电子专业外文翻译

MEASUREMENT OF TEMPERATURE AND HUMIDITY USING SHT11/71 INTELLIGENT SENSORAssist. Prof. Grisha Spasov, PhD, BSc Nikolay KakanakovDepartment of Computer Systems, Technical University branch Plovdiv, 25,“TzankoDjustabanov” Str., 4000 Plovdiv, Bulgaria, +359 32 659 576, e-mail: gvstu-plovdiv.bg, kakanaktu-plovdiv.bg Keywords: temperature and humidity measurements, intelligent sensors,distributed automation and control The paper discusses the advantages of intelligent sensors. It presents an SHT11/71 temperature and humidity combined sensor from Sensirion. This sensor is ideal for developing distributed embedded systems for monitoring environmental parameters. An example application using this sensor is added to present SHT11/71 in real working condition. The application is distributed system for monitoring temperature and humidity.It uses a microcontroller with integrated web server to organize the communication and management of sensors. This application is realized and tested.1. INTRODUCTION Measurement and control of temperature and relative humidity has significant appliance in industry, science, healthcare agriculture and controlling technological processes. These two environmental parameters strongly influence each other and it is critical in some application to measure them in parallel. Using modern technologies it is possible to combine temperature measurement element, humidity measurement element, amplifier, ADC, digital interface, calibration memory and CRC calculationlogic in a single chip with very small size 1,3. Using intelligent sensors of this kind can shorten the development time and cost. Integrating ADC and amplifier into sensors chip allow developers to optimize sensor elements for accuracy and long-term stability. And that is not all integrating digital interface logic simplifies connectivity and management of sensors. These advantages can reduce whole time-to-market time and even price 1,3. In presented paper we use SHT11/71 intelligent sensor from Sensirion as an example and present its advantages and measurement procedures. An example application is also presented to demonstrate its work in real conditions. This application is realized and tested.2. INTELIGENT SENSORS SHT11/71 SHT11/71 is a single chip relative humidity and temperature multi sensor module comprising a calibrated digital output. The device includes a capacitive polymer sensing element for relative humidity and a bandgap temperature sensor. Both are seamlessly coupled to a 14bit ADC and a serial interface circuit on the same chip. This results in high signal quality, a fast response time and insensitivity to external disturbances (EMC). Each SHT11/71 is individually calibrated and calibration coefficients are programmed into the OTP memory. The 2-wire serial interface andinternal voltage regulation allow easy and fast system integration 1. The SHT11/71 is shown on fig. 1 1. figure. 1: Sensors organizaion Combining temperature and humidity sensing elements in single unit enables precise determination of dewpoint, without incurring errors due to temperature gradients between elements. The signal amplification near the sensor allows the polymer layers to be optimized not for signal strengths, but rather for long-term stability. Performing analog-to-digital conversion “in place” makes the signal extremely insensitive to noise. A checksum generated by the chip itself is used for additional reliability. The calibration data loaded on the chip memory guarantees that humidity sensors have identical specifications and thus they are 100% replaceable1. Some of the advanced functions of the SHT11/71 are available trough the status register. Some of them are: internal heating element; regulation of measurement resolution to optimize for precision or for fast response; End-Of-Battery (EOB) detection (low voltage detection). Status register size is 8 bits but only four of them are used 1.SHT11/71 can be connected directly to any microcontroller by means of the digital 2-wire interface. This interface is optimized for sensor readout and power consumption and is not compatible with I2C interfaces 1. (See fig. 2) figure. 