Re: [PSES] Safety cost and ESD

[Cortland Richmond]

Humidified air is a very nice, slow discharge path; either a humidifier 
or a good "huff" from the mouth works well.


Cortland Richmond

On 4/24/2012 1853, Conway, Patrick wrote:


This is a classic test problem.  I've seen this several times.  For 
this setup, there is no place for the charge to dissipate between 
zaps.  So, how to discharge between zaps?  The easy answer  is to 
briefly connect a strap from apparatus to ground.  But that casues 
lots of problems, including false "failures".


The reason?  The discharge created when using a zero Ohm strap is 
uncontrolled.  If you remove the "bleed" resistor, then the discharge 
is not bleeding slowly, it becomes another form of an ESD discharge.  
The problem is that the waveform will not be representative of the 
human-body-model.  ...






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Re: [PSES] IEC/EN 61010-1

[Doug Powell]

Thanks Brian,

Very similar to what we are doing now.  Plan to simply make a note of the
test conditions in the test report.

:Doug



On Wed, Apr 25, 2012 at 2:01 PM, Kunde, Brian wrote:

>  As the manufacturer you have to decide what a typical operator position
> is, then document it in the report. We give a distance from the front of
> the device (varies from 200cm – 500cm) and a distance off the floor (or off
> the table for table mounted equipment).
>
>
>
> For the bystander position, we take measurements on all four sides at a 1
> meter distance and 1.6 meters off the floor.
>
>
>
> The Other Brian
>
>
>
>
>
> *From:* emc-p...@ieee.org [mailto:emc-p...@ieee.org] *On Behalf Of *Doug
> Powell
> *Sent:* Wednesday, April 25, 2012 12:47 PM
> *To:* emc-pstc
> *Subject:* IEC/EN 61010-1
>
>
>
> The in the acoustics section 12.5 of 61010-1 are the concepts of operator
> and bystander positions.  The standard clearly states dimensions for the
> "test room", yet it does not clearly state what distances are for
> personnel.  Let's assume a control panel is mounted in a rack system, at
> eye-level, and with buttons that must be pressed. What would be the typical
> distances for the operator and the bystander?
>
>
>
> For the bystander, 1 meter seems about right.  In the past, I have seen as
> little as 12 inches for the operator, but this seems a bit close.  My
> original thought was this may represent a person leaning with one shoulder
> against a rack mounted panel.  While the distance from the panel surface to
> the ear of this person can be quite short, it is not likely to be an
> operator's position.
>
>
>
> A difference of only a few inches can make all the difference in your
> results.
>
>
>
>
> --
> Thanks, -doug
>
>
>
> Douglas E Powell
>
> doug...@gmail.com
>
> http://www.linkedin.com/in/dougp01
>
>
>
>
>
> -
> 
>
> This message is from the IEEE Product Safety Engineering Society emc-pstc
> discussion list. To post a message to the list, send your e-mail to <
> emc-p...@ieee.org>
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> All emc-pstc postings are archived and searchable on the web at:
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>
> Attachments are not permitted but the IEEE PSES Online Communities site at
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> well-used formats), large files, etc.
>
> Website: http://www.ieee-pses.org/
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> List rules: http://www.ieee-pses.org/listrules.html
>
> For help, send mail to the list administrators:
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> Mike Cantwell 
>
> For policy questions, send mail to:
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>  --
> *LECO Corporation Notice:* This communication may contain confidential
> information intended for the named recipient(s) only. If you received this
> by mistake, please destroy it and notify us of the error. Thank you.
> -
> 
>
> This message is from the IEEE Product Safety Engineering Society emc-pstc
> discussion list. To post a message to the list, send your e-mail to <
> emc-p...@ieee.org>
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>
> Attachments are not permitted but the IEEE PSES Online Communities site at
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> well-used formats), large files, etc.
>
> Website: http://www.ieee-pses.org/
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>
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-- 
Thanks, -doug

Douglas E Powell
doug...@gmail.com
http://www.linkedin.com/in/dougp01

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Re: [PSES] IEC/EN 61010-1

[Kunde, Brian]

As the manufacturer you have to decide what a typical operator position is, 
then document it in the report. We give a distance from the front of the device 
(varies from 200cm - 500cm) and a distance off the floor (or off the table for 
table mounted equipment).

For the bystander position, we take measurements on all four sides at a 1 meter 
distance and 1.6 meters off the floor.

