Which variables are measured by a sensor depends on the applications and the various technologies. The range of sensors on the market is equally vast and diverse. Sensors in consumer applications are usually very different to sensors in industrial applications. The consumer market is dominated by big sensor manufacturers. For us, the industrial sector is far more exciting: it offers numerous interesting niches in which the right sensors usually remain in one design for several years. The whole sensor market is worth hundreds of billions and grows by five to 10% every year. However, it is also inhomogeneous and segmented as there are hundreds of measurement variables and countless applications.
Sensors for force measurement
Force is one of the most important and common physical measured variables. In principle, every force sensor could also be used to measure weight. Weight can be calculated via force and gravity.
However, it must be noted that force and gravity are vectors.
This means that the angles must also be taken into account. In practice, this is a problem for numerous applications. If the load is not transmitted 100% vertically to the load cell, this will affect the measurement. This can be illustrated with a bathroom scale: if you shift your weight on the scale, the measured value changes – an effect we’re all likely to have observed. If a weight or mass is to be determined precisely, then the vectorial relationships must also be considered. This seems clear but is not always easy in practice, and the execution often requires a great deal of design work. Let’s use as an example one of the most common and oldest electronically analysable sensor technologies – the strain gauge.
The strain gauge, developed in 1938, is based on an electrical resistance that changes its value when stretched or compressed. Owing to this simple principle and the cost-effective production, the strain gauge has become commercially established and is now one of the most commonly used sensors. Nevertheless, further principles have been established for load measurement in addition to the strain gauge. One major disadvantage of the strain gauge is the aforementioned vectorial relationship. Depending on the application, ensuring that the load to be measured is correctly ‘redirected’ to result in a resistance expansion can involve highly complex design work. When it comes to bathroom scales, as an example, this is very simple. This is reflected in the price of a consumer scale, particularly if high precision is not a crucial criterion. High-precision scales are usually based on other principles, such as an inductive control loop. Most high-precision weighing systems of the renowned American company headquartered in Switzerland rely on this principle. In other applications, where the redirection of the load is not as easy to implement, the manufacturing costs of the mechanical construction often greatly exceed the cost of the actual sensor. Different measurement principles are required here since the cost of production in complex designs can usually only be reduced to a limited extent, even at high volumes.
«New cost-effective, application-specific sensor technology will make possible the predicted exponential growth of IoT.»
Philipp Kistler, Business Segment Manager
Fewer mechanical parts means lower costs
A great everyday example is the good old video recorder. Despite unit sales in the millions, it was almost impossible to find a device for under USD 100 in shops during the peak of the video recorder’s popularity. But when DVD players hit the market, it wasn’t long before their price dropped to below USD 50. This is because these consist of significantly fewer mechanical components. This clearly illustrates the advantage of electronic solutions – they can always be produced more cheaply or made more efficient over time. The main reason is Moore’s Law (transistors double every one to two years). It cannot be applied to mechanics, but it brilliantly explains the rapid development in electronics in recent decades. In other words, sensors with the simplest possible mechanics have the best potential for low production costs. Although simple concepts have many advantages, they also have one disadvantage: they are usually relatively easy to copy. However, in the field of sensor technology, imitability must be viewed in relative terms. The key knowledge lies in the compensation algorithms, the material properties and the production and calibration process. Nevertheless, the issue of imitability should be taken into account as with any product development. The capacitive measurement principle is conceptually very simple, but places high demands on the specific expertise of developers.
Capacitive sensors: a future technology
Loads are applied to two conductive layers. This reduces the distance – and the smaller the distance, the higher the capacity. This measurement principle has been understood for many years. So far, however, capacitive sensor technology has been quite limited, particularly when compared to resistive sensor technology. This is because in comparison to a simple resistive bridge circuit, the electronics for the measurement of a capacitance were much more complex, inaccurate or expensive. This has changed in recent years. Owing to the development of touchscreens in popular consumer products, this technology has evolved rapidly. Now is the time for precise and attractively priced capacitive sensors. We must now ask the question: what are the key components in such a sensor? The first component is the material between the two electrodes (capacitor plates). This material forms both the spring element and the dielectric. Further important components are the algorithms for the compensation of temperature, humidity, non-linearities, ageing and other undesirable effects. The less the material properties change as a result of environmental conditions, the easier and better the compensation.
In-house collaboration for innovative solutions
Thanks to a setup that combines Angst+Pfister Sensors and Power sensor technology expertise and the material expertise of Angst+Pfister, specialised knowledge from all disciplines flowed into the development of the Angst+Pfister Sensors and Power LoadSensor. This expertise is notably combined for the elastomer – it forms the aforementioned spring element/dielectric. The consolidation of comprehensive specific knowledge in one company is arguably unique. This is because most sensor companies have in-depth knowledge in the field of electronics and of the typical materials used in sensors such as silicon, ceramic and often stainless steel. However, knowledge in the field of elastomers is lacking. Conversely, companies that deal with materials and elastomers lack the expertise in the fields of internal electronics and sensor technology.
Here, both come together under one roof. This arrangement has enabled us to develop the capacitive LoadSensor within a very short time – it also guarantees the further development of this technology in coming years. Driven by key customers from Angst+Pfister Sensors and Power, the sensor is already being optimised and produced for individual customer-specific applications.
Further applications for the LoadSensor are certainly expected. It is essential that the main advantages bring real added value to the customer: they benefit from the low thickness, the ‘integrated mounting’, the customer-specific design and, above all, from the attractive price in high quantities – in contrast to traditional solutions with strain gauges or load cells. How many such applications exist is yet to be seen. The market for sensors is enormous, and the trend in the field of IoT will see pronounced growth over the next few years. This will certainly bring forth countless new applications that we cannot even fathom today. The future will unveil them.
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published: 1 Eyl 2020 13:34:00 by: Angst+Pfister Group