Development of PC-Based SCADA Training System Syed Umer Abdi, M.Eng.
Kamran Iqbal, Ph.D.
Jameel Ahmed, Ph.D.
University of Ottawa Ottawa, ON, Canada Email:
[email protected]
University of Arkansas at Little Rock Little Rock, AR, USA E-mail:
[email protected]
Riphah International University Islamabad, Pakistan E-mail:
[email protected]
management system, electrical power distribution from nuclear, renewable resources, gas or coal fired, and so on.
Abstract— This paper describes successful and cost effective design & implementation of PC-based SCADA training system for the natural gas transmission and distribution industry. The design provides robust and automated environment for centralized control of a geographically scattered process. Microcontroller based data acquisition (DAQ) control units for distributed data processing are designed and serially connected with COM port of the remote terminal units (RTUs) via RS485/232 convertor. The real-time information gathered in RTU from sensors is fed to the master terminal unit (MTU) through a dedicated communication link. Visual Basic (VB) is used to develop Human-Machine Interface (HMI) environment for technicians and operators. The in-house HMI development aimed at reliable, cost effective, user friendly and easy to troubleshoot and update software. PC-based SCADA training system and HMI were developed to meet the training needs of Sui Northern Gas Pipelines Ltd. (SNGPL). The design work supports future updates and provides opportunities of research in rapidly evolving field of industrial automation and control.
Fig. 1. The general SCADA system [5].
Keywords— HMI, PC, SCADA, Training
I.
INTRODUCTION
SCADA (Supervisory Control and Data Acquisition) system can formally be defined as a system that allows the collection of data from remote sites coupled with supervisory control over various decisions that need to be made using the collected information [1]. SCADA provides the combination of data acquisition and telemetry to incorporate information gathering, transferring it back to central location, functioning essential control and analysis, and exhibition of information on screens and displays for operators and decision makers. Control actions required to tune the process are then fed back to process [2]. SCADA is utilized for remote measurement and control on modern industrial facilities in addition to critical infrastructures [3]. In practice, SCADA is an industrial control system which consists of an HMI, computer system monitoring, data acquisition and processing, and advanced visualization [4,5] (Fig. 1). The aim of the SCADA system is collection of real-time data to monitor and control equipment and processes in a critical infrastructure. Examples include oil and gas production, telecommunication, distribution and transmission, pollution and soil fertility and moisture monitoring, railways, industrial plant control, distribution and management of fresh, irrigation and waste water, system control of communication network (SYSCON), early warning siren system, process monitoring, transportation management, mass transit system, energy
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SCADA system includes analytical instruments which senses process variables across field data interface devices, or RTUs. The RTUs connect to sensors, convert sensor signals to digital data, and transmit digital data to the supervisory system. Host computers, called SCADA servers or MTUs, enable human control and monitoring of the processes by keeping databases and displaying statistical process control charts and reports. The HMI is used to display process data to a human operator who has the ultimate responsibility to monitor and control the process [6]. SCADA systems are employed to collect real-time data from pipeline sensors, such as valves and pumps, and present it to operators, who observe data from pipeline control equipment [7]. A. Evolution of SCADA Systems SCADA system has progressed with the increasing complexity of latest computational technology. First generation SCADA systems lacked connectivity to other systems and employed wide area networks (WAN) for connecting with RTUs. The communication protocols used in those networks were designed by RTU vendors and were proprietary in nature. Redundancy in the first generation systems was furnished by using two mainframe systems, i.e., dual primary and backup systems connected at bus level. Second generation SCADA systems benefited from advancement in system miniaturization and development of LAN technology, whereby multiple stations with explicit functions could be connected to LAN and shared information in real-time. A few distributed stations served as communication processors for field devices/RTUs. Other units
