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Load Pins 101

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A load pin is a type of load cell that can replace bolts, clevis, sheave, and equalizer pins, as well as other load-bearing components to measure tensile and compression forces. Load pins are internally gauged with a bored center containing strain gauges, allowing them to convert force into an electrical signal for engineers to accurately collect data.

Most applications for load pins in the past have been for overhead equipment like cranes and lifts. Load pins have expanded in popularity and are now often used to test and measure force, load, and limitations in a much larger variety of applications. This includes uses not only for cranes and lifting devices, but also construction equipment, industrial machines, nautical craft and equipment, aerospace, and civil engineering applications. A primary system approach with structural applications is for safety and to prevent excesses in loading and lifting.

New model types with wireless and Bluetooth technology are also resulting in more use cases for these specialized force measurement solutions. This applies to both test and measurement as well as for installed OEM components within a larger structure or apparatus.

Top Load Pin Benefits

  • Easy to install new or retrofit
  • Robust construction
  • Replaces existing load bearing pins without any system modifications
  • Engineered to order designs available
  • Can be supplied with integral connector
  • Custom sizes and higher capacities available

Load pins come in many standard shapes and sizes, as well customization options to meet a specific design or use requirement. Interface provides these measuring devices, which often replace a bolt or pin, for safety and application monitoring. Some of our load pins are exclusively designed to meet the needs of applications in hazardous environments like the oil and gas industry, or marine industry where they’ll be submerged in water during testing and for continuous use.

The Interface Load Pins are machined from high tensile stainless steel and are suitable for exposed situations including seawater. We offer standard load pins with ratings between 1.1K lbf to 3.3M lbf (500kgs to 1500 MT). We also offer custom manufactured load pins suit applications from 100 kgs to 1500+ MT.

LP Stainless-Steel Load Pin – Great for lifting applications for both short and long distances. This product can be amplified with 5VDC, 10VDC or 4-20mA Outputs. It can also be made to meet ATEX requirements. Model LP Load pin is available in capacities up to 3,000,000 lbf (13.3 kN).

WTSLP Wireless Stainless-Steel Load Pin – This advanced load can transmit wirelessly up to 600 (1,969 feet) meters in distance (clear line of sight) to a handheld display or USB base station.  The capacities range goes all the way up to 3,000,000 lbf (13.3 kN). The wireless option utilizes low power consumption for long battery life. It is configured and calibrated via PC using a base station and telemetry toolkit and compatible with Interface WTS Wireless products. The load pin is robust and uses a lightweight housing. It is environmentally sealed to IP67.

Load Pin Application

One of the largest scale applications of load pins we provided were used to measure force on a large bridge infrastructure project in the western U.S. The goal was to continuously monitor the standard force created by regular traffic, as well as the seismic force before, during, and after earthquakes. The monitoring sensors needed to be integrated into a dampener that would be attached to the structural tower.

The solution allows the company to monitor force from emitted data to cross-reference the standard traffic force with the seismic force to understand its effect on the bridge. Its purpose is to help with predictive maintenance and influence future bridge designs to better compensate for the forces of an earthquake or other natural disasters, which are common in this part of the world.

READ THE SEISMIC BRIDGE MONITORING APPLICATION NOTE HERE

READ THE INFRASTRUCTURE CASE STUDY HERE

The project required a custom product that could handle the inimitable and considerable force of a bridge under every scenario of distress. Engineers developed a custom load pin to handle the force of movement in the bridge in the event of an earthquake. This load pin was much larger than our standard version and is rated at 900,000 lbf. The large load pins were designed to be integrated into the dampener with wireless data acquisition modules connected to the load pins to allow for remote access to the data. With the integration of Interface’s custom load pins and data acquisition module, the customer was always able to continuously collect data for real-time evaluation. The sturdy construction of our load pins and 900,000 lbf rating allowed for readings during all degrees of seismic activity.

To learn more about our wide variety of load pins and there many applications, please contact our application specialists today.

