溫濕度單片機(jī)文獻(xiàn)翻譯(1)

1、簡化了的濕度測量與單片機(jī)相對(duì)濕度傳感器簡化了的濕度測量與單片機(jī)相對(duì)濕度傳感器January 1, 2013By: John Gammel, Silicon Laboratories Inc.Sensors摘 要：隨著工業(yè)科技日新月異，濕度傳感技術(shù)得到廣泛應(yīng)用。相較傳統(tǒng)的機(jī)械濕度計(jì)現(xiàn)代電子濕度傳感器通過吸濕材料的電容或者電阻監(jiān)測濕度等相關(guān)系數(shù)的變化。相對(duì)濕度傳感器實(shí)現(xiàn)了溫度和濕度的控制。SI7005溫濕度傳感器采用疏水性覆蓋材料，使用聚酰亞胺莫變化檢測濕度變化。SI7005S集成了一個(gè)ADC，采用了非易失性存儲(chǔ)技術(shù)， 具有一個(gè)12C接口，這種高集成度提高了耐用性和可靠性。關(guān)鍵詞： 相對(duì)濕度；電子

2、傳感器；濕度傳感器1 濕度測量濕度測量變得越來越重要。本文中我們討論單芯片的相對(duì)濕度（RH）傳感器，該單片機(jī)提供了強(qiáng)大的性能，便攜，低功耗，并且可以在各種各樣的應(yīng)用中實(shí)現(xiàn)精確的濕度檢測。濕度傳感技術(shù)被廣泛應(yīng)用于生活中：比如應(yīng)用于暖通空調(diào)和制冷技術(shù)中及醫(yī)療設(shè)備的CPAP呼吸機(jī)技術(shù)中；資產(chǎn)跟蹤和用于食品和醫(yī)藥等行業(yè)的存儲(chǔ)設(shè)備，工業(yè)控制系統(tǒng)，氣象儀器，汽車氣候控制和除霧，移動(dòng)計(jì)算設(shè)備。相對(duì)濕度（RH ）的測量是環(huán)境檢測較困難的技術(shù)挑戰(zhàn)。濕度感測儀器通常依賴于溫度，壓力，質(zhì)量，一個(gè)機(jī)械，電的變化等物質(zhì)，當(dāng)水分被吸收，然后濕度感測儀器導(dǎo)出測量結(jié)果。機(jī)械濕度計(jì)在傳統(tǒng)上用人或動(dòng)物的毛發(fā)來測量濕度，因?yàn)轭^發(fā)的

3、長度隨濕度測量發(fā)生變化。如今，現(xiàn)代電子濕度傳感器通過測量電容或電阻或與濕氣相關(guān)的變化顯示濕度。相對(duì)濕度傳感器，特別是那些依賴于吸濕的聚合物電介體材料的電容變化進(jìn)行測量的，具有包括應(yīng)用程序和使用要求：需要電路板裝配過程中保護(hù)傳感器，特別是在焊料回流，并需要隨后補(bǔ)充水分傳感器 需要保護(hù)傳感器不受損壞或污染。在產(chǎn)品的生命周期中，若長時(shí)間暴露的溫度或濕度傳感器精度受影響，需要溫度校正和線性化適用于濕度讀數(shù)，其中的一些要求，源于電容式濕度傳感器使用的聚酰亞胺薄膜的自然特性。其它的是傳感器的開放式腔體組件暴露的管芯和傳感器薄膜對(duì)環(huán)境的結(jié)果1。 CMOS的制造技術(shù)使人們有可能建立一個(gè)國家的最先進(jìn)的電容式濕度

4、傳感器，提供創(chuàng)新的，具有成本效益的封面?zhèn)鞲性?。服用前仔?xì)看看這些單芯片濕度傳感器，讓我們回顧一些相對(duì)濕度測量的基本原理。2 濕度基礎(chǔ)在空氣中發(fā)現(xiàn)的水蒸汽量相差很大，從接近零到飽和點(diǎn)。不足或過度的濕度，或在兩者之間擺動(dòng)時(shí)，可能會(huì)損壞敏感的材料和物體。人體使用蒸發(fā)冷卻作為其主要的溫度調(diào)節(jié)機(jī)制2。事實(shí)上，人類感覺到從身體而不是溫度本身的熱傳遞的速率。圖1顯示了相對(duì)濕度如何影響我們的舒適性。當(dāng)濕度太高，汗液不易蒸發(fā)，人體可能會(huì)過熱，引起不適。高溫和低濕度的組合可以更有效的冷卻。 露點(diǎn)溫度相對(duì)濕度在90°F人類感知如圖1。>75°F>62，Extremely uncom

