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...
The Uses & Advantages of Load Pins
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 durable and accurate measurement, even in extreme environments such as space, oceans, mines, and deserts, amongst others. An example of the value of load pins, due to their design, is identifying applied forces, and measuring and preventing overloads transferred through the pin joints.
One of the major advantages of force sensors overall, and load pins in particular, is the incorporation of the internal strain gage. Patented by Strainsert, the internal gage technology facilitates a much wider utilization of load pins. This well-established technology has been proven for over sixty years.
This is possible because the pin is not completely solid, a small internal bore is machined along the neutral axis to house and protect the internal instrumentation, isolating the gages from the surrounding environment. The load pins are further manufactured from high strength stainless or alloy steel materials to optimize linearity and repeatability.
Standard load pins fit many applications, but custom pins have also become necessary and popular as applications to use load pins have significantly increased. The ability to purchase a custom load pin designed for their unique specifications is a big advantage. Strainsert has optimized the custom design process to allow cost effective and expedient manufacturing to meet demanding schedules.
How Do Load Pins Work?
Load Pin Strain gages are typically interwired into a Wheatstone bridge circuit. When excited by a fixed voltage source, the bridge circuit produces a variable output voltage that is proportional to the force applied to the elastic element. Therefore, in a load pin, the input quantity (mechanical) is converted into an output quantity (electrical) by successive conversion of several physical quantities:
- Force is converted to mechanical stress according to the fundamental equations of strength from materials science.
- Stress is converted to strain according to Hooke's law.
- Strain becomes a relative resistance variation.
- Variation in relative resistance is converted to a change in the output voltage by means of the Wheatstone bridge.
In summary, applying a load produces a deformation in the Load Pin it, which is then measured by the strain gauges and, finally, converted into a measurable electrical signal in the Wheatstone bridge.
Applications for Load Pins
When a force acting on a structure needs to be quantified, the necessary equipment is often expensive and difficult to install. Load pins are a key element which solves that problem as they are installed as another direct component of an assembly to replace non-instrumented pins or shafts already existing in the load path. When a force is applied to the instrumented load pin, the strain gages produce an output signal that allows load measurement, including high stress and overload conditions.
Load pins are utilized in many different applications, a sampling is provided below:
- Bearing Blocks
- Brake Anchors
- Structural Tests
- Flight Simulators
- Winch/Crane/Lifting Systems
- Landing Gear Clevis Joints
- Mooring Lines/Lanyards
- Sprocket/Pulley Axles
- Bombay/Cargo Doors
- Railroad/Towbar Connections
- Armament Suspension Systems
- Rocket Reaction Forces
- Aircraft Wing Joints
- Conveyors
- Test Machines
- Hydraulic Actuators
- Nuclear Fuel Rod Control
- Robotic Pin Joints
- Sheave Axles
- Ground Support Equipment
Typical Features of a Load Pin
The load pins are manufactured from robust stainless-steel or other high strength alloy steel materials. Therefore, they have a high corrosion resistance composition and can be designed for use in very harsh environments.
Most load pin systems include thermal compensation. In addition, they are easy to install and maintain, representing an economical solution to difficult load measurement conditions. An optional wireless transmitter for the load pin incorporates integrated electronics that enables monitoring without cables. Properly installed and calibrated load pins can be designed as drop-in replacements, minimizing installation costs and also mitigating the requirement to add additional hardware components into the load path.
Why is Calibration of Load Pins Essential?
Load pins are critical to many industries including aerospace, marine, oil/gas exploration, military, aviation and automotive. Product liability and safety issues demand that force measurements are demonstrated to be accurate. Focus on traceability to NIST standards is also typically a requirement for compliance to ISO and AS certifications.
As all load pins are subject to deterioration due to use, mistreatment, drift or aging, calibration at regular intervals is necessary to ensure the load pin is performing within specification. Over time, wear and tear can degrade performance of the load pin and can become less reliable due to electrical influence, mechanical effects, instrumentation faults and loose cables etc. Failure to inspect or clean load pins is another significant factor that can lead to operational issues, as particulate matter can build up around load pins even in clean environments. Regular yearly calibrations help to ensure optimal performance is achieved.
Ştefănescu, D. M. (2020). Handbook of Force Transducers: Characteristics and Applications. Springer Nature.
Ştefănescu, D. M. (2011). Handbook of Force Transducers: Principles and Components. Springer-Verlag.
