濕度傳感器系統(tǒng)畢業(yè)論文中英文資料外文翻譯

1、<p><b>　　中文2386字</b></p><p><b>　　英文:</b></p><p>　　The right design for a relative humidity sensor system</p><p>　　Optimizing the response characteristic

2、s and accuracy of a humidity sensor system</p><p>　　1 Overview</p><p>　　To make the right choice when selecting a relative humidity sensor for an application, it is important to know and to be

3、able to judge the deciding factors. In addition to long-term stability, which is a measure on how much a sensor changes its properties over time, these factors also include the measurement accuracy and the response chara

4、cteristics of the sensor. Capacitive humidity sensors are based on the principle that a humidity-sensitive polymer absorbs or releases moisture as a function o</p><p>　　Measurement accuracy</p><p&

5、gt;　　The term measurement accuracy of a humidity sensor is understood primarily to refer to the deviation of the value measured by the sensor from the actual humidity. To determine the measurement accuracy, references, s

6、uch as chilled mirror hygrometers, whose own tolerance must be taken into account, are used. In addition to this trivial component, humidity sensors require a given time for reaching stable humidity and temperature equil

7、ibrium (the humidity is a function of temperature and decreases w</p><p>　　Response characteristics and response time</p><p>　　The response characteristics are defined by various parameters. The

8、se are:</p><p>　　The actual response characteristics of the humidity sensor at constant temperature.</p><p>　　(1) How quickly the sensitive polymer absorbs or releases moisture until equilibrium

9、 is reached (intrinsic response time)</p><p>　　(2) How fast the entire system reaches humidity equilibrium (housing effect)</p><p>　　The thermal response characteristics of the humidity sensor a

10、t a non-constant temperature</p><p>　　(3) The thermal mass of the sensor</p><p>　　(4) The system's thermal mass, which is thermally coupled to the sensor (e.g. printed circuit board)</p

11、><p>　　(5) Heat sources in the direct surroundings of the sensor (electronic components)</p><p>　　(1) and (3) are determined entirely by the sensor itself, (1) primarily by the characteristics of t

12、he sensitive polymer.</p><p>　　(2) and (4) are primarily determined by the construction of the entire system (shape and size of housing andreadout circuitry).</p><p>　　(5) is determined by heat-

13、emitting electronic components.</p><p>　　These points will be discussed in more detail in the following.</p><p>　　The intrinsic response time (1)</p><p>　　Qualitatively, the respons

14、e characteristics of capacitive humidity sensors look like the following (Fig. 1).</p><p>　　Fig. 1: Typical and idealized response characteristics of capacitive humidity sensors (schematic)</p><p&

15、gt;　　Because these response characteristics are especially pronounced at high humidity values, an isothermal humidity jump from 40% to 100% was selected here for illustration. The desired ideal behavior of the sensor is

16、indicated in blue. In practice, however, the sensor behaves according to the red line, approximately according to:</p><p>　　Here, the time span 1 is usually very short (typ. 1 – 30 min.), in contrast, the ti

17、me span 2 is very long (typ. Many hours to days). Here the connection of measurement accuracy and response characteristics becomes clear (t until RH=100% is reached). The value at t4 (Fig. 1) is considered to be an exact

18、 measured value. However, this assumes that both the humidity and also the temperature remain stable during this entire time, and that the testing waits until this very long measurement time is com</p><p>　　

19、1.The measured value at t2 (Fig. 1) is used as a calibration reference.</p><p>　　Advantage:</p><p>　　The required measurement time for reaching the end value (in the example 100%) is clearly sho

20、rtened,corresponds to practice, and achieves an apparent short response time of the sensor (cf. Fig. 2).</p><p>　　Disadvantage:</p><p>　　If the conditions are similar for a long time (e.g., wet

21、periods in outdoor operation), the sensors exceed the correct end value (in the example 100%) undesirably by up to 10% (cf. Fig. 2).</p><p>　　2. The measured value at t4 (Fig. 1) is used as a calibration ref

22、erence.</p><p>　　Advantage:</p><p>　　Even for similar conditions over a long time (e.g., wet periods in outdoor operation), an exact measurement result is obtained (cf. Fig. 2).</p><p

23、>　　Disadvantage:</p><p>　　For a humidity jump like in Fig. 1, the sensors very quickly deliver the measured value at t2, but reaching a stable end value (about 3-6% higher) takes a long time (apparent lon

24、ger response time)(cf. Fig. 2).</p><p>　　In order to take into account both approaches optimally, the measured values at t3 (cf. Fig. 1) are used as the calibration reference by Sensirion AG.</p><

