WIXLIB

International Journal of Applied Control, Electrical and Electronics Engineering (IJACEEE) Vol 2, No.4, November 2014enable multi-hopping [7]. Recently, mesh networks were finally standardized under IEEE802.11s standard and can be applied in future instead of WirelessHART or ZigBee.WiFi is already in common use for a wide variety of industrial applications. It is being mainlyused as a replacement of wired Ethernet whenever it is difficult, expensive or impossible toinstall cables or system is often reconfigured.2.6.3. BluetoothBluetooth has been standardized in IEEE 802.15.1. Currently, its usage for manufacturing israther limited to tunneling wired interfaces (Ethernet, RS-485, CAN) to interconnect automationislands.Bluetooth Low Energy (Bluetooth 4.0) is a new standard of wireless communication. It isoptimized for low power consumption. Although, the standard is not compatible withpredecessors, many devices implement both classic and low energy version. The new standardwas created for low cost sensor applications with short data telegrams and working most of thetime in sleep mode.Anticipating a significant increase of popularity in customer electronics, especially smartphones, Bluetooth Low Energy technology has a big chance to be adapted for industrialpurpose. Sensors operating for several years on button-cell battery would find manyapplications in plant automation.2.6.4. Passive sensorsOne of challenges for wireless technology is powering devices. Available battery life time is notyet sufficient for many applications. Using cables to transfer power reduces mobility andincreases cost. Wireless energy transfer is one of the possible solutions to the problem.Typically, the energy is transferred via alternating magnetic field. Power loops are installedaround the production cell and fed by alternating current. Sensors inside have small coils whichpick up energy from a magnetic field and convert it to electric power. This idea was applied inABB’s WISA technology. The WISA stands for Wireless Interface to Sensors and Actuators.WISA system consists of two parts: WISA-COM responsible for communication and WISAPOWER for energy transfer [8]. The communication protocol is based on IEEE 802.15.1(physical layer) and customized for factory automation. It is now standardized byProfibus&Profinet International as Wireless Sensor Actuator Network (WSAN).Similar technology for wireless energy transfer is used by RfId tags, anti-thief devices andrecently in NFC payments. Especially, the NFC technology has potential to take advantage ofincreasing popularity of NFC chips in smart phones and be implemented in industrialapplications.Other interesting approach to passive sensors is based on Surface Acoustic Wave (SAW)phenomena. The solution utilize a piezoelectric effect to transduce an electric signal into amechanical wave which is distorted by measured physical value and converted back to electricsignal in next transducer. SAW technology allows to measure various physical parameters liketemperature, torque, strain or pressure. The main advantage of such sensors is that they aresmall, can be mounted on rotating parts, do not require battery and are immune to magneticfields.2.6.5. OthersThere are multiple other fieldbuses: EtherCAT, EtherNet/IP or LonWorks to name just a few.Author of this publication has chosen for more detail description only those communicationprotocols in which he has the greatest experience. Currently, there is no dominant industrialprotocol used at factory floor, and due to different requirements it is believed it will not change.The main observation is increasing popularity of Ethernet base fieldbuses.5

