The resistance strain-type weighing sensor operates based on the principle that an elastic body (elastic element, sensitive beam) undergoes elastic deformation under external force, causing the resistance strain gauge (conversion element) attached to its surface to also deform. After the resistance strain gauge deforms, its resistance value will change (increase or decrease). Then, the corresponding measurement circuit converts this electrical resistance change into an electrical signal (voltage or current), thus completing the process of converting external force into an electrical signal.
From this, it can be seen that resistance strain gauges, elastomers, and detection circuits are essential components of resistance strain-type weighing sensors. An elastomer is a structural component with a special shape. It has two main functions: firstly, it bears the external force acting on the weighing sensor, generating a reactive force to achieve relative static equilibrium. Secondly, it generates a high-quality strain field (zone), enabling the resistance strain gauges attached to this zone to perform the conversion of strain to electrical signals more accurately.
Using the elastic body of the cantilever beam series weighing sensor from Shanghai Zhizhan Measurement and Control as an example, let's introduce the stress distribution.
Consider a rectangular cantilever beam with perforations. The center of the bottom of the borehole is subjected to pure shear stress, but tensile and compressive stresses will occur in the upper and lower parts. The principal stress directions are tension and compression. If a strain gauge is attached here, the upper half of the strain gauge will be stretched, causing its resistance to increase, while the lower half of the strain gauge will be compressed, causing its resistance to decrease. Below is a list of strain expressions for the center point of the bottom of the borehole, without further derivation.
Detection Circuit
The function of the detection circuit is to convert the electrical changes of the resistance strain gauge into voltage output. The Wheatstone bridge is widely used in weighing sensors because it has many advantages, such as suppressing the influence of temperature changes, suppressing lateral force interference, and easily solving the compensation problem of weighing sensors.
Since the sensitivity of a full-bridge equal-arm bridge is the highest and the parameters of each arm are consistent, the effects of various interferences are easily offset. Therefore, weighing sensors typically use the full-bridge equal-arm bridge.
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