SCADA systems are used to monitor and control a variety of industrial processes. Ensuring their optimal performance is essential to ensure the safety and reliability of the operations they manage. This article outlines the system sizing, spare capacity and expansion, and performance requirements for SCADA systems.
System Sizing, Spare Capacity and Expansion
System Expansion and Upgrading
System expansion and upgrading of system operating and application software should be achievable with no impact to the running facilities operation. This should be done without losing the operator interface, without losing access to any control function, and without impacting the controlled or monitored process.
All displays on all workstations should be updated and responsive to controls throughout the alarm burst and during primary/backup server synchronization processes.
System Database Size
The system database size should be expandable to handle the system expansion requirements without the need to expand the hardware, or perform any software or purchase additional licenses.
System Performance Requirements
All displays and graphics should be completed within 2 seconds of the graphic display being requested. This should include fully active dynamic elements for up to 100 fields, displaying their current values.
The update frequency for real time data should be at least once every 2 seconds for all displays and graphics. This should be both alphanumerically and symbolically (shape change, color change, etc.).
Operator command initiation should receive feedback response within 2 seconds. If the system fails to respond to a command, then a fail-to-operate event should be displayed.
The system should update calculation algorithms and dynamic fields of the displays within one second of actual events and data values received at the system real-time database.
SCADA Host
The SCADA host should upload the RTU data after restoring the communication and fetch the data in the real-time database with the correct time stamp.
Historical Data Display
Historical data display updates should occur within two seconds of display call up.
RTU Per Communication Channel
The number of RTU per communication channel should be determined based on the number and type of data points per RTU including the connected subsystem IOs, the scan frequency specified in the project functional specification document (FSD) for each data point type, the round trip delay of data packets for the provided data network, and the channel utilization (for serial communication this should be between 40-80%, and for IP communication this should be between 10-30%).
System Components Utilization
SCADA system components utilization, such as memory, disk space, CPU loading, disk access should not exceed 30% under normal conditions for the system size and the future expansion requirement specified in the project functional specification document.
Alarm Burst
The system should be able to fully process a continuous alarm throughput of 50 alarms per second for at least 60 seconds on receipt of the alarms at the host.
System Events
PAS server and workstation operating systems should be configured to capture all necessary systems related events to detect performance and availability related information. This should include system alarms and failures, CPU utilization, memory utilization, IO rates, device utilization, file store utilization, applications, databases, network utilization, and response time for SCADA system and application transactions.
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