SSI absolute encoder interface for ET 200S
The 6ES7138-4DB01-0AB0: It occupies a single 15 mm wide slot on the terminal module, reads gray or binary code from a connected SSI encoder, and includes a trigger input to unlatch the current actual value — useful for precise length measurement at a defined event.
Settable monoflop and cable length limits
The monoflop time is configurable to 16, 32, 48, or 64 µs, but must satisfy the condition: (1/baud rate) < monoflop time < 64 µs + 2×(1/baud rate). This is a common integration constraint — ignore it and the encoder will not sync reliably. Maximum cable length depends on baud rate: 320 m at 125 kHz, 160 m at 250 kHz, 60 m at 500 kHz, 20 m at 1 MHz, and 8 m at 2 MHz, with twisted-pair shielded cable. Unshielded runs are limited to 32 m, shielded general-purpose to 50 m.
Encoder power and input characteristics
Maximum delay is 300 µs in both directions. Input type 2 accepts 2-wire proximity sensors. Group error via SF LED.