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 level in vessels. There are various 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 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 thus 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 a part of weighing technology.
Gravimetric level measurement is specially suitable when uneven distribution can occur within the vessels.
Gravimetric level measurement: Advantages
This type of weighing has several advantages. Possibly the greatest advantage is that the force transducers useful for gravimetric level measurement can be found beyond your vessel. Thus, they don’t come into contact with the product. Nor is it necessary to open or modify the vessels. Contamination can thus be eliminated. Cleaning can be much easier. Furthermore, very precise measurement can be done ? 0.02 % of the rated load is not uncommon when it comes 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 merchandise does not influence the measurement. The 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 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 merely ensure that the weight force is properly led into the force transducers, in addition they 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 placed 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 the application. Results are mainly distorted when force shunts cannot be prevented. Ideally, the vessel should be mechanically decoupled. Used, however, it could always happen that, for example, struts are essential. Then it depends on what great their supporting effect is. Fascinating 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 could 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 merely have a minimal 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 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 of which reaches around 300 t. With Truth , vessels as high as 1,200 t can 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 has the right sensor for each application. Do you want to buy the products? Inside our WIKA online-shop you will find a few of our standard designs. Should you have any questions, your contact will gladly help you.
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