Both in production and in everyday life, a variety of liquid reservoirs are used. To control their filling level, sensors of different types are used, of which the simplest and most common are float liquid level sensors. How are they arranged, what are their varieties and where is it possible to use them? What is their advantage over other types of sensors?
Content
- Design and principle of operation
- Mechanical variety
- Electric type
- Features of the magnetic design
- Overview of pros and cons
Design and principle of operation
Structurally, the float-type level sensor consists of three elements:
- float;
- information transmission systems;
- working body or indicator.
The float is a sealed plastic reservoir filled with air. Its density is much lower than that of water or other liquid. Therefore, it always remains on the surface of the liquid medium and is the primary element that determines its level.
Both mechanical and electrical or magnetic systems can act as information transmission systems. It transmits data on the degree of filling of the reservoir to the control unit or controls the mechanical filling system.
Most float liquid level sensors transmit information in one way or another to an indicator or to a control unit. The first and simplest sensors, through a mechanical system of rods and levers, directly opened or closed the flow of liquid into the reservoir.
Mechanical variety
Historically, this variety appeared the very first. Its design is as simple as possible:
- the float is on the surface of the liquid;
- mechanical connection of the float with a valve or indicator;
- indicator or capan.
When the liquid level changes, the float rises or falls, the mechanical connection moves indicator pointer outside the tank or acts on the valve to open or close the intake liquids. In everyday life, such a sensor can be found in an ordinary toilet cistern. When the drain button is pressed, the level in the tank drops, the float drops, and the lever opens the needle valve. Water enters the tank until the float rises and will not close the needle valve by means of the lever. Similar devices can be used in other tanks, where the pressure when supplying liquid is relatively small.
Electric type
This type is the most accurate and is used in cases where it is necessary to measure the liquid level with maximum accuracy. The principle of operation is as follows: the float moves up or down in a special shaft as the level of liquid increases or decreases, movement the float causes a change in the position of a special conductive slider along the windings of the rheostat, the indicator displays the "edited" resistance in rheostat.
This type has its own advantages and disadvantages, which determine the scope of its application. Most often, the electric type is found in float systems for measuring the fuel level in automobile tanks. The change in resistance in the rheostat is transmitted to the dial indicator on the dashboard.
Features of the magnetic design
A distinctive feature of magnetic float sensors is the presence of reed contacts and a permanent magnet built into the float. When it moves, the magnetic field closes or opens contacts in a sealed enclosure, which transmit a signal to the indicator or to the control unit.
There are various modifications of this type of sensors, designed for different environments and readings accuracy (reed switch placement step). Most often, float-type reed switches are used in industrial tanks where reliability and durability of the measuring system is required.
Overview of pros and cons
The advantages of the mechanical subspecies of the float sensor are the simplicity of its design and non-volatility during operation. The transfer of information to the indicator or action on the opening and closing valve is carried out due to the force of Archimedes, acting on the float when the water level in the tank increases or decreases. The disadvantages are: low accuracy of readings and a relatively short service life due to the influence of the medium on the mechanical part.
The electric type is distinguished by greater accuracy of readings, but its service life also has a limitation: when the slider moves along the windings of the rheostat, the contact is worn out. After a certain time, the pressure density of the contact pair becomes insufficient, and the readings of the measuring element become incorrect.
The main advantage of magnetic float sensors is their reliability and durability. They are used to measure the level of corrosive liquids. There is only one drawback - discrete readings: the sensor is triggered after a certain period of increasing or decreasing the water level.
