Hi Bill,
Not sure of your question about the current loop. The discharge is one of a
small capacitor, and the air path is not negligible (displacement current
completing the loop). Low frequency analysis does not apply here.
Doug
On 10/27/11 11:14 PM, Bill Owsley wrote:
And what might the current loop be?
ps. what was the intial intentional ESD current into the EUT? to bring
it up to equal charge?
If you are really quick, you might get the discharge brush in before
the voltage has decayed a lot.
________________________________
From: Doug Smith <d...@emcesd.com> <mailto:d...@emcesd.com>
To: Bill <wdows...@yahoo.com> <mailto:wdows...@yahoo.com>
Cc: Scott Douglas <emcp...@radiusnorth.net>
<mailto:emcp...@radiusnorth.net> ; "emc-p...@ieee.org"
<mailto:emc-p...@ieee.org> <emc-p...@ieee.org> <mailto:emc-p...@ieee.org>
Sent: Friday, October 28, 2011 12:29 AM
Subject: Re: ESD Brush
Anything really conductive like copper or low resistance carbon fibers
will subject the EUT multi-ampere CDM-like (charged device model) ESD events.
In addition the 470K resistors are good low value capacitors to ESD and can
also allow fast high peak currents as well. Plus the wire from the closest
resistor to the tip has capacitance as well. Note: I = Cdv/dt = 1pF * 2000V/1ns
= 2 Amperes of current!! At 8 kV thus would be a fast peak of 8 Amperes.
I am currently writing a new Technical Tidbit on the best way to do
this. It will be up this weekend so don't want to write it twice here. Will
post link to the article.
Doug
Tel: 408-356-4186
Mobile: 408-858-4528
Email: d...@dsmith.org
Sent: from my iPhone
On Oct 27, 2011, at 19:30, Bill <wdows...@yahoo.com> wrote:
When used with the two 470 Kohm resistors, anything conductive
to brush the contact locations and EUT to reduce any induced charge back to the
"ground" level will work just fine.
As will just standing around for a minute or two, or an ion
generator that is turned on after the discharge and NOT during the discharge.
The brush is a speed enhancer.
The resistors in the line are an attempt to reduce a secondary
discharge due to the build up from the initial discharge or a wimpy discharge
into an already charged item - low current since the voltage delta is less than
expected, or larger than expected discharge if you reverse polarity for the
next shot.
A breath of warm moist human exhalation across the item will
knock the charge build up out rather quick.
PS. you'll find this is a highly variable test. I don't think
any results have ever been duplicated. ;-)
On 10/27/2011 09:58 PM, Scott Douglas wrote:
Sending for the subscriber by List Admin.
Subject:
ESD Brush
From:
"Sundstrom, Michael" < <mailto:michael_sundst...@overheaddoor.com>
michael_sundst...@overheaddoor.com>
List-Post: emc-pstc@listserv.ieee.org
Date:
10/27/2011 9:47 AM
To:
" <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> EMC-PSTC@LISTSERV.IEEE.ORG" <
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> EMC-PSTC@LISTSERV.IEEE.ORG>
I’m looking to test an ungrounded module to IEC
61000-4-2 . Of which 7.2.4.deals with ungrounded equipment. In 7.2.4.1 General
(toward the end ) it says you can: sweeping of the EUT with a grounded carbon
fibre brush with bleeder resistors (for example, 2 × 470 kÙ) in the grounding
cable.
Where can I find a carbon fiber brush I can then ground
(with two 470Kohm resistors)? Would a fanned out multi-strand copper wire work
just as well to dissipate the ESD charge buildup?
Thanks for any help,
Michael Sundstrom
OHD / TREQ Dallas
Electronic Lab Analyst, EMC Lead
2170 French Settlement Rd, Suite B
Dallas, Texas 75212
(214) 579 6312
(940) 390 3644c
KB5UKT
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