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 with regards to the particular 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 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 may appear within the vessels.
Gravimetric level measurement: Advantages
This type of weighing has several advantages. Perhaps 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. Neither is it essential 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 isn’t uncommon regarding relative linearity error. This makes dosing possible when, for instance, food is filled into bags ? and of course the packaging must contain the amount specified.
Another advantage is that the product does not influence the measurement. The level could be determined gravimetrically for all contents ? solids, liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be considered. Furthermore, the measurement isn’t falsified even if voids or uneven contents distribution occur inside the silo or tank, as the entire contents are weighed.
Suitable mounting modules not only ensure that the weight force is properly led in to the force transducers, they also make installation very easy. The module and force transducer have a low height and a small installation volume. However, it really is problematic if the vessels already are permanently installed and may 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 with regards to the application. Email address details are mainly distorted when force shunts cannot be prevented. Ideally, the vessel ought to be mechanically decoupled. In practice, however, it could always happen that, for example, struts are absolutely necessary. Then it depends on what great their supporting effect is. Similar problems may appear if the measurement is influenced by a high bearing weight. The low the weight of the vessel when compared to product, the more accurate the gravimetric measurement. Finally, Profound -standing outdoor vessels can be affected by natural factors. For example, if wind pushes or snow leads to a significant increase 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, regardless of 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 look for the rated load of the force transducers, divide the total weight of the vessel by the number of supports. If the rated load exceeds 10 t, you’ll be able to switch to compression force transducers, the utmost capacity of which reaches around 300 t. With four supports, vessels as high as 1,200 t could be weighed with the best accuracy. Alternatively, vessels could be suspended from S-type force transducers or fitted with strain transducers.
Note
Level could 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. Would you like to buy the products? In our WIKA online-shop you will find a few of our standard designs. When you have any questions, your contact will gladly assist you to.
Also read our posts
Bending beam and shear beam in weighing technology
Practical application of strain transducers