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 when it comes to the particular level in vessels. There are many possibilities for weight measurement or weighing. The filling level can 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 is composed of 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 form a meaningful value and thus the level is determined by weighing vessels (the filling level results from the density of the medium and the geometry of the vessel). This makes gravimetric level measurement a part of weighing technology.
Gravimetric level measurement is specially suitable when uneven distribution may appear within the vessels.
Gravimetric level measurement: Advantages
This type of weighing has several advantages. Perhaps the greatest advantage is that the force transducers used for gravimetric level measurement can be found beyond your vessel. Thus, they don’t touch the product. Nor is it necessary to open or modify the vessels. Contamination can thus be eliminated. Cleaning is also easier. Furthermore, very precise measurement is possible ? 0.02 % of the rated load is not uncommon regarding relative linearity error. This makes dosing possible when, for example, food is filled into bags ? and of course the packaging must support the amount specified.
Another advantage is that the merchandise does not influence the measurement. The particular level could be determined gravimetrically for all contents ? solids, liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be viewed as. Furthermore, the measurement isn’t falsified even if voids or uneven contents distribution occur inside 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, in addition they make installation super easy. The module and force transducer have a low height and a small installation volume. However, it really is problematic if the vessels are already permanently installed and will only be positioned on modules with significant amounts of effort. Then it really is probably advisable to bolt strain transducers to the supports. The 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 according to the application. Results are mainly distorted when force shunts cannot 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 can occur 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, Confidential -standing outdoor vessels can be suffering from natural factors. For example, if wind pushes or snow results in a significant upsurge in weight.
Typical force transducers for the weighing of vessels
Single point load cells are classically useful for scales. These not only have a low price and high accuracy, however the weight can be 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 these force transducers, divide the total weight of the vessel by the number of supports. If the rated load exceeds 10 t, it is possible to switch to compression force transducers, the maximum capacity of which reaches up to 300 t. With four supports, vessels of up to 1,200 t can be weighed with the best accuracy. Alternatively, vessels can be suspended from S-type force transducers or fitted with strain transducers.
Note
Level can be measured in many various ways. Whether gravimetric as described, or with a submersible pressure sensor, float switch or pressure sensor ? WIKA has the right sensor for every application. Do you want to buy the products? In our WIKA online-shop you will discover a few of our standard designs. When you have any questions, your contact will gladly help you.
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