外文翻譯---溫度控制和pid控制器簡介

1、<p><b>　　淮 陰 工 學(xué) 院</b></p><p>　　畢業(yè)設(shè)計(jì)(論文)外文資料翻譯</p><p>　　注：請將該封面與附件裝訂成冊。附件1：外文資料翻譯譯文</p><p>　　溫度控制和PID控制器簡介</p><p>　　過程控制系統(tǒng)：自動過程控制系統(tǒng)是指把溫度、壓力、流量、成份等相關(guān)的過程

2、變量保持在要求的運(yùn)行值的一類系統(tǒng)。過程實(shí)際上是動態(tài)的。變化總是時時在發(fā)生的，此時如果不采取相應(yīng)的措施，那些與安全、產(chǎn)品質(zhì)量和生產(chǎn)率有關(guān)的工藝參數(shù)就不能滿足設(shè)計(jì)要求。</p><p>　　為了理清思路，讓我們來看一下熱交換器，流體在這個過程中被過冷凝蒸汽加熱，過程如圖1所示。</p><p><b>　　圖1熱交換器</b></p><p>　　

3、這一裝置的目的是將流體由入口溫度Ti（t）加熱到某一期望的出口溫度T(t)。如前所述，加熱介質(zhì)是冷凝蒸汽。</p><p>　　只要周圍沒有熱損耗，即熱交換器和管道間的隔熱性都很好，過程流體獲得的熱量就等于蒸汽釋放的熱量。</p><p>　　在這個過程中很多變量會發(fā)生變化，導(dǎo)致出口溫度偏離期望值。如果出現(xiàn)這種情況，就應(yīng)該采取一些措施來校正溫度偏差，目的是控制出口溫度至期望值。</p

4、><p>　　實(shí)現(xiàn)該目的的一種方法是首先設(shè)定初始溫度T(0)，然后與期望值相比較，由比較結(jié)果決定如何校正偏差。蒸汽的流量可用于偏差的校正。就是說，如果溫度高于期望值，就關(guān)小蒸汽閥來減小進(jìn)入熱交換器的蒸汽流量；若溫度低于期望值，就開大蒸汽閥來增加進(jìn)入換熱器的蒸汽流量。所有這些操作都可由操作員手動完成，操作很簡單，不會出現(xiàn)什么問題。但是，由于多數(shù)過程對象都有很多變量需要保持為某一期望值，這個校正過程就需要許多的操作員來進(jìn)

5、行。因此，我們想自動完成這種控制。就是說，我們需要一種無需操作人員介入就可以控制變量的設(shè)備。這就是所謂的自動過程控制。</p><p>　　為了實(shí)現(xiàn)上述目標(biāo)，就需要設(shè)計(jì)一個可行的控制系統(tǒng)。圖2為一個可行的控制系統(tǒng)及其基本構(gòu)件。</p><p>　　圖2熱交換器的控制回路</p><p>　　首先要做的是測量過程流體的出口溫度，這一任務(wù)由傳感器(熱電偶、熱電阻等)完成

6、。傳感器連接到發(fā)射器上，發(fā)射器將傳感器的輸出信號轉(zhuǎn)換為足夠大的信號傳送給控制器?？刂破鹘邮张c溫度相關(guān)的信號并與期望值進(jìn)行比較。根據(jù)比較的結(jié)果，控制器決定如何保持溫度為期望值。基于這一結(jié)果，控制器再發(fā)一信號給執(zhí)行機(jī)構(gòu)來輪流控制蒸汽流量。</p><p>　　以上的敘述表明整個控制系統(tǒng)有四個基本組成部分，分別是：</p><p>　　(1)傳感器，也稱為一次元件。</p><

7、;p>　　(2)發(fā)射器，也稱二次元件。</p><p>　　(3)控制器，控制系統(tǒng)的“大腦”。</p><p>　　(4)執(zhí)行機(jī)構(gòu)，通常是一個控制閥，但并不全是。其他常用的執(zhí)行機(jī)構(gòu)有變速泵、傳送裝置和電動機(jī)。</p><p>　　這些元件的重要性在于它們執(zhí)行每個控制系統(tǒng)中都必不可少的3個基本操作，即：</p><p>　　(1)測量：被