Load Cell Test Protocols and Calibrations

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In the Interface Load Cell Field Guide, our engineers and product design experts detail important troubleshooting tips and best practices to help test and measurement professionals understand the intricacies of load cells and applications for force measurement devices. In this post, our team has outlined some helpful advice for testing protocols, error sourcing and calibrations.

The first step in creating test protocols and calibration use cases is to define the mode you are testing. Load cells are routinely conditioned in either tension or compression mode and then calibrated. If a calibration in the opposite mode is also required, the cell is first conditioned in that mode prior to the second calibration. The calibration data reflects the operation of the cell only when it is conditioned in the mode in question.

For this reason, it is important that the test protocol, which is the sequence of the load applications, must be planned before any determination of possible error sources can begin. In most instances, a specification of acceptance must be devised to ensure that the requirements of the load cell user are met.

Typical error sources in force test and measurement are usually identified as being related to:

  • Lack of protocol
  • Replication of actual use case
  • Conditioning
  • Alignment
  • Adapters
  • Cables
  • Instrumentation
  • Threads and loading
  • Temperature
  • Excitation voltage
  • Bolting
  • Materials

In very stringent applications, users generally can correct test data for nonlinearity of the load cell, removing a substantial amount of the total error.  If this can’t be done, nonlinearity will be part of the error budget.

An error budget is the maximum amount of time that a technical system can fail without service level consequences. In force test and measurement, it is sometimes referred to as uncertainty budget.

Nonlinearity is the algebraic difference between output at a specific load and the corresponding point on the straight line drawn between minimum load and maximum load.

Nonrepeatability is essentially a function of the resolution and stability of the signal conditioning electronics.  Load cells typically have nonrepeatability that is better than the load frames, fixtures and electronics used to measure it.

Nonrepeatabillty is the maximum difference between output readings for repeating loading under identical loading and environmental conditions.

The remaining source of error, hysteresis, is highly dependent on the load sequence test protocol.  It is possible to optimize the test protocol in most cases, to minimize the introduction of unwanted hysteresis into the measurements.

Hysteresis is the algebraic differences between output at a given load descending from maximum load and output at the same load ascending from minimum load.

There are cases when users are constrained, either by requirement or product specification, to operate a load cell in an undefined way that will result in unknown hysteresis effects. In such instances, the user will have to accept the worst-case hysteresis as an operating specification.

Some load cells must be operated in both tension and compression mode during their normal use cycle, without the ability to recondition the cell before changing modes. This results in a condition called toggle, a non-return to zero after looping through both modes. The magnitude of toggle is a broad range. There are several solutions to the toggle problem, including using a higher capacity load cell so that it can operate over a smaller range of its capacity, use a cell made from a lower toggle material or require a tighter specification.

ONLINE RESOURCE: INTERFACE TECHNICAL INFORMATION

For questions about testing protocols, conditioning, or calibration, contact our technical experts. If you need calibration services, we are here and ready to help.  Click here to request a calibration or repair service today.

Load Button Load Cells 101

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Manufactured devices, technology advancements and product designs are getting smaller and smaller as innovations demand less space to do more for their consumers. As engineers are designing products with miniaturized components, they also need high quality test and measurement solutions that produce accurate results within these smaller testing spaces.

Interface has created a series Load Button Load Cells to meet these exact requirements. These load buttons are designed and manufactured to specifically fit into small and confined spaces, providing the precision-based measurements as expected from larger load cells.

Interface Load Button Load Cells are compact strain gauge-based sensors used in a wide variety of applications, including test and measurement and for general measurement applications. Interface standard LBM and LBS Load Button Load Cells can fulfill the need for compression force measurements at a very respectable precision level for most applications.

Product diameters range from 1 inch to 3 inches, with heights from 0.39 inch to 1.5 inches. The shaped load button load cell has a spherical radius to help confine misaligned loads to the primary axis of the cell. And while these products are small, they are capable of measuring compression forces from 10 lbf all the way to 50,000 lbf. The spherical radius of our Load Cell Load Buttons also help to confine misaligned loads to the primary axis of the cell.

