In this issue:

~ RxMS's New Products

~ PFC - What's that?

~ Temperature and Humidity Focus

Waveform of the Month

~ Below is a Voltage Waveform that has slight Voltage distortion on the output of the UPS during normal daily system operation. Phase-to-Phase Voltage is good, but Phase-to-Ground is highly distorted. This waveform clarifies why it is important to monitor both Phase-to-Phase and Phase-to-Ground.

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~ Power Factor Correction events are caused by the turning on or off of capacitors (often by the utility). These events occur daily during the work week and are often on a timer so that they will be constantly turning on and off at the same time every work day. The utility often places these on lines that have a high amount of electronics. And they are designed to bring the voltage back in to phase with the current (the utility is allowed to switch these in according to the Public Utility Commission). According to the PUC, any instrument that is susceptible to the waveform distortion that this switching action brings, will have to be classified as requiring “computer grade power” and additional power protection will have to be added at the customers expense.

~ Now that we know it is allowed, what harm can this waveform be to my electronic system? There are two major issues with the waveform. First, the ringing of the low frequency (typically 3-5 kHz.) can cause over voltages for a short amount of time (1-2milliseconds). While this seems very short time, it is plenty of time to destroy sensitive internal parts. These over voltages most often affect the FCC, UL and CE filtering and surge suppressor components that are required by these international organizations. We often see an increase in the leakage current that is caused by the PFC events degrading the capacitors and MOVs to a point where they start to leak current to ground (prior to complete failure) which is why (one of several reasons) it is always critical to monitor the ground current. Another problem resulting from these waveforms is “multiple zero-crossings” that occur. The crossing of zero multiple times can cause many component (e.g. laser diodes, bridge diodes) to turn on and off at the wrong time. Since many of these diodes are in strings of 8, 16 or 32, some of the diodes will see the false zero crossing (turn on or off) and the other will not. This causes instability problems and often leads to what appears to be a "random system reset”. These resets will occur for some unknown time until the component eventually reverse-biases and destroys itself (we like to call this letting the “magic smoke out” and once the magic’s gone, it does not work.)

~ Solving this issue is critical to many high speed electronics, but not to all. For instance, near as we can tell, this waveform has little or no affect on home computer systems. Other devices require a power protection device that rebuilds the fundamental source (50 or 60Hz.) voltage waveform. These technologies include on-line (or double conversion) UPS’s, Ferroresonant transformers (although these can have other complications with electronics) and certain types of voltage regulators (often called VRDU) that are basically a UPS without the battery. Please be careful as not all UPS’s are the same. Most are line interactive and will not filter this low frequency event out. Always contact RxMS tech support line if there are any questions on power protection strategies.