mobile human machine interface based in opc ua for the control … · 2015-09-18 · hand, hmi...

Mobile Human Machine Interface based in OPC UA for thecontrol of industrial processes.

Jose Miguel Gutierrez Guerrero and Juan Antonio Holgado TerrizaSoftware Engineering Department. University of Granada

C/ Periodista Daniel Saucedo Aranda s/n 18071, Granada, Spainemail: [email protected], [email protected]

Resumen

This paper exposes how mobile devices can be in-tegrated and used for monitoring and supervisingindustrial processes into an industrial automationsystem. An analysis is carried out determiningthree possible architectonical models to include amobile device as a HMI system. Finally, we pro-pose an approach for developing a HMI (HumanMachine Interface) system for mobile device usingthe standard OPC UA, showing how it is imple-mented on a real system.

Palabras clave: HMI, Mobile, OPC UA,SCADA.

1 Introduction

The management of information is a critical issuein business processes, being important to knowhow data is collected, stored and analysed. Inan industrial environment the information deter-mines the production process, and helps in makingdecisions, decisions that can be very significant forthe companies and it will be able to give advantageover their competition.

An industrial process for a production process in-cludes a set of several computing systems that maybe organized at different levels [1]. Figure 1 showsthe levels and the computing systems involved ateach level around a network. The first level isthe Control Level on which control devices, sen-sors, and actuators are interconnected each otherthrough a fieldbus, that is, the control network;e.g., at this level we can find control devices sucha PLC (Programable Logic Controller), a simpleRTU (Remote Terminal Unit) or a DCS (Distri-bution Control System). In general a control de-vice controls automatically the production processby reading several inputs (from sensors) and then,after applying a set of control rules, taking somedecisions generating a set of outputs (for actua-tors).

The next level, named Manufacturing Level, in-cludes the set of computing systems used for mon-itoring and supervising the industrial processes in-

Figura 1: Architecture for industrial system basedin SCADA with TPC/IP network

terconnected in a manufacturing network. On onehand, HMI (Human machine interface) systems ingeneral and SCADA systems (Supervisory ControlAnd Data Acquisition) in particular are special-izes computing systems designed for monitoring,supervising, customizing the control parametersand actuating into the industrial process.

Finally the last level is the Business Level com-posed of business systems like ERP (EnterpriseResource Planning), Database System or,WebServer, among others, that are interconnectedthrough a business network. All these systemsonly can interact with the systems at manufactur-ing level in order to send information about theschedule of the production.

This work is focused in OPC-UA standard andexplores how a mobile solution based on tabletor smartphones can be used to develop HMI sys-tems that can access to process data of indus-trial processes. The use of mobile technologies forthe developing of HMI systems provides many ad-vantages with respect to traditional HMI systems

Actas de las XXXVI Jornadas de Automática, 2 - 4 de septiembre de 2015. Bilbao ISBN 978-84-15914-12-9 © 2015 Comité Español de Automática de la IFAC (CEA-IFAC) 1073

such an enhanced user experience using a moreflexible way to interact with data of industrial pro-cesses. Furthermore the use of OPC-UA improvesthe interoperability and connectivity with indus-trial devices.

In section II a contextualization of HMI systemsinto the industrial system is summarized and thecurrent situation of relevant standards relatedwith industrial systems is revised. The section IIIexplores three possible architectural models thatcan be defined to include a mobile HMI system.Section IV explains the design and implementa-tion of the mobile HMI system developed in thiswork in a modelled climate room. Finally, the lastsection includes the conclusions and future works.

2 Background

In an industrial environment there are many ele-ments that have to coexist such as the control de-vices, sensors, actuators, fieldbuses and HMI sys-tems [2]. HMI systems are responsible to providean interaction environment where the interactionbetween a human operator and a machine occurs,for instance, visualizing the status of an industrialprocess, or initiating a command execution. Theinterface is generally composed of several inputand output devices represented by graphic com-ponents (buttons, comboboxes, sliders ...) in agraphical user interface (GUI) for visualizing theparameters that define the industrial process [3].All these parameters can be changed by humanoperators to modify the behaviour of the machinesthat are responsible of the industrial process. Forinstances, the human operator could modify set-points or manage alarms, interacting with graph-ical interface of HMI.

