A Truck scale (US), weighbridge (non-US) or railroad scale is a large set of scales, usually mounted permanently on a concrete foundation, that is used to weigh entire rail or road vehicles and their contents. By weighing the vehicle both empty and when loaded, the load carried by the vehicle can be calculated.
Weight certification in the United States
Commercial scales have to be National Type Evaluation Program (NTEP) approved or certified. The certification is issued by the National Conference on Weights and Measures (NCWM), in accordance to the National Institute of Standards and Technology (NIST), “Handbook 44” specifications and tolerances, through Conformity Assessment and the Verified Conformity Assessment Program
Electronic (deep pit type)
Electronic (pit less type)
Digital (deep pit type)
Digital (shallow pit)
Digital (pit less type)
Mechanical (digital type)
Portable ramp end scales
Scale Design Concept
Truck scales can be surface mounted with a ramp leading up a short distance and the weighing equipment underneath or they can be pit mounted with the weighing equipment and platform in a pit so that the weighing surface is level with the road. They are typically built from steel or concrete and by nature are extremely robust.
In earlier versions the bridge is installed over a rectangular pit that contains levers that ultimately connect to a balance mechanism. The most complex portion of this type is the arrangement of levers underneath the weighbridge since the response of the scale must be independent of the distribution of the load. Modern devices use multiple load cells that connect to an electronic equipment to totalize the sensor inputs. In either type of semi-permanent scale the weight readings are typically recorded in a nearby hut or office.
Many weighbridges are now linked to a PC which runs truck scale software capable of printing tickets and providing reporting features.
Truck scales can be used for two main purposes:
Selling or charging by weight over the bridge (Trade Approved)
Check weighing both axle weights and gross vehicle weights. This helps to stop axle overloading and possible heavy fines.
They are used in industries that manufacture or move bulk items, such as in mines or quarries, garbage dumps / recycling centers, bulk liquid and powder movement, household goods, and electrical equipment. Since the weight of the vehicle carrying the goods is known (and can be ascertained quickly if it is not known by the simple expedient of weighing the empty vehicle) they are a quick and easy way to measure the flow of bulk goods in and out of different locations.
A single axle truck scale or axle weighing system can be used to check individual axle weights and gross vehicle weights to determine whether the vehicle is safe to travel on the public highway without being stopped and fined by the authorities for being overloaded. Similar to the full size truck scale these systems can be pit mounted with the weighing surface flush to the level of the roadway or surface mounted.
For many uses (such as at police over the road truck weigh stations or temporary road intercepts) weighbridges have been largely supplanted by simple and thin electronic weigh cells, over which a vehicle is slowly driven. A computer records the output of the cell and accumulates the total vehicle weight. By weighing the force of each axle it can be assured that the vehicle is within statutory limits, which typically will impose a total vehicle weight, a maximum weight within an axle span limit and an individual axle limit. The former two limits ensure the safety of bridges while the latter protects the road surface.
source : wikipedia