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 particular level in vessels. There are many 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 comprises 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 create 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 particularly 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 used for gravimetric level measurement are located beyond your vessel. Thus, they don’t touch the product. Nor is it necessary to open or modify the vessels. Contamination can thus be eliminated. Cleaning is also easier. Furthermore, very precise measurement is possible ? 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 contain the amount specified.
Another advantage is that the product will not influence the measurement. The level can be determined gravimetrically for all contents ? solids, liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be considered. Furthermore, Last Chance 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 make sure that the weight force is properly led in to the force transducers, in addition they make installation super easy. The module and force transducer have a low height and a little installation volume. However, Life-changing might be problematic if the vessels are already 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 due to 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 with respect to the application. Results are mainly distorted when force shunts can’t be prevented. Ideally, the vessel ought to be mechanically decoupled. In practice, however, it could always happen that, for instance, struts are essential. Then it depends on how great their supporting effect is. Revengeful can occur if the measurement is influenced by 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 instance, 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 merely have a minimal 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 determine the rated load of these force transducers, divide the total weight of the vessel by the amount 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 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 and every 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