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Transfer
time
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This
describes the amount of time it takes from the initial loss of
AC power to the time the UPS takes over the load. The importance
of time for the computer translates into the computer locking
up or freezing and thereby losing any unsaved information. Instantaneous
transfer time means that the computer would not even notice that
its power source had switched from one input to another.
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Isolation
from line
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A
characteristic of a UPS in which the output is completely electrically
disconnected from the input. Power is coupled from input to output
by magnetic fields in a transformer. Because there is no connection
from input to output, transients cannot cross the magnetics thereby
eliminating any transients in the AC output.
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Neutral
to Ground bond
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The
neutral to ground bond provides protection from transients on
the neutral line which could feedback into sensitive electronic
equipment.
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EMI/RFI
Noise Filtering
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EMI
refers to electro-magnetic interference which is unwanted electrical
noise present on the power line. This noise may "leak" from the
power lines and affect equipment that is not even connected to
the power line. Such "leakage" is called a magnetic field. Magnetic
fields are formed when unwanted noise voltages give rise to noise
currents. Such noise may adversely affect electronic equipment
and cause intermittent data problems. EMI protection is provided
by noise filters placed on the AC power line. The filter reduces
the noise voltage on the protected line, and by doing so eliminates
the magnetic fields of noise generated by the protected line.
Noise signals that act over a significant distance are called
Radio Frequency Interference (RFI). Equipment power cords and
building wiring often act as antennas to receive RFI and convert
it to EMI.
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Surge/Spike
Protection
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This
category is fairly self explanatory. The higher your protection,
the better your equipment is insulated from momentary increases
in voltage on the AC line.
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Output
voltage regulation
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Voltage
regulation, especially in areas where the power quality is low,
is essential to equipment performance. Computer equipment will
identify if the voltage is within the operating parameters and
if it falls below those parameters, the computer will shut down
and will lose any unsaved information. Furthermore, with a constant
voltage, the internal components in the computer will run more
efficiently and will extend the life of the computer’s hardware
substantially.
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Inverter
waveform
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Sinewave
inverter waveform is the best. Pseudo-sinewave (typically modified
squarewave) is suitable for computers and other switchmode power
supply driven equipment, but not motors or fans.
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Energy
Efficiency
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The
ratio of output power to input power as expressed as a percent.
For example, if a UPS has an efficiency of 80%, then 20% of the
input energy in lost as heat.
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Source
Impedence
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Small
engine generators (1kW to 10kW range) have very high source impedence,
which means output voltage will drop as more load is connected
to the output. This is the reason for oversizing a generator.
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Operating
environment
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An
overall description of the AC environment which includes in its
definition frequency of transients (i.e. surges, spikes, sags),
blackouts, and voltage fluctuations to name a few. Often contributing
factors can be industrial growth, poor utility maintenance, poor
power management or erratic weather. The areas in which your computers
are operating are easily described as poor AC environments.
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Unit
Surge Voltage Withstand
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This
denotes the amount of voltage surge the UPS itself can handle
before damage and failure of the unit. If the UPS fails, the computer
equipment becomes vulnerable to the transients on the AC line.
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Price
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The
range of prices, as you’ve discovered, is widely disparate because
the standby UPS is using the cheapest but least reliable technology,
whereas the ferroresonant and online technologies are very high
quality and durable.
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