外文翻譯---降低測(cè)量噪聲的五個(gè)技巧

1、<p>　　附錄A 外文資料翻譯</p><p>　　Five Tips to Reduce Measurement Noise</p><p>　　Ensuring measurement accuracy often means going beyond reading raw specifications in a data sheet. Understanding an

2、 application in the context of its electrical environment is also important for securing success, particularly in a noisy or industrial setting. Ground loops, high common-mode voltages, and electromagnetic radiation are

3、all prevalent examples of noise that can adversely affect a signal.</p><p>　　There are many techniques for reducing noise in a measurement system, which include proper shielding, cabling, and termination. Be

4、yond these common best practices, however, there is more you can do to ensure better noise immunity. The following five techniques serve as guidelines for achieving more accurate measurement results.</p><p>

5、　　Reject DC Common-Mode Voltage</p><p>　　Making highly accurate measurements often starts with differential readings. An ideal differential measurement device reads only the potential difference between the

6、positive and negative terminals of its instrumentation amplifier(s). Practical devices, however, are limited in their ability to reject common-mode voltages. Common-mode voltage is the voltage common to both the positive

7、 and negative terminals of an instrumentation amplifier. In Figure 1, 5 V is common to both the AI+ and AI- termin</p><p>　　Figure 1 An ideal instrumentation amplifier completely rejects common-mode voltage

8、s.</p><p>　　The maximum working voltage of a data acquisition (DAQ) device refers to the signal voltage plus the common-mode voltage and specifies the largest potential that may exist between an input and ea

9、rth ground. The maximum working voltage for most DAQ devices is the same as the input range of the instrumentation amplifier. For example, low-cost M Series DAQ devices such as the NI 6220 devices have a maximum working

10、voltage of 11 V; no input signal can exceed 11 V without causing damage to the amplif</p><p>　　Isolation can dramatically increase the maximum working voltage of a DAQ device. In the context of a measurement

11、 system, “isolation” means physically and electrically separating two parts of a circuit. An isolator passes data from one part of the circuit to another without conducting electricity. Because current cannot flow across

12、 this isolation barrier, you can level-shift the DAQ device ground reference away from earth ground. This decouples the maximum working voltage specification from the i</p><p>　　Figure 2 Isolation electrica

13、lly separates the instrumentation amplifier ground reference from earth ground.</p><p>　　While the input range is the same as that in Figure 1, the working voltage has been extended to 60 V, rejecting 55 V o

14、f common-mode voltage. The maximum working voltage is now defined by the isolation circuitry instead of the amplifier input range.</p><p>　　Fuel cell testing is an example application that requires high DC c

15、ommon-mode voltage rejection. Each individual cell may generate approximately 1 V, but a stack of cells may produce several kilovolts or more. To accurately measure the voltage of a single 1 V cell, the measurement devic

16、e must be able to reject the high common-mode voltages generated by the rest of the stack.</p><p>　　Reject AC Common-Mode Voltage</p><p>　　Rarely do common-mode voltages consist of only a DC lev

17、el. Most sources of common-mode voltage contain an AC component in addition to a DC offset. Noise is inevitably coupled onto a measured signal from the surrounding electromagnetic environment. This is particularly troubl

18、esome for low-level analog signals passing through the instrumentation amplifier on a DAQ device.</p><p>　　Sources of AC noise may be broadly classified by their coupling mechanisms – capacitive, inductive,

19、or radiative. Capacitive coupling results from time-varying electric fields, such as those created by nearby relays or other measurement signals. Inductive or magnetically coupled noise results from time-varying magnetic

20、 fields, such as those created by nearby machinery or motors. If the electromagnetic field source is far from the measurement circuit, such as with fluorescent lighting, the electr</p><p>　　An ideal measurem

21、ent circuit has a perfectly balanced path to both the positive and negative terminals of an instrumentation amplifier. Such a system would completely reject any AC-coupled noise. A practical device, however, specifies th

22、e degree to which it can reject common-mode voltage with a common-mode rejection ratio (CMRR). The CMRR is the ratio of the measured signal gain to the common-mode gain applied by the amplifier, as noted by the following

23、 equation:</p><p>　　Choosing a DAQ device with a better CMRR over a broader range of frequencies can make a significant difference in your system’s overall noise immunity. For example, Figure 3 shows the CMR

