Author Topic: Building a cheap EMC chamber in the UK?  (Read 1841 times)

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Online trevwhite

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Building a cheap EMC chamber in the UK?
« on: November 28, 2017, 07:37:26 pm »
I thought it would be useful to get some views/experience/suggestions from people on building an emc chamber on the cheap. I know EMC and cheap are rarely found in the same sentence but hey!

So my initial thought was if I bought a 20ft shipping container do I just line it with the right material and job done? I think there is more to this else people would be doing it but how much more work would be required?

Also, anyone can anyone recommend a source for the lining material for an emc chamber? Thinking it is probably very specialised and hence expensive but be good to find out.

Thanks

Trev
 

Offline nctnico

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Re: Building a cheap EMC chamber in the UK?
« Reply #1 on: November 28, 2017, 09:26:39 pm »
You'd need to line with 10x10 cm ceramic tiles costing a few pounds each. Don't go overboard here but try to rent a chamber from someone else for pre-compliance testing. There is a lot you can do on your bench once you get the hang of EMC testing.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Jay_Diddy_B

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Re: Building a cheap EMC chamber in the UK?
« Reply #2 on: November 28, 2017, 09:40:48 pm »
I thought it would be useful to get some views/experience/suggestions from people on building an emc chamber on the cheap. I know EMC and cheap are rarely found in the same sentence but hey!

So my initial thought was if I bought a 20ft shipping container do I just line it with the right material and job done? I think there is more to this else people would be doing it but how much more work would be required?

Also, anyone can anyone recommend a source for the lining material for an emc chamber? Thinking it is probably very specialised and hence expensive but be good to find out.

Thanks

Trev

Hi,

You might be better looking at TEM cells and GTEM cells for pre-compliance testing. It depends on the size of your product.

I built a open TEM cell and it is quite useful.

Regards,

Jay_Diddy_B
 

Online trevwhite

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Re: Building a cheap EMC chamber in the UK?
« Reply #3 on: November 28, 2017, 09:43:45 pm »
I thought it would be useful to get some views/experience/suggestions from people on building an emc chamber on the cheap. I know EMC and cheap are rarely found in the same sentence but hey!

So my initial thought was if I bought a 20ft shipping container do I just line it with the right material and job done? I think there is more to this else people would be doing it but how much more work would be required?

Also, anyone can anyone recommend a source for the lining material for an emc chamber? Thinking it is probably very specialised and hence expensive but be good to find out.

Thanks

Trev

Hi,

You might be better looking at TEM cells and GTEM cells for pre-compliance testing. It depends on the size of your product.

I built a open TEM cell and it is quite useful.

Regards,

Jay_Diddy_B
Hi Jay. Any info on the TEM You built?

Thanks

Trev

 

Offline Jay_Diddy_B

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Re: Building a cheap EMC chamber in the UK?
« Reply #4 on: November 28, 2017, 10:18:21 pm »
Hi,

Here is a link where I found the how to information:

http://www.ewh.ieee.org/soc/emcs/acstrial/newsletters/summer08/pp2.pdf

Here is a picture of mine:



You might want to look at this link:

https://www.tekbox.net/test-equipment/open-tem-cells

These are some commercially available ones, similar design.

The open TEM cell is not as good as GTEM cell, but it is much easier to construct.


Regards,

Jay_Diddy_B
 

Online coppice

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Re: Building a cheap EMC chamber in the UK?
« Reply #5 on: November 28, 2017, 10:29:13 pm »
You might be better looking at TEM cells and GTEM cells for pre-compliance testing. It depends on the size of your product.

