This International Standard relates to definitions, test methods and procedures for density gauges utilizing ionizing radiation, designed for measuring the density of liquids, gas vapours, slurries, or fluidized solids. The output signals from density gauges may be either analogue or digital. The measurement system may also include multiple input signals with various means of compensation and signal conditioning prior to the output signals. Reference to compliance with this standard shall identify any deviations and the reasons for such deviations. Safety aspects are covered in other IEC and ISO standards (for example IEC 60405, ISO 2919, ISO 7205, ISO 9978). Consideration should also be given to compliance with all applicable national and local regulations and codes of practice. NOTE 1 Many density measuring systems in use today have multiple sensors (i.e. temperature and pressure) and employ various means of compensating the basic sensor signals to minimize the effects of extraneous influence quantities that introduce measurement errors, or to correct the density reading to a standard reference temperature or pressure. Dedicated microprocessors have further enhanced multiple input signal processing and error compensation techniques. NOTE 2 In this standard, the term "density" means the density of the irradiated material being measured. It is used interchangeably to mean mass per volume or per cent solids. Radiometric sensors in density applications generally measure mass attenuation of a photon beam. The object of this standard is to establish definitions, specifications and test methods for nuclear density gauges.