Chapter 10
ARC – Data archiving

The RexCore executive of the REXYGEN system consists of various interconnected subsystems (real-time subsystem, diagnostic subsystem, drivers subsystem, etc.). One of these subsystems is the archiving subsystem. The archiving subsystem takes care of recording the history of the control algorithm.

The function blocks can be divided into groups by their use:

• Blocks for generating alarms and events – ALB, ALBI, ALM, ALMI, ALN, ALNI, ARS.
• Blocks for recording trends – ACD, TRND, TRNDV.
• Blocks for handling archives – AFLUSH, ACLEAR.

Functionality of the archiving subsystem
The archive in the REXYGEN system stores the history of events, alarms and trends of selected signals. There can be up to 15 archives in each target device. The types or archives are listed below:

RAM memory archive

– Suitable for short-term data storage. The data access rate is very high but the data is lost on reboot.

Archive in a backed-up memory

– Similar to the RAM archive but the data is not lost on restart. Data can be accessed fast but the capacity is usually quite limited (depends on the target platform).

Disk archive

– The disk archives are files in a proprietary binary format. The files are easily transferrable among individual platforms and the main advantage is the size, which is limited only by the capacity of the storage medium. On the other hand, the drawback is the relatively slow data access.

Not all hardware platforms support all types of archives. The individual types which are supported by the platform can be displayed in REXYGEN Studio in the Diagnostics tree view panel after clicking on the name of the target device (IP address). The supported types are listed in the lower left part of the Target tab.

General archive properties
The archiving and trending blocks have several common properties which are listed below.

Archive list
The list of archives is specified in the blocks by the arc parameter in the form e.g. 1,3..5,8. Details about the archive numbering are in the ARC block. Third-party programs (Simulink, OPC clients, etc.) work with the whole number which is a bit mask – for the example above it is 157, in binary form 10011101.

Event identification code
The event identification code in the archive id must be unique in the entire target device with the REXYGEN control system (i.e. in all archive blocks). If id = 0, no alarm is generated. For id = -1, the alarm is identified by its name (i.e. the block name must be the same as the Name column in the alarm definition table).

Types of events and alarms
Events and alarms are differentiated in the REXYGEN system by the lvl parameter. If $1\le \mathtt{\text{lvl}}\le 127$, it is an alarm where the start, end and acknowledgment are stored in the archive. The range $128\le \mathtt{\text{lvl}}\le 255$ is reserved for events where only the time instant of the event is stored in the archive.

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