Now consider the suitability of a station with 1200 interval histories, each with a collection interval of 10 to 15 minutes. Planning for the “biggest load” configuration, that is all histories at 10 minute intervals:
1200 histories changing every 10 minutes yields 7,200 changes/hour (1200 * 6/hr * 60 min/hr).
Note this example station results in a rate of history changes nearly 18 times less than the first (Unsuitable station example), where the ratio of these two “total changes per hour” is 17.6 (126,720/7,200).
Let’s assume everything else is equal between this station and the first (unsuitable) example, including the same amount of free flash space. Then in this case, ongoing automatic database saves would occur approximately every 1.5 hours (6 minutes * 17.6, or 105 minutes)—well inside the “ideal range”.
A number of different variables factor into the actual operation of SRAM support, including:
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Rate of changes that need to be persisted.
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Types of changes (histories, alarms, and setpoint changes all have different sizes).
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Amount of free flash disk space on the controller.
Also see the following related sections:
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The next section, Disabling SRAM support.
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For detailed background information on the operation of SRAM support, see How SRAM support in a JACE works.
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For tools to monitor operation, see Diagnostic tools for the DataRecoveryService.