> Be aware that a DVM or DMM has an internal battery (actually, one or > more), and that the DVM/DMM battery is also part of the "reference" > circuit for computation of voltage (and resistance and possibly other > measurements, but primarily voltage and resistance) and a worn-out > internal battery in such an instrument can lead to mis-read voltages and > resistances. > > For example, it is possible for the voltage on a nominally 3.6 volt, 1/2AA > battery to read over 6 volts, if the internal battery of the DVM or DMM is > nearly worn-out. > > If suspicious reading are obtained, replace the internal battery, or > retest using a known voltage source. > > For example, the ac line voltage is usually about 125 volts, but it could > be as low as 115 volts or as high as 135 volts. > > If your DVM or DMM, when set to read ac volts, reads significantly outside > the range of 115 to 135 volts, you should immediately suspect the > instrument's internal battery, and discount any readings taken of any > other batteries under test.
As an example, my Fluke DMM was measuring a Mac PRAM battery at about 6 volts. This same instrument measured my ac line voltage at over 200 volts. After replacement of the internal 9 volt battery with a new one, the very same Mac PRAM battery measured 3.69 volts (essentially new) whereas my ac line voltage measured 123.5 volts (about average for my premises at this time of day, with this voltage often being higher than 123.5 during the middle-of-the-night, and often being lower than 123.5 during dinner-time). -- You received this message because you are a member of G-Group, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to g3-5-list@googlegroups.com For more options, visit this group at http://groups.google.com/group/g3-5-list
