384 lines
8.9 KiB
HTML
384 lines
8.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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>An Overview of Power Protection</TITLE
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>UPS HOWTO</TH
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><DIV
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CLASS="sect1"
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><H1
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CLASS="sect1"
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><A
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NAME="AEN71"
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></A
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>2. An Overview of Power Protection</H1
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><P
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>Power protection guards your equipment against blackouts,
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brownouts, surges, and spikes. All these events are anomalies in the flow
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of mains power that can damage your electronic equipment.</P
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><P
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>A <EM
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>blackout</EM
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> is a complete interruption of
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power; some literature considers a voltage drop below about 80V to be a
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blackout as well since most equipment will not operate below that
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level.</P
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><P
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>A <EM
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>dropout</EM
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> is a very short (less than one second)
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blackout.</P
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><P
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>A <EM
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>brownout</EM
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> or <EM
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>sag</EM
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> is a
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decrease in voltage levels which can last for periods ranging from
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fractions of a second to hours. This can be caused by heavy equipment coming on
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line such as shop tools, elevators, compressors etc. Also occurs when
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utility companies deliberately do this to cope with peak load times.</P
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><P
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>A <EM
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>spike</EM
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> is a tremendous increase in voltage over
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a very short period of time often caused by a direct lightning strike on a
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power line or when power returns after a blackout.</P
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><P
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>A <EM
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>surge</EM
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> is a substantial increase in voltage
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lasting a small fraction of a second, often caused when high powered
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appliances such as air conditioners are switched off.</P
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><P
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>There are three levels of power protection available to the
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home computer user. The levels are:</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>Surge Suppressor</P
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></LI
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><LI
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><P
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>Line Conditioners</P
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></LI
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><LI
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><P
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>Uninterruptible Power Supplies</P
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></LI
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></OL
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><P
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>While this HOWTO mainly focuses on UPSs, we'll start with some basics
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about the other two kinds of power filtering to help you understand where
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UPSes fit in. This is useful even though plummeting UPS prices have made
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the low-end alternatives less interesting than they used to be.</P
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="surge"
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></A
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>2.1. Surge suppressors</H2
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><P
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>These are basically a fancy fuse between the source and your
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hardware; they clamp down spikes, but can't fill in a low voltage
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level or dropout.</P
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><P
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>This is a bare minimum level of protection that any piece of
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expensive electronics should have. Note that this applies to more
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than just AC power; surge suppressors are available for (and should be
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used on) phone lines, and RS-232 and parallel connections (for use on
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long lines; generally not needed if the devices are colocated with the
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computer and all devices are protected from outside sources). Note
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also that <EM
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>all</EM
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> devices connected to your computer
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need to be protected; if you put a surge suppressor on your computer
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but not your printer, then a zap on the printer may take out the
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computer, too.</P
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><P
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>An important fact about surge suppressors is that <EM
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>they
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need to be replaced if they absorb a large surge</EM
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>. Besides
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fuses, most suppressors rely on on components called Metal-Oxide
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Varistors (or MOVs) for spike suppression, which degrade when they
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take a voltage hit. The problem with cheap suppressors is that they
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don't tell you when the MOV is cooked, so you can end up with no spike
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protection and a false sense of security. Better ones have an
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indicator.</P
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><P
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>You can buy surge suppressors at any Radio Shack; for better prices, go
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mail-order through Computer Shopper or some similar magazine. All of
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these are low-cost devices ($10-50).</P
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></DIV
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="conditioners"
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></A
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>2.2. Line Conditioners</H2
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><P
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>These devices filter noise out of AC lines. Noise can degrade
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your power supply and cause it to fail prematurely. They also protect
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against short voltage dropouts and include surge suppression.</P
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><P
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>The Tripp-Lite 1200 I used to have was typical of the better class of
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line conditioners; a box with a good big soft-iron transformer and a couple
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of moby capacitors in it and <EM
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>no</EM
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> conductive path
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between the in and out sides. With one of these, you can laugh at
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brownouts and electrical storms. A fringe benefit is that if you
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accidentally pull your plug out of the wall you may find you actually have
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time to re-connect it before the machine notices (I did this once). But a
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true UPS is better.</P
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><P
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>Netter Trey McLendon has good things to say about Zero Surge
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conditioners. He says: "Our systems at work [...] have been protected for
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2.5 years now through many a violent storm...one strike knocked [out] the
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MOV-type suppressors on a Mac dealer's training setup across the street
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from us. The Zero Surge just sort of buzzed when the surge came in, with
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no interruption whatsoever. The basic principle is this: ZS units slow
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down the surge with a network of passive elements and then sends it back
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out the neutral line, which is tied to ground <EM
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>outside at the
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box</EM
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> by code. MOV units shunt the surge to ground <EM
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>at
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the computer</EM
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>, where it leaps across serial ports, network
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connections, etc. doing its deadly work."</P
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><P
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>Price vary widely, from $40-400, depending on the power rating
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and capabilities of the device. Mail-order from a reputable supply
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house is your best bet. Line conditioners typically
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<EM
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>don't</EM
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> need to be replaced after a surge; check to
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see if yours includes MOVs.</P
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></DIV
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="AEN112"
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></A
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>2.3. Uninterruptible Power Supplies</H2
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><P
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>The remainder of this document will focus on UPSes. A UPS does three
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things for you. First, it filters the power your machine sees, smoothing
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out spikes and voltage fluctuations that can stress or even damage your
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electronics. Secondly, it provides a certain amount of dwell time in the
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event your power goes out entirely — this can often get you through
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brownouts and short blackouts. Third, when the UPS is about to run out of
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power it can arrange a graceful shutdown of your computer so that no
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unpleasant things happen to your disk filesystems. While the risks of
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unexpected shutdown are much lessened in these days of journalling
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filesystems like Linux's EXT3 or JFS from what they once were, ensuring a
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clean shutdown is still a valuable contribution to any system
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administrator's peace of mind.</P
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><P
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>Here's what a UPS will do for you:</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>Absorb relatively small power surges.</P
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></LI
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><LI
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><P
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>Smooth out noisy power sources.</P
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></LI
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><LI
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><P
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>Continue to provide power to equipment during line
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sags.</P
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></LI
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><LI
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><P
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>Provide power for some time after a blackout has
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occurred.</P
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></LI
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></OL
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><P
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>In addition, some UPS or UPS/software combinations provide the
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following functions:</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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> Automatic shutdown of equipment during long power outages.
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</P
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></LI
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><LI
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><P
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> Monitoring and logging of the status of the power supply.
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</P
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></LI
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><LI
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><P
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> Display the Voltage/Current draw of the equipment.
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</P
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></LI
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><LI
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><P
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> Restart equipment after a long power outage.
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</P
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></LI
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><LI
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><P
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> Display the voltage currently on the line.
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</P
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></LI
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><LI
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><P
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> Provide alarms on certain error conditions.
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</P
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></LI
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><LI
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><P
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> Provide alarms on certain error conditions.
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</P
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></LI
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></OL
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><P
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>Many pronounce UPS as "ups", but most of the literature seems to
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favor "you pee ess", since they use "a UPS" instead of "an UPS". This
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document will try to follow the literature. Neither pronunciation will get
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you laughed at by those who are experienced in the field.</P
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