Getting Started With Load Cell

Getting Started With Load Cell

What is a load cell?

A load cell (or loadcell) is a transducer that measures mechanical force by producing an electrical signal output. Load cells primarily measure the weight of an object. Today, practically all electronic weighing scales determine weight using load cells. The accuracy with which they measure weight has led to their widespread use. There are many different force sensors, but strain gauge load cells are the most common. Load cells are used in many industries that need high levels of accuracy and precision.

Origin of the load cell

Mechanical lever scales were commonly utilized until strain gauge-based force sensors became the preferred technique for industrial weighing applications. If properly calibrated and maintained, mechanical scales can weigh everything from pills to train carriages precisely and dependably. The operation technique may employ a weight balancing mechanism or the sensing of force generated by mechanical levers. Hydraulic and pneumatic designs were among the first pre-strain gauges load sensors.

Sir Charles Wheatstone, an English physicist, created a bridge circuit that could gauge electrical resistances in 1843. The Wheatstone bridge circuit is the best way to measure how the resistance of strain gauges changes. Although the first bonded resistance wire strain gauge was invented in the 1940s, the new technology did not become technically and commercially practical until modern electronics caught up. However, since then, strain gauges have become increasingly commonplace, not just as components of mechanical scales but also as stand-alone load cells.

Strain gauge load cells are the most common way in the weighing industry today, except in some labs that continue to make use of precise mechanical scales.

Pneumatic load cells are occasionally employed when safety and hygiene are essential.

Hydraulic load cells are an option for remote areas because they don't need a power source.

Strain gauge load cells have accuracy ranges of 0.03% to 0.25% full scale and are suited for nearly all industrial applications.

Mechanical platform scales are still often employed in tasks that don't need a high degree of accuracy, such as in bulk material handling and truck weighing. Load cells are commonly used in these applications to detect the forces transferred by mechanical levers because of their natural compatibility with digital, computer-based equipment.

How does a load cell work?

When using load cells, one end of the device is often fastened to a base or frame, leaving the other end free to connect the weight or other weight-bearing component. The load cell's body bends a little bit when force is applied. This process is comparable to what occurs when a fisherman hooks a fish with a fishing rod.

The fisherman will hold the rod securely in their hands as the fish exert a pulling force at the other end of the fishing line. As a result of this force, the fishing rod bends. More significantly, stronger fish generate a more extreme bend.

When this occurs on a load sensor, the deformation is extremely slight and not visible to the human eye. Strain gauges are connected to the load cell body at predetermined positions to detect deformation. This act forces the strain gauges to deform in harmony with the body. According to the amount of deformation generated by the applied load, the resulting movement modifies the electrical resistance of the strain gauges. Electronic signal conditioning converts the measured electrical resistance from the strain gauges into a weight or force reading.

Technology Of A Load Cell

Most load cells have two parts:

  • The main body of the sensor
  • An attached electrical circuit

The main body, which makes up the majority of the load cell's size, is what endures the weight or force. It is often made of high-quality steel or aluminum, which makes it mechanically reliable and ensures predictable and uniform strain distribution.

The electrical circuit is inside the load cell and is firmly attached to the main body. The circuit contains strain-gauges, which are specialized circuit components intended to detect deformations in the main body.

Strain gauges are thin, electrically conducting wires or foil organized in a zig-zag pattern. This design makes them stretch and compression-sensitive throughout their length but insensitive across their width. As a result, they can be placed precisely to detect forces along specific axes. For instance, shear beam load cells include strain gauges angled 45 degrees to the loading axis to maximize shear strain detection running via the load cell.

Proper Detailed Considerations

Environmental Protection

A load cell can be employed in various environmental conditions based on the setting. A clean room in a medical lab and the underbelly of an open-cast mining truck are pretty different, and both require various types of load cells. So, protecting them from the outside environment is essential to maintain their long-term performance for their intended application. The majority of load cells are potted. This means that the voids are filled with an epoxy-or resin-based substance that completely covers the electrical components. This protects the circuits from external damage and humidity and also aids in heat dissipation.

Hermetic sealing is available on some load cells to provide the best environmental protection. A wholly welded seal creates an airtight, durable enclosure that can withstand the harshest conditions.

Some load cells come with ATEX and FM certifications. These certifications demonstrate that the product is suitable for use in potentially explosive settings without the danger of sparking. This is appropriate for operations that create flammable gases or vapors, such as spraying car paint, or workplaces that deal with fine organic dust, like grain flour or wood.

Load Cell Accuracy

Different tasks demand various levels of accuracy. A medical scale measuring medicine dosages requires a higher resolution than an industrial scale weighing enormous quantities of gravel or sand. So, there are numerous kinds of load cells, each of which offers a varied level of precision and capacity to suit the requirements of a particular application.

International rules and agreements are designed to ensure the quality of weighing and force measurement equipment. Such regulation helps establish harmony across various jurisdictions, promoting trade and economic activities.

The International Organization of Legal Metrology (OIML) governs these metrological rules on a global scale, and in the United States, the National Type Evaluation (NTEP) Committee does so.

Legal-for-trade weighing equipment is necessary for many commercial activities since products are frequently sold based on weight. This equipment has been approved for use in such applications by the appropriate authorities (OIML, NTEP, or national standards). Commercial weighing scales are typically certified to the C3 level under OIML.

Load cells certified by OIML or NTEP will be appropriate for legal-for-trade applications. Depending on the market or are being offered to, they may have both OIML and NTEP certifications or only one. Load cells are called "general purpose (GP)" if they don't have these certifications. Although they are not certified, they frequently give comparable levels of accuracy. This is especially useful in instances in which legal-for-trade rules do not apply.

Installation And Use

Numerous factors affect a load cell's performance. Among these, correct installation and alignment are crucial. It is commonly stated that the installation of a load cell determines its quality. Also, it is critical to carefully follow the manufacturer's instructions to achieve the most excellent results from your equipment and to guarantee safe and long-term operation. In these guidelines, you'll often find information about how to correctly mount and align your load cell, choose the suitable fixings and fasteners, use extra mounting hardware and electronic adjuncts, and calibrate your scale.

You can trust that your solution will be efficient and long-lasting by collaborating closely with your load cell provider to select the appropriate strategy and product to meet your specific demands.

Load Cell Abbreviations

All abbreviations are in lowercase, should not be pluralized, and lack trailing periods.

ampere A meganewton MN
combined error CE meter m
degree Celsius °C milliampere mA
degree Fahrenheit °F millimeter mm
degree Kelvin °K millivolt mV
foot ft millivolt/volt mV/V
foot-pound 1 ft-lb minimum dead load MDL
full-scale FS newton N
gram g newton-meter Nm
gram force gf ohm ohm
hertz Hz ounce-inch oz-in
inch in pound lb
inch-pound 2 in-lb pound-foot lb-ft
kilogram kg pound-inch lb-in
kilogram-force kgf pound force lbf
kiloohm Kohm pound per square inch psi
kilonewton kN rated output RO
kilonewton-meter kNm static error band SEB
kilopound-foot Klbf-ft ton, metric t
kilopound-inch Klbf-in volt V
kilopound force Klbf volt direct current VDC
kilopound (kip) K volt alternating current VAC
megaohm Mohm watt W
12th Oct 2022

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