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The term downtime is used to refer to periods when a system is unavailable. Downtime or outage duration refers to a period of time that a system fails to provide or perform its primary function. Reliability, availability, recovery, and unavailability are related concepts. The unavailability is the proportion of a time-span that a system is unavailable or offline. This is usually a result of the system failing to function because of an unplanned event, or because of routine maintenance (a planned event). The term is commonly applied to networks and servers. The common reasons for unplanned outages are system failures (such as a crash) or communications failures (commonly known as network outage). The term is also commonly applied in industrial environments in relation to failures in industrial production equipment. Some facilities measure the downtime incurred during a work shift, or during a 12 or 24-hour period. Another common practice is to identify each downtime event as having an operational, electrical or mechanical origin. The opposite of downtime is uptime. ==Types== Industry standards for the term "Outage Duration" or "Maintenance Duration" can have different point of initiation and completion thus the following clarification should be used to avoid conflicts in contract execution: # "Turnkey" this is the most engrossing of all outage types. Outage or Maintenance starts with operator of the plant or equipment pressing the shutdown or stop button to initiate a halt in operation. Unless otherwise noted, Outage or Maintenance is considered completed when the plant or equipment is back in normal operation ready to begin manufacturing or ready be synchronized with system or grid or ready to perform duties as pump or compressor. # "Breaker to Breaker" This Outage or Maintenance starts with operator of the plant or equipment removing the power circuit (Main power breaker at "off" or "disengaged" or "On-Cooldown"), not the control circuit from operation. This still would allow for the equipment to be cooled down or brought to ambient such that outage/maintenance work can be prepared or initiated. Depending on equipment types, "Breaker to Breaker" outage can be advantageous if contracting out controls related maintenance as this type of maintenance work can be performed while main equipment is still on cool-down or on stand-by. Unless otherwise noted, this type of outage is considered complete when power circuit is re-energized via engaging of the power breaker. # "Completion of Lock-out/Tag-out" This Outage or Maintenance (sometimes mistaken for "Off-Cooldown" but not the same) starts with operator of the plant or equipment removing the power circuit, disengaging the control circuit and performing other neutralization of potential power and hazard sources (typically called Lock-Out, Tag-Out "LOTO") This point of maintenance period is typically the last phase of the outage initiation stage before actual work starts on the facility, plant or equipment. One should note that safety briefing should always follow the LOTO activity, before any work is conducted. Unless otherwise noted, this type of outage is considered complete when the equipment has reached mechanical completion and ready to be placed on slow-roll for many heavy rotating equipment, Bump-test or rotation check for motors, etc., but must follow return or work permit per LOTO procedures. Any on-line testing, performance testing and tuning required should not count towards the outage duration as these activities are typically conducted after the completion of outage or maintenance event and are out of control of most maintenance contractors. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Downtime」の詳細全文を読む スポンサード リンク
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