Siemens 6ES7551-1AB00-0AB0 SIMATIC S7-1500 TM PosInput 2 2-Channel Position Detection I/O Module

The Siemens 6ES7551-1AB00-0AB0 is a SIMATIC S7-1500 TM PosInput 2 counter and position-detection module with 2 independent channels, each accepting an RS-422 incremental encoder or SSI absolute encoder at up to 4 MHz counting frequency with quadruple evaluation or a 2 MHz SSI clock. Each channel also provides 2 digital inputs and 2 digital outputs, and the module runs on 24 V DC.

Technical Specifications

Selection Notes

Two independent counting channels each run up to 4 MHz counting frequency with quadruple evaluation on an RS-422 or 5 V TTL incremental encoder, or up to 2 MHz SSI clock on an absolute encoder with 10 to 40-bit telegrams in binary or Gray code, so one module covers either encoder type without a separate interface card per channel. The 2 DI and 2 DQ per channel support gate start/stop, capture, and synchronization functions tied directly to the counting hardware, useful for latching a count on an external trigger without CPU-cycle jitter. Isochronous mode with a 250 microsecond minimum bus cycle time keeps position values synchronized to Motion Control functions in the S7-1500 CPU.

Applications

Position and speed feedback on conveyors, indexing tables, and cut-to-length lines using RS-422 incremental encoders, plus absolute positioning with SSI encoders on axes that must retain position after a power cycle. The per-channel DI/DQ pair lets a reference switch or brake output share the same channel as the encoder feedback.