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Distributed Control Systems (DCS) - Maintenance Considerations

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DOCUMENT DESCRIPTION
The full course on Distributed Control Systems (DCS) consists of 19 training modules. This document refers to the 17th training module only, Maintenance Considerations. Specific topics covered include:

* Mean Time between Failures
* Spare Parts
* Types of Failures
* Types of Faults
* Diagnostics

Upon the successful completion of the full DCS course (all 19 modules), you will be able to:

* Apply an in-depth knowledge and skills in DCS systems and implement systematic applications, selection and troubleshooting techniques and methods
* Identify the DCS hardware & software particularly the traditional process controllers, programming, execution time, configuration, etc.
* List the parts and configuration of the SCADA system and determine its basic architecture and levels of hierarchy
* Differentiate DCS from PLC and SCADA and discuss their features and functions
* Determine the types of DCS used in petroleum refining processes and explain their specific function in each process
* Employ the concepts of alarm management system including its types, features, architecture and functions
* Discuss the concepts of humans in control and identify the factors that contribute in the following concept
* Recognize the safety considerations involved in DCS such as intrinsic safety, explosion, approval standards, oxygen, etc.
* Identify types of redundancy and recognize how it works
* Appreciate the principles analogue and digital field communications and discuss its transmitter classifications, intrinsic safety, fieldbus communications & technologies, etc.
* Discuss the concepts of safety instrumented systems and explain its functions, integration and hazard and risk analysis
* Explain the maintenance considerations of DCS and identify the various types of failures and faults
* Select the proper DCS system for each application and determine the system specification, its functional description, and diagrams
We can also furnish additional materials via email relevant to your purchased document(s).

For an additional fee, we can provide technical support to relevant engineering projects.

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Distributed Control Systems (DCS) - Maintenance Considerations

