Siemens 6ES7321-7RD00-0AB0 SIMATIC S7-300 SM 321 4xDI NAMUR Ex Hazardous Area PLC I/O Module

The Siemens 6ES7321-7RD00-0AB0 is a SIMATIC S7-300 SM 321 digital input module with 4 isolated NAMUR inputs per DIN 19234, built to bring signals from a hazardous area into the control system. It runs from an internal 8.2 V DC supply circuit, is PTB tested under number Ex-96.D.2094X, and carries an ATEX II 3 G (2) GD Ex nA [ib Gb] [ib IIIC Db] IIC T4 Gc marking.

Technical Specifications

Selection Notes

The NAMUR two-wire interface distinguishes signal states by current draw (0.35-1.2 mA for signal 0, 2.1-7 mA for signal 1) rather than voltage, which is what lets this module read proximity switches and sensors mounted inside the classified area itself. Its Ex(i) limits (Uo 10 V, Io 14.1 mA, Po 33.7 mW) size the loop for gas group IIC — the tightest of the standard groups — so it also covers IIB and IIA installations. The parameterizable 0.1-20 ms input delay lets a project trade noise immunity against response speed per channel group, which matters when some inputs are fast limit switches and others are slower level sensors on the same module.