8、控量的測量通常由傳感器和發(fā)射器共同完成。</p><p>　　(2)決策：根據(jù)測量結(jié)果，控制器必須決定如何進(jìn)行操作維持輸出為期望值。 </p><p>　　(3)操作：根據(jù)控器的處理，系統(tǒng)必須執(zhí)行某種操作，這通常由執(zhí)行機(jī)構(gòu)來完成。</p><p>　　如上所述，每個控制系統(tǒng)都必須有M，D和A這三種操作。</p><p>　　

9、PID控制器可以是獨(dú)立控制器（也可以叫做單回路控制器），可編程控制器（PLCS）中的控制器，嵌入式控制器是用VB或C#編寫的計(jì)算機(jī)程序軟件。</p><p>　　PID控制器是過程控制器，它具有如下特征：</p><p>　?。?）連續(xù)過程控制；</p><p>　?。?）模擬輸入（也被稱為“測量量”或“過程變量”或“PV”）；</p><p&g

10、t;　　（3）模擬輸出（簡稱為“輸出”）；</p><p>　?。?）基準(zhǔn)點(diǎn)（SP）；</p><p>　　（5）比例、積分以及微分常數(shù)；</p><p>　　“連續(xù)過程控制”的例子有溫度、壓力、流量及液位控制。例如：控制一個容器的熱量。對于簡單的控制，你需要兩個具有溫度限定功能的傳感器（一個溫度下限，一個溫度上限）。當(dāng)?shù)蜏叵薅▊鞲衅鹘油〞r就會打開加熱器，當(dāng)溫度升高

11、到高溫限定傳感器時就會關(guān)閉加熱器。這類似于大多數(shù)家庭使用的空調(diào)及供暖設(shè)備的溫度自動調(diào)節(jié)器。</p><p>　　反過來，PID控制器能夠接受像實(shí)際溫度這樣的輸入，來控制閥門，這個閥門能夠控制進(jìn)入加熱器的氣體流量。PID控制器自動地找到加熱器中氣體的合適流量，這樣就保持了溫度在基準(zhǔn)點(diǎn)穩(wěn)定。溫度穩(wěn)定了，就不會在高低兩點(diǎn)間上下跳動了。如果基準(zhǔn)點(diǎn)降低，PID控制器就會自動降低加熱器中氣體的流量。如果基準(zhǔn)點(diǎn)升高，PID控制

12、器就會自動的增加加熱器中氣體的流量。同樣地，對于高溫，晴朗的天氣(當(dāng)外界溫度高于加熱器時)及陰冷，多云的天氣，PID控制器都會自動調(diào)節(jié)。</p><p>　　模擬輸入（測量量）叫做“過程變量”或“PV”。你希望PV能夠達(dá)到你所控制過程參數(shù)的高精確度。例如，如果我們想要保持溫度為+1度或—1度，我們至少要努力使其精度保持在0.1度。如果是一個12位的模擬輸入，傳感器的溫度范圍是從0度到400度，我們計(jì)算的理論精確度

13、就是400除以44096 ，即0．097656度。我們之所以說這是理論上的因?yàn)槲覀兗僭O(shè)溫度傳感器，電線及模擬轉(zhuǎn)換器上沒有噪音和誤差。還有其他的假定，如線性等等。即使是有大量的噪音和其他問題，按理論精確度的1／10計(jì)算，1度精確度的數(shù)值應(yīng)該很容易得到的。</p><p>　　模擬輸出經(jīng)常被簡稱為“輸出”。經(jīng)常在0％到100％之間給出。在這個熱量的例子中閥門完全關(guān)閉(0％)，完全打開(100％)。</p>

14、<p>　　基準(zhǔn)點(diǎn)(SP)很簡單，即你想要什么樣的過程量。在這個例子中你想要該過程處于怎樣的溫度。</p><p>　　PID控制器的任務(wù)是維持輸出在某一個程度上，這樣在過程變量(PV)和基準(zhǔn)點(diǎn)(SP)上就沒有偏差(誤差)。</p><p>　　在圖3中，閥門用來控制進(jìn)入加熱器的氣體，冷卻器的制冷，水管的壓力，水管的流量，容器的水位或其他的過程控制系統(tǒng)。PID控制器所觀察的是