2.1 Commercial SCADA System

Currently the SCADA software have evolved interms of robustness, reliability, availability, safety[4], increasing the supported communication pro-tocols and PLC’s, but still maintaining the samephilosophy since its inception. Current SCADAsystems supply an environment where you can addgraphics (sometime are used graphs representa-tion of the real elements) and, then, assigning in-put values or outputs from the software modulethat controls the PLC to interact with the systembeing controlled [2].

2.2 OPC and OPC UA

One of the major challenges in the industrial worldis to achieve the interoperability between hetero-geneous devices at communications level, regard-

less the manufacturer, the device type and theused software. The manufacturers of HMI sys-tems faced the same problems, in 1995, and theyare allied around a non-profit organization denom-inated Foundation OPC (Object Linking and Em-bedding for Process Control) to standardize theaccess to data and process control systems by us-ing Windows platforms. The result is the firstspecification of OPC-DA (OPC Data Access) inAugust 1996. Virtually all vendors which offerproducts for automation and industrial monitor-ing were made members. Thus, the new foun-dation was able to do modifications of the stan-dard, and manufacturers adopted these amend-ments much faster in comparison with other or-ganizations. The main reason of the success ofthis standard was the use of Application Program-ming Interface (API) based on COM (MicrosoftComponent Object Model) and Distributed COM(DCOM). The adoption of DCOM was because itwas widely available in Windows systems used inmost computers. It contributes also to their fastadoption by the manufacturers.

Due to its success, in 1998 the second versionof OPC-DA was published. Currently it is themost used standard in the industry for the controland monitoring of industrial processes, because ofits widespread adoption and the large number ofde- vices that support this technology [5]. Conse-quently any HMI system, distributed control sys-tem, PC-based control system and manufacturingsystem must have supporting of OPC today [6] [2].

The first and most successful specification OPC(OPC-DA) was designed with the purpose of act-ing as a communication interface between automa-tion devices. Its greatest utility was its applicationfor SCADA and HMI systems, because the com-mon interface was able to make working devicesfrom different manufacturers each other.

OPC XML-DA was the first attempt by the OPCFoundation to maintain the functionality of OPCbut over a neutral platform. However the versionof OPC based in web services does not meet therequirements of new devices and new needs aris-ing in the industry. One of the main reasons wasthe low performance that has a web service basedon XML compared to the COM-based standardversion.

The OPC Unified Architecture (OPC UA)[7] ap-pears for substituting COM specifications butwithout losing any of the functionality of the orig-inal OPC and without sacrificing performance.One of the main problems of COM/DCOM in-terfaces was the inability to use them from ex-ternal networks through internet. The new stan-dard provides a secure access to control process


in industrial systems regardless of the platform.Therefore, the interoperability between differentindustrial systems can be possible.

The OPC UA specification includes two main is-sues that were poorly managed in the classic OPC,the Transport Layer and the Data Modelling. TheTransport layer defines the optimized mechanismsfor transmiting and receiving data between OPCUA systems. The Data modelling defines the rulesand establishes a common framework for mod-elling new structures, facilitating the representa-tion of complex data types hierarchically.

2.2.1 Architecture

OPC UA is designed in layers. At the bottomthe base OPC UA layer has an implementationof the base specification. Above it, some specificdata modelling for OPC UA are incorporated toextend the application scope of OPC UA; that is,OPC DA [8], Alarm & Conditions (AC) [9], Ac-cess Historical (HA) [10] or Prog execution code[11]. Other organizations can develop their ownmodels above the base specification, or on top ofthe data model of OPC UA [12]. Examples ofthese models developed by others manufacturersare the Field Device Integration (FDI), the Elec-tronic Device Description Language (EDDL), theField Device Tool (FDT) and PLCopen standardfor PLC programming. Additionally, the manu-facturer can define their own extensions above thebase OPC UA information model [13].

2.2.2 Implementation

OPC UA uses a client server paradigm as OPCClassic. The OPC UA server is consequently thesystem that exposed the information of industrialprocesses managed by remote industrial devices,while the OPC UA client is the system that con-sumes this information. However, an applicationmay act as both client and server. One reasonfor this is that the servers could be integrated di-rectly into devices, and, if a client is implemented,it is possible to establish device to device commu-nication. The communication stack can be imple-mented in C/C++, .NET or Java, but is not lim-ited to these programming languages. The OPCFoundation is in charge of maintaining its imple-mentation.

3 Architectures for HMI MobileSolutions

Advances in mobile devices (e.g., smartphones andtablets), particularly the processing capacity, itsmobility, the connectivity capabilities and newGUIs have made them good candidates to be con-

sidered for the control and monitoring of industrialprocesses. However their use in HMI systems forthe control of industrial processes is still not ma-ture and more studies are necessary to evaluatehow it can be applied to industrial environments[14].

