IEC 61831:2011(E) is a guide applicable to on-line analyser systems. It provides the necessary guidance for the system supplier and user to specify or design a complete analyser system from sample point in the process to the final output for display or control purposes. This second edition cancels and replaces the first edition published in 1999. This edition constitutes a technical revision. The main changes with respect to the previous edition are: - Updated references; - Made consistent with current practices and regulations; - Incorporating new technologies where applicable.