International Journal of Applied Control, Electrical and Electronics Engineering (IJACEEE) Vol 2, No.4, November 20143. SCADA LEVELThe SCADA term stands for Supervisory Control And Data Acquisition. It generally refers to aset of applications to control and monitor an industrial process. The OPC (OLE for ProcessControl) was mostly created to enable interoperability at the SCADA level. Currently, OPCtechnology is a widely accepted industrial communication standard that enables exchange ofdata between multi-vendor field level devices and software for advance control andvisualization. Multiple OPC specifications were defined, currently the most widely spread isOPC Data Access. OPC DA deals only with real-time process data. For historical data andalarms separate specifications were created.In OPC DA with each process value time stamp and signal quality value is associated. The OPCtechnology has a Client – Server architecture. Usually OPC Server is an application running onPC, communicating with industrial equipment via proprietary interface. Manufacturing MessageSpecification (MMS) was proposed to standardize exchanging data between networked devicesand computers [9], but it had little success.An OPC Client can subscribe in Server chosen data with a minimal refresh rate. The maindisadvantage of OPC DA technology is its dependency to Microsoft’s DCOM/COM. It limitsusage of OPC DA in non-Windows base systems. As a solution for this problem OPC XML hasbeen proposed, but till now there are not many implementations of it. In practice, OPC UnitedArchitecture (OPC UA), which include features of all previous OPC standards, has a chance tobecome a true replacement of OPC DA. OPC UA is based on Web Services and ServiceOriented Architecture (SOA). SOA bases on the idea of service as an independent piece ofsoftware with specified interface and is capable to provide described functionality. It is a crossplatform solution. It offers two protocols for communication between Server and Clients. One isa binary TCP protocol, optimized for high performance and the second is XML based webservice. OPC Foundation provides exemplary implementations of OPC UA for ANSI C/C ,Java and C#. Server can be implemented directly in a device which reduce need of installingthis software on the PC.To provide vertical integration most of SCADA systems can be configured to be the OPCServer for higher levels of the factory. In this case OPC UA is a step towards interoperability,while using XML, generic SOAP clients can access data.4. ENTERPRISE LEVELEnterprise network is used mainly by high level production management applications(Enterprise Manufacturing Intelligence). The network traffic does not contain real-time data, buttrend is to increase that amount of production data processed and stored. Company executivesmore often relay on those information to make critical decisions in near real-time.To exchange data between multiple Enterprise Resource Planning software modules (i.e.Material Resource Planning (MRP), Customer Relationship Manager (CRM), Supply ChainManagement (SCM) and more) common vendor independent architecture is needed. ServiceOriented Architecture (SOA) is well established solution in this area. It is frequent that bothservice interface and communication protocol are defined with XML. Other solution for datasharing between modules of ERP is common database.5. CONCLUSIONS AND FUTURE TRENDSIn approach described in Figure 1 usually there is defined number (or even single) gatewaysbetween tiers of the pyramid. Data exchange is taking place between different levels, but rarelybetween devices within the same level. Recently, due to increase of popularity of Ethernet,those both statements are not always valid. Growing number of sensors equipped with Ethernetport allows accessing process data directly by the devices located in highest layers of an6

International Journal of Applied Control, Electrical and Electronics Engineering (IJACEEE) Vol 2, No.4, November 2014automation pyramid. Multiple clients can access the same data provider. Information can beread from sensors at the same time both by the process controllers and SCADA/MRP systems.It is more common that industrial devices provide embedded web page for configuration. Itreduce need of installing and managing proper version of configuration software. This solutionis also more platform independent - sensor configuration can be performed both on theWindows, Linux or smartphone. Advances in real-time web design techniques allows tosmoothly show not only the static device configuration, but also process variables.Another aspect of Ethernet popularity at the factory floor are changes in the way howmaintenance is performed. Many companies operate their production facilities spread all overthe world. It is often the case, that to solve not standard problem or perform non-routinediagnostic, expertise not available locally at the plant is needed. Providing remote access tofactory devices enables possibility to involve several experts placed in distant locations to solvethe problem [10].We can also observe emergence of new forms of service offered by automation devices vendors.To ensure uninterrupted operation of their equipment they offer extended service contractswhich involves early diagnostic, preventive maintenance and emergency help base on remoteaccess. Term Intelligent Devices Management (IDM) was created to describe software whichallows manufacturers to monitor and manage remote equipment, systems and products viathe Internet [11]. Providing adequate level of security is a demanding task, but it is a win-winscenario for both customer and device vendors. Customers will receive help in better and costeffective assets management. Manufactures can use this data to improve their devices.6. EXEMPLARY INSTALLATIONDedicated demo stand has been created to demonstrate in practice data flow in an industrialplant. The model of a process consists of pipes, valves, and two containers for water. The upper,cylindrical shape tank, which is considered in this study as main, has gravity outflow to thelower one used as the water reservoir. Main tank can be refilled by pump which is connectedwith water reservoir through delay element. The purpose of the regulator is to control the pumpspeed to maintain a constant water level in the upper container. Various kind of disturbance canbe introduced to the system (i.e. changing flow resistance, simulating leakages). Field devicesare interconnected with PLC via various industrial field buses. OPC standard is used to accessPLC data.6.1. Data flowTo show how numerous fieldbuses can be integrated, field devices has been chosen in the wayalmost each of them uses different communication protocol. Main object is separated from theprocess controller part. Profibus over fiber is used to make interconnection. Dedicated modulewas used to extend internal PLC commulication bus by Profibus DP. Numerous extensionsmodules were installed to handle different fieldbus connections (Profibus PA, HART, AC800MModuleBus).To provide Ethernet network main object was connected with the PLC controller by dedicatedEthernet switches with fiber extension. ABB 800xA Industrial Platform was installed on the PC.It provides a comprehensive set of features for production plant management. Only a smallsubset of its functionalities was used to show process variables. Few screens have beenprepared. They allow to perform standard maintenance operations (i.e. manual control of motorspeed, valve position change, enabling automatic level control. etc). Since all PLC variables areavailable via OPC, SCADA software from other vendors may be used.To simulate low bandwith connection (approx. 1 Mb) with enterprise level network Ethernetover Bluetooth tunnel was established.7

