16-channel 120 VAC input for ET 200L – what it handles
The Siemens 6ES7131-1EH00-0XB0 is a 16-channel digital input module for the ET 200L distributed I/O system, communicating over PROFIBUS DP at baud rates from 9.6 kbit/s up to 6 Mbit/s. It senses 120 VAC signals: a logic '1' spans 74 to 132 V AC, drawing 9 to 27 mA per channel; logic '0' is 0 to 20 V AC. This makes it the module to pick when your field devices are legacy 120 VAC prox or limit switches rather than 24 VDC. Input filtering is non-adjustable: the off-to-on delay is 2 to 14 ms, on-to-off delay 6 to 25 ms. That's fast enough for most discrete sensing but not for high-speed counting or encoder edges — those need a 24 VDC module with hardware counters.
Panel fit and field wiring
IP20 rated, so it belongs inside a sealed enclosure, not on the machine frame. It uses the TB 16L AC terminal block, a 16-way screw-clamp that accepts up to 1.5 mm² wire. The module draws up to 90 mA from the 120 VAC supply rail and dissipates 5.4 W typical — budget that into the enclosure thermal calculation. Unshielded sensor cables can run up to 600 m; shielded cables reach 1000 m. For 120 VAC signals in an industrial environment, shielded cable is cheap insurance against coupled noise on long runs.
Diagnostics and status at a glance
Each channel has a green LED status indicator. A red bus fault (BF) LED flags PROFIBUS communication errors, and a green LED monitors the 24 V supply voltage. Diagnostic functions are built in — the module reports channel-level faults over the bus to the controller. Channel-to-channel isolation is 1500 V AC tested, and the channels are isolated from the PROFIBUS DP backplane. That means a short on one input won't take down the whole station or the bus segment. The module supports FREEZE capability — the input states can be latched on a bus command for synchronous capture across multiple stations.