15、PV和SP之間的偏差(或誤差)。它觀察絕對偏差和偏差變換率。絕對偏差就是'PV和SP之間偏差是大還是小。偏差變換率就是——PV和SP之間的偏差隨著時間的變化是越來越小還是越來越大。</p><p>　　SETPOINT P，I，&D</p><p><b>　　CONSTANTS</b></p><p>　　D

16、ifference error PID control</p><p><b>　　algorithm</b></p><p>　　process output</p><p><b>　　variable</b></p><p><b>　　圖3

17、 PID控制器</b></p><p>　　如果存在過程擾動，即過程變量或基準(zhǔn)點(diǎn)迅速變化時，PID控制器就要迅速改變輸出，使過程變量快速返回到基準(zhǔn)點(diǎn)。如果你有一個PID控制的可進(jìn)入的冷凍裝置，某個人打開門進(jìn)入，溫度（過程變量）將會迅速升高。因此，PID控制器不得不提高冷卻(輸出)來補(bǔ)償這個溫度的升高。</p><p>　　一旦過程變量等同于基準(zhǔn)點(diǎn)，一個好的PID控制器就不會改變

18、輸出。你所要的輸出是非常穩(wěn)定的(不會改變)。如果閥門(發(fā)動機(jī)或其他控制器件)不斷改變，而不是維持恒量，這將造成控制元件更多的磨損。</p><p>　　這樣就有了兩個矛盾的目標(biāo)。當(dāng)有“過程擾動”時能夠快速反應(yīng)（快速改變輸出）。當(dāng)PV接近基準(zhǔn)點(diǎn)時就緩慢反應(yīng)（平穩(wěn)輸出）。</p><p>　　我們注意到輸出量經(jīng)常超過穩(wěn)定狀態(tài)輸出使過程變量回到基準(zhǔn)點(diǎn)。比如，一個制冷器通常打開它的制冷閥門的34％

19、，就可以維持在零度（在制冷器關(guān)閉和溫度降低后）。如果某人打開制冷器，走進(jìn)去，四處走，找東西，然后再走出來，再關(guān)上制冷器的門，PID控制器會非?；钴S，因?yàn)闇囟瓤赡軐⑸仙?0度。這樣制冷閥門就可能打開50％，75％甚至100％，目的是趕快降低制冷器的溫度，然后慢慢關(guān)閉制冷閥門回到它的34％。</p><p>　　讓我們來考慮一下如何設(shè)計(jì)一個PID控制器。</p><p>　　我們主要集中在過程

20、變量(PV)和基準(zhǔn)點(diǎn)(SP)之間的偏差(誤差)上。有三種定義誤差的方式。</p><p><b>　　絕對偏差</b></p><p>　　他說明的是PV和SP之間的偏差有多大。如果PV和SP之間偏差小，那我們就在輸出時作一個小的改變。如果PV和SP之間偏差大——那我們就在輸出時作一個大的改變。絕對偏差就是PID控制器的比例環(huán)節(jié)。</p><p&g

21、t;<b>　　累積誤差</b></p><p>　　給我們點(diǎn)時間，我們將會明白為什么僅僅簡單地觀察絕對偏差(比例環(huán)節(jié))是一個問題。累積誤差是很重要的，我們把它稱為是PID控制器的積分環(huán)節(jié)。每次我們運(yùn)行PID算法時，我們總會把最近的誤差添加到誤差總和中。換句話說，累積誤差，誤差1+誤差2+誤差3+誤差4+……</p><p><b>　　滯后時間</b

22、></p><p>　　滯后時間指的是PV引起的變化由發(fā)現(xiàn)到改變之間的延時。典型的例子就是調(diào)整你的烤爐在合適的溫度。當(dāng)你剛剛開始加熱，烤爐熱起來需要一定時間，這就是滯后時間。如果你設(shè)置一個初始溫度，等待烤爐達(dá)到這個初始溫度，然后你認(rèn)為你設(shè)定了錯誤的溫度，烤爐達(dá)到這個新的溫度基準(zhǔn)點(diǎn)還需要一段時間。這也被認(rèn)為是PID控制器的微分環(huán)節(jié)。這就抑制了某些將來的變化因?yàn)檩敵鲋狄呀?jīng)發(fā)生了改變，但并不是受過程變量的影響。&

23、lt;/p><p>　　附件2：外文原文（復(fù)印件）</p><p>　　Introductions to temperature control</p><p>　　and PID controllers</p><p>　　Process control system. </p><p>　　Automatic proc

