S-type, cantilever, single beam, double beam, pancake… Those are just a few of the possible load cell types available for industrial scale design today — but how do companies know which one to choose?
The reason there are so many load cell designs is that there are many variables that engineers must account for when they consider which one will be the best. Those found in laboratories will measure less than 100kg but can offer the highest levels of accuracy, while those on manufacturing floors or in the transportation sector must be much more rugged and can measure hundreds of thousands of pounds.
Electrical controls, maximum capacity, analysis mechanisms, and load type are just a few parameters that will determine which load cell is best. Because we know the choice can be overwhelming, we’ve put together this 101 guide to help you decide which one suits your process best.
What Is a Load Cell?
Essentially just another class of transducer, a load cell is any device that receives mechanical force (tensile or compressive) as an input and converts it to an electrical signal to display its quantity. They are most often used to measure weight, but tension, shear stress, and torque can be measured with load cells, too.
Types of Load Cells
There are four primary types of load cells. They are:
- Strain gauges. Built by attaching a series of voltage sensors to a four-bar assembly that deforms under the load, strain gauges generate a voltage when a mechanical force is applied to them. These are the most common in industrial applications.
- Piezoresistive load cells. Made from piezoelectric materials that create an electric current when their crystal structure is deformed — i.e., when they’re compressed or strained — these can be attached directly to a readout meter, making them ideal for simpler systems.
- Hydraulic load cells. Relying on force-balance principles, these use fluids to measure the weight placed on them, and have no need for electricity. This makes them ideal for remote, potentially hazardous applications, and they’re often used to weigh tanks, bins, and hoppers.
- Pneumatic load cells. These work similarly to hydraulic load cells except that they use air instead of fluids and generally offer higher levels of precision. Best suited for smaller weighing applications where cleanliness and temperature resistance are a must, these are often used in the healthcare sector.
While piezoelectric, hydraulic, and pneumatic load cells can all be used effectively in their proper niche, strain gauges are the most common load cell type used in industry today, so we’ll devote most of our attention to load cells that use strain gauges to measure industrial weights.
Choosing a Load Cell: What to Consider
Once you know the different types that are available, you can then decide which criteria your load cell must meet.
These are the most important factors you should consider:
This will determine which properties your load cell will need, so evaluate the demands of your application first. For instance, a load cell used in the manufacturing industry will likely need higher impact resistance and a greater max capacity, while those used in the agri-food or pharmaceutical industries may require greater accuracy and chemical resistance. Your application may also make certain classes of load cells more suitable than others, as hydraulic or pneumatic load cells could be more effective than strain gauges.
How much force will your load cell need to measure? Maximum capacities can vary greatly, especially by application, so answering this question can help you narrow down your search. For instance, some load cells like our BT-ASP-1 Single Point Load Cell may be rated for 5–100 kg, while others like the CPD-M Digital Compression Column have maximum capacities of 44,000–110,000 lbs, depending on the model.
As you choose your load cell, select one with a maximum capacity that’s well above the force you plan to measure. Vibration, wind, unexpected loads, and shock loading should all be added into your estimated maximum load, and it’s important to consider both the ultimate overload (the amount of weight at which the load cell fails completely), as well as the safe overload limit (the maximum load that can be applied without creating permanent distortions in readings).
At American Scale, several of our load cells have a safe overload limit of 150% of the maximum weight capacity and an ultimate overload of 300%.
Whether it’s the manufacturing, agri-food, healthcare, or transportation industry, the environment that your load cell will need to operate in will have a significant impact on which one you choose.
Your facility’s operating conditions could include several factors, like:
- Temperature. In extreme hot or cold, the materials inside your load cell could expand or contract, resulting in inaccurate readings or even a break. Be sure to select a load cell that operates effectively within your facility’s temperature range.
- Moisture. Load cells that use electronics (like strain gauges) can short-circuit if moisture enters their electronics — an especially common risk in the agri-food sector. Choose a moisture-resistant strain gauge if there’s a risk of getting it wet, or opt for a hydraulic load cell instead.
- Chemicals. Some chemicals must be present in certain manufacturing processes, and these could corrode your load cell if you choose the wrong one for the job. Our Coti CG-26S2 Compression Stainless Load Cell is engineered to withstand corrosive environments and intense washdowns, so it can withstand most manufacturing conditions.
Whatever environmental extremes are present in your application, be sure to account for them in your load cell selection.