5、fortable70°F-74°F52-60Quiteuncomfortable65°F-69°F44-50Somewhat uncomfortable60°F-64°F37-42，Comfortable but humid55°F-59°F1-35Comfortable50°F-54°F26-30Very comfortable<49°F<25A bit dry圖1 RH水平的人類感知傳統(tǒng)上，基于溫度的控制在許多環(huán)境中已被很好地應(yīng)用3。近年來，濕度的測量已經(jīng)越來越重要，特

6、別是在居住，存儲(chǔ)和制造場所。溫度和相對(duì)濕度的控制對(duì)許多材料，包括藥物，食品，織物和木材產(chǎn)品的保存是至關(guān)重要的。不可接受的濕度水平，尤其是在與極端溫度相結(jié)合，顯著到材料的擊穿貢獻(xiàn)。熱加速惡化，以及高濕度提供水分，促進(jìn)有害的化學(xué)反應(yīng)。當(dāng)結(jié)合時(shí)，這些因素可以鼓勵(lì)昆蟲活性和霉菌的生長。非常低的相對(duì)濕度也可有破壞作用，除濕敏感材料和使它們變脆。波動(dòng)較大的溫度和濕度也會(huì)造成損害，通過膨脹和收縮，加速惡化。準(zhǔn)確的濕度測量控制濕度，可以防止損壞和不適，或檢測到儲(chǔ)存或運(yùn)輸過程中造成的產(chǎn)品損壞事件的重要因素。相對(duì)濕度傳感必須是以可用的組件形式實(shí)現(xiàn)與電子控制結(jié)合及經(jīng)濟(jì)有效的集成4。3 測量濕度的技術(shù)濕度可以量化在許

7、多方面，但對(duì)于維持大氣質(zhì)量的最重要的測量是相對(duì)濕度（RH ） 。這是水蒸汽存在于空氣中的實(shí)際量，這是不能吸收任何更多的水分的比率5。絕對(duì)濕度被定義為水蒸汽的質(zhì)量溶解在潮濕的空氣在給定溫度和壓力下的總體積。飽和電平通常被稱為露點(diǎn)或霜點(diǎn)，這取決于相對(duì)濕度值是否可以隨溫度細(xì)微變化或者顯著變化，在溫度變化將引起相對(duì)濕度為的變化。較高的溫度增加了空氣中吸收水分的能力和較低的溫度降低其吸收水分的能力?？諝獾南鄬?duì)濕度降低的空氣被加熱，當(dāng)潮濕的空氣被冷卻時(shí)，其吸收水分的能力降低，從而導(dǎo)致相對(duì)濕度增加。其結(jié)果是，所需要的水蒸汽中空氣的量達(dá)到使溫度露點(diǎn)升高。10的露點(diǎn)，例如，對(duì)應(yīng)于26相對(duì)濕度在32下。最知名的儀

8、器用于濕度測量的是干濕計(jì)，它使用“ wet-bulb/dry-bulb ”的方法6。該裝置由兩個(gè)溫度計(jì)，一個(gè)是普通的干球（干球），另用濕布覆蓋在燈泡（濕球） 。從濕布蒸發(fā)時(shí)，濕球溫度計(jì)將顯示的溫度低于干球只要空氣不飽和的水蒸汽。一個(gè)查找表被用來從兩個(gè)溫度讀數(shù)推導(dǎo)出相對(duì)濕度。濕度傳感器的缺點(diǎn)包括響應(yīng)時(shí)間慢，物理尺寸精度低，確保它周圍的氣流良好的維護(hù)問題。用于測量當(dāng)前濕度最準(zhǔn)確的方法是冷鏡濕度計(jì)。這種技術(shù)使用一個(gè)光電機(jī)制來檢測縮合形成的溫度控制鏡面7。鏡子維持在一個(gè)準(zhǔn)確的測量溫度，冷卻到凝結(jié)形式?？s合散射發(fā)射LED的光，這會(huì)導(dǎo)致在接收光電晶體管的輸出突然下降。在此凝結(jié)形成提供了可用于濕度值可以計(jì)算

