Development of a New Type Non-contact Speedometer

Chen Zhaozhang Yang Zhenglin (Jiangsu University of Science and Technology)

Instrument, Sensor, Filter, Microprocessors

Before 1990's, a five wheel meter was widely used to check vehicle travel performance. As a sensor, the test wheel was not convenient in use, low in precision and narrow in check range. In this paper, the photo electrical, non contact test technology was used and a narrow bandwidth follow up filter that supported the technology was designed. Its bandwidth was 0 2 f s , and the center frequency of the passband f n changed with the signal frequency f s . The follow up acceleration of the filter reached 2 g . The problem of the electromagnetic interference caused by a high vehicle speed and a wide signal frequency band was resolved effectively, which was not surmounted by a common band pass filter. Through amplifying, limiting and shaping circuits, the variable output signal of the photo electrical, non contact sensor became a pulse packet that was adaptable to a microcomputer. Then the speed, acceleration and travelling distance of the checked vehicle were calculated by the software. According to this technology a new type non contact speedometer was developed and the commercial products have been used for years. As a the matter of fact, the speedometer is reliable, convenient and high in precision.