Positioning module for the S7-300 rack
The Siemens 6ES7351-1AH02-0AE0 is a FM 351 positioning module for the SIMATIC S7-300 family, handling rapid traverse, creep, run right, and run left motion profiles for a single axis. It accepts incremental encoders (symmetrical or asymmetrical) via a 5 V differential RS-422 input, and also supports absolute encoders with SSI protocol — the telegram length is parameterizable to 13 or 25 bits. Eight digital inputs and eight digital outputs, each rated 400 mA per channel with short-circuit protection, handle the limit-switch and actuator interface on the machine side.
Encoder interface and cable limits
The incremental encoder input accepts A/B quadrature with a zero-mark signal (N), and the clock frequency for the SSI interface reaches 1.5 MHz. Maximum input frequency is 50 kHz at 25 m cable length, derating to 25 kHz at the full 100 m cable run — so a long cable on a fast axis costs you pulse resolution. For shielded encoder cables, the maximum length extends to 200 m when the input frequency is kept at or below 188 kHz — useful for remote encoder mounting in a mill environment.
Power, environment, and lifecycle
The module draws up to 350 mA from the 24 V DC field supply and 150 mA from the 5 V backplane bus, with a typical power loss of 7.9 W.
Sourcing the 6ES7351-1AH02-0AE0
No official Siemens successor order code is listed for this module; the closest functional replacement in the S7-300 family would be the FM 350-1 or FM 350-2 counter modules, but they are not pin-compatible and require a wiring change.