Jim Wheeler 2015-06-09 00:29:34
Why use true RMS meters? We all should be grateful Nicolai Tesla beat out Thomas Edison in his bid to provide the first major electrical service to parts of our country. The direct current Edison proposed would never have worked practically since it would not have allowed the use of transformers, which step the voltage of power lines up for longline transmission, then back down for domestic use. DC electricity is what you get from a battery where the current constantly flows from negative to positive. But alternating current pushes the flow of electricity up and back in the power lines, hopefully in a smooth and continuous motion. And I say hopefully because that isn't what you'll always find, especially in large industrial areas where the power coming into a building may not be a smooth "sinusoidal" wave. When this happens, very costly equipment can be mysteriously damaged. Also understand there are two types of power meters your company likely sells, averaging meters and true RMS meters. And many of your customers probably don't understand why they should shell out more hard cash for the latter. So here is an explanation with a story. A few years ago, I traveled with a very good HVAC technician to a local country club where they had a large 3-phase A/C compressor that kept kicking out on overloads. They thought the problem was with the compressor since the voltage and current through the motor windings were pretty consistent on all three legs; so they changed the compressor. However, the new compressor mysteriously started having the same problem and that's why they asked me to look at it (I used to be a wholesaler's regional service manager and a manufacturer's national service manager). When we arrived at the job, I checked the voltage to and the current through all three of the compressor's legs with the service tech's averaging meter and found nothing wrong - everything looked fine. Then I asked the tech if he had a true RMS meter. He said he did out in his truck (he was a true techie and he had just bought one). So I took the same readings with that meter and found the actual voltage to and current through one leg of the compressor windings was in fact too low. It was this imbalance that were causing the problem. Why were we getting different readings? It was because a process in a nearby factory was chopping up the electricity on one leg that came from the same transformer so that the current to our compressor wasn't smooth but distorted. And though this distortion it showed up on an averaging meter. The true RMS meter was looking at what was really happening. Long story, short: We called the power company and showed them the differences in the readings. They denied responsibility. However, later that afternoon I noticed one of their techs up on a pole adding capacitors to the line to smooth out the power. My point to you? Have your people explain why true RMS meters are the better bet and worth the extra bucks.
Published by SupplyHouseTimes. View All Articles.
This page can be found at http://digital.bnpmedia.com/article/The+Air+Side/2027375/261427/article.html.