International Journal of Applied Control, Electrical and Electronics Engineering (IJACEEE) Vol 2, No.4, November 20146.2. Control algorithmPreparation of the control algorithm was a subject of separate paper [12]. Model of the objecthas been prepared and identified. The system has been divided into a few elements: pump, maintank and reservoir. Each of them has been described with separate differential equation. Pumpspeed is estimated by the drive (SZ-1) base on internal model of motor.Several control algorithms have been realized. As the most basic a single PID has been used.This solution is not very effective in this case since the object has high inertia and large delaysintroduced by piping. In next step, idea of cascade PID has been used to better compensate flowdisturbances. The system was divided into two parts – fast changing flow control and slowchanging level control (Figure 3). The additional control loop allows to react faster on flowdisturbances.Process PID1Set level-Set flow Set speedPID2-e-sτG2(s)G1(s)Actual flowActual levelFigure 3. Cascade PID controlTo fully eliminate delay introduced by the piping, Smith predictor has been implemented(Figure 4). Assuming that the model of the process is correct, its output is cancelled by outputfrom real object. Hence, the feedback signal used by the regulator consists only of the outputfrom non-delayed process.-Set level Set speedPIDG(s)eActual level-sτ-e-sτmGm(s) - Set level PIDSet speedG(s)e-sτActual level-Gm(s)Figure 4. PID control with Smith predictorThe most complex control algorithm which was realized is based on Model Predictive Control.The idea of MPC control is to cyclically solve optimal control task with initial condition equalto estimation of the current state of the object. Only the first control vector is used as the inputof the object. The model of the system was linearized and discretized in working point. Kalmanfilter was used to estimate state of the object. Due to limited performance of PLC most of thecalculations is done offline for given object state.8

International Journal of Applied Control, Electrical and Electronics Engineering (IJACEEE) Vol 2, No.4, November 2014OPC DAKY1,KY2,KY3,KY4LT2PDT-1XML-RPCLT1Digital IOHARTProfibus PACorporatenetworkSZ-1ModuleBus over fiberFT1Profibus DPProfibus DPProfibusDPProfibusover thernetover fiber800xA ITPlatformRS232 over EthernetOPCOPCFigure 5. Communication flow in prepared demo standFigure 5. Picture of demo stand6.3. Protection relayREF543R feeder terminal is designed to be used for protection, control, measurement andsupervision of medium voltage networks. Based on measurements of currents, voltage,frequency, etc., the protection device is programmed to disconnect parts or equipment of thesystem. In the described automation object the protection relay is measuring motor feed currentand voltage. It provides various measurements (i.e. THD, power, frequency, power factor. etc.).With such approach it is also possible to observe how ACS800 drive is controlling motor speed.REF543R provides transient disturbance recorder which is able to record up to 16 currents orvoltages signals with high frequency.9

