[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Panel meter problem



Original poster: David Speck <dave@xxxxxxxxxxxxxxxx>

Adam,

You didn't mention of your panel meter has a compressed scale at the lower end. If it does, then it is a pretty common rectifier type meter (It's a lot cheaper to make a basic DC movement and feed it with rectified AC than one that works directly of AC.)

The only problem with a rectifier type meter is that it shows a zero reading until the voltage across its input terminals exceeds about 1.2 volts, when the diode bridge inside starts to conduct.
There do exist premium AC meters for voltage and current that have a linear scale (usually starting at about $50 on eBay, as opposed to $5-10 for a compressed scale meter). Inside, they have a network of resistors and Zener diodes that allows them to respond with near perfect linearity. If one of these linearizing diodes is blown, then the response will be decidedly non-linear.
To be honest, you meter sounds about as good as can be expected. As previously mentioned, most of the best panel meters are rated to 5% accuracy at full scale. 10% is more common. Digital panel meters off eBay are usually closer to two percent, but can be driven crazy if not totally blown out in a TC environment. Most coilers stick with moving coil analog meters for TC work.
Try eBay searches for "Yokogawa", "Crompton", "GE meter", "Westinghouse meter", "KA-241", or "KX-241" to find the nice 270 degree switchgear panel meters that give somewhat better resolution than the 90 degree movements. A lot of them come up with regularity, so don't fall for the ones with the $60 - $200 "Buy it now" prices. If you're lucky, you can get them for $10-25 each.
HTH,
Dave