2: Connection ofSTH11/71 to the C Two wires are used to transfer serial clock (SCK) and data (DATA). The SCK is used to synchronize the communication between a microcontroller and the SHT11/71. Since the interface consists of fully static logic there is no minimum frequency. The DATA tristate pin is used to transfer data in and out of the module. It changes after the falling edge and is valid on the rising edge of the SCK. During the transmission the DATA line must remain stable while SCK is high 1. Signals over the two lines during an example transmission are shown on fig. 3 1.figure. 3: Example signals over 2-wire interface3. MEASUREMENT OF TEMPERATURE AND RELATIVE HUMIDITY A measurement using SHT11/71 is a two-step procedure. First, it is necessary to send command for measurement to the sensor and get the data through the digital interface. Second, it is necessary to convert data from sensor to real physical values and to calculate the temperature compensation of the humidity data 1.3.1 Sending a command and receiving data To initiate a transmission, a “transmission start” sequence has to be issued. It consists of a lowering of the DATA line while SCK is high, followed by a low pulse on SCK and raising DATA again while SCK is still high 1. The subsequent command consists of three address bits (only .000. is currently supported) and five command bits. The SHT11/71 indicates the proper reception of a command by pulling the DATA pin low (ACK bit) after the falling edge of the 8th SCK clock. The DATA line is released (and goes high) after the falling edge of the 9th SCK clock. Two bytes of measurement data and one byte of CRC checksum are transmitted. The C must acknowledge each byte by pulling the DATA line low.All values are MSB first, right justified. Possible commands are: “get temperature”, “get humidity”, “change measurement resolution”, “get status register value”, “set status register value” 1. Communication terminates after the acknowledge bit of the CRC data. If CRC-8 checksum is not used the controller may terminate the communication after the measurement data LSB by keeping ACK high. The device automatically returns to sleep mode after the measurement and communication have ended. 13.2 Converting Output to Physical Values To compensate for non-linearity of humidity sensing element and to obtain thefull accuracy it is recommended to convert the readout with the following formula1,3:RHlinear = c1 + c2 + c3.SORH2 Coefficients c1, c2 and c3 depend only on measurement resolution. For 12bit resolution: c1= 4, c2= 0.0405 and c3= 2.8*10-6. For 8bit resolution: c1= 4, c2=0.648 and c3= 7.2*10-4.For temperatures significantly different from 25C the temperature coefficient of the humidity sensor should be considered 1,3:RHtrue = (TC 25).(t1 + t2 + SORH) + RHlinear . where t1 = 0.01 and t2 = 0.00008 for 14bit and t2 = 0.00128 for 8bit resolution 1. The bandgap PTAT (Proportional To Absolute Temperature) temperature sensor is very linear by design. Use the following formula to convert from digital readout to temperature 1,3: Temperature = d1 + d2.SOT. Table1: Temperature conversion coefficients Since humidity and temperature are both measured on the same monolithic chip, the SHT11/71 allows superb dewpoint measurement.4. DISTRIBUTED SYSTEM FOR MONITORING TEMPERA- TURE AND HUMIDITYOn the figure 4 below a functional scheme of distributed system for monitoring temperature and humidity, based on IPCChip is shown 2,4.figure. 