Cable length and wiring constraints
The 6ES7138-4DB00-0AB0: Maximum cable length depends on the clock frequency used. For shielded twisted-pair cable: 600 m is achievable at lower frequencies up to 125 kHz; at 250 kHz the limit is 160 m; at 500 kHz it drops to 60 m; at 1 MHz to 20 m; and at 2 MHz to 8 m. Unshielded cable is limited to 32 m. The input is isolated from the backplane bus but shares a common load voltage L+ (no isolation between channels and L+). Short-circuit protection and reverse polarity protection are included.
Status and diagnostics
The module provides per-channel status indicators: a green LED for the digital input, green LEDs for forward/backward counting direction, and a red group-error SF (system fault) LED. The output voltage type is L+ minus 0.8 V, with a maximum output current of 500 mA — sufficient for encoder supply.