>> Robert Baer wrote:
>>> email@example.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????
>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.
Not true; most DMMs have an accuracy less than the digits. A typical 3.5 digit DMM has +/- 0.5% +/- 1 digit (DC voltage, the best scale). A typical 4.5 digit DMM has +/- 0.1% +/- 3 digits (DC voltage, the best scale). The HP5326/27B (5.5 digits) has +/- 0.04% +/- 1 digit (DC voltage, the worst scale, as it is made for measuring frequency or time). The B&K 5492 (5.5 digits) has +/- 0.012% +/- 1 digit (DC voltage, the best scale).
3 digits implies a possible 0.1% absolute best case; granularity makes it worse.
The photo showed a falsely stable FIVE DIGITS! Gee, maybe i can measure microns with a meter stick after all!