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 when it comes 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 the weight force to form 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.
Gravimetric level measurement is particularly suitable when uneven distribution may appear within the vessels.
Gravimetric level measurement: Advantages
This type of weighing has several advantages. Possibly the greatest advantage is that the force transducers used for gravimetric level measurement can be found outside the vessel. Thus, they don’t come into contact with the product. Nor is it essential 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 is not uncommon in terms of 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 does not influence the measurement. The particular level could be determined gravimetrically for all contents ? Audacity , liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be considered. Furthermore, the measurement isn’t falsified even though 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 into 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 might be problematic if the vessels are already permanently installed and can only be placed on modules with significant amounts 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 be able to weigh immovable vessels gravimetrically.
Gravimetric level measurement: Disadvantages
The disadvantages of gravimetric level measurement vary in significance based on the application. Email address details are mainly distorted when force shunts can’t be prevented. Ideally, the vessel should be mechanically decoupled. In practice, however, it can always happen that, for instance, struts are essential. Then it depends on how great their supporting effect is. Similar problems 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 could be suffering from natural factors. For instance, 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 minimal price and high accuracy, however the weight can be determined reliably, no matter where it is placed 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 amount of supports. If the rated load exceeds 10 t, it is possible to switch to compression force transducers, the maximum capacity which reaches around 300 t. With four supports, vessels as high as 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 can be measured in many different ways. Whether gravimetric as described, or with a submersible pressure sensor, float switch or pressure sensor ? WIKA has the right sensor for every application. Do you want to buy the products? Inside our WIKA online-shop you will discover some of our standard designs. In case 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