Hi from one Chris to another,
I'm going to address your "ground rod" concerns (Question 3).
In our lab here, we have a new building with new wiring and a reliable third
wire Earth ground, so I simply tie my Ground Reference Plane ("GRP") to the
third wire of one of the AC outlets in the room. I have a cable from the
GRP to the outlet with a ring lug. The ring lug is screwed to the ground
connection with a lock washer and screw. I occassionally verify this ground
connection with a ohmmeter. All devices under test are plugged into these
same AC outlets (unless they're battery powered), so my GRP is "common" with
all of my device under test Earth ground connections.
If you used a doctored plug, the only concern that I would have would be
with regard to the connection coming loose. However, I noticed that you're
in the UK where they use that three pound broad sword for the AC ground
terminal. It would probably take an earthquake to loosen that thing. But,
I would still verify the connection with an ohmmeter.
I have talked to many people about this; and this is the "collective
rationale" that I have gathered. An ESD test setup needs to have a stable
reference potential set by the GRP. The ESD gun's ground strap is tied to
the GRP and all discharge potentials are then referenced to the GRP. Since
the GRP is large and wide; it has low inductance along with a large amount
of free space capacitance. The GRP is a very good high frequency ground
potential. This means that the GRP's potential won't change much when the
ESD current is bled into it. This keeps results repeatable. Just by having
a GRP, you have satisfied 99% of the grounding requirements for a good ESD
test . Now, why tie the GRP to Earth?
The GRP's connection to Earth ground serves two purposes. It is a low
frequency ground connection to ensure that, over time, the GRP's DC
potential won't change with respect to Earth ground. The GRP's Earth ground
connection also ensures that the GRP has a low frequency common with any
Earth grounds that the device under test may have.
It is my belief that you don't need a dedicated ground rod for your ESD
setup to satisfy this requirement.
My opinions only; not to be confused with fact, company policy or gospel
under any circumstance :-)
Chris Maxwell
Design Engineer -
NetTest Optical Division
email chris.maxw...@nettest.com
phone +1 315 266 5128
fax +1 315 797 8024
NetTest
6 Rhoads Drive,
Utica, NY 13502 USA
web www.nettest.com
> -----Original Message-----
> From: Chris Chileshe [SMTP:chris.chile...@ultronics.co.uk]
> Sent: Tuesday, June 19, 2001 5:22 AM
> To: emc-p...@majordomo.ieee.org
> Subject: ISO TR 10605 test setup (ESD)
>
>
> Hi group
>
> For those of you unfamiliar with ISO TR 10605, it is the ESD
> test standard for automotive electronics (8kV contact, 25kV
> air).
>
> I am trying to perform quick ESD tests on a product which has
> bottom entry proprietary cable. Picture if you an upside-down
> bottle of coke with push buttons at the top and cable entry at
> the bottom end.
>
> The cable itself is screened multicore with a molded end connector
> so there is a minimum length it must protrude from the product before
> it even thinks about bending. This is about an inch and a half
> (about 40mm).
>
> According to ISO TR 10605, if insulation is required under the
> EUT, the insulation must support the EUT some 25mm above
> the ground plane.
>
> Question 1: Does this insulation have to be 25mm thick or can
> I make a table like structure with thinner insulating sheet and
> supporting pillars at the corners?
>
> Question 2: Would a more 'compliant' test set-up have the bottle
> of coke lying on its side rather than standing vertically as it would
> in practice?
>
> The setup for the ESD test shows a ground strap connect the plane
> to a grounding rod. We had a specialised ESD test area where I worked
> before but we took everything for granted and didn't really bother finding
> out where or how the ground connection was made!
>
> Question 3: Can I connect the ground strap via say a UK 3-pin plug
> (with live and neutral prongs removed) into a mains socket or is this
> asking for trouble (RCD's etc).
>
> Grateful for any advice
>
> Regards
>
> - Chris Chileshe
>
>
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