4: Functional scheme of the application The functions of the system are separated between the four main blocks, asfollows 2,5: The internet browser assures that the system has a familiar user interface. The visualization of the monitored parameters is placed here. The integrated Web server in conjunction with the CGI deals with the control of the remote processes and the transfer of dynamic HTML pages tot he client. The real-time operating system (RTOS) of the IPCChip manages with the Web servers tasks, TCP/IP communication, local peripherals, user tasks and interconnection between them. Users applications and tasks, running on the controller, are used for automation purposes. In our case, this is the sensor driving and management of the SMS communication. The software of this system consists of several blocks. One block is for temperature and humidity measurement, one for communication with the GSM gateway and sending SMS and one is for generating dynamic HTML documents with the data from the sensor. Before every measurement a software restarting of the sensors interface take place. After that an initialization command is sent and controller waits 11ms. After this procedure a real measurement can start. The measurement block consists of two identical parts, one for temperature measurement and one for humidity measurement. The microcontroller sends a command to the sensor to get data. After getting data C normalizes and stores it in the operating memory. The two identical parts are executed sequentially and are repeated together. Between every two iterations of this cycle the task “sleeps” for about one minute to free the processor for tasks with low priority (like FTP, Web, Telnet). The communication between the controller and the sensor is trough 2-line interface (data and synchronization). A C-library based on the software interrupts of the RTOS is made for this communication. This library has the following functions: shttransstart() starts a transmission; shtreset() for restarting of the sensor; shtinit() initializes the sensor interface; shtsend() sends a command; shtrecv() receives data from sensor. These functions are used to control the sensors work trough the 2-wire interface and to get temperature and humidity data. This data is stored in the controller memory and then converted using formulas for non-linearity and temperature compensation.To see the results of the measurement the client sends a HTTP request to the web server and the server sends a HTML document as a reply. CGI is the instrument that connects the web server with the internal data on the controller. It runs as a task and do not use data received from the client, but rather uses data from the measurement block. This transfer of data is carried out with a block of shared memory. The measurement block writes data in this memory and the CGI task reads and use this data. It generates a short HTML document containing the temperature and humidity values from the last measurement.Example web document sent as a reply from the integrated web server with the results is shown on figure 5.figure. 