Measuring Large resistances

Hmm.. I think you're right on that point. I do have one that does, but probably most do not. Benchtop instruments like my Agilent 34401A meters do have an "infinite impedance" setting.

1M? What a POS. What do you expect for dollar store prices. Even the Chinese can't make a worthwhile meter for what Harbor Fright wants to pay.

Carbon? AFAIK something like Ruthenium oxide is more common in chip resistors. Ohmcraft makes their using a kind of printing method which is automated, so it should be consistent. Here is a white paper on their process:

Fluke 87-5, for example. DC voltage accuracy is 0.05% + 1 count on the

6V range.

But only 1% in the 60nS range (infinity to 16.667M ohm), unfortunately. A 100M resistor would have a conductivity of 10.00nS so the resolution is pretty much there, but not the accuracy.

Probably lots of other 4-1/2 digit handheld meters too.

Hi guys Thanks for all the enlightening on the subject. The model of the meter I use at the Lab is the Agilent 34401A which Spehro incidently mentions has an infinite resistence setting. I couldn't find that ... which means I'll have to browse through the thick manual. It doesn't seem to deliver more then then a 10V output though. I suspect it might be measuring the limitations in its accuracy readings or the thermal noise in the resistors.

Kreyen

Thanks.

Oh drear, it has a 10M ohm input when measuring voltage; measuring resistance is entirely different.

The measurement problems may be exactly that, measurement method. For

100 Mohm and up i suggest putting the DUT in a closed conductive box with holes for the test leads. And use minimum length test leads, not touching anything if possible.