Gravimetric level measurement in vessels

In the pharmaceutical, building materials and food industries, on vessels and silos, on platforms and dosing systems, right around kitchen and bathroom scales ? ไดอะแฟรม ซีล is measured everywhere. In industry, it becomes particularly interesting in terms of the level in vessels. There are various 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 short 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 create 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 can occur 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 are located outside the vessel. Thus, they don’t come into contact with the product. Neither is it essential 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 in terms of relative linearity error. This makes dosing possible when, for instance, food is filled into bags ? not to mention the packaging must contain the amount specified.
Another advantage is that the merchandise will not influence the measurement. The level could be determined gravimetrically for several contents ? solids, liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be considered. Furthermore, the measurement is not 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 make sure that the weight force is properly led into the force transducers, they also 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 can only be placed 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 due to 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 based on the application. Results are mainly distorted when force shunts cannot be prevented. Ideally, the vessel ought to be mechanically decoupled. In practice, however, it can always happen that, for instance, struts are essential. Then it depends on how 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 compared to the 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 increase in weight.
Typical force transducers for the weighing of vessels
Single point load cells are classically used for scales. These not only have a minimal 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 full total weight of the vessel by the amount of supports. If the rated load exceeds 10 t, you’ll be able to switch to compression force transducers, the utmost capacity which reaches up to 300 t. With four supports, vessels as high as 1,200 t can be weighed with the best accuracy. Alternatively, vessels could be suspended from S-type force transducers or fitted with strain transducers.
Note
Level could be measured in many different ways. Whether gravimetric as described, or with a submersible pressure sensor, float switch or pressure sensor ? WIKA has the right sensor for each application. Would you like to buy the products? Inside our WIKA online-shop you will discover a few of our standard designs. For those who have any questions, your contact will gladly help you.
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