null
Types Of Load Cell Based On Technology

Types Of Load Cell Based On Technology

Four common types of these sensors are available, including:

  • Pneumatic
  • Hydraulic
  • Strain gauge
  • Capacitance
  • Pneumatic Load Cell

    Pneumatic Load Cell

    Pneumatic load cells function according to the force balance principle. Compared to a hydraulic device, these devices employ multiple dampener chambers to achieve superior accuracy. In some configurations, the first dampener chamber serves as a tare weight chamber.

    Because it is pneumatic, we know it will handle air pressure. A pneumatic load cell comprises an elastic diaphragm connected to the measuring platform's surface. In addition to a pressure gauge, there will be an air regulator that controls the amount of air pressure allowed into the system. Therefore, a pneumatic load cell employs pressurized air or gas to balance the weight of the object placed on it. The amount of air necessary to balance the weight determines the object's weight. The pressure gauge transforms the measured air pressure into an electrical signal.

    In industries where hygiene and safety are top priorities, pneumatic load cells are the preferred choice to measure relatively light weights.

    One of the benefits of this sort of load cell is that it is explosion-proof and can operate in a wide temperature range without compromising its accuracy. Also, if the diaphragm ruptures, they don't contain any fluids that might contaminate the procedure. Slow response time and the requirement for clean, dry, controlled air or nitrogen are disadvantages of this method.

    Hydraulic Load Cell

    The term hydraulic indicates that this sensor operates by utilizing a fluid, such as water or oil. These load cells are pneumatic, but they use pressurized liquid instead of air.

    The following components make up hydraulic load cells:

    • An elastic diaphragm
    • A piston with a loading platform over the diaphragm
    • Oil or water that will be contained within the piston
    • A bourdon tube pressure gauge

    Hydraulic cells are force-balance instruments that measure weight by changing the pressure of the fluid inside the cell.

    Hydraulic force sensors use a piston to apply pressure to a filling fluid within an elastomeric diaphragm chamber to measure the force or load exerted on a loading head. This form of the hydraulic force sensor is known as a rolling diaphragm type.

    The hydraulic fluid's pressure rises as force increases. This pressure can be shown locally or transferred for remote display or control. The linear output has no impact on filling fluid volume or temperature.

    Hydraulic Load Cell

    If the load cells are correctly mounted and calibrated, accuracy can be 0.25% full scale or adequate for most process weighing applications. This sensor is appropriate for hazardous environments since it contains no electric components.

    Weighing in tanks, bins, and hoppers are typical applications for hydraulic load cells. To achieve maximum accuracy of the tank's weight, place one force sensor at each point of support and total their outputs. A pressure sensor can provide a direct analog measurement or convert the pressure to electronic signal output.

    Strain Gauge Load Cell

    Strain Gauge Load Cell

    The most popular style of the load cell is the strain gauge load cell.

    Strain gauge load cells use a strain gauge assembly inside the load cell enclosure to convert the load applied to them to an electrical signal. The load cell's weight is determined by the voltage fluctuations induced by the strain gauge's deformation.

    Strain Gauge Load Cell

    Modern strain gauge load cells contain four strain gauges in a "Wheatstone" bridge configuration. A Wheatstone bridge is a type of electrical circuit used to measure unknown electrical resistance by balancing two bridge circuit legs. One of the circuit's legs includes an unknown component. The "Wheatstone bridge" circuit allows for extremely accurate measurements. The gauges are attached to a beam or structural part, which deforms when weight is applied. Each strain gauge will have the same resistance when no load is applied to the load cell. However, under load, the strain gauge's resistance changes, resulting in a change in output voltage. A digital meter measures and converts the output voltage fluctuations into readable values.

    Strain Gauge Basics

    Gauge Factor

    Each strain gauge has a distinct strain sensitivity, which is quantified by the gauge factor (GF). The gauge factor is the fractional change in electrical resistance ratio to the fractional change in length. It is a gauge sensitivity measure (GF is commonly about 2) for metallic strain gauges.

    Small Changes in Strain

    Each strain gauge has a distinct strain sensitivity, which is quantified by the gauge factor (GF). The gauge factor is the fractional change in electrical resistance ratio to the fractional change in length. It is a gauge sensitivity measure (GF is commonly about 2) for metallic strain gauges.

    After establishing a strain gauge load cell and measuring the resulting change in resistance, we conclude that everything is functioning OK. Wait up and do not act too quickly. Strain measurements are usually limited to a few millistrain (e \cdot 10^{-3})(fancy units for strain, but still very small).

    For example, suppose you apply a strain of 500µε. An electrical resistance change for a strain gauge with a gauge factor of 2 is limited to:

    2 * (500 * 10-6) = 0.1%

    This is a 0.12-charge for a gauge reading of 120Ω.0.12 is an extremely little change that, for most equipment, cannot even be detected, let alone accurately measured. Therefore, we will need a new device that can accurately measure tiny resistance changes that are costly. Or a device that can convert these extreme changes in resistance into a form that can be precisely measured.

