Basic principle of load cell - Solutions - Huaqiang Electronic Network

inductance

When an external force is applied to the elastic body—also known as the sensitive beam—it undergoes elastic deformation. This deformation causes the strain gauge, which is attached to its surface, to also deform. As the resistance strain gauge stretches or compresses, its resistance value changes, either increasing or decreasing. This change in resistance is then converted into an electrical signal by a measurement circuit, effectively transforming the applied force into an electrical output. Therefore, the strain gauge, the elastic body, and the detection circuit are all essential components of a resistance-type load cell. Below is a more detailed explanation of each part.

1. Resistance Strain Gauge A resistance strain gauge consists of a thin metal wire or foil that is bonded to a flexible organic substrate. One of the key parameters of a strain gauge is its sensitivity coefficient, denoted as K. When force is applied, the gauge elongates, causing the cross-sectional area to decrease and the radius of the wire to shrink. The change in resistance is directly proportional to the relative change in length of the wire. It's important to note that the sensitivity coefficient K is a material-dependent constant and does not vary with the size or shape of the strain gauge. Different materials have K values ranging from approximately 1.7 to 3.6. Since K is dimensionless, it has no units. In mechanics, the ratio of ΔL/L (change in length over original length) is called strain and is usually denoted by ε. To make it easier to handle, strain is often expressed in microstrain (με), where 1 με equals 10⁻⁶.

2. The Elastic Body The elastic body, or elastomer, is a specially designed structural component that serves two main purposes. First, it supports the external force applied to the load cell and generates a counteracting force, maintaining static equilibrium. Second, it provides a consistent and uniform strain field in the area where the strain gauges are mounted. This ensures that the strain gauges can accurately measure the deformation, allowing for efficient conversion of mechanical force into an electrical signal.

3. Detection Circuit The detection circuit is responsible for converting the small resistance changes in the strain gauge into a measurable voltage output. Among various circuit configurations, the Wheatstone bridge is widely used due to its advantages, such as temperature compensation, suppression of lateral forces, and ease of calibration. In load cells, a full-bridge configuration is typically employed because it offers the highest sensitivity, with all arms having equal resistance values. This setup helps cancel out disturbances and improves overall accuracy and stability.