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functioned as operator interfaces, catering to the HMI for system operators. SCADA systems’ distribution utilities interconnecting multiple systems provided more processing power at system level as compared to a single processor. Third generation SCADA systems include the networked systems enabled by the application of WAN/ Internet Protocols (IP) for communicating between MTUs and the RTUs. This allowed separation of the communication function from the monitoring functions. Disaster survivability enabled through distributed processing has been a major improvement in distributed SCADA systems. Today’s SCADA system can survive complete loss of one or more locations, which accords SCADA a super-critical function. B. PC based SCADA Systems PC-based SCADA systems are extensively used in oil and gas industry due to the enhanced power and lower price of PCs, and extensive use of PCs in field operations and offices. PCs are therefore preferred for SCADA networks for making the process data accessible all over company’s operations. As PCs have become more powerful, it has prompted SCADA software developers to add novel features to system. PC based SCADA systems facilitate field operators to execute their work more proficiently and thus assist in optimizing production wells. PCs deliver active interface to monitor and control plants and compressors, and deliver real-time and historical data to operators to facilitate them in developing strategies for optimization of field operations. A model that has significantly decreased design and execution time of regular SCADA systems has been reported in [8] that comprises of an MTU and a single RTU. Its core methodology is to place regular PC configuration on both MTU and RTU sides of a dedicated communication link. Development of a PC-based SCADA research and training laboratory was reported in [9]. PC-based SCADA systems comprise PC-based RTU with customized software that permits communication with MTU. The key benefits of PCbased SCADA are reduced design and maintenance cost, significant reduction of development time and implementation complexity, and its effectiveness with sophisticated SCADA systems available in market. Traditional SCADA systems utilize PC with proprietary software for data collection from RTUs and displaying it through HMI. The architecture requires PC to be available to serve and display data, and take HMI requests for reliable operation. Additional software installed on SCADA PC and remote PC permits remote access to multiple users. New features in SCADA software includes the web server feature. It enables remote users to access common HMI/SCADA views on remote computers that are serviced by MTU. Furthermore, advanced tele-control system may propose embedded SCADA and HMI at remote stations, thus permitting remote and local users the proficiency to directly access individual outstations. C. HMI in SCADA Systems HMI, or the interface between industrial control systems and human operators, is a vital element in the operation and
configuration of industrial facilities [10] (Fig 2). Balanced and well managed interfaces results in business benefit and safety achievement; an unbalanced interface spells potential danger and loss of control [11]. Engineers and operators use HMI for set point configuration, control algorithms and to adjust controller parameters. HMI also displays historical and process status information. It allows human operators to observe the state of the process, modify control settings to meet changing control objectives, and manually override automatic control in state of emergency.
People
HMI
Equipment
Management
Process
Fig. 2. Interaction of Equipment, Process and People
HMI computer proficiently manages higher level control functions that are dependent on central monitoring station of SCADA [12]. HMI design offers wide functionality including graphical displays to deliver information about the operation and status of the process to the operator in a format that enables easy interpretation, and determining the need for action. It facilitates inputs from operator to adjust the operation, perform machine setups, and respond to events. It offers data logging and storage of historical machine operating data for part traceability and analyzing methods of quality improvement and productivity. HMI is also used to store and retrieve machine setup data; trending to offer means for analyzing visually the data on present or previous machine operation and alarm function to provide notification to operator of abnormal operating conditions and events [13]. The prime objective of HMI development is to support the operator in the execution and management of an industrial process. A well-developed HMI will enhance productivity of operator and process, rise uptime, and facilitate in providing constant product quality. Requisite functionality of HMI will vary depending on the type and complexity of product manufactured, the type of equipment used, skill-set of operator, and degree of automation of the process. Object oriented technologies and VB programming language have gained worldwide recognition for designing HMIs. Features such as COM, ActiveX and OPC are used with applications developed in VB to solve these problems and offer flexible and economical information delivery system.
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D. SCADA Communication Links Historically, microwave links have been used in SCADA communication networks. Microwave radio link employs high frequency, line of sight (LoS) terrestrial radio transmission medium using parabolic dishes as antennas. Microwave link has advantages like high data rate and bandwidth transmission, easy linkage with remote areas and, most importantly, a constant dedicated connection, which is mandatory for SCADA systems. Sui Northern Gas Pipelines, Ltd., uses Microwave Radio Link for their nationwide network (Fig 3). Microwave repeaters regenerate, re-time, re-synchronize and re-strength the signals and pass it to SCADA stations (Fig 4).
