6.7 OB 129: Battery State
Function
With OB 129, you can check the state of the back-up battery with a
STEP 5 program (OB 129 scans the BAU signal). Depending on the
result, you could, for example, set a fault indicator (lamp).
How the BAU signal is
formed
The power supply contains two back-up batteries, a lithium cell (MB
for main battery) and an accumulator (RB for reserve battery). The
BAU signal is formed by ANDing the battery monitoring signals.
Jumper setting in the power
supply
In the power supply of the PLC, there are two jumpers with which the
monitoring of the batteries can be influenced. Jumper MB-NB
determines when the BAU signal is generated (if this jumper is not
inserted, BAU is generated once following POWER UP). Otherwise
the signal is monitored cyclically during operation. The monitoring
signal of the accumulator can be disabled with the jumper MA-NA.
The possible combinations of jumper settings and the resulting battery
monitoring by OB 129 are illustrated in the following table:
Jumper MB-NB Jumper MA-NA Time when BAU signal
generated
BAU signal generated from
monitoring signal of ...
open open after POWER UP lithium cell
open closed after POWER UP lithium cell and accu
closed open cyclic lithium cell
closed closed cyclic lithium cell and accu
Parameters
none
Result
RLO = ’0’: battery OK
RLO = ’1’: battery run down
OB 129: Battery State
CPU 948 Programming Guide
C79000-G8576-C848-04
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