What types of force transducers/ force sensors are there?
The new magnetization technology revolutionizes measurement technology
The traditional force transducer or force sensor has the task of measuring a tensile force or compressive force. To this end, similar technology agreements have been available until now. All work on the principle of converting a mechanically induced material change into a measurable signal. A new technology, the so-called magnetostriction, is able to exclude the problems of the previous methods.
Applications for force transducers or force sensors
A revolution in this type of measurement technology has far-reaching consequences, considering the wide range of applications:
– Process control: For joining or riveting processes, the correct pressing pressure is of great importance for the proper functioning of the workpiece. The same applies in the pharmaceutical industry for the pressing of an active ingredient in tablet form.
– Process control: Conveyor belts in a production plant must maintain a constant belt tension.
– Test measurements: In production, test series are used to determine the correct prestressing force for a screw connection.
– Traffic engineering: Reaction moments in eddy current brakes or water vortex brakes, as well as the load capacity of a crane, must be measured.
– Biomechanical measurement: In medical diagnostics, hand pressure or impression are measured by sensors on the corresponding devices. Many scales operate on the same principle.
The traditional force transducer or force sensor has its drawbacks
The examples given illustrate the importance of technology, but also its difficulties. How to find the right configuration for these very different challenges? Strain gauges, or DMS for short, are a tried and tested method. This strain gage, conveniently designed and positioned, converts the force applied to it into a measurable signal. A first problem is to place the strain gage at the measuring point in a mechanically correct way. A second problem is how the sensor behaves under a long life load. If the characteristic curve of the sensor changes due to a changed mechanical coupling, the measurement becomes inaccurate. Therefore, many measuring devices must be maintained
and recalibrated until the measuring strips are no longer suitable at some point.
What happens to the measuring strips
Today, the conventional force sensor or force transducer evaporates mainly in polymers. These are applied to the corresponding measuring points with a special adhesive. Special adhesives must ensure the necessary mechanical coupling and must not be eroded. There are technical requirements under which adhesion is difficult and necessary, e.g. for the hardening of the adhesive, do not occur. But even if a measuring point can be installed, the measured value must be taken, resent and read. One attempt to avoid these problems is to build prefabricated complete modules that an end user can install in their entirety.
DMS application variant
The classic use of a DMS is not always practicable for many end users. Alternatively, strain gages and signal processing can be integrated into a carrier. This workpiece with its stretching and tensile properties defines the characteristic curves of a force sensor or force transducer. However, this complete package must also be mechanically coupled into an application. Such a force sensor or force transducer is screwed or welded. On the one hand, this is often complex, costly and also has an irritating effect on the accuracy of the sensor.
The revolution in force measurement: the inductive force sensor
In order to arrive at a completely new technology that avoids many of the disadvantages and difficulties mentioned above, it is necessary to take a decisive step: This is a step beyond the use of existing strain gauges in classical force transducers. How is this possible? Strain gages are replaced by a magnetic inductive force sensor. The use of this new technology is based on the principle of reverse magnetostriction. This means that the magnetic properties change at a measuring point under tensile or compressive load. These can be easily collected and recorded. In a first approximation, they represent the deformation or compression of the material. Magnetic changes are causal and in their order of magnitude are related to the force experienced by a material.
Magnetostrictive technology instead of strain gauges
The new force measurement technique represents a quantum leap: For the first time, it does not depend on the mechanical coupling to a measurement point, just like the other techniques described. This unit of measurement consists of a magnetostrictive waveguide and a variable position magnet. A pulse of induced current in the waveguide generates a circular magnetic field. If this strikes the magnetic field of the position magnet, a type of density wave is generated, which is detected by a special sensor. According to the time-of-flight principle, the time difference between the current pulse and the density wave serves as an indicator of the placement of the position magnet. In this way, a non-contact measurement is performed. These measurement methods are suitable for applications where strain gages reach their limits. This magnetostrictive method is safe, durable and maintenance-free and eliminates mechanical coupling problems.
