IEC 61869-13:2021 is a product standard and covers only additional requirements for stand-alone merging units (SAMUs) used for AC applications having rated frequencies from 15 Hz to 100 Hz. The digital output format specification is not covered by this document; it is standardized in IEC 61869-9 as an application of IEC 61850, which specifies the power utility communication architecture. This document covers SAMUs having standardized analogue inputs (for example: 1 A, 5 A, 3,25 V / √3 or 100 V / √3) provided by instrument transformers compliant with relevant product standards (e.g. IEC 61869-2 to IEC 61869-5, IEC 61869-7, IEC 61869-8, IEC 61869-10, IEC 61869-11, IEC 60044-1 to IEC 60044-6, IEC 60185, IEC 60186, IEEE C57.13), and aims to convert them to the digital output compliant with IEC 61869-9. Other input and output types are outside the scope of this document. Appropriate SAMU functionality can be combined with switchgear controller functionality defined in IEC 62271-3 or other IED functionality defined in IEC 60255 (all parts). Cyber security requirements are outside the scope of this document and are covered by the IEC 62351 series. IEC 61869-13:2021 is to be used in conjunction with IEC 61869-9:2016, Digital interface for instrument transformers, and IEC 61869­6:2016, Additional general requirements for low-power instrument transformers, which, in turn, are based on IEC 61869-1:2007, General requirements.