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13 XPRESSION BUILDER
D
T
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 the figure below. The PU = 300 indicates the pickup
delay in milliseconds and DO = 250 indicates the dropout delay in milliseconds. In both parts A and B, 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.
The second type of timer is basically a pickup delay timer with a reset input/output feature. As shown in Figure
13–4: PICKUP DELAY TIMER, there are two inputs, two outputs, and a user selected pickup delay (in millisec-
onds). In its "initial" state with no inputs applied, both R and S are low (binary 0), the timer outputs RO and SO
are both low (binary 0). The timer starts counting when the S input is high (binary 1). When the count becomes
equal to the set time delay (1000 ms for our example), the SO output is set high (binary 1) and the RO output
is set low (binary 0). If the R input becomes high (binary 1) while the timer IS NOT counting, then both outputs
RO and SO are set low (binary 0) which returns the timer to its "initial state". See Table 13–1: PICKUP DELAY
TIMER TRUTH TABLE for a summary of the pickup delay timer function.
GE Power Management
Q
Figure 13–2: LATCH AND TRUTH TABLE
PU = 300
300
IN
DO = 250
D O
P U
(A)
Figure 13–3: PICKUP/DROPOUT TIMER
LPS-D Line Protection System
13.2 DESIGN CONSIDERATIONS
T
D
L
X
H
L
H
H
O U T
250
P U
P U
D O
(B)
Q
Q
0
L
H
13
13-
3
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