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How the loadcell works
The elastic body of the loadcell (elastic element, sensitive beam) is elastically deformed under the action of external force, so that the resistance strain gauge (conversion element) pasted on its surface is also deformed. After the resistance strain gauge is deformed, its resistance value will occur. Change (increase or decrease), and then convert this resistance change into an electrical signal through the corresponding measuring circuit, thus completing the process of converting the external force into an electrical signal. It can be seen that the resistance strain gauge, the elastic body, the detection circuit, and the transmission cable are the indispensable main parts of the resistance strain loadcell.
1. Detection circuit
The function of the detection circuit is to convert the resistance change of the resistance strain gauge into a voltage output. Because the Wheatstone bridge has many advantages, such as it can suppress the influence of temperature changes, can suppress the lateral force interference, and can easily solve the compensation problem of the loadcell, so the Wheatstone bridge can be obtained in the loadcell. a wide range of applications.
Because the full-bridge equal-arm bridge has the highest sensitivity, the parameters of each arm are the same, and the influence of various interferences can easily cancel each other, so the loadcells all use the full-bridge equal-arm bridge.
An elastomer is a structural member with a special shape. It has two functions. First, it bears the external force of the loadcell, and generates a reaction force to the external force to achieve relative static equilibrium; The resistance strain gauge is ideal to complete the transformation of the electrical signal of the strain.
3. Resistance strain gauge
A resistance strain gauge is a resistance wire mechanically distributed on a substrate made of an organic material, that is, a strain gauge. One of his important parameters is the sensitivity coefficient K. When its two ends are subjected to F force, it will elongate, that is to say, deform. Assuming that it is elongated, its cross-sectional area is reduced, that is, its cross-sectional circle radius is reduced. The proportional relationship between the resistance change rate (relative change in resistance) of a resistance strain gauge and the elongation rate (relative change in length) of the resistance wire. It should be noted that the K value of the sensitivity coefficient is a constant determined by the properties of the metal resistance wire material. It has nothing to do with the shape and size of the strain gauge. The K value of different materials is generally between 1.7 and 3.6; Secondly, the K value is a dimensionless quantity, that is, it has no dimension. In the mechanics of materials, ΔL/L is called strain and is denoted as ε. It is often too large to express elasticity, which is very inconvenient. It is often used as a unit of one millionth and denoted as με.