The Other Brian


From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Doug Powell
Sent: Wednesday, April 25, 2012 12:47 PM
To: emc-pstc
Subject: IEC/EN 61010-1

The in the acoustics section 12.5 of 61010-1 are the concepts of operator and 
bystander positions.  The standard clearly states dimensions for the "test 
room", yet it does not clearly state what distances are for personnel.  Let's 
assume a control panel is mounted in a rack system, at eye-level, and with 
buttons that must be pressed. What would be the typical distances for the 
operator and the bystander?

For the bystander, 1 meter seems about right.  In the past, I have seen as 
little as 12 inches for the operator, but this seems a bit close.  My original 
thought was this may represent a person leaning with one shoulder against a 
rack mounted panel.  While the distance from the panel surface to the ear of 
this person can be quite short, it is not likely to be an operator's position.

A difference of only a few inches can make all the difference in your results.


--
Thanks, -doug

Douglas E Powell
doug...@gmail.com
http://www.linkedin.com/in/dougp01


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LECO Corporation Notice: This communication may contain confidential 
information intended for the named recipient(s) only. If you received this by 
mistake, please destroy it and notify us of the error. Thank you.

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Re: [PSES] IEC/EN 61010-1

[John Woodgate]

In message 
, 
dated Wed, 25 Apr 2012, Doug Powell  writes:


The in the acoustics section 12.5 of 61010-1 are the concepts of 
operator and bystander positions.  The standard clearly states 
dimensions for the "test room", yet it does not clearly state what 
distances are for personnel.  Let's assume a control panel is mounted 
in a rack system, at eye-level, and with buttons that must be pressed. 
What would be the typical distances for the operator and the bystander?


For the bystander, 1 meter seems about right.  In the past, I have seen 
as little as 12 inches for the operator, but this seems a bit close. 
 My original thought was this may represent a person leaning with one 
shoulder against a rack mounted panel.  While the distance from the 
panel surface to the ear of this person can be quite short, it is not 
likely to be an operator's position.


A difference of only a few inches can make all the difference in your 
results.


Basically, as you describe it, it's acoustic heresy. The environment 
won't be anechoic, so it's anyone's guess what the sound level will be 
anywhere. It could be much less 30 cm from the source than at 1 m.

--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Instead of saying that the government is doing too little, too late or too
much, too early, say they've got is exactly right, thus throwing them into
total confusion.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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[PSES] IEC/EN 61010-1

[Doug Powell]

The in the acoustics section 12.5 of 61010-1 are the concepts of operator
and bystander positions.  The standard clearly states dimensions for the
"test room", yet it does not clearly state what distances are for
personnel.  Let's assume a control panel is mounted in a rack system, at
eye-level, and with buttons that must be pressed. What would be the typical
distances for the operator and the bystander?

For the bystander, 1 meter seems about right.  In the past, I have seen as
little as 12 inches for the operator, but this seems a bit close.  My
original thought was this may represent a person leaning with one shoulder
against a rack mounted panel.  While the distance from the panel surface to
the ear of this person can be quite short, it is not likely to be an
operator's position.

A difference of only a few inches can make all the difference in your
results.


-- 
Thanks, -doug

Douglas E Powell
doug...@gmail.com
http://www.linkedin.com/in/dougp01

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Re: [PSES] CS116 shielding

[McInturff, Gary]

Good quality means high coverage braid, and Charlie's note about the 360 
bonding and how the shield is attached is critical and should prove successful 
from my past experience. The only times I failed with a good shield is when I 
didn't terminate the shield at both ends or poorly at one end or the other.

Gary

From: Charlie Blackham [mailto:char...@sulisconsultants.com]
Sent: Wednesday, April 25, 2012 8:34 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] CS116 shielding


David



You appear to already have concerns about the cable - suggest that they use a 
good braid shield, properly 360deg bonded at each end such that it provides an 
interconnect resistance between the EUT and support kit of only a few milliohms 
(measured with 4-port bonding meter).



Regards

Charlie





-Original Message-
From: Schaefer, David [mailto:dschae...@tuvam.com]
Sent: 25 April 2012 15:47
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] CS116 shielding



All,



I am looking for some guidance on shielding for protection against the CS116 
waveform.  Our customer failed at as much as 20 dB down from the limit.  They 
have a basic braid shield, but that was obviously insufficient.



Anyone have a suggestion, or advice on where I may start looking?



Thanks,



David Schaefer

Senior EMC Engineer

TÜV SÜD America Inc

Office: 651 638 0251

Cell: 612 578 6038

Fax: 651 638 0285



-



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Re: [PSES] CS116 shielding

[Charlie Blackham]

David



You appear to already have concerns about the cable - suggest that they use a 
good braid shield, properly 360deg bonded at each end such that it provides an 
interconnect resistance between the EUT and support kit of only a few milliohms 
(measured with 4-port bonding meter).



Regards

Charlie





-Original Message-
From: Schaefer, David [mailto:dschae...@tuvam.com]
Sent: 25 April 2012 15:47
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] CS116 shielding



All,



I am looking for some guidance on shielding for protection against the CS116 
waveform.  Our customer failed at as much as 20 dB down from the limit.  They 
have a basic braid shield, but that was obviously insufficient.



Anyone have a suggestion, or advice on where I may start looking?



Thanks,



David Schaefer

Senior EMC Engineer

TÜV SÜD America Inc

Office: 651 638 0251

Cell: 612 578 6038

Fax: 651 638 0285



-



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Re: [PSES] CS116 shielding

[Ken Javor]

I would first look at the shield terminations. Any decent braid ought to
work if the shields are properly terminated.
  
Ken Javor
Phone: (256) 650-5261


> From: "Schaefer, David" 
> Date: Wed, 25 Apr 2012 10:47:26 -0400
> To: "EMC-PSTC@LISTSERV.IEEE.ORG" 
> Conversation: CS116 shielding
> Subject: CS116 shielding
> 
> All,
> 
> I am looking for some guidance on shielding for protection against the CS116
> waveform.  Our customer failed at as much as 20 dB down from the limit.  They
> have a basic braid shield, but that was obviously insufficient.
> 
> Anyone have a suggestion, or advice on where I may start looking?
> 
> Thanks,
> 
> David Schaefer
> Senior EMC Engineer
> TÜV SÜD America Inc
> Office: 651 638 0251
> Cell: 612 578 6038
> Fax: 651 638 0285
> 
> -
> 
> This message is from the IEEE Product Safety Engineering Society emc-pstc
> discussion list. To post a message to the list, send your e-mail to
> 
> 
> All emc-pstc postings are archived and searchable on the web at:
> http://www.ieee-pses.org/emc-pstc.html
> 
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> formats), large files, etc.
> 
> Website:  http://www.ieee-pses.org/
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> 
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> Mike Cantwell 
> 
> For policy questions, send mail to:
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Re: [PSES] Safety cost and ESD

[John Woodgate]

In message 
, 
dated Wed, 25 Apr 2012, "McInturff, Gary"  
writes:


How does the charge exceed the applied gun discharge. If I am at 4kV 
for example, the ungrounded equipment rises to 4kV until it's removed 
or disappointed, but how would another charge of the same level 
increase it.


This takes me back to the 'Boy's Book of Electricity' and experiments 
with an electrophorus (a metal baseplate, a layer of dielectric that can 
be charged by friction and a cover disc with an insulated handle). There 
IS a way of doubling a static voltage and it DOES involve grounding 
something, but I can't remember the way to do it, 60 years later.


I don't mean charging the electrophorus as a capacitor and then lifting 
the cover off, thus reducing the capacitance and increasing the voltage.

--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Instead of saying that the government is doing too little, too late or too
much, too early, say they've got is exactly right, thus throwing them into
total confusion.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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[PSES] CS116 shielding

[Schaefer, David]

All,

I am looking for some guidance on shielding for protection against the CS116 
waveform.  Our customer failed at as much as 20 dB down from the limit.  They 
have a basic braid shield, but that was obviously insufficient.

Anyone have a suggestion, or advice on where I may start looking?

Thanks,

David Schaefer
Senior EMC Engineer
TÜV SÜD America Inc
Office: 651 638 0251
Cell: 612 578 6038
Fax: 651 638 0285

-

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Re: [PSES] Safety cost and ESD

[Conway, Patrick]

I do have one story from the trenches, involving a laptop, ESD and
"non-standard testing".  

...back in the day, at a previous company...  

we had a customer complaint about a mysterious lockup.  There is a
side-story about sales, management, pressure, schedule, cost and all
that noise.  But sparing that, the lockup could only be duplicated by
floating the laptop and discharging to the MODEM connector several
times.  No bleed-off between zaps.  Eventually a secondary discharge was
heard inside the laptop.  

Apparently the MODEM circuit has some floating circuits due to TELCO
hi-pot requirements.  The circuit did fine under TELCO testing, which I
recall went to 3kV.  But if the stored charge in the MODEM circuit got
to about 7 kV, then there was a secondary arc to another circuit and
havoc ensued.

It was an interesting lesson for me about the (negative)virtues of
isolated circuits inside an apparatus.  As far as I know, this type of
test was never adopted by any standards body, but it became a regular
part of my internal engineering testing.  


//
Patrick 


-Original Message-
From: Brian Oconnell [mailto:oconne...@tamuracorp.com] 
Sent: Tuesday, April 24, 2012 6:05 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Safety cost and ESD

For automotive stuff (ISO10605), I have to be careful about bleeding
charge
after each iteration because test level = 25kV. I use a 470k Resistor
attached in series with a short braid that is screwed into the ref
plane,
and touch the UUT. The strap is used for discharge only and is not
attached
during testing.  I have seen the commercial CISPR25 labs do similar.

I have not seen the discharge create additional problems - perhaps I
have
just been lucky. Opinions whether this is a 'respectable' test
technique?

Brian

-Original Message-
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Conway,
Patrick
Sent: Tuesday, April 24, 2012 3:53 PM
To: McInturff, Gary; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Safety cost and ESD

This is a classic test problem.  I've seen this several times.  For this
setup, there is no place for the charge to dissipate between zaps.  So,
how
to discharge between zaps?  The easy answer  is to briefly connect a
strap
from apparatus to ground.  But that casues lots of problems, including
false
"failures".
 
The reason?  The discharge created when using a zero Ohm strap is
uncontrolled.  If you remove the "bleed" resistor, then the discharge is
not
bleeding slowly, it becomes another form of an ESD discharge.  The
problem
is that the waveform will not be representative of the human-body-model.

 
Designers of ESD equipment go to a lof trouble designing those ESD guns.
They must conform to an exact waveshape.  But the zero-Ohm ground strap
has
none of the circuit elements to shape the curve.  So there is a
likelyhood
of a faster rise time, more ringing, etc.  All things that no longer
represent the HBM.If ths waveshape causes upset in the appratus it
cannot be considered a failure since the waveform is not HBM.
 
Check with your customer on how they are testing.  If the appratus
survives
the zap from the gun, but is upset when they discharge with the strap,
then
you have the asnwer.  The easy solution for "Test" is to place the bleed
resistor back into the discharge strap and see if the appratus survives.

 
The zero Ohm ground strap is not a real-world HBM scenario, and
certainly
not in conformance with EN61000-4-2 or any of the HBM standards.  On the
other hand, if your product is not subject to HBM, or your product needs
testing to a user-scenario that includes a strap discharge, then that is
a
perfectly good test.
 
//
Patrick
 

 
Different question about ESD.
 
I have a component we tested on the normal 55024 directed ESD table for
a
table top mounted device. Worked fine, problem is that the customer
places
this on a large metallic roll around pedestal on rubber wheels. When
they
send it to a lab and test it this way there is a problem. I don't have
the
pedestal so I'm trying to simulate with my table and removing the 1 mohm
bleeder resistor. Between discharges to the table, I ground a braided
strap
attached to the table top to my reference plane below. I get very
similar
results then. What should the braid really look like - should it just be
a
short, should it have some bleed resistance in it. I chose none since
the
discharge is going to be people touching the pedestal or other furniture
that is grounded. 
 
What does the standard say about  the VCP and HCP?
 
Gary McInturff
Reliability/Compliance Engineer  

 
//
Patrick 
 
From: McInturff, Gary [mailto:gary.mcintu...@esterline.com] 
Sent: Monday, April 23, 2012 12:37 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Safety cost and ESD
 
Given the implementation differences between US/Canada(?) and EU on the
medical 60601-1 standards. EU the June, US June 2013. How are folks
handling
new products being intro

Re: [PSES] Safety cost and ESD

[Conway, Patrick]

>> Opinions whether this is a 'respectable' test technique? <<

In my opinion, your technique legitimate.  I observe that the entire
world of ESD testing is centered around a defined stimulus of current
and voltage.  Any time a "zap" deviates from this then it is not part of
a test.  

