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 with regards to the particular level in vessels. There are numerous 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 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 part of weighing technology.
Gravimetric level measurement is specially suitable when uneven distribution may appear 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 are located outside the vessel. Thus, เกจวัดแรงดันเชื้อเพลิง don’t come into contact with the product. Neither is it essential to open or modify the vessels. Contamination can thus be eliminated. Cleaning is also easier. Furthermore, very precise measurement can be done ? 0.02 % of the rated load is not uncommon with regard to relative linearity error. This makes dosing possible when, for instance, food is filled into bags ? and of course the packaging must support the amount specified.
Another advantage is that the merchandise will not influence the measurement. The particular level can be determined gravimetrically for all contents ? solids, liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be considered. Furthermore, the measurement is not 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, in addition they make installation very easy. The module and force transducer have a minimal height and a little installation volume. However, it can be problematic if the vessels are already permanently installed and may only be placed on modules with a great deal of effort. Then it 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 be able to weigh immovable vessels gravimetrically.
Gravimetric level measurement: Disadvantages
The disadvantages of gravimetric level measurement vary in significance based on the application. Results are mainly distorted when force shunts can’t be prevented. Ideally, the vessel should be mechanically decoupled. Used, however, it can always happen that, for instance, struts are absolutely necessary. Then it depends on how great their supporting effect is. Similar problems may appear if the measurement is influenced by a high bearing weight. The lower 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 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 minimal price and high accuracy, but the weight is also 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 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 utmost 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 can be measured in many various 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? In 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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Practical application of strain transducers