Traceable measurements of speed

Speed is important to measure both when it comes to vehicles and industrial processes. One example in industrial processes is to measure the speed of production lines to indirectly calculate how much has been produced.

There are several methods of measuring speed. For larger objects or vehicles, radar or laser are most common. For vehicle-borne systems, inertial navigation with accelerometers and gyroscopes combined with GNSS (Global Navigation Satellite Systems such as GPS or European Galileo) is state of the art. Industrial processes are usually measured with encoders, equipment that is attached directly to or built into moving parts. Camera-based technology is also common both for vehicles and industrial processes.

Weak traceability to SI

Common to all methods is weak traceability to SI. The methods are often validation rather than calibration. There is also a lack of standards that can be used to compare different speed measuring systems with each other.

Accurate measurements of speed require accurate measurements of both time and length. But even if it is possible to measure both time and length with very low measurement uncertainty, speed measurements are complicated and often have high measurement uncertainty. This is because, for example, the time that an object's speed can be measured is limited and often not possible to repeat. Comparative measurements are also complicated as the systems must be coordinated in time and space.

RISE has previously developed a traceable reference system to be able to verify Sweden's system for automatic traffic safety control, i.e. speed cameras. But the need for traceable speed measurements is great from industry and business and currently there is a lack of equipment to be able to meet these needs.

A speed standard

The principle of a speed standard or reference is simple. The system needs to contain something that moves at a well-defined and known speed, with traceability to both length and time. During calibration, the speed of the standard is measured with the equipment to be calibrated, and then the measured value is compared with the known speed in the system. In practice, it is more difficult than it sounds. Speed standards with established measurement uncertainty and traceability chain are currently missing in the literature and BIPM's database does not contain any approved calibration methods for speed.

The goal is therefore to investigate two principles for speed standards, choose based on practical feasibility and measurement uncertainty and then construct the speed standard, evaluate and disseminate the results. The speed standard must be able to realize different speeds to be able to verify different existing reference systems for speed measurement and other speed measuring instruments.