25、p>　　Fig. 2: Response characteristics of different humidity measurement systems</p><p>　　The housing effect on the response time (2)</p><p>　　Here, two types of transport phenomena play a deci

26、ding role:</p><p>　　Convection: For this very fast process, the air, whose humidity is to be determined, is transported to the sensor by means of ventilation.</p><p>　　Diffusion: This very slow

27、process is determined by the thermal, molecular self-motion of the water molecules. It occurs even in "stationary" air (e.g., within a housing), but leads to a long response time.</p><p>　　In order

28、 to achieve favorable response characteristics in the humidity measurement system, the very fast convection process must be supported by large housing openings and the slow diffusion process must be supported by a small

29、housing around the sensor (small "dead volume") with "stationary" air reduced to a minimum. The following applies:</p><p>　　Thermal effects (3), (4), and (5)</p><p>　　Because

30、 the total thermal mass of the humidity measurement system (sensor + housing) has a significant effect on its response time, the total thermal mass must be kept as low as possible. The greater the total thermal mass, the

31、 more inert the measurement system becomes thermally and its response time, which is temperature-dependent, increases. In order to prevent measurement errors, the sensor should not be mounted in the vicinity of heatgener

32、ating components.</p><p>　　Summary – what should be taken into account when designing a humidity measurement system</p><p>　　In order to achieve error-free operation of a humidity-measurement sy

33、stem with response times as short as possible, the following points should be taken into account especially for the selection of the sensor and for the design of the system.</p><p>　　The selection of the hum

34、idity sensor element. It should</p><p>　　● be as small as possible,</p><p>　　● have a thermal mass that is as low as possible,</p><p>　　● work with a polymer, which exhibits mini

35、mal fluctuations in measured values during the time span 2(cf. Fig. 1); testing gives simple information on this condition,</p><p>　　● provide calibration, which corresponds to the requirements (see above),

36、 e. g.,</p><p>　　SHT11/SHT15 from Sensirion.</p><p>　　The housing design (cf. Formula 1). It should</p><p>　　● have air openings that are as large as possible in the vicinity of th

37、e sensor or the sensor should be operated outside of the housing à good convection!</p><p>　　● enclose a "dead volume" that is as small as possible around the sensor à little diffusion!&

38、lt;/p><p>　　The sensor should be decoupled thermally as much as possible from other components, so that the response characteristics of the sensor are not negatively affected by the thermal inertia of the entir

39、e system.(e.g., its own printed circuit board for the humidity sensor, structurally partitioning the housing to create a small volume for the humidity sensor, see Fig. 3)</p><p>　　Fig. 3: Mounting example fo

40、r Sensirion sensors SHT11 and SHT15 with slits for thermal decoupling</p><p>　　The sensor should not be mounted in the vicinity of heat sources. If it was, measured temperature would increase and measured hu

41、midity decrease.</p><p>　　Design proposal</p><p>　　The challenge is to realize a system that operates cleanly by optimally taking into account all of the points in section 4. The already calibra

42、ted SMD humidity sensors SHT11 and SHT15 from Sensirion are the ideal solution. For optimum integration of the sensors in a measurement system, Sensirion AG has also developed a filter cap as an adapter aid, which takes

43、into account as much as possible the points in section 4 and also protects the sensor against contaminants with a filter membrane. Fig. 4</p><p>　　Fig. 4: Filter cap for SHT11 and SHT15</p><p>　

44、　In addition to the advantages mentioned above, there is also the option of building an IP67-compatible humidity measurement device (with O-ring, cf. Fig. 4) with optimal performance. Detailed information is available on

45、 the Sensirion Web site.</p><p><b>　　譯文：</b></p><p>　　相 對 濕 度 傳 感 器 系 統(tǒng) 的 正 確 設(shè) 計</p><p>　　濕度傳感器系統(tǒng)精度及響應(yīng)特性的優(yōu)化</p><p><b>　　綜述</b></p><p

46、>　　為了在相對濕度的應(yīng)用方面對傳感器做出正確的選擇，了解和評估那些起決定作用的因素是非常重要的。除了衡量傳感器性能隨時間變化而變化的長期穩(wěn)定性這個因素以外，還應(yīng)考慮傳感器的測量精度和響應(yīng)特性這兩個因素。電容式濕度傳感器工作是基于這樣一個原理；其濕敏聚合體元件能吸收或釋放濕氣被看作是與周圍環(huán)境濕度相關(guān)的一項功能，由于這種方法僅僅測量了傳感器所在位置這一點的濕度，而通常是要測量其周圍濕度這個數(shù)值，所以傳感器必須在周圍環(huán)境濕度平衡的狀

