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SCADA Data Acquisition and Processing

Data Acquisition and Processing is an essential part of SCADA (Supervisory Control and Data Acquisition) systems. It is the process of collecting data from RTU (Remote Telemetry Unit) devices and processing it for use in the SCADA system. Data acquisition and processing involves the collection of data from RTUs, the conversion of data from raw values to engineering units, the application of limits to determine alarm conditions, the logging of data values and alarm conditions, and the presentation of data in graphical or tabular formats.

What is Data Acquisition and Processing in SCADA System?

Data Acquisition Protocols

Data Acquisition and Processing involves the use of communication protocols that support report by exception scanning (RBE). RBE is a method of scanning RTU devices for data changes only when a change is detected. This reduces the amount of data transmitted and ensures that only current data is presented to the user. The dead band setting for all analog values must ensure conformance to the application data transmission frequency update and data value resolution.

Status Data Processing

Status data processing involves the decoding of two or three-state status points. For two-state status points, the user must define the names and colors associated with each state, such as ON and OFF or Open and Closed. For three-state status points, the user must define the names and colors associated with each state, such as Open, Closed and Moving, or Failed.

Analog Data Processing

Analog data processing involves the scanning of analog inputs in the RTUs at predefined intervals. Any failure to complete a scan must be marked with a Telemetry Failed data quality flag. The user must also specify the scale factor and offset to represent the conversion factors for a linear conversion of the telemetered analog values to engineering units. The deadband associated with each limit is used to prevent multiple alarms from being generated when the value hovers near a limit value.

Pulse Accumulator Data Processing

Pulse accumulator data processing involves sending commands to freeze the accumulators either to all RTUs or to selected RTUs. Upon receiving the accumulator readings at the master station, the system must automatically calculate the difference from the last reading. The RTU can also implement a cyclic freeze based on synchronized RTU clock, such as on an hour change without freeze command from SCADA. The system must also be able to retrieve accumulators at user-definable intervals from 15 to 60 minutes.

Sequence of Events Data Processing

For power and substation automation applications that require sequence of events data processing (SOE), the SCADA system must process digital indications from the RTUs which are tagged with the time of event occurrence. Sequence of Events data must have a 1 millisecond time stamp. The system must provide a filtered view for all SOE signals.

Control Output Requirements

Control output must be performed in a safe and secure manner. The operator must be promptly informed if any anomalies occur during the control sequence. The system must allow the system operator at any HMI workstation to issue control commands (Digital outputs and Analog outputs) to operate equipment, close valves and/or change analog set points through a select-before-operate sequence and automatically monitor the field device to ensure full and successful command operation. Control action response times must take the highest priority over all other data communication.

Supervisory Control

Supervisory control applications must be able to be scheduled, run on demand or triggered by events.

Alarm and Message Handling

SAER-5895 must be followed to provide the required consistency and avoid configuration of unnecessary alarms. Priority must be established by severity of consequence and time to respond for each process variable, rather than a blanket policy such as setting alarms on all analog inputs at 80%.

Data Historization

There must be a configurable, real time and historical data collection package to support trending, logging, and reporting. On-line storage media must be redundant. When a process point is not collected, an unavailable code must be entered in the history file. The system must support configurable historical data collection rates ranging from point scan time to one hour averages. The historical data collection package must be capable of storing the following number of recent alarms and events as a minimum: 10,000 Process alarms, 5,000 System Alarms, 5,000 Operator Actions and 5,000 Engineering Actions. The stored historical data must be accessible to other applications for data review and analysis and to trending displays. The historical database must be able to store any data from the real-time database on a periodic or snapshot basis definable by the user.

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