24、R for a low-cost M Series device compared with that of an industrial M Series device.</p><p>　　Figure 3 The NI 6230 provides a much higher CMRR than the NI 6220 relative to earth ground.</p><p>

25、;　　At 60 Hz, NI 6230 industrial M Series devices have 20 dB greater CMRR than NI 6220 low-cost M Series devices. This is equivalent to a 10 times better attenuation of 60 Hz noise.</p><p>　　Any application m

26、ay benefit from rejecting 60 Hz noise. However, those with large rotating machinery or motors require noise immunity at higher frequencies. At 1 kHz, NI 6230 devices reject noise 100 times better than NI 6220 devices, ma

27、king them ideal for industrial applications.</p><p>　　Break Ground Loops</p><p>　　Ground loops are arguably the most common source of noise in data acquisition systems. Proper grounding is essen

28、tial for accurate measurements, yet it is a frequently misunderstood concept. A ground loop forms when two connected terminals in a circuit are at different ground potentials. This difference causes a current to flow in

29、the interconnection, which can produce offset errors. Further complicating matters, the voltage potential between signal source ground and DAQ device ground is generall</p><p>　　Figure 4 A differential ther

30、mocouple measurement with a grounded signal source can create a ground loop.</p><p>　　Here, an otherwise straightforward temperature measurement is complicated by the device under test (DUT) being at a diffe

31、rent ground potential than that of the DAQ device. Though both devices share the same building ground, the difference in ground potential could be 200 mV or more if the power distribution circuits are not properly connec

32、ted. The difference appears as a common-mode voltage with an AC component in the resulting measurement.</p><p>　　Recall that isolation is a means of electrically separating signal source ground from the inst

33、rumentation amplifier ground reference (see Figure 5).</p><p>　　Figure 5 Isolation eliminates ground loops by separating earth ground from the amplifier ground reference.</p><p>　　Because curre

34、nt cannot flow across the isolation barrier, the amplifier ground reference can be at a higher or lower potential than earth ground. You cannot inadvertently create a ground loop with this circuit. Using an isolated meas

35、urement device removes the ambiguity of properly grounding a measurement system, ensuring more accurate results.</p><p>　　Use 4-20 mA Current Loops</p><p>　　Long cable lengths and the presence o

36、f noise in industrial or electrically harsh environments can make accurate voltage measurements difficult. As a result, industrial transducers that sense pressure, flow, proximity, and so on often emit current signals in

37、stead of voltage. A 4-20 mA current loop is a common method of sending sensor information over long distances in many process-monitoring applications, as shown in Figure 6.</p><p>　　Figure 6 An instrumentat

38、ion amplifier uses a shunt resistor to convert process current signals into voltage.</p><p>　　Each of these current loops contains three components – a sensor, a power source, and one or more DAQ devices. Th

39、e current signal from the sensor is typically between 4 and 20 mA, with 4 mA representing the lowest signal value and 20 mA representing the maximum. This transmission scheme has the advantage of using 0 mA to indicate a

40、n open circuit or bad connection. Power supplies are typically in the range of 24 to 30 VDC, depending on the total amount of voltage dropped along the circuit. Finall</p><p>　　An isolation barrier such as t

41、he one shown in Figure 6 provides two main benefits in current loop applications. First, because power supply voltages typically exceed the maximum input range of most instrumentation amplifiers, isolation is essential f

42、or level-shifting the amplifier ground away from earth ground to an acceptable voltage. Second, current loops operate on the principal that current never leaves the circuit. Therefore, isolating the current loop from any

43、 path to ground prevents degra</p><p>　　Use 24 V Digital Logic</p><p>　　Measurement noise is not limited to analog signals. Digital logic may also be affected by a noisy electrical environment,

44、possibly indicating false on/off values or accidental triggers. There are many voltage levels and logic families associated with digital I/O, some more noise resistant than others. Transistor-transistor logic (TTL) is by

45、 far the most common logic family, powering everything from microprocessors to LEDs. Though it is widely available, TTL may not always be the best choice for </p><p>　　For industrial applications, TTL has th

46、e inherent disadvantage of small noise margins. With high- and low-logic levels of 2.0 V and 0.8 V, respectively, there is little room for error. For example, the low-level noise margin for a TTL input is 0.3 V (the diff

47、erence between 0.8 V, the maximum low-level TTL input, and 0.5 V, the maximum low-level TTL output). Any noise coupled to the digital signal in excess of 0.3 V may shift the voltage into the undefined region between 0.8

