This standard relates to definitions, test methods, and procedures for ionizing radiation measurement systems designed for either continuous or discrete measurements and checks of mass per unit area, mass per unit length, or thickness of materials produced in industrial processes. The measured process material may be in such forms as sheets, coatings, laminates, tubes, or rods. This standard applies to systems with one or more outputs for display or control purposes. The signals 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. Safety aspects are covered in other IEC and ISO standards (for example IEC 405, ISO 2919, ISO 7205). Consideration will also be given to compliance with all applicable national and local regulations and codes of practice. Thickness measurement systems which are the object of this standard are generally built for industrial applications covering a very broad range of industries, applications, and specifications. The objective is to identify the common parameters and variables, and to specify standard tests and documentation that will facilitate direct comparison of the performance characteristics of the different measurement systems which are available. These tests are applicable to systems with either fixed or traversing measuring heads and with transmission, backscatter, or X-ray fluorescence sensors. Many ionizing radiation measurement systems in use today have multiple sensors, and employ various means of compensating the basic sensor signals to minimize the effects of extraneous influence quantities that introduce measurement errors. Dedicated microprocessors and minicomputers have further enhanced multiple input signal processing and error compensation techniques. In the more complex systems, it is difficult to fully evaluate the effectiveness of interactive signal processing and compensation algorithms by static testing. For example, the response times and data collection times for sensors, whose signals are to be combined in some analytical function, are of little importance under the static testing conditions in this standard, but they can lead to large errors under dynamic measuring conditions if they are not properly matched. The relative magnitude of the influence quantity errors to be compensated is also quite important. The compensation means for sensors with high sensitivity to influence quantities should be more precise than for sensors which exhibit smaller errors in order to achieve the same overall results. Therefore, it is necessary to have performance tests, in the standard, which may include all the interactive signal processing and compensations. This has been facilitated in this standard by identifying different test points throughout the measurement system under evaluation.It is important to estimate the potential performance degradation in adverse environments. Although it is difficult to duplicate exactly the influence of long-term and short-term process conditions during a limited test period, this set of procedures includes some artificially introduced environmental disturbances. In this standard the term “thickness” is used interchangeably to mean mass per unit area, mass per unit length, or thickness. Radiometric sensors, in general, measure mass per unit area and the output signals can be expressed in true thickness units only if the effective atomic number and density of the material being measured are known, or if the system is calibrated against actual production samples, and if the effective atomic number and density of the material produced do not change relative to those samples. In the case of rod-shaped products, with a known or constant cross-sectional area, the output signal may be expressed in terms of mass per unit length. NOTE – It is recommended that the reader refers to the block diagram of annex B for a better understanding of the specification.