Position: in the world of process weighing technology is being used in more and more applications. Which are the most important weight sensor technologies, trends and future developments here?
It is difficult to think of many measurement processes as familiar and ever-present as weighing. Whether you’re experiencing the often unpleasant check on the bathroom scales or handing over your suitcase at the airport, process weighing is virtually everywhere.
Weighing sensor technology
Today’s weighing solutions are usually based on two sensor technologies:strain gauge technology and force compensation.Traditionally,high-resolution force compensation cells were found mainly in laboratories. Incontrast,many industrial weighing applications were covered by straing auge weighing technology. Two important trends have already be gun to bridge this division:The higher resolution of strain gauge cells and the increase duse off or ce compensation cells in process weigh applications.
Weighing as part of quality control
Product recall can result in immensef in ancial losses,together with unquantifiable damage to reputation. Even worse than this is when a person is injured or property is damaged before a product can be recalled.Another as pect of quality control is compliance with packaging regulations. Regulations must be met, yet for economic reasons manufacturers are keen not to exceed the requirements of such regulations.Asaresult,moreand more companies are endeavoring to carry out 100% product control.Weighing plays an important role in this process.Modern dynamic weighing systems can already reach frequencies of over ten measurements a second and can be combined with X-ray machines and metal detectors for the detection of foreign bodies. And in these cases, a compromise must also generally be found between a ccuracy and speed.We can observe an increased use of force compensation cells in this field as a way of achieving a higher degree of accuracy and greater speed.
Gagemount weigh module
Weighing technology: Centralized – decentralized – integrated Classic weighing solutions have generally carried out auto nomous control and monitoring to a high degree,more or less integrated with a master control system or a weight controller. Today, all levels of integration can be covered. From direct PLC integration to practically autonomous weighing solutions with local control of valves,conveying elements and other process equipment.
In future,it is likely that weighing solutions will be even more directly integrated in an automation concept. Following fromthis,the percent age off ieldbuseson
weighing solutions is increasing.However, it is also clear that in the world of processing,such changes in technology will happen over a longer period of time than,for example,in office environments.
Availability and process reliability
Even the best and most reliable sensor can fail from time to time.For system swith several load cells,METTLER TOLEDO already offer sasophisticated solution:Runflat.If a car is able to complete its journey with a flattire thanks to the emergency running properties known as‘Runflat’,a virtual weighing cell allows a batch that has already been started to be completed. An auto matically generated e-mail or SMS will report an incident such as this to the plant manager or super visor.As a result,repairs can be planned without fear of production losses or alost batching control.
Strain gauges
Measuring element as a strip-type electrical resistor, which is glued onto elastic deformation elements. The resistance of the unit changes as mechanical deformation takes place, and it is this change in resistance that is then used to measure the force applied during deformation.
Strain gauge technology
Straing auge-based sensor salways achieve a higher degree of weighing accuracy.The last ten years have seen an improvement by a factor of five, which means that strain gauge weighing cells can be used in applications that were previously only as sociated with force compensation.Today,strain gauge-based measuring systems are used for tank and boiler weighing, filling systems, weighing platforms and check weighers.Thanks to its mechanical robustness and the ability to design extremely compact sensors,this measuring principle is likely to enjoy a high degree of popularity in the future.
Force compensation
The desiretouse force compensation cells in production environments makes sense. No other measuring principle can offer such a ccurate and reliable result sacross such a large range.With recent industrial developments, these cells are now used in hazardous zones with a high degree of IP protection. Sophisticated filter algorithms, in combination with powerful micro processors, distinguish reliably between effective changes in mass and environmental influences. Built-in test weights allow measurements to be calibrated and verified at anytime.Along side platform scales, typical applications include dispensing, high-precision filling and checkweighing.
When a higher degree of weighing accuracy is required
Due to a reduction in the use of solvents and the availability of more powerful substances, there is increasing demand for weighing systems to be more accurate. Studies have shown, for example, that with new sweeteners,deviations as small as 1 ppm can be identified by consumers. This correlates to an one gramdeviation in an one to nne batch.Weighing technology is one of the very few measurement processes that can measure so accurately and reliably across such a large range. As the weighing process is so highly dynamic,iwt also allows the flexible use of measuring devices,which is important when the products to be manufactured are changed frequently.To guarantee the quality and reproducibility of processes, METTLER TOLEDO’s Min Weigh provides the user with a smart function that calculates and monitors the minimum weight based on the balance used and the degree of accuracy required.
In this context,it is important to understand what accuracy, repeatability and resolution actually mean.In the field of weighing technology ,several manufacturer shave begun to display high resolutions without increasing the relevant parameters for accuracy and repeat ability.As a result,an apparent degree of accuracy is produced, which further analysis proves to be incorrect.Even for level measuring intanks,the demand for more weighing accuracy from standard level measurements that useultrasoundhasresultedinsolutions based on weighing. Today, even tanks weighing more than a hundred tons can be “placed on the balance”. Thanks to direct mass measurement with ou tmedia contact and the immunity to foam and mist,a number of other critical applications can be covered.
Force compensation
The weight of the load is held in the balance using a force of equal magnitude, positioned opposite to achieve an equilibrium. This compensatory force can be any type of force (e.g. using weighted pieces, elastic force, etc.) but today it is usually an electromagnetic force.
Modulo, the high precision weigh module, directly integrated into automatic weighing process.