Basic principle of load cell - Solutions - Huaqiang Electronic Network

inductance

The elastic body, also known as the sensitive beam or the elastic element, undergoes elastic deformation when an external force is applied. This deformation causes the strain gauge—also referred to as the conversion element—which is attached to its surface, to deform as well. When the resistance strain gauge is stretched or compressed, its resistance value changes, either increasing or decreasing. This change in resistance is then converted into an electrical signal by a corresponding measurement circuit, effectively transforming the mechanical force into an electrical output. It's clear that the resistance strain gauge, the elastic body, and the detection circuit are all essential components of a resistance strain-type load cell. Let’s take a closer look at each of these elements. 1. **Resistance Strain Gauge** A resistance strain gauge is constructed by mechanically distributing a thin metal wire onto a flexible organic substrate. One of the most important characteristics of a strain gauge is its sensitivity coefficient, denoted as K. When forces are applied to both ends of the gauge, it elongates, causing a reduction in cross-sectional area and radius. The rate of resistance change in the strain gauge is directly proportional to the relative elongation of the wire. Notably, the sensitivity coefficient K is a material-dependent constant and does not vary with the size or shape of the gauge itself. Typically, K values range from 1.7 to 3.6 depending on the material used. Importantly, K is a dimensionless quantity, often expressed in microstrain (με), which is a common unit for measuring strain in engineering applications. 2. **Elastomer (Elastic Body)** The elastomer is a specially designed structural component that serves two key purposes. First, it supports the external force applied to the load cell and generates a counteracting force, helping to maintain static equilibrium. Second, it creates a high-quality strain field in specific areas where the strain gauges are mounted. This ensures that the strain gauges can accurately measure the deformation, allowing the load cell to convert the mechanical input into an electrical signal efficiently. 3. **Detection Circuit** The detection circuit plays a crucial role in converting the resistance changes detected by the strain gauge into a measurable voltage output. Among various circuits, the Wheatstone bridge is widely used due to its advantages, such as its ability to minimize the effects of temperature variations and lateral forces, and its ease in compensating for load cell errors. In particular, the full-bridge configuration is commonly used in load cells because it offers the highest sensitivity and allows for better cancellation of disturbances. All four arms of the bridge have equal resistance, making it more stable and accurate in real-world applications.