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Backup Power for Extended Runtime For some systems, more backup time is needed than the minimum for operating through a brief power outage and a controlled shutdown. Critical path systems need more reserve time to keep the systems online. Following are a few examples.
Power conditioning is especially important when generators are used for power backup because generators are tested periodically. Generator tests create significant transients in the building electrical system as the generator switches in and out of the AC supply line. UPSs with Intelligent System Interfaces A UPS supplies power until its batteries rundown. If a system administrator is not present when the UPSs audible alarm sounds, the system will crash when battery power fails. To solve this problem, a UPS can communicate with the supported operating system and CPU and trigger an automated system shutdown routine. Most network operating system (NOS) vendors (e.g., Novell, IBM, Banyon) provide basic UPS monitoring modules as a standard part of the delivered NOS package. For UNIX, OS/2, and Windows (including Windows 95 and NT), third-party applications that monitor UPS communications and initiate automatic system shutdown are available. All basic UPS automated monitoring systems can send two types of signals, one for the detection of a power failure and one for a low battery (when the system is working on the battery) warning. Some basic monitoring systems support a third signal typeUPS inverter offthat shuts the UPS off after a controlled shutdown of the system. This saves any energy left in the battery, maintaining some reserve in the event that a second outage occurs before the UPS battery has had enough time to fully recharge. The next level of sophistication for UPS status reporting is a UPS status display of information about the UPS (e.g., load level used, condition codes, service alerts) as well as more information about the operating environment. Stage 4: UPSs as Manageable Network Devices In each of the previous monitoring and reporting examples, a file server is the primary recipient of UPS communications. As UPS are pressed into other networking applications (e.g., backing up bridges, routers, and hubs) other means of status monitoring will be required. Inband through SNMP A standard management information base (MIB) for UPS allows management through the Simple Network Management Protocol (SNMP), providing a standard definition of attributes of interest to developers of SNMP-based network management systems. In this mode, a UPS signals its condition directly over network communications pathways to a management console that can then shut down all dependent devices, call for service, reroute wide area traffic around the troubled hub, or take whatever action minimizes the effects of the outage. An SNMP-controlled UPS can also reboot a frozen system by allowing remote control of a UPSs output power. Output could be cycled off and on to force an attached system to go through a cold boot restart. Out of Bank Through a Modem For the less sophisticated network, UPSs can be configured to communicate with a modem that is programmed to call a predetermined number, a pager for example, that will alert a mobile system administrator that there is a fault in a particular location. ELECTRONIC EQUIPMENT SENSITIVITIES This section reviews equipment sensitivities from three perspectives. The first is a theoretical model of expected system sensitivities that is based on the physical characteristics of various system elements, from power supply to mother-board components. Next, the results of laboratory experiments are summarized; these experiments measured system responses to induced electrical transients. Last, a real-word example of the effects of interference from the electrical environment on system reliability is examined.
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