24 V DC input module with integrated counter
The Siemens 6ES7521-1BL00-0AB0 is a digital input module for the SIMATIC S7-1500 system, supporting 24 V DC P-reading inputs that can be used as a 32-bit counter. It also provides MSI (Motion Sensor Interface) capability, meaning it can directly connect to incremental encoders or proximity sensors that output A/B signals, reducing the need for a separate counting module.
Signal thresholds and wiring length
Signal '0' is detected from -30 to +5 V, signal '1' from +11 to +30 V with a typical input current of 2.5 mA at 24 V. Unshielded cable runs up to 600 m; shielded runs up to 1000 m, which covers most panel-to-field distances in a typical plant. The module supports wire-break detection for input currents below 350 µA, so a broken field wire is flagged as a diagnostic alarm rather than a false '0'.