Fundamentals of Metrology

The area "Fundamentals of Metrology" covers the work as defined in the Statutes for the realization and dissemination of the SI units and of legal time. These activities encompass in particular the development and provision of primary standards and standard measuring devices as well as of the secondary and transfer standards needed for the dissemination of the units. The mission is "to provide the foundation for the national metrology system, which meets the present and foreseeable future requirements".

Especially challenging is the task to provide traceability of the SI units to fundamental constants, as has already succeeded for the second, the metre, the volt and the ohm, because, at least in our present understanding of physics, it can then be assumed that the individual units have been realized independently of location and time. The decision of the Comité International des Poids et Mesures (CIPM) to initiate preparatory measures for the redefinition of the units ampere, kelvin, kilogram and mole on the basis of natural constants has conferred additional topicality and importance to these activities. The central point of origin, thereby, is the precise determination of the values of the underlying fundamental constants. Here, too, the PTB makes a considerable contribution in the form of very complex experiments (Avogadro constant, Boltzmann constant). But also for the realization of units on the basis of classical principles, e.g. for dimensional metrology, the requirements for tolerable uncertainties increase permanently so that the existing technologies must be improved or new technologies be developed. Of increasing importance is the traceability of measurements in analytical and especially in clinical chemistry to internationally recognized standards or standard measuring devices developed and operated at the PTB and by its cooperation partners (BAM, UBA, DGKL) for selected organic and anorganic analytes. Of particular importance to society is the development of standards and standard measuring devices for medical diagnostics and therapy followup, for example for the dosimetry of ionizing radiation, ultrasound diagnostics or optical, bioelectric, biomagnetic and NMR diagnostic methods.

Not only in the case of modern production engineering is the field of nanometrology gaining increasingly in importance, encompassing not only the quantitative dimensional determination of micro or nanostructures with a resolution in the range of a few atomic diameters but also that of macroscopic objects, e.g. lens or mirror systems for lithography with atomic resolution. For these applications, the PTB develops and advances various measurement procedures such as scanning probe microscopy, optical microscopy including optical near field microscopy, electron microscopy and interferometry, which partly supplement one another.

The development and manufacture of standards for electric voltage on the basis of superconductors (Josephson effect) was moved forward very significantly due to ongoing work in the PTB. Through successful technology transfer, space for expansion was created for new challenges such as, e.g., the development of programmable voltage standards for ac applications or the development of elements and circuits for quantum-limited measurement processes. Now that the PTB, with its cooperation partners (NRC (Canada) and METAS (Switzerland)), has achieved a breakthrough also with the ac quantum Hall effect, the electric impedance measurement up to frequencies into the kHz range can also be traced back with fundamental accuracy to the von Klitzing constant.

The list of promising topics from the field of "Fundamentals of Metrology" could be continued almost endlessly - from the realization of the force scale in the range of very small and extremely great forces to frequency standards for future optical atomic clocks, enhanced standards for photometry and the dosimetry of ionizing radiation to the realization of the temperature scale at very deep and very high temperatures.

In the area "Fundamentals of Metrology", the share of research and development is very large, covering essential fields of modern natural and engineering sciences. The results not only provide the prerequisite for the development and realization of precise standards but also furnish – often in cooperation with university and non-university partners – important findings for the natural and engineering sciences in general.