In the pharmaceutical, building materials and food industries, on vessels and silos, on platforms and dosing systems, right around kitchen and bathroom scales ? weight is measured everywhere. In industry, it becomes particularly interesting with regards to the level in vessels. There are many possibilities for weight measurement or weighing. The filling level could be determined optically, hydrostatically, by ultrasound, microwaves and radar, mechanically, capacitively, by heat dissipation, by displacement and resistance or, what this article is about, gravimetrically.
The term gravimetric comprises the Latin ?gravitas? for ?gravity? and the Greek ??? ??????? for ?measure?. In gravimetric measurement, therefore, the heaviness of the mass is combined with the weight force to create a meaningful value and thus the level depends upon weighing vessels (the filling level results from the density of the medium and the geometry of the vessel). This makes gravimetric level measurement part of weighing technology.
Gravimetric level measurement is particularly suitable when uneven distribution may appear within the vessels.
Gravimetric level measurement: Advantages
This sort of weighing has several advantages. Possibly the greatest advantage is that the force transducers used for gravimetric level measurement are located outside the vessel. Thus, they do not touch the product. Nor is Special to open or modify the vessels. Contamination can thus be eliminated. Cleaning is also much easier. Furthermore, very precise measurement is possible ? 0.02 % of the rated load isn’t uncommon when it comes to relative linearity error. This makes dosing possible when, for instance, food is filled into bags ? not to mention the packaging must support the amount specified.
Another advantage is that the product does not influence the measurement. The level can be determined gravimetrically for all contents ? solids, liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be considered. Furthermore, Emergency isn’t falsified even if voids or uneven contents distribution occur in the silo or tank, as the entire contents are weighed.
Suitable mounting modules not merely ensure that the weight force is properly led into the force transducers, they also make installation very easy. The module and force transducer have a minimal height and a small installation volume. However, it usually is problematic if the vessels already are permanently installed and may only be positioned on modules with significant amounts of effort. Then it is probably advisable to bolt strain transducers to the supports. Any risk of strain transducers determine the compression of the supports caused by the weight of the contents. They thus be able to weigh immovable vessels gravimetrically.
Gravimetric level measurement: Disadvantages
The disadvantages of gravimetric level measurement vary in significance depending on the application. Email address details are mainly distorted when force shunts can’t be prevented. Ideally, the vessel should be mechanically decoupled. In practice, however, it could always happen that, for instance, struts are essential. Then it depends on what great their supporting effect is. Similar problems may appear if the measurement is influenced by a high bearing weight. The low the weight of the vessel when compared to product, the more accurate the gravimetric measurement. Finally, free-standing outdoor vessels can be affected by natural factors. For instance, if wind pushes or snow leads to a significant upsurge in weight.
Typical force transducers for the weighing of vessels
Single point load cells are classically used for scales. These not merely have a minimal price and high accuracy, but the weight is also determined reliably, regardless of where it is positioned on the platform. For optimal force introduction, bending or shear beams with the corresponding weighing modules are usually installed under tanks, silos or vessels that stand on supports. To determine the rated load of the force transducers, divide the full total weight of the vessel by the number of supports. If the rated load exceeds 10 t, you’ll be able to switch to compression force transducers, the maximum capacity of which reaches around 300 t. With four supports, vessels as high as 1,200 t could be weighed with the best accuracy. Alternatively, vessels can be suspended from S-type force transducers or fitted with strain transducers.
Note
Level could be measured in many various ways. Whether gravimetric as described, or with a submersible pressure sensor, float switch or pressure sensor ? WIKA gets the right sensor for each application. Do you want to buy the products? In our WIKA online-shop you will discover some of our standard designs. If you have any questions, your contact will gladly assist you to.
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Practical application of strain transducers