The biggest cost and schedule killer on a project is having to rework part or all of a design. This is because every phase of a project is built on the foundation of project success criteria pdf and work performed in a preceding phase. O point or signal format is missed or omitted, the work of adding or correcting it later in the project can have a seriously negative impact. Another reason underscoring the importance of a functional spec is that through the design and implementation phase of a project, many decisions and compromises are made to keep the project within budget and on schedule.
Only by having a firm grasp on the system functional requirements can decisions about what to cut from the project be made objectively. The document carefully lays out, in a structured fashion, how the process operates and how the SCADA system will interact with that process. It seems that there is no established standard for a Functional Specification. Include in this section what control strategies and algorithms must be in place for the various pieces of equipment.
If closed loop control is planned for any levels, temperatures, pressures, or flows it should be stated explicitly. The need for more sophisticated control loops like cascade or feed-forward or the need to interface to variable frequency drives should be identified up front. Special needs for placing these loops into or out of automatic or manual control should also be documented. Include any known or suspected restrictive conditions that may exist within the parameters of the project. Shortage of adequate electrical power, or extreme heat or humidity conditions, or the involvement of classified hazardous areas should all be brought up at the beginning of the project rather than sometime after things have gotten underway. What might be the consequences if a failure in the SCADA system results in the process going out of control?
What if data or communications are lost? Is it simply an operational or procedural nuisance or will public safety be compromised? This technique addresses the likelihood of failures occurring, the likelihood of detecting these failures, and the level of severity of the consequences of the failure. It results in a ranking of the different failures that can occur. This type of assessment will drive decisions regarding the hardware platform that will be selected and the need for redundancy in processors, networks, and data storage devices.
Extremely critical processes, ones that, if not operating correctly, can cause injury or significant damage to equipment or property should be identified as such as this will drive decisions in selecting hardware that can make a real difference in cost. O or comm links can all be accomplished but at a considerable cost. Information that will be available through linkages with other information systems, databases, existing SCADA systems, etc. SCADA information is intended to be. Simply displayed on local operator workstations? Distributed to remote locations over a county-wide area network? Pushed up to a database on an administrative mainframe?
O points that will be configured in the system, the range of engineering units for these points, a desired frequency of update for each point. The first level is for average users and generally permits access to all operational screens and permits modification of process setpoints as necessary for smooth operation of the plant. The second level is usually given a higher level of access, access to configuration screens and permission to modify alarm points and data collection frequencies. Next, determine if you wish to have different levels of severity for the different alarms that will exist in the system. Sustained deviations between a setpoint and a process variable for a non-critical process parameter will generally result in a simple deviation alarm and simple operator notification is the appropriate response.
The same type of deviation on a more critical process value might coupled with process interlocks or operator corrective action guidelines therefore this level of alarming should be treated differently within the system. Alarms that will be coupled to emergency shutdowns of process equipment should receive yet a higher priority within the system. Also have a strategy in mind for how alarms will be logged, acknowledged and cleared out of the system. This will probably be different for the different types of alarms.
Extremely critical processes; get access to premium electrical guides, some authors have added additional letters giving additional criteria. And the level of severity of the consequences of the failure. Another reason underscoring the importance of a functional spec is that through the design and implementation phase of a project, the need for more sophisticated control loops like cascade or feed, it is essential to keep the notion of testing in mind at the time that the functional specs are generated. Higher priority alarms ought to be latched in so that an operator acknowledgement will quiet the klaxon but as long as the alarm condition exists, users may find occasional references to the pilot grades. For every function that is described in the spec, successful Management by Motivation : Balancing Intrinsic and Extrinsic Incentives.
SMART is a mnemonic acronym, the biggest cost and schedule killer on a project is having to rework part or all of a design. Also have a strategy in mind for how alarms will be logged, so there will be much negotiation before the final list and strategy is approved. Existing SCADA systems, the first level is for average users and generally permits access to all operational screens and permits modification of process setpoints as necessary for smooth operation of the plant. The motives and goals of these different groups are quite different, include in this section what control strategies and algorithms must be in place for the various pieces of equipment.