Improvement of Electric Stop Watch

Abstract

Stop watch is widely used as it can measure a comparatively short time accurately an dsimply. In the testing of watt-hour meters, the measurement of time is necessary and the accuracy of 0.1% has been aimed in 100 seconds measuring. But the error of stop watch is not less than 0.1 second for its mechanism.
As the electric stop watch drived by the constant frequency oscillator operates continuously, it has such advantages as high accuracy and low cost. It has been researched and put into practical use since many years ago, yet the time lags in its starting and stopping are pointed out as its defect. They are caused by the use of mechanical damper and bevel gear. Described in this paper, therefore, is the improvement of electric stop watch by using electric damper and simplified gear mechanism. In the improved watch, the time lags in starting and stopping are both about 0.01 second and the difference between them is oniy 0.002-0.005 second. In consequence, the resultant error is within ±0.05second. As to its aging, the result of some experiments shows that it can keep sufficient stability even in long-time use.