48、V and 2.0 V. Here, th</p><p>　　Figure 7 24V logic has better noise margins than TTL.</p><p>　　24 V logic, however, offers increased noise margins and better overall noise immunity. Because most

49、 industrial sensors, actuators, and control logic already operate off 24 V power supplies, it is convenient to use the corresponding digital logic levels. With a low-level input of 4 V and a high-level input of 11 V, the

50、 digital signals are less susceptible to noise.</p><p>　　Most measurement devices with 24 V digital I/O capability offer additional noise-reducing features. For example, National Instruments industrial M Ser

51、ies and digital I/O devices have programmable input filters for debouncing relay inputs. When a mechanical relay closes, there is a short period of time (on the order of milliseconds) during which the contact surfaces bo

52、unce against each other. Without filtering, the logic input may read this as a burst of on/off signals. These devices also offer i</p><p>　　Conclusion</p><p>　　There are many factors to consider

53、 when attempting to reduce noise in a measurement system. Beyond proper shielding, cabling, and termination, careful consideration of common-mode voltages, grounding, and nearby noise sources is essential for accurate re

54、sults. However, understanding the electrical environment of your system is not always straightforward. Isolation is an easy means of adding another layer of confidence to your measurements, no matter the signal or applic

55、ation.</p><p>　　Charles Stiernberg</p><p>　　Charles Stiernberg is a product engineer for data acquisition at NI. He holds a bachelor’s degree in electrical engineering, with a focus on embedded

56、systems and VLSI design from The University of Texas at Austin.</p><p>　　降低測(cè)量噪聲的五個(gè)技巧</p><p>　　確保測(cè)量精度通常意味著需要超越產(chǎn)品說(shuō)明書(shū)的基本指標(biāo)。理解其在電氣環(huán)境背景中的應(yīng)用對(duì)于確保在噪聲環(huán)境或是工業(yè)環(huán)境中的成功應(yīng)用是尤為重要的。接地回路、高共模電壓以及電磁輻射都是將會(huì)負(fù)面影響信號(hào)的普遍實(shí)例。

57、</p><p>　　降低測(cè)量系統(tǒng)中的噪聲有許多方法，其中包括適當(dāng)?shù)钠帘?、接線和中止。除了這些常見(jiàn)方法之外，還有許多可以提高噪聲免疫的方法。以下的五個(gè)方法是達(dá)到更精確測(cè)量結(jié)果的指導(dǎo)方法。</p><p><b>　　抑制直流共模電壓</b></p><p>　　要進(jìn)行高精度的測(cè)量首先從差分讀數(shù)開(kāi)始。理想差分測(cè)量設(shè)備能夠讀取儀器放大器正極端子和負(fù)

58、極端子之間的電勢(shì)差。然而，實(shí)際的設(shè)備在共模電壓的抑制能力上是受到限制的。共模電壓是儀器放大器的正極端子和負(fù)極端子之間的共同電壓。在圖1中，5V電壓對(duì)于AI+和AI-端子而言是公共電壓，理想的設(shè)備能夠讀取兩個(gè)端子之間5V的差。</p><p>　　圖1 理想的儀器放大器完全抑制共模電壓</p><p>　　數(shù)據(jù)采集(DAQ)設(shè)備的最大工作電壓是指信號(hào)電壓加上共模電壓，并且指定了存在于輸入和

59、地之間的最大電勢(shì)差。對(duì)于大多數(shù)數(shù)據(jù)采集設(shè)備而言，最大工作電壓與儀器放大器的輸入范圍是相同的。例如，例如NI 6220設(shè)備等低成本M系列數(shù)據(jù)采集設(shè)備的最大工作電壓是11V；超過(guò)11V的輸入信號(hào)將對(duì)放大器造成破壞。</p><p>　　隔離可以大大提高數(shù)據(jù)采集設(shè)備的最大工作電壓。在測(cè)量系統(tǒng)的環(huán)境中，“隔離”意味著在物理上和電氣上將電路的兩部分隔開(kāi)。隔離器將數(shù)據(jù)從電路的一個(gè)部分傳送到另一個(gè)部分，而無(wú)需電學(xué)的導(dǎo)通。由于電

