Web-Based Monitoring for Frequency Converters with USS Interface

Transcription

1 Advanced Materials Research Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Web-Based Monitoring for Frequency Converters with USS Interface Sun jinsheng 1,a, Guo zhipan 2,b 1 School of Mechanical & Electrical Engineering, Dalian Nationalities University, Dalian, China 2 School of Information Engineering, Hebei Polytechnic University, Tangshan, China a sunjinsheng@dlnu.edu.cn, b hitsun@sina.com Keywords: web-based monitoring; USS protocol; HTTP; frequency converter. Abstract: With the rapid growth of the Internet, the interest for connecting devices such as frequency converters into Internet has increased. Web browser is used by remote operator to control and monitor frequency converters via Internet and this application will be widely utilized. This article makes a study of web-based monitoring for frequency converters with USS interface. It is based on TCP/IP stack and the real time operating systemμc/os-ii. Then this paper presents a detailed analysis of the Web server, and the interactive method of the browser and the Web server. In the design of the server, it emphasizes the USS protocol telegram processing method. The architecture of embedded monitoring system, hardware and software implementation are also described in this article. Introduction The application technology in network of embedded system is becoming mature with the development and application of Internet. Using Web interface, people can interact with the frequency converters in real time, they can control its movement, observe it s state. In order to be able to communicate over the Internet, an implementation of the TCP/IP protocol stack is needed. Since 32-bit micro-controllers memories are limited, the standard TCP/IP has to be minimized. This paper described an implementation of embedded Web server for frequency converters with USS interface using minimal TCP/IP stack. The embedded Web server was implemented using an LM3S8962 microprocessor. The server stores the available information including the network protocols such as HTTP, TCP/IP, and the application codes. The end user can control the frequency converters by sending data through the Web browser. The HTML codes from embedded Web server are sent out in response to HTTP requests from remote browsers. USS telegrams received by the server have to be processed so that the user can monitor the device using browsers. 1 Hardware Description This article makes a study of Web-based monitoring for frequency converters with USS interface in EasyARM8962 experiment platform. EasyARM8962, adopting ARM7 TDMI-S core of Philips Company, is a powerful 32 bit processor developing board. LM3S8962 micro-controller, having 64kB Bit-Banding SRAM and 256kB Flash, offers three types of serial interface: UART, SSI, I 2 C. In addition, Ethernet controller is integrated within the chip. Figure 1 illustrates the hardware system structure chart. APB UART0/UART1 Ethernet controller SP3485 Cortex-M3 MAC PHY LM3S8962 Fig.1 Hardware structure Isolation transformer RJ-45 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/16,13:14:31)

2 Advanced Materials Research Vols Software Implementation A. Designing the Minimal TCP/IP Stack Implementing the embedded Web server requires very small TCP/IP to suite with the size of memory in the embedded microprocessor. The main requirement of Web server is that it must accept a request string in hypertext transfer protocol (HTTP) format. The HTTP protocol essentially works by exchanging text messages followed by transfer of web data across TCP connection. Base on the studies,this design adopts ZLG Company s ZLG/IP software protocol stack.the ZLG/IP stack was designed for embedded system with little RAM. The stack has small code size and low RAM usage, configurable at compile time. The cfg_net.h file is modified to configurate ZLG/IP protocol stack. MAC address (My_Mac_IID), subnet mask (IP_MARK_IID), IP address (My_IP_ID1) and the local gateway (My_GATEWAY_IID) should be set applicably. B. TCP Protocol Programming Based on TCP/IP Protocol Stack The very important part in implementing the network communication protocol is TCP protocol. TCP is a connection oriented protocol which means, a connection must be established between two ends, and in this case we call them as a client and server. In contrast, UDP send the data to the IP layer, does not guarantee either they reach to their destination or not. The TCP provides reliable transmission of data, stream data transfer, efficient flow control, sequencing, error checking and retransmission. Therefore it requires acknowledgment message (ACK) of transmitted and received data across the link.some application layer protocols use TCP transmission. These applications include the following: FTP File Transfer Protocol HTTP Hypertext Transfer Protocol SMTP Simple Mail Transfer Protocol This article performs web service using HTTP. Application programs use protocol stack by calling Socket API. The TCP communication model is divided into server and client.the server way is needed to listen the connection. C. USS Protocol telegram processing The UART middle-ware is added in the operating to send and receive serial data. RS-485 serial interface basic settings are as follows: initialize serial interface 1, baud rate 9600, and interrupt priority being set to 1. The interrupting service program, i.e. UART1ISR (void), is responsible for receiving USS telegram and sending to the Web server. Telegram structure is as the table 1. Each telegram starts with the STX character (= 02 hex), followed by the length specification (LGE) and the address byte (ADR). The useful data characters then follow. The telegram is terminated by the block check character (BCC). Table 1 USS protocol telegram structure STX LGE ADR 1 2 n BCC < - useful data characters - > The useful data block is divided into two areas, the PKW area (parameter ID value area) and the PZD area (process data). Structure of PKW area: The first two words of the PKW area (PKE and IND) give information regarding the task requested by the master (Task ID) or the type of reply elegram (Reply ID). They also define the inverter parameter number (PNU)which is being accessed by the telegram. The 3rd and 4th words, PWE1 and PWE2 contain the parameter value for the parameter being accessed. There are a number of different parameter value types on MM440, integer values (single or double words), decimal values given in IEEE float values, always double words) and indexed parameters referred to here as array values). PZD area (Process Data area): The PZD area of the telegram is designed for control and monitoring of the inverter. The received PZD is always processed with high priority in the master and

