snipped-for-privacy@gmail.com wrote:
>> Robert Baer wrote:
>>
>>> snipped-for-privacy@gmail.com wrote:
>>>
>>>>I would appreciate your opinions about the following device:
>>>>
>>>>"Smart Tweezers LCR RCL RLC Meter Digital MultiMeter SMD"
>>>>
>>>>I found on eBay. Looks like an interesting concept but is it as
>>
>> good as
>>
>>>>the seller tells?
>>>>
>>>
>>> Without a link, to look and evaluate????
>>> Forgeddit!
>>
>>
>>formatting link
>>
>1) For the size, Priority Mail Flat Rate is $3.85; the envelope could be
>distorted more by adding padding. As long as one can fit something in
>that envelope and seal it, there is no limit to the weight.
>Theoretically, one could ship about 42 pounds of pure osmimum (the most
>dense element known).
>2) ?Five? digits? Forget it.
> a) Impossible for capacitors and impractical as the best accuracy one
>could possibly find in an SMD capacitor might be 5%. Stray capacitance
>around the probe leads can add anything from 0.2pF to 5-10pF. The PCB,
>the PCB traces, and all parts in parallel with the capacitor to be
>?measured? can add another 2-20pF on strays alone.
> b) Impossible for non-PCB resistors; maybe 3 digits for the low values
>as the probe is *not* kelvin - and maybe 4 digits for higher values to a
>few megs. If the resistors are on a PCB, then there are too many parts
>that can be in parallel, and the reading can me orders of magnitude off.
> c) Inductors: maybe 2 digits at best in a PCB environment. The stray
>capacitances mentioned previously can royally mess up readings.
>3) Parts sorting - Possible; 3 digits at most.
>**
> Now i see their specs; the best is 1%, which absolutely KILLs 5
>digits and underscores my 3 digit statement above.
There is a difference between resolution and accuracy. Most DMMs have at least 1 more digit of resolution than their accuracy spec. The extra digits can be useful for part matching, and evaluation of tempcos and mechanical stability. Nobody needs 5 digit accuracy on an LCR meter.