Spang Power Electronics The 851 digital SCR power controller operates in three firing modes: phase-angle, zero crossover, and zero crossover into a transformer. Through network conductivity, manufacturers can improve system performance by cost-effectively linking multiple controllers for central control through a programmable logic controller (PLC) or an industrial computer. The unit's flexibility, on-board diagnostics, computerized setup and calibration, and advanced process and fault monitoring features make it possible to have real-time information about key aspects of high temperature process control applications.