The conservative nature of the manufacturers andtheir reticence to make modifications to industrialcontrol systems have hindered the inclusion of newfeatures and the developing of new industrial de-vices. The main reasons are usually the lack ofsecurity with the management of critical data aswell as the lack of safety of the industrial pro-cess. Therefore, the advances in this sector arerelatively slower compared with other sectors suchas the consumer electronics. The HMI systemsfor mobile devices are at an early stage of devel-opment. Then, large manufacturers are not con-fident on such solutions and even less that theycan be applied into real systems as first class soft-ware systems. However, the massive penetrationof mobile devices in our lives, and their advancesand progresses in issues such as the security, flex-ibility, connectivity and mobility, will change thecurrent barrier in the industrial sector and willpromote this type of solutions.Some experiencesof the applicability of mobile devices were appliedfor monitoring scientific laboratories [15].

3.1 Architectural Models

The inclusion of smartphones and tablets for themonitoring and supervision of industrial processesby means of industrial automation systems maynot be trivial. Some restrictions have to be im-posed to the solutions:

• Connectivity. A wireless network is requiredto com- municate to industrial systems. Themost usual wireless networks are based onWiFi, Bluetooth or 3G (4G).

• Lack of connection. Mobile devices can havefrequent temporary disconnections.

• Screen. The display in mobile devices canbe very limited in the case of smartphones,although the tablets are the preferred mobiledevices for managing industrial processes.

• Security. It is a vital property which mustbe assured by mobile devices that managesdelicate information of industrial processes.

We can define several architectural models to in-clude mobile HMI into industrial systems:

• Mobile HMI Architecture based on control de-vices.


Figura 2: Mobile HMI Architecture using aspecific application developed for communicatingPLCs, RTUs with Mobile devices.

• Based on SCADA.

• or Based on OPC

3.1.1 Mobile HMI Architecture based oncontrol devices

In this architecture, a specific implementation ofmobile HMIs is performed for connecting to indus-trial systems of the Control Level as PLC, RTU orDCS as it can be shown in figure 2 . In this case,the developer has to implement a native applica-tion for Windows Phone, Android or iOS, decidingthe communication network and, finally, develop-ing a specific application into control device. Thisis the architectural model used in the first imple-mentations of industrial systems. This approachrequires great effort in terms of developing, withthe consequent costs in time and money. Con-versely, the solution can be more efficient and de-terministic, but with a great costs.

An interesting example is the solution namedScadaMobile available for iPhone and iPad [16]. Itprovides native support for a wide range of PLCdevices from manufacturers such as Allen Bradley,Siemens, Mitsubishi or Opto22 by means of theimplementation of their own specific connectors.Thus, the mobile app allows users to control dif-ferent PLCs on the same device.

3.1.2 Mobile HMI Architecture based onSCADA

In this case the mobile devices are connected toSCADA server systems (or specific HMI system)and, consequently, this allows access to industrialprocesses. Figure 3 shows the industrial systemsrequiring for this architectural model.

We may choose two alternatives to implement a

Figura 3: Mobile HMI Architecture based onSCADA.

solution based in this architecture. A native im-plementation of mobile HMI system can be devel-oped establishing a specific protocol to communi-cate with SCADA server based on Wifi or Blue-tooth. However, the solution based on web tech-nology is usually more frequent. It is preferred bymanufacturers because we only need a web navi-gator for accessing to SCADA data [17], and theweb application can be deployed both on desktopcomputers and mobile devices. This solution isvery flexible, and makes available a mobile HMIdevice with a limited inversion. However, the per-formance of the system in term of the responsive-ness depends strongly on the chain of nested callsrequired to modify or read any control parameter.

In spite of its recent integration into industrialsystems, there are many manufacturers that havealready offered compatibility of its HMI throughmobile devices:

• Web and Mobile HMI SCADA [18][19], in-sisting of an add-on software package onits desktop software which allows monitoringand control the industrial process on a mo-bile device that supports HTML5 through abrowser. It requires no installation on theside of customer.

• CitectSCADA Pocket [20]is an applicationmobile application for Windows Mobile thatwas developed in the .NET Compact Frame-work. It is also a plug-in of the desktopapplication, allowing access to it via GPRS,WLAN or Bluetooth.

