Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

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7.16
SEL-351-5, -6, -7 Relay Instruction Manual
Date Code 20070117
Inputs, Outputs, Timers, and Other Control Logic
Latch Control Switches
Settings Change or Active Setting Group Change
If individual settings are changed (for the active setting group or one of the
other setting groups) or the active setting group is changed, the states of the
latch bits (Relay Word bits LT1–LT16) are retained, much like in the
preceding
Power Loss on page 7.15 explanation.
If individual settings are changed for a setting group other than the active
setting group, there is no interruption of the latch bits (the relay is not
momentarily disabled).
If the individual settings change or active setting group change causes a
change in SEL
OGIC
control equation settings SET n or RST n ( n = 1 through
16), the retained states of the latch bits can be changed, subject to the newly
enabled settings SET
n or RST n .
Reset Latch Bits for
Active Setting Group
Change
If desired, the latch bits can be reset to logical 0 right after a settings group
change, using SEL
OGIC
control equation setting RST n ( n = 1 through 16).
Relay Word bits SG1–SG6 indicate the active setting Group 1 through 6,
respectively (see
Table 7.3 ).
For example, when setting Group 4 becomes the active setting group, latch bit
LT2 should be reset. Make the following SEL
OGIC
control equation settings in
setting Group 4:
SV7 = SG4
RST2 =
!SV7T + ...
[= NOT(SV7T) + ...]
Figure 7.16 Time Line for Reset of Latch Bit LT2 After Active Setting Group
Change
In Figure 7.16 , latch bit LT2 is reset (deasserted to logical 0) when reset
setting RST2 asserts to logical 1 for the short time right after setting Group 4
is activated. This logic can be repeated for other latch bits.
Note: Make Latch
Control Switch
Settings With Care
The latch bit states are stored in nonvolatile memory so they can be retained
during power loss, settings change, or active setting group change. The
nonvolatile memory is rated for a finite number of “writes” for all cumulative
SV7 = SG4
SV7T
RST2 = !SV7T
Setting Group 4 Activated
Latch Bit LT2
Reset to Logical 0
SV7PU
SV7 = SG4 SV7T
SV7PU = 3
SV7DO = 0
SV7PU
SV7D0
Relay
Word
Bit
SEL
OGIC
Setting