Recently updated on September 19th, 2024 at 05:30 am

Load cells are essential devices used to measure force, weight, and load in various applications, converting mechanical force into an electrical signal. While there are multiple types of load cells, strain gauge load cells are the most common due to their high accuracy and versatility. This article provides an overview of how load cells work, with a focus on the principles and operation of strain gauge load cells.

How Load Cells Work

Think of a load cell like a flexible ruler secured at one end. When you push down on the free end, it bends slightly. This bending is similar to how a load cell deforms under an applied force.

When a force is applied to the load cell, it causes a slight deformation. This deformation is very small and not visible to the naked eye, much like how a ruler bends slightly under a gentle force.

Strain gauges, which consist of thin, electrically conductive wire or foil, are tightly bonded to the load cell. Imagine these strain gauges as tiny rubber bands. When the load cell deforms, these “rubber bands” stretch or compress, changing their electrical resistance.

To ensure the spring element deflects with minimal permanent deformation, the deflection must be kept to a minimum. Calculations relying solely on the minute resistance change of a single strain gauge may lack precision and be susceptible to errors. To achieve high accuracy in load cell measurements, multiple strain gauges are employed.

These strain gauges are arranged in a Wheatstone bridge configuration. This setup allows the overall change in resistance across all four strain gauges to be determined using Ohm’s law and appropriate equations. This arrangement compensates for potential errors and enhances measurement precision.

Finally, this electrical signal is processed by signal conditioning electronics, which amplify and convert it into a readable output, indicating the exact weight or force. This process ensures accurate force measurement, making load cells essential in various applications, from weighing scales to industrial machinery.

Load Cell Anatomy and Components

A typical load cell consists of two main parts: the main body and an attached electrical circuit. The main body bears the weight or force and accounts for most of the load cell’s size. It is typically made from high-grade steel or aloy steel, ensuring mechanical reliability and uniform strain distribution.

Housed within the load cell, the electrical circuit is tightly bonded to the main body. This circuit includes strain gauges, which are specialized components designed to sense the deformations of the main body.

These strain gauges consist of thin, electrically conductive wire or foil arranged in a tight zig-zag pattern. This pattern makes them sensitive to stretch and compression along their length but insensitive across their width, allowing precise measurement of forces along specific axes. For exmaple, In shear beam load cells, the strain gauges are positioned at a 45-degree angle to the loading axis to maximize the detection of shear strain running through the load cell.

Technology Of A Load Cell

The technology of a load cell encompasses not just the mechanical and electrical design, but also the methods used to protect and certify the load cells for various applications. Environmental protection and accuracy are critical aspects that ensure load cells perform reliably and meet regulatory standards.

Environmental Protection

Load cells need to be protected from various environmental conditions to ensure their longevity and accurate performance. This involves using materials and designs that protect the internal electronic components from damage due to moisture, dust, heat, and other environmental factors.

• Potting: Filling the cavities with epoxy or resin to protect circuits from damage and humidity while helping to dissipate heat.
• Hermetic Seals: Providing an airtight and robust enclosure for the load cell, ideal for harsh environments.
• ATEX and FM Certificates: Ensuring load cells can be safely used in potentially explosive environments, which is crucial for industries dealing with flammable gases, vapors, or fine dust.

Load Cell Accuracy

Different applications require varying levels of accuracy from load cells. Regulations and certifications ensure that load cells meet the necessary standards for their intended use.

• Accuracy Requirements: Vary by application, with medical scales requiring higher accuracy compared to industrial scales.
• Regulations and Standards: OIML and NTEP certifications provide quality control for weighing and force measuring equipment, facilitating trade and ensuring accurate measurements.
• Legal-for-Trade Certification: Essential for commercial activities where products are sold by weight. Certified load cells meet specific accuracy standards and are approved for commercial use.

Different Types Of Strain Gauge Load Cells

There are many different types of load cell sensors, each designed to cater to specific applications through various body shapes and geometries. Below is a selection of some of the most popular load cell sensor types that Microtess offers:

Single Point Load Cells

Single Point load cells are compression load cells designed for applications like deli scales, bench scales, and checkweighing. Known for their moment compensation, they provide accurate weight measurement regardless of load placement on the scale platform. This flexibility ensures precise and reliable readings, ideal for varying weight distributions and versatile load placements.

Beam Load Cells

Beam load cells are used in vessel/tank weighing and floor scales, available in bending beam, single-ended shear beam, and double-ended shear beam types. Bending beam load cells are cost-effective for lower capacities. Single-ended shear beams mount on one end, with force applied to the opposite end, providing accurate measurements. Double-ended shear beams mount on both ends, with force applied in the middle, suitable for medium to high-capacity applications.

Compression Load Cells

Compression load cells measure force by compressing under load, ideal for heavy-duty applications such as weighbridges and industrial scales. Made from durable materials like stainless steel or aluminum, they ensure precise and reliable measurements. These load cells are essential for environments requiring accurate force measurement and high capacity handling.

Canister Compression Load Cells

Canister compression load cells are cylindrical load cells designed for high-capacity applications, such as tank and silo weighing systems. Made from robust materials like stainless steel, they provide durability and high accuracy. These load cells are ideal for environments requiring precise large force measurements and are commonly used in heavy-duty industrial applications.

Digital Load Cells

Digital load cells convert mechanical force into a digital signal, offering high accuracy and easy integration with electronic systems. These load cells feature built-in electronics for signal processing, reducing noise and improving precision. Ideal for industrial applications, they provide real-time data and seamless connectivity with control systems, enhancing efficiency and reliability in weight measurement tasks.

Conclusion

Load cells, particularly strain gauge load cells, are indispensable tools for accurate force and weight measurements across various industries. By understanding their working principles, components, and applications, you can select the right load cell for your specific needs and ensure optimal performance and accuracy in your measurements. For a complete understanding of load cells, load cells types, and best practices for maintenance and calibration, visit our Load Cell Guide.