Instruction manual

ControlWave Gas Flow Computer (GFC Plus) Instruction Manual (CI-ControlWave GFC Plus)
5-8 Service & Troubleshooting Revised Feb-2013
5.2.4 Removing/Replacing the Backup Battery
Note: The CPU/System Controller board draws power from the battery
only if the board loses power. The system SRAM has a standby
current draw of 20 μA maximum for each part plus 2 μA for the
real time clock. For a ControlWave GFC Plus containing 2MB
of SRAM, a worst-case current draw of 42 μA allows a battery
life of approximately 9000 hours. This means you should not
need to replace a battery until the ControlWave GFC Plus has
been in service for an extended period (normally many years).
The CPU/System Controller board accommodates a 3 V, 300 mA
lithium coin cell backup battery housed in a coin-cell socket (S1).
A
supervisory circuit on the CPU switches to battery power when the
regulated 3.3 Vdc falls out of specification. The battery then provides
backup power for the real-time clock (RTC) and the system SRAM on
the CPU/System Controller board.
Note: If the backup battery is working properly, the _BAT_OK system
variable is set ON; if the battery fails, this is OFF. The Ram
Backup Battery Status shows on the Station Summary page in
the standard measurement application. If the real-time clock
loses its battery backup, the ControlWave system variable
_QUEST_DATE turns ON. You can monitor this to generate an
alarm. See the System Variables section of the ControlWave
Designer Programmer's Handbook (D5125) for more
information. See the ControlWave Flow Measurement
Applications Guide (D5137) for information on the standard
measurement application.
Caution
You lose SRAM contents when you remove the backup battery.
If you replace a backup battery, wait at least one minute before re-
powering the system. This enables the SRAM to completely discharge.
After you install the new battery, ensure that you have placed jumper
W3 on pins 1-2 (to enable the battery).