Programmable Logic Controllers, SCADA and Distributed Control Systems, Industrial Data Communication
Advanced Diploma of Electrical and Instrumentation (E & I) Engineering for Oil and Gas Facilities
(DEI 52684WA)
Module 19 : SCADA and Distributed Control Systems
Written Assignment
V1.2
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DATE: 23 aug 2017
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General Information for Candidates
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with depth in areas of specialisation, in contexts subject to change
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across a broad range of technical or management functions with accountability for personal outputs and
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the assessment tasks are the student’s own work, except as appropriately acknowledged by the use of referencing.
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Module 19 Assignment
Assessment Points:
Supply the required answers below in blue font (not red or black).
You must submit this assessment along with the practical component.
You must answer all questions.
Topic Module 19.1: SCADA for Monitoring Installations Across a Wide Geographical Area
| Question 1 (6 marks) |
Describe the fundamental principles of Wide Area SCADA systems. |
| Your Answer | In mining industries, public and private utilities, leisure and security industries there is a need to connect equipment and systems separated by large distances. Range from tens to thousands of kilometres. Control and monitoring equipment is used to send commands, programs and receive monitoring information from these remote locations. |
| Assessor Feedback | |
| Question 2 ( 7 marks) | List the benefits of a SCADA system. |
| Your Answer | Improved operation of the plant or process resulting in savings due to optimization of the system. Increased productivity of the personnel. Improved safety of the system due to better information and improved control. Protection of the plant equipment. Safeguarding the environment from a failure of the system. Improved energy savings due to optimization of the plant. Improved and quicker receipt of data so that clients can be invoiced more quickly and accurately. Government regulations for safety and metering of gas (for royalties & tax etc.). |
| Assessor Feedback | |
| Question 3 ( 4 marks) | List at least four points the Sub Master site that RTUs may report to performs |
| Your Answer | Radio, telephone line, microwave and possibly even satellite. |
| Assessor Feedback | |
| Question 4 ( 7 marks) | A SCADA system monitors an application through an RTU out in the field. Please list typical RTU hardware that may be encountered. |
| Your Answer | User Interface Graphics Displays Alarms, Trends RTU (and PLC) Interface Scalability, Access to Data Database, Networking Fault Tolerance and Redundancy Client/Server Distributed Processing |
| Assessor Feedback | |
| Question 5 ( 6 marks) | Describe the main approaches that was followed in designing the SCADA software system and the new approach for current systems |
| Your Answer | User Interface Graphics Displays Alarms, Trends RTU (and PLC) Interface Scalability, Access to Data Database, Networking Fault Tolerance and Redundancy Client/Server Distributed Processing |
| Assessor Feedback | |
| Question 6 ( 4 marks) | Describe the two MODBUS transmission modes in which data is exchanged |
| Your Answer | Modbus RTU (also called Modbus-B for binary)) Modbus ASCII(MODBUS-A) |
| Assessor Feedback | |
Topic Module 19.2: SCADA for Process Plant Installations and Common Issues
| Question 7 ( 5 marks) | When thinking of Operator screens list five hardware components that go hand in hand with it. |
| Your Answer | Problems that need operator attention Process changes that require corrective action Unsafe operating conditions before emergency shut-down of plant Hazardous conditions Deviations from desired/normal conditions |
| Assessor Feedback | |
| Question 8 ( 2 marks) | List the two categories that HMIs can broadly be classified into. |
| Your Answer | Graphic system , communication |
| Assessor Feedback | |
| Question 9 ( 8 marks) | Describe the information/data exchanges for Fieldbus Systems on device and control level as well as examples of network/communication protocols used. |
| Your Answer | One wire – multiple signals, bidirectional communication, one input output card for all signal types – only one signal type but different packets for analog and discrete. |
| Assessor Feedback | |
| Question 10 ( 5 marks) | Describe the assistance required by an operator from the SCADA alarm system |
| Your Answer | Monitoring the system for any problems. Get the relevant technician to correct the problem. Make sure that the system does not crash. |
| Assessor Feedback | |
| Question 11 ( 9 marks) | List nine general firewall policies |
| Your Answer | No direct connections from Internet to the SCADA network Restricted access from enterprise network to control network. Unrestricted (but only authorized) access from the enterprise network to shared PCN/enterprise servers. Secure methods for authorized remote support of control systems. Secure connectivity for wireless devices (if used). Well-defined rules outlining type of traffic permitted on network. These are enforced via mechanisms such as access control lists (ACLs) and virtual local area networks (VLANs). Monitoring of traffic attempting to enter and on the network |
| Assessor Feedback | |
| Question 12 ( 8 marks) | Describe the purposes within the organization for data collection by the SCADA historian |
| Your Answer | Calculation Engine: real-time arithmetical operations User Interfaces: Users have multiple methods of accessing historian data. Redundancy: For the most robust system possible, a redundant architecture is desirable. Integration with Business Systems: All major historian platforms have the capability of interfacing with business systems via open standards. Provide data sanity checking and annotation: Ex abnormal readings - removal of service equipment. |
| Assessor Feedback | |
| Question 13 ( 5 marks) | Describe the software infrastructure required in order to make this information in the SCADA historian easily accessible and usable. |
| Your Answer | The master site computer facilities, antennas and antenna feeder systems, any sub-master station, associated equipment interfaced to the RTU (PLCs), the RTU and component modules, radio transceivers. |
| Assessor Feedback | |
| Question 14 ( 3 marks) | List a typical procedure to follow when reviewing the operation of the Digital input module for faults. |
