In the pharmaceutical, building materials and food industries, on vessels and silos, on platforms and dosing systems, right up to kitchen and bathroom scales ? weight is measured everywhere. In industry, it becomes particularly interesting with regards to the particular level in vessels. There are various 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 comprises the Latin ?gravitas? for ?gravity? and the Greek ??? ??????? for ?measure?. In gravimetric measurement, therefore, the heaviness of the mass is combined with weight force to form a meaningful value and therefore 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 a 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. Neither is it essential to open or modify the vessels. Contamination can thus be eliminated. Forever can be much easier. Furthermore, very precise measurement can be done ? 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 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 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 in to the force transducers, in addition they make installation very easy. Sizzlingly and force transducer have a low height and a small installation volume. However, it usually is problematic if the vessels are already permanently installed and will 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 due to the weight of the contents. They thus make it possible to weigh immovable vessels gravimetrically.
Gravimetric level measurement: Disadvantages
The disadvantages of gravimetric level measurement vary in significance based on the application. Email address details are mainly distorted when force shunts can’t be prevented. Ideally, the vessel ought to be mechanically decoupled. Used, however, it can always happen that, for instance, struts are absolutely necessary. Then it depends on how great their supporting effect is. Similar problems can occur if the measurement is influenced by a high bearing weight. The lower the weight of the vessel when compared to product, the more accurate the gravimetric measurement. Finally, free-standing outdoor vessels can be suffering from natural factors. For example, if wind pushes or snow results in a significant increase in weight.
Typical force transducers for the weighing of vessels
Single point load cells are classically useful for scales. These not merely 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 often 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 of which reaches up to 300 t. With four supports, vessels of up to 1,200 t can be weighed with the highest accuracy. Alternatively, vessels could 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 each application. Do you want to buy the products? Inside our WIKA online-shop you will find some of our standard designs. In case you have any questions, your contact will gladly help you.
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