5:Web interface of the application For controlling the parallel execution of these tasks a small program is written.This program read initialization data from files on the controller memory, installs and uninstalls the CGI processes, declares a semaphore from RTOS and frees it, releases the unused memory and stops the unneeded tasks. The other purpose of this program is to allow adding a security to the project using identification and authorization 2.5. CONCLUSIONS AND FUTURE WORK Intelligent sensors with their advantages like combining temperature and humidity sensing elements, integrating ADC, amplifiers and serial interface make development of measurement systems easier. These advantages also decrease development time and cost and the size of the product. One application where these sensors find place are distributed measurement and monitoring systems like meteorological stations,HVAC systems, automotive temperature control and many others. The SHT11/71 has an address of 3bits, which in present sensors cannot be changed from “000”. This address can be used for future applications like sensor networks and adhoc sensor networks which are leading tendencies in automation and control technologies.6. REFERENCES1 /sensors/humidity/ SHT71 datasheets and info.2 Spasov G., Kakanakov N. CGI-based applications for distributed embedded systems for monitoring temperature and humidity, CompSysTech04, 17-18 June 2004, Rousse, Bulgaria3 /sensors/ measurement technology.4 IPCChip info and applications.5 Djiev, S. Communication Networks in controlling systems, Automation and Informatics, No.2, pp 13-17, 2003.基于SHT11/71智能传感器的温湿度检测 本文章阐述了智能传感器的优点并介绍瑞士Sensirion公司推出的SHT11/17温湿度传感器，这是一款具有分布嵌入式系统的传感器，可理想的用于监测环境参数。 这里用一个使用这种传感器的实例应用来加强对SHT11/71在实际工作条件下的介绍。该应用是用于监测温湿度的分布式系统，使用单片机与集成网络服务器来实现传感器的信息传输和传感器管理，并且具有可实现性和可测试性。关键词：温湿度检测，智能传感器，分布式自动控制1.导言温度和相对湿度的监测和控制在工业，科学，医疗保健农业和控制技术的进程中具有重要应用。温湿度这两个环境参数相互影响，在许多应用中衡量温湿度的平衡性是至关重要的。利用现代技术使将温度检测元件，湿度检测元件，放大器，模数转换器，数字接口，校准存储器和CRC算数逻辑结合在在一个体积非常小的单片机上成为可能1,3。采用这种智能传感器可以缩短产品开发时间和成本，将模数转换器ADC和放大器的芯片嵌入传感器使开发人员能够优化传感器精度和长期稳定性， 除此之外，集成数字接口逻辑简化了传感器的连接和管理，这些优势可以降低整体上市时间，甚至价格1,3。 在这篇文章中我们以来自瑞士Sensirion的SHT11/71智能传感器为例，用一个在现实条件下应用实例展示其优势和检测程序，并证明此应用具有现实性和可测试性。2.智能传感器SHT11/712.智能传感器SHT11/71SHT11/71是一种包含相对湿度、温度多元传感器模块的校准数字输出的单芯片，包括一个电容性聚合体湿度敏感元件和一个用能隙材料制成的温度敏感元件。这两个敏感元件分别将湿度和温度转换成电信号，该电信号首先进入微弱信号放大器进行放大；然后进入一个14位的AD转换器；最后经过二线串行数字接口输出数字信号。这样可以提供一个具有高信号质量，快速相应时间和抗干扰能力（电磁兼容性）的信号,每一个SHT11/71都是被独立校准的并且将校准系数被编程到OTP存储器，2线串行接口和内部电压调节允许方便快捷的系统集成1。该SHT11/71内部结构如图1所示。 图1 SHT11/71的内部结构结合温度和湿度敏感元素在单一的单元可以做到精确的误差测定误差，而免受露点由于温度变化而产生的波动影响。传感器周围信号的放大能够优化聚合物层，但并不是简单的加强信号而是利于长期的稳定。进行模数转换可以加强信号的抗干扰性，同时使该芯片自身的校验功能的可靠性也得到了提高。下载到芯片存储单元的标定数据确保了湿度传感器也具有相同的规格，使它们之间实现完全可替换1。 使用SHT11/71的一些先进的功能，如内部元件加热、调节优化的检测精度优化分辨率或加快反应速度、低电压检测（EOB）时可使用状态寄存器，状态寄存器大小是8位的，但是只有其中四个常规使用，这些状态寄存器大小是8位的，但是只有其中四位被使用。 SHT11/71可以通过2线数字接口直接连接到任何一个微控制器。该接口可有效的进行传感器数据的读取并且能优化能源消耗，但是它却不能和12C接口兼容1。（参见图2）图2 SHT11/71与C的连接示意图两线主要用于传送串口时钟(SCK)和数据(DATA)。SCK负责微控制器和SHT11/71之间的同步通信。由于接口包含了完全静态逻辑，所以对SCK最低频率没有要求数据三态引脚用于传送数据进出模块，它在下降沿时发生跳变并且在SCK上升沿时有效。在传输中，当SCK是高电平时DATA线必须保持不变1。信号的两线传输过程的一个例子如图3. 图3 2线接口的示例信号3温度和相对湿度的检测使用SHT11/71进行温湿度监测分两步。首先，必须向传感器发出监测命令并且通过数字接口取得数据。其次，必须将传感器的数据转换成确切的物理数据并且计算湿度数据的温度补偿1。3.1 发送命令与接收数据开始传送，一个“传输开始”序列必须发出。其过程为当SCK时钟为高电平时，DATA翻转为低电平；紧接着SCK变为低电平，随后又变为高电平；在SCK时钟为高电平时，DATA再次翻转为高电平。命令序列由三个地址位（只有000是目前支持的）和五个命令位组成。SHT11/71通过第八个SCK时钟的下降沿后的DATA的下拉为低电平来指示命令的正确接收。数据线在SCK时钟的第九个下降沿时，DATA线被释放（升为高电平），传输两个字节的检测数据和一个字节的CRC校验和传输，C必须通过DATA线的下拉为低电平接收每一个字节，所有的计算结果都是首先是最高有效位经过无误的判断。常用命令为“取得温度”“取得湿度”“转换检测结果”“获取状态寄存器电平设置”、“设置状态寄存器电平”1。CRC校验数据位收到后通信结束。如果CRC-8位值没有被使用，控制器可能会在监测数据最低有效位被应答高时而终止通信。当监测和传输结束后该设备自动进入睡眠状态1。3.2转换输出到物理值为了补偿非线性的湿度敏感元件，并获得充分的准确性，建议用如下公式转换读出1，3：系数,和只依赖检测的分辨率对于12位解决方法：= -4, = 0.0405, = -2.8*；对于8位解决方法：= -4, =0.648, = -7.2*.温度完全不同于25时必须考虑湿度传感器的温度系数1,3：，式中对于14bit的 t1=0.01,t2=0.00008;对于8bit的 t2=0.00128.温度传感器的带隙PTAT（与温度绝对正比）的设计采用线性设计。使用下列公式将温度转换成数字信号。1,3:表1：温度转换系数由于湿度和温度都在同一检测芯片，SHT11/71允许很精确的露点检测。4.用于监测温度和湿度的分布式系统在下面的图4中用于监测温湿度的分布式系统的功能方案是基于IPCChip 的。图4：功能应用的实现方案系统职能在四个主要模块中被区