What Is a Floatless Level Switch?
A floatless level switch is a device that senses liquid level without the use of a float. A float is a buoyant object, and a floatless switch is also known as a floatless relay.
A floatless level switch is an electrode-type level switch consisting of a main body, an electrode retainer, and an electrode rod (electrode strip). On the other hand, a float switch is a switch that floats on the liquid surface by buoyancy and output signals in response to the rise or fall of the liquid level.
Uses of Floatless Level switches
Floatless level switches are often used in industrial and infrastructure equipment. The following are examples of uses for floatless level switches:
- Level control and liquid level alarm output for waste tanks
- Level control and level alarm output for sewage tanks
- Level control and level alarm output for calcium carbonate tanks
This switch is used to detect slurry liquids such as sewage and wastewater. In addition, calcium carbonate tanks are generally stirred with an agitator because they solidify when left unattended. Since using a float switch for agitated liquids will fail due to the water flow, a floatless level switch is used to detect the liquid level.
On the other hand, floatless level switches can only be used with conductive liquids due to their principle. In addition, because they use electricity to detect the water level, they are not suitable for liquids that are explosion-proof. Float switches should be used when measuring the liquid level of insulating liquids or hazardous materials such as heavy oil or light oil.
Principle of Floatless Level switches
A floatless level switch consists of an electrode rod, an electrode retainer, and a floatless relay.
1. Electrode Rod
One to five electrode rods are used per floatless level switch. They are generally threaded at the end for connection to an electrode retainer or other device.
Generally, metal is used as the material, and a wide range of products are available depending on the type of liquid. SUS304 or SUS316 is used for liquid-level detection of rainwater or tap water, while titanium or Hastelloy may be used for seawater or chemicals.
Electrode rods are often sold at about 1 meter per rod. When measuring the liquid level in tanks that are taller than that, they can be extended using a connecting nut or similar device. When extending, there is a risk that the electrodes will contact each other at the bottom, so pull them apart across the separator.
2. Electrode Retainer
The electrode retainer is a component that insulates the electrode while securing it to the tank. Insulating materials such as synthetic resin are used to insulate the electrode from metal tanks.
Insulators are sometimes used to connect two to five electrode rods. This structure allows connection to external wiring while securing the electrodes with screws.
3. Floatless Relay
The floatless relay is a relay that generates a weak voltage on the electrode rods to check the water level while outputting a contact point. It is also called the body of a floatless level switch. It is generally installed by sticking it into a dedicated socket and mounting it on a DIN rail or the like.
It requires an external supply of 100 VAC or 200 VAC. It has a transformer inside and applies a weak voltage of about 12V or 5V between electrodes. When the liquid level rises and two or more electrodes are immersed in the liquid, the floatless relay transmits an output corresponding to the liquid level.
How to Select a Floatless Level Switch
Floatless level switches are selected based on the application, target liquid, and supply voltage. If the floatless level switch is used to control the tank liquid level, use three electrode rods. For alarm only, 1 to 3 electrode rods can be used.
The materials of electrode rods and connection nuts are selected according to the target liquid. Typical materials are SUS304, SUS316L, titanium, and Hastelloy. The reason for using multiple electrodes is to introduce hysteresis: one electrode is always immersed in the liquid, and the lengths of the other two electrodes are varied to create hysteresis.
If the output continues until the long electrode leaves after the short electrode is immersed, it can be used as a tank drain control or high liquid level alarm, and vice versa for tank water supply control or low liquid level alarm. The type of relay is selected according to the target liquid and supply voltage.
When used for pure water tanks, a high-sensitivity type should be used due to the high electrical resistance of the liquid, while a general type should be used for rainwater. The voltage can be 100 VAC, 200 VAC, or 24 VDC, etc. Check the power supply voltage to be supplied and select the appropriate type.