This has two effects on testing of a "floating" apparatus.  The first
effect is with the second ZAP.  Without a bleed of charge the second ZAP
no longer conforms.  It is no longer a "X" kV ZAP.  The display on the
ESD gun reads "X" volts, which is between ESD gun tip and ground.  But
since the apparatus is no longer @ ground potential, the "X" voltage
reading is invalid.  And the same is true for the third, fourth, etc.  

The second effect is the one discussed in this thread- where the bleed
happens with a strap.  The wave shape of current during that event is
undefined.  Any response from the apparatus during the bleed event is
not part of the test and cannot be considered in the pass/fail criteria.


My opinion only...
//
Patrick 

-Original Message-
From: Brian Oconnell [mailto:oconne...@tamuracorp.com] 
Sent: Tuesday, April 24, 2012 6:05 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Safety cost and ESD

For automotive stuff (ISO10605), I have to be careful about bleeding
charge
after each iteration because test level = 25kV. I use a 470k Resistor
attached in series with a short braid that is screwed into the ref
plane,
and touch the UUT. The strap is used for discharge only and is not
attached
during testing.  I have seen the commercial CISPR25 labs do similar.

I have not seen the discharge create additional problems - perhaps I
have
just been lucky. Opinions whether this is a 'respectable' test
technique?

Brian

-Original Message-
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Conway,
Patrick
Sent: Tuesday, April 24, 2012 3:53 PM
To: McInturff, Gary; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Safety cost and ESD

This is a classic test problem.  I've seen this several times.  For this
setup, there is no place for the charge to dissipate between zaps.  So,
how
to discharge between zaps?  The easy answer  is to briefly connect a
strap
from apparatus to ground.  But that casues lots of problems, including
false
"failures".
 
The reason?  The discharge created when using a zero Ohm strap is
uncontrolled.  If you remove the "bleed" resistor, then the discharge is
not
bleeding slowly, it becomes another form of an ESD discharge.  The
problem
is that the waveform will not be representative of the human-body-model.

 
Designers of ESD equipment go to a lof trouble designing those ESD guns.
They must conform to an exact waveshape.  But the zero-Ohm ground strap
has
none of the circuit elements to shape the curve.  So there is a
likelyhood
of a faster rise time, more ringing, etc.  All things that no longer
represent the HBM.If ths waveshape causes upset in the appratus it
cannot be considered a failure since the waveform is not HBM.
 
Check with your customer on how they are testing.  If the appratus
survives
the zap from the gun, but is upset when they discharge with the strap,
then
you have the asnwer.  The easy solution for "Test" is to place the bleed
resistor back into the discharge strap and see if the appratus survives.

 
The zero Ohm ground strap is not a real-world HBM scenario, and
certainly
not in conformance with EN61000-4-2 or any of the HBM standards.  On the
other hand, if your product is not subject to HBM, or your product needs
testing to a user-scenario that includes a strap discharge, then that is
a
perfectly good test.
 
//
Patrick
 

 
Different question about ESD.
 
I have a component we tested on the normal 55024 directed ESD table for
a
table top mounted device. Worked fine, problem is that the customer
places
this on a large metallic roll around pedestal on rubber wheels. When
they
send it to a lab and test it this way there is a problem. I don't have
the
pedestal so I'm trying to simulate with my table and removing the 1 mohm
bleeder resistor. Between discharges to the table, I ground a braided
strap
attached to the table top to my reference plane below. I get very
similar
results then. What should the braid really look like - should it just be
a
short, should it have some bleed resistance in it. I chose none since
the
discharge is going to be people touching the pedestal or other furniture
that is grounded. 
 
What does the standard say about  the VCP and HCP?
 
