving transients can be up to 20 times the rated pressure of a system,and will destroy electronic pressure sensors unless they are protected using snubbers and restrictors.These protection devices can be installed as an integral part of the sensor or as a stand-alone device.The devices,while protecting the sensor from damaging fast moving transients,can dampen the response time of the sensor(depending upon the design).Figure 4 shows details of integral and external pressure spike snubbing techniques.For system optimization,such as response time and snubbing,the length,L,and diameter,D,must be carefully selected.In an ideal condition,the snubber must be able to snub all signals that are between 100-150%of applied pressure to maintain fast throughput,but remains dependent upon the type of sensing technology and packaging.EMI/RFI protection In mobile hydraulic applications,electrical pollution in the form of fast electrical transients,Electro Static Discharge(ESD)and EMI/RFI must be contained for system stability.Examples of this interference include communications equipment,switching power supplies,welding equipment,and electric motors.The sensor package must not generate or be influenced by unwanted external electrical signals from 100 kHz to 2 GHz.It must also be able to withstand radiated and conducted susceptibility and operated within its published specs in critical applications such as mobile cranes,scissor jacks,forklifts and many others.Typical protection used can be seen in Figure 5.Figure 4.Snubbers can use internal or external techniques to minimize pressures spikes.Figure 5.Typical EMC,ESD,and electrical fast transient protection scheme in pressure sensors.The danger of pressure spikes Pressure spikes are microsecond to millisecond bursts of pressure that can reach 15 times the normal system operating pressure.For example,if a valve shifts abruptly to block flow,a shock wave can be generated within the system.Likewise,if a hydraulic system is moving a load and the load suddenly stops,the system may react with a brief surge of pressure.System control electronics such as PLCs with millisecond scan times are not fast enough to detect spikes of such short duration.Often,the first indication that a system is generating pressure spikes is a positive shift in a pressure transducers zero output.System control electronics commonly indicate the shift in transducer output as a pressure out-of-range condition,which could cause the system controller to shut down.Pressure transducers are the components most vulnerable to damage from pressure spikes.Transducers,with much quicker response,react to spikes and can show signs of having been over-pressurized.This is not because the transducer is less durable than the mechanical gauge it replaced.Actually,a transducer designed for severe service should have been specified.Spikes also damage the machines that generate them.The erratic flow of liquid,common in systems that generate spikes,reduces efficiency and accelerates wear on valve ports and seals.