Electric Swivel with screened paths

[fuz83]

Hi All,
I was wondering how is arranged/manufactured an electric swivel with screened paths. It is not clear to me if an electric penetration is different from a screen penetration or if they're exactly the same and they are simply located next to each other.

I suppose an electric swivel is only a brush with an electric ring, so how can be arranged a screen which wraps such items and also rotates?

Thanks,
Stefano

 

[MacGyverS2000]

I get the impression you're talking about sliprings, but I think the language barrier is getting in the way... can you try rephrasing the question? What is the application? What information are you specifically looking for?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[jraef]

I think maybe you want a slip ring that is compatible with shielded conductors? If so, look for radar system slip rings.

http://www.spinner-group.com/en_P_rotary_joints_slip_rings

http://www.mercotac.com/?gclid=CNOYxdH56qkCFQQnbAodGRPBZQ

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— Kilgore Trout (via Kurt Vonnegut)
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[fuz83]

I'm assessing some types of electric swivels for offshore use, but it is not clear to me how is manufactured and arranged a screen in an electric communication path (slipring). Is it only an electric penetration next to the considered electric penetration or is it a "real" screen? (with real screen I mean an electric path concentrically wrapped by the copper screen).
Must it be located next to the path to be screened or can it be located in another ring?

Stefano

 

[MacGyverS2000]

I've always seen screening done by using adjacent rings as ground... I suppose if I thought about it I could come up with a more 3D screen, but if it works well enough as is, why fight it.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

It sounds like you're asking if the slip ring shield maintains its shielding function throughout the slipring. The answer is NO. The shielding in the slipring would be provided by the external shell of the slip ring, which would be connected to the outermost shield connection of the cables entering and leaving the slipring.

This is no different than for a bulkhead connector, wherein the individual incoming shields are terminated into a wire, which is passed through the connector body and pins, and re-emerges to mate with the outgoing shields. Again, such cable bundles have a bundle shield that is mated to the body shields of the two parts of the connector.

NOTE: in both cases, the outermost shield is usually carried through a connector pin, just like the signals. This is to ensure that if a break in the mechanical connection of the outershield occurs, there will still be an electrical connection between the shields on either side of the connector.

To summarize, a typical construct would have individual shields around critical signal cables. Signal cables are then bundled together, and an overall shield protects the bundle. All shields are terminated into a connector pin and passed through the connector. The outer shield is the only one that maintains a full shield through the mechanical structure of the connector.

TTFN

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[VEBill]

Actually there are various multipin connectors, both 38999 and ARINC series as examples, that can be populated with true coaxial contacts.

For the OP, hopefully the system uses differential signalling and any shielding is simply bulk shielding.

Also (just in case you're interested) a company called Focal in Halifax reportedly offers fibre-optic (!) slip rings. If you're worried about electrical noise then that might be the ultimate solution.

 

[BobJones]

There are quite a few companies making fiber optic slip rings or rotary joints now. Moog is the company that makes them for the Bradley Fighting Vehicle.

I have passed DeviceNet and Ethernet/IP over mechanical slip rings without a problem. There is less noise if the slip ring diameter is small, such as the cartridge style with no through-bore, and if the rpm is low.

As MacGyver mentioned, a common practice is to locate your ground conductor next to your data conductors. You could even locate a ground conductor on each side of your data conductors. It is also common to segregate your signals into data and power, and grounding any spare conductors between those groups.

If the outside shell of the slip ring is metal, then you also have the option of grounding it to further provide shielding. Since you should be routing a ground through the slip ring to ensure ground reliability, you can connect it to that ground. On rotating equipment you can't rely on point contacts of lubricated bearings to convey fault current so need a ground circuit through the slip ring.