毕业论文（设计）基于PLC 的石油储运监控系统的设计与实现.doc

基于PLC的石油储运监控系统的设计与实现杨 柳，黄晓玲(天津大学自动化学院，天津300072)    摘  要文中介绍了基于PLC的石油储运监控系统的设计方案、系统组成、控制方式与通讯网络，阐述了采用Pakscan主站控制器控制的智能电动阀的特点及其与PLC的通讯方法。    关键词PLC；智能电动阀；主站控制器；石油储运1 前言    罐区中原油储罐和输油管道所使用的各种控制阀门是石油储运过程中必不可少的现场仪表，其智能化程度的高低、所含信息的多少和对故障的诊断与容错能力直接影响到数据采集与监控系统的可靠性、稳定性和易用性。通常罐区中的控制阀数量众多且分散，普通的控制阀所含信息量少而布线繁多，这在一定程度上使罐区监控系统的设计复杂化。该系统采用英国Rotork公司的智能电动阀及其主站控制器，大大简化了监控系统的复杂设计，而且借助其丰富的诊断信息和对故障的容错能力，使系统的可靠性得以提高。2 监控系统的硬件实现2.1 Rotork智能阀控制设备        Rotork智能阀控制设备是一个阀门数据采集、监视与控制系统，它由一台主站控制器和与它相连的现场电动阀组成。主站控制器通过一条两线电流环路可以控制挂于环路上的多达240个现场控制阀，该电流环路可长达20 km。    现场电动阀的智能化程度较高，其内部含有丰富的数据和诊断信息。但最主要的特点是多个智能阀仅通过两线互联成一个环路，最终接入主站控制器的只有起始和末端两线，所有阀门信息通过两线通讯进入主站控制器。现场电动阀还具有线路故障屏蔽功能，当环路出现开路、短路或接地故障时，智能阀可以将故障端的线路屏蔽掉，使主站控制器仍能与线路上的所有智能阀通讯而不受影响，同时将故障信息发给主站控制器。其两线屏蔽原理如图21所示。    正常操作情况下，通讯电流信号沿环路的一条线从主站控制器的端口A流出，经该环路从端口B流回。此时，另一条线路是冗余的。当有一处线路发生故障时，该处故障线路被阀门屏蔽，故障线路两边的智能阀可通过各自的环路与主站控制器通讯；当有两处线路发生故障时，这两处故障之间的智能阀都被屏蔽，两处故障之外的智能阀依然可以通过两“臂状”环路与主站控制器通讯。    主站控制器是由主CPU卡、环路通讯卡、电源、液晶显示器和16按钮键盘组成的盘装智能仪表。它内部有两个固定的数据库，一个是现场单元数据库，负责接收并记录从两线环路传来的智能阀的地址、转矩、开度等数据，根据从上位机传来的读写命令控制阀门的运动，该数据库从逻辑上划分为4个区，每个区记录60个阀门的数据；另一个数据库为主站控制器状态及自诊断数据库，负责记录通讯协议的有关状态并向智能阀发布命令。通过主站控制器的按键和液晶显示器，可以实现读取智能阀的开度、转矩、地址等数据，控制阀门的开闭，接收报警信号及与PLC通讯等功能。        Pakscan IIE Master Station是Rotork主站控制器中的一种，它为双重热备结构，在主控制器出现故障时可以自动切换到热备控制器。图22为Pakscan IIE主站控制器与现场智能阀通过两线环路相连的情况。        Pakscan IIE Master Sation有一个RS485通讯口和一个RS232通讯口，它们可通过Modbus协议与PLC通讯。其中RS232通讯口可以不通过PLC直接连接打印机，打印报警信号。2.2 监控系统结构    图23所示为现场智能电动阀监控系统的结构框图。    该系统的控制部分采用美国GE Fanuc公司的HBR双重热备型PLC系统，通过PLC控制140个智能阀(IQ actuator)的开停闭。上位监控站可监视各个智能阀的阀位回信状态、阀位值以及报警信号，并可执行开阀、停阀和关阀操作。        Pakscan IIE主站控制器与PLC之间采用Modbus协议通讯，以port 1的RS485接口连接。正常运行情况下，主PLC和主控制器工作，从PLC和热备控制器分别与主PLC和主控制器保持同步。智能阀将数据传送给主控制器，主PLC通过RS485接口从主控制器中读取数据，并向其发布命令，主控制器再执行命令，驱动智能阀按命令运转。当主PLC或主控制器出现故障时，系统能分别自动切换到从PLC或热备控制器。    由于系统中采用的是Modbus通讯协议，一台PLC可以连接多台Pakscan IIE主站控制器，因此，若现场智能阀较多，系统可以很方便地扩展而且连线简单。3 软件设计3.1 通讯程序设计        PLC选用Modbus RTU主通讯模块(master)。Pakscan IIE主站控制器是一个远程终端单元，做为Modbus从设备(slave)。PLC的CPU通过Modbus RTU主通讯模块控制Pakscan IIE主站控制器的读写，被称为Modbus host。系统采用单Modbus host两线通讯方式，该方式最多可以连接32个Pakscan IIE主站控制器。    主通讯模块的程序设计有3部分内容：初始化通讯模块；读写Modbus/RTU数据；监测通讯状态。    通讯模块的初始化工作主要是配置3个初始化控制块的参数：Slave控制块(SCB)，信息控制块(MCB)和通讯要求参数块(COM_REQ)。SCB是一个15个寄存器长的数据块，功能是定义与其通讯的Slave的型号、个数、状态等参数，每一个Slave需要定义一个SCB块。MCB是一个6个寄存器长的数据块，功能是定义Master要求每个Slave执行的命令信息，包括命令类型、RTU引用地址偏移、PLC引用地址偏移、主机号等参数，每一种命令需要定义一个MCB块。COM_REQ是一个17个寄存器长的数据块，功能是定义通讯方式、端口控制字及监测SCB和MCB的状态参数等，每一端口需要定义一个COM_REQ块。所有这些初始化参数在PLC上电或冷启动初始化的第一个扫描周期内加载到RTU主通讯模块，此后RTU主通讯模块负责与PakscanIIE主站控制器通讯，而PLC则与RTU主通讯模块交换数据。    读写ModbusRTU数据和监测通讯状态的编程相对简单，只要读写初始化时定义的相应的PLC参数地址即可。3.2 监控软件设计    上位监控站可以准确的监测和控制储运过程的所有信息和设备。通过编程、组态、连接，形象地反映实际工艺流程、显示动态数据，设置PID控制参数以及过程参数，并可以查看历史趋势、报警历史报表等。        Rotork的现场电动阀配置在流程的输油管线上，通过按钮可以人工启动、停止和关闭任一个阀门，并显示任意时刻的阀门状态和阀位值。设计良好的人机界面使操作简便、直观。4 结束语        Rotork的智能阀控制设备与PLC的结合使得罐区储运监控系统布线简洁、控制方便，PLC的冗余以及Pakscan IIE主站控制器的双热备保证了系统的高可靠性，也提高了控制系统的自动化程度。该系统已投入工业现场使用，效果良好。Editor's note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the world's first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist, I've still seen many important weather and space events, but right now, if you were sitting next to me, you'd hear my foot tapping rapidly under my desk. I'm anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.It's like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line "we" would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and "capcom" (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, "Fearless Felix" will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, he'll be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes it's not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it won't. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way I'd miss this.