4.119
Date Code 20100129 Instruction Manual SEL-751A Relay
Protection and Logic Functions
Front-Panel Settings (SET F Command)
Local Bits
Local bits are variables (LBnn, where nn means 01 through 32) that are
controlled from front-panel pushbuttons. Use local bits to replace traditional
panel switches. Each local bit requires three of the following four settings,
using a maximum of 14 valid characters for the NLBnn setting, and a
maximum seven valid characters (0–9, A–Z, -, /, ., space) for the remainder:
➤ NLBnn: Name the switch (normally the function that the
switch
performs, such as SUPERV SW) that will appear on the LCD
display.
➤ CLBnn: Clear local bit. Enter the text that describes the
intended operation of the switch (this text appears on the
display) when LBnn deasserts (OPEN, for example).
➤ SLBnn: Set local bit. Enter the text that describes the intended
operation of the switch (this text appears on the display) when
LBnn asserts (CLOSE, for example).
➤ PLBnn: Pulse local bit. When selecting the pulse operation,
LBnn asserts for only one processing interval before
deasserting again. Enter the text that describes the intended
operation when LBnn asserts (START, for example).
➤ Omit either SLBnn or PLBnn (never CLBnn) by setting the
omitted setting to NA.
For the transformer in our example, configure two local bits: one to replace a
supervisory switch, and the other to start a fan motor. Local bit 1 replaces a
supervisory switch (SUPERV SW) and we use the clear/set combination.
Local bit 2 starts a fan motor (START) that only needs a short pulse to seal
itself in, and we use the clear/pulse combination. Figure 4.74 shows the
settings to program the two local bits.
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