[Elecraft] RE: I can't convince myself that it works (was K3 Kit vs Ready Built)

[Alan Bloom]

Hi Gary,

Yes, I know an anti-static mat is supposed to have high resistance, but
I'm surprised the Radio Shack model measures infinity ohms with my DVM. 
The meter is capable of reading resistance over 30 megohms (confirmed by
measuring my skin resistance).  I just tried your cake pan method and
still get no reading.

If you assume 100 pF body capacitance for the human body model, 30
megohms gives a 3 millisecond time constant.  A 1000V static zap would
discharge to 6.7V in 5 time constants = 15 ms.  So I guess maybe it's
OK, but it still makes me nervous that I can't confirm that the mat is
actually doing anything.

Al N1AL


On Sat, 2008-02-23 at 12:56, Gary Hvizdak wrote:
> At 11:58:34 EST on Sat 23 Feb 2008 Alan Bloom (N1AL) wrote ...
> 
> ... bought one of those ESD mats.  But I can't convince myself that it
> works.  If I touch my meter probes to the mat I measure infinity ohms, no
> matter how close together the two probes are.  I know the meter works - If I
> hold one probe tip in each hand the meter measures a few 10's of megohms.
> 
> --
> 
> Al,
> 
>     An ESD mat is designed to very slowly dissipate static charges of up to
> many thousands of volts, so it has a fairly high surface resistance and is
> going to present essentially infinity ohms to your meter.  That said, if you
> use probes with several square inches of surface area (such as by placing a
> couple of cake pans from the XYL's kitchen) on the thing, then you "might"
> measure something by placing your probes on the cake pans.  Note!  Even if a
> single cake pan is larger than your mat, you can still use two of them by
> separating them by perhaps an inch and letting both hang off opposite sides
> of the mat.
> 
>     If you don't measure anything using the cake pan method, there is
> another "science experiment" you could do to test your mat, although it
> requires that you can reliably draw a spark between a finger tip and ground
> by doing something such as walking across a carpet.  If you can, then you
> could first place your palm on the ESD mat for ten seconds after walking
> across the carpet and then (with your palm still on the mat) touch ground
> and see that you don't draw such a spark.  BTW, be sure that the mat is
> grounded.
> 
> --- - - - ---
> 
>     Keeping your mat clean of any contaminants (mostly oils from your hands,
> but also solder flux splashes) will ensure that it continues to do its job.
> Under heavy use, you should clean it at least every other week, or more
> frequently if you notice that the surface appearance has "changed".  Only
> use products specifically designed for this purpose.
> 
>     FYI, a quick Google for "esd mat cleaner" yielded 196 hits.
> 
>     Then again, if you are only using the mat to build your K3, there's no
> need to be concerned about cleaning it.
> 
> 73,
> Gary  KI4GGX
> 
> P.S.  Even though I'm a Software Engineer, I work at an aerospace manufac-
> turing facility where we are required to attend periodic training on such
> subjects.