Schweitzer Engineering Laboratories SEL-787, Instruction Manual, Page: 155 / 564

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Date Code 20081022 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Logic Settings (SET L Command)
the NOT operator as long as the NOT operator precedes the R_TRIG operator.
The NOT R_TRIG combination produces a logical 0 for one processing
interval when it detects a rising edge on the specified element.
Boolean Falling-Edge Operator (F_TRIG)
Apply the falling-edge operator, F_TRIG, to individual Relay Word bits only;
you cannot apply F_TRIG to groups of elements within parentheses. The
falling-edge operator, F_TRIG, operates similarly to the rising-edge operator,
but operates on Relay Word bit deassertion (elements going from logical 1 to
logical 0) instead of Relay Word bit assertion. When the Relay Word bit
deasserts, F_TRIG interprets this logical 1 to logical 0 transition as a “falling
edge” and asserts to logical 1 for one processing interval, as shown in
Figure 4.49 .
Figure 4.49 Result of Falling-Edge Operator on a Deasserting Input
You can use the falling-edge operator with the NOT operator as long as the
NOT operator precedes the F_TRIG operator. The NOT F_TRIG combination
produces a logical 0 for one processing interval when it detects a falling edge
on the specified element.
Math Arithmetic Operators (*, /, +, and –)
If Relay Word bits (which are effectively Boolean resultants, equal to logical 1
or logical 0) are used in mathematical operations, they are treated as
numerical values 0 and 1, depending on if the Relay Word bit is equal to
logical 0 or logical 1, respectively.
Boolean Comparison Operators (<, >, <=, and >=)
Comparisons are mathematical operations that compare two numerical values,
with the result being a logical 0 (if the comparison is not true) or logical 1 (if
the comparison is true). Thus, what starts out as a mathematical comparison
ends up as a Boolean resultant. For example, if the output of a math variable is
above a certain value, an output contact is asserted:
OUT103 := MV01 > 8
If the math variable (MV01) is greater than 8 in value, output contact OUT103
asserts (OUT103 = logical 1). If the math variable (MV01) is less that or equal
to 8 in value, output contact OUT103 deasserts (OUT103 = logical 0).
Boolean Equality (=) and Inequality (<>) Operators
Equality and inequality operators operate similar to the comparison operators.
These are mathematical operations that compare two numerical values, with
the result being a logical 0 (if the comparison is not true), or logical 1 (if the
comparison is true). Thus, what starts out as a mathematical comparison, ends
up as a Boolean resultant. For example, if the output of a math variable is not
equal to a certain value, an output contact is asserted:
OUT102 := MV01 <> 45
F_TRIG IN101
IN101
Falling Edge
One Processing Interval
One Processing Interval