3 1868 New Technologies for Engineering Research and Design in Industry the slave. PZD processing has priority over PKW processing, and always transfers the most current data available at the interface. Take MM440 as an example, its USS protocol should be simplified. The USS parameters are to be set as follows: P2010=6 ( USS Baud rate is 9600), P2011=1 ( USS communication address), P2012=0 (USS PZD length is 0), P2013=4 (USS PZD length is 4), P1000=1 ( the source of setted frequency is MOP value). D. HTTP Protocol and Web Server Implementation Web browsers communicate with Web server, using the HTTP. Browser sends requests to server, asking: Specific web pages are provided by the server. The server returns the page if it is available, also using the HTTP protocol. Web server run programs based on information entered in fill-in forms. The HTTP protocol consists of two different groups of data; the set of requests from browsers to servers, and the set of responses return from servers to browsers. These groups involve in the replacement of text messages throughout the data transmission between the client and server. This protocol was implemented by using the simplest request of HTTP text messages. Fundamentally, when the clients attempt to access the Web page for the first time, they must enter the IP address of the Web serve. The browser locates the IP address and opens a TCP connection to server port 80, then uses HTTP protocol to send a request consist of a single GET line: GET / HTTP/1.0 Considering the characteristic of the information offered by system, Web server designed only receives the GET method. In monitoring webpage, we set up two buttons: Submit and Monitor. Their methods are set GET. GET add the data filled in form in the back of URL. If we enter the value 45 and submit, the Web server will receive the URL from the browser as follows: GET /9?text1=45&B3=%CC%E1%BD%BB HTTP/1.1 In the Web server, we have set up a received data buffer array named tempdata[400], where all of the data got from browser is saved. So we can get the data that we enter in fill-in form from the URL. According to the format of URL, tempdata[13] and tempdata[14] are the data entered in fill-in form.they are saved in the array SndData[12] finally. The drawn data will be processed by the designed program, then be sent out to frequency converter via serial interface. If push the monitor button, web server will send the webpage of the frequency converter working state to the browser. taskf ( receive and transmit USS datagram ) Prio 5 semaphore taske ( web server application task ) Prio 5 Socket API semaphore taskc ( TCP datagram processing ) Prio 3 Message queue taskstart (datagram receptiontask) Prio 0 Fig.2 Tasks in the software InμC/OS-II, four tasks are created for realizing the design. They are: taskstart. It creates the other five tasks and start tasks. Its priority is 0. taskc. It waits for the TCP semaphore, Its priority is 3. taske. It receives and transmits TCP telegram. It sends webpages to browser according to request from the browser.in this task, USS telegram and TCP telegram will be converted each other. Its priority is 5. taskf. It receives and transmits USS telegram via serial interface. Its priority is 6. The overall variable Web [ ] array with HTML form is as follows: uint8 web[ ] = {

4 Advanced Materials Research Vols "<HTML>\r\n" "<HEAD>\r\n" "<TITLE>TEST WEBPAGE</TITLE>\r\n" "<BODY bgcolor=#f1f1dd link=red\r\n" "vlink=#321afd>\r\n" "<H1>Embedded WEB Frequency converter Monitoring webpage </H1>\r\n" "<form method=\"get\" enctype=\"text/plain\" action=9>\r\n" "<p><h3>working frequency(h):</h3><input type=\"text\"name=\"text1\" size=\"20\"><input type=\"submit\"value=\"submit\" name=\"b3\"> <input type=\"reset\" value=\"reset\" name=\"b4\"></p>\r\n" "</form>\r\n" "<form method=\"get\" enctype=\"text/plain\" action=8>\r\n" "<p><h3>monitor:<input type=\"submit\" value=\"monitor\" name=\"b4\"></h3></p>\r\n" "</form>\r\n" "</BODY>\r\n" "</HEAD>\r\n" "</HTML>\r\n" }; 4 Conclusion In this work, we design the minimal TCP/IP stack and the embedded web server. Web-based monitoring for frequency converters with USS interface has been realized practically. Users can monitor the frequency converters using the browser. Now, as long as the devices are connected with Internet, the frequency converters with USS interface can be remote monitored conveniently. Acknowledgments This paper is partially supported by the fundamental research funds for the central universities (DC130464). References [1] Bentham, J. TCP/IP Lean, Web Servers for Embedded Systems. 2 nd Ed. Lawrence,Kansas, USA.: CMP Books [2] Zhang Haijun, He Wen, Jia Shushi, Remote Control of Inverters Based on USS Protocol, Mechanical & Electrical Engineering Magazine, vol. 20, no. 6, 2003, pp [3] Siemens AG: Universal Interface Protocol USS Protocol, Siemens Manual, [4] Wang Huaide, Guo Wenchuan, Reserch and design of embedded web server, Computer Engineering and Design, vol. 29, no. 10, 2008, pp [5] Huang Xiaofen, Liu Damao, Application and Study of Web Server inμc/os-Ⅱbased on Ethernet Interface, Modern Electronic Technology, no. 16, 2006, pp

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