[PSES] RFID antenna parasitic resonances affect operation

[Doug Smith]

  
  
Hi Everyone,

I just posted my Technical Tidbit for September 2013 on how
parasitic resonances in ane RFID antenna can affect RFID operation
and how to measure these parasitic resonances as well as an example.


Technical
Tidbit - September 2013
Parasitic Resonance in an RFID
  ~10 MHz Antenna - Measurement and Characterization


Abstract: Low frequency RFID transmitting
  antennas often have self-resonances at much higher frequencies
  than the
  frequency of operation that can cause problems, such as unintended
  radiated emissions. Such a case is described.

If you have trouble following the links below, please contact me. XO
Communications had a nearly one day outage yesterday and not all
browsers may get access yet. On my computer this afternoon Safari,
Opera, and Google Chrome worked but Firefox did not (yes, I cleared
the cache and tried reloading).

link to the article:  http://emcesd.com/tt2013/tt090813.htm
(If your Windows computer adds a "[1}" to the link, you need to
manually remove it.)

Link to the home page of the site: http:emcesd.com

Doug
-- 
--
 ___  _Doug Smith
  \  / )   P.O. Box 60941
   =   Boulder City, NV 89006-0941
_ / \ / \ _TEL/FAX: 702-570-6108/570-6013
  /  /\  \ ] /  /\  \  Mobile:  408-858-4528
 |  q-( )  |  o  | Email:   d...@dsmith.org
  \ _ /]\ _ /  Web: http://www.dsmith.org
--

  

-

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

Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc.


Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas 
Mike Cantwell 

For policy questions, send mail to:
Jim Bacher  
David Heald 

Re: [PSES] Spark Gap PCB Layout on AC Mains

[ce-test, qualified testing bv - Gert Gremmen]

That depends of course how the transient/surge has been coupled into the
mains.
If that is due to a ligtning event at a short range,  the impedance may
be much less. 
Your analysis is right when the even has been generated far away.

Regards,

Ing.  Gert Gremmen, BSc



. 



-Oorspronkelijk bericht-
Van: John Woodgate [mailto:j...@jmwa.demon.co.uk] 
Verzonden: Saturday, September 07, 2013 11:35 AM
Aan: EMC-PSTC@LISTSERV.IEEE.ORG
Onderwerp: Re: [PSES] Spark Gap PCB Layout on AC Mains

In message ,
dated Sat, 7 Sep 2013, "ce-test, qualified testing bv - Gert Gremmen" 
 writes:

>Anyway, the primary circuit always need to be build for high surge 
>currents,
>
>and one should always insert induction to limit surge currents.
>
>As the impedance of the spark gap is low, only a small amount of 
>induction
>
>will reduce the surge current substantially

Quite true, but the mains supply itself (unless it's from a very nearby
private MV/LV transformer, has inductance of the order of a millihenry
(0.3 ohms at 50 Hz), so there is not much point in adding only a few
microhenrys.

IEC TR60725 gives 'reference impedances' for various types of mains
supply. While these tend to be higher than the actual impedance at the
'point of common coupling', they are a guide to the impedance at a
typical wall-socket. This impedance limits the prospective short-circuit
current.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk If
dictionaries were correct, we would only need one, because they would
all give the same information.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

-

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

Attachments are not permitted but the IEEE PSES Online Communities site
at http://product-compliance.oc.ieee.org/ can be used for graphics (in
well-used formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to
unsubscribe) List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas 
Mike Cantwell 

For policy questions, send mail to:
Jim Bacher:  
David Heald: 

-

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

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas 
Mike Cantwell 

For policy questions, send mail to:
Jim Bacher:  
David Heald: 

Re: [PSES] Spark Gap PCB Layout on AC Mains

[John Woodgate]

In message , 
dated Sat, 7 Sep 2013, "ce-test, qualified testing bv - Gert Gremmen" 
 writes:


Anyway, the primary circuit always need to be build for high surge 
currents,


and one should always insert induction to limit surge currents.

As the impedance of the spark gap is low, only a small amount of 
induction


will reduce the surge current substantially


Quite true, but the mains supply itself (unless it's from a very nearby 
private MV/LV transformer, has inductance of the order of a millihenry 
(0.3 ohms at 50 Hz), so there is not much point in adding only a few 
microhenrys.


IEC TR60725 gives 'reference impedances' for various types of mains 
supply. While these tend to be higher than the actual impedance at the 
'point of common coupling', they are a guide to the impedance at a 
typical wall-socket. This impedance limits the prospective short-circuit 
current.

