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 and thedebounced 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 0 again.Each binary input has a filter time parameter DebounceTimex, where x is the number ofthe binary input of the module in question (for example DebounceTime1).The debounce time should be set to the same value for all channels on theboard.4.1.2 Oscillation filterBinary input wiring can be very long in substations and there are electromagnetic fieldsfrom for example nearby breakers. Floating input lines can result in disturbances to binaryinputs. These disturbances are unwanted in the system. An oscillation filter is used toreduce the disturbance from the system when a binary input starts oscillating.Each debounced input signal change increments of an oscillation counter. Every time theoscillation time counter reaches the set OscillationTime, the oscillation counter is checkedand both the time counter and the oscillation counter are reset. If the counter value is abovethe set OscillationCount value the signal is declared as oscillating and not valid. If thevalue is below the set OscillationCount value, the signal is declared as valid again. Duringcounting of the oscillation time the status of the signal remains unchanged, leading to afixed delay in the status update, even if the signal has attained normal status again.1MRK 502 048-UUS A Section 4Binary input and output modules57Technical manual
