[Q&A Question 156] 2016.09.23

A float level gauge is a device used for measuring liquid levels and density, designed by combining Archimedes’ principle with magnetic coupling principles. The main problem is that the rotation axis of the magnetic flip plate gets stuck; this sticking is caused by corrosion and adhesion, which prevent smooth rotation

Principle； When the liquid level varies, the volume of the sinker submerged in the liquid changes, resulting in different buoyant forces that cause displacement; this displacement is converted into an angular displacement through mechanical transmission to measure the liquid level. Changes in the properties of the medium and in density measurement have a significant impact on the measurement results.

Measurement principle of the caisson type level gauge； When the liquid level varies, the volume of the sinker submerged in the liquid changes, resulting in different buoyant forces that cause displacement; this displacement is converted into an angular displacement through mechanical transmission to measure the liquid level. Changes in the properties of the medium and in density measurement have a significant impact on the measurement results.

The principle of operation for a caisson level gauge is the principle of buoyancy. The causes of measurement errors include: temperature changes ； Change in medium density ； The liquid level changes frequently

The variable buoyancy level gauge, also known as the float tube level gauge – which is what we refer to as a float-type level gauge – sees the volume of the float tube submerged in the liquid change as the liquid level varies; this results in different buoyant forces and thus displacement. This displacement is converted into an angular displacement through mechanical transmission, thereby enabling the measurement of the liquid level.

The cylinder-type level gauge is an early type of variable buoyancy level gauge. It has a simple structure, reliable operation, is not easily affected by the external environment, and is easy to maintain. Compared to differential pressure level gauges, it eliminates the need for isolation and purging in many applications, and there are no issues such as vaporization within the pressure transfer tube or density differences, which is why it remains widely used to this day. Figure 4-8 shows a schematic diagram of the structure of a torsion tube caisson-type level gauge. Cