[sdiy] 'seeing' esd

[Magnus Danielson]

From: "Trevor Page" <trevor at resonance.fsnet.co.uk>
Subject: [sdiy] 'seeing' esd
Date: Thu, 19 Apr 2001 22:23:00 +0100

> Hi list,

Hi Trev,

> I noticed tonight that when I touched the metallic enclosure of my
> oscilloscope after having just walked into the room and across the carpet, I
> see a large spike register on the scope as I discharge myself through the
> scope's earth. Then nothing if I touch it again. But rub my feet on the
> carpet, I build up a charge again and can again 'see' this being discharged
> on the scope.
> 
> Bit of a dumb thing to bring up I guess, obvious to most folk maybe, but I
> just found it rather curious. It kinda gives you 'proof' that you really do
> build up quite charge and it's interesting to see how quickly you can build
> up this charge again after messing about on your bench for a few minutes.
> Now I'm convinced I need to get a wrist strap.

Just so you know. That hand of yours is worthy of a risetime of about
1 ns (or less) where as the body is much slower and take about a 1 us.
The thing is, the charge can be many kV so the slewrate of onces hand
can be quite something! ;)

When you discharge yourself you will effectively bring a voltage
difference over your enclosure and for that brief moment in time will
the whole chassi have an uneven voltage distribution. Stable ground
voltage is just gone with the wind when you look into these frequencies.

> Anyway, back to reality...
> 
> Trev (currently replacing ram chips in a couple of TB303s, so I guess it's
> about time I became a bit more esd conscious)

Most probably ;)

Cheers,
Magnus