Telemetry panels have output interfaces that send analog and digital signals produced by the programmable logic controller (PLC) to control the actuators. Input interfaces that condition the field signals provided by the sensors. These may be built into the PLC or be external modules. A power supply that converts AC voltage from the mains into standard DC voltages, usually 24 VDC, and manages battery charging for operation in the event of a power outage. A radio modem, which can be spread spectrum or GPRS/GSM radios, allows the remote control to communicate with the CCO or other remote units.