Calibration of Stopwatches by Utilizing High Speed Video Recordings and a Synchronous Counter

Abstract

Abstract:A new method for the calibration of stopwatches, called video totalize method, has been developed at the Hong Kong Standards and Calibration Laboratory (SCL). The method starts with the taking of two short video clips of the display of the stopwatch under test, together with the reading of an in-house designed synchronous counter, with the two clips separated by an interval of six to seven hours. The 10-digit synchronous counter is driven by a 1 kHz clock which is phase locked to the cesium frequency standard of SCL. The elapsed times measured by the stopwatch and the synchronous counter are obtained by viewing the recorded video to search frame-by-frame for the instant at which the reading of the stopwatch changes. Using this method, the measurement uncertainty is no longer constrained by the display resolution of the stopwatch, but instead is limited only by the frame rate of the video recording. Digital cameras that can record video at 420 frames per second with usable image quality are commer...