Output Waveform
- Why the Need for Uninterruptible Power?
- Ten compelling reasons for buying a UPS
- Why every network needs a UPS
- Off-line (or Passive Standby)
- Line Interactive (or Active Stand By)
- On-line Technology
- Voltage Regulation
- Output Waveform
- Connecting a UPS to a network
- Remote Monitoring
- UPS management using SNMP
- The MGE Office Protection Systems MIB
- Com Port Settings
- Security vulnerabilities
Compatibility with power supplies
The electrical waveform provided by the mains power supply
The term « electrical waveform » refers to the shape of the wave supplied by a power source, such as the mains or a UPS. Electricity suppliers distribute a current with a sinus waveform, in other words, in the form of a sine wave.
The Sine Wave
This type of waveform is mandatory for supplying devices comprising motors or transformers: lamps, ATMs, radiators, laser printers, etc. Fifteen years ago, UPSs delivered an exclusively sinus output signal, as early computers contained numerous motors. In order to re-create a sine wave from a direct current signal, complex and costly technology is required. All Eaton MGE Office Protection Systems On-line UPSs implement this technology to produce a sinus output waveform.
The Square Wave
With the appearance of PCs and what is known as switch-mode power supplies, the earlier need almost disappeared. The power supplies on PCs and their peripherals use only electrical components which can cope with a lower-quality electrical waveform. This in turn led to the appearance, about ten years ago, of UPSs delivering a squarewave, rather than a sine wave. As this approach was easier to implement, significant savings were made possible.
However, the square wave has its share of hazards for computer systems: the vertical front of the signal tends to « stress » components in the power supply, which shortens the latters working life. In addition, the pulse width tends to increase towards the end of battery backup time, delivering too much power for the load. This may also damage components. These two reasons explain why Merlin Gerin does not use this technology, even on entry-level products.
The square wave may be adequate if the PCs are not supplied by it for too long. This may be the case for Off-line UPSs, which only convert the power in the event of an outage, or in other words for a few seconds or minutes, from time to time. On the other hand, this type of waveform should not under any circumstances be used on On-line UPSs which convert power continuously or on UPSs with long battery backup times (several hours).
Eaton MGE Office Protection Systems UPS using square wave output: Protection Center, Ellipse ASR and Ellipse MAX.
Output Waveform and Technology
The shape of a UPS output wave is not dependent on the technology used (On-line, Off-line, or Line Interactive). Although On-line UPSs often deliver a sine wave and Off-line devices a square wave, it would be a mistake to generalise. Some manufacturers of bottom-of-the-range On-line UPSs use a square wave, thus cutting product costs (and the quality of protection) as far as possible. These products should be avoided at all costs: they will result in premature ageing of the power supplies on the PCs to which they are connected. The only problem is identifying these products: their sales documents never mention the existence of a square wave. Their manufacturers prefer to skirt around the issue by using terms such as « computer grade output waveform ». It is indeed the case that PC power supplies are sufficiently tolerant to be able to support this type of signal, but only for so long.