Each DSCA30/31 voltage input module provides a single channel of analog input which is filtered, isolated, amplified, and converted to a high level voltage output. Signal filtering is accomplished with a five pole filter which provides 85dB of normal-mode rejection at 60Hz and 80dB at 50Hz. An anti-aliasing pole is located on the field side of the isolation barrier, and the other four poles are on the system side. After the initial field side filtering, the input signal is chopped by a proprietary chopper circuit. Isolation is provided by transformer coupling, again using a proprietary technique to suppress transmission of common mode spikes or surges.