Ethernet slip rings: series compared and how to specify

What an ethernet slip ring is

An Ethernet slip ring is a rotary joint designed to pass industrial Ethernet, such as 100 Mbit/s or gigabit links, through continuous rotation without unacceptable packet loss. The data rings are laid out as matched pairs with controlled impedance, short stubs and screening from power rings, and the brushes are chosen for low, stable contact resistance. Some units use contactless capacitive, inductive or optical channels for the highest rates. Most combine the Ethernet channels with power and discrete signal rings in one housing.

When to choose an ethernet slip ring

Choose an Ethernet slip ring when the rotating part carries cameras, drives, remote I/O or sensors on a network, which cuts the ring count compared with hard-wiring every signal. It suits indexing machines, packaging turrets and gimbals running EtherCAT, PROFINET or EtherNet/IP. The trade-offs are cost and validation: contact rings add small resistance changes, and gigabit links are more sensitive than 100 Mbit/s. For very high data rates, long life or high speed, a fibre optic or contactless channel may be better.

How to specify ethernet slip rings

Protocol and data rate, such as EtherCAT, PROFINET or gigabit Ethernet
Number of Ethernet channels and pairs per channel
Required test standard or bit error rate target
Power circuits and current per circuit (A)
Speed (rpm) and expected life (revolutions)
Cable type and connectors on each side, such as RJ45 or M12
Cable lengths to the nearest switch or node (m)

Common mistakes

Specifying gigabit when the network only needs 100 Mbit/s, which adds cost and complexity
Ignoring the cable runs on each side, which count towards the total channel length and loss
Routing motor power next to data rings without screening or separation
Not testing the full link with the real protocol under rotation before production

Series compared

Brand	Series	Circuits	Current	Speed	Bore / OD
Motion Control Products	Ethernet Slip Ring	100	30 A	300 rpm	bore up to 100 mm
Moog	SRA-73799 / SRA-73806	6	2 A	250 rpm	OD up to 11.2 mm
Moog	SRA-73798 / SRA-73805	12	2 A	250 rpm	OD up to 15.5 mm
Moog	AC7203	—	10 A	250 rpm	OD up to 22.1 mm
Moog	AC7188	—	5 A	250 rpm	OD up to 22.1 mm
Moog	SRA-73810	12	2 A	250 rpm	OD up to 15.5 mm
Moog	SRA-73811	4	2 A	250 rpm	OD up to 22.1 mm
Moog	AC7195	43	10 A	250 rpm	OD up to 25.4 mm
Moog	AC7217	23	10 A	250 rpm	OD up to 25.4 mm
Moog	AC7183	—	10 A	250 rpm	OD up to 34 mm
Moog	SRA-73801 / SRA-73808	12	2 A	250 rpm	bore up to 12.7 mm
Servotecnica	SVTS A 03 / A 04 Ethernet	55	2 A	500 rpm	—
Servotecnica	SVTS C 04 / C 05 / C 06 Ethernet	65	20 A	500 rpm	bore up to 50 mm
MOFLON	ME Series Ethernet slip rings	46	10 A	—	bore up to 50 mm
MOFLON	MB Series industrial bus slip rings	—	—	—	—
Senring	Industrial bus slip rings (BM/BH)	168	—	—	bore up to 50 mm
Conductix-Wampfler	USR30 Ethernet slip rings	—	—	100 rpm	—
Conductix-Wampfler	MiniEth slip rings	—	—	100 rpm	—
Rotary Systems	Ethernet capsule SR020	—	—	750 rpm	—
United Equipment Accessories	5 Gbps Ethernet slip rings	—	—	—	—

Maximum figures across each series, summarised from manufacturers' published data on the date shown on each series page. Always confirm against the current datasheet.

Where ethernet slip rings are used

Wind turbines (pitch & yaw)Robotics & robot wrists Packaging machines & rotary indexing tables CCTV & pan-tilt cameras Cranes & slewing machinery Defence turrets & weapon stations Bottling & filling machines Stretch-wrapping & flow-wrapping machines Amusement rides Stage revolves & entertainment

Ethernet slip rings: frequently asked questions

Can EtherCAT and PROFINET run through a slip ring?

Yes, when the slip ring is designed for it. Real-time protocols are sensitive to link drops, so the data rings need controlled impedance, good screening and stable contact resistance. Tell the supplier the protocol, cycle time and number of nodes on the rotating side, and test the full network under rotation. Many suppliers validate their Ethernet rings against standard cabling test methods.

What is the difference between a contact and a contactless Ethernet slip ring?

A contact slip ring passes the signal through brushes on rings, which is economical and handles 100 Mbit/s and often gigabit links well. A contactless channel uses capacitive, inductive or optical coupling, so there is no wear on the data path and very high rates or speeds are possible. Contactless channels cost more and usually still need contact rings for power.

Ethernet slip rings