9、露點(diǎn)溫度。因?yàn)樗麄兯枰臋C(jī)械系統(tǒng)，冷鏡濕度計(jì)儀器體積大，往往價(jià)格昂貴，不切實(shí)際的大批量消費(fèi)電子、汽車和住宅應(yīng)用。機(jī)械濕度計(jì)通常具有較差的精度，通常在±10的范圍內(nèi)。最常見的例子使用了一塊動(dòng)物毛發(fā)張力下保持。隨著濕度的增加，頭發(fā)松弛和伸展和該長度變化可以由應(yīng)變儀來測量。4 電子濕度傳感技術(shù)電子濕度傳感器克服了許多困擾解決了舊技術(shù)的尺寸和成本的問題。最常用的技術(shù)依賴于任何的吸濕性材料的電阻或電容的改變。一種電容傳感器包括由電介質(zhì)材料分隔開的兩個(gè)電極。典型地，如在空氣中增大的水蒸汽含量，傳感器的介電常數(shù)增大，改變對(duì)應(yīng)于該濕度水平所測量的電容。一個(gè)電阻傳感器包括一個(gè)導(dǎo)電層隔開的兩個(gè)電極8。

10、在這種情況下，變化的濕度導(dǎo)致的變化的傳感層的導(dǎo)電性。新技術(shù)用于生產(chǎn)薄膜，這些類型的濕度傳感器準(zhǔn)確，穩(wěn)定，易于制造大量。吸濕材料的選擇保證了快速的響應(yīng)時(shí)間有小的滯后。例如，聚酰亞胺膜，它可以在厚度為小于5微米來制造，可以在小于10秒濕度變化的響應(yīng)，同時(shí)提供良好的穩(wěn)定性。電子濕度傳感器的精度通常隨時(shí)間漂移，通常是由溫度和濕度或污染物的存在很大的差異的限制。以提高相對(duì)濕度測量的精度，這也是有效的測量溫度，以提供給設(shè)備在必要時(shí)的相對(duì)濕度測量的溫度補(bǔ)償。以確定的露點(diǎn)或絕對(duì)濕度，也需要環(huán)境空氣溫度。例如，在測量溫度1° C錯(cuò)誤將在露點(diǎn)計(jì)算生產(chǎn)約1錯(cuò)誤。為獲得最佳精度，濕度和溫度的測量，應(yīng)采取盡可

11、能接近彼此，并且理想共同位于同一芯片上。這樣的接近度可以是難以實(shí)現(xiàn)與許多傳統(tǒng)的電子傳感器的設(shè)計(jì)9。許多當(dāng)今的電子傳感器設(shè)計(jì)中使用分立的電阻和電容式傳感器，混合，和多芯片模塊。這些傳統(tǒng)方法因材料清單（BOM）成本和元件數(shù)量大，以及需要?jiǎng)趧?dòng)密集，客戶校準(zhǔn)高的法案。進(jìn)一步的問題是，離散傳感器解決方案通常是用標(biāo)準(zhǔn)不兼容的表面貼裝技術(shù)（SMT ）裝配流程。5 單片機(jī)傳感器技術(shù)傳感器必須保持清潔和完好的制造過程中，因?yàn)閭鞲衅髟仨毐槐┞对诃h(huán)境中，以執(zhí)行其功能回流焊的極端熱循環(huán)以及轉(zhuǎn)移濕度傳感器的性能，這并不總是包含在制造商的精度指標(biāo)，產(chǎn)品的生命過程中的濕度傳感器需要保護(hù)，需要使用某種類型的覆蓋物或過濾器