47、態(tài)下獲得精確的測量值（參</p><p>　　照“響應(yīng)時間的殼體（1）效應(yīng)”這一部分）。這個濕度平衡過程可以通過各種用時間常數(shù)表征的傳輸現(xiàn)象得以實現(xiàn)。測量精度和響應(yīng)時間是如此地接近并且相互依賴，使?jié)穸葴y量系統(tǒng)的結(jié)構(gòu)設(shè)計成為一項挑戰(zhàn)。</p><p><b>　　測量精度</b></p><p>　　濕度傳感器的測量精度這個術(shù)語主要用于表述濕度傳

48、感器的測量值與實際濕度之間的偏差值。要確定測量精度，應(yīng)參考使用冷鏡式濕度計，同時必須考慮冷鏡自身的誤差范圍。除了這個微不足道的部件以外，濕度傳感器還需要給定一個達(dá)到濕度與溫度穩(wěn)定平衡的時間。（濕度是溫度的函數(shù)，濕度會隨著溫度升高而降低，傳感器與被測環(huán)境之間的溫差會導(dǎo)致濕度測量誤差）更詳細(xì)的說明請見下一節(jié)。</p><p>　　3．響應(yīng)特性和響應(yīng)時間</p><p>　　響應(yīng)特性的各種定義：

49、</p><p>　　恒溫狀態(tài)下濕度傳感器的實際響應(yīng)特性：</p><p>　　1. 濕敏聚合體吸收或釋放濕氣達(dá)到濕度平衡狀態(tài)時的時間快慢。（固有的響應(yīng)時間）</p><p>　　2. 整個系統(tǒng)到達(dá)濕度平衡時所需要的時間快慢。（殼體效應(yīng)）</p><p>　　非恒溫狀態(tài)下濕度傳感器的熱響應(yīng)特性</p><p>　　3.

50、 傳感器的熱質(zhì)量。</p><p>　　4. 與傳感器相關(guān)的系統(tǒng)熱質(zhì)量。（例如印刷線路板的結(jié)構(gòu)影響）</p><p>　　5. 傳感器周圍的直接熱源。（例如電子元器件發(fā)熱影響）</p><p>　　1 和3 完全取決于傳感器自身特性。1 主要取決于敏感聚合體的特性。</p><p>　　2 和4 主要取決于整個系統(tǒng)的結(jié)構(gòu)設(shè)計。（殼體的形狀和尺

51、寸設(shè)計以及輸出電路設(shè)計）5 取決于電子元器件的發(fā)熱量。</p><p>　　以上幾點將在下面做詳細(xì)討論；</p><p><b>　　固有的響應(yīng)時間1</b></p><p>　　電容式濕度傳感器的時間響應(yīng)特性看起來就和下面圖1 所示一樣</p><p>　　圖 1 典型的和理想的電容式濕度傳感器響應(yīng)特性（示意圖）<

52、;/p><p>　　由于在高濕階段其響應(yīng)特性表現(xiàn)的特別明顯，故選擇了濕度從40%RH 到100%RH 的等溫階躍來說明。所期望的傳感器的理想響應(yīng)特性用藍(lán)色虛線表示，而實際的響應(yīng)特性用紅線表示，其近似公式為：</p><p>　　這里，時間段1 通常非常短（大約1--30 分鐘）。相比之下時間段2 是很長很長的，（數(shù)小時至數(shù)天），測量精度與響應(yīng)特性的關(guān)系在這張圖上看得更清晰了（t 延續(xù)到濕度達(dá)到

53、100%RH 時為止）。t4 時間所對應(yīng)的測量值是非常精準(zhǔn)的。無論如何，得假定在整個t4測試時間段內(nèi)濕度和溫度都要保持穩(wěn)定并且等候完成測試所需要的時間也很長。在實踐中這些不尋常的工作條件是很難實現(xiàn)的。實際的校準(zhǔn)工作通常用以下兩種方法（參見圖2）：</p><p>　　1. 以t2 時間對應(yīng)的測量值作為校驗參考基準(zhǔn)；</p><p><b>　　優(yōu)點：</b></

54、p><p>　　到達(dá)終端值（例如100%RH）所需要的測量時間明顯地縮短了，對應(yīng)于實際上的快速響應(yīng)傳感器。（參考圖2）</p><p><b>　　缺點</b></p><p>　　如果相類似的條件長時間不變，（例如雨季時在戶外測量）傳感器的測量值將超過校準(zhǔn)參考點（100%RH）令人遺憾地達(dá)到110%RH。 （參考圖2）</p>&l

