The Siemens 6ES7521-1BP00-0AA0 is a current-production digital input module for the S7-1500 family. It gives you 16 channels, each configurable as source or sink input, running on 24 V DC. The signal thresholds are tight: a '0' sits between -5 and +5 V referenced to COM, and a '1' needs -11 to -30 V or +11 to +30 V. That bipolar capability means it'll handle both NPN and PNP sensors without extra wiring tricks — handy when you're swapping a field device mid-shift and all you've got is what's on the van.
Power consumption is 4.8 W typical, and the module sits in a 35 x 147 x 129 mm envelope — standard S7-1500 width, so it slots into any existing U-rail without recalculating your panel fill. The firmware is at V1.0.0 and supports FW updates, though the hardware functional status starts from FS01. Remember to order the cable and connection modules separately; they're not in the box.