International Journal of Applied Control, Electrical and Electronics Engineering (IJACEEE) Vol 2, No.4, November 2014Information is read from protection relay by RS-232 and Ethernet tunnel. Virtual COM port isavailable on the PC. Dedicated OPC server is running on the PC to allow accessing this data byOPC clients.6.4. Vendor independent to OPC DAThere are a few implementations of DCOM in Linux, but in fact they are almost never used forcreating OPC in non-Windows based systems (Android, QNX, iOS) [13]. Tunneling approach ispopular to enable vendor independent access to data provided by OPC DA. One solution is touse OPC DA to OPC UA tunnel, second is to prepare custom software which translates OPC tochosen protocol.In the presented system, dedicated software was prepared to translate OPC to XML-RPC. Thereare several reasons for using XML based protocol. XML-RPC uses HTTP as a transportmechanism to exchange XML data between client and server. It provides less functionalitiesthan SOAP and number of transferred data is larger than while using JSON. The mainadvantage of XML-RPC is that it can be easy debug with Wireshark. There are a few openimplementations of XML-RPC for various operating systems. Android application was preparedto check feasibility of the idea (Figure 6). Additionally, PC gateway was prepared to run on thePC where OPC server is installed. Since security was not a concern in this situation, it ispossible to access process anywhere within corporate network.Figure 6. Main view of prepared Android application7. SUMMARYTo sum up, this paper describes data flow in the typical industrial object. It was shown that withdedicated equipment it is easy to integrate multiple industrial communication fieldbuses intoone system. Growing popularity of Ethernet is a game changer in area of field levelcommunication. It is expected that popularity of Ethernet based protocols will increase.Currently, OPC DA is most popular standard for accessing process data by SCADA levelapplications. Its usage is limited to Windows and it is expected that OPC UA will replace it.Service Oriented Architecture is used for communication between elements at the enterpriselevel software. Growing popularity of SOA increases interoperability and allows to createvendor independent solutions.10

International Journal of Applied Control, Electrical and Electronics Engineering (IJACEEE) Vol 2, No.4, November 2014REFERENCES[1]Dietrich R., Industrial Ethernet. from the Office to the Machine, Harting, 2005.[2]Modbus Application Protocol Specification V1.1b3, Modbus Organization, 2012.04.[3]Profibus Installation Guideline for Commisioning, Version 1.0.2, PI International, 2006.[4]Tovar E., Vasques F., Cycle Time Properties of the PROFIBUS Timed Token Protocol, IEEProceedings - Software, 1998.[5]Zhu Yu, CAN and FPGA Communication Engineering, Diplomica Verlag, 2010.[6]HART Communication protocol, ABB Information Bulletin, IB/INST–016 Issue 1.[7]Wei H.Y., Rykowski J., Dixit S., WiFi, WiMAX and LTE Multi-hop Mesh Networks : BasicCommunication Protocols and Application Areas, Wiley, 2013.[8]Steigmann R., Endresen J., Introduction to WISA, ABB White Paper, July 2006[9]Overview and Introduction to the Manufacturing Message Specification (MMS), Rev 2, SISCO,1995[10]Hollender M., Collaborative Process Automation Systems, ISA, 2010.[11]Dong J., Network Dictionary, Javvin Technologies Inc., 2007.[12]Bubak M., Sterowanie i diagnostyka obiektów nieliniowych na przykładzie układu dwóchzbiorników, Praca magisterska, Kraków 2010[13]What is DCOM? DCOM implementations. http://linuxopc.info, (access 2013.10.30)AuthorsMarcin Bajer graduated from Uni

automation systems, pure analog/digital signals or classic fieldbus system (Profibus, HART, Modbus RTU) are still commonly used for connection with sensors and actuators. In the following part of the paper the most popular field level communication protocols ar e described. Usually they interconnect PLCs with sensors and actuators.