Section 4 Binary input and output modules4.1 Binary input4.1.1 Binary input debounce filterThe 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 millisecondwhen a binary input is high, or decreased when a binary input is low. A new debouncedbinary input signal is forwarded when the time counter reaches the set DebounceTimevalue and the debounced input value is high or when the time counter reaches 0 andthe 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 thecounter does not reach 0 again. The same happens when the signal goes down to 0again.Each binary input has a filter time parameter DebounceTimex, where x is the numberof the binary input of the module in question (for example DebounceTime1).The debounce time should be set to the same value for all channels onthe board.4.1.2 Oscillation filterBinary input wiring can be very long in substations and there are electromagneticfields from for example nearby breakers. Floating input lines can result indisturbances to binary inputs. These disturbances are unwanted in the system. Anoscillation filter is used to reduce the disturbance from the system when a binary inputstarts oscillating.Each debounced input signal change increments of an oscillation counter. Every timethe oscillation time counter reaches the set OscillationTime, the oscillation counter ischecked and both the time counter and the oscillation counter are reset. If the countervalue is above the set OscillationCount value the signal is declared as oscillating andnot valid. If the value is below the set OscillationCount value, the signal is declared asvalid again. During counting of the oscillation time the status of the signal remainsunchanged, leading to a fixed delay in the status update, even if the signal has attainednormal status again.1MRK 511 287-UEN A Section 4Binary input and output modules51Technical manual
