Force Sensors
Force sensors are transducers that transform mechanical input forces like weight, tension, compression, torque, strain, stress, or pressure into an electrical output signal whose value can be used to...
Please fill out the following form to submit a Request for Quote to any of the following companies listed on
This article will take a detailed look at load pins.
This article will look at the following topics:
A shaft instrumented with a Wheatstone bridge for detecting double shear deformation is a load pin, also known as a "Clevis pin" or a "dynamometric axle," or a particular type of weight sensor for overhead equipment. A load cell called a load pin can serve as a pivot, clevis, sheave, equalizer pin, or another weight-bearing component.
Load pins are common in cranes, winches, elevators, hoisting apparatus, sheaves, shackles, bearing blocks, and pivots. Load pins are internally gauged with a drilled center carrying force-measuring strain gauges. Like other load cells, these strain gauges monitor the change in the electrical signal caused by force, which is then converted into weight measurement.
The area of the load pin between the forces measured on the exterior is defined by two grooves. The pressure the fixed support applies is the polar opposite of that produced by the lug or sheave. The load pin measures this force or pressure, and one of many output options enables it to be transmitted to a weight display. Standard pins can be replaced with load pins without reducing headroom or jeopardizing the device's functionality or safety. Load pins can, therefore, continuously monitor the load's weight, promoting safe behavior and preventing costly overload damage. Any industry with overhead machinery that requires safe working conditions, such as agriculture, chemical processing, energy generation, marine freight, and port shipping activities, can use a load pin. Load pins are corrosion-resistant stainless steel, and the strain gauges are entirely internal so they can be used in almost any environment.
A load pin is a strain gauge made up of a Wheatstone bridge circuit. The bridge circuit generates a variable output voltage proportional to the force acting on the elastic element when activated by a fixed voltage source. As a result, with a load pin, the mechanical input quantity is changed into the electrical output quantity by successively changing multiple physical quantities:
To summarize, when a load is applied, the load pin deforms. The strain gauged, then recorded, this deformation and transformed it into a quantifiable electrical signal in the Wheatstone bridge.
The materials used to make the load pins are high-strength alloy steel or durable stainless steel. As a result, they are used in extremely hostile settings and have a high corrosion resistance composition. Thermal compensation is a feature of most load-pin systems. Additionally, they are simple to install and maintain, offering a cost-effective solution to challenging load-measuring circumstances. Electronics built inside an optional wireless transmitter for the load pin allows cable-free monitoring. The need for extra hardware components in the load path can be avoided, and installation costs can be reduced using load pins installed and calibrated properly as drop-in replacements.
The amount of force that will be evaluated and the size of an increment are necessary. To weigh safely and accurately without running the risk of overloading or operating too close to capacity, the user must make sure that their load cells are rated for a high enough weight. On the other hand, one does not want their capacity to be so enormous that one cannot draw the appropriate conclusions. Since load cells rely on electrical impulses to function, the true millivolt output of each increment drops as the resolution increases. As a result, as the measured millivolt output decreases, it may become harder to detect minor changes.
It is important to consider the setting where the load pin will be used. The first environmental element to consider will always be whether or not users demand fundamentally safe components. The user must ensure that the system's components comply with recommended certification requirements, such as FM if utilized in a hazardous environment. Working in naturally safe situations is important to emphasize, and it is strongly advised against purchasing equipment for these settings without contacting experts. After that, any other materials that might come into touch with the load pin must be considered, such as corrosive gases, liquids, or solids they may encounter. Next, the user must consider the load pin's IP or ingress protection rating in that case. The temperature at which the load pins will function may impact the product selected. If the user intends to use the load pins in extremely hot or cold conditions, the system must function properly in that particular environment. If one wants a very high resolution, one should consider factors like vibration and wind/airflow close to the measurement equipment. While some indicators can counteract these impacts, it will depend on the application's exact needs.
Legal for trade requirements: The customer is responsible for ensuring that the load pins they use are NTEP certified for the capacity and resolution for which the user plans to use them and that the device they are incorporated into can meet the relevant requirements of the NIST Handbook 44. The load pins are not considered legal for trade if the resolution is extended beyond the parameters listed on the Certificate of Conformance.
A load pin is a sensor used in various research, control, measuring, and testing applications to quantify force or weight. The load pin force sensor transforms a force into an electrical signal. The load pins offer reliable and accurate measurements even in harsh environments like space, the ocean, mines, and deserts. Identifying applied forces, measuring overloads, and preventing them from being transferred via the pin joints are some examples of the utility of load pins due to their design.