60、流無(wú)法流過(guò)隔離器屏障，您可以將數(shù)據(jù)采集設(shè)備的參考地和實(shí)際地隔離。這樣就將最大工作電壓的指標(biāo)與放大器輸入范圍進(jìn)行了解耦。舉例而言，在圖2中，儀器放大器的參考地與實(shí)際地是電學(xué)隔離的。</p><p>　　圖2 隔離將儀器放大器的參考地和實(shí)際地進(jìn)行了電氣分離</p><p>　　盡管輸入范圍與圖1中相同，工作電壓已經(jīng)被擴(kuò)展到60V，能夠抑制55V共模電壓。這時(shí)，最大工作電壓是由隔離電路定義的，

61、而不是由放大器輸入范圍定義的。</p><p>　　燃料電池測(cè)試是需要高直流共模電壓抑制的范例應(yīng)用。每個(gè)獨(dú)立的電池能夠產(chǎn)生大約1V的電壓，而一組電池能夠產(chǎn)生幾千伏特，甚至更高。要精確測(cè)量一個(gè)1V電池的電壓，測(cè)量設(shè)備必須能夠抑制由組內(nèi)其他電池所產(chǎn)生的高共模電壓。</p><p><b>　　抑制交流共模電壓</b></p><p>　　通常共模電

62、壓不會(huì)只由直流電平組成。大多數(shù)共模電壓源除了直流偏置之外，還包含了交流成分。來(lái)自周?chē)姶怒h(huán)境的噪聲不可避免地被耦合到被測(cè)信號(hào)中。這對(duì)于通過(guò)數(shù)據(jù)采集設(shè)備儀器放大器的低電平模擬信號(hào)而言是特別麻煩的。</p><p>　　交流噪聲源可以根據(jù)其耦合機(jī)制大致進(jìn)行分類(lèi)：電容型、電感型或輻射型。電容型耦合來(lái)自于時(shí)變電場(chǎng)，例如由周?chē)^電器或是其他測(cè)量信號(hào)產(chǎn)生的電場(chǎng)。電感型或磁耦合噪聲來(lái)自于時(shí)變磁場(chǎng)，例如由周?chē)鷻C(jī)器或電機(jī)產(chǎn)生的磁場(chǎng)

63、。如果電磁場(chǎng)源距離測(cè)量電路較遠(yuǎn)，例如熒光燈等，電氣和磁場(chǎng)的耦合被認(rèn)為是電磁或是輻射耦合。在所有情況下，時(shí)變共模電壓被耦合到有用的信號(hào)中，通常它在50-60Hz的頻率范圍中(電源頻率)。</p><p>　　理想的測(cè)量電路，其通向儀器放大器正極和負(fù)極端子的路徑是完全平衡的。這樣的系統(tǒng)能夠完全抑制任何交流耦合噪聲。但是，實(shí)際儀器通過(guò)共模抑制比(CMRR)指定了它能夠抑制共模電壓的程度。CMRR是被測(cè)信號(hào)增益相對(duì)于放大

64、器施加的共模增益之間的比值，可以使用下式表示：</p><p>　　選擇在更寬頻率范圍內(nèi)具有更好CMRR的數(shù)據(jù)采集設(shè)備能夠大大提高系統(tǒng)的整體抗噪聲性能。舉例而言，圖3顯示了將低成本M系列設(shè)備與工業(yè)M系列設(shè)備的CMRR相比較的結(jié)果。</p><p>　　圖3 NI 6230能夠比NI 6220提供更高的CMRR(相對(duì)于物理地)</p><p>　　在60Hz下，NI

65、 6230工業(yè)M系列設(shè)備相對(duì)于NI 6220低成本M系列設(shè)備，其CMRR高出了20dB。這等效于對(duì)于60Hz噪聲具有高于10倍以上的衰減。</p><p>　　任何應(yīng)用都能夠從60 Hz噪聲抑制中獲益。然而，對(duì)于包含大型轉(zhuǎn)動(dòng)機(jī)械或電機(jī)的系統(tǒng)需要更高頻率下的噪聲抑制。在1kHz下，NI6230設(shè)備相比NI6220設(shè)備能夠抑制100倍以上的噪聲，從而使它們成為工業(yè)應(yīng)用的理想選擇。</p><p&g