12、，它可以阻礙傳感器的響應(yīng)在一些實(shí)施方式中的先進(jìn)設(shè)備，在最先進(jìn)的傳感器解決方案10。該Si7005溫濕度傳感器由Silicon Labs公司解決了許多由離散，混合，模塊化和濕度傳感器系統(tǒng)所帶來的設(shè)計(jì)和制造方面的挑戰(zhàn)。該Si7005傳感器采用疏水性覆蓋材料，為傳感器的終身保障。該溫濕度傳感器有膨脹聚四氟乙烯（ePTFE）的疏水性過濾器的材料制成，可以防止灰塵和液體的大部分，并且其結(jié)構(gòu)允許水蒸汽通過它，以確保過濾器不會(huì)影響傳感器的響應(yīng)時(shí)間。因?yàn)樵赟i7005傳感器的可選的蓋被安裝在工廠，沒有時(shí)間或勞力花費(fèi)PCB組裝過程中添加和除去保護(hù)帶，蓋不必被設(shè)計(jì)在產(chǎn)品設(shè)計(jì)中。該Si7005使用的聚酰亞胺膜的變化

13、來檢測濕度。此敏感薄膜被沉積在一個(gè)金屬手指的電容中。精密帶隙參考電路，位于同一芯片作為濕度傳感器，提供溫度測量。在同一裸片上檢驗(yàn)，確保溫度和濕度測量相似，提供出色的測量精度。該Si7005使用的聚酰亞胺膜的變化來檢測濕度11。如果冷凝集上的傳感器，芯片上的加熱器可以被激活以干燥該傳感器和還原操作，一旦傳感器是在露點(diǎn)以上，管芯上的溫度傳感器確保微控制器（MCU ）收集的濕度讀數(shù)可以采取這種加熱效應(yīng)。該器件的長期測量漂移由于老化是不超過0.25 RH /年。 ，這是不到許多同類競爭器件漂流的一半。指定的精度包括津貼對(duì)回流焊的影響。作為一個(gè)整體的解決方案， Si7005也是出廠時(shí)校準(zhǔn)。該Si7005

14、需要額外的單片集成來簡化系統(tǒng)設(shè)計(jì)，并提供更大的模塊功能單一，緊湊的4毫米×4 mm QFN封裝的優(yōu)勢。除了感測元件時(shí)， Si7005集成了一個(gè)ADC信號(hào)處理和非易失性存儲(chǔ)器來用于校準(zhǔn)的數(shù)據(jù)，以及一個(gè)I2C接口（圖2） 。這種高集成度提高了耐用性和可靠性，降低了成本和開發(fā)時(shí)間，并簡化電路板設(shè)計(jì)，也有助于降低功耗。該Si7005平的平均值， 1微安用于執(zhí)行一個(gè)溫度和每分鐘1濕度讀數(shù)。圖2 Si7005濕度傳感器通過使用單片集成的創(chuàng)新設(shè)計(jì)，該Si7005傳感器帶來的成本效益和精確的相對(duì)濕度和溫度監(jiān)測，使其在濕度監(jiān)測和控制應(yīng)用范圍日益擴(kuò)大。 參考文獻(xiàn) 1 HU Hongbin. M

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20、rogramming language M.john wiley&sons press. 2005.180  190. Simplifying Humidity Measurement with Single-Chip Relative Humidity Sensors January 1, 2013 By: John Gammel, Silicon Laboratories Inc. SensorsAbstract: With changing industrial science and technology,

21、the humidity sensing technology is widely used. Compared with traditional mechanical hygrometer modern electronic humidity sensor by hygroscopic material capacity or resistance monitor changes in humidity, such as correlation coefficient. Relative humidity sensor for temperature and humidity control

22、. SI7005 temperature and humidity sensor is hydrophobic cover material, the use of polyimide testing humidity changes. SI7005S integrates a ADC, used the nonvolatile storage technology, with a 12 c interface, the high level of integration to improve the durability and reliability.Keywords：Relative h

23、umidity; electronic sensors; humidity sensor1 Humidity measurementHumidity measurement is increasingly important in an expanding number of industries. In this article we discuss a single-chip relative humidity (RH) sensor that offers robust performance, a small size, and low power consumption and ca

24、n enable accurate humidity sensing in a wide variety of applications.Humidity sensing technology is critical to a wide range of applications, including HVAC and refrigeration; healthcare equipment, such as CPAP machines and ventilators; asset tracking and storage devices for the food and pharmaceuti

25、cal industries; industrial control systems; meteorological instruments; automotive climate control and defogging; and mobile computing devices. Despite the number of industries and applications that require it, relative humidity (RH) measurement is among the more difficult technical challenges in en