  1. 1. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 1 Section 1 XRS Consulting Engineers and Project Managers 1 Section 10 XRS Consulting Engineers and Project Managers 1 Appendix XRS Consulting Engineers and Project Managers 1 Section 17 Section 17 Maintenance Considerations
  2. 2. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 4 Section 1 XRS Consulting Engineers and Project Managers 4 Section 10 XRS Consulting Engineers and Project Managers 4 Appendix XRS Consulting Engineers and Project Managers 4 Section 17 Prior to 1962, by the military specifications that were in use at the time, the concept of availability was calculated to be equal to the mean time before failure, divided by the sum of the mean time before failure plus the Mean Time To Repair (MTTR). This concept, in process control, is the calculation of what is in the path of the control signal from the input through to the output that could contribute to the failure of that loop. MEAN TIME BETWEEN FAILURES Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  3. 3. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 7 Section 1 XRS Consulting Engineers and Project Managers 7 Section 10 XRS Consulting Engineers and Project Managers 7 Appendix XRS Consulting Engineers and Project Managers 7 Section 17 Maintenance Considerations Ratio: Time system is operating correctly to total hours of scheduled operation. ● MTBF – Mean Time Between Failures = MTTF + MTTR Not always symmetrical Stated or published period of time for which user may except device or system to operate before failure occurs; computed arithmetical mean of time, … not a tested value! Value will drop by about 50% for every 10oC increases; All other ambient factors will have similar impact. ● MTTF – Mean Time To Failure; calculated measure of overall reliability. ● MTTFD – Mean Time To Failure (to) Dangerous condition. ● MTTFS - Mean Time To Failure (to) Safe condition. ● MTTR - Mean Time To Repair; average time required to perform corrective maintenance on failed device or system. Availability = MTTF/(MTTF + MTTR) This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  4. 4. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 10 Section 1 XRS Consulting Engineers and Project Managers 10 Section 10 XRS Consulting Engineers and Project Managers 10 Appendix XRS Consulting Engineers and Project Managers 10 Section 17 Many buyers of distributed control systems who ask for this MTBF number do not realize that the intention of this calculation has been to ensure the signal path integrity. They frequently request the MTBF for all the hardware in a system. MEAN TIME BETWEEN FAILURES Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  5. 5. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 13 Section 1 XRS Consulting Engineers and Project Managers 13 Section 10 XRS Consulting Engineers and Project Managers 13 Appendix XRS Consulting Engineers and Project Managers 13 Section 17 No two systems are ever alike, even those from the same vendor. There is no way an MTBF can have meaning in many of those attempts to look for system security and availability. MEAN TIME BETWEEN FAILURES Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  6. 6. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 16 Section 1 XRS Consulting Engineers and Project Managers 16 Section 10 XRS Consulting Engineers and Project Managers 16 Appendix XRS Consulting Engineers and Project Managers 16 Section 17 Spare Parts Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  7. 7. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 19 Section 1 XRS Consulting Engineers and Project Managers 19 Section 10 XRS Consulting Engineers and Project Managers 19 Appendix XRS Consulting Engineers and Project Managers 19 Section 17 The modules or cards themselves are usually far too complex for the average service department to make detailed repairs. Sometimes it’s easy enough to replace chips, but if the problem goes further it is far easier to replace the entire module with a replacement spare and send the damaged module back to the vendor. Of course, more things to stock would be fuses and lamps. SPARE PARTS Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  8. 8. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 22 Section 1 XRS Consulting Engineers and Project Managers 22 Section 10 XRS Consulting Engineers and Project Managers 22 Appendix XRS Consulting Engineers and Project Managers 22 Section 17 TYPES OF FAILURES Physical Failures Physical failures are almost always permanent and are usually caused by a component or module which has worn out, burned out, or has physically broken because of vibration or shock. If all the physical components in a system are working, and the system still fails to perform its function, the failure is classified as “functional.” Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  9. 9. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 25 Section 1 XRS Consulting Engineers and Project Managers 25 Section 10 XRS Consulting Engineers and Project Managers 25 Appendix XRS Consulting Engineers and Project Managers 25 Section 17 Types of Faults Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  10. 10. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 28 Section 1 XRS Consulting Engineers and Project Managers 28 Section 10 XRS Consulting Engineers and Project Managers 28 Appendix XRS Consulting Engineers and Project Managers 28 Section 17 Manufacturing Faults Manufacturing faults occur when some step in the process of manufacturing a component or module or system is done incorrectly. An example of this kind of fault is when a resistor in a circuit has a corroded wire that no longer conducts properly. Now, this resistor was coated to protect against corrosion, but closer examination shows that the coating was not applied correctly when the resistor was made. Small voids in the coating occur because the coating machine was not cleaned on schedule. TYPES OF FAULTS Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  11. 11. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 31 Section 1 XRS Consulting Engineers and Project Managers 31 Section 10 XRS Consulting Engineers and Project Managers 31 Appendix XRS Consulting Engineers and Project Managers 31 Section 17 Moisture & Corrosion Humidity and corrosive chemicals in the atmosphere can cause serious failures in electronics. The first, and by far the most effective, layer of protection is the use of conformal coating on all PC boards. Some vendors dislike this approach because the coating can retain the heat. If the coating material is selected properly, it can be a conductor of heat, helping it to dissipate. Components that cannot be coated, such as connectors, use gold-plated contacts that are lubricated with a special anti-fretting compound. TYPES OF FAULTS Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  12. 12. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 34 Section 1 XRS Consulting Engineers and Project Managers 34 Section 10 XRS Consulting Engineers and Project Managers 34 Appendix XRS Consulting Engineers and Project Managers 34 Section 17 Diagnostics Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  13. 13. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 37 Section 1 XRS Consulting Engineers and Project Managers 37 Section 10 XRS Consulting Engineers and Project Managers 37 Appendix XRS Consulting Engineers and Project Managers 37 Section 17 The results of such diagnostic checks are usually displayed on video screens so they can be used to identify the trouble. By providing continuous online monitoring of system performance, self-diagnostics minimizes the component Mean Time To Repair (MTTR) through the prompt and timely reporting of component failures. DIAGNOSTICS Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  14. 14. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 40 Section 1 XRS Consulting Engineers and Project Managers 40 Section 10 XRS Consulting Engineers and Project Managers 40 Appendix XRS Consulting Engineers and Project Managers 40 Section 17 Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  15. 15. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 43 Section 1 XRS Consulting Engineers and Project Managers 43 Section 10 XRS Consulting Engineers and Project Managers 43 Appendix XRS Consulting Engineers and Project Managers 43 Section 17 PROM Check Sum Test — The contents of a PROM is banked into RAM, and the check sum is computed. The result can be compared with the value check sum result, which can be burned into PROM. Dead Man (Watchdog) Timers (DMTs) — Timers that must be reset at specified intervals to determine that the programs are still executing. Some dead man timers will alarm if the reset is too often, indicating a program loop around the reset command. DIAGNOSTICS Processor Cards Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  16. 16. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 46 Section 1 XRS Consulting Engineers and Project Managers 46 Section 10 XRS Consulting Engineers and Project Managers 46 Appendix XRS Consulting Engineers and Project Managers 46 Section 17 Memory Cards If there is a large database common to many processor cards, then in many systems it is often stored on a single memory card. The Random Access Memory (RAM) of this card should be either nonvolatile or battery backed up. If battery backup is used, the capacity (the ability of the battery to sustain current over time) of the battery should be known to the system, and low capacity should be alarmed. DIAGNOSTICS Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  17. 17. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 49 Section 1 XRS Consulting Engineers and Project Managers 49 Section 10 XRS Consulting Engineers and Project Managers 49 Appendix XRS Consulting Engineers and Project Managers 49 Section 17 Communications Communication Between Cards on a Back-plane Since back-plane noise might be responsible for an error in data, a second attempt can be made when a fault is detected. If successive attempts fail, transfer to backup is called for. The number of attempts allowed before the transfer to backup depends upon the amount of time available to complete the communication and the likely duration of transient noise. DIAGNOSTICS Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
  18. 18. Modern DCS Applications, Selection & Troubleshooting XRS Consulting Engineers and Project Managers 52 Section 1 XRS Consulting Engineers and Project Managers 52 Section 10 XRS Consulting Engineers and Project Managers 52 Appendix XRS Consulting Engineers and Project Managers 52 Section 17 Communications Communication between devices is a likely source of short disruptions. As the distances between communicating devices increase, the likelihood of disruptions caused by the environment may increase. Extra precautions must be taken to make such communications secure and to provide a fault-tolerant system. DIAGNOSTICS Maintenance Considerations This document is a partial preview. Full document download can be found on Flevy: http://flevy.com/browse/document/distributed-control-systems-dcs-maintenance-considerations-3070
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