(Note that pressure spikes do not pose serious problems in pneumatic systems because the air is compressible,which tends to dampen shock.Cyclic pressure surges,caused by pulsation from compressors,pose a greater potential problem because the pressure surges while not as sharp occur repeatedly and frequently.)Pressure spikes usually can be detected with an oscilloscope through a transducer of,say,five times the normal operating pressure range.Once it is determined that spikes exist in a system,any of several practices can be used to prevent them from damaging the transducer.A transducer with a higher pressure rating can be used.However,doing so sacrifices accuracy in the normal operating range because a transducer with a wider operating range has poorer resolution.As an alternative,a snubber can be used to dampen the spike.A snubber is an orifice installed in piping between the transducer and the source of the spike.A potential disadvantage of this practice is that it slows the response of the measurement.If neither measurement resolution nor response can be compromised,a transducer that can tolerate spikes should be specified.Obviously,these transducers cost more.This information came from the 2008/2009 edition of the Fluid Power Handbook&Directory.To order your copy in printed form or on CD-ROM,visit and click on the Bookstore button.Copyright 2008 Penton Media,Inc.&Hydraulics&Pneumatics magazine.液壓氣動從海上到航空航天的應用，液壓系統可在實驗室或條件惡劣情況下,比如溫度的極端變化，沖擊，振動，電磁干擾（EMI），射頻干擾（RFI）和脈動。電子控制作為一個新的控制系統出現于20世紀70年代初，電動水力學開始進入了工業化國家。這些早期的控制系統開始了工業的自動化革命。 隨著時間的推移，更好的傳感技術和低成本的微處理器和控制器的供應加速液壓控制的增長。今天，壓力測量通過整體性能，安全手段和反饋方式在確定液壓系統健康的起了重要作用。根據不同的應用，最先進的液壓系統工作于1000至10,000磅/平方英寸的，但也有一些可能會高達60,000磅/平方英寸的。壓力測量一個簡單的開關壓力轉換或一個電子壓力傳感器就可以完成，這種電子壓力傳感器提供了一個線性電子輸出信號。由于其靈活性和其它方面的優良性能，電子壓力傳感器正在逐步取代換壓力開關，但是，在液壓應用的性能和可靠性方面還有一些必須解決的課題。壓力傳感技術，傳感器封裝，液壓系統暫態保護和EMI / RFI保護，這些方面的應用都必須仔細考慮。圖1。一個典型的電容傳感器包含一個固定和移動盤。壓力傳感技術傳感壓力的兩個主要技術是電容和壓阻。電容技術采用一兩個板塊之間的電容變化的差距的手段，固定一個和移動其他的，如圖1所示。該電容通常是連接到一個復雜的電子電路，可以轉換如1-5 V或4-20毫安輸出的電容信號。因為電容變化在1微法拉到1法拉級，電子電路安裝的位置很接近感應板，以減少雜散電容。由于這種媒體和電容之間的距離很短，能夠限制了傳感器的工作溫度。 如果是金屬或摻雜半導體拉伸或壓縮，因為尺寸變化（長度和橫截面積的電阻變化）和電阻率變化（這后者的屬性稱為壓阻）它的抵抗力會改變。應變傳感器技術是用來測量當長度由L變到L和阻力從R變到R的變化。應變計的敏感性因素，可以計算G： 變化（R注冊商標）（L長）金屬應變計，典型的應變系數為2。這些應變電測設備，因為其不同的大小通常稱為應變計。圖2顯示了一個保稅箔應變計的輪廓。保稅箔應變計是由鎳鉻或鎳康斯坦丁物質通常具有絕緣聚酯薄膜作后盾。這種可以粘一個金屬或陶瓷基片。薄膜測量儀通過濺射金屬而焊接在金屬絕緣基片上，所以不需要任何粘合膠。在20世紀60年代初，開發半導體測量儀提供更高的量規因素（55-200），具有更小的封裝尺寸。