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MELSEC-Q
10 MAINTENANCE AND INSPECTION
10.3 Battery Replacement
When the voltage of the program and power interrupt hold-on function backup battery
is lowered, the special relays SM51 and SM52 are energized.
Even if these special relays are energized, the contents of the program and power
interrupt hold-on function are not erased immediately.
If the energization of these relays is recognized, however, these contents may be
deleted unintentionally.
While a total of the power interrupt hold-on time after the SM51 is energized is within a
specified time, replace the battery with a new one.
POINTS
The SM51 is used to give an alarm when the capacity of the battery is lowered.
Even after it is energized, the data is held for a specified time.
For safety, however, replace the battery with a new one as early as possible.
The SM52 is energized when the battery causes a complete discharge error.
Immediately after the relay has been energized, replace the battery with a new one.
Whichever voltage of the battery of the CPU module and SRAM card is lowered, the
SM51 and SM52 are energized.
To identify the specific battery of the memory of which voltage is lowered, check the
contents of the special resisters SD51 and SD52.
When the voltage of the battery of each memory is lowered, the bit corresponding to
each of SD51 and SD52 memories is turned on.
Bit No. of SD51 and SD52 Object
Bit 0 CPU module
Bit 1, 2 SRAM card
POINTS
The relation between the backups of the memories preformed by the batteries
which are installed on the CPU module and SRAM card is described below.
The items that must be considered are the following two points.
1) The battery installed on the CPU module cannot backup the memory of the
SRAM card.
2) The battery installed on the SRAM card cannot backup the memory of the CPU
module.
Power supply
Module
Battery of CPU
Module
Battery of
SRAM Card
Memory of CPU
Module
Memory of
SRAM Card
ON
Connection
OFF
ON
ON
Unconnection
OFF
ON
Connection
OFF
ON
OFF
Unconnection
OFF
: Backup enable : Backup unable
The standard service life and replacement procedures of the battery is described on
the next page.