Removal and Replacement Procedures - Safety Considerations - PLAN AHEAD!
Revision 19 HC900 Process Controller Installation and User Guide 191
06/14
Battery Installation/Replacement
Advisory Regarding Battery Installation
Memory for the CPU in the Controller Module includes:
• Volatile memory and
• Non-volatile memory (Flash)
Only volatile RAM requires battery backup.
When power is applied to the Controller Module, the CPU is initialized automatically. If the battery is
installed after initialization, and if site power is maintained, the current draw from the battery is very low -
approximately 4 microamps. If site power is disconnected with the battery in place and with the CPU in
the initialized state, the current draw on the battery is approximately 800 microamps. However, if the
battery is installed before power is applied (and the CPU initializes), the SDRAM will draw approximately
40 milliamps.
At the 4 microamp level, the battery will retain energy over an extended period.
At the 800 microamp level, the battery will retain sufficient energy to maintain the content of SDRAM for
50 weekends (approximately 100 days) of backup service.
At the 40 milliamp level, battery life is severely reduced. The battery could be rendered useless in less than
60 hours.
CAUTION
Installing the backup battery when the CPU is not initialized will cause undue battery drain.
Do not install or replace the backup battery until after site power is applied.
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