26、vironmental sensing.Humidity sensing instruments typically rely on measurements of temperature, pressure, mass, or a mechanical or electrical change in a substance when moisture is absorbed from which the humidity can then be derived. Mechanical hygrometers (Figure 1) have traditionally used human o

27、r animal hair to measure humidity because the length of the hair changes measurably with increasing humidity. Nowadays, modern electronic humidity sensors operate by measuring the moisture-related changes in electrical capacitance or resistance or the temperature at which condensation appears1.RH se

28、nsors, in particular those that rely on measurements of the capacitance changes of hygroscopic polymeric dielectric materials, have application and usage requirements that include:The need to protect the sensor during board assembly, especially during solder reflow, and the need to subsequently rehy

29、drate the sensor.2.The need to protect the sensor from damage or contamination during the product life cycleThe potential impact on sensor accuracy of prolonged exposure to extremes of temperature and/or humidity.The need to apply temperature correction and linearization to the humidity readings.Som

30、e of these requirements stem from the natural characteristics of the polyimide films used in capacitive RH sensors. Others are a result of the sensor's open-cavity package that exposes the die and the sensor film to the environment. CMOS manufacturing techniques have made it possible to build st

31、ate-of-the-art capacitive humidity sensors that provide innovative, cost-effective covers for the sensing element. Before taking a closer look at these single-chip humidity sensors, let's review some of the basic principles of RH measurement4.2 Fundamentals of HumidityThe amount of water vapor f

32、ound in air can vary dramatically, from close to zero to the point of saturation. Insufficient or excessive humidity, or swings between the two, can damage sensitive materials and objects. The human body uses evaporative cooling as its primary temperature-regulation mechanism. In actual fact, humans

33、 feel the rate of heat transfer from the body rather than temperature itself. Figure 2 shows how the relative humidity affects our comfort. When humidity is so high that perspiration cannot easily evaporate, the body may overheat, causing discomfort. A combination of high temperature and low RH allo

34、ws more effective cooling.Figure 1. Human perception of RH levelsDew Point TemperatureRH at 90°FHuman Perception >75°F>62%Extremely uncomfortable70°F74°F52%60% Quiteuncomfortable65°F69°F44%50%Somewhat uncomfortable60°F64°F37%42%Comfortable but humid55

35、76;F59°F31%35%Comfortable50°F54°F26%30%Very comfortable<49°F<25%A bit dryTraditionally, many environments have been controlled based on temperature. In recent years, the measurement of humidity has grown in importance, especially in living, storage, and manufacturing sites.

36、 Control of temperature and RH is also critical in the preservation of many materials including medications, foods, fabrics, and wood products5.Unacceptable humidity levels, especially when combined with temperature extremes, contribute significantly to the breakdown of materials. Heat accelerates d

37、eterioration, and high RH provides moisture, which promotes harmful chemical reactions. When combined, these factors can encourage insect activity and the growth of mold. Extremely low RH can also have damaging effects, desiccating sensitive materials and causing them to become brittle. Large fluctu

38、ations in temperature and RH also cause damage through expansion and contraction, accelerating deterioration.Accurate humidity measurement is a vital part of controlling humidity to prevent damage, discomfort, or to detect events that may have caused product damage during storage or transit. For wid

39、espread use, RH sensing must be available in a component form that enables easy, cost-effective integration with electronic controls6.3 Techniques for Measuring HumidityHumidity can be quantified in a number of ways, but the most important measurement for maintaining atmospheric quality is relative

40、humidity (RH). This is the ratio of the actual water vapor present in air to the amount of water vapor present in saturated air, which cannot absorb any more moisture. Absolute humidity is defined as the mass of water vapor dissolved in a total volume of moist air at a given temperature and pressure

41、7.The saturation level is generally called the dew point or frost point, depending on the temperature. The RH value can change significantly with even slight variations in temperature; a 1°C change in temperature at 35°C and 75% RH will introduce a 4% change in RH. A higher temperature inc

42、reases the ability of air to absorb moisture and a lower temperature decreases its ability to absorb moisture. The RH of air decreases as the air is heated; when moist air is cooled, its capacity to absorb moisture decreases, causing the RH to increase. As a result, the amount of water vapor in air