• General Electric ProficySCADA [21] providesan iPad version of its desktop application asa simple remote control.

• Ignition Mobile supplies [22] a software exten-sion to its desktop software with JavaScriptsupport, allowing access and control of indus-


Figura 4: Mobile HMI Architecture based onOPC.

trial processes through a mobile device via in-ternet.

In all cases, the mobile app of a HMI system ismerely an extension or a plug-in of HMI desktopsystems. This mobile app depends directly on thedesktop system that acts as a gateway betweenmobile device and the industrial system. The mostusually implementation is based on a web serverthat enables access to mobile devices by means ofa browser with a screen adapted to these smallerinterface.

3.1.3 Mobile HMI Architecture based onOPC

In this architecture the mobile devices are con-nected to an OPC server to get access to controldevices as it is shown in Figure 4. The mobile HMIdevices have to be implemented as native OPCclient application on mobile devices for commu-nicating with OPC server [6]. The architecturalmodel exhibites a trade-off between performanceand flexibility. The solution is very flexible be-cause the Mobile HMI can be implemented as aspecific OPC Client using the API offered by OPCFoundation. Moreover, the solution is also veryefficient since the data does not circulate amongmany intermediary systems as the architecturalmodel based on SCADA [2].

Solutions based in this architectural model [23][24]are still scarce; an example is the Tesla SCADAthat allows the control and data acquisition of con-trol devices operating as an OPC-UA client [12].The mobile app based on Android shows the sig-nals and alarms triggered by the industrial processusing a binary OPC UA protocol [25].

Figura 5: Mobile HMI Architecture using OPCUA.

4 Design and implementation of aHMI system using OPC UAspecification for mobile device.

The implementation of a mobile HMI systembased on the OPC-UA standard entails a client-server paradigm between the mobile HMI (OPCUA client) and the OPC Server. Figure 5 showsthe architecture based on OPC UA which has beenused to develop the hmi system of this work too.

The OPC UA server acts as an intermediate sys-tem or a gateway which exposes the industrialprocess through the signals, data and parametersmaintaining by the automated devices. The infor-mation managed in OPC UA server is accessibleby any OPC UA client that uses a valid OPC UAtransport protocol with a specific data encoding.By default the binary protocol based on TCP isthe more efficient, standing the option to establisha secure communication link that allows encryptedtransmission with authenticated and authorizedaccess. However, other transport protocols can bepossible applied based in SOAP/HTTP, especiallywhen the support of web services is required.

Besides, OPC UA includes a set of operations orfunctionality that may be requested by any OPCUA client to access to the resources exposed onthe OPC UA server, that is, the status, data andparameters that regulates the industrial processthrough field devices. Each callable operation isdefined in OPC as a service, and the services areorganised into the Service Sets (e.g., Session Ser-vice Set). The services are invoked by a message-based data exchange protocol with a binary encod-ing using the defined transport layer (TCP in ourcase). Each service request follows the request-response paradigm and it is composed of two mes-sages: a request and a response. OPC UA pro-vides the structure of each type of message ac-


Figura 6: Software Life Cycle of an OPC UAClient.

cording to the OPC UA Service Sets [26]. Duringthe interaction between the OPC UA client andOPC UA server, the OPC UA client changes itsstate depending on the service request executedon OPC UA server, following a life cycle. Figure6 shows the available states set of the OPC UAclient.

Accessing to an OPC-UA server implies a firststage on which the client must open the session.Once the opening is authenticated and authorized,the server provides an authentication token thatwill be used next to maintain opening the sessionwhile the client invokes the execution of consecu-tive services in OPC UA server through a securechannel. Then, the client can send requests to theserver for exploring the available namespaces, andfor reading or writing variables in field devices.Finally the session will be closed explicitly by theclient or implicitly by the expiration of the sessiontimers that was set at the opening of the session.

The OPC Foundation provides the specificationand a complete implementation of the OPC basestack in Java standard. Then, the developmentof an OPC UA client require to understand theservice mapping defined in OPC UA, and a de-scription of how the request of services by a serverOPC UA is performed [27].

The Service Sets available for OPC UA clients are:

• Discovery Service Set : Set contains a set ofservices related with the discovery of OPCUA servers.

• Session Service Set : Set includes services forthe management of the session in OPC UAservers.

• Session Service Set : Set includes services forthe management of the session in OPC UA

servers.

• View Service Set : Set contains services re-lated with the handling of the namespace ofan OPC UA server.

