National optical density standards: Principles of optical scheme implementation, designs, and metrological characteristics

The article describes the current metrological support for precision optical density measurements. In order to analyze the principles of optical scheme implementation, structural, design, and operating characteristics of the elements comprising measurement standards, as well as the metrological characteristics of national optical density standards, the author considers high-precision optical density measuring instruments developed by the national metrology institutes of Russia, Germany, China, and the USA. Measurement equations for calculating optical density are presented, i.e., a mathematical model representing the process of measuring the transmittance density of materials. The article describes the operating principles of transmittance density standards relying on luminous flux filtering. Research data on the geometric and spectral characteristics of five national optical density standards used in four countries are presented, as well as an analysis of the optical schemes and characteristics of measurement standards in terms of the following aspects: compliance with international standards; characteristics of optical schemes; methods of luminous flux filtering and creation of diffuse radiation; specifics of object positioning; radiation detector type; metrological characteristics. Data on the international comparisons of national measurement standards are given. The metrological characteristics of these national measurement standards are summarized in a table. Consideration and use of the examined characteristics of optical schemes and design solutions together with the metrological characteristics of the described instruments contribute to a more advanced improvement of GET 206-2016 State Primary Optical Density Standard.