Re: multimeter question

From: budgie (me_at_privacy.net)
Date: 12/20/04 

Date: Mon, 20 Dec 2004 09:49:13 +0800

On Sun, 19 Dec 2004 14:40:01 GMT, Noah Little <me@privacy.net> wrote:

>slight wrote:
>> an example would be measuring a 10k resistor in-circuit.
>> by reversing the lead polarity i get two readings, 10k and 5.8k.
>> im guessing that is because the meters i have use 3.3v across the leads
>> and this is triggering a diode or something in the circuit.
>> are all meters like this? the ones i have are pretty cheap.
>> do the flukes do this? been looking at one for Christmas.
>
>You broke the code. Most likely reason for different readings when the
>leads are reversed is a diode (or other semiconductor junction) that's
>in the circuit with the resistor under test. You should find if you
>lift one leg of the resistor that the readings are the same in both
>directions.
>
>Cheap meters, expensive meters, they'll behave about the same in this
>regard. But you'll be happy you went with the Fluke.

Not really. Most half-decent DMMs have some ranges which use a source voltage
below the conduction threshold of (at least silicon) semiconductor junctions.
There is ususally some marking on the DMM face which will indicate which ranges
will/won't bias a diode into conduction.

OTOH most el cheapo DMMs lack this feature.

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