II.
SYSTEM ARCHITECTURE AND DESIGN
PC-based SCADA training system was designed and developed to meet the training needs of SNGPL, the largest integrated natural gas distribution and transmission company in Pakistan. The architecture of the PC-based SCADA training system includes a central monitoring and control station connected to PC-based RTUs via Industrial Ethernet (Fig. 5).
Fig. 5. Architecture and design of SCADA System.
Fig. 3. SCADA System in SNGPL.
Interference and noise are significant factors in planning and installing data communication systems. As SCADA systems normally use small operating voltage they are intrinsically vulnerable to noise. Compared to radio links, optical fiber offers many advantages such as high speed reliable communication, high security, data rate and bandwidth; resistance against EMI, radio interference, and noise, elimination of spark hazards, immunity against ground faults and transients, etc. Optical fiber has high capital cost but low recurring cost. Fiber optic cables also reduce the risk of interception and modification of SCADA system’s data [14]. SNGPL is using optical fiber link in some parts of its network mainly in Punjab and KPK provinces of Pakistan.
Fig. 4. Microwave Repeater in SNGPL’s SCADA Network.
A. Visual Basic: WinSock Control The Winsock control in Visual Basic 6.0 is used to connect multiple terminals to each other and provide easy access to network services. WinSock control of Visual Basic enables the connection to remote machine and interchange data using Transmission Control Protocol (TCP). TCP can be used to generate server and client applications. Similar to Timer control, WinSock control does not possess visible interface at run time. Utilization of Winsock in this project is to create client application that collects user information prior to sending it to central server and to create server application that acts as central collection point for data. TCP protocol control is a connection-based protocol similar to telephone in which user should establish a connection before continuing. B. Industrial Ethernet Industrial Ethernet protocol is commonly used in industrial environment. Industrial Ethernet uses LAN UTP Cat 5 Cable with mesh and ring topologies for communication between PC-based RTU & MTU. Industrial Ethernet has robust devices and high level of traffic prioritization. Industrial Ethernet equipment is designed for harsh environment to sustain high temperature, high pressure, high voltage, vibration and shocks. Use of Industrial Ethernet in SCADA systems (Fig 6) offers several advantages including faster speed (1 G bit/s with IEEE 802 over Cat5e/Cat6 cables or optical fiber), enhanced performance and communication distance, use of standard access points, routers, switches, hubs, cables and optical fiber, capacity of having 2 or more nodes on link (only possible with RS-485), peer-to-peer architecture that may swap master-slave roles, and improved interoperability. Network topology of SCADA system is static. Communication paths between nodes are identified in advance.
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Fig. 6. Industrial Ethernet Application in SCADA System.
C. RS-485 and RS-232 Communication: RS-232 serial link is commonly used for connecting DCE (Data Circuit-terminating Equipment) and DTE (Data Terminal Equipment). RS485 is a two-wire, half-duplex, multipoint serial communications channel; it employs a differential balanced line over twisted pair, and can cover comparatively large distances. RS-485 can be designed for either half or full duplex. Half duplex typically uses one pair of wires; full duplex requires two pair (similar to RS-232, which is used for single mode transmission). The relevant features of RS-232 and RS-485 are compared in Table 1. TABLE I. COMPARING PARAMETERS OF RS-232 AND RS-485 CABLE
Regulators: Series Voltage Regulators LM78XX were used to supply 05 and 12 Volts DC. Bipolar Analog Integrated Circuit UPC 1093 Adjustable Precision Shunt Regulators were used. The output voltage can be set at any reference voltage between 2.5v and 36v by two external resistors. These ICs can apply to error amplifier of switching regulators. Converters: 0832 8-bit Buffered D/A Converter was used having an advance CMOS 8-Bit Multiplying D/A Conversion. 8 bit 0831 series successive approximation A/D converters with 8 channels were used.
