The Schneider Electric (Viconics) R820-PCB-A01 Multi-Signal Input Board is an electronic replacement circuit board designed for R820 series silicon-controlled rectifier (SCR) power controllers. Operating on 24 VAC, it accepts compatible control signals from thermostats or building automation systems and converts them into output signals that regulate electric heating loads. It is used... https://www.partshnc.com/r820-pcb-a01-schneider-electric-viconics-multi-signal-input-board