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From: JosephKK on 15 Nov 2009 15:20
On Thu, 12 Nov 2009 13:57:18 -0800 (PST), George Herold
<ggherold(a)gmail.com> wrote:

>On Nov 12, 3:12 pm, Kreyen <Ihates...(a)nospam.com> wrote:
>> I am having problems trying to measure resistance values above
>> 100MegaOhms. My Laboratory Ohmeter gives unstable values.
>>
>> Is ther anyway apart from the usual dc bridges of getting accurate
>> resistance measurements.
>>
>> Thanks guys.
>>
>> Kreyen
>
>I've got a fluke 189 multimeter that reads 100M ohms just fine.
>(Ohmite brand.) Since the meter has 10 Meg input impedance they must
>do some tricks in software. Which suggests that you might measure a
>good 10M ohm resistor and then try putting the 100M in parallel. See
>if you get better numbers... of course you will have reduced accuracy,
>but it might work. At least you might learn if it's the meter or the
>resistors that are flakey.
>
>George H.

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.
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