Research on Integration of Coal Mine Monitoring and Control System with Field Bus Control System

Mar.2006J. China Univ, of Mining Tech(English Edition)VoL 16 No. 1Research on Integration of Coal Mine moni-toring and control System with Field busControl SystemwU Jian-xin, DING Ying, JIANG Xiu-zhuSchool of Information and Electrical Engineering, China University of Mining Technology, Xuzhou, Jiangsu 221008, ChinaAbstract: According to the construction of current coal mine monitoring and control systems in China, the paper proposes three kinds of applicable schemes of integrating PLC and DCS systems with field bus technology to digitize thesystem and to improve the flexibility and extent of the system. Essentially, the paper introduces the integration of FCSon IO layers. Based on a real coal mine safety-monitoring and control system applied with a CAn field bus, the majortechnology of system relays and extensions is discussed. We believe that one of the most applicable methods is currently replacing the connection between function-stations and field-sensors with a can bus on IO layers for systemKey words: monitor and control; field bus control system; CAN; integrationCLC number: TD6761 Coal Mine Monitoring and Control Sys-CenterstationDisplaytem and Field bus technologyAs one of the most important methods to imo Sensorprove modern management and production efficiencyin coal mines, monitoring and control technoloon groundhave been widely adopted to maintain safety in coalproduction. Taking advantage of foreign technologiesSensorfrom the 1980s, coal mine monitoring and controlsystems have expanded rapidly in China. At presentautomatic control has come into use in most largescale coal mines, which greatly improved productionefficiency and safety and lowered costsTraditional Structure of Coal Mine MonitoringIn China, most sub-systems of coal mine sys-and Control Systemtems work independently. They follow a DCS systemstructure of three layers (center layer, sub-stationBy means of field bus technology, a digital, du-lyer and sensor layer)which consists of a tree to- plex, multi-node communication link can be providedpology. They are composed of sensors, sub-stations between intelligent field devices and automatic syson or under the ground, center stations, multiple con- tems. The application of a field bus can greatly entrollers and display terminals(Fig. 1). They work hance the digitalization and network of field devices,with analogue signals of 4-20 mA or 200-1000 Hz. to make monitoring and the control system moreEach coupled cable can only act as one line for open. Therefore, the system can be a comprehensivetransmissionnetwork with the functions of measurement controlCurrently control networks have been developed execution and diagnosis. FCS is used for the serialfor digitalization and networking. Because traditional duplex multi-node digital communication betweenanalogue signals of 4-20 mA or 200-1000 Hz can computerized instruments and control devices in proonly carry simple measurement information and con- duction. It is called an open, digital, multi-nodetrol signals. the communication rate is restricted. communicational low-level control network. Since itTherefore, it is necessary to digitalize and network was put into practice in the 1990s, it has expandedthe entire monitoring and control systemvery fast and h中国煤化工 nced controlCNMHGReceived 18 July 2005; accepted 25 September 2005Correspondingauthor.Tel:+86-516-83995973:E-mailaddress:jxwu(@cumtcdu.cnWU Jian-xin etResearch on Integration of Coal Mine Monitoring and Control System withsystem. As a booming technology of automation, itwill be of interest to more and more manufacturersTraditional/OFieldand users. FCS is superior for the following reaneriastationsmodulesons1)Whole digital communicationSensor 1 Sensor 2 Sensor 32) Structure of multi-branche3)Devices controlled in the fieldFig. 2 Integration Proposal of FCS on I/O layer4)Co-operation and exchange5)Distributed control2)Integrate the field bus in the dcs or PLC6)Open systemnetwork while field bus devices are connected toIt can be predicted that the traditional control DCS or PlC through gateways. These are all moni-systems such as DCs, PlC will be replaced by FCStored and managed in groupsFCS has changed the structure of the traditionalIn this mode, some basic control and diagnosticcontrol system. Point-to-point links were always used functions are distributed to the intelligent field defor control loops separately in traditional analogue vices. The center stations will function as advancedsystems; for example, links between measure con- control and negotiation stations between devices. Theverters in the field and controllers in the controlling field bus sets up the communication with the centerroom, links between operators, switches, motors, etc. station through the gateway and plays the role of conThese are all physically point-to-point links. Since trolling the 1O interface. It is better suitable in moreFCS is equipped with intelligent field devices, it is complicated situations when there are more controlpossible to put 1/O modules and control modules into devices and more relations between them. Users canfield devices which were originally located in the distribute the control functions to devices and controlcontrol room. With the communication ability that stations freelyield devices can support, measure converters in the3)Integrate the information independently fromfield can transmit signals directly to the operating