SSI Encoder Input on ET 200S
The Siemens 6ES7138-4DH00-0AB0 is an SSI absolute encoder module for the ET 200S distributed I/O system. It reads 13-, 21-, or 25-bit position data over RS-422, supporting Gray or binary code. The latch time sits at 400 µs plus age of encoder value—that's the window for synchronizing the position capture across multiple axes. Shielded cable runs to 1 000 m; unshielded drops to 600 m. On a noisy plant floor, shield it properly. Three digital inputs and three digital outputs ride alongside the encoder input on the same module. The inputs handle 24 V DC signals (L+ -1 V minimum) with type 2 2-wire sensor compatibility. Outputs switch inductive loads up to 2 Hz or resistive loads at 100 Hz. Short-circuit and reverse-polarity protection are onboard.
vs. the SIPLUS Variant
The 6AG1123-2DB03-2AX0 is the SIPLUS version of this encoder module, built for extended temperature ranges and conformal-coated boards. If the panel lives in a conditioned room, the standard 6ES7138-4DH00-0AB0 is the correct call. If the cabinet faces -40 °C or corrosive atmospheres, the SIPLUS is the better fit. Footprint and wiring are identical—drop-in from a panel layout perspective.