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UNINTERRUPTIBLE POWER SUPPLIES
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A UPS without adequate communications capability is only partially effective and in some situations , entirely useless . If the UPS can ’ t warn its critical load of a power blackout likely to exceed its battery autonomy period , and give it time to shut down gracefully , then a system crash is merely delayed rather than prevented .
Communications contribute to UPS performance in other ways as well . For example , indications of current UPS status can be used to trigger pre-emptive maintenance , rectifying faults before they develop into system failures .
Keeping it simple On some sites , especially if the load isn ’ t considered to be critical , implementation simplicity is valued above highly detailed data . If this is the case , simple volt-free contacts may suffice . These provide ‘ True / Not True ’ alarms and messages to cover situations such as Mains Failure , Load on Inverter , or Battery Low . Such contacts can be connected to remote , but on site , alarm panels and monitoring systems such as a Remote Status Panel ( RSP ) or Building Management System ( BMS ).
These contacts can also trigger network software running on the critical load computers to initiate an orderly system shutdown . Support for this is available within almost all Windows , Mac , Linux and Unix variants . The necessary software may be embedded in the system , or available from the network operating system supplier or UPS supplier .
In any case , the software uses the contact signals together with timers to decide if or when a system shutdown should be initiated . If the software is installed on a computer network server , that server can be designated as a master and used to relay UPS alarms to other network devices , which can also be configured to respond appropriately .
If more information is required than volt-free contacts can deliver , an RS-232 serial communications port offers a reasonably simple improvement . It can monitor and exchange analogue data rather than just ‘ True / Not True ’ signals . For example , a remote RS-232 connected terminal could display :
• Inverter output voltage , frequency , current , kVA and kW
• Bypass voltage , frequency , current , kVA and kW
• Battery voltage , charge / discharge current and remaining battery time
• Statistics regarding mains failures and UPS operation
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