PARAMETERS Operation Mode Total No. of Drivers and Receivers on One Line (One driver active at a time for RS485 networks) Max. Cable Length Max. Data Rate
RS-232 Single Ended 1 Driver Receiver
Maximum Driver Output Voltage Driver Output Signal Loaded Level (Loaded Min.) Driver Load Impedance (Ohms) Max. Driver Current Power On in High Z State Slew Rate (Max.) Receiver Input Voltage Range Receiver Input Resistance (Ohms), (1 Standard Load for RS485)
+/-25V +/-5V to +/-15V
4000 ft. 10Mb/s100Kb/s -7V to +12V +/-1.5V
3k to 7k N/A
54 +/-100uA
30V/uS +/-15V 3k to 7k
N/A -7V to +12V >=12k
Transceivers: Octal Bus Transceiver with 3-State Output SN74LS245 were used which drive bus lines directly. It has pn-p inputs that reduce dc loading. Low-Power RS-485/RS-422 Transceivers have been used in hardware design.
DATA ACQUISITION AND CONTROL UNIT DESIGN
MAX485 is low-power transceivers for RS-485 and RS422 communication. Each part contains one driver and one receiver. MAX232 Dual EIA-232 Driver/Receivers were used. MAX232 device is a dual driver/receiver which contains voltage generator to provide EIA-232 voltage levels from a single 5-V supply. Each receiver converts EIA-232 inputs to 5V TTL/CMOS levels
III.
50 ft. 20kb/s
1
RS-485 Differential 32 Driver 32 Receiver
Fig. 7. Final implementation of DAQ Cards with I/O’s
Sensors: LM 35 precision temperature sensors with LM 358 dual operational amplifier were used as sensors. LM 358 consists of two independent, high gain, internally frequency compensated operational amplifiers. Triac BT 136 is a bidirectional thyristor commonly used in ac-phase control. It can be considered as two SCRs connected in anti-parallel with a common gate connection. Octal D-Type Latch has 3-state bus-driving true outputs, buffered control p-n-p inputs reduce dc loading on data lines. It is suitable for implementing buffer registers, I/O ports, bidirectional bus drivers and working registers.
Data acquisition and control units (DAQs) consisting of 8 digital inputs and outputs and two analog inputs were designed and developed to connect MTU to a PC-based RTU through RS 485/232 convertor and RS 485 Bus. A photograph of the DAQ Card with Inputs/Outputs appears in Fig. 7. The layout of the DAQ unit is shown in Fig. 8.
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Fig. 8. Block Diagram of the DAQ Unit
Opto-Couplers: PC 817 Series High Density Mounting Type Photo-coupler is used in signal transmission between circuits of different potentials and impedances. MOC 3021 Opto-Couplers / Opto-Isolators were used for 250V Photo Triac Driver Output. Microcontroller: AT89C52 is a powerful microcomputer for providing highly flexible and cost effective solution to many embedded control applications. AT89C52 implements 256 bytes of on-chip RAM. The upper 128 bytes occupy a parallel address space to the Special Function Registers. Microcontroller was programmed in C language. Flow chart of Source Code embedded in Micro Controller is shown (Fig. 11). IV.
HUMAN-MACHINE INTERFACE DESIGN
This section describes the design and development of VBbased human-machine interface (HMI) for the PC-based SCADA training system. Fig. 9 shows typical operation of the HMI in a SCADA system.
Fig. 9. Operation of HMI in SCADA System
The prime objective of the HMI is to support operator in execution and management of process. A well-developed HMI will enhance productivity of operator and process, rise uptime, and facilitate in providing constant product quality. Requisite functionality of HMI will vary depending on the type and complexity of product manufactured, the type of equipment used, skill-set of operator and degree of automation of process. In this study a Visual Basic (VB) based HMI environment for PC based SCADA Training system is developed that enables real-time monitoring and control of industrial parameters and process variables. The central monitoring and control / MTU display is shown in Figure 10. The proposed HMI design allows real sense monitoring of pressure, temperature, level, light, humidity, security switches, AC input, A/D and D/A conversion values, whereas fire alarm, start/stop of water pump, speed control of DC motor are carried out through emulation and human interaction through dedicated Graphical User Interface (GUI).
