Off-Line technology, sometimes called standby. These UPSs are designed to protect a single PC or workstation. It is normally that most inexpensive UPS and only offers back up in the event of a total power cut and does not incorporate any significant power conditioning facility. It is called off-line because the UPS circuit only comes on stream when there is a power outage. Such units use a mechanical switch to transfer over to battery power when the voltage drops below a certain level. This causes a delay of two to three milliseconds but generally most computers are able to ride this out. An inverter inside the UPS changes the DC power from the battery into AC which can be used by the computer\'s power supply.
Line-Interactive technology, offers better protection than off-line, but at a lower cost than double-conversion. It protects your computer in the event of an outage and also line conditions, which smoothes out peaks and troughs in the power supply. If the voltage drops below a predetermined level the UPS will "boost" it back to normal or if the voltage rises above a predetermined level the UPS will "buck" it back to normal. The inverter operates in reverse during times when the input AC power is normal to charge the battery. If the power fails the UPS transfers over to battery power and the inverter supplies AC to the output to power the equipment.
On-Line technology, provides the highest levels of network power protection, power conditioning and UPS back-up available. The quality of power from On-Line UPS is significantly better then that of other UPS technologies. On-line UPS provide completely regenerated power; there is no switching from mains to battery, so switch over time is not an issue. On-line UPS systems are the only UPS that protect against frequency variations and waveform distortions, essential for use with back-up generator systems. On-Line UPS is the clear choice for mission critical, high availability computer installations.