Dimensional Metrology Group

The Dimensional Metrology Group (683.01) in the Semiconductor & Dimensional Metrology Division (683) of the Physical Measurement Laboratory (PML) at the National Institute of Standards and Technology (NIST) realizes and disseminates the SI units of length, concentrates on dimensional measurements in the range of one millimeter to several kilometers, and provides the delivery of those measurements, standards and infrastructural technology services that promote U.S. innovation and industrial competitiveness. We use general and special-purpose feature and coordinate measuring systems for measurements of complex shape, such as, turbine blades, threaded fasteners, and gears, and coordinate measuring machines and frameless coordinate length-metrology systems for mechanical-probe, laser-ranging, theodolite, and related interferometric systems. We perform research into advancing the state of the art of coordinate dimensional metrology and developing a method to quantify the performance evaluation of dimensional measurement instrumentation. We actively support international and national dimensional metrology standards committees by our participation and leadership and with emphasis on rigorous uncertainty evaluation.

Large-scale Coordinate Metrology: technology for large-scale measurements (L > 1 m) has had a tremendous growth over the last 5 years and is the primary focus for this project. Our efforts have focused on developing and standardizing the adoption of these new methods by testing and validation of new technology and development of uncertainty budgets. We are also very active in standards bodies such as ISO and ASME to develop acceptance tests that are acceptable to both buyer and seller.

Large-scale Coordinate Metrology Activities:

	Calibrations and Special Tests—Our objective is to provide US industry with very high accuracy length calibrations with rapid turnaround time.
	National and International Standards—The LSCM Group leverages its expertise in dimensional metrology through participating in national and international standards development.
	Research Activities—Our goal is to continuously improve the accuracy of our measurements, develop new characterization techniques, and provide industry with technical information.

Optical Frequency Comb and Refractometry: length measurement accuracy originates with the realization of the SI meter via the wavelengths of stabilized lasers used for interferometer-based length measurement. This project will enable the Dimensional Metrology Group to realize the meter more accurately, at multiple optical wavelengths, using the optical frequency comb. Currently, corrections to the laser wavelength for the refractive index of air are a significant source of uncertainty in all of our basic calibrations. The development of an absolute refractometer will reduce the uncertainty to one part in 10^-8, effectively removing this significant source of uncertainty.

Micro-feature Measurement System Development: parts with small features (0.05 mm to 1 mm) are becoming increasingly important to our economy, but systems for their measurement are still in their infancy. We currently have measurement systems with unique capabilities, providing accuracy beyond the commercial state-of-the-art, for measurements of fluid flow nozzles, radiometric apertures, optical fiber ferrules and micro-volume standards. This year we have two new microprobes for our high-accuracy coordinate measuring machine. The new probes employ completely different technologies from our three existing probe systems; characterizing and comparing the five probing systems will provide a very high level of assurance that we understand the capabilities and limitations of the various probing technologies.

Ongoing Reimbursable Dimensional Calibrations and Quality System: provides industry with high accuracy dimensional measurements within an internationally accepted quality system. Either our measurements provide results that are of very high value to our customers or high leverage into the industrial metrology community, that is, a single calibration may propagate into hundreds or thousands of subsequent measurement results. In addition, there is a focus on continuous improvement of these services with incremental gains in accuracy and efficiency.

Selected Publications on Dimensional Metrology:

	Gage Blocks
	Uncertainty and Statistics
	Other Calibrations
	Measurement Assurance
	20-Degree Celsius Paper