SSI sensor interface for S7-300 racks
The Siemens 6ES7338-4BC00-0AB0 is a SIMATIC S7-300 signal module purpose-built to read position values from up to three SSI absolute encoders, with two additional digital inputs configurable as freeze inputs to capture simultaneous position snapshots. It operates on a 24 V DC load voltage (L+ minus 0.8 V) and draws a typical 3 W from the backplane bus, plus up to 160 mA from the 5 V DC backplane supply.
Cable-length budget at clock speed
The SSI clock frequency is programmable up to 1 MHz, but the maximum shielded cable length drops with frequency: 320 m at 125 kHz, 160 m at 250 kHz, 60 m at 500 kHz, and 20 m at 1 MHz. For a 600 m cable run at lower data rates, the module supports that length when clocked below 125 kHz.
It requires a 20-pin front connector (sold separately) and supports 2-wire sensor connections on the digital inputs.