7-2
Inputs, Outputs, Timers, and Other Control Logic
Date Code 20020215
SEL-351R Instruction Manual
Figure 7.1: Example Operation of Optoisolated Inputs IN101 Through IN106
Input Debounce Timers
Each input has settable pickup/dropout timers (IN101D through IN106D) for input
energization/deenergization debounce. Note that a given time setting (e.g., IN101D = 0.50) is
applied to both the pickup and dropout time for the corresponding input.
Time settings IN101D through IN106D are settable from 0.00 to 1.00 cycles (or to “AC”—
discussed below). The SEL-351R takes the entered time setting and internally runs the timer at
the nearest 1/16-cycle. For example, if setting IN5D = 0.80, internally the timer runs at the
nearest 1/16-cycle: 13/16-cycles (13/16 = 0.8125).
The “AC” setting (e.g., IN101D = AC) allows the optoisolated inputs to sense ac voltage
correctly. In this “AC” operation mode, an optoisolated input has a maximum pickup time of
0.75 cycles and a maximum dropout time of 1.25 cycles for the application or removal,
respectively, of ac voltage on the input.
For most dc applications, the input pickup/dropout debounce timers should be set in 1/4-cycle
increments. For example, in the factory default settings, all the optoisolated input
pickup/dropout debounce timers are set at 1/2-cycle (e.g., IN104D = 0.50). See
SHO Command
(Show/View Settings)
in
Section 10: Serial Port Communications and Commands
for a list of
the factory default settings.
Only a few applications (e.g., communications-assisted tripping schemes) might require input
pickup/dropout debounce timers set less than 1/4-cycle [e.g., if setting IN105D = 0.13, internally
the timer runs at the nearest 1/16-cycle: 2/16-cycles (2/16 = 0.1250)].
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