The Siemens 6ES7221-3BD30-0XB0 is a SIMATIC S7-1200 signal board (SB 1221) providing 4 digital inputs, 24 V DC, current-sourcing type, with a 200 kHz switching frequency. It draws 40 mA from the 5 V DC backplane bus and dissipates 1 W typical.
What the ratings mean for fit
The 200 kHz per-channel input rate means this board is intended for high-speed counting or pulse measurement — not general-purpose pushbutton or limit-switch sensing. The 24 V DC sourcing input type expects the load to supply the current; verify your sensor outputs are sourcing-compatible (PNP). Signal "1" is detected from 0 V up to (L+ minus 10 V DC), with a minimum current of 2.9 mA and typical 7 mA. Signal "0" spans (L+ minus 5 V DC) up to L+, with a permissible quiescent current up to 1.4 mA. This gives a clean threshold window for industrial noise immunity. The board measures 38 mm wide, 62 mm high, 21 mm deep — it clips onto the S7-1200 CPU front panel, not a DIN rail. No additional panel space is consumed. Temperature range: -40 °C to 70 °C ambient, with derated limits for vertical installation (max 50 °C) and horizontal installation (max 60 °C). Minimum for both orientations is -20 °C. The wider storage range covers transport conditions. Maximum unshielded cable length is 50 m; use shielded twisted pair for runs approaching that limit.
Approvals and compliance
Carries cULus, CE, UL, CSA, FM, KC, marine, and RCM (formerly C-TICK) approvals — covering North American, European, Korean, and maritime regulatory jurisdictions.