Level Sensors
Solid Level Sensors
Level sensors are used to detect the level of substances within a container or some physical boundary. Solid level sensors measure the levels of substances such as slurries, granules or powders. Level sensors that use point-level detection to measure solids include vibrating point level sensors, rotating paddle level sensors, mechanical (diaphragm) level sensors, microwave/radar level sensors, capacitance (RF) level sensors, optical interface level sensors and ultrasonic level sensors. Two of these are explained below:
Vibrating point level sensors are used to detect levels of fine and very fine powders (between 0.02g.cm³ to 0.5g/cm³) and granular solids (density of 0.5g/cm³ or greater). Single-probe vibrating level sensors tend to eliminate build-up of material on the probe, are not affected by dust or static-charge build-up, changes in conductivity or temperature, pressure or humidity.
Rotating paddle level sensors involve a low speed gear motor that rotates a paddle wheel, sensing the level through the amount of resistance it encounters from the material. It cannot be used for very low density materials as its weight is insufficient to resist the paddle. The main drawback is that material may build up on the paddle.
Liquid Level Sensors
Liquid level sensors can measure continuously or at point-level. Common liquid measurement sensors include magnetostrictive level sensors, resistive chain level sensors, hydrostatic pressure level sensors and air bubbler level measurement systems. Magnetostrictive level sensors consists of a magnet sealed inside a float which travels up and down a stem that has a magnetostructive wire. These are usually used for continuous level measurement in storage and shipping containers holding liquids. They provide a high degree of accuracy as long as the the right float is chosen according to the gravity of the liquid.
Air bubbler systems are suitable for all sorts of liquids containing suspended solids as it contains no moving parts, whether sewage, drainage water, etc. It contains a bubble tube with an external sensor, making it appropriate for hazardous liquids as well. One of the main advantages it that it is self-cleaning through high-pressure air.