The internal strain gauge's inclusion into force sensors, and load pins, is one of their key benefits. The internal gauge technology enables a wider application of load pins. This wider application is made feasible because the pin is not entirely solid; instead, a small internal bore is machined along the neutral axis to house and safeguard the internal instrumentation, separating the gauges from the outside world. In addition, the load pins are made from high-strength stainless or alloy steel materials to maximize linearity and repeatability.
Numerous applications are suitable for standard load pins, and as the number of applications for load pins has substantially increased, custom pins have also grown in demand and necessity. Therefore, a significant benefit is the option to acquire a custom load pin made to fit their requirements.
The equipment required to quantify a force operating on a structure is frequently pricy and challenging to install. Load pins are inserted as another direct component of an assembly to replace non-instrumented pins or shafts already present in the load path; this is a key component in the solution to the problem. The strain gauges generate an output signal that enables load measurement under high stress and overload conditions when a force is applied to the instrumented load pin.
Figure 4: Load Pin Application on Structures
Various force measurement applications across various industries use load cells, load pins, tension links, bolts/studs, and other force sensors and systems. Simple force-measuring systems to cutting-edge products like NASA's Mars rovers, the Space Shuttle launch pad, and hydrostatic or submersible vehicles utilized deep below the ocean's surface are all examples of uses. Generally speaking, there are two types of applications for load cells:
Using load cells for product, component, and system research, development, and testing falls under this first category. For example, load sensors are frequently used for testing and requirement verification for new hardware designs, force distribution analysis, operational force determination, and overload or structural capabilities. In addition, computer modeling and simulation tools are increasingly used as design tools for new hardware development. As a result, the load cells are frequently used to collect real-world load and force data.
Load sensing is also used to test established, mature hardware designs when use is expanded to encompass new requirements or some form of enhanced scope or capacity and additional testing is necessary. Load cells are not just used to test/evaluate new hardware designs.
The second utilization area is centered on product or process control applications rather than new or used hardware design or testing. In these situations, the load cell products regulate a certain force or operation to guarantee that the desired force is achieved, either directly monitored or incorporated into a full-fledged automated system. The load cell systems can alert or set off various programmed actions or events. As an alternative, other control applications include monitoring forces during an operation to guarantee that specific overload or unsafe circumstances, if encountered, are identified promptly.
Several applications and illustrations of how load cells are used in control applications to make sure process force is attained, or conversely, that it is not over-ranged or exceeded are provided in this area.
There are several applications for load pins; a selection is given below.
Many industries, including aerospace, marine, oil and gas exploration, the military, aviation, and the automobile, depend on load pins. It is necessary to show that force measurements are correct to avoid product liability and safety concerns. Compliance with ISO and AS certifications frequently focuses on traceability to NIST standards.
Calibration at regular intervals is required to ensure the load pin is operating within specifications, as all load pins are susceptible to degradation through usage, abuse, drift, or aging. Electrical impact, mechanical effects, instrumentation errors, loose wires, etc., can reduce load pin performance and reliability over time. As particulate matter can accumulate around load pins even in clean surroundings, failure to inspect or clean load pins is another important aspect that might result in operational problems. Performing annual calibrations helps to guarantee optimal performance.
Dual bridge, two independent strain gauge circuits, is offered by clevis pins. Dual bridge transducers can utilize just one bridge for measurement while saving the other bridge as a backup, or they can use both bridges simultaneously for control and measurement.
With either single or dual connectors, electrical terminations can be either radial or axial (dual shown below). Cables that are permanently attached are also an option.
In situations where cable installation may be challenging, expensive, or unwelcome, the wireless load pin offers a high-performance wireless telemetry solution. The system offers great measurement precision, resolution, and stability combined with long battery life. In addition, software tools enable rapid and simple device configuration, calibration, data logging, and recording interfaces.
Force sensitivity load pins, sometimes called clevis pins or clevis bolts, are special load sensors that utilize the internal strain gauge transducer technology created and used in flat load cells and tension links. By replacing the existing shear pins, clevis bolts, load pins, shear axles, and many other types of pinned joints for the aerospace, automotive, marine, and military industries, these load pins, and clevis bolts provide exact force measurement.
The strain gauges are installed at two sites at the clevis to clevis eye interfaces and are sealed inside tiny axial holes within the load pin. The strain gauges are carefully positioned and orientated at a neutral plane concerning one particular direction of pin loading to detect just those strains caused by the shear stresses at these two sections.
