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 when it comes to 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 the weight force to create a meaningful value and thus the level depends upon 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.
digital pressure gauge is particularly 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 outside the vessel. Thus, they don’t touch the product. Nor is it essential to open or modify the vessels. Contamination can thus be eliminated. ไดอะแฟรม can be 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 ? not to mention the packaging must contain the amount specified.
Another advantage is that the merchandise does 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, the measurement is not falsified even if voids or uneven contents distribution occur in the silo or tank, because the entire contents are weighed.
Suitable mounting modules not merely ensure 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 small installation volume. However, pressure gauge can be problematic if the vessels are already permanently installed and will only be positioned on modules with significant amounts of effort. Then it is probably advisable to bolt strain transducers to the supports. Any risk of strain transducers determine the compression of the supports caused by 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 depending on application. Results 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 essential. Then it depends on how great their supporting effect is. Similar problems can occur if the measurement is influenced by way of 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 low price and high accuracy, however the weight is also determined reliably, no matter 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 maximum capacity of which reaches up to 300 t. With four supports, 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 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. Would you like to buy the products? Inside our WIKA online-shop you will find some of our standard designs. When you have any questions, your contact will gladly assist you to.
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