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In the previous section we dealt with the equipment working perfectly but being interfered with. At no time was the equipment malfunctioning or failing. Data was not getting lost, programs weren't crashing, machines were not losing timing, and all the other good things that we are going to investigate here. In this section we deal with what is probably the primary reason that power quality investigators are kept busy - the report of something "not quite working right". In this section we show some likely causes of equipment malfunction, and what to look out for. But saying 'cause' has to be used with care. In many circumstances the cause of malfunction is, in itself, a symptom. The cause for a specific malfunction may be low voltage, but the low voltage is caused by high impedance on the cables (which was caused by bad design, but, we have to stop somewhere!). If a cause is mentioned, do consider whether this is in fact not just a lower level symptom. Under Voltage: Although too little power can damage equipment, it usually just causes malfunction. we investigate why. Over Voltage: This stresses components, increases heat loss, and has been known to cause damage, but little is known how this causes equipment to merely malfunction, especially as it is usually considered "there's more than enough to keep it going!". Bad Zero-Crossing: With many devices now taking their timing from the mains the need for a perfect transition from the positive to negative portions of the cycle is paramount. When it isn't..... We investigate the effects on clocks running fast, jittery controls, and phase unlocked loops. Brown-out Protection: Although hailed as a good thing, brownout protection can be a device's worst enemy. Ground Voltages and Currents: Extraneous currents will always exist, but when uncontrolled these can cause the most interesting (if not dangerous) things to happen. We investigate their effect on 2452 computer terminals. Stray Magnetic Fields: are as a direct result of bad installation and their effect on modern computer screens is kaleidoscopic to say the least!
© 08.08.02 |
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