55、t;p>　　2. 以t4 時間（參考圖1）對應(yīng)的測量值作為校驗參考基準(zhǔn)；</p><p><b>　　優(yōu)點：</b></p><p>　　應(yīng)用于相類似的條件且長時間不變，（例如雨季時在戶外測量），可以得到精準(zhǔn)的測量結(jié)果。（參考圖2）</p><p><b>　　缺點</b></p><p>　

56、　對于像圖1 那樣的濕度躍升，傳感器會很快在t2 時間達(dá)到相應(yīng)的測量值。但是，要到達(dá)距其還有3%RH -- 6%RH的終端測量值還需要很長的時間。（顯然其響應(yīng)時間更長，參考圖2）</p><p>　　綜合以上兩種處理方法的優(yōu)點，Sensirion AG 采用t3時間（參考圖1）對應(yīng)的測量值作為校驗參考基準(zhǔn)。</p><p>　　圖2. 不同測量系統(tǒng)的響應(yīng)特性</p><

57、p>　　響應(yīng)時間的殼體效應(yīng)（2）</p><p>　　在這里有兩種傳輸現(xiàn)象扮演重要的角色。</p><p>　　對流：這是個很快的過程，空氣中被測量的濕氣是利用通風(fēng)的方法實現(xiàn)傳輸?shù)摹?lt;/p><p>　　傳導(dǎo)：這是個很慢的由水分子的分子熱運(yùn)動決定的過程，它出現(xiàn)在“靜止的”空氣中（例如在殼體內(nèi)部），使響應(yīng)時間變長。</p><p>　　要

58、在濕度測量系統(tǒng)中獲得良好的響應(yīng)特性，必須增大殼體開孔以得到快速的對流，同時努力減小傳感器周圍“靜止的”空間（即減小“死區(qū)”）。以下公式適用：</p><p>　　熱影響（3）、（4）及（5）</p><p>　　由于濕度測量系統(tǒng)（傳感器+殼體）總的熱質(zhì)量對其響應(yīng)特性有著重要的影響，所以設(shè)計時必須盡可能地減小其熱質(zhì)量。測量系統(tǒng)逐漸變熱，受溫度影響的的系統(tǒng)響應(yīng)時間就會增加；系統(tǒng)總熱質(zhì)量越大，其

59、惰性也越大。為了防止附加的測量誤差，傳感器不要安裝在發(fā)熱的電子元器件附近。</p><p>　　4 . 總結(jié)—設(shè)計濕度測量系統(tǒng)時應(yīng)該考慮的問題</p><p>　　為了實現(xiàn)濕度測量系統(tǒng)的無誤差運(yùn)行，系統(tǒng)的響應(yīng)時間應(yīng)盡可能的短。以下幾點在選擇系統(tǒng)傳感器時應(yīng)當(dāng)引起特別注意：</p><p>　　所選擇的濕度傳感元件應(yīng)該是：</p><p>　　●

60、 幾何尺寸越小越好</p><p>　　● 其熱質(zhì)量越小越好</p><p>　　● 具有濕敏聚合體結(jié)構(gòu)；其在時間段2 上的測量值波動極小(參考圖1)，在測試條件下能提供簡單的測試報告。</p><p>　　● 能提供校準(zhǔn)以對應(yīng)上述的各種需求，就像Sensirion SHTXX 系列傳感器所能提供的那種校準(zhǔn)。</p><p>　　殼體設(shè)計(參

61、考公式1)應(yīng)考慮：</p><p>　　● 傳感器周圍空氣流通口的尺寸要盡可能地大，或者直接將傳感器置于殼外 → 對流性最好封入套管內(nèi)時傳感器周圍的“死區(qū)”要盡可能地小，→ 傳導(dǎo)性最小。</p><p>　　傳感器應(yīng)盡可能地減少與其它元器件的熱連接，只有這樣整個系統(tǒng)的熱慣性才不至于對其響應(yīng)特性產(chǎn)生負(fù)面作用。（例如：印刷線路板被分隔成很小的一個體積來支撐傳感器。見圖3）</p>

62、<p>　　圖3 Sensorion SHT1X 系列傳感器帶有減少熱連接的縫隙的安裝設(shè)計舉例</p><p>　　傳感器絕不要安裝在熱源附近。那樣會導(dǎo)致被測溫度比實際溫度高，而濕度則降低的結(jié)果。</p><p><b>　　5. 設(shè)計指南</b></p><p>　　要實現(xiàn)一個操作簡捷的濕度測量系統(tǒng)，應(yīng)充分考慮到第4 部分的所有重