Archived from groups: alt.comp.hardware.homebuilt,alt.comp.hardware.pc-homebuilt (
More info?)
On Mon, 22 Aug 2005 16:36:58 +0000 (UTC), Andrew Smallshaw
<andrews@sdf.lonestar.org> wrote:
>On 2005-08-22, kony <spam@spam.com> wrote:
>>
>> That circuit is a good test of a cheap multimeter's accuracy
>> as it cannot be cost effective to have one calibrated (if
>> anyone would even attempt to do such service on a cheap
>> one?). The really, really cheap ones I have observed to be
>> off more than +-2% though, especially after they've aged a
>> few (too few) years. Unfortunately having the reference
>> doesn't easily allow one to calibrate those cheap ones, as
>> they dont' have internal adjustment and would have to be
>> reverse engineered and parts substitutions made, usually.
>>
>> Even so, I fully agree that any (working as well as the
>> manufacturer *intended*) multimeter should be higher
>> accuracy than the motherboard sensor, particularly at
>> measuring voltage at any given point in the circuit(s),
>> which is obvious enough but to someone who doesn't have a
>> multimeter yet.
>
>Try using a proper multimeter: the pocket types are guaranteed for +/-
>5 or 10% in general.
The proper multimeter for field, PC voltage testing is a
pocket type. It is pointless to take a PC to a bench to
gain a level of accuracy not needed, as many pocket meters
do in fact have better than 5 or 10% accuracy, particularly
those that come with (or are set away for) calibration.
These are, like anything else, more expensive pocket meters
meant for professional use, not a $10 hardware store
special. For example, some Fluke pocket meters come spec'd
and certified at under 0.1% accuracy (for this posts' use,
DC voltage). Of coure, they too can be certified and
recalibrated, IF the task(s) required that level of
precision.
While I have seen some in excess of 5%, in general they are
not ever spec'd as loose as 10%. I'd consider 2% about
average for a low-end meter... at least when new, though
after aging it may drift off more.
Inbetween poor and great, there's an ocean of meters.
"Typically" an average market price of around $40 or more is
needed to get above poor junk, not just accuracy but
features and sturdy construction. Even so, it can still be
expected that the average $20 meter is sufficient for basic
voltage tests many enthusiasts would perform, such as basic
measurements of the power supply rail DC level. It's not
the ultimate test but a distinct increase in accuracy over a
motherboard voltage sensor's report.
>My bench meter is guaranteed +/- 0.5% though that
>precision costs more than any $9, and indeed it takes a new NAMAS
>
>certificate every year. Pocket meters have their role but precision
>measurement isn't among them.
Great, so long as you need that level of precision. One
need not spend as much as the yearly certification alone for
a pocket meter sufficient to get useful data on many PC
voltage levels from an end-user or troubleshooter
perspective.