測控技術與儀器 外文翻譯 外文文獻 英文文獻 高穩(wěn)定性電容傳感器系統(tǒng)及其性能評價

1、譯文標題A High-St Capacitance Sensor System and Its Evaluation ability原文標題高穩(wěn)定性電容傳感器系統(tǒng)及其性能評價作 者Svetlana .譯名斯維特拉娜國籍美國Avramov-Zamurovic原文出處IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 58, NO. 4, APRIL 2009摘要一種安裝有微控制器，商用溫濕傳感器，電容容量數(shù)字化轉換器 和一個特制的電容傳感器的新型傳感器系統(tǒng)誕生了。我們通過仿真和 對樣機的測試對該系統(tǒng)的性能進行了評價。我們通過對周邊

2、環(huán)境條件 的變化對系統(tǒng)的影響的分析制作了一個溫濕補償器。根據(jù)在不受控環(huán) 境條件下，用1pF標準電容進行實驗獲得的數(shù)據(jù)，我們知道系統(tǒng)24 小時穩(wěn)定性是在30/106以內。高穩(wěn)定性和高靈敏性使該系統(tǒng)在物體 探測領域能夠得到有效的應用。根據(jù)在不同狀況下對不同材料的探測 要求，我們設計出了幾種傳感器并對它們的性能進行了評價。關鍵詞一電容測量，電容傳感器，電場仿真，濕度，溫度變化。導言最近的技術進步提供了輸入范圍在幾皮法之間的高分辨率（24 位）Z 電容容量數(shù)字化轉換器（CDC），這些CDCs的潛在的應用領 域是非常廣泛的。電容傳感器與人手操控的用來區(qū)分物品種類的機械 手的一體化工程促進了我們的研究實驗

3、。在這個應用項目里設計要求 的關鍵之處在于測量所要求的微小尺寸和高靈敏性和可靠性（穩(wěn)定精 度和重復精度）。最近研究出的一種簡單的電容傳感器用來測量介電 常數(shù)的變化，以此來作為區(qū)分有界目標集內不同物體的標準。Avramov-Zamurovic和Lee的關注點是以下幾個方面：1）使用一個充滿氮氣的1-pF標準電容來評測CDC。2）制造一個溫濕 度補償器。3）制造一個有效的傳感器系統(tǒng)來探測不同狀況下包括機 場安檢在內的特定物品的探測。電容傳感器系統(tǒng)設計一個先進的電容傳感器系統(tǒng)的簡圖如圖1所示。它是建立在控制CDC， 環(huán)境溫濕度傳感器和收集測量數(shù)據(jù)的微控制器之上的。CDC與特制的 電容傳感器相連，電容

4、傳感器安裝在目標物體之下。個人電腦用來處 理數(shù)據(jù)和開發(fā)微控制器的軟件。在這種應用領域里微控制器的擴展包 是由美國海軍軍官學校武器和系統(tǒng)開發(fā)系研制開發(fā)的。所使用的微型 電腦是8位機，頻率為30MHz，具有卓越的計算系能。之所以選擇這 種硬件是因為它具有I2C的信息通訊能力，這對于CDC和傳感器的使 用是必要的。在本文中展示了微控制器的性能在電容傳感器系統(tǒng)領域 的應用中表現(xiàn)出的特點，更多的微處理器和擴展包的詳細信息可以在 產品說明書中找到。在我們的應用中CDC使用單極輸入，其輸入的變化范圍為4 pF， 內部的激勵信號為16 kHz。該CDC支持16-和32-kHz的信號源。所 選擇的16-kHz的

5、信號用來將CDC的讀入與商用的經電容橋處理升高 到20 kHz的信號進行比對。CDC是為移動電容傳感器而設計，測量電 容與地面相隔離。它的對地寄生電容達到了 60 pF。使用一個集成了 芯片的可編程的電容數(shù)模轉換器可以消除電容測量過程中最大17pF 的偏差。廠家申明直線性（0.01%）,有效分辨率（21 bit），和精確度 （4 fF）必須使用標準的電容來校驗，此外還需要確定它的不確定度。 這是未來研究的焦點內容。CDC各方面的詳細解釋請參閱廠家說明，其與電容傳感器系統(tǒng)相關的特點在本文中已給出。CDC是安裝在表面上的電路，安裝板上設計有數(shù)字接口，用來與 微控制器(I2C)連接。特弗綸隔熱同軸電