24、ess control is concerned with maintaining process variables temperatures pressures flows compositions, and the like at some desired operation value. Processes are dynamic in nature. Changes are always occurring, and if

25、actions are not </p><p>　　taken, the important process variables-those related to safety, product quality, and production rates-will not achieve design conditions. </p><p>　　In

26、 order to fix ideas, let us consider a heat exchanger in which a process stream is heated by condensing steam. The process is sketched in Fig.1 </p><p>　　

27、Fig. 1 Heat exchanger</p><p>　　The purpose of this unit is to heat the process fluid from some inlet temperature, Ti(t), up to a certain desired outlet temperature, T(t). As mentioned, the heating medium is

28、condensing steam.</p><p>　　The energy gained by the process fluid is equal to the heat released by the steam, provided there are no heat losses to surroundings, that is, the heat exchanger and piping are wel

29、l insulated.</p><p>　　In this process there are many variables that can change, causing the outlet temperature to deviate from its desired value. If this happens, some action must be taken to correct for thi

30、s deviation. That is, the objective is to control the outlet process temperature to maintain its desired value.</p><p>　　One way to accomplish this objective is by first measuring the temperature T(t) , then

31、 comparing it to its desired value, and, based on this comparison, deciding what to do to correct for any deviation. The flow of steam can be used to correct for the deviation. This is, if the temperature is above its de

32、sired value, then the steam valve can be throttled back to cut the steam flow (energy) to the heat exchanger. If the temperature is below its desired value, then the steam valve could be opened </p><p>　　To

33、accomplish this objective a control system must be designed and implemented. A possible control system and its basic components are shown in Fig.2.</p><p>　　Fig. 2 Heat exchanger control loop</p><

34、p>　　The first thing to do is to measure the outlet temperature of the process stream. A sensor (thermocouple, thermistors, etc) does this. This sensor is connected physically to a transmitter, which takes the output f

35、rom the sensor and converts it to a signal strong enough to be transmitter to a controller. The controller then receives the signal, which is related to the temperature, and compares it with desired value. Depending on t

36、his comparison, the controller decides what to do to maintain the t</p><p>　　The preceding paragraph presents the four basic components of all control systems. They are</p><p>　　(1) sensor, also

37、 often called the primary element.</p><p>　　(2) transmitter, also called the secondary element.</p><p>　　(3) controller, the "brain" of the control system.</p><p>　　(4) fi

38、nal control system, often a control valve but not always. Other common final control elements are variable speed pumps, conveyors, and electric motors. </p><p>　　The importance of these components is that th

39、ey perform the three basic operations that must be present in every control system. These operations are </p><p>　　(1) Measurement（M）: Measuring the variable to be controlled is usually done by the combinati

40、on of sensor and transmitter.</p><p>　　(2) Decision (D): Based on the measurement, the controller must then decide what to do to maintain the variable at its desired value.</p><p>　　(3) Action (

41、A): As a result of the controller's decision, the system must then take an action. This is usually accomplished by the final control element. </p><p>　　As mentioned, these three operations, M, D, and A,

42、must be present in every control system.</p><p>　　PID controllers can be stand-alone controllers (also called single loop controllers), controllers in PLCS, embedded controllers, or software in Visual Basic

43、or C# computer programs.</p><p>　　PID controllers are process controllers with the following characteristics:</p><p>　　Continuous process control</p><p>　　Analog input (also known a

44、s "measurement" or "Process Variable" or "PV")</p><p>　　Analog output (referred to simply as "output")</p><p>　　Setpoint (SP)</p><p>　　Propor

45、tional (P), Integral (I), and/or Derivative (D) constants</p><p>　　Examples of "continuous process control" are temperature, pressure, flow, and level control. For example, controlling the heating

46、of a tank. For simple control, you have two temperature limit sensors (one low and one high) and then switch the heater on when the low temperature limit sensor turns on and then turn the heater off when the temperature

47、rises to the high temperature limit sensor. This is similar to most home air conditioning & heating thermostats.</p><p>　　In contrast, the PID controller would receive input as the actual temperature and

48、 control a valve that regulates the flow of gas to the heater. The PID controller automatically finds the correct (constant) flow of gas to the heater that keeps the temperature steady at the setpoint. Instead of the tem