Fig. 10. VB-based central monitoring & control/MTU display
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and operators who desire hands on experience on SCADA Systems. DAQ cards are with time stamping which would lead to SOE monitoring. It will also provide better understanding of Industrial SCADA systems to undergraduate students. Regular Training programs for industries in Pakistan like PARCO, SSGCL, IRSA, WAPDA/NTDC have been proposed. In house built HMI environment has shown promising results, and is cost effective compared to more expensive proprietary software. Compared to Lab View; Visual Basic based HMI Environment which is compatible with Windows Operating System, is particularly designed to facilitate and ease the learners in real time user-friendly environment. "Winsock" control in visual basic performs the main function to connect multiple terminals to each other. The interactive and descriptive HMI software has the ability to remotely issue monitoring and control commands, generate reports, fault diagnosis and troubleshooting can be carried out, modified, reinstalled and improved for future upgradation easily. Functional Block Diagrams can be displayed in backend as well to program process variables and industrial parameters. REFERENCES [1] [2] [3]
[4] [5] [6] [7] [8]
[9]
[10]
[11]
Fig. 11. Flowchart for the 8052 Microcontroller program.
V.
[12]
DISCUSSION AND CONCLUSION
PC based SCADA Training System was successfully designed and implemented as required by the sponsors (SNGPL). This training system will facilitate understanding of real-time monitoring and control of natural gas transmission and distribution network by trainee engineers, technologists
[13] [14]
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Stuart A. Boyer, SCADA “Supervisory Control & Data Acquisition, 4th Edition, The Instrumentation, System and Automation Society. 2009 Bailey David and Wright Edvin, “Practical SCADA for Industry”, Elsevier and Newnes, 1st Edition, Burlington 2003. D. J. Keng and Hak Man Kim, “A Proposal for key policy of symmetric encryption application to cyber security of KEPCO SCADA Network” Future Generation Communication & Networking, pp 609-613, Volume 2, 2007. National Communications System, “Supervisory control and data acquisition (SCADA) systems” Technical Information Bulletin 04-1, 2004. Michael LeMay, SCADA Protocols: Overview of DNP3 Hyung Jun Kim “Security and Vulnerability of SCADA Systems over IP-Based Wireless Sensor Networks” International Journal of Distributed Sensor Networks, 2012 USA National Transportation Safety Board, Supervisory Control and Data Acquisition (SCADA) in Liquid Pipelines, pp. 1, 2005 Elmir Babovic & Jasmin Velagić, “Lowering SCADA development and implementation costs using PtP concept” XXII International Symposium on Information, Communication & Automation Technologies (ICAT) 2009, pp 1-7 M.S. Thomas, P. Kumar, V.K. Chandna, “Design, development, and commissioning of a supervisory control and data acquisition (SCADA) laboratory for research and training,” IEEE Trans. Power Sys. Vol. 19(3), 2004, pp 1582-88. Bernhard Dorninger, Wolfgang Beer, Michael Moser, Rene Zeilinger and Albin Kern, “Automated Reengineering of Industrial HMI Screens by Static Analysis” IEEE Conference on Emerging Technology and Factory Automation (ETFA) 2014 pp 1-4. Higgs M.A., “Electrical SCADA systems from the operators perspective”; Condition Monitoring for Rail Transport Systems (Ref. No. 1998/501), IEE Seminar on 10 Nov. 1998. Soumitra K. Ghosh, “Changing Role of SCADA in Manufacturing Plant” 31st IAS Annual Meeting Industry Application Conference 1996 pp 1565-1566 (vol 3). John B. Weber, “Applying Visual Basic for Human Machine Interface Applications”. http://www.softwaretoolbox.com/ims99/swtoolboxims99final.pdf E. Chikuni and M. Dondo, “Investigating the Security of Electrical Power Systems SCADA”, IEEE AFRICON 2007 pp 1-7.