FCS with that from DCS or PLC, which means FCSdevices such as valves. Therefore, the control system DCS and PlC should work independently. They cancan work independently in the field without com- map and access each other through gatewaysputers or instruments in control rooms and still acIn this mode control and communication can becomplish the distributional control thoroughlyimplemented through their own networks. FCS staysindependent from the original DCS or PLC systems2 System Integration ProposalsThe link between field bus and control sub-stationswill always be used for transmitting field device inFCS is an open, entirely distributed, co-operationally DCs or PLc and the control can be implementedtional dCs and plc systems have been used forthrough the gateway which usually acts as the condecades and developed into a practical system with verter of protocol. This mode is more suitable whengreat reliability. These methods have captured a largebuilding a new system or one which functions indeproportion of the industrial market for automation. Itpendentlywill take a long time for the advanced field bus technology to find a wider use. We can make its devel- 3 Application of Field Bus in Coal Mineopment and application easier in a step by step apMonitoring and Control Systemsproach. With the experience gained from some pro-ject applications, FCS and traditional control systems 3. 1 Mining safety monitoring system based oncan be integrated by the following methodsCAN1)Integrate FCS in the 1O layer while field busas the first kind of field bus recommended asdevices are regarded as lo plug-cards and integrated the international standard filed bus by the ISO, CANin dcs or plcadopts the physical and data link layers of the IsoIn this mode, the field bus modules are added to model, which can greatly improve the real-time abil-devices are connected to the extended field bus. as an ity of the system. Its nodes are prioritized and canextension of DCS, good use is made of all kinds of send messages at any time. They support point-to-ontrol functions and algorithms, while the advanpoint, point to multi-points and broadcasting commutasges of FCS as a simple and low cost system are also nications. a twist-pair cable is usually used as thebrought into full play. FCS is easy to integrate with transmission medium and the data rate is related tothe original system in this mode and there are many the length of the field bus. Short telegrams ofexamples for this. The logical infrastructure of thismessages are中国煤化工1. There arekind of system is shown in Fig. 2only 8 bytesCNMHGOnding nodewill be shut down adwnlaucanly wuel some errorJ. China Univ, of Mining Tech (English EditionVol 16 No. 1occurs. It is therefore anti-interference and has greater shows the mine safety monitoring system based onreliability. The signal can be transmitted farther spCan developed by the China University of miningcially by cables (reaching 10 km at 5kbps). It is im- Technology and the Hunan Mining Safety Equipmentminently suitable for use in coal mines. Fig. 3 PlantCenter stationRS232L Gateway nodesergroundOE cable- can bus、O/Branch relay oE Cableo/E branch relayO/E branch relayO/E CableCableCableMulti-functionMulti-functionsubstationsSensorsSensorsSensorsControllersControllersControllersControllersFig 3 Mining Safety Monitoring System Based on CANHere the traditional client/seBecause there are many kinds of monitoringtained. The system is composed of six parts. They are sub-stations and lots of sensors in coal mines, CANthe center stations on the ground, gateway nodes, must be extended. In its implementation, we canbranch relays, under-ground sub-stations, all kinds of connect the segments of the same rate or differentsensors and controllers and transmission media. Cen- rates through CAN-to-can bridge or gateway in theter stations collect, store, calculate and display all network. The can bus can also be extended to serialkinds of data from underground sub-stations, then ports through CAN-to-RS232(485)gateways. Wesend the corresponding configuration and control can even connect each other through Ethernet by thecommands back. Underground sub-stations are not PCI card of the Can bus which is on sale commer-only the information collecting nodes, but also the ciallycommunication nodes of the network. They collectIn mine safety monitoring systems, the requiredata from sensors, communicate with the center sta- ments for transmission length are specific. But theretions and send all kinds of control signals. Gateway are intelligent sub-stations which can deal with innodes act as the conversion of data formats from formation in time. so control functions can be em-can bus protocols and general PC interface proto- ployed in emergencies. The data rate of the Can buscols. Branch relays are set up at exact places to can be set lower for longer transmission 5!. In applicbranch, relay and convert transmitted signals. Sensors tions, we usually choose the data rate of 5 kbps, soor controllers are in charge of data collection and getting rid of fiber relays; we can obtain a maximumcommand execution. All devices in the monitoring length of 15 km while with a cable we can reach onlysystem are connected through the transmission me- 8 km. In special situations, the data rate can be lowdium. It follows the topology of the Can bus. As the ered to 2.5 kbps to extend the transmission lengthtest results, with a 1.3 mm diameter cable indicate, without relay. Taking into account the largest trandata