Date Code 20020215
Inputs, Outputs, Timers, and Other Control Logic
7-11
SEL-351R Instruction Manual
Remote Bit Application Ideas
With SEL
OGIC
control equations, the remote bits can be used in applications similar to those in
which local bits are used (see the preceding section on
Local Control Switches
).
Remote bits can be used much as optoisolated inputs are used in operating latch control switches
(see discussion following Figure 7.14). Pulse (momentarily operate) the remote bits for this
application.
Remote Bit States Not Retained When Power Is Lost
The states of the remote bits RB1 through RB8 (RB1 through RB16 for the SEL-351R-2) are not
retained if power to the relay is lost and then restored. The remote control switches always come
back in the OFF position (corresponding remote bit is deasserted to logical 0) when power is
restored to the relay.
Remote Bit States Retained When Settings Changed or Active Setting Group Changed
The state of each remote bit RB1 through RB8 (RB1 through RB16 for the SEL-351R-2) is
retained if a relay setting within any group, or the active setting group, is changed. If a remote
control switch is in the ON position (remote bit is a logical 1) before a setting change or an
active setting group change, it comes back in the ON position after the change. If a remote
control switch is in the OFF position (remote bit is a logical 0) before a settings change or an
active setting group change, it comes back in the OFF position after the change.
If settings are changed for a setting group other than the active setting group, there is no
interruption of the remote bits; the relay is not momentarily disabled.
L
ATCH
C
ONTROL
S
WITCHES
The latch control switch feature of this relay replaces latching relays. Traditional latching relays
maintain their output contact state when set. The SEL-351R latch bit retains memory even when
control power is lost. If the latch bit is set to a programmable output contact and control power
is lost, the state of the latch bit is stored in nonvolatile memory but the output contact will go
into its de-energized state. When control power is applied back to the relay, the programmed
output contact will go back to the state of the latch bit.
The state of a traditional latching relay output contact is changed by pulsing the latching relay
inputs (see Figure 7.10). Pulse the set input to close (“set”) the latching relay output contact.
Pulse the reset input to open (“reset”) the latching relay output contact. Often the external
contacts wired to the latching relay inputs are from remote control equipment (e.g., SCADA,
RTU).
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