Accuracy and Precision
Accuracy is another essential load cell variable, and some sectors would shut down without it. Applications like the pharmaceutical industry depend upon the highest degree of accuracy as they measure out life-saving chemicals, and the manufacturing sector must have accurate enough load cells that they can use to ensure that they have the proper amount of inventory.
High-accuracy load cells may be able to render a reading within +/- 0.02–0.05% of the true value, while less accurate load cells can measure a load to within +/- 0.5–1% of the true value.
It’s not enough for load cells to be accurate; they must also be consistent. Because they must measure forces again and again, load cells must have a high repeatability to ensure that they get the right value every time. Many of our load cells like the Coti CG-53 Double-ended Shear Beam have a repeatability of within 0.01% of the full-scale value, proving that it will measure the correct amount with the reliability you need.
Tension, compression, and torsion are the main loads that a load cell can evaluate, but these have several variations — and they can all affect which type of load cell you choose.
The three loading conditions are:
- Static, where the load does not cause motion
- Dynamic, where the load does cause motion
- Fatigue, where repeated rotation causes tensile and compressive forces to alternate along the part where the load is applied
A load may be varying or constant, and placing the load off-center may result in a skewed load cell readout. In some applications like the transportation sector, proper weight distribution can mean the difference between success and failure, and having a load cell large enough to measure the force placed upon it in whatever direction it’s applied is a must.
American Scale offers many different solutions to accommodate the loading conditions that industries may face. Objects that are too unwieldy to evenly place on a scale can be weighed with a crane scale, and the massive objects in the transportation sector can be weighed with railroad scales or truck scales — even while on the go.
Load cells come in many different forms and have too many features for us to mention each one here. Some other features you may need to consider are:
- Data capture and analysis. Whether tracking past measurements or keeping track of inventory, you’ll likely need a load cell that has some way of exporting or analyzing your measurements. PC Interface Modules, USB and software options, indicators, and signal conditioners are some tools that may help you store, transfer, and analyze your data, making your weighing process run smoother.
- Connections. Even if it has all the right properties, your load cell won’t help you much if it can’t be properly connected. We offer a number of interconnection solutions, though, so that you can attach your load cell to the parts you use every day.
- Electronics. If you plan to use a strain gauge or piezo-based load cell, you’ll need to match your electrical requirements, as well as your physical interconnects. We carry load cells with electronic components like internal amplifiers, controllers, and voltage ratings to meet the electrical requirements of your application.
Material selection can also play a role in determining the load cell you choose, as some may corrode, overheat, or fracture under certain conditions. A lightweight yet durable material like the anodized aluminum used in our B-Tek BT-ASP-1 Single Point Load Cell often works well.
Which Kinds of Load Cells Are Available?
Now that you know what classes of load cells exist and which properties to consider, you can evaluate the different load cell designs to see which one works for you. A few load cell designs include:
- S-Type. Named for their three-part S-shaped geometry, these load cells have a high endurance level and can offer both tension and compression. They’re often used for light performance testing, and their geometry makes them susceptible to high bending moments, so they may work best with lighter loads.
- Single-ended shear beam. These simple, affordable load cells work well for medium-weight load capacities and consist of a beam that is fixed on one end while a load is applied to the other. These work well in applications where space is at a premium, and our Celtron SQB Single-ended Shear Beam models are rated for 1,000–10,000 lbs. with non-certified models covering the 500, 15,000, and 20,000 lb ranges. They are ideal for large load applications where multiple cells are attached to form a single measurement system.
- Double-ended shear beam. These load cells are similar to their single-ended counterparts, but they are fixed on both ends and have the load applied at the midpoint. The double-fixed structure gives them a higher load capacity, and our Coti CG-16 Double-ended Shear Beam load cells have a maximum load capacity ranging from 1,000–125,000 lbs.
- Weigh bars. Consisting of a cantilevered beam encasing a strain gauge and all the necessary components, weigh bars are stronger than conventional load cell designs. Most often used for heavy-duty weighing, our BWB Batching Weigh Bars can be used to weigh containers, bins, and hoppers, and have a maximum capacity of over 80,000 lbs.
Pin load cells, tension links, and compression columns are other load cell designs that are suited for heavy-duty loads, so you’re sure to find the device that measures up to your application.
American Scale: Your Leading Load Cell Provider
At American Scale, we’ve been offering top-quality scales, load cells, and weigh bars since 1985. Our team has experience across a number of industries, and we pride ourselves on finding a load cell solution that meets each client’s needs. We’re proud to be the Midwest’s primary scale provider, so contact us today and see how we measure up.