32 inputs, 24 V DC, -40 to 70 °C — the operating envelope
The Siemens 6AG1421-1BL01-2AA0 is a 32-channel digital input module that sinks 7 mA typical per channel at 24 V DC. The signal-1 threshold is 13 V DC to 30 V DC, with a signal-0 range of -30 V DC to +5 V DC. Input filtering is symmetrical: 1.2 ms to 4.8 ms for both rising and falling edges. The 6 W typical power loss is low enough that adjacent modules in a dense row won't force derating.
NRND — plan the BOM transition now
This module carries a lifecycle status of NRND (Not Recommended for New Designs). It remains available through independent distribution while channel stock lasts, but new projects should evaluate the current-production successor. For a like-for-like 32-channel 24 V DC input module in the current S7-1500 portfolio, the closest functional equivalent is the standard 6ES7521-1BL10-0AA0 — confirm backplane compatibility and form factor before substituting.
Panel fit and wiring constraints
The module measures 25 mm wide by 290 mm tall by 210 mm deep, fitting a standard S7-1500 slot. The 32 inputs are isolated as one group of 32, with isolation between channels and the backplane bus tested at 500 V DC. No channel-to-channel isolation means all inputs share a common reference — plan the field wiring accordingly. Supports 2-wire sensors with a permissible quiescent current up to 1.5 mA. The signal-0 threshold allows up to 1.3 mA quiescent, so proximity sensors with a residual leakage below that value will read reliably as off.