A scale is a device that, according to the dictionary of the Royal Spanish Academy ( RAE ), is used to measure weights . The term comes from the French word bascule .
Scales, therefore, are balances : devices that allow weighing. The act of weighing, in turn, refers to determining the mass or weight of a body .
Scales usually have a horizontal surface on which the items to be weighed must be placed. Thanks to their structure, it is possible to know the weight of very heavy objects, something that was impossible with the old instruments that required hanging the things to be weighed.
There are various types of scales. Broadly speaking, it is possible to differentiate between electronic scales and mechanical scales .
Electronic scales have load cells : sensors with metal parts attached to strain gauges that, when compressed, modify their electrical resistance and allow weight to be measured. These scales display the weight in question on a screen.
In the case of mechanical scales, they are usually equipped with an elastic spring nowadays. In the past, however, they worked with levers and measured the weight indirectly through a counterweight .
It is important to note that, although they are used as synonyms, there are differences between mass and weight . Mass refers to the amount of matter in a body and is expressed in grams , while weight reflects the action of the force of gravity on the body and is indicated in newtons . Depending on their characteristics, scales specifically measure mass or weight.
Bathroom scales are used in many homes. People who care about their physical appearance often combine physical exercise with a balanced diet and, to control their weight, place a scale in the bathroom to keep an eye on any irregularities.
On the other hand, there is the so-called weighbridge , a fundamental tool for measuring the weight of heavy vehicles, such as trucks, tractors, train wagons, dump trucks and even aircraft . At first glance, it consists of a platform made of metal or concrete that is placed on top of interconnected load cells. The latter are linked to a summing box, from which the electrical signal is sent to a terminal where the weight of the object can be seen.
The most sophisticated weighbridge models also have access barriers, card readers, elements to correctly position the vehicle, traffic lights and devices to identify the license plate, among other features. Before use, they must go through a legal process of verification, sealing and approval by an authorized body. In Spain, for example, there are some public companies that depend on the Government that provide this service . Sometimes, certain private entities can also provide it.
Among the technical features of a scale of this type, we can highlight the following:
* As expected, it must be able to withstand a really considerable load, amounting to tens of tons;
* the readings must give reliable results, as the weight of vehicles is closely linked to traffic regulations . For example, it is not possible to use a bridge or highway with a truck of any weight, but there is a limit to avoid wear and tear;
* must have a work platform with sufficient width for the different types of vehicles;
* One of the most important points is that the measurement should not be affected by meteorological phenomena, such as humidity, rain and atmospheric pressure.
In the military field, finally, a scale is a machine used to raise a drawbridge .