6、纜直接將CDC上的測量輸入 針腳與Bayonet - Neill - Concelman連接器連接起來。連接器安裝在 圍繞著CDC的地面屏蔽盒上。CDC上有一個在自我校驗程序上有應用 的集成了芯片的溫度傳感器。當發(fā)現(xiàn)CDC受濕度變化，和在小范圍內 受溫度變化影響顯著時，溫濕度傳感器就被用來監(jiān)測周圍環(huán)境條件的 變化。來自于溫濕傳感器的數(shù)據(jù)被用來評估環(huán)境條件的變化造成的電 容修正，和用于交叉比對CDC集成芯片的溫度讀數(shù)，這些提高了測量 程序的可靠性。CDC計算出一系列電容讀數(shù)的平均數(shù)。測量結果以c部分全刻度 的形式被記錄下來。測量中要求使用16 kHz的頻率和2.5 V的電壓。 在每一次測量中應用

7、的內部噪聲過濾器和軟件周期性的處理CDC的偏 差和進行自我校核。廠家指定的最大的電容數(shù)據(jù)比率是90 Hz，但是 將所有的過濾器，溫濕傳感器讀數(shù)和自我校核程序的執(zhí)行都考慮在 內，系統(tǒng)的實際數(shù)據(jù)率為3 measurement/min。電容傳感器系統(tǒng)的穩(wěn)定性和修正模型的評價在實驗室環(huán)境里(26 土 1 C)，用一個充滿氮氣的標準的1-pF 的標準電容在非主動熱控狀態(tài)下構建電容傳感器系統(tǒng)的穩(wěn)定性實驗。 通過應用高精度的商用電容橋測得標準電容的24小時穩(wěn)定性為土 2/106。環(huán)境濕度和溫度的讀數(shù)被用來建立一個彌補系統(tǒng)對環(huán)境條件變 化依賴性的模型。通過對濕度對電容傳感器的影響的觀察發(fā)現(xiàn)在濕度 的變化和CD

8、C的讀數(shù)之間存在一個時滯。濕度時間常數(shù)t被定義為在 環(huán)境濕度變化的開始和電容讀數(shù)開始漂移之間流逝的時間。一個動態(tài) 的窗口用來顯示電容和濕度的數(shù)據(jù)。優(yōu)質的原型的時間常數(shù)據(jù)估計為 30 min。除去隨機噪聲，組成電容，濕度，溫度讀數(shù)的數(shù)據(jù)集的平均 數(shù)約為3分鐘。迅速的突發(fā)型的相對于平均值的濕度偏差并不會顯著 影響電容的讀數(shù)，約為30 min的增益平均值在濕度數(shù)據(jù)的處理中得 到了應用。在電容修正之前的預處理進程（時間常數(shù)，噪聲過濾，增 益平均）要求大約1小時的時間。應用和測試結果在本文中，我們敘述了應用電容來探測一定距離處不同目標物體 的設計方案。探測器的設計根源于對交叉電容原理的更改。在測量中 電

9、容變化的高穩(wěn)定性已經實現(xiàn)了。一些銅電極被固定在特弗綸支撐 上，相隔0.47 cm。傳感器的底部接地，同軸電纜用于測量電容。原 型傳感器被嚴格的建立了起來，類似的傳感器可以用柔性的印制電路 板來構造，使它適用于其他方面的應用。在設計階段，運用基于篩分 實驗的aMAXWELL 3-D v4.1電氣現(xiàn)場仿真軟件對傳感器的拓撲結構進 行了分析。在仿真電容評估和實際測量之間，精確性方面存在的6% 的差異要歸因于仿真和原型之間存在的幾處差異。測量是在一個巨大 的接地盤上進行的以便將環(huán)境的影響降到最低。仿真模型有一個小一 點的接地護罩。實際上，電極通過特弗綸絕緣材料直接連接在信號源 上，仿真使用二維設計，其

10、連接線路與電極平行。作為樣品的塑料瓶 里的自來水與棱柱型模型的測量結果不同，它的介電常數(shù)為81。仿真 和測試顯示出一個區(qū)域，當目標物體特別靠近傳感器時（少于1cm）， 電容趨向于改變方向。為了解釋靠近目標時傳感器的變化，一個仿真 建立了起來。在平行板電容幾何學中預測到如果一種電介質插入電容 器中，電容器的電容會增加。這種設想是基于平行電場線在電容計算 中的相關原理提出的。根據(jù)使用1-pF的電容進行的穩(wěn)定性測試實驗 中濕度和溫度的變化，計算而得的修正值在電容傳感器測量中獲得了 很好的應用。經過修正之后的殘差仍然伴隨著相對濕度值。在高濕度 環(huán)境中（濕度范圍為27%到43%），水分的吸收會對木頭的介

