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Speed Measurement
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 always requires more than one sensor subsystem, at least two of them. The simplest method of measuring speed is measuring the time between detection of an axle by two sensors of known distance by means of a clock. SENSOR LINE's fiber optic axle sensors are an excellent means for this, due to their exact response to the wheels' pressure and their insensitivity to pavement deformations and vibrations. Speed enforcement systems always use more than two sensors (up to four) for reasons of evidence. But the need for speed measurement is not restricted to trapping speeders. All road traffic applications more sophisticated than simple axle detection and counting make use of speed measurement as part of the measuring process.
Speed measurement can also be done without starting and stopping a clock. One alternative method is to determine the time delay between two similar events by means of cross-correlation. This is especially adequate in cases where these events are better described as being processes which last relatively long compared to their delay. For speed measurement with axle sensors this happens when the sensor distance approaches the dimensions of the area where tires touch the pavement. Making it that small enhances reliability where slow speeds occur, e.g. in urban districts and traffic restraint zones. SENSOR LINE offers a correlation-based speed measuring process (TKV process) which makes use of the special characteristics of fiber optic axle sensors and gives access to completely new problem solutions. |
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