In technical systems, the forces must be just right - if they are too weak, the application will not work and if they are too strong, the system will be damaged. To be safe, you need to measure the forces using specific force sensors, the force transducers, also known as load cells. We will show you what options are available and what the advantages and disadvantages of the different sensors are.
The functional principle is similar for all force transducers: strain gauges, e.g. made of a certain metallic alloy, are stretched under load. This changes the electrical resistance of the measuring strip, from which the applied force can be calculated. The difference between the various types of force transducers essentially lies in the design and in the number and arrangement of the strain gauges.
Durable, but relatively large:
Low profile force transducers
Low-profile force transducers (with shear beam) are constructed using several struts and are therefore highly rigid and designed for many cycles. They provide a good signal and can handle large shear forces. One disadvantage is that they are relatively large.
The functionality of this type of sensor is based on shear beams that connect the outer and inner rings of the sensor. Under load, the beams are subjected to shear, which is measured by strain gauges. In most cases, eight or more strain gauges are installed in order to precisely record the forces and ensure high measurement accuracy. At the same time, this design makes it possible to compensate for the effects of lateral forces. This increases the reliability of the force measurement.
Robust and durable
Low profile force transducers offer a robust design and long service life. These sensors can also withstand higher lateral and transverse forces. Low profile force transducers are designed to withstand up to 100 million cycles (loading and unloading or loading in tension and compression of a transducer). This makes them suitable for long-term loads.
Low-profile force transducers are often used in areas where high precision and durability are required. A typical application example is the use in testing machines for material testing, which repeatedly load a material. They are also used in calibration systems to calibrate other force transducers. Their ability to withstand high lateral forces also makes them interesting for applications in building monitoring, where the stability of structures under changing loads must be tested.
For centrically acting forces: cylindrical force transducers
Cylindrical force transducers, also known as ring force transducers, often have the highest rigidity and are therefore suitable for dynamic applications. However, they do not offer the same signal height as low-profile force transducers and cannot withstand lateral forces. As ring force transducers, they are also very sensitive to non-centric forces - a defect is possible at just one third of the compression force range.
For high-precision applications
Cylindrical load cells are preferably used in applications where the force acts centrally on the sensor. Their design makes them suitable for applications in which the forces act very linearly and evenly. This is the case, for example, when monitoring screw force, where the force transducers are dimensioned in such a way that the screw is guided through the force transducer with a precise fit. The tolerance must be kept extremely low in order to ensure exact force measurement.
They are also predestined for monitoring bolt connections. A typical example is their use in high-precision applications such as cranes, where the tensile forces must be measured accurately. Cylindrical force transducers are also an indispensable component in other safety-critical applications.
Pancake (low profile) force sensors
- Measuring range 20 N to 1 MN
- Used for static fatigue testing
- Bi-directional versions available
Cylindrical force sensors
- Measuring range 30 N to 5 MN
- With quantified extraneous load
- Accuracy from 0.5% to 0.05%
The all-rounder:
Bending beam load cells
Bending beam load cells, also known as single-point load cells, are the all-rounders among force transducers. They are often the sensors with the highest precision and can be compensated for transverse forces, for example the ALF300. However, they are usually not designed for fatigue and tend to operate at a higher mechanical stress than flat profile or cylindrical load cells. Therefore, their service life is shorter in dynamic applications. A sub-category would be an S-shaped load cell for tensile forces, which has the same advantages as a bending beam, but is very sensitive to side loads.
Bending beam load cells are used in weighing and measuring technology, especially in platform scales. The design of single-point load cells makes it possible to measure the weight precisely regardless of the position of the load on the platform. This is achieved by the milling and arrangement of the strain gauges, which are glued to the bending beam and record the deformation of the beam under load. The arbitrary positioning of the load saves you having to use several load cells.
Simultaneous measurement of tension and pressure
In addition, bending beam force transducers are used in applications where tensile and compressive forces need to be measured, but no extremely high forces occur. One example of this is industrial systems that are regularly raised or lowered. S-shaped load cells, which are designed for such applications, are often used here. However, as they are very sensitive to side loads, the force application must be linear in order to achieve accurate measurement results.
Compared to other force transducers, bending beam force transducers are both more cost-effective and more accurate in their measurements.
If there is no installation space:
Diaphragm force transducer
Diaphragm force transducers, also known as miniature force transducers, are ideal for applications where a small size is crucial. The ALF259, for example, has a diameter of just 12.7 millimetres. This makes it ideal for use in confined spaces. One example would be measuring the gripping force in a robot arm.
Membrane force transducers consist of a thin membrane to which the strain gauges are applied. This design makes them very sensitive to lateral forces and moments. They are also not the most precise sensors and operate at a much higher load than the other types. For this reason, they often have an output of 1.5 mV/V or less so that they are not overloaded. They do not have high stiffness and are not suitable for highly dynamic applications in terms of accuracy and service life.
For dynamic loads
Special diaphragm force transducers are used in the automotive industry, for example, to measure pedal force. Here, the force transducer is connected to the brake pedal and measures the forces that occur when the pedal is pressed. This data is crucial for adjusting the brake actuator.
However, the applications of diaphragm force transducers are generally diverse and range from industrial applications such as production processes and machine monitoring, testing and inspection systems to robotics and materials research.
Bending shear beam force sensors
- Measuring range 1 N to 160 kN
- With moment immunity
- Ideal for weighing applications
Miniature force sensors
- Measuring range 2 N to 200 kN
- Ideal for application in small spaces
- Various load directions available
S-beam force sensors
- Measuring range 1 N to 100 kN
- Measures compression & tension forces
- Moment immunity for accurate output
Single point load cells
- For smaller and medium-sized weighing platforms
- Excellent off-centre load compensation
Trends in force measurement
Current trends in the field of force sensors focus heavily on miniaturisation, specialisation and integration into intelligent systems. These developments are aimed at making force sensors more powerful and flexible in order to meet the growing requirements in various industries.
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Miniaturisation and integrationThere is a clear trend towards smaller, lighter force sensors that can be better integrated into compact systems. This is particularly important in electronics, medical technology and robotics, where space and weight are decisive factors.
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Customised designsEver more specialised applications require ever more specific force sensors, e.g. for cryogenic or high temperatures and certain environmental conditions such as hydrogen, vacuum, etc.
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Intelligent systems and IoTThe integration of force sensors into the Internet of Things (IoT) and other intelligent systems is a growing trend. These sensors will be able to collect and transmit data in real time. This supports the development of predictive maintenance and real-time monitoring.
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High-precision applicationsIn sectors such as the automotive and aerospace industries, the demand for force sensors that can accurately measure both tensile and compressive forces is growing. These sensors are crucial for quality control processes and the improvement of safety systems.
Summary
Low-profile force transducers are characterised by their high rigidity and durability, but are very large. Cylindrical force transducers offer maximum rigidity for centrically acting forces, but are susceptible to defects with non-centric forces. Bending beam force transducers impress with their precision and versatility, but have a shorter service life in dynamic applications. Diaphragm force transducers are compact and ideal for tight installation situations, but are less precise and not suitable for highly dynamic loads.
These trends show that force sensors are not only becoming smaller and smarter, but are also being used in an increasingly diverse range of applications, from precise measurement in research to integration in everyday consumer goods.
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