I'm about to resuscitate an AVO mark 2 valve characteristic meter. When I bought it some years ago the readings, as I recall, were inaccurate. This led me to suspect the meter movement, since this is well known to be the main problem point with these testers.
Anyway, the meter is out of the case, and measures at exactly 500uA full scale, and shows an internal resistance of 112 ohms. Various internet sources indicate that fsd should be achieved at 440 uA, but others say that it is in fact a 500uA movement. The measured resistance of 112 ohms (117 ohms with the little internal pigtail connecting wire included) appears to be generally agreed on however.
Does anyone have chapter and verse on this? Clearly, if 440uA is the required value then the magnet has gone soft and needs a little cobalt-samarium assistance. If 500uA is correct then it's back into the case and press on with calibration.
Any comments will be appreciated.
Anyway, the meter is out of the case, and measures at exactly 500uA full scale, and shows an internal resistance of 112 ohms. Various internet sources indicate that fsd should be achieved at 440 uA, but others say that it is in fact a 500uA movement. The measured resistance of 112 ohms (117 ohms with the little internal pigtail connecting wire included) appears to be generally agreed on however.
Does anyone have chapter and verse on this? Clearly, if 440uA is the required value then the magnet has gone soft and needs a little cobalt-samarium assistance. If 500uA is correct then it's back into the case and press on with calibration.
Any comments will be appreciated.
