Gravimetric level measurement in vessels

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 several 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 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 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 can occur within the vessels.
digital pressure gauge : Advantages
This kind of weighing has several advantages. Possibly the greatest advantage is that the force transducers used for gravimetric level measurement can be found beyond your vessel. Thus, they don’t come into contact with the product. Nor is it essential to open or modify the vessels. Contamination can thus be eliminated. Cleaning is also easier. Furthermore, very precise measurement can be done ? 0.02 % of the rated load is not 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 support the amount specified.
Another advantage is that the product 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 considered. Furthermore, the measurement is not falsified even though voids or uneven contents distribution occur in the silo or tank, as the entire contents are weighed.
Suitable mounting modules not only ensure that the weight force is properly led into 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 could be problematic if the vessels already are permanently installed and can only be positioned on modules with significant amounts of effort. Then it really is probably advisable to bolt strain transducers to the supports. Any risk of strain transducers determine the compression of the supports caused by 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 the application. Results are mainly distorted when force shunts can’t be prevented. Ideally, the vessel should be mechanically decoupled. Used, however, it can always happen that, for example, struts are absolutely necessary. Then it depends on what great their supporting effect is. Similar problems can occur if the measurement is influenced by way of 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 affected by natural factors. For example, if wind pushes or snow leads to 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 is also determined reliably, no matter 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 number of supports. If the rated load exceeds 10 t, it is possible to switch to compression force transducers, the maximum capacity which reaches up to 300 t. With four supports, vessels as high as 1,200 t could be weighed with the best 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 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.
Also read our posts
Bending beam and shear beam in weighing technology
Practical application of strain transducers

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