HMI with integrated I/O — what this part does
The Siemens 6AG1688-3CD13-4AX0 is a panel-mount HMI with a membrane keyboard, 16 function keys, and 16 digital inputs plus 16 digital outputs built into the same housing. It communicates via MPI and PROFIBUS (1x RS-485, up to 12 Mbit/s) — no MODBUS or TCP/IP on board, so the control network needs to be Siemens-native or gatewayed in. The front is IP65-rated for washdown environments; the rear is IP20 for the panel interior.
The 16 digital outputs are rated 100 mA per channel resistive or inductive, grouped in fours with a 500 mA group limit — so each output drives a small pilot relay or indicator directly, but not a contactor coil without an interposing relay. The 16 digital inputs accept 24 VDC and include an enable input, a key and signal lamp test function, and short-circuit protection. The membrane keyboard supports multi-key operation and the LEDs flash at 0.5 Hz for status indication. Active power draw is 10 W typical at 24 VDC.