NIST helping to Improve Speed Measurements for Cars, Bullets (May 22, 2009) — The Office of Law Enforcement Standards (OLES) at the National Institute of Standards and Technology (NIST) has developed the two devices—down-the-road (DTR) radar used in speed enforcement and the ballistic chronograph, which measures the speed of bullets — soon should be more useful tools for police officer.

nistThe NIST researchers John Jendzurski and Nicholas Paulter examined the four methods commonly used by law enforcement officers to calibrate DTR radar devices and, for each one determined the uncertainty it places on the measurement of a moving target.

The calibration methods studied included a radar target simulator, tuning forks, a calibrated speedometer and a fifth wheel.

Based on the data they obtained, the researchers developed the uncertainty measurement formulas for each calibration method. These formulas will help DTR radar users clearly understand the impact of proper calibration for making accurate speed measurements.

In the second OLES publication, researchers Donald Larson and Nicholas Paulter developed a ballistic chronograph—an instrument used to measure of the velocity of a fired bullet—that is 20 times more precise than a typical manufacturer-provided chronograph.

The new instrument has an uncertainty of only ± 0.2 meters per second compared to ± 4 meters per second for a bullet travelling 400 meters per second.

The NIST chronograph may be used as a reference standard to calibrate and/or characterize the performance of chronographs available on the market.

Law enforcement agencies and the military use chronographs during the testing of ballistic resistant body armors because their effectiveness is determined by how many bullets fired at specific velocities perforate or don’t perforate the protective gear.

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