The essential
An end-of-shaft slip ring part number such as SR36AW/R360/AX reads from left to right: series, number of rings, rotor diameter, weatherproof option, rotation sensor and its resolution, rotor connection, stator connection, then special modifications. Solder terminals are the default for the lead wires; a circular connector is chosen when the assembly needs a quick disconnect or a sealed connection.
S series or SR series?
The rotor diameter decides. The S series has a 41.3 mm (1.625 in) rotor: models S4 to S10 and their short versions, most with solder terminals. The SR series covers every end-of-shaft unit with a rotor of 50.8 mm (2 in) or more: SR, SR/PE, SR/E60 and SR/ERT. It has the widest choice of terminals, connectors, rotor diameters, seals and rotation sensors.
How is the part number built?
From nine positions, read left to right. Take SR 36 A W /R 360 /A X as the example.
- 1. S or SR: the series.
- 2. Number of rings: 36.
- 3. Rotor diameter: blank for 1.625 in, M for 2.0 in, A for 2.5 in, G for 2.9 in, Y for 3.0 in.
- 4. Weatherproofing: W for contacting rotary seals (2 000 rpm maximum), B for non-contacting labyrinth seals, blank for none.
- 5. Speed or angular position sensor: E incremental optical encoder, PE precision incremental optical encoder, R resolver, T tachometer circuit, blank for none.
- 6. Resolution of the sensor: 360.
- 7. Rotor connection: blank for solder terminals on the front face of the flange, A for an axial connector on the back, R for a radial connector, T for solder terminals on the back.
- 8. Stator connection: blank for solder terminals, X for a circular connector on the side of the stator housing. A rubber boot or metal cap is the alternative way to add a stator connector.
- 9. Special modifications.
Solder terminals or connectors?
Solder terminals for most applications: slip rings are stocked with them, and they are small and reliable. Circular connectors when a quick disconnect or weatherproofing is needed. The connector series follows the ring count.
- Up to 20 rings: Bendix PT series connectors are usually recommended.
- Above 20 rings: Bendix JT series.
How is the connector sealed?
At the mating face by the connector itself; at the rear of the plug, where the lead wires exit, by RTV sealant or a sealing backshell. Both are needed for a completely weatherproof connector.
- Electrical grade RTV silicone sealant can be used.
- A sealing backshell around a jacketed cable or a thin wall tube is more reliable than sealant and easier to rework. It replaces the cable clamp and adds up to 38 mm (1.5 in) to the length.
- Either method, correctly applied, allows temporary immersion from −40 to 121 °C (−40 to 250 °F).
- On a wheel, the tube can engage a bracket at the top of the wheel well and stop the stator from rotating.
How is a connector added to a stator with solder terminals?
With an accessory fitted on the end of the cylindrical stator, chosen by the stator diameter. It carries a tube or a connector.
- Rubber boot (C209): the cable or the tube exits radially.
- Connector bracket (C574).
- Weatherproof metal cap (C225) with a radial connector, or metal cap (C232) with an axial connector.
How is a wheel instrumentation package numbered?
In three fields, given in the same note: WIP6 or WIP8 for a 6 in or 8 in diameter package; blank for a full bridge passed through, SG for a strain amplifier or SGD for a dual range one; then the thermocouple channels, passed through or amplified, with their type (J, K, E or T). Thermocouples passed through without amplification are not available with the dual range strain amplifier.
The technical note
The original note carries the connector dimension tables and the accessory part numbers.
To remember
- Series, rings, rotor diameter, seals, sensor, resolution, rotor connection, stator connection, specials.
- W seals limit the speed to 2 000 rpm.
- Solder terminals by default; Bendix PT up to 20 rings, JT above.