How does load cell work? A load cell, also called a transducer, converts a mechanical force into an electrical signal or digital value that users can review and record.
In its simplest form, the load cell bends when weight is applied. In a compression-mounted load cell, where the load cell is beneath the weighing vessel, like a truck scale, the load cell compresses when a load is applied. It then produces an analog output signal proportional to the applied weight or force that is transmitted to a controller that converts the signal into a digital weight measurement. It is crucial for the device to work properly to get accurate weight measurements. Almost all electronic weighing scales utilize load cells for accurate measurements of weight – in fact, the reason they are so widely used is because of the precision in which they can effectively measure weight.
When an application requires multiple load cells, each one should measure the same proportion of the total load. Therefore, in a four-load-cell system, each load cell should measure exactly one-quarter of the load.
Many load cells are propriety to a specific manufacturer and may require additional maintenance and costs of ownership. Carefully discuss with your scale supplier all options for load cell systems.
What are the different types of load cells?
Load Cell types (or designs) can be distinguished according to the type of output signal – either pneumatic, hydraulic, or electric. They can also be distinguished by the way they detect weight – bending, shear, compression, tension, are a few examples.
Analog Load Cells
The most common load cells on the market work on the strain gauge principle. All load cells need to convert their analog values to digital before the load’s weight reading can be displayed on an indicator.
Some load cells are directly cabled to the digital weight indicator where the translation occurs. Other cells are connected to summing junction boxes on the scale where the box sums analog readings from multiple load cells, converts it to a digital signal and sends that signal to the digital weight indicator.
Hydraulic Load Cells (Pressure Transmitters)
Unlike most other load cells, hydraulic load cells do not use strain gauges or internal circuitry. Instead, hydraulic load cells contain hydraulic fluid, and during compression, a change in pressure is created and transmitted via tubing to a summing system where the pressure is applied to an analog load cell to determine weight. Learn more about the working of hydraulic scale systems.
Analog–to–Digital Load Cells
Some analog load cells perform the analog-to-digital signal conversion within the load cell housing. Although sometimes referred to as digital load cells, the cell still measures in analog.
Making the conversion from an analog signal to a digital signal in the load cell allows the system to compare the output of individual load cells and perform a diagnostic analysis based on that information, but because the conversion happens in the load cell, sensitive electronic components are increased throughout the scale system, making them susceptible to damage from vibration, moisture and increased solder joints.
Load Cell Materials
Truck scale load cells are generally made of stainless steel or steel alloy, but most manufacturers offer a variety of load cell solutions that best fit your application needs.
Tool Alloy Steel Load Cells
Load cells manufactured from tool alloy steel elements are by far the most popular cells in use today. The cost to performance ratio is better compared to either aluminium or stainless steel designs.
The most popular alloys are 4330 and 4340 because they have low creep (the change in load cell output over time while under load) and low hysteresis (the difference between load cell output readings for the same applied load).
Stainless Steel Load Cells
Stainless steel cells are more expensive than tool alloy steel load cells. They are sometimes fitted with hermetically sealed web cavities, which make them an ideal choice for corrosive, high-moisture applications.
Stainless steel load cells that are not hermetically sealed have little advantage over comparable cells constructed of tool alloy steel, other than a higher resistance to corrosion.
As Canada’s largest manufacturer of electronic truck scales, portable scales and weigh systems, Active Scale has a proud history of innovation in the weighing industry and we know our fair share about load cells. Providing vehicle scales of legendary quality and value, contact Active Scale today for all of your weighing needs.
