Applies to all systems which utilize ionizing radiation for continuous measurement or detection of the level of materials in vessels. The process material may be liquid or a solid in the form of grains or powder and the output signal may be either continuous or switched. Safety aspects are covered in other IEC and ISO standard. The systems covered by this standard are generally built for industrial applications covering a very broad range of industries, applications and specifications. The aim is to define the common parameters and variables and to specify standard tests which facilitate direct comparison of the performance characteristics of the different measurement systems which are available. The signal processing for these measuring systems may be analogue, digital or a combination of both.