Gary McInturff
Reliability/Compliance Engineer  

 
//
Patrick 
 
From: McInturff, Gary [mailto:gary.mcintu...@esterline.com] 
Sent: Monday, April 23, 2012 12:37 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Safety cost and ESD
 
Given the implementation differences between US/Canada(?) and EU on the
medical 60601-1 standards. EU the June, US June 2013. How are folks
handling
new products being introduced now or in the very near future? Just got 

Re: [PSES] Safety cost and ESD

[McInturff, Gary]

Once I got the my standard back I found all of the pertinent data and learned a 
few new things.
Section 7.1.3 ungrounded equipment (this is edition 1.2) so the paragraph 
numbering could differ
Basically it says the couple planes must be discharged via the 470K bleeder 
resistors - I had been using a braid with no resistance since I wasn't sure 
what the lab did and I couldn't replicate their data 
For any points of the EUT that can have a direct discharge they also require a 
similar cable to earth reference plane. 
Unfortunately the standard then goes back to discussing the HCP and the VCP in 
the next paragraph and again discusses the bleeder cable.
It's unfortunate because the paragraph that follows then mentions that the 
bleeder resistor can influence the test results of some equipment stating that 
in case of dispute a test with the cable disconnecting during ESD pulse takes 
precedence.
I read that to mean the cable to the directed discharge points of the EUT, two 
paragraphs previously, and not the HCP and VCP planes referenced in the 
immediately preceding paragraph. My thought is that throughout the tests these 
coupling plane resistors are always in place - again except the floor standing 
units which sit over the ground reference rather than a HCP - and the removed 
cable having test preference is to any metallic parts of the EUT. One still 
discharges between ESD events - apply ESD to metallic part, discharge with 
bleeder cable, ESD event .etc.

One last item - the Rationale for all of this discharge between ESD events 
makes note that "it is possible that the EUT or part(s) of the EUT can be 
stressed up to twice the intended test voltage. Therefore, double-insulated 
equipment could be charged at an unrealistically high charge, by accumulating 
sever ESD discharges on the capacitance of the class II insulation..." Ho

How does the charge exceed the applied gun discharge. If I am at 4kV for 
example, the ungrounded equipment rises to 4kV until it's removed or 
disappointed, but how would another charge of the same level increase it. If I 
switch from a positive to a negative polarity I see the doubling of the level, 
but not during repeated discharges of the same polarity and same level. I can 
see that if I don't' drain the charge from the ungrounded system it will remain 
at 4 kV and then next discharge attempt may not occur since the gun and the 
surface of the EUT are at the same potential - but I don't see the doubling.

Any clues for me?

Thanks all that have responded

I think Doug Smith mentioned a cheap ESD brush in one of his tid-bits but I 
couldn't find the reference. In my case the cable will work fine but all of a 
sudden I have a need to have this brush in my arsenal

Gary


-Original Message-
From: Scott Douglas [mailto:sdoug...@radiusnorth.net] 
Sent: Tuesday, April 24, 2012 6:49 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Safety cost and ESD

Brian,

In a prior life we had several products that were sensitive to charge 
build-up. When they asked me about the problem I showed them where the 
ESD standard allows discharging between hits. We used the same sort of 
process - 470k resistor in series with the ground braid attached to the 
HCP. I once saw a brush with a ground strap (with the resistors in it) 
used for this sort of thing. Never have been able to source one though.

Scott

On 4/24/2012 8:04 PM, Brian Oconnell wrote:
> For automotive stuff (ISO10605), I have to be careful about bleeding charge
> after each iteration because test level = 25kV. I use a 470k Resistor
> attached in series with a short braid that is screwed into the ref plane,
> and touch the UUT. The strap is used for discharge only and is not attached
> during testing.  I have seen the commercial CISPR25 labs do similar.
>
> I have not seen the discharge create additional problems - perhaps I have
> just been lucky. Opinions whether this is a 'respectable' test technique?
>
> Brian
>
> -Original Message-
> From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Conway,
> Patrick
> Sent: Tuesday, April 24, 2012 3:53 PM
> To: McInturff, Gary; EMC-PSTC@LISTSERV.IEEE.ORG
> Subject: RE: [PSES] Safety cost and ESD
>
> This is a classic test problem.  I've seen this several times.  For this
> setup, there is no place for the charge to dissipate between zaps.  So, how
> to discharge between zaps?  The easy answer  is to briefly connect a strap
> from apparatus to ground.  But that casues lots of problems, including false
> "failures".
>
> The reason?  The discharge created when using a zero Ohm strap is
> uncontrolled.  If you remove the "bleed" resistor, then the discharge is not
> bleeding slowly, it becomes another form of an ESD discharge.  The problem
> is that the waveform will not be representative of the human-body-model.
>
> Designers of ESD equipment go to a lof trouble designing those ESD guns.
> They must conform to an exact waveshape.  But the zero-Ohm ground