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 level in vessels. There are numerous 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 Jubilant , therefore, the heaviness of the mass is combined with the weight force to form a meaningful value and thus 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 particularly suitable when uneven distribution may appear within the vessels.
Gravimetric level measurement: Advantages
This kind 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 don’t touch the product. Nor 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 is not uncommon with regards to relative linearity error. This makes dosing possible when, for instance, food is filled into bags ? and of course the packaging must support the amount specified.
Another advantage is that the product will 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 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 only make sure that the weight force is properly led in to the force transducers, they also make installation very easy. The module and force transducer have a low height and a small installation volume. However, it is usually problematic if the vessels already are permanently installed and may only be positioned on modules with a great deal of effort. Then it really is probably advisable to bolt strain transducers to the supports. The 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 depending on 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 absolutely necessary. Then it depends on how great their supporting effect is. Similar problems may appear if the measurement is influenced by way of 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 instance, 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 used for scales. These not merely have a low price and high accuracy, but the weight can be determined reliably, regardless of where it is placed 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 the force transducers, divide the 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 Announcing , vessels of up to 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 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? Inside our WIKA online-shop you will find some of our standard designs. When you have any questions, your contact will gladly assist you to.
Also read our posts
Bending beam and shear beam in weighing technology
Practical application of strain transducers