Everything You Need to Know About Load cells
This blog introduces people to load cells and dynamometers. It explains how a load cell works, explores the different types on the market, and reveals the applications where they are commonly found.
Did you know?
Load cells are everywhere. They are in your kitchen scales, bathroom scales, under your car seat, on grain silos, laboratories and, as is most relevant in the lifting industry, they hang beneath the hook of a crane or hoist. A load cell is a force transducer, converting tension, compression, pressure, or torque into an electrical signal that is measured and standardized. As a force is applied to the sensor, this electrical signal changes proportionally.
How does a load cell work?
At the heart of a load cell is a spring element, typically made from 17-4PH stainless steel or high spec aluminum, such as 2014T6. This component is key because it provides the product with its mechanical strength and returns it to the point at which it started. If you imagine a one-inch spring that is compressed to ¼ inch by a load, when that load is released, it returns to one inch again. The principle is the same.
Wheatstone bridge circuit
Strain gauges (used to measure strain on an object) are bonded to that spring element and wired in the configuration of a Wheatstone bridge, which is an electrical circuit used to measure changes in electrical resistance across the strain gauges of the bridge circuit.
When the load cell is connected to instrumentation or an amplifier, it gives a variable output depending on the load or force that is being applied. That variable output is then calibrated into engineering units, such as tons or pounds, using known loads or masses.
Strain gauge illustration
Why are load cells useful?
Safety is enhanced when people know the weight they are dealing with. Load cells can also be used to calculate center of gravity, which is equally essential information especially where large or unusually-shaped loads are involved. Utilizing modern day force measurement technologies, all this information can be gathered at a safe distance from the load—and in real time.
Take Crosby Straightpoint’s best-selling load cell, the Radiolink plus, for example. The long-range, 2.4GHz version provides an industry-leading wireless range of 3,280 feet to the manufacturer’s SW-HHP handheld or software options. A Bluetooth output version, meanwhile, can be connected to any smartphone running its free HHP app on iOS or Android at ranges up to 328 feet.
Radiolink plus load cell—a world renowned best-seller
Knowledge is power
Think about what we can do when we know things like the weight and center of gravity of a load. We know how much force is required to move the load to its desired location. This will influence the selection of the lifting appliance needed, such as the overhead or mobile crane capacity required for the material handling activity. We know how much force is required to support the load, helping the proper selection of the rigging gear.
In industries like renewable energy, there is a frequent requirement to lift heavy items, such as jackets and monopiles (foundations), transition pieces, tower sections, nacelles, and blades. An installation itself might involve lifting items weighing hundreds of tons but also might require aligning components to within a few inches of each other. Having better systems giving real time, accurate information can help with that.
We can extract information about loads from paperwork such as the bill of ladings, drawings, manufacturer's catalogs or literature, labels, nameplates, and tags. However, information does not always come from a reliable and trusted source, and objects can be modified or added to since an original weight was determined. Dynamometers are an increasingly popular technology to eliminate any doubt.
What are the different types of load cell?
In simple terms, there are three options:
- Tension and compression
As the categories suggest, the choice is based on the application and the force generated. Examples of a tension load cell include load shackles and dynamometers, while compression load cells calculate weight and center of gravity. Crosby Straightpoint’s range of stainless steel ‘S’ beam load cells test in tension and compression; they are suitable for smaller silo, vessel, and tank weighing applications, or for building into original equipment manufacturer (OEM) projects and testing machines.
Load shackles test in tension
Within these three categories, there are many different types of load cell:
- Shear beams
- Double-ended shear beams
- Load pins
- And so on…
Again, there are many examples of each. The earlier-mentioned Radiolink plus is, as the name suggests, a link-style dynamometer; shackle load cells are load pins; and Crosby Straightpoint’s wireless compression product, LoadSafe, is a column type of design.
Choosing your load cell
It’s clear that there is a lot of choice when buying a load cell, but oftentimes the type of application will point you in the direction of a certain product.
Simple questions about the project, lift, or move can quickly eliminate certain load cells. Firstly, do you want to measure load or force in tension or compression? If you want to measure in tension how do you want to attach the load to the load cell?
A set of shackles—Crosby manufactures them—will be used to rig a load link or dynamometer-style load cell. In other applications headroom is limited so a load shackle solution will be required rather than a load link.
Crosby G2140 alloy bolt type shackle
If the application requires measurement in compression, it’s important to think about how many load cells are required to spread the load. Also, what data is to be captured? Total weight, individual weight or center of gravity?
Where will it be used?
Always an important consideration is the environment where the product will be used. Temperature, rain and humidity are just a few things to think about. In some cases, the load cell will be submerged and used underwater. Then there are questions about depth and duration of use to ask.
Load cell applications
There are hundreds of uses for load cells, even in the lifting and industrial space where most FAD Equipment Store customers put them to use. These are just a few examples:
- Crane tests (using water bags, block weights)
- Bollard pull tests
- Tug tests
- Center of gravity tests
- Pad eye or fly point tests
- Crash barrier tests
- Lifting equipment tests (slings, chains, wire rope, hooks)
- Construction equipment tests (shoring columns, lintels)
- Lifting and spreader beam tests
- Hydraulic cylinder load tests
Of course, in some cases more than others, things like environmental protection is necessary. Crosby Straightpoint dynamometers and load cells are environmentally protected to IP67 or NEMA6. The National Electrical Manufacturers Association (NEMA) number is typically used in North America but it equates to IP67. The IP Code, typically a European or international code, is sometimes called the International Protection or Ingress Protection rating.
It is typically followed by two digits (67). The first one gives the level of protection that the enclosure provides against access to hazardous parts; and the second gives the level of protection that the enclosure provides against harmful ingress of water.
NEMA6 means that the product is dust-tight and immersible up to 3 feet, 3 inches in depth. Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time.
In oil and gas, and petrochemical, applications ATEX and IECEx intrinsically safe load cells are required. Many Crosby Straightpoint products meet Zone 0, 1 and 2 hazardous area classification. The manufacturer also boasts a DNV GL Type Approval Certificate, acknowledging that its equipment meets the rigorous standards of the global quality assurance and risk management company for their use offshore. All the while, the products are powered by standard AA batteries and protection to NEMA6 is achieved even with the battery cover missing.
ATEX and IECEx intrinsically safe load cells are often required
Buy your load cell
FAD Equipment Store stocks the full range of Crosby Straighpoint’s load cells, from the world’s most popular dynamometer, the Radiolink plus, to its BlueLink Bluetooth tension load cell, CableSafe running line dynamometer, and even its clamp on line tensionmeter (or COLT).
There are also load cells in the store’s range of Intelligent Weighing pallet truck scales and steel platform scales. In the case of a platform scale, the load will be placed on the platform, with a lifting technology such as a forklift truck, and the measurements taken. Pallet truck scales, meanwhile, are pump trucks integrated with the scale, allowing users to lift, move and weigh at the same time.
Stainless steel platform scale
Load cells, particularly those in the Crosby Straightpoint range, are commonly rigged with other products, and they are often purchased with, say, Crosby shackles or chain slings. In fact, the Radiolink plus is designed to be rigged with Crosby standard shackles. Think about the connection point between the crane hook and the load; that’s where a load monitoring device must be ‘sandwiched’ in between. The type of shackle, sling, or other rigging gear sourced will therefore be dependent on the application.
Do you really know as much about your loads as you should?