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 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 the weight force to form 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 can occur within the vessels.
Gravimetric level measurement: Advantages
This kind of weighing has several advantages. Perhaps the greatest advantage is that the force transducers useful for gravimetric level measurement can be found outside the vessel. Thus, they don’t come into contact with the product. Neither is it essential to open or modify the vessels. ไดอะแฟรม ซีล 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 ? not to mention the packaging must support the amount specified.
Another advantage is that the merchandise will not influence the measurement. The particular level could 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 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, they also make installation super easy. The module and force transducer have a low height and a small installation volume. However, it might be problematic if the vessels are already permanently installed and will 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 cannot be prevented. Ideally, the vessel ought to be mechanically decoupled. Used, however, pressure gauge could 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 way of a high bearing weight. The low the weight of the vessel compared to the 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 useful for scales. These not only have a low price and high accuracy, however the weight can be 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 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 of which reaches around 300 t. With four supports, vessels of up to 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 could be measured in many different ways. Whether gravimetric as described, or with a submersible pressure sensor, float switch or pressure sensor ? WIKA gets the right sensor for each application. Do you want to buy the products? Inside our WIKA online-shop you will discover some of our standard designs. If 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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