On 11/13/2015 12:20 PM, Systems Glitch via vcf-midatlantic wrote:
I prefer an analog meter for troubleshooting -- like you said, easier to detect an "is it off" condition, especially with intermittent circuits. And, the loading of the analog meter can be an advantage in many situations. My Simpson 260 is always on the bench, and I keep the Simpson 160 in my toolkit since it's just the tiny version of the 260.
Same here, and the 260 is the king of 'em all. I have an HP 3458A on my bench (google it) but I end up using the 260 more, especially during calibrations. Stuff like the 3458A and other ultra-precision digital meters are great for measurement, while analog meters are much better for *adjustments*...a distinctly different application, while both involve measuring voltage. (or current, resistance..) The difference of course being that it takes less real-time brain processing to see whether a meter needle swings left or right than to read a displayed number, interpret it, decide if it's higher or lower than the last displayed number, ad infinitum. Doing that in real-time while tweaking an adjustment is a lot less efficient.
I opened it up this afternoon, it looks like the shunt for the 100 mA scale is wire (nichrome?) wrapped on a phenolic bobbin, typical of old small-value precision resistors. It's sleeved in some sort of plastic tube which appears to have been clear originally, but is now green over the section of wire. I'm guessing you're right and corrosion has thrown the value off.
The resistance wire alloy would be manganin (copper/manganese/nickel). Nichrome is rarely if ever used for actual resistors due to its very high temperature coefficient. Manganin's is negligible. You should be able to replace that with a modern resistor without trouble and get the ol' girl back up and running. Those DMMs are far from elegant, but they work very well. -Dave -- Dave McGuire, AK4HZ New Kensington, PA