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
If dictionaries were correct, we would only need one, because they would all
give the same information.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

-

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

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas 
Mike Cantwell 

For policy questions, send mail to:
Jim Bacher:  
David Heald: 

Re: [PSES] Spark Gap PCB Layout on AC Mains

[ce-test, qualified testing bv - Gert Gremmen]

The First Google hit .

 

http://www.littelfuse.com/products/gas-discharge-tubes/high-voltage-gdt.aspx

 

(no connections with them)

 

Anyway, the primary circuit always need to be build for high surge currents, 

and one should always insert induction to limit surge currents.

As the impedance of the spark gap is low, only a small amount of induction

will reduce the surge current substantially.

 

Regards,

Ing.  Gert Gremmen, BSc

 

 

 

 

 

Van: Joe Randolph [mailto:j...@randolph-telecom.com] 
Verzonden: Friday, September 06, 2013 11:32 PM
Aan: EMC-PSTC@LISTSERV.IEEE.ORG
Onderwerp: Re: [PSES] Spark Gap PCB Layout on AC Mains

 

Hi Gert:

Do you know of a source for a small, inexpensive gas tube with a rated 
breakdown voltage in the range of 6 KV to 10 KV?  I don't, but I'd like to know 
of a suitable source.

As I noted, conventional gas tubes are typically rated at a few hundred volts.  
Putting a 400 volt gas tube across a barrier that breaks down at 6 KV to 10 KV 
invites surge currents that otherwise would not occur.


Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com  









An air gap is a gas tube without the tube..
And the air properties vary, and so the performance with altitude , humidity 
and pollutions.
So just use a commercial available gas discharge tube !
 
I have seen and recommended ( in that order ;<) mains wire coiled into
a 10 cm coil before being connected to a spark device., thus adding a bit of 
inductance
to reduce the current. That fits nice with  your observations on high breakdown 
voltages.
 
Gert Gremmen
 
Van: Joe Randolph [mailto:j...@randolph-telecom.com] 
Verzonden: vrijdag 6 september 2013 21:06
Aan: EMC-PSTC@LISTSERV.IEEE.ORG
Onderwerp: Re: [PSES] Spark Gap PCB Layout on AC Mains
 
Hi Doug:

You mention that there are companies that make air gaps.  Are these devices 
anything like what I described?  

What I have in mind is an inexpensive component about the same physical size 
and cost as a gas tube, with two tungsten electrodes separated by an air gap of 
5 to 10 mm to achieve a nominal air breakdown levels in the range of 6 KV to 10 
KV.  I don't think corona would be an issue in an application where the normal 
working voltage is just 120/240 VRMS AC main voltages.

The intended use would be what I think Brian had in mind, which is to provide a 
known path for surges that exceed the rating of the insulation.  If the size of 
the air gap is coordinated properly with a good insulation barrier, the gap 
could be expected to trigger very rarely (if ever) in the product's lifetime.



Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com  





Joe,
 
Yes we are in agreement, and you make several valid points regarding gas 
discharge tubes.  As is always the case in any design, there are trade-offs.  
 
I have found it beneficial to use a combination of the very good ideas being 
discussed on this thread.  For example, solid insulation barriers in 
combination with EMI filtering and surge suppression.  The solid insulation an 
be judicially placed with thickness sufficient to prevent punch-thru and 
sufficient creepage distance to prevent flashover.  An EMI filter adds come 
level of series impedance to high frequencies and surge suppression devices 
behind this are less likely to fail.  Gas discharge tubes have another problem 
in that a poorly selected voltage breakdown may cause the gas to glow under 
normal operating conditions and these devices are nothing like the old neon 
lamps, they will fail as a result.  In addition, when they do fire, they are 
unlike MOVs in that they clamp to near zero volts and the only way to 
extinguish the plasma within the tube is a zero crossing of the line voltage.  
MOVs are always suspect because of the leakage current heating problem and 
catastrophic failure mode where they sputter metal on nearby surfaces.  There 
are companies who make air gaps and these are viable so long as they do not 
have a problem with corona when the electrodes erode (due to arcing) into 
ragged edges.  Sharp points can lower the breakdown voltage (e-fields) just as 
the ice pick experiment did back in high school.  You would also need a way to 
replenish the air supply within the gaps since corona can build up and 
eventually arc over without requiring a surge event.
 
In any design it is useful to test your mitigation attempts in the actual 
product design.  
 
thanks, -doug

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

 
From: Joe Randolph   
Sent: Friday, September 06, 2013 11:34 AM
To: Doug Powell   ; EMC-PSTC@LISTSERV.IEEE.ORG 
Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains
 
Hi Doug:

I think