The four strain gauges—two at each location—are electrically connected to create a full bridge. Since each strain gauge's signal is additive, the output of the bridge is proportional to the total loads communicated by the pin's shear planes. The circuit often includes temperature compensation, signal trim (if applicable), and balancing resistors that terminate in suitable connector sockets or integral cables.
Detailed calibration data up to 500,000 lbs. are included in standard force sensing load pins/bolts. Therefore, standard force sensing load pins/bolts need higher capacity calibration data. Although calibrations are meant to mimic installed settings, it is advised that an in-place calibration be carried out to take into account any installation, tolerance, and alignment impacts that may alter sensor data.
These standard clevis pins are often utilized in new applications where the designer can construct the exact load pin joint around the standard clevis pin specifications to maximize the performance of force measurement. Additionally, the conventional clevis pin may suit existing load pin joints or can be added by using bushings or changing the clevis assembly.
Force sensitivity load pins, sometimes referred to as clevis pins or clevis bolts, are load sensors that use internal strain gauge transducers and are used in flat load cells and tension links. By swapping out the current clevis pins in typical wire rope socket gear, these load pins and clevis bolts provide precise force measurement and monitoring.
The force sensing shackle bolts use the internal strain gauge transducer technique, also used in their flat load cells and tension links. By swapping out the current pins or bolts in typical Crosby anchor and chain shackles, these shackle bolts provide precise force measuring and monitoring.
Detailed calibration data up to 500,000 lbs. are included with standard force sensing shackle load bolts. Therefore, standard force sensing shackle load bolts need higher capacity calibration data. Although calibrations are meant to mimic installed settings, it is advised that an in-place calibration be carried out to take into account any installation, tolerance, and alignment impacts that may alter sensor data.
Clevis pins or bolts are incredibly resilient even under the worst weather and working conditions. As a result, these goods are widely applicable and have a long useful life. And are being utilized on numerous installations that call for force measuring in a shackle application.
Sheave and pulley systems use a variety of instrumented load pin designs. The user can create a sheave around our basic CPA clevis pin or have a bespoke pin made for an existing sheave design with a specific measurement capacity and geometry, enabling easy installation and maximizing measurement capacity. Observing the pin's reaction load, the instrumented sheave pins are frequently used to gauge line tension. The following formulae can be used to calculate the line tension.
Axis of Maximum Sensitivity: Position the load sensing pin's keeper flat so it is perpendicular to the axis of maximum sensitivity at a wrap angle of one-half. In this case, the wrap angle is 105 degrees, and the angle is divided by two to get 52.5 degrees. See the specification illustration below.
Ø= Wrap Angle
T = Line Tension
P = Resultant Force on Sheave Pin
Line Tension (T): Utilize the specification picture and the following calculations to calculate the tension in a line by measuring the reaction force on the sheave:
P = 2T cos (Ø/2) or T = P ÷ 2 cos (Ø/2)
Example: For a measured sheave load of 10,000 lbs. and a wrap angle of 105. The formula: can also be used to calculate the Line Tension (T).
The bi-axial clevis pin's cross section is an example of gauge alignment. The load component Py will be sensed by the gauges designated Y, whereas the load component Px will be sensed by the gauges marked X. The resultant force P is calculated using constants (Kx, Ky) derived from calibration data* and the outputs from the two bridges as Ex and Ey.
Px = Kx Ex
Py = Ky Ey
and the resulting force P = [Px]2 + [Py] squared2
Calculating the Line Tension (T) and Wrap Angle () can be done by using the following:
T = Py2 + Py2 ÷ 2Px and Ø = 2 inverse cosine ( P ÷ 2T)
Where P, Px, and Py are cross-talk effects corrected.
The advantage of load pin design is that it may be integrated into a system, ensuring the mechanical link between the components and providing data on applied forces. The most typical examples include clevis pins set at dead-end anchor points or the upper sheave/equalizer beam of EOT cranes, used to suspend a chain hoist to its trolley, on a fairlead sheave of a winch, at the head of a hydraulic cylinder, etc.
The design approach is based on controlling smaller load pin widths where the holding plates (flanges) and the center tool exerting the most force are separated. These smaller sizes produce deformation zones where strain gauges will be installed to assure accuracy and repeatability by ensuring sufficient strain concentration.
The mechanical resistance of the load pin is determined by these smaller sizes, which explains why a load pin cannot always replace a simple shaft because doing so would necessitate increasing the diameter. Instead, aeronautic-grade steels' high resistance level makes up for this mechanical change.