11、電常數(shù) 產生影響，而上面提到的作用會加重這種影響。關于系統(tǒng)的動態(tài)容量和它的校準的研究是最富有意義的。此篇文 章關注的是穩(wěn)定性分析，做了耗時很長的實驗，穩(wěn)定性結果揭示出了 系統(tǒng)良好的性能。CDC可以配置兩個電容輸入端。這一特點提高了測 量的精度。結論本文敘述了一種簡單而有效的電容傳感器系統(tǒng)，它能夠辨別10cm 以上距離的不同材料的目標物。其原型是由基于測量系統(tǒng)的微型電腦 構成，包括一個CDC，環(huán)境傳感器，和電容探測器。已經構建了一個 模型來降低系統(tǒng)對環(huán)境溫濕度變化的敏感性。溫濕度變化的時間常數(shù) 來源于測量數(shù)據(jù)。本系統(tǒng)經過實驗室和野外條件的測試，并且相對于 實驗室標準進行了校準。當使用1-pF電容

12、進行測量實驗時，實驗顯 示出了 30/106以上的穩(wěn)定性和對于材料介電常數(shù)變化的高靈敏性。致謝作者對于美國海軍學院的J. Bradshaw和N. Tyson給予作者技 術上的支持表示衷心的感謝。對聯(lián)邦標準與技術協(xié)會的A. KoffmanAbstractA new capacitance sensor system was developed with a microcontroller, commercial humidity and temperature sensors, a capacitance-to-digital converter, and a custom-built capa

13、citance sensor. The performance of the system was evaluated by simulation and testing of the prototype. The impact of variations of ambient conditions on the system performance was analyzed, and a model for correcting the humidity and temperature influence was developed. Based on the experimental re

14、sults obtained in an uncontrolled environment using a standard capacitor of 1 pF, the 24-h stability of the system was estimated to be within 30 parts in 106. The high stability and sensitivity of the system allow its effective use in object-detection applications. Several sensors were constructed a

15、nd evaluated while sensing various materials under different scenarios.Indx TermsCapacitance measurement, capacitance sensor, electric field simulation, humidity, temperature variations.INTRODUCTIONRECENT technological advancements have made available a high-resolution (24-bit) L A capacitance-to-di

16、gital converter (CDC) with a capacitance input range on the order of a couple of picofarads 1. Potential applications of these CDCs are numerous. The project that motivated our research involves a capacitance sensor incorporated on a robotic arm to classify the objects to be manipulated by the arm 2

17、. The critical design requirements in this application were small physical size and high sensitivity and reliability (stability and repeatability) of measurements. A simple capacitive sensor was developed to measure the variations in the dielectric constant as a classification criterion for a limite

18、d object set 3. Avramov-Zamurovic and Lee focusedon the following: 1) evaluating the CDC using a nitrogen-filled standard 1-pF capacitor; 2) developing a correction model for the humidity and temperature influences on measurements; and 3) building useful sensors for detecting the presence of selecte

19、d materials under different scenarios related to airport security applications.CAPACITANCE SENSOR SYSTEM DESIGNA block diagram of the developed capacitance sensor system is shown in Fig. 1. It is based on a microcomputer that controls the CDC and ambient humidity and temperature sensors and collects

20、 measurement data. The CDC is connected to a custom made capacitive sensor placed under a target object. A personal computer is used to display the data and develop the microcontroller software. The microcontroller development kit used in this application was developed at the U.S. Naval Academy in t

21、he Weapons and Systems Department. The microcomputer used is an 8-bit processor operating at 30 MHz, with excellent math performance. This hardware was selected because it has I2C communication capability, which is necessary in the use of CDC and sensors. The features critical to the performance of

22、the microcontroller in the capacitive sensor system application are presented in this paper, and more detailed information on the microprocessor and the development kit can be found in the product manuals in 5 and 6. The CDC in our application uses a single-ended input in the range of 4 pF with an i

23、nternal excitation signal at 16 kHz. The CDC supports 16- and 32-kHz sources. The 16-kHz signal was chosen to compare the CDC readings with those of a commercially available capacitance bridge that operates up to 20 kHz. The CDC is designed for floating capacitance sensors, and the measured capacita

24、nce is isolated from the ground. It is tolerant of parasitic capacitance to ground of up to 60 pF. There is an option to eliminate the offset in measured capacitance of up to 17 pF using an on-chip programmable capacitance digital-to-analog converter. Manufacturer statements on linearity (0.01%), ef

