In order to determine the type of level measurement technique to be applied, a number of questions ought to be borne in mind. First, a complete knowledge of the type of vessel, including internal obstructions, size and depth, and existing connections, must be acquired. The technique applied will also depend on the type of substance to be measured – whether it is solid, liquid, dielectric, as well as the temperature and pressure of the substance. Moreover, any possible chemical reactions and the amount of electricity that can be consumed must also be checked.
There are several kinds of level measurement techniques, of which some are described as follows:
- Displacers: These devices measure the volume of a solid body that is submerged in a liquid, by providing an accurate reading of its buoyancy and the amount of liquid displaced. However, in this case, we must be careful so as to ensure that the density of the floating body is greater than the density of the liquid in which it is submerged.
- Pressure gauges: These devices measure the level of a substance by reading the hydrostatic pressure created at the bottom of the container in which the substance is stored. The level is calculated by reading the difference between the pressure created at the top and at the bottom of the liquid.
- Balance technique: This technique calculates the level of the substance by subtracting the weight of the tank from the total weight of the substance and the tank. This method, however, is not very reliable, because atmospheric conditions such as rain or wind may interfere with the readings.
- Radar system: In this method, short electromagnetic waves are sent out to read the distance and location of the substance. When this method is applied, a radiation angle becomes important, as the short electromagnetic waves may be reflected by the container within which the substance exists. The reflected waves are received by a set of antennae.
- Laser technique: These level measurement diodes or devices emit short electromagnetic waves, which work pretty much on the same principle as the radar method. This is also known as the time-of-flight technique, and is an important non-contact technique.
Level measurement techniques are widely divided into contact and non-contact techniques depending on the type of substance to be measured. These are used in the chemical, plastics and food and beverages industries, among many others.