Original 24V Automation Fanuc Power Supply Module A02B-0303-C205

FANUC A02B-0303-C205 | SDU1 Basic 4-Axis Separate Detector Interface — FSSB / Position Feedback / Series 30i/31i/32i

What the SDU1 Does in the FANUC Architecture

The A02B-0303-C205 is the SDU1 Basic — a Separate Detector Interface unit that connects external position detectors (linear scales, rotary encoders mounted on the machine structure rather than the servo motor shaft) to the FANUC CNC via the FSSB fibre-optic serial bus. On CNC machine tools with full closed-loop position control, the detector mounts at the machine table or ballscrew nut, feeding back actual axis position independent of the servo motor's encoder. This closes the position loop at the mechanical work point, eliminating error from ballscrew pitch deviation, thermal expansion, and mechanical compliance between motor and table.

The A02B-0303-C205 receives signals from up to four separate detectors and communicates position data to the CNC over FSSB — the same optical bus that FANUC's FSSB servo amplifiers use. The SDU1 connects into the FSSB chain alongside the amplifiers, and the CNC manages all position feedback through this single high-speed optical network.

Key Specifications

4-Axis Capacity in One Module

The SDU1 Basic handles four detector channels from a single module — four separate detector connections returning position data to the CNC simultaneously. For a machining centre with separate scale feedback on all four primary linear axes (X, Y, Z, B), a single A02B-0303-C205 covers the complete closed-loop position system. For machines requiring more than four separate detector axes, additional SDU1 units chain into the FSSB network.

Selection — Exact Part Number Required

The A02B-0303 series covers different SDU variants. Confirm A02B-0303-C205 specifically from the installed module's label — adjacent part numbers may differ in axis count, interface version, or functional role. The CNC's FSSB configuration and axis parameter set are built around the specific SDU variant; substituting a different suffix risks communication or axis configuration errors.

FAQ

Q1: What does the SDU1 do that the servo motor encoder does not?

The servo motor encoder provides position feedback from the motor shaft — adequate for semi-closed-loop control. The separate detector feeds back actual axis position at the machine table or ballscrew nut, closing the loop at the mechanical work point. This eliminates positioning error from ballscrew pitch deviation, thermal expansion, and mechanical compliance. The A02B-0303-C205 is the FSSB interface unit that connects these separate detectors to the CNC.

Q2: Which FANUC CNC generations are compatible?

The SDU1 Basic uses FSSB fibre-optic interface, making it compatible with FANUC i-series controls supporting FSSB: Series 30i, 31i, 32i, 16i, 18i, and 160-MC. It is not compatible with earlier CNC generations that used non-FSSB servo communication architectures.

Q3: How many SDU1 units can connect on one FANUC CNC system?

Multiple SDU1 units can chain into the FSSB network alongside servo amplifiers. One A02B-0303-C205 provides four detector channels. For more than four separate detector axes, additional SDU1 modules extend the system. The CNC's FSSB axis parameter set must reflect the complete chain topology.

Q4: Does replacing the A02B-0303-C205 require CNC parameter changes?

For a like-for-like replacement in the same FSSB chain position, the existing CNC FSSB topology parameters cover the replacement without change. If the chain topology is modified or the replacement unit has a different axis configuration, the CNC's FSSB axis assignment and detector interface parameters must be reviewed before recommissioning.

Q5: Where is the A02B-0303-C205 sourced?

Through the FANUC i-series aftermarket — FANUC CNC parts dealers and repair specialists. Exchange and tested surplus availability. Confirm A02B-0303-C205 specifically. For production-critical machines with separate detector closed-loop control, holding a verified spare minimises recovery time — SDU1 failure disables separate detector feedback on all four connected axes simultaneously.