25、fective resolution (21 bit), and accuracy (4 fF) have to be verified using standard capacitors, and the uncertainty levels need to be established. This is a focus of future research. Detailed explanation of all aspects of the CDC is given in the manufacturer manual 1, and the characteristics relevan

26、t to the capacitance sensor system are given in this paper. The CDC is a surface-mounted circuit, and the mounting board is designed to have digital connections to the microcontroller (I2C). A Teflon-insulated coaxial cable directly connects the measuring input pins on the CDC to the Bayonet-Neill-C

27、oncelman connectors. The connectors are mounted on the grounded shielded box that encloses the CDC. The CDC has an on-chip temperature sensor used in a selfcalibration process. Since it was observed that the CDC is significantly impacted by humidity variations and, to a lesser extent, by temperature

28、 variations, humidity and temperature sensors are used to measure ambient conditions. The data from humidity and temperature sensors are used to estimate capacitance corrections due to ambient variations and to cross check the CDC on-chip temperature readings, contributing to an improved measurement

29、 process reliability. The CDC averages a preset number of capacitance readings. The measurements are recorded as a fraction of the full scale. The measured frequency of 16 kHz and an applied voltage of 2.5 V are specified. Internal noise filters are applied to each measurement, and the software peri

30、odically executes the CDC offset and gain self-calibration. The manufacturer-specified maximum capacitance data rate is 90 Hz, but with all of the filtering, temperature and humidity sensor readings, and self calibration procedures implemented, the practical system data rate is 3 measurement/min.EVA

31、LUATION OF THE CAPACITANCE SENSOR SYSTEMSTABILITY AND CORRECTION MODELA nitrogen-filled standard 1-pF capacitor with no active thermal control was used to establish the stability of the capacitance sensor system in the laboratory environment (26 1 oC). The 24-h stability of the standard capacitor, w

32、hich was measured using a high-accuracy commercial capacitance bridge, is 2 parts in 106. The ambient humidity and temperature readings were used in developing a model for correcting the capacitance system dependence on environmental condition changes.Observation of the effect of humidity on the cap

33、acitance sensor system showed that there was a time lag between the change in humidity and that in CDC readings. Humidity time constant t is defined as the time elapsed between the onset of the ambient humidity change and the start of the capacitance reading drift. A sliding window was used to match

34、 the capacitance and humidity data. The time constant for the developed prototype was estimated to be 30 min. To eliminate random noise, the data sets consisting of capacitance, humidity, and temperature readings were averaged over 3 min. Since the rapid burst-type deviations of humidity from the av

35、erage value do not significantly influence the capacitance readings, a running average AH over 30 min was applied on the humidity data. The preprocessing (time constant, noise filtering, and running average) requires about 1 h of lead time before the capacitance corrections can be applied.APPLICATIO

36、N AND TEST RESULTIn this paper, we describe the design of capacitance probes for possible use in sensing different target materials at a distance. The probe design evolved from modifications on the cross-capacitance principle. A high level of stability in measuring the capacitance changes was achiev

37、ed. The copper electrodes are fixed on Teflon support and separated by 0.47 cm. The bottom of the sensor is grounded, and coaxial cabling is provided to measure the capacitance. The prototype sensor is rigidly built, but similar sensors could be constructed using flexible printed board circuit, maki

38、ng it suitable for other applications. In the design phase, the sensor topology was analyzed using a MAXWELL 3-D v4.1 electric field simulation software based on mesh analysis. The 6% difference in accuracy between the simulation capacitance values and the measurements is attributed to several discr

39、epancies between the simulation and the prototype realization. Measurements were made on a large grounded plate to minimize the effect of the surroundings, where the simulation has a smaller grounded shield. Practically, the electrodes are directly connected to the source through the Teflon insulati

40、on, and the simulation used 2-D layouts and had the connection traces parallel to the electrodes. Tap water in a plastic bottle measured as a sample differed from the prism shared model in size and had a dielectric constant of 81. Note that both the simulation and measurements show a zone when the t

41、arget sample is very close (less than 1 cm) to the sensor where the capacitance trend changes direction. To explain the sensor behavior at close proximity to the target, a simulation was performed. In the parallel-plate capacitor geometry, it is expected that the capacitance will increase if a diele

42、ctric sample is inserted. This assumption is based on the parallel electric field lines used in capacitance calculation. The corrections were applied using humidity and temperature factors calculated from the stability tests using a 1-pF capacitor. Note that the residual pattern after corrections still follows the relative humidity. This effect could be attributed to the dielectric constant of the wood sample changing due to the water absorption in a high level of humidity (ranging from 27% to 43% humidity). The most significant is the research on the systems dynampabiliti