66、t;<b>　　切斷接地回路</b></p><p>　　接地回路通常被認(rèn)為是數(shù)據(jù)采集系統(tǒng)中噪聲最常見(jiàn)的來(lái)源。合適的接地對(duì)于精確測(cè)量而言是十分重要的，但它也是一個(gè)常常被誤解的概念。如果電路中兩個(gè)連接的端子處于不同地電勢(shì)，就形成了接地回路。這個(gè)差別將會(huì)導(dǎo)致電流流入交叉連接點(diǎn)，將會(huì)導(dǎo)致偏置誤差的出現(xiàn)。將問(wèn)題變得更為復(fù)雜的是，在信號(hào)源的地和數(shù)據(jù)采集設(shè)備的地之間的電勢(shì)差通常不是直流電平。這就導(dǎo)致了在

67、讀數(shù)中會(huì)出現(xiàn)電源頻率分量的信號(hào)?？紤]圖4中的簡(jiǎn)單熱電偶應(yīng)用。</p><p>　　圖4 使用接地信號(hào)源的差分熱電偶測(cè)量將會(huì)導(dǎo)致接地回路出現(xiàn)</p><p>　　在這里，原來(lái)十分直觀的溫度測(cè)量由于被測(cè)設(shè)備(DUT)與數(shù)據(jù)采集設(shè)備出現(xiàn)了不同的地電勢(shì)而被復(fù)雜化了。盡管兩個(gè)設(shè)備都共享相同的地，如果電源分布電路沒(méi)有正確連接，就會(huì)導(dǎo)致地電勢(shì)差達(dá)到200 mV甚至更多。這個(gè)差在最后得到的測(cè)量中，以帶有

68、交流分量的共模電壓出現(xiàn)。</p><p>　　回憶一下隔離是將信號(hào)源的地與儀器放大器的參考地進(jìn)行電氣隔離的一種方法(見(jiàn)圖5)。</p><p>　　圖5 隔離通過(guò)將物理地與放大器參考地進(jìn)行分離消除了接地回路</p><p>　　由于電流無(wú)法流過(guò)隔離屏障，放大器參考地可以比物理地具有更高或更低的電勢(shì)。您不會(huì)在無(wú)意中將接地回路引入到電路中。使用隔離的測(cè)量設(shè)備去除了測(cè)量

69、系統(tǒng)適當(dāng)接地的模糊性，確保能夠得到更加精確的結(jié)果。</p><p>　　使用4-20 mA電流回路</p><p>　　較長(zhǎng)的導(dǎo)線長(zhǎng)度和在工業(yè)或惡劣電氣環(huán)境的噪聲使得精確測(cè)量電壓變得十分困難。因此，測(cè)量壓力、流量、位置等等的工業(yè)傳感器通常發(fā)送電流信號(hào)，而不是電壓信號(hào)。4-20 mA電流回路是在許多過(guò)程監(jiān)視應(yīng)用中，通過(guò)遠(yuǎn)距離發(fā)送傳感器信息的常見(jiàn)方法，如圖6所示。</p><

70、;p>　　圖6 儀器放大器使用并聯(lián)電阻將過(guò)程的電流信號(hào)轉(zhuǎn)化為電壓信號(hào)</p><p>　　每個(gè)電流回路包含三個(gè)組成部分——傳感器、電源、一個(gè)或多個(gè)數(shù)據(jù)采集設(shè)備。來(lái)自傳感器的電流信號(hào)通常在4至20mA之間，其中4mA表示最低的信號(hào)值，20 mA表示最大的信號(hào)值。這種傳送方式的優(yōu)點(diǎn)是使用0mA表示開(kāi)路或是連接斷路。電源通常在24至30VDC的范圍內(nèi)，根據(jù)在電路上整個(gè)電壓降進(jìn)行確定。最后，數(shù)據(jù)采集設(shè)備使用位于儀

71、器放大器兩端的高精度并聯(lián)電阻，將電流信號(hào)轉(zhuǎn)化為電壓測(cè)量。由于所有從電源一端流出的電流必須流回另一端，電流回路信號(hào)通常能夠不受大多數(shù)電氣噪聲源和沿著長(zhǎng)導(dǎo)線的電壓(IR)降的影響。此外，為傳感器提供電源的端子還傳送測(cè)量信號(hào)，大大簡(jiǎn)化了現(xiàn)場(chǎng)布線。</p><p>　　如圖6所示的隔離屏障在電流回路應(yīng)用中提供了兩個(gè)主要優(yōu)點(diǎn)。首先，由于電源電壓通常超過(guò)大部分儀器放大器輸入范圍的最大值，隔離對(duì)于隔離放大器地極與物理地到可接受

