PURE SINEWAVE AND MODIFIED SINEWAVE

DIFINITION OF PURE SINEWAVE AND MODIFIED/SIMULATED SINEWAVE

The easiest way to compare waveforms is like comparing them to petrol - a pure sinewavpe is like Optimax and a modified sinewave is like regular unleaded. Use a pure sinewave UPS on your expensive equipment (i.e. servers) and save the modified sinewave for cheap equipment (i.e. PC Workstations).

When electricty is produced and delivered to your premises it arrives in as alternating current (AC) and as such has an alternating waveform (DC power does not have a waveform). When UPS were first invented they were designed to mimic and output this pure waveform after they cleaned up the original waveform. As time went on and everything started getting cheaper design engineers (and their bosses) discovered that they could save money and build a cheaper UPS by using less complicated UPS components (mainly the inverter) by having it output a sinewave that wasn't quite as perfect as the true version - it would look more like a series of steps rather than a curve. Since that time many manufactures have opted to produce modified or square wave UPS systems for low end equipment.

Using a modified sinewave UPS is generally not a problem for low end equipment as most switch mode power supplies like the ones found in your PC don't mind the square wave, even though they were designed to run on a pure sinewave. Problems start however when you start using them with more sensitive equipement. Anything with a transformer in it won't work to start with. Higher end systems may dislike the power supply and function (or disfunction) accordingly.

The other problem with simulated sinewaves is that they can cause equipment they power to to run hotter than normal which can shorten the lifespan of the power supply. This is generally ok with a workstation or PC where the power supply only costs $50-60 but it will be concern in a server grade system where the replacment costs (let alone the down time expenses) are much higher. 

The other drama with modified sinewave UPS is that they are less efficient, as more energy is used up to deliver the same result. For example a 1kVA simulated sinewave UPS with the same battery as a 1kVA pure sinewave UPS will provide less backup time in the event of a power failure.