半導體壓力表制作方法有兩種：散裝硅或鍺材料，現有的任一P型如硼或N型材料如磷，能摻雜使用以提供電力和熱性能;使用磷，離子植入n組的材料在一起，形成一個PN結。這些應變計通常是連接在一個惠斯通電橋配置如圖3（4活性武器是為最高賠償所示）提供有限的溫度補償。對于金屬或薄膜應變計，1100顯微應變才輸出信號3mV/V，而半導體計300微變將提供高達50mV/V。壓力傳感器包裝最初的壓力傳感包裝是基于傳感技術的應用程序和經營條件。作為這次討論的一部分，信號調理電路和電氣接口可被視為次要問題。讓我們回顧其中一些包裝的優點和問題。大多數低成本的陶瓷電容傳感元件采用了陶瓷膜與氧化鋁96個，機械壓力，扣環，外殼和O型環。通常陶瓷膜片由O形圈連接。一個O形圈是用于與對面扣環連接的陶瓷膜片受到壓力時應用。在這個設計中，媒介用來連接陶瓷隔膜，小學的O型環接觸和壓力材料。對于低壓應用中，往往是陶瓷膜片大而薄。這就在高沖擊和振動條件下可能導致失敗。陶瓷傳感器用于工業和越野高達1500 磅/平方英寸的應用，然而，耐壓（也稱為壓力超負荷）被限制到1.2倍額定壓力。如今，這項技術已高于1500磅/平方英寸的用途有限，因為與更好的性能和壽命的低成本應變片技術的可用性。在循環的環境中，證明壓力等級必須減少到相同的操作壓力范圍，以避免對O形圈密封失效。由于這種設計沒有納入一個密封蓋章，這些傳感器不適合操作氨，氫，石油和天然氣生產，液壓系統，氧氣服務，以及許多其他關鍵輕度到苛刻的應用程序。O形圈可在指定的材料范圍受到特定媒介的攻擊，可能會導致在某些惡劣環境的系統故障。傳感器制造商通常提供的O型圈材料，如丁腈橡膠，氟橡膠清單，三元乙丙橡膠，可以由客戶指定。由于金屬箔應變計往往會相當多，他們通常把一前束或膜片焊接壓力端口。薄膜傳感器體積更小，但他們還需要焊接壓力端口。在這兩種情況下，焊接需要足夠深，使他們不超過載情況下- 2500磅/平方英寸以上的操作。在高循環和壓力條件下，的壓力傳感器的壓力脈動可以在相差50范圍內變動，傳感器包裝設計必須包括一個機制，確保焊縫壓縮條件下，以避免傳感器故障。因為這兩個金屬箔和薄膜技術，在高工作壓力（通常為1000微觀）低產出，膜片材料必須是經過精心挑選，以便有足夠的空間用于超壓傳感器的性能而不犧牲的轉變。普通隔膜在金屬箔和薄膜傳感器使用的材料往往是15-5，17-4和17-7 PH值與屈服強度高強度不銹鋼達190,000磅/平方英寸和低熱膨脹系數。壓力端口必須是相同的隔膜材料，以避免任何溫度條件下焊接分離。傳感器采用半導體應變計技術可分為兩類，一類充油傳感器采用薄的隔離膜片和離子注入技術和新興的保稅體硅克里斯塔爾擴散焊工藝。充油壓阻式傳感器主要采用與硅芯片植入離子小應變計，孤立于真實世界的一個薄金屬膜（介乎0.0010.0015英寸典型厚度的手段，這取決于壓力范圍）。隨著批量半導體應變計技術，應變計是直接安裝到一個加工傳感元件，其中光圈和壓力端口是在同一進程中加工的。這消除了與焊接有關的問題，油填充了空腔以及內部O形圈。一個直接的擴散過程中使用的無機半導體測量儀器，以使被放置在一個金屬膜片準確高效，準確地對是不會受到媒體的隔膜一側。該密封設計與液壓泵和馬達相關的高循環環境優良。高應變系數，以及低操作壓力，使膈肌要厚。這提供了強有力的證明。 圖2。查看一個典型的保稅箔應變計。圖3。半導體測量儀使用惠斯通電橋電路。 壓力尖峰和瞬態保護迅速開放和閥和液壓系統電磁閥關閉往往產生快速、高頻尖峰和瞬態壓力可能從幾微秒到最后的幾百毫秒。這些快速移動瞬變幅度可高達20倍的一個系統的額定壓力，而且會破壞電子壓力傳感器，除非它們是受保護的使用緩沖器和節流器。這些保護裝置可以安裝在傳感器作為一個不可分割的組成部分或作為一個獨立的設備。這些設備，同時保護損壞移動瞬變快速傳感器，可以挫傷傳感器（取決于設計反應時間）。圖4顯示詳細積分和外部壓力穗冷落技術。對于系統優化，如響應時間，長度L和直徑必須仔細挑選。在理想的條件下，緩沖器必須能夠緩慢對100-150之間的所有信號的施加壓力，以保持快速吞吐量，但仍然依靠傳感技術和包裝類型而定。電磁干擾/射頻干擾在移動式液壓應用的保護，在快速電瞬態電污染，靜電放電（ESD）和電磁干擾/射頻干擾，必須對系統的控制保持穩定。這種干擾的例子包括通信設備，開關電源，焊接設備，電動馬達。該傳感器包不能產生或受到從100千赫信號至2千兆赫的不必要的外部電力的影響。它也必須能夠抵御輻射，并進行了敏感性，并在其發布的規格嚴格運作，如移動式起重機，剪式千斤頂，叉車和許多其他關鍵應用。典型的保護使用中可以看到圖5。 圖4。緩沖器可以使用內部或外部的技術，以減少壓力尖峰圖5。典型的EMC公司，公共服務電子化，并在壓力傳感器，電快速瞬變保護計劃。壓力峰值壓力峰值危險微秒到毫秒的壓力，可以達到15倍，正常的系統操作壓力掃射。例如，如果一個閥門突然轉向以阻止流動，產生的沖擊波可以在系統內產生。同樣，如果是移動的液壓系統負載和負載突然停止，系統可能會作出反應，系統的壓力可能短時間激增。電子控制系統 - 例如與微差掃描時間 - 沒有足夠快，檢測時間短穗的PLC等。通常，第一個跡象是生成一個系統壓力尖峰，是在一個壓力傳感器的零輸出的積極轉變。電子控制系統中的傳感器通常表明輸出作為轉移的需求壓力范圍外的條件，這可能導致系統控制器關閉。壓力傳感器組件最容易受到壓力尖峰的損害。傳感器的反應很快，能作出反應的峰值有跡象顯示壓力已經過度。這是不是因為換能器是小于機械衡量它取代耐用。其實，一個傳感器服務，旨在為嚴重的應該已被指定。斯派克斯也破壞產生他們的機器。不穩定流動的液體一般在系統產生不穩定的尖峰流量，降低效率，加快閥門和密封件的磨損。(請注意，不構成壓力峰值在氣動系統的嚴重問題，因為空氣是可壓縮的，這往往會挫傷休克。循環壓力驟增，由壓縮機脈動造成的，構成一個更大的潛在問題，因為壓力驟增 - 而不是劇增 是經常反復發生。）壓力峰值通?？梢酝ㄟ^一個換能器來檢測，例如，5倍的正常工作壓力范圍示波器。一旦確定存在于一個系統尖峰脈沖，這些應用中的任何一個都可以用來防止損害他們的傳感器。具有更高壓力等級傳感器都可以使用。但是，這樣做犧牲在正常范圍的準確性，因為一個擁有更廣泛的工作范圍傳感器它的解決方案會更難。 作為替代方案，一個緩沖可以用來限制峰值脈沖。是一個緩沖的傳感器之間和峰值脈沖源管道安裝一孔。這種做法的潛在缺點是，它減緩了測量反應。如果測量途徑和反應都能被控制，則對可以耐受峰值脈沖傳感器應作出具體規定。顯然，這些傳感器成本更高.6