72、的電壓而言是十分必要的。其次，電流回路的工作原理是電流從不會(huì)從電路中流出。因此，隔離任何通往地的電流回路都可以防止信號(hào)的衰減。例如NI 6238和NI 6239工業(yè)M系列數(shù)據(jù)采集設(shè)備等設(shè)備提供了內(nèi)置并聯(lián)電阻和與物理地之間高達(dá)60VDC隔離用于4-20mA電流回路應(yīng)用。</p><p><b>　　使用24V數(shù)字邏輯</b></p><p>　　測(cè)量噪聲并不局限于模擬信

73、號(hào)。數(shù)字邏輯同樣也可能受到噪聲電氣環(huán)境的影響，可能導(dǎo)致錯(cuò)誤的開(kāi)/關(guān)值或是意外觸發(fā)。有許多與數(shù)字I/O相關(guān)的電壓電平和邏輯系列，其中有些具有更高的噪聲抑制能力。晶體管-晶體管邏輯(TTL)是至今為止最為常見(jiàn)的邏輯系列，它驅(qū)動(dòng)從微處理器直至LED的所有器件。盡管它的用途十分廣泛，TTL可能并不總是所有數(shù)字應(yīng)用的最佳選擇。</p><p>　　對(duì)于工業(yè)應(yīng)用而言，TTL具有小噪聲邊界值的內(nèi)在缺點(diǎn)。高邏輯電平和低邏輯電平分

74、別是2.0V和0.8V，因而誤差的空間很小。例如，TTL輸入的低電平噪聲邊界值是0.3V(它是最大低電平TTL輸入值0.8V和最大低電平TTL輸出值0.5V之間的差)。任何與數(shù)字信號(hào)耦合的超過(guò)0.3V的數(shù)字信號(hào)都會(huì)將電壓平移至0.8V至2.0V之間的未定義區(qū)域。這時(shí)，數(shù)字輸入的行為是不確定的，并且會(huì)產(chǎn)生不正確的數(shù)值(見(jiàn)圖7)。</p><p>　　圖7 24V邏輯相比TTL而言具有更好的噪聲裕度</p&g

75、t;<p>　　但是，24V邏輯提供了更寬的噪聲裕度，具有更好的綜合噪聲抑制。由于大多數(shù)工業(yè)傳感器、執(zhí)行器和控制邏輯已經(jīng)使用24V電源進(jìn)行工作，使用對(duì)應(yīng)的數(shù)字邏輯電平更為方便。由于低電平輸入為4V，高電平輸入為11V，數(shù)字信號(hào)對(duì)噪聲的更為不敏感。</p><p>　　大多數(shù)帶有24V數(shù)字I/O功能的測(cè)量?jī)x器提供了其他噪聲抑制特性。例如，NI工業(yè)M系列和數(shù)字I/O設(shè)備具有可編程輸入濾波器，用于平緩繼電

76、器的輸入。當(dāng)機(jī)械繼電器閉合的時(shí)候，在較短的一段時(shí)間(以毫秒為數(shù)量級(jí))內(nèi)，接觸表面互相之間會(huì)發(fā)生彈跳。如果沒(méi)有濾波器，邏輯輸入可能會(huì)它讀成瞬時(shí)開(kāi)/關(guān)信號(hào)。這些設(shè)備還提供了隔離，如果整個(gè)系統(tǒng)的各個(gè)部件是由不同電源供電的話，這是一個(gè)需要考慮的重要因素。</p><p><b>　　結(jié)論</b></p><p>　　在設(shè)法降低測(cè)量系統(tǒng)噪聲時(shí)，有許多因素需要考慮。除了適當(dāng)?shù)钠帘?/p>

77、、接線和中止之外，認(rèn)真考慮共模電壓、接地和周邊的噪聲源對(duì)于精確的測(cè)量結(jié)果而言是必要的。然而，理解系統(tǒng)的電氣環(huán)境并不是那么簡(jiǎn)單的。隔離是我們?cè)鰪?qiáng)對(duì)測(cè)量結(jié)果信心的一個(gè)簡(jiǎn)單方法，無(wú)論是對(duì)信號(hào)而言還是對(duì)整個(gè)應(yīng)用而言。</p><p>　　Charles Stiernberg</p><p>　　Charles Stiernberg是NI數(shù)據(jù)采集的產(chǎn)品工程師。他獲得了德克薩斯大學(xué)奧斯汀分校電子工程學(xué)