| Your Answer | Check the basic parameters such as is the baud rate, data format and data format correct for both communicating devices. Identify which is the DTE and which is the DCE device and ensure that the transmit pin is connected to the receiver pin at the other end. Clarify what is happening with the hardware handshaking. Examine the protocol being used if the first few suggestions above do not help. |
| Assessor Feedback | |
| Question 15 ( 3 marks) | List the important considerations when selecting and dimensioning an equipment cabinet. |
| Your Answer | Produce a complete and thorough inventory of every piece of equipment in the telemetry system. This should include all single items of equipment. It should be the responsibility of the maintenance personnel to keep this current on a computer database. Define goals for system and equipment item working availability. Depending on the size and quality of the system: System availability of between 99.5% and 99.9% over 12 months. Individual equipment item availability of between 95% and 98% over 12 months. Set up a direct line of communications from the maintenance personnel to the company representative in charge of the telemetry system. All problems and potential problems should be directly and immediately relayed to that person |
| Assessor Feedback | |
Topic Module 19.3: Summary of Typical Distributed Control Systems
| Question 16 ( 3+4 =7 marks) | List the typical components that are used in a Control System as well as the multiple engineering disciplines that are involved when developing DCS systems |
| Your Answer | Master station, communication system and marshalling terminals and RTUs. Distributed control system or DCS is the main control system used in the refining process to manage a plant’s output and performance. It is a vital part of the plant’s architecture & cannot be allowed to shut down. Redundant systems are an essential part of the design of any DCS. All devices and facilities including main and backup control stations, main and backup controllers, hot and hot standby devices, dual LANs, dual communication modules and interfaces, and dual detecting devices must be backed up by a redundant system. |
| Assessor Feedback | |
| Question 17 ( 8 marks) | List typical reasons (any eight) for the implementation of a DCS system. Note – This question is mandatory. It should be answered and students are expected to get this question completely right to be assessed as competent with a score for this module. |
| Your Answer | If separate FGs need to communicate some signals, the same is done through Hardwire or Network/protocol such as OPC, modbus, profibus etc. As most of the processing is already done in the other FG the cabling is also reduced. Protection system and critical systems can be made into a separate FG and this processor having low input and controls can work with low loading and higher speed. People use term PLC and DCS interchangeable. DCS are an advanced or a larger implementation of the PLCs. Vendors call the same processor - PLC or DCS depending on the execution or architecture used for the application as illustrated. In some cases, multi-redundant systems are required to realize higher system reliability. When Ethernet is used, it is common to set up two independent networks. When the default network crashes, devices can continue to transmit data through the backup network. Similarly, all controllers, servers & HMI/SCADA systems are equipped with dual communication interfaces & data is transmitted simultaneously through both interfaces to prevent data loss. |
| Assessor Feedback | |
| Question 18 (marks allocated below) | Consider the following inputs and outputs associated with a DCS system. It is interesting to note that EXACTLY the same could be applicable to a SCADA system (although the SCADA system could use either a dedicated RTU or else a PLC). Break the following signals up (either going to, or away from the RTU-type devices) and indicate which are:
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| 18.1 | START signal |
| Your Answer | |
| Assessor Feedback | |
| 18.2 ( 1 mark) | Speed control signal of a VSD (going to the VSD – Please think in terms of a SPEED UP button and a SLOW DOWN button). |
| Your Answer | |
| Assessor Feedback | |
| 18.3 ( 1 mark) | An I/P (current to pressure) transducer for a butterfly valve (going to the valve). |
| Your Answer | |
| Assessor Feedback | |
| 18.4 ( 1 mark) | Solenoid Valve (operating something in the field). |
| Your Answer | |
| Assessor Feedback | |
| 18.5 ( 1 mark) | A light. |
| Your Answer | |
| Assessor Feedback | |
| 18.6 ( 1 mark) | An electric motor’s contactor (which will be used to start a motor in the field) |
| Your Answer | |
| Assessor Feedback | |
| 18.7 ( 1 mark) | An RTD temperature probe. |
| Your Answer | |
| Assessor Feedback | |
| Question 19 ( 2 marks) | When dealing with PID algorithms inside a DCS system various algorithms can be used such as Equation A, Equation B, Equation C and Equation D. Briefly discuss what Equation A and Equation D are in a DCS system. |
| Your Answer | |
| Assessor Feedback | |
Topic Module 19.4: The Operator Interface
| Question 20 ( 4 marks) | List four key points for designing an effective alarm for a control system. |
| Your Answer | Level 1 – displays show an overview Level 2 – Level 2 displays act as operator’s primary interacting displays during normal condition Level 3 – displays are system detail displays that the operator uses to perform non-routine tasks-line-up changes, equipment switching Level 4 –used to provide operating procedures for a piece of equipment or help for control & diagnostics |
| Assessor Feedback | |
| Question 21 ( 8 marks) | DCS dependability must be evaluated not only by its reliability but also on other factors. List any eight of these other factors. |
| Your Answer | noise voltages power surges missing line cycles cycle drop out power sag, brownout clipped sine waves frequency variations blackout |
| Assessor Feedback | |
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| Question 22 ( 8 marks) | Outline the steps (any eight) required to be taken for the successful implementation of a DCS system / project |
| Your Answer | No direct connections between the Internet to the PCN / SCADA network . Restricted access from the enterprise network to the control network. Unrestricted (but only authorized) access from the enterprise network to shared PCN/enterprise servers. Secure methods for authorized remote support of control systems. Secure connectivity for wireless devices (if used). Well-defined rules outlining the type of traffic permitted on a network. Monitoring of traffic attempting to enter and on the network. Secure connectivity for management of the firewall. |
| Assessor Feedback | |
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