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It looks like this is Top 10 EMC issue, so there should not be any prob­lem dur­ing EMC test­ing. But unfor­tu­nately, really often prob­lems arise in radi­ated emis­sion tests, radi­ated sus­cep­ti­bil­ity tests, elec­tro­sta­tis­tic dis­charge immu­nity (ESD).

When “old school” engi­neers, man­agers, staff respon­si­ble for test­ing are informed that their prod­uct is fail­ing dur­ing the EMC test­ing and the prob­lem is improper shield connection→“pigtail”. They have at least few com­ments regard­ing EMC lab mea­sure­ment equip­ment qual­ity, EMC lab tech­ni­cians wrongly applied test­ing method­ol­ogy or solar storm. But “pig­tail” is not a problem:“It is so short, nearly cen­time­ter.” (It’s fine with engi­neers who have EMC basics. They under­stand the problem.)

As for a lec­turer in uni­ver­sity it is impor­tant to explain the sit­u­a­tion not only in terms of math, but also in real life mea­sure­ments and visu­al­iza­tion, using mod­el­ing. Visu­al­iza­tion of com­plex math­e­mat­i­cal prob­lems has always helped students.

There­fore, I’ve decided to make easy way to explain the sit­u­a­tion visu­ally. Show­ing what hap­pens around cable, shield­ing and “pig­tail”.
For this pur­pose I’ve cho­sen setup with two shielded enclo­sures in 0.9m dis­tance, Fig.1. Enclo­sure dimen­sions are 5cm x 5cm x 5cm. Cable is cre­ated by two non twisted con­duc­tors and shield­ing all round them. In one of the box con­duc­tor pair is dri­ven by source, Fig.2. Load is located in the other shielded box, Fig.3. Cable shield­ing is “pig­tailed” next to the load, Fig.4. Shield­ing is vio­lated at the length of 1cm.

model opt

Fig.1. Mod­eled test setup with two shielded enclo­sures and shielded cable

source opt

Fig.2. Sig­nal source in shielded enclosure

load opt

Fig.3. Load in shielded enclosure

pigtail opt

Fig.4. Cable shield­ing con­nected using “pigtail”

There have been dis­cus­sions on: “What if “pig­tail” is spit­ted in two? It should be bit­ter than one.” There­fore, there are four sit­u­a­tions pre­sented:
1. Shield­ing is con­nected with one pig­tail– Fig.4.
2. Shield­ing is con­nected with two pig­tails– Fig.5.
3. Shield­ing is con­nected four pig­tails– Fig.6.
4. Shield­ing is prop­erly ter­mi­nated in 3600– Fig.7.

pigtail2 opt

Fig.5. Cable shield­ing con­nected using two “pigtails”

pigtail4 opt

Fig.6. Cable shield­ing con­nected using four “pigtails”

pigtail360 opt

Fig.7. Cable shield­ing con­nected in right man­ner– no EMC problems

Mod­eled radi­ated field results are rep­re­sented through Fig.8 to Fig.12. Mod­el­ing is car­ried out at 500MHz.

CST 500 no opt

Fig.8. Cable shield­ing is not connected

CST 500 1 opt

Fig.9. Cable shield is con­nected using 1cm long pigtail

CST 500 2 opt

Fig.10. Cable shield is con­nected using two 1cm long pigtails

CST 500 4 opt

Fig.11. Cable shield is con­nected using four 1cm long pigtails

CST 500 360 opt

Fig.10. Cable shield is con­nected using no pig­tails (360deg termination)

Tak­ing a look at mod­el­ing results you can make your own con­clu­sions– bad/​good EMC engi­neer­ing. But definetly there is dif­fer­ence between one “pig­tail” and four “pigtails”!

Some mod­el­ing vizual­iza­tions
Shield­ing not con­nected at one end cre­at­ing a lot of radi­ated emis­sions. Usu­ally it means that tests in EMC lab­o­ra­tory are failed.

Shield­ing con­nected using one pig­tail, also cre­at­ing great amount radi­ated emis­sions. Also this con­fig­u­ra­tion will lead to fails in EMC laboratory.

Shield­ing con­nected using four pig­tails. It is a lot bet­ter to use four pig­tails instead of one. But it’s not the best con­fig­u­ra­tion to present at elec­tro­mag­netic com­pat­i­bil­ity test­ing laboratory.

Shield­ing con­nected using 360deg ter­mi­na­tion. Best solu­tion to go to EMC test­ing laboratory.

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