Distributed Control System Design And Implementation Based On Field Control Layer

MACS system is DCS product which is based on field control layer.Widely usedin process control of industrial enterprises, the system is an all-round comprehensiveintegrated informational system. It comply with the relevant standards and norms fordesigning, adopting advanced field bus technology, not only using safety and reliableFM/SM series hardware modules to collect field data, but also connecting with avariety of field bus devices like remote I/O, CAN, PROFIBUS etc. With efficientimplementation of redundant controllers, it can complete I/O signal processing, logicalcontrol and sequence control fast and accurately.The paper discusses the structure of MACS system, software and hardwareconfiguration, and basic composition and programming principle of the host controller.Under these basis, the key to be studied is design and implementation of filed controllayer. Field control layer is core of the whole MACS system, accomplishing maincontrol functions of MACS system. System performance, reliability and otherimportant indicators also depends mainly on the main controller. Filed control layer ismade of two-parts including real-time control software and DP communicationsoftware. Real-time software refers to the software running on the controller, includingcommunication module, redundancy module, power fail module and fault diagnosismodule. Communication module is refers to communication among the controller,engineer station and DP master. Controller communicates with engineer station inTCP/IP way, and with DP master by dual RAM protocol. Redundancy module meansdouble redundant structure of controller and network. Controller using dual mode,when host controller runs, slave controller is also in hot operation but not output data.Network is in double nets way and two networks woke in parallel. Power failprotection is needed to store data periodically to SRAM to keep it if controllers powerfail. Fault diagnosis is to diagnose and report controller and equipment faultimmediately.Field bus is a bridge of communication between field devices and controllers. Inthis paper, PROFIBUS-DP field bus can distribute I/O modules to the scene to achievea complete distributed control, while PROFIBUS-DP master unit has an ability tocommunicate to ensure the system centralized management. During DP mastersoftware design, this paper proposes three software design scheme, special ASIC chipplus expanded fixed programs, soft DP master and embedded module master. Last choose the second scheme through comparing three schemes. The scheme realize DPprotocol stack completely by software, adopting core state machine and auxiliaryprocessing function. According to state of DP master, the state machine could divideinto four state groups: offline, stochastic communication, cycle and nonperiodiccommunication state. In the paper four state groups of state machine are made adetailed description to realize communication among the controller, DP master andfield equipments.In the paper basic functions of controller system software is realized. Thecontroller can communicate with super machine and DP master accurately, but beprovided with redundancy, power fail protection, module diagnosis and other functions,improving various performance indicators of the controller effectively.