• Attribute Service Set : Set comprises servicesfor reading and writing variables in a names-pace of the OPC UA server

4.1 Prototype.

In order to check the range of applicability of Mo-bile HMI systems, we have developed an imple-mentation of Mobile HMI based on OPC, specifi-cally in OPC UA, because of the advantages withrespect to other architectural models. OPC UAgives a more flexible approach than classic OPC,although its penetration grade to the market isstill limited. For testing our solution we are goingto use a small control system for regulating thetemperature of a scale modelled-room. The con-trol system is composed of four actuators to setthe following actions:

• opening/closing the roof

• moving wall to the left/right

• regulating the speed of the fan from 0 to 100

• regulating the intensity of the heating systemfrom 0 to 100.

For monitoring the system we have included atemperature sensor which can be measured thetemperature by an analog signal of 0-10v. Ad-ditionally the speed of the fan and the intensityof heating are also measured by analog signals of0-10v. The roof and the wall the system has limitswitches to indicate the end of the movement. Wecan see the model in the Figure 7 and 8.

The prototype was developed according the archi-tecture shown in Figure 7. The mobile HMI sys-tem was a Android native application placed intoan Android Tablet. The app includes a full Java-implementation of the OPC UA client and showsthe controlled environment in a graphic user in-terface to simplify the management of the controlsystem. The OPC UA server is an implementationof the manufacturer Kepware that it is deployed atPC, and finally the PLC is a Soft-plc of Beckhoffwith a fieldbus Ethercat for communicating withthe sensors and actuators. The hardware specifi-cation of the PC and Android tablet in Table 1.

For the experiment we have taken 100 measuresthat include the service requests for reading andwriting variables from mobile HMI system to the


Type Hardware Specifi-cation

System Operat-ing

PC Corel 2 Duo, 2.66GHz, 4GB Ram

Windows 7.

Tablet AcerIconia A510.

Quad-core Tegra1.3 GHz, 1GB Ram

Android 4.1Jelly Bean.

Tabla 1: HardWare Specification.

Figura 7: Study case.

OPC Server. The average, maximum and mini-mum value of execution time is shown in the Table2.

The obtained results are acceptable for the moni-toring of a control process by mobile devices. Wecan observe that a write operation has an execu-tion time lower than a read operation. The reasonof this result is because during the execution ofthe write operation we measured only the time re-quired to store variables to OPC UA server; later,the server updates the variables into control de-vices. In contrast, a read operation needs to waitthe response of the OPC UA server which requiresthe reading of the variables from control devicesto OPC UA server before giving a response.

Figura 8: Android OPC UA Client.

Opera-tion

Average Max Min

Read. 41,38ms 108ms 26msWrite. 4,60ms 11,72ms 3,91ms

Tabla 2: Time Measures.

5 Conclusion and Future works

In this paper we have conducted a survey of cur-rent technologies used in automation industry forthe development of HMI systems with mobile de-vices. At the moment of the paper writing the so-lutions offered by manufacturers are very scarce.Only a few mobile HMI systems are availablealigned with the standards applied to the automa-tion systems.

The majority of them are developed following anarchitectural model based on SCADA. The im-plementation of mobile HMI systems is funda-mentally based on web technologies adapting thedisplay size to the screen of mobile devices. Al-though it can be a good flexible approach in somecases, the visualizations of variables and alarm no-tifications depend on a permanent connection toSCADA system and the mechanism employed toupdate the dynamic content of the web.

A more predictive and responsive option is actu-ally possible using an architectonical model basedon OPC, and more particularly based on the re-cent OPC-UA. In this case, we can find only onepossible solution based on OPC-UA. This paperprecisely shows how a mobile HMI can be de-veloped using OPC-UA profiting the advantagesin terms of mobility, flexibility and performanceby the connection to an OPC server. Despitethe reticence of some manufacturers to adopt theOPC UA standard, the capabilities introduced bynew standard promise a more stringent control ofthe industrial processes from high-level computingsystems, including the mobile devices. The resultachieved demonstrates that the approach followedin this work is feasible without sacrificing the per-formance.

As a future work we want to develop a libraryof graphical components representing valves, but-tons, indicators, etc ... for helping developers thedesign of the industrial processes available on mo-bile devices. A detailed testing will be also per-formed in order to study the applicability to othermobile ecosystems as Windows Phone and iOS.

Acknowledgment

We would like to acknowledge the participation ofMario Orozco in this research paper for his helping


in the elaboration of the prototype carried out inthis work.

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