Message text written by Randall Young
>> This is why a cheap DVM is $29.95 and a good Fluke sells for over $300.
Even a $300 Fluke can have 0.5 ohm or more contact resistance. It's not a
question of quality, it's a question of how big is the contact area between
a
pointed probe and a flat contact.
Randall
<
The difference I have seen between cheap meters and better meters is not in
the probe tips but in the contact between the probe and the meter (where
they plug in) and in the selector switch that selects the function. Most
Flukes (maybe all, I don't know for sure) use dedicated connections for the
current measurements and a rather expensive fuse to prevent the whole thing
exploding when you plug the probes into the wall outlet with it set for
current. A better meter uses a better switching arrangement that costs
more (that's why the meters cost more.
Probe contact resistance is usually a function of the level of conductivity
of the metal test points. Corrosion and dirt and oil or grease all have an
effect on how well electricity will pass from the probe to the circuit.
Frequently this is exhibited by a total lack of reading but sometimes it
can manifest itself as meerly an erroneous reading.
Dave
|