8-channel 24 V DC input module for ET 200SP
The Siemens 6ES7131-6BF00-2BA0 is an ET 200SP digital input module providing 8 channels at 24 V DC, P-reading (source input). It snaps onto a 15 mm-wide base unit type A0 (BU type A0) — the narrowest form factor in the ET 200SP family, so it packs eight inputs into a single slot width on the DIN rail. Signal thresholds are standard for 24 V PLC inputs: a logic 0 spans -30 to +5 V, logic 1 from +11 to +30 V, with a typical input current of 2.5 mA per channel at 24 V. The module draws a maximum of 50 mA from the backplane bus and dissipates 1 W typical.
Wire-break diagnostics and encoder supply
Wire-break diagnostics is supported module-by-module, with an optional protective circuit using a 25 kOhm to 45 kOhm resistor to prevent false wire-break alarms on simple encoder contacts. This is useful when monitoring dry-contact limit switches or proximity sensors where the open-circuit voltage might otherwise trigger a diagnostic. The module provides a total encoder supply current of 700 mA across all eight channels — enough to power a bank of 3-wire proximity sensors without an external power supply. Short-circuit protection is module-wise, and the group error LED (green/red DIAG LED) gives a visual fault indication.
Cable length and isolation
Maximum cable length is 1 000 m shielded, 600 m unshielded — the shielded limit covers long runs from remote junction boxes back to the panel. Isolation is tested at 707 V DC type test between channels and the backplane bus; there is no channel-to-channel isolation, so all inputs share a common reference.