43、needed to reach the dew point increases with temperature. The dew point at 10°C, for example, corresponds to a RH of 26% at 32°C.The best-known instrument for humidity measurement is the psychrometer, which uses the "wet-bulb/dry-bulb" method. The device consists of two thermomet

44、ers, one with an ordinary dry bulb and the other with a moist cloth covering the bulb (the wet bulb). As evaporation from the moist cloth occurs, the wet-bulb thermometer will show a lower temperature than the dry bulb as long as the air is not saturated with water vapor8. A look-up table is used to

45、 derive the RH from the two temperature readings. The disadvantages of a psychrometric sensor include slow response time, large physical size, and the maintenance issues of keeping one thermometer bulb wet and ensuring good airflow around it.The current most accurate method for measuring humidity is

46、 the chilled mirror hygrometer. This technique uses an optoelectronic mechanism to detect condensation that forms on a temperature-controlled mirror surface. The mirror is maintained at an accurately measured temperature and cooled until condensation forms. The condensation scatters the transmitting

47、 LED's light, which results in a sudden drop in the output of the receiving phototransistor. The temperature at which condensation forms provides the dew point from which the humidity value can be calculated. Because of the mechanical systems they require, chilled-mirror hygrometer instruments a

48、re bulky, often expensive, and impractical for use in high-volume consumer, automotive, and residential applications.Mechanical hygrometers typically exhibit poor accuracyoften in the range of ±10%. The most common example uses a piece of animal hair kept under tension. As humidity increases, t

49、he hair relaxes and stretches and this length change can be measured by a strain gauge.4 Electronic Humidity Sensing TechnologyElectronic humidity sensors overcome many of the size and cost problems that plague older techniques. The most commonly employed techniques rely either on a change in the re

50、sistance or capacitance of a hygroscopic material. A capacitive sensor consists of two electrodes separated by a dielectric material. Typically, as the water vapor content in the air increases, the sensor's dielectric constant increases, changing the measured capacitance corresponding to the hum

51、idity level. A resistive sensor consists of two electrodes separated by a conductive layer. In this case, variations in humidity result in changes in the conductivity of the sensing layer9.New techniques for producing thin films have made these types of RH sensors accurate, stable and easy to manufa

52、cture in large quantities. The choice of hygroscopic material assures fast response times with little hysteresis. For instance, a polyimide film, which can be fabricated in thicknesses of <5 µm, can respond to changes in humidity in <10 s while providing excellent stability. The accuracy

53、of an electronic RH sensor is limited by its drift over time, generally caused by wide variations in temperature and humidity or the presence of pollutants.To enhance the accuracy of RH measurements, it is also helpful to measure the temperature to provide temperature compensation for the RH measure

54、ment of the device if necessary. To determine the dew point or absolute humidity, the ambient air temperature is also required. For instance, a 1°C error in the measured temperature will produce approximately a 1°C error in the dew-point calculation. For the best accuracy, humidity and tem

55、perature measurements should be taken as close as possible to each other, and ideally co-located on the same chip. Such proximity can be difficult to achieve with many traditional electronic sensor designsMany of today's electronic sensor designs use discrete resistive and capacitive sensors, hy

56、brids, and multi-chip modules, as shown in Figure 3. These legacy approaches suffer from high bill of materials costs and component counts, large footprints, and the need for labor-intensive customer calibration10. A further problem is that discrete sensor solutions are often incompatible with stand

57、ard surface mount technology assembly flows.5 A monolithic sensor A monolithic sensor still has to contend with the following manufacturing issues:The sensor must be kept clean and undamaged during manufacturing because the sensor element must be exposed to the environment to perform its functionThe

58、 extreme thermal cycle of solder reflow can shift the performance of humidity sensors, an effect that is not always included in manufacturers' accuracy specificationsThe humidity sensor requires protection during the life of the product, requiring the use of some type of cover or filter, which c

59、an impede sensor responsiveness in some implementations.State-of-the-Art Sensor SolutionThe Si7005 temperature and humidity sensor from Silicon Labs addresses many of the design and manufacturing challenges posed by discrete, hybrid, and modular humidity sensor systems. The Si7005 sensor uses a hydrophobic cover material to provide lifelong protection for the sensor underneath. The cover, made from an expanded polytetrafluoroethylene hydrophobi