Data Collector Functions

A Historian Data Collector performs the following functions:

• Connects to the data source using a specific data acquisition interface, such as EDA, OPC 1.0, or OPC2.0.
• Groups tags by collection interval for efficient polling.
• Reads data as frequently as 10 times/sec, depending on the configuration parameters of individual tags. An OPC Collector configured for unsolicited collection can read data as frequently as 1 millisecond (or 1000 times/second).
• Scales the collected value to the EGU Range.
• Compresses collected data based on a deadband specified on a tag by tag basis, and forwards only values that exceed the deadband to the Historian Server for final compression and archiving.
• Automatically stores data during a loss of connection to the server and forwards that data to the server after the connection is restored.

Each collector performs some functions common to all types of collectors (except the File collector). These functions are:

• Maintains a local cache of tag information to sustain collection while the server connection is down.
• Automatically discovers available tags from a data source and presents them to Historian Administrator.
• Buffers data during loss of connection to the server and forwards it to the server when the connection is restored.
• Automatically adjusts timestamps, if enabled, for synchronizing collector and archiver timestamps.
• Supports both collector and device timestamping, where applicable.
• Schedules data polling for polled collection.
• Performs first level of data compression (collector compression).
• Responds to control requests, such as pause/resume collection.