SfAR-S-8DI8DO User Manual
www.ismacontrolli.com
DMP275en | 3rd Issue rev. 2 | 05/2022
page 19 of 25
8 Input Filter
Digital inputs allow connection of the AC signal. However, due to the fact that these inputs
are fast and allow counting pulses at 1 kHz frequency, it is not possible to use them to
monitor the presence of a variable frequency signal like 50 Hz because, depending on the
moment at which the input state is read with the Modbus protocol, different results can
be obtained despite the fact that AC voltage is still present. To be able to monitor the AC
signals, the possibility of filtering the digital inputs has been introduced. Filtration works in
a way that the high state occurs if the voltage is maintained for at least 40 ms. The low
state appears when there is no voltage for at least 80 ms.
The filter can be turned on for each input of the device independently using the 40018
register.
