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 in terms of the level in vessels. There are numerous 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 comprises the Latin ?gravitas? for ?gravity? and the Greek ??? ??????? for ? Moneygrubbing ?. In gravimetric measurement, therefore, the heaviness of the mass is combined with weight force to create 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 part of weighing technology.
Gravimetric level measurement is specially suitable when uneven distribution can occur within the vessels.
Gravimetric level measurement: Advantages
This sort of weighing has several advantages. Perhaps the greatest advantage is that the force transducers used for gravimetric level measurement can be found outside the vessel. Thus, they do not come into contact with the product. Nor is it essential to open or modify the vessels. Contamination can thus be eliminated. Cleaning can be easier. Furthermore, very precise measurement can be done ? 0.02 % of the rated load isn’t uncommon with regards to relative linearity error. This makes dosing possible when, for example, food is filled into bags ? not to mention the packaging must contain the amount specified.
Another advantage is that the merchandise does not influence the measurement. The level can be determined gravimetrically for several contents ? solids, liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be viewed as. Furthermore, the measurement is not falsified even though voids or uneven contents distribution occur inside the silo or tank, because the entire contents are weighed.
Suitable mounting modules not only ensure that the weight force is properly led in to the force transducers, in addition they make installation super easy. The module and force transducer have a minimal height and a little installation volume. However, it can be problematic if the vessels already are permanently installed and will only be placed on modules with a great deal 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 depending on application. Email address details 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 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 when compared to product, the more accurate the gravimetric measurement. Finally, free-standing outdoor vessels can be suffering from 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 useful for scales. These not merely have a low price and high accuracy, however 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 often installed under tanks, silos or vessels that stand on supports. To look for the rated load of these force transducers, divide the total weight of the vessel by the amount of supports. If the rated load exceeds 10 t, it is possible to switch to compression force transducers, the maximum capacity of which reaches around 300 t. With four supports, vessels of up to 1,200 t can be weighed with the best accuracy. Alternatively, Apocalypse could be suspended from S-type force transducers or fitted with strain transducers.
Note
Level can 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 and every application. Would you like to buy the products? Inside our WIKA online-shop you will find a few of our standard designs. In case you have any questions, your contact will gladly help you.
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Bending beam and shear beam in weighing technology
Practical application of strain transducers