At HVAC we sell level switches for liquids. But what is a level switch? How does it work? Where can it be used? Level switches, also known as level sensors, are instruments that work with an electrical contact (reed switch) and a magnetic float. The movement of the float opens or closes the electrical contact. With them it is possible to have versatile low-cost solutions for automation.
Danfoss AKS 38
The Danfoss AKS 38 is an electromechanical float switch produced to provide a stable electromechanical response to liquid level fluctuations. The simple and basic design ensures long-lasting performance and reliable operation for various applications. The AKS 38 can monitor the liquid level in vessels and accumulators or can be used as a low/high level alarm.
Liquid level switch
What are liquid level switches used for?
A level switch is an electrical or mechanical method of measuring the level of a liquid, powder, or granular material. It is designed to trigger an alarm if the level of material in a container exceeds a predetermined height or depth. When a level switch detects that a tank is full, it is called full or upper limit detection. If the material level drops, indicating the tank is nearly empty, the switch will also provide an alert, known as low level or empty detection. Level switches are an essential part of production operations and are used in harsh conditions where extreme temperatures, pressures and vibrations are present. The diversity of level switches makes them applicable to any condition to measure a wide range of products. Its accuracy, reliability, and durability are a must for efficient industrial applications.
Liquid level switch types
What are the different types of liquid level sensors? The different types of liquid level sensors include:
Optical liquid level sensors
Optical sensors work by solid state. They use an infrared LED and a phototransistor that are optically coupled when the sensor is in the air. When the sensing tip is immersed in liquid, infrared light escapes and causes the output to change state. These sensors can detect the presence or absence of almost any liquid. They are not sensitive to ambient light and are not affected by foam when in the air or small bubbles when in a liquid state. This makes them useful where the change of state needs to be noticed quickly and reliably, and where they can be operated reliably for extended periods without maintenance. For example, the SST Optomax digital liquid level sensor is a popular low-cost, low-maintenance infrared LED sensor. The disadvantage of an optical liquid level sensor is that it can only determine whether liquid is present or not. If variable levels are required (25%, 50%, 100%, etc.), each requires an additional sensor.
Capacitive Liquid Level Sensors
Capacitive liquid level switches use 2 conductive electrodes (usually metal) in a circuit that are a short distance from each other. When the electrodes are immersed in a liquid, a circuit is completed. The advantage of a capacitive liquid level switch is that it can be used to determine the rise or fall of liquid in a vessel. By making the electrodes the same height as the container, the capacitance between the electrodes can be measured. No capacitance means no liquid. Full capacitance means a full container. Measurements of "empty" and "full" should be recorded, then a gauge calibrated with 0% and 100% to show liquid level. Although capacitive liquid level sensors have the advantage of having no moving parts, one of their disadvantages is that corrosion of the electrodes will change the capacitance of the electrode, eliminating cleaning or recalibration. They are also more sensitive to the type of fluid used.
Conductive liquid level sensors
Conductive liquid level switches are sensors with an electrical contact at a specific liquid level. Two or more insulated appliances with exposed prongs are used inside a pipe submerged in the liquid. A longer appliance carries a low voltage, while a shorter one is used to complete the circuit when the liquid level rises to meet it. Like capacitive liquid level switches, conductive liquid level switches depend on the conductivity of the liquid. Therefore, they are only useful for measuring certain types of liquids. Also, the tips of these sensors should be cleaned at regular intervals to reduce fouling.
Diaphragm Liquid Level Sensors
Pneumatic or diaphragm liquid level switches rely on air pressure to push a diaphragm which is coupled to a micro switch inside the body of the unit. As the liquid level increases, the internal pressure within a sensing pipe increases until the microswitch or a pressure sensor is activated. As the liquid level drops, the air pressure also drops and the switch trips. The advantage of a diaphragm based liquid level switch is that an in-tank power supply is not required, it can be used with many types of liquids and since the switch does not come into contact with the liquid. However, because it is a mechanical device, time consuming maintenance is required.
Floating Liquid Level Sensors
Float switches are the original liquid level sensors. They are mechanical devices. A hollow float is connected 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 pressure gauge that rises from full to empty as liquid levels drop. The ball float switch in a toilet tank is the most common type of float liquid level sensor used. Sump pumps also use float switches (see right) as a cost-effective way to gauge the water level in a basement sump pit. Float switches can measure any type of liquid and can be designed to require no power to operate. The downside to float switches is that they are larger than other types of switches, and because they are mechanical, they need to be serviced more often than other liquid level switches.