The essence of any weighing system is a load cell. These load cells are precision transducers which provide general information, clear, precise and concrete, which can not be obtained by other technological means. This load cells are designed to take the force or weight under a wide range of conditions. In order to get the most benefits from a load cell, the user should have a basic and deep knowledge regarding technology, construction and operation of the device used.
The load cell is one of the most important elements of an electronic or digital scale, it is responsible for translating the force into a voltage signal (analog load cell) or into a digital value (digital load cell). The analog load cell strain gauge is the most widely used. In addition, we must take into account the type and selection of the correct load cell for the application you want to use, so it will provide the correct information; also, we must have a care in the use of the load cell during its lifetime. Before the tension load cells became the primary method of measurement applications, the mechanical scales were widely used; they can weigh everything you want using the correct cell, where they may be weighing from one gram of gold to tons or anything that is required to have an accurate weight and can do it accurately. The operation method may involve the use of a weight balancing mechanism or detecting the force generated by mechanical levers.
The first force sensors previous calibration voltages were hydraulic and pneumatic designs. In 1843, the English physicist Sir Charles Wheatstone devised a bridge circuit that could measure electrical resistances. The Wheatstone bridge circuit is ideal for measuring resistance changes occurring in the tension calibration. The first set of weight resistance welded tension was created 1940, but it was not until modern electronics came, the new technology and technique became economically feasible at that time.
At present , except for some laboratories that are still using mechanical precision scales , load cells dominate the industry voltage measurement weight .
A load cell usually consists of four strain gauges connected in a bridge-like, you can purchase load cells with only one or two strain gauges. The electrical signal output is typically on the order of a few millivolts and must be amplified by an instrumentation amplifier before it can be used. The transducer output after being amplified is processed by an analog / digital converter, this conversion is applied and a suitable algorithm is achieved so it is possible to calculate the force applied to the transducer. The load cells are manufactured measures on specific conditions with either a metal alloy steel or stainless steel, and the metal is deformed as a force is applied. This metal is calculated to withstand a force range (from 0 to the maximum force). The deformation takes place in the “elastic part” that is limiting the capacity of a load cell. Upon exceeding the elastic metal part suffers permanent deformation and a spring that is stretched over and no longer returns to its starting point (when it detects zero force).
The cells consist of a metal that varies its resistance to bending. Cells are connected in a Wheatstone bridge arrangement, by feeding deliver a voltage signal proportional to the force applied voltage. The voltage signal is delivered in millivolts. This voltage is proportional to the supply voltage and maximum load.
The cell signal is fed to a digital/analog indicator, it will convert to a digital numeric value, this value is multiplied by a factor to make it as weighing units kg, lb, etc.; scales measure the force generated by an object and as the Force equals mass times acceleration (F = ma) and the acceleration is a constant (the gravity of the earth) can be said that the mass is directly proportional to the force. The factor which is set to a gain calibration will give us an accurate data.