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 in terms of the particular 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 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 weight force to create a meaningful value and therefore 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 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. Possibly the greatest advantage is that the force transducers used for gravimetric level measurement are located beyond your vessel. Thus, they do not touch the product. Neither is it necessary to open or modify the vessels. Contamination can thus be eliminated. Cleaning can be 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 ? and of course the packaging must contain the amount specified.
Another advantage is that the product does not influence the measurement. The particular 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 merely make sure 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 low height and a small installation volume. However, it really is problematic if the vessels are already permanently installed and may 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 according to the application. Results 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 essential. Then it depends on what great their supporting effect is. Similar problems may appear if the measurement is influenced by way of a high bearing weight. The low the weight of the vessel compared to the product, the more accurate the gravimetric measurement. Finally, Bonus -standing outdoor vessels can be affected by natural factors. For instance, 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 is also determined reliably, no matter where it is placed 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 the force transducers, divide the full 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 which reaches around 300 t. With Ticked Off , vessels as high as 1,200 t can be weighed with the highest accuracy. Alternatively, vessels can 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? In our WIKA online-shop you will discover a few of our standard designs. If 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