When evaluating instruments you will want to check the manufacturer’s ratings for: Accuracy, Sensitivity and Responsiveness You will need to consider material to be measured as well as tank or bin size and shape and available mounting locations for the level switch.

Air Bubbler Level Tubes can be used in open tanks. They have no moving parts and are self cleaning. They are good for continuous measurement on wastewater and sludge. Air or gas is forced through a tube submerged in the liquid to be measured. The depth of the process fluid is measured by the change in hydrostatic pressure in the storage tank.

Capacitance level sensors also know as RF (Radio Frequency) sensors are used on a variety of solids, liquids and slurries. Capacitance probes have an outer shell and a metal probe that serve as the plates of the capacitor. When the material to be measured covers the probe and a relay is energized. The relay can be used to acuate a pump or alarm. One tank may have several different probes. A high level switch and a low level switch are often used in one tank.

Ultrasonic level sensors can be very accurate when used with humidity and temperature sensors. These are non-contact sensors that emit a high frequency and reflect it back to the sensor. The frequency will change when the path is blocked by material in the tank.

Vibrating point level switches are good for use on very fine powders and granular solids. Some units have a single probe so material bridging between a gaps is never a problem. The constant vibration of the unit prevents build up of material on the probe which could result in false readings. When the unit is covered the vibrating frequency drops causing a relay to open or close. This can be used to actuate pumps or controllers for automatic process control.