    Amplifiers and Wheatstone Bridge

    Using a Wheatstone bridge is a valuable method to take minute changes in resistance and convert them into a more measurable value. A Wheatstone bridge is a four-resistor configuration with a known voltage applied as follows:

    Amplifiers-and-Wheatstone-Bridge

    Where Vin represents a constant voltage, the output Vout is calculated. Vout is 0 if R1/R2 = R3/R4; however, if the value of one of the resistors changes, Vout will vary in a way that can be measured. This change is regulated by the following equation based on Ohm's law:

    Vout = [(R3/(R3 + R4) - R2/(R1 + R2))] * Vin

    We can measure the change in Vout by substituting one of the resistors in a Wheatstone bridge with a strain gauge. We can then use this information to determine the amount of the applied force.

    Different kinds of strain gauge load cells;

    Beam

    What Is A Beam Load Cell, And How Does It Work?

    What Is A Beam Load Cell, And How Does It Work?

    One of the main groups or types of load cells frequently seen in the weighing industry is the beam load cell. They are probably the most common type of load cell used today.

    When exposed to a force or weight, beam load cells act as basic cantilevers that bend slightly. Single-ended designs are attached at one end and free at the other, acting much like a diving board. However, double-ended versions are available that are fastened at both ends and loaded in the middle, acting more like a hammock.

    Furthermore, beam load cells are frequently divided into two subcategories depending on how they detect force or weight. Shear beam cells see shear distortion, whereas bending beam cells measure bending distortion.

    The most significant and most adaptable class of load cells are beam load cells, which provide a wide range of potential capacities and various mounting styles and accessories. When the usage of a single-point cell is no longer practicable, they are frequently combined in more extensive weighing equipment and scales.

    Working Principle

    Like other recent load cells, Beam load cells are strain gauge-based transducers that transform force or weight into an electrical signal. The elastic characteristics of the metal used to construct the load cell's body cause it to bend when a load is applied. Strain gauges attached to the load cell's surface, carefully positioned and fixed, will also extend or compress alongside the main body. This changes their electrical resistance, causing the voltage across the circuit to shift. This effect is measurable since it is proportionate to the starting force or weight.

    Design

    Beam load cells are available in a wide range of sizes and forms to fit a variety of applications. They all have a low vertical profile compared to their length. This shape is in contrast to many column-shaped compression load cells, which are typically narrower than tall. When force is applied to certain parts of the bending beam load cell, the load cell body itself bends or curves to accommodate the force. They often provide a significant degree of strain or flex at relatively modest forces, making them suitable for applications with smaller capacities.

    When put on the convex surface, strain gauges will stretch, but when placed on the concave surface, they will contract. This situation implies that two surfaces are always under equal and opposing strain, which helps establish a full-bridge circuit or temperature compensation.

    Although shear beam load cells appear identical at first glance, they operate differently. Each side of the load cell has a machined recess, creating a relatively thin vertical web in the center. This makes the load cell look like a cross-section of an I-beam used in construction, and just like I-beams, most of the shear strain is concentrated in this thinner vertical web. Strain gauges are attached at 45-degree angles to the side surfaces of this web To measure the strain. The top and bottom flanges simultaneously aid in resisting any moment or bending.

    Due to their exceptional side force resistance, shear beam load cells have grown in popularity for medium and large capacity applications. They are often not designed for low capacity since creating a web thin enough to achieve the necessary strain levels is challenging. Bending beams and single-point load cells would be better suited for such applications.

    Single Point

    What Is A Single-Point Load Cell, And How Does It Work?

    What Is A Single-Point Load Cell, And How Does It Work?

    One of the most common types of load cells in the weighing industry is the single-point load cell. Compression, tension, and beam are examples of other types. The capability of a single point to handle off-center loading is its defining feature. To achieve accurate readings, you must align the load with the cell. When the weight goes off-axis, it makes an error. Because of their geometric design that enables some flexibility, single points can retain accurate readings even if the weight is unevenly spread. They are, therefore, ideally suited for usage in platform scales, where the positioning of the weight may vary. The accuracy of the weight measurement will not be affected by where on the platform an object is placed; it can be in any place. This feature eliminates human errors in positioning, which is quite helpful. Businesses can get accurate measurements without investing in specialized equipment or training. Additionally, a scale can be constructed using a single cell rather than a group of cells at each corner.

    working Principle

    As with all other contemporary load cells, single-point load cells are simply transducers that transform force or weight into an electrical signal. They do this by attaching strain gauges to the load cell's body. The load cell shape somewhat deforms when subjected to a load. The strain gauges, which deform simultaneously with the body, detect this change and produce a voltage change. This voltage signal can be used to measure the initial force or weight because it is proportional to it.

    Design

    Single-point load cells are available in a wide range of sizes and forms to fit various application types. They all have an interior aperture that is a geometrically exact body cut-out. This interior design is what separates them visually from beam load cells. This aperture is crucial to the load cell's ability to handle off-center loads because it regulates the metal thickness at different points across the body. Most Single-points are made of stainless steel or high-grade aluminum, best suited for lesser-capacity applications. Depending on how much environmental protection is needed, they can be potted or hermetically sealed. Some models have ATEX approval for use in hazardous areas.

