Athena Controls offers two types of power controllers, namely Zero Voltage Switched Controllers and Phase Angle Fired Controllers. The 19Z and 39Z SCR Power Controllers are zero crossover fired, high-power solid state switched devices. Zero crossover firing eliminates the RFI (radio frequency interference) generation associated with mechanical relays. With zero crossover firing, the output appears as bursts of full sine waves of line voltage which provides excellent regulation to the load. The 19P and 39P SCR Phase-Angle Fired Power Controllers turn on each SCR for a controlled portion of a half-cycle of the line voltage. The effective line voltage is determined by the portion of the line voltage delivered, which is proportional to the input control signal. Additionally, the voltage is regulated as the line voltage changes.