I built a open TEM cell and it is quite useful.
Whenever I see an in house chamber in a smaller company its a TEM cell or something similar. I haven't seen anyone build a full sized chamber that didn't cost a fortune to line. A chamber is massively more flexible, as it removes most barriers to equipment size, but its just too expensive for most companies to justify having in house, unless they are doing full scale testing day in, day out. A TEM cell imposes equipment size restrictions, but you can play around all day, experimenting with solutions to EMI/EMC issues, at low cost.
« Last Edit: November 29, 2017, 12:39:16 am by coppice »
 

Offline Jay_Diddy_B

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Re: Building a cheap EMC chamber in the UK?
« Reply #6 on: November 28, 2017, 10:51:25 pm »
Hi,
The open TEM cell and TEM cell have a relationship between size and maximum Frequency. The open I showed is 18 inches by 12 inches and the maximum frequency is 1GHz. If you double the dimensions the frequency drops to 500MHz.

The GTEM cell, G stands for GHz, does not have this limitation, but you are back to needing absorbing cones at the large end.



The good thing is that the GTEM cell is closed, therefore less background. And you need fewer absorbers than a room.

Regards,

Jay_Diddy_B
 

Online tautech

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Re: Building a cheap EMC chamber in the UK?
« Reply #7 on: November 28, 2017, 11:00:59 pm »
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Offline Jay_Diddy_B

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Re: Building a cheap EMC chamber in the UK?
« Reply #8 on: November 29, 2017, 12:03:05 am »
This old thread is worth some study:
https://www.eevblog.com/forum/testgear/emc-chamber-build-log/

Interesting thread. Some great insight into how a chamber is built. It is far from cheap. Probably around $250K or more. Then you need to antennae, filters and measuring equipment.

The TEM cell or GTEM cell is the best route for pre-compliance.

Regards,
Jay_Diddy_B
 

Offline josechow

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Re: Building a cheap EMC chamber in the UK?
« Reply #9 on: June 27, 2018, 02:00:12 am »
Hi,

Here is a link where I found the how to information:

Regards,

Jay_Diddy_B

Hey Jay, did you happen to do any VSWR readings on your TEM cell? I am curious how you decided to move the septum up a bit without affecting the characteristic impedance too much? In the near future I will need to test an "electrically large" DUT and I saw in some papers that the device being tested should generally be <1/3 of the septum height otherwise you through off the characteristic impedance of the cell.

I suppose I can do some impedance measurements and throw in my aluminum enclosure to see what it does without any active electronics in it.
 

Offline BrianHG

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Re: Building a cheap EMC chamber in the UK?
« Reply #10 on: June 27, 2018, 03:03:16 am »
Depending on your needs and the strictness of size & application, here is a cheaper alternative to a shipping crate which would still need a little work and material, and it's easily movable with a car...
« Last Edit: June 27, 2018, 03:06:24 am by BrianHG »
__________
BrianHG.
 

Offline Jay_Diddy_B

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Re: Building a cheap EMC chamber in the UK?
« Reply #11 on: June 27, 2018, 09:49:32 am »

Hey Jay, did you happen to do any VSWR readings on your TEM cell? I am curious how you decided to move the septum up a bit without affecting the characteristic impedance too much? In the near future I will need to test an "electrically large" DUT and I saw in some papers that the device being tested should generally be <1/3 of the septum height otherwise you through off the characteristic impedance of the cell.

I suppose I can do some impedance measurements and throw in my aluminum enclosure to see what it does without any active electronics in it.

I moved the septum to increase the working height in the TEM cell.

The width of the septum was adjusted to obtain a nominal 50 \$\Omega\$

I did measure the impedance using a TDR. The TEM cell was connected to the TDR with a piece of Goreflex cable that was known to be 50 \$\Omega\$

The TEM cell was open at the far end.

The measured impedance is about 58 \$\Omega\$




I also measured VSWR with the TEM cell terminated with a 50 \$\Omega\$ load.

The bottom of the screen is 0.6, so the VSWR was better 1:1.6 over the range 300kHz to 1GHz with a small exception which is 1: 2.2, indicated by the marker.

I did not bother to try and correct any of this, because when you put the device under test in the TEM it will change the impedance.




I use my TEM cell for relative measurements.

Regards,

Jay_Diddy_B
« Last Edit: June 27, 2018, 09:51:25 am by Jay_Diddy_B »
 


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