Digital status inputs from the field are fed directly to the digital input card of the RTU, which performs signal conditioning and sensing of the digital input signal. The digital input module senses the input voltage, and generates ON/OFF status for that channel accordingly. This status is then acquired by the CPU over the I/O communication bus.
The DI card is capable of scanning each DI channel at a frequency better than 1 millisecond. It also time-stamps the status of each channel at 1-millisecond resolution, for SoE recording. The CPU retains this time stamp for further transfer to the remote SCADA. The DI card is also capable of filtering input chatters.