can be transmitted more than 10 km at the rate of mission length that we can reach without relay2.5 kbpsthrough Can the largest transmission length is lim3.2 Relay and Extension of canIted by bit timingwhen using a cable the largest transmission length isIn implementation, we should pay more atten- limited by the decay of the signal in the cabletion to CAN relay and rate converters. When fiber Therefore, we should be concerned with branchingis used as a medium, the length that CAN is able to when using optical cables while we should be conreach is a function of the delay of signals. If we cerned with relays whena normal cableexpect Can to reach farther, a network bridge or aTwo can transceivers can be set back to back forCAN relay of gateways should be chosen. Relays of cional shaping and driving to implement the trans-gateways cannot only extend the transmission length, mission relay of CAn through the cable(See Fig. 4but also inter-connect local networks operating at below. in which the circuit theory is clearly presented)different rates 41The standardovered whileeoretically a Can buck propeCAn transceivmatter how many nodes are added. But in practice bus 1 correctl凵中国煤化工 ignals fromCN MH Gnt to bus 2nodes are limited to 110 for communication qualitythrough interface 2. Gates A and b here are used toWU Jian-xin et alResearch on Integration of Coal Mine Monitoring and Control Systemret rid of "dead lock.and achieve the function of can be realizedCSMA/CD and negotiate the connection between theSince the above design can be compatible withtransceivers. Receiving a bit of CANH, Can trans- traditional applications and there are no sensors andceiver I will pull its Rx to low-level and make gate a controllers complying with Can or other field busoutput a high level signal. Then a CAnl bit which specifications which can be used in mines underwill not change the state of the bus will be drawn by ground, the client/server model is used here. It dothe transceivernot conform to FCS. But obviously it is better thanBut the circuit shown in Fig. 4 can only get rid traditional systems. If integration proposal l, pre-of the decay of the signal during Can transmissions. dicted in the second part, is used in practice, the linksIt cannot solve the limitation of bit timing. Can bus between sub-stations and sensors in Fig. 3 are rerelay circuits with bridge and gateway shown in Fig. placed by a Can bus in 1O layers, which will meet5 can solve both problems at the same time. It uses a the requirements of fCs. There is a more reasonableMCU and two Can controllers with each driving one proposal which suggests the sub-stations in Fig 3 beindependent network separately. If AT89C51CC01 replaced by the gateways in Fig. 5. The originalwhich has one inner CAn controller is used, the sec- sub-stations will be simplified to be independent conusing AT89C51 and two external SJA1000. Or we tributed FCS mine monitoring and control system 9.d controller can use SJA1000. It can also work if trol nodes. Thus it will result in an exact, totally dican choose MCU with two inner Can controllerssuch as dS80C390CANCANCAN transceiverN transceiverdriver 2 Network 2CANCANBus 1RxLABus2Fig 5 Bridge and Gateway of CANFig 4 Circuit implementation of CAn relay5 ConclusionsThe exact circuit can be used as bridge or gateIt will take a lot of time to improve the currentway. Both networks connected by the circuit can monitoring and control systems with FCS technologywork at the same or different rates. It will be moreWe should analyze, integrate and operate according toreasonable to set each network to its preferred rate the function and character of every system. Thereforeaccording to its own transmission length and itsthree kinds of integration have been presented. Theamount of informationsystem structure, relay and extension of the systemhave been discussed on the basis of the current can4 Mine Safety Monitoring System Based mine safety monitoring system. The reform of theon FCS with Integration Proposal 1first kind of integration for FCS is considered for thtotal. distributed Fcs mine monitoring and controlMine safety monitoring systems based on FCs systemshould be a kind of totally distributed DCs CenterFCS can support global digital communication,stations can test, configure and set any node in the multiple branches, exchangeability, so that it can be-network into groups, so that mass management can be come a more popular monitoring and control systemcarried out!. All the sensors, controllers and opera- With the development of this intelligent device, mul-tors can work as independent nodes and they can tiplexing technology of digital transmission andcommunicate and link with each other. They can also gateway protocols, it is expected that FCS will bebe grouped by software, so that the distributed control widely used in the futureReferences[1 Department of Industrial Mining. Theory and Application of Mining Safety Monitoring. Xuzhou: China University of MiningTechnology Press, 1996.( In Chinese)[2] Yang X H. Field Bus Technology and Application. Beijing: Tsinghua University Press, 1999.( In Chinese)[3]Cheng JX. Research on field bus standard in mine. Journal of Mining, 2001, 26(6): 657-662. In Chinese)[4] Jonas Berge. Process Control Field Bus--Engineering, Running and Maintenance. Beijing: Tsinghua University Press, 200[5] Sun J P. Research on mining monitoring bus. Mining Design, 1996(10): 33-35.( In Chinese)[6 Jiang X Z. 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