Capacitance Level Detection: Mechanism And Benefits
Capacitance level detection systems use the varying electrical capacitance of a capacitor to detect the level of material in a container.
These containers have a capacitor level switch or capacitor probe installed, which gauges the level of material inside. As the level increases, the capacitive level switch stops it from overflowing, ensuring safety from spillage and contact with the material in the container.
Working Principle
The operating principle of a capacitance level detection system works on the capacitor’s varying capacitance which the capacitor forms between itself, the container wall, and the dielectric material/content that separates the two.
A capacitor has two electrode plates that are placed at a distance, separated by this dielectric material. One is a detection electrode the other a grounding electrode.
When the container begins to fill the dielectric value of the contents causes an electrical polarization between the content and the capacitor plates.
The detecting plate has a value of R (or resistance), and the grounding electrode has a value of C (or capacitance), as the container gets filled, the polarization causes a change in the value.
The capacitor switch computes this change to denote the level of contents in the container. Once the contents reach the brim, the switch ensures that the material level does not overflow.
When the container is empty, the resistance value is 0, and the capacitance value is the specific value given on installation. A capacitance probe only measures materials with a high dielectric value. The usual method of level detection is with the use of a capacitor probe.
The capacitor probe signals the level of material in a container based on the electrical difference between the dielectric value of the empty container and that of one filled with material.
The probe is inserted into the tank/container and is immersed in its contents if any. When the container is empty, the air inside acts as the dielectric material, helping to denote the level in the container as 0. As the container with the capacitor probe gets filled, the value changes. These non-conductive materials have a different dielectric value than that of the air inside.
This value causes a change in the capacitance of the metal plates. The switch then detects this change in the interior of the container. As the level of material in the container gets higher, the capacitance value changes as well.
While the container fills, the capacitor probe gets immersed in the contents, changing the dielectric value. The change is from that of air to that of the material. The capacitor computes this and signals the change in the level of air and material in the container.
The difference in this capacitance value gets smaller and smaller, when the difference is nil the switch signals an output value through a relay, denoting that the container has reached full capacity.
This method is sometimes called RF level detection after the radio frequencies used by the capacitors to signal the level in the container. While using capacitor probes, an essential factor to note is the dielectric value of the material.
Every non-conductive material has different dielectric values. The dielectric value of materials differs based on temperature, moisture content, density, and humidity.
A change in these factors also changes the dielectric value and has to be taken into account and corrected in the capacitive level switch.
Uses
A capacitive level switch system is capable of measuring levels of solids and liquids in tanks, silos and any other large container that can support the capacitor probe instrument. This aspect allows for a wide range of uses for the capacitor probe.
Bunkers, manufacturing plants, factories, and many other industries use capacitor probes in their processes. A capacitor level switch does not only detect the level of material in a container but also continuously gauges the changes in level in the container.
This continuous output is vital for many processes to ensure precision in manufacturing.
Benefits
Compared to other systems, capacitor-level detection systems offer a more real-time value of the container’s content levels as it is continually updated.
Capacitor level sensors can detect levels of solids, liquids, and even slurries allowing for a wide range of applications of the capacitor probe. The probe also measures levels when immersed in highly corrosive materials, making it a truly versatile system of level measurement.
A capacitor probe once installed requires no adjustments to detect material levels, as it has no movable parts it ensures the accuracy of its output value.
