In the 802.3af standard, devices within the power supply allow it to ramp up to the proper voltage. For example, the power supply looks for a proper capacitive or resistive signature and if detected, it ramps up to four volts. The process is repeated by checking for the signature again. If detected and there are no faults, the power supply ramps up to eight volts. The process is repeated one more time and if the proper signature is again found, it will ramp up to the full forty-eight volts to power the system.