49、perature bouncing back and forth between two points, the temperature is held steady. If the setpoint is lowered, then the PID controller automatically reduces the amount of gas flowing to the heater.</p><p>

50、　　The analog input (measurement) is called the "process variable" or "PV". You want the PV to be a highly accurate indication of the process parameter you are trying to control. For example, if you wa

51、nt to maintain a temperature of + or - one degree then we typically strive for at least ten times that or one-tenth of a degree. If the analog input is a 12 bit analog input and the temperature range for the sensor is 0

52、to 400 degrees then our "theoretical" accuracy is calculated to be 400 degrees div</p><p>　　The analog output is often simply referred to as "output". Often this is given as 0~100 percent

53、. In this heating example, it would mean the valve is totally closed (0%) or totally open (100%).</p><p>　　The setpoint (SP) is simply--what process value do you want. In this example--what temperature do yo

54、u want the process at?</p><p>　　The PID controller's job is to maintain the output at a level so that there is no difference (error) between the process variable (PV) and the setpoint (SP).</p>&l

55、t;p>　　In Fig. 3, the valve could be controlling the gas going to a heater, the chilling of a cooler, the pressure in a pipe, the flow through a pipe, the level in a tank, or any other process control system. What the

56、PID controller is looking at is the difference (or "error") between the PV and the SP. </p><p>　　SETPOINT P，I，&D</p><p><b>　　CONSTANTS</b></p><p>

57、　　Difference error PID control</p><p><b>　　algorithm</b></p><p>　　process output</p><p><b>　　variable</b></p><p>　　Fig .3 P

58、IDcontrol</p><p>　　It looks at the absolute error and the rate of change of error. Absolute error means--is there a big difference in the PV and SP or a little difference? Rate of change of error means--is

59、the difference between the PV or SP getting smaller or larger as time goes on. </p><p>　　When there is a "process upset", meaning, when the process variable or the setpoint quickly changes--the PI

60、D controller has to quickly change the output to get the process variable back equal to the setpoint. If you have a walk-in cooler with a PID controller and someone opens the door and walks in, the temperature (process v

61、ariable) could rise very quickly. Therefore the PID controller has to increase the cooling (output) to compensate for this rise in temperature.</p><p>　　Once the PID controller has the process variable equal

62、 to the setpoint, a good PID controller will not vary the output. You want the output to be very steady (not changing) . If the valve (motor, or other control element) is constantly changing, instead of maintaining a con

63、stant value, this could cause more wear on the control element.</p><p>　　So there are these two contradictory goals. Fast response (fast change in output) when there is a "process upset", but slow

64、response (steady output) when the PV is close to the setpoint.</p><p>　　Note that the output often goes past (over shoots) the steady-state output to get the process back to the setpoint. For example, a cool

65、er may normally have its cooling valve open 34% to maintain zero degrees (after the cooler has been closed up and the temperature settled down). If someone opens the cooler, walks in, walks around to find something, then

66、 walks back out, and then closes the cooler door--the PID controller is freaking out because the temperature may have raised 20 degrees! So it ma</p><p>　　Let's think about how to design a PID controller

67、.</p><p>　　We focus on the difference (error) between the process variable (PV) and the setpoint (SP). There are three ways we can view the error.</p><p>　　The absolute error</p><p>

68、;　　This means how big is the difference between the PV and SP. If there is a small difference between the PV and the SP--then let's make a small change in the output. If there is a large difference in the PV and SP--

69、then let's make a large change in the output. Absolute error is the "proportional" (P) component of the PID controller.</p><p>　　The sum of errors over time</p><p>　　Give us a minu

70、te and we will show why simply looking at the absolute error (proportional) only is a problem. The sum of errors over time is important and is called the "integral" (I) component of the PID controller. Every ti

71、me we run the PID algorithm we add the latest error to the sum of errors. In other words Sum of Errors = Error 1 q- Error2 + Error3 + Error4 +… </p><p>　　The dead time</p><p>　　Dead time refers

72、to the delay between making a change in the output and seeing the change reflected in the PV. The classical example is getting your oven at the right temperature. When you first turn on the heat, it takes a while for the

73、 oven to "heat up". This is the dead time. If you set an initial temperature, wait for the oven to reach the initial temperature, and then you determine that you set the wrong temperature--then it will take a w