Interface Load Button Load Cells 

Interface’s Custom Solutions Team and Product Engineers can also help to design a specific size and capacity to fit our customer’s exact requirements. Let us know what you need by contacting us here.

Load Button Load Cells Functionality and Proper Use

Applications that use compression loads on load button load cells requires an understanding of the distribution of forces between surfaces of various shapes and finishes.

The first and most important rule is to always avoid applying a compression load flat-to-flat from a plate to the top surface of a load button hub. The reason for this is simple, it’s impossible to maintain two surfaces parallel enough to guarantee that the force will end up being centered on the primary axis of the load button load cell. Any slight misalignment, even by a few micro-inches, could move the contact point off to one edge of a hub, thus inducing a large moment into the measurement.

Minor misalignments merely shift the contact point slightly off the centerline. In addition to compensating for misalignment, the use of a load button load cell of the correct spherical radius is necessary to confine the stresses at the contact point within the limits of the materials. Generally, load button load cells and bearing plates are made from hardened tool steel, and the contacting surfaces are ground to a finish of 32µ inch RMS. If you use too small of a radius it will cause a failure of the material at the contact point, and a rough finish will result in galling and wear of the loading surfaces.

Interface Load Button Load Cells in the Real World 

The evolving world of technology and product design has created a high demand for these types of small and accurate testing equipment. Innovative industries are looking at new ways to fit more capabilities into a single device that is the same size or even smaller. OEM applications that require this type of testing equipment include medical devices, drones, industrial automation, packaging and robotics.

We have highlighted a few examples of how Interface Load Button Load Cells have been used in the medical industry to solve complex challenges related to measuring compression force in confined spaces.

Measuring Vascular Clamp Force

A customer in the medical industry wanted to test various types of vascular clamps to see which type would generate the best clamping force for surgery. Using a Model LBS Load Cell, the clamps were secured onto the compression button. A Model 9330 High Speed Data Logging Indicator provided compression force measurements and allowed the customer to determine the most appropriate clamp type. Read the full application use case here.

Optimizing Surgical Stapler Force

Another customer needed to optimize the design of their surgical stapler to make it easier and more efficient for a medical professional to use. The original equipment manufacturer mounted the surgical stapler onto a test rig to enable force verification, and then connected a Model LBMU Compression Load Cell Button to a Model 9890 Load Cell Indicator. The indicator would collect compression force data from the stapler, and that data was then analyzed to allow the OEM to determine the design changes needed to reduce the amount of force applied to use the stapler.  Learn more about this application here.

For more information on our expanding lineup of Load Button Load Cells, see the overview below. In addition, say tuned in to the IQ Blog for an exciting announcement about new Interface Load Button Load Cell technology.  Most standard Load Button Load Cells are available to ship within 2 business days. Contact us for more information or visit our QS48 now.

Click here to see the full line of Load Button Load Cells.  

Strain Gages 101

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A strain gage is a sensor that varies its resistance as it’s stretched or compressed. When tension or compression is applied, the strain gage converts force, pressure, and weight into a change that can then be measured in the electrical resistance.

At the heart and soul of every load cell is a strain gage. This is the pinnacle technology that allows engineers to collect and analyze force data. In the industry, it is known as force measurement.

Strain gages are made through a photo-etch process using a flexible backing and a very thin foil. The way a strain gage works is when the backing and foil stretches or compresses, resistance goes up and down respectively. We know this as force. Think of stretching like a three-lane highway switching to two lanes, and vice versa for compression with two lanes going into three. As the load cell’s internal strain gage experiences force, it sends a signal with a precise measurement of the amount of force it’s experiencing.

There are many different types of strain gages for a variety of environments and force measurement needs. The major difference in strain gages is the base material used in the manufacturing process. Different materials are used when a load cell needs to perform optimally in a variety of temperatures, humidity levels, and elevations. Matching the correct strain gage and a load cell to the customer’s needs is critical to accuracy.

“Here at Interface, we pride ourselves on developing the most accurate force measurement tools, and it starts with our proprietary manufacturing of the strain gage.”  Scott Dunne, Production Engineering Manager

More than 52 years ago, when our founder Richard F. Caris started Interface, he purchased over a mile of foil, which is the base material used in strain gages. Caris understood the only way to ensure Interface customers received quality results from their force measurement products was to control every aspect of engineering design, product development, and production.

