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It is not just additive transients that can cause equipment failure, subtractive transients and dips/sags can also. Many don't understand the reasons behind this. Those who have worked with older CMOS technology will be well acquainted with the term 'latch-up' and how destructive it can be (and how hot the circuit board got!). For those who don't, latch-up is simply when the circuitry within an IC (especially true of complimentary output stages) allows current through itself which in turn switches everything on and causing all portions to conduct. This is not just true of ICs, certain circuits made from discrete components can do this too. The surprise comes when a power quality investigator is called in to ascertain why some equipment is failing, but upon doing a survey discovers the voltage dips as opposed to surges. It is taught that surges and transients damage equipment, not sags or dips. During a dip some of the circuitry may malfunction while others remain fully operational. When the power is fully restored the malfunctioning circuitry and working circuitry work against each other, this whole process taking an extortionate amount of current and damaging portions along the way. A fuse blowing is merely an indication that such a fault has occured, seldom is it protection against damage. Good 'brown-out' detection and protection can combat this, and was dealt with under "equipment malfunction". However, things are improving dramatically. This is especially true of devices using "universal input" (switch-mode) power supplies. This is the latest trend and most adapters and electronic devices are now capable of a rather wide 100-260VAC input. This makes the more modern equipment immune to the voltage dip and/or prolonged low volts condition. When last did you see a computer reboot on a brownout condition? One PSU tested was still delivering full volts to the motherboard with as low as 60VAC on the input. Component Failure After the PSU >>
© 26.10.01 |
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