Types of Load Cells

What is a Load Cell?

At the heart of every weighing device is a sensor called a load cell. When an item is put on a load cell, it senses the force of the gravitational pull of the weight, which an electronic circuit processes to display as data. Load cells are highly accurate mechanical transducers used to provide measurements and readings.

A load cell is a force transducer that converts force, such as tension, compression, pressure, or torque, into an electrical signal that can be measured and standardized. As force applied to the load cell increases, its electrical signal changes.

The most common types of load cells are hydraulic, pneumatic, and strain gauge, which are load monitors, or an electromechanical tool, that is found in every aspect of life.

Load cell measurements are displayed in newtons (N), meganewtons (MN), or kilonewtons (KN).

Design

Load cells measure weight in the inner workings of a mechanism. They have a spring, made of steel or aluminum, with a strain gauge. The spring is very sturdy but minimally elastic and responds to every load regardless of how small.

The strain gauge is a small device that measures the strain of an object by converting internal deformation into an electrical signal, precisely measuring weight, force, tension or strain. The sensing element can also be a piezoelectric sensor with crystals. The circuit connects the gauges or sensors in the load cell.

The strain gauge is an electrical conductor attached to a film. When the film is pulled, it gets longer and gets shorter when it contracts. The changes of elongation and contraction create resistance in the conductor. As the film lengthens, the strain increases resistance. When the film contracts, resistance lessens.

The types of load cell output include analog voltage, current, frequency, switch or alarm, serial, and parallel. Basic designs of load cells have four gauges, while complex load cells can have up to thirty gauges for measuring circuits. The more gauges a load cell has, the more sensitive are its measurements.

When determining the capacity of a load cell, manufacturers examine force value, the dynamics of the system, the effects of placing the transducer in the force path, and the maximum extraneous loads that the load cell can handle.

The factors that are considered when a load cell is mounted are will it be in the primary load path or see forces indirectly. Physical constraints include size and mounting, the level of accuracy, and environmental conditions. Accurately assessing these factors ensure that the proper load cell is being installed.

Types

Force, compression, and tension are the three categories of load cells. The majority of load cells measure more than one of these criteria. Below are short descriptions of the various types of load cells.

Hydraulic Load Cell

Measures weight as a change in pressure on a fluid and are used for tank, bin, and hopper weighing.

Canister Load Cells

Are compact and cost effective. They can measure a variety of capacities and are used for weighing tanks, hoppers, and vehicles.

Compression Load Cells

Have a strain gauge to measure pushing force along a single axis, which is denoted as negative force. They are perfect for applications with limited space and have excellent long-term stability.

Tension Load Cells

Have a strain gauge to measure pulling apart or positive force along a single axis.

Strain Gauge Load Cells

Are the most common type of load cell with a capacity rate between 5 N to more than 50 MN. They have high-res digital indicators with ideal force transfer standards.

Force Sensors

Use strain gauges to test push-pull and measure flow. They are similar to "load cells" but measure loads in all directions. Earth's gravitational force is not relevant to how they are installed.

Pressure Sensors

Are transducers that are similar to load cells that measure pressure, applied force, and strain in gas pressure, altitude, and liquid pressure. Their sensors are often piezoelectric.

Piezoelectric Crystal Force Transducers

Are used for measuring crystalline materials. When a force is applied to a crystalline material, an electrical charge is generated. A piezoelectric force transducer, with its charge amplifier, measures the electrical charge and converts the measurement into a digital signal.

Miniature Load Cells

Provide precise measurements for small applications.

Donut Load Cells

Also known as thru-hole load cells, measure compressive forces and are called donut load cells because of their shape. They are smooth and round with a hole in the middle for parts or bolts and are used in oil and gas pumps.

Shear Beam Load Cells (S-Beam Load Cell)

Have a straight block of material fixed on one end and loaded material on the other. Beam load cells, known as bending load cells, are used for industrial weighing, including industrial floor scales and tank, silo, and on-board vehicle weighing.

Low Capacity Transducers

Are miniature transducers used in medical testing equipment, wind tunnel sensors, and weight counting machines. They are limited to measuring weights between 0.9 ounce and 150 pounds, which makes them suitable for residential and retail machines.

Mid Capacity Transducers

Can accurately measure weights between 200 to 20,000 pounds and are ideal for industrial and manufacturing applications. Common uses are industrial scales, truck and truck weighing, bolt force measurement machines, and platform scales.

Micro Load Cells

Are resistive load cells, which use the principle of zero piezo-resistivity. When a load, force, or stress is applied to the sensor, the resistance changes, which causes the output voltage to change because the input voltage has changed.

Multi-Axis Load Cells

Are designed and manufactured to measure a multitude of forces simultaneously using a single load cell. They provide multiple bridges that precisely measure force from one direction with little or no cross-talk from other forces or moments.

High Capacity Transducers

Can measure materials that weigh more than 25,000 pounds.

Specialty Transducers

Are used underwater or in outer space. They can measure compression, tension, pressure, or capacity and much more.

Pin Load Cell

Is made with load measuring pins, or load pins, that sense applied force using strain gauges installed in a small bore that runs through the center of the load cell. They are used on anchors, shackles, sheaves, bearing blocks, and pivots. They work well underwater because the pin is protected, and the load cell is made of cable and stainless steel with hermetically sealed end caps.

Pancake Load Cells

Can be used for both tension and compression measurements in materials and component fatigue testing as well as axial force measurements, where a high accuracy, low-profile device is needed.

Dynamometer Load Cells

Or dynos, are used to measure force, torque, and power. A dyno, combined with load cell sensing technology, creates a dyno load cell, which is used to measure engine power output. They are rather expensive and only used when absolutely necessary.

Single Point Load Cells

Have only one operating load cell and are used in individual device applications, such as supermarket scales.

Applications

Load cells help measure physical quantity or mass and convert force or energy into another form, such as force, light, torque, or motion. They are used in mechanical testing, system monitoring, and as components in industrial scales. There are many common applications that use load cells, such as scales in the home and measuring devices for heavy industries.

Industries in which load cells are used include:

• Food Processing measure ingredients and proper distribution of products during packaging
• Industrial Warehousing determine the precise weight of a loaded pallet, which is crucial for filling and accepting orders
• Building and Construction used to test building materials, such as beams, for tension and structural strength
• Transportation truck and railroad car scales
• Research Laboratory and Pharmaceutical Production weighing equipment, calibrating systems, and doing fatigue testing

Load cells are part of security systems, electrical weighing scales, personal scales, thermometers, machines in the defense sector, industrial automation, submarine pressure sensing, and material testing.