The key ingredient to our precision accuracy and reliability is the fact that we have vertically integrated the entire manufacturing process from design to production and have a deep understanding of the materials necessary to suit every client’s need for optimal results

Many load cell makers purchase their strain gages from a third party. This means there’s more variability in their manufacturing process and you often find the variances in their materials clash and diminish the accuracy, or they are not correctly suited for the customer’s project requirements.  Interface makes all their own strain gages.

We have learned everything there is to know about strain gage manufacturing and can guarantee the quality of our load cells in any environment based on this tenured expertise and having manufactured and calibrated hundreds of thousands (ok, millions) of force measurement devices. And here’s a fun fact, although we’ve manufactured hundreds of thousands of load cells and strain gages, we haven’t even used half of the original mile of foil we purchased in 1968. Good product managed well can go a long way!

For more information on Interface’s commitment to accuracy and reliability, we have written The Load Cell Field Guide, the definitive resource on load cells. It is available on Amazon. You can also download our latest technical white paper, Contributing Factors to Load Cell Accuracy, for free by clicking here.

Contributor:  Scott Dunne, Production Engineering Manager, Interface

Compression Force Testing 101

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Compression is a type of force that we apply every day often without thinking and compression is intensely tested in many of the products we use on a daily basis.

Compression force is defined as the energy generated from compressing an object or substance. Compressive force is simply the direction of the force applied to the load cell. The compressive strength of materials and structures is an incredibly important engineering consideration in both designs and build.

Whether you are clicking the keys on your laptop at work or slamming on your brakes to avoid an accident on your morning commute, you are using the compression force. Testing of the compression force is essential in developing a reliable and sturdy product that can withstand the pressure applied to it many times over. Often, safety is at the core of compression testing.

Load cells incorporated into the testing process work by measuring the pushing force of an application on a single axis. The strain gage compresses to measure the load applied. The deformation of the strain gage provides the measurement data. Application tests measure the total compression force the products or structures can handle, as well as the effects of compression over time through stress tests. In both cases, original equipment manufacturers (OEMs) need accurate measurements to guarantee their products can withstand compression in the short and long-term.

Interface supplies a variety of compression-focused load cells and accessories for all types of applications, both for test and measurement, as well as for inclusion in originally manufactured products and solutions. These compression load cells are often used in vehicles, industrial automation, aerospace, and defense industries. Applications are wide-ranging, from testing the impact of drones dropping packages to the material strength of bridges during an earthquake. Interface load cells are highly-rated to provide the most accurate data and reliability over time, which is why engineers rely on Interface compression-only load cells.

Here are a few of the compression load cells available from Interface:

1601 Gold Standard® Calibration Compression-Only LowProfile® Load Cells – Interface’s Gold Standard® Load Cells are designed for calibrating other load cells. The 1601 load cell is compression-only and has options available for a second and third bridge and overload protection.

1201 Compression-Only Standard Precision LowProfile® Load Cells – The Interface 1201 LowProfile® load cell provides a “compression-only” force measurement. Its spherical-shaped top surface helps provide minimal off-axis loading. 1201 is our most popular load cell designed for static applications and has a higher output than most competitive load cells.

2101 Dual Range Standard Compression-Only Load Cells – The Interface Model 2101 consists of lower and higher capacity model 1200 type load cells which are stacked with overload protection built into the lower capacity load cell permitting the high resolution to be obtained at both low and high levels of capacity. The Model 1201 is LowProfile® moment compensated.

LBM Compression Load Button Load Cells – The Interface LBM Compression Load Button is constructed from stainless steel and has a small size for all types of sensor apps and testing. This product is available in capacities that range from 25 lbf up to 50K lbf.

There is a variety of other standard compression-only load cells, including modified and custom Interface compression testing options in multiple capacities. For more information on our compression-only products or any of Interface’s industry-leading force measurement solutions, contact our Application Engineers.