Power monitoring unit, control method therefor, and exposure apparatus

摘要

A power monitoring apparatus monitors the voltage fluctuation range of an AC power supply and the duration of voltage fluctuations within the voltage fluctuation range. The power monitoring apparatus looks up a power failure rank table for determining the power failure rank of the power supply on the basis of the voltage fluctuation range and the duration obtained as the monitoring result to determine the power failure rank of the power supply. The power monitoring apparatus sends a power failure signal indicating the power failure rank to a power supply destination of an AC power supply.