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 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 All things that no longer
represent the HBM.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 a
quote back and the US certifier wants to charge me twice once for the 2nd
edition and then to transition to the 3rd edition. I anyone else running
aground on this. Seems like this should be happening on both sides of the
pond - since a CB report to 3rd edition would run into the second edition
enforcement in the US (and maybe Canada - I don't know their implementation
date).
To be fair - I get good service once I get past the sticker shock and don't
have any complaints from that standpoint. In fact I enjoy the engineering
staff I work with.
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
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