    Compression

    What Is A Compression Load Cell And How Does It Work?

    What Is A Compression Load Cell And How Does It Work?

    A compression load cell is one of the most popular load cells employed in the weighing business.

    Compression load cells, as their name implies, measure the pressing or squashing force. They are usually put under what is being measured or weighed. In contrast to tension load cells, these load cells are unidirectional and solely intended to monitor downward compression (Tension load cells frequently have the ability to measure compression as well.).

    The internal operations of a compression load cell might vary considerably. They may be determined by shear, bending, ring-torsion, or column measures. Even though their applications are numerous, one of the primary uses for these load cells is in extremely high-capacity static weighing, such as in silos and truck scales.

    Working Principle

    Compression load cells are transducers that transform force or weight into an electrical signal. They achieve this by attaching strain gauges to the load cell's body. The load cell body deforms somewhat when subjected to compressive force. This is detected using strain gauges that deform along with the body, causing a voltage change. Since this voltage signal is proportional to the starting force or weight, it can be utilized to measure it.

    Design

    The column or canister-style load cell is a typical example of a compression load cell. These devices are generally cylindrical-shaped, installing surfaces at the top and bottom ends. The main column or core inside operates as the weight-bearing element. Strain gauges are attached to the surface of this column to detect the deformations that take place under load. Usually, the load cell has an outer sheath that protects and keeps the internal parts from the outside environment. Many of them are hermetically sealed to withstand hazardous conditions.

    These load cells provide reliable and accurate readings, making them ideal for high-capacity static weighing applications. The cells must be correctly aligned during installation to achieve accurate readings. This is often achieved by connecting them with specifically designed mounting hardware.

    Button load cells are another popular form of compression load cells; they are small, low profile, and frequently suitable for test and measurement applications. Also, through-hole load cells, also known as doughnut load cells, include a central aperture that allows the equipment to be moved through it. An instance of such an application is a pump monitoring system in the oil and gas sector.

    Tension

    What Is A Tension Load Cell, And How Does It Work?

    What Is A Tension Load Cell, And How Does It Work?

    A tension load cell is one of the most frequent and essential varieties of load cells seen in the weighing industry. As their name suggests, tension load cells are most often used to measure tension or pulling force. Because of their bi-directional sensitivity, most of them can also detect compression, making them extremely flexible. Because of their design, tension load cells are called 'S-type' load cells. They have an upper and lower arm to mount points properly to the central axis in suspended applications.

    Working Principle

    Tension Load cells, as well as all other types of contemporary load cells, are transducers that use strain gauges to translate force or weight into an electrical signal. The load cell's main body somewhat deforms when exposed to a load. The strain gauges, which are tightly attached to the load cell body, bend, changing their electrical resistance. This results in a voltage signal proportionate to the original force or weight.

    Design

    Tension load cells are intended for use in applications involving suspended weights. As a result, they frequently have to position themselves in line with the dependent objects and are generally included in the supporting equipment. Because of this, these load cells are in the shape of an "S" or "Z."The mounting holes on the upper and lower limbs are aligned with the central axis.

    These are essentially specialized beam load cells. Strain gauges are placed along the center bar to measure bending or shear strain, making it function like a beam load cell. What makes this different is the lack of a fixed end to cantilever against. Conventional beam load cells usually have one end fastened to a base and the load imposed on the other 'free' end, similar to a diving board. Neither end of an S-type tension cell is fixed. Instead, one end is linked to the apparatus above by the upper arm, while the other is attached to the equipment below via the lower arm.

    When the load cell is under tension, there is a draw-up at one end of the central bar and a pull-down at the opposite end. The strain gauges detect distortion caused by the difference across the center bar.

    Capacitive Load Cell

                                                                     

    Capacitive load cells operate based on the concept of capacitance, which is a system's capacity to hold a charge. The load cell is composed of two parallel flat plates. A current will be applied to the plates, and once the charge is steady, it will be stored between them. The capacitance, or the capacity to hold a charge, depends on the gap size between the plates.

    When a load is applied to the plate, the gap decreases. This results in a change in capacitance that may be used to determine a weight.

    Piezoresistive load cell

    Piezoresistive force sensors operate similarly to strain gauges. They give a high-level output signal, making them excellent for simple weighing systems since they can be linked directly to a reading meter. However, the availability of inexpensive linear amplifiers has reduced this benefit. The nonlinear output of piezoresistive devices is another problem with them.

    Inductive and reluctance load cells

    Both of these devices respond to the movement of a ferromagnetic core proportionate to its weight. The movement of an iron core in one causes a change in the solenoid coil's inductance, while another modifies the reluctance of a tiny air gap.

    Magnetostrictive load cells

    This force sensor changes ferromagnetic materials' permeability in response to applied stress. It consists of a stack of laminations that create a load-bearing column around a pair of primary and secondary transformer windings. When a force is exerted, the stresses cause the flux pattern to become distorted. This makes the output signal change proportional to the applied load. In rolling and strip mills, this robust sensor is still used to detect forces and weights.

    .

    15th Oct 2022

    Recent Posts