Section 4 Binary input and output modules
4.1 Binary input
4.1.1 Binary input debounce filter
The debounce filter eliminates bounces and short disturbances on a binary input.
A time counter is used for filtering. The time counter is increased once in a millisecond
when a binary input is high, or decreased when a binary input is low. A new debounced
binary input signal is forwarded when the time counter reaches the set DebounceTime
value and the debounced input value is high or when the time counter reaches 0 and
the debounced input value is low. The default setting of DebounceTime is 5 ms.
The binary input ON-event gets the time stamp of the first rising edge, after which the
counter does not reach 0 again. The same happens when the signal goes down to 0
again.
Each binary input has a filter time parameter DebounceTimex, where x is the number
of the binary input of the module in question (for example DebounceTime1).
The debounce time should be set to the same value for all channels on
the board.
4.1.2 Oscillation filter
Binary input wiring can be very long in substations and there are electromagnetic
fields from for example nearby breakers. Floating input lines can result in
disturbances to binary inputs. These disturbances are unwanted in the system. An
oscillation filter is used to reduce the disturbance from the system when a binary input
starts oscillating.
Each debounced input signal change increments of an oscillation counter. Every time
the oscillation time counter reaches the set OscillationTime, the oscillation counter is
checked and both the time counter and the oscillation counter are reset. If the counter
value is above the set OscillationCount value the signal is declared as oscillating and
not valid. If the value is below the set OscillationCount value, the signal is declared as
valid again. During counting of the oscillation time the status of the signal remains
unchanged, leading to a fixed delay in the status update, even if the signal has attained
normal status again.
1MRK 511 287-UEN A Section 4
Binary input and output modules
51
Technical manual
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