A power supply that employs automatic switching of main power supply from primary to secondary (usually battery and/or diesel generator) upon failure of the primary. A means of providing uninterrupted power to critical instrumentation for a limited period of time even in the event of a plant power failure. Usually accomplished by an inverter, transfer switch and batteries. Alternatives means may include motor generators. A type of power supply that can provide electrical power even when line power is lost. An inverter (AC from DC batteries) which provides a bumpless transition of power to the process control system in the event of plant power failure. The UPS will supply for a limited period (e.g., 15 minutes).
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