Chapter 23: Electrical Power Issues^609
EMI and RFI (radio frequency interference) and electric motor noise are the primary
electrical interferences from which you need to protect your PC. Electrical line noise is
measured in decibels, the same measurement that’s used for audio sound volume. If
there is an excessive amount of electrical noise on the power supply, you can often hear it
on a TV, radio, or stereo. The good news is that nearly all surge suppressors and UPS
unitsfilteroutcertainlevelsoflinenoise.However,ifyoursystemislocatednearagener-
ator or compressor, like those found in a soda pop vending machine, it is unlikely that
your surge suppressor or UPS will be able to filter all of the electrical noise on the circuit
unless it is a very high-end model. In this type of environment, it may be wise to invest in
a line conditioner and use it in place of a surge suppressor to protect your PC and periph-
eral devices.Uninterruptible Power Supply (UPS)
Although its name perhaps promises more than the unit is actually able to deliver, an
uninterruptible power supply (UPS) is designed to provide a number of power-related
services to the devices connected to it: Power source The UPS unit is placed between the devices you wish to protect
from blackouts, brownouts, and other power line events and the electrical outlet
from the normal AC electrical service.
Line conditioning Virtually all but the very least expensive UPS units
provide line conditioning to filter line noise from the electrical supply.
Surge suppression UPS units provide protection from power surges and
spikes on the electrical line.
Brownout and sag protection UPS units fill in the power loss during a power
sag or a brownout. Most UPS units cannot make u pthe power loss of a brownout
indefinitely, but unless the brownout is severe they can replace most of the power
loss for a short period.
Backup power The primary purpose of a UPS is to provide backup electricity
to the devices plugged into it for a certain amount of time.
Alarm system Most of the quality UPS units now available include a means
to connect the UPS unit to some means of notifying you of an electrical event
serious enough to invoke the UPS. On most units, this is a network connection,
but some also offer a telephone line connection used to send an e-mail, a paging
call, or the like to notify you of the event. Some also include software that is
installed on the protected PC that will initiate shutdown procedures when
notified by the UPS over a serial line connection of a serious electricity supply
system event.UPS Technologies
The basic structure of a UPS is an incoming power source, typically an AC wall outlet, a
switch that detects the incoming power level, a battery that is constantly being recharged
for use should the power source fail, and an outlet to which a device, such as a PC can
connect with its power cord. Figure 23-4 illustrates this structure.