This document specifies parameters for the design and usage of axle counter systems. For this, this document specifies the technical parameters of axle counter systems associated with the magnetic field limits for RST in the context of interoperability. In addition, test methods are defined for establishing the conformity and the performance of axle counter detector. The specified parameters are structured and allocated according to their basic references as follows: axle counter system parameters; train based parameters; track based parameters; environmental and other parameters. Each parameter is defined by a short general description, the definition of the requirement, the relation to other standards and a procedure to show the fulfilment of the requirement as far as necessary. An overview on the safety relevance of each parameter is given in the context of this document in a separate table. This document is intended to be used to assess compliance of axle counter systems and other forms of wheel sensors used for train detection, in the context of the European Directive on the interoperability of the transEuropean railway system and the associated technical specification for interoperability relating to the controlcommand and signalling track-side subsystems. This document can also be used for axle counter systems installed on lines which are not declared as interoperable (including metro and tram lines). For wheel sensors and wheel detectors in other applications than axle counters but utilizing the same sensors on the rail and detection circuits, transient and continuous interference can be considered as equivalent to axle counter detectors or axle counter sensors. The frequency bands and rolling stock emission limits are currently defined in the axle counter FrM as specified in the ERA/ERTMS/033281 document.