Different types of liquid level sensors include:
Optical type
Capacitive
Conductivity
Diaphragm
Float ball type
1. Optical liquid level sensor
Optical level switches are solid. They use infrared leds and phototransistors, which are optically coupled when the sensor is in the air. When the sensing end is immersed in the liquid, the infrared light escapes, causing the output to change state. These sensors can detect the presence or absence of almost any liquid. They are insensitive to ambient light, unaffected by bubbles in air, and unaffected by small bubbles in liquids. This makes them useful in situations where state changes need to be recorded quickly and reliably, and can work reliably for long periods of time without maintenance.
The disadvantage of an optical level sensor is that it can only determine if a liquid is present. If variable levels are required, (25%, 50%, 100%, etc.) each requires an additional sensor.
2. Capacitive liquid level sensor
Capacitive level switches use two conductors (usually made of metal) in a circuit with a short distance between them. When the conductor is immersed in a liquid, it completes a circuit.
The advantage of a capacitive level switch is that it can be used to determine the rise or fall of liquid in a container. By making the conductor the same height as the container, the capacitance between the conductors can be measured. No capacitance means no liquid. A full capacitor means a full container. You need to record the “empty” and “full” measurements and then calibrate the meter with 0% and 100% to show the level.
Although capacitive level sensors have the advantage of having no moving parts, one of their disadvantages is that corrosion of the conductor changes the capacitance of the conductor and requires cleaning or recalibration. They are also more sensitive to the type of liquid used.
3. Conductive liquid level sensor
A conductive level switch is a sensor with an electrical contact at a specific level. Use two or more insulated conductors with exposed inductive ends in a pipe that descends into a liquid. The longer carries the low voltage, while the shorter conductor is used to complete the circuit when the level rises.
Like capacitive level switches, conductive level switches depend on the conductivity of the liquid. Therefore, they are only suitable for measuring certain types of liquids. In addition, these sensor sensing ends need to be cleaned regularly to reduce dirt.
4. Diaphragm level sensor
The diaphragm or pneumatic level switch relies on air pressure to push the diaphragm, which engages with a micro switch in the body of the device. As the level rises, the internal pressure in the detection tube rises until the microswitch or pressure sensor is activated. When the liquid level drops, the air pressure also drops and the switch is disconnected.
The advantage of a diaphragm-based level switch is that there is no need for a power supply in the tank, it can be used with many types of liquids, and since the switch does not come into contact with the liquid. However, since it is a mechanical device, it will require maintenance over time.
5. Float liquid level sensor
The float switch is the original level sensor. They are mechanical devices. A hollow float is attached to an arm. As the float rises and falls in the liquid, the arm is pushed up and down. The arm can be connected to a magnetic or mechanical switch to determine on/off, or it can be connected to a level gauge that rises from full to empty as the level drops.
The spherical float switch in the toilet tank is a very common float level sensor. Sump pumps also use floating switches as an economical way to measure water levels in basement sumps.
Float switches can measure any type of liquid and can be designed to operate without a power supply. The disadvantage of float switches is that they are larger than other types of switches, and because they are mechanical, they need to be serviced more frequently than other level switches.
Post time: Jul-12-2023