Weigh in motion
Weigh-in-motion or Weighing in Motion (WIM) devices are designed to capture and record axle weights and gross vehicle weights as vehicles drive over a measurement site. Unlike older static weigh stations, current WIM systems are capable of measuring at normal traffic speeds and do not require the vehicle to stop or drive at low speed, making them much more efficient.
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[edit] Road applications
Especially for trucks gross vehicle and axle weight monitoring is useful in an array of applications including:
- Pavement design, monitoring, and research
- Bridge design, monitoring, and research
- Size and weight enforcement
- Legislation and regulation
- Administration and planning
Recent years have seen the rise of several "specialty" Weigh in Motion systems. The most popular of these is the front fork garbage truck scale. In this application, a container is weighed—while it is full—as the driver lifts, and again—while it is empty—as the container is returned to the ground. The difference between the full and empty weights is equal to the weight of the contents.
[edit] Rail applications
Weighing in Motion is also a common application to railtransport. Known applications are[1]
- Infracharging
- Asset protection (imbalances, over loading)
- Asset management
- Maintenance planning
- Legislation and regulation
- Administration and planning
[edit] System's basics
The measurement systems are divided into two main parts: the track side and rail mounted components. The track side equipment contains hardware for communication, power, computation, data acquisition etc. The rail mounted part consists of the actual sensors and cabling. Known sensor principles are:
- strain gauges: measuring the strain usually in the hub of the rail
- fiber optical sensors: measuring a change of light intensity caused by the bending of the rail [2]
- load cells: Measuring the strain change in the load cell rather than directly on the rail itself.
- laser based systems: measuring the displacement of the rail
[edit] Yards and main line
Trains are weighed, either on the main line or at yards. Weighing in Motion systems installed on the main lines measure the complete weight (distribution) of the trains as they pass by at the designated line speed. Weighing in motion on the mainline is therefore also referred to as "Coupled in motion weighing": all of the railcars are coupled. Weighing in Motion at yards often measure individual wagons. It requires that the railcar are uncoupled on both ends in order to weigh. Weighing in Motion at yards is therefore also referred to as "Uncoupled in motion weighing". Systems installed at yards usually works at lower speeds and are capable of higher accuracies.
[edit] Air applications
In addition to trucks and railcars, airplane weighing is in use in some airports, whereby the plane taxis acros the scale bed, and its weight is measured. The weight may then be used to correlate with the pilot's log entry, to ensure there is just enough fuel, with a little margin for safety. This has been used for some time to conserve jet fuel.
Also, the main difference in these platforms, which are basically a "transmission of weight" application, there are checkweighers, also known as dynamic scales or in motion scales. There is more information at Checkweigher.
[edit] References
- ^ Buurman, Gerlof and Zoeteman, Arjen. "A vital instrument in asset management", Europen Railway Review, Issue 3, 23 August 2005.
- ^ Gotcha Monitoring Systems "Longer life for track and rollingstock", EurailMag, Issue 22, September 2010.
