Weigh in motion
Encyclopedia
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 station
s, 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.
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.
Known applications are
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.
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.
Weigh station
A weigh station is a checkpoint along a highway to inspect vehicular weights. Usually, trucks and commercial vehicles are subject to the inspection....
s, 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.
Road applications
Especially for trucks gross vehicle and axle weight monitoring is useful in an array of applications including:- Pavement design, monitoring, and research
- BridgeBridgeA bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...
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.
Rail applications
Weighing in Motion is also a common application to railtransport.Known applications are
-
- Infracharging
- Asset protection (imbalances, over loading)
- Asset management
- Maintenance planning
- Legislation and regulation
- Administration and planning
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 gaugesStrain gaugeA strain gauge is a device used to measure the strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable...
: 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
- load cellsLoad cellA load cell is a transducer that is used to convert a force into electrical signal. This conversion is indirect and happens in two stages. Through a mechanical arrangement, the force being sensed deforms a strain gauge. The strain gauge measures the deformation as an electrical signal, because the...
: Measuring the strain change in the load cell rather than directly on the rail itself. - laserLaserA laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
based systems: measuring the displacement of the rail
Yards and main line
Trains are weighed, either on the main line or at yards.Weighing in Motion systems installed on the main lines
Main line (railway)
The Mainline or Main line of a railway is a track that is used for through trains or is the principal artery of the system from which branch lines, yards, sidings and spurs are connected....
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
Rail yard
A rail yard, or railroad yard, is a complex series of railroad tracks for storing, sorting, or loading/unloading, railroad cars and/or locomotives. Railroad yards have many tracks in parallel for keeping rolling stock stored off the mainline, so that they do not obstruct the flow of traffic....
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.
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.