The safety coefficient of the clevis pin is defined by the load pin diameter, reduced diameters, and size of strain gauge pockets to reach the neutral fiber of the pin and concentrate the required strain:
The maximum overload for which we promise the load pin won't permanently distort is known as the permissible overload ("0" offset).
Strain limitation on the various shaft components serves as the foundation for the design requirements (the most critical being those parts in contact with the holding plates that are generally thinner than the central tool). For "FORCE" load pins, the range must stay between 150 and 200 N/mm2; for "HOIST" load pins, the range must be between 100 and 120 N/mm2; and for "LIFT" execution, a strain of about 50 N/mm2 is the target. If the working span of the pin is greater than those strain values, the shortfall of the span is made up of a larger diameter.
These design requirements ensure the mechanical and fatigue resilience of the load pin and the mechanical mounting supported by the load pin. In any event, aeronautic-grade steels with 1150 to 1350 Mpa (or N/mm2) are utilized to comprehend the well-known safety aspects.
The accuracy of the load pin is affected by various circumstances. First, if the load pin diameter is too close to the size of its active span, its accuracy performance will be poor (>3%). This low accuracy performance is due to the ratio diameter/operation span (load pin supports and deformation zone). Good decoupling is essential because if the holding plates make contact with the central tool (or sheave in hoisting applications), they will cause friction that will increase uncertainty, cause non-repeatability problems, and, in extreme cases, prevent the signal from returning to "0". After all, the releasing strains will not be able to be applied to the load pin due to friction (the central tool/sheave will remain blocked in the loaded position). There should be air gaps of at least 0.5 to 1
A load pin is designed to move with just one effort. When a force is introduced at an angle to the operating direction, the output signal is greatly reduced for any applied force that remains constant once the angle exceeds 10°. The reduction becomes even greater as the angle increases. For example, when the wire rope is wrapped around a sheave at an angle of 180°, the load pin will be acting in the direction of both wire rope falls; in the event of a 90° wrap angle configuration, the load pin will be operating at a 45° angle from both wire rope falls. For designs where the force direction is continually changing, it is also possible to use double-direction load pins (X and Y).
Thus, the pin diameter decreased, and the span of the mechanical components retaining and applying stresses to the pin affected the clevis pin's sensitivity (output signal). The "FORCE" design will produce between 1.5 and 2 mV/V, the "HOIST" design about 1 mV/V, and the "LIFT" version about 0.5 mV/V. But it also relies on how the load pin is mounted. Half-moon components that support and exert force on the pin will produce a particular sensitivity. However, a different sensitivity will be produced by mounting the pin diameter entirely. The span of the matching mounting, as well as the hardness of the material holding the pin and exerting stresses on it, both have an impact on load pin sensitivity.
It becomes clear that a single live calibration on a live mounting can produce the true image of applied efforts with the matching output signal by combining the mechanical mounting with the design and hardness of the material utilized. Any laboratory calibration will be more of a pre-calibration with its associated uncertainty than a calibration on a live mounting with actual stresses, even using a calibration instrument replicating identical mounting conditions.
Dimensionally, load pins as small as 7 mm in diameter can be made, and there is no upper limit; a load pin with a diameter ranging from 360 to 480 mm has already been constructed. By following a detailed examination of the application, nominal capacities between 2000N (0.2t) and 30MN (3000t) and even beyond can be created. For most applications, external bonding of strain gauges is used (models 5000-5300-5600 with visible pocket covers). In contrast, internal bonding of strain gauges (design 5050) is reserved for submerged/subaerial requirements (up to -5000m and more), high-pressure applications (up to 700 bars), or ATEX Ex d requirements (explosion-proof).
In terms of output signals, load pins can be fitted with inbuilt amplifiers for the following signals in addition to the conventional mV/V output: 4-20mA, 0-10V (and derived), RS485, Modbus, and CAN. In addition, analog amplifiers can be tuned to allow overloads without signal saturation using a range from "0" to nominal capacity or any other capacity.
Force sensors are transducers that transform mechanical input forces like weight, tension, compression, torque, strain, stress, or pressure into an electrical output signal whose value can be used to...
A load cell is a transducer which converts mechanical energy (tensile and compressive forces) into electrical signals. There are different transducer operating principles that can be utilized to convert forces...
A load pin is a sensor utilized to measure force or weight in various research, control, measurement and testing applications. The load pin force sensor converts a force into an electrical signal. The load pins provide...
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...
A platform scale is a scale that measures the weight of objects loaded on a flat platform. The function of the platform is to transmit the weight of the object to the internal measuring device and to support the object during weighing...