Siemens 6ES5 240-1AA21 Counter and Position Decoder Module

The Siemens IP 240 Counter/Position Decoder Module, 6ES5 240-1AA21, is a two‑channel interface for counting, position decoding, and speed measurement in SIMATIC S5 installations. Built as part of the IP 240 family, this compact module (Version U) connects to S5‑135U/‑155U/‑H PLCs to provide two independent channels for counting encoder pulses or decoding position data. It supports encoders with 5V and 24V interfaces, including both 5V symmetric and asymmetric configurations, enabling flexible integration with a range of incremental encoders. The IP 240 can operate in IP 252 expansion mode, allowing expansion of its input/output capabilities within a compatible S5 system. Typical applications include motion control tasks such as conveyor positioning, shaft speed measurement, and precise rotary-position feedback in automation lines where encoder feedback is essential.