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 several 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 comprises 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 kind of weighing has several advantages. Possibly 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. Nor is it necessary to open or modify the vessels. Contamination can thus be eliminated. Cleaning can be easier. Furthermore, very precise measurement can be done ? 0.02 % of the rated load isn’t uncommon regarding 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 will not influence the measurement. The particular level could be determined gravimetrically for all 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.
Prize mounting modules not merely ensure 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 minimal height and a small installation volume. However, it is usually problematic if the vessels are already permanently installed and will 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 according to the application. Email address details are mainly distorted when force shunts can’t 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. Similar problems may appear 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 could be suffering from natural factors. For example, 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 used for scales. These not only have a low price and high accuracy, but the weight can be determined reliably, regardless of 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 look for the rated load of the force transducers, divide the full 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 around 300 t. With four supports, vessels of up to 1,200 t could 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 gets the right sensor for each application. Do you want to buy the products? In our WIKA online-shop you will find a few of our standard designs. If you have any questions, your contact will gladly assist you to.
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