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13.2 DESIGN CONSIDERATIONS
data on the D input line is stored in the flip-flop. If the T input line is low (binary 0), the D input line is not recog-
nized. The Q output line directly reflects the state of the flip-flop. If the flip-flop is set, then Q equals a high
(binary 1). If Q equals a low (binary 0), then the flip-flop is reset.
D
T
13
c) TIMERS
There are two types of timers used in the Xpression Builder program, the Pickup/Dropout Timer and the Pickup
Relay Timer.
The simplest type is the Pickup/Dropout timer. Shown in Figure 13–6: PICKUP/DROPOUT TIMER, the 300
indicates the pickup delay and 250 indicates the dropout delay, both in milliseconds. In both parts A and B of
Figure 13–6: PICKUP/DROPOUT TIMER, the IN/OUT time charts describe how the timer functions. If the input
is high (binary 1) for a time equal to the pickup delay, the output becomes high (binary 1). Any reset of the input
(high to low) causes the accumulated pickup time to reset immediately to zero. Once the output occurs, it
remains high as long as the input remains high, and when the input subsequently goes low the output stays
high for a time equal to the dropout delay. Once the dropout timer has started, it will continue to time out even
if the input goes high during the reset time. Time chart A shows a second input pulse occurring after the output
goes low. Since this pulse length is less than the 300 ms pickup delay, the output stays low. Time chart B
shows a second input pulse occurring 100 ms after the first input pulse goes low. The output goes low as
shown in time chart B, but the output then goes high 300 ms after the leading edge of the second input pulse or
150 ms after the trailing edge of the first output pulse. The pickup and dropout timers are independent of each
other.
13-
6
T
L
Q
H
H
Figure 13–5: LATCH AND TRUTH TABLE
IN
PU = 300
DO = 250
I
N
PU
DO
O
U
T
(A)
Figure 13–6: PICKUP/DROPOUT TIMER
LPS-O Line Protection System
D
Q
X
Q
L
H
H
300
O U T
250
PU
I
N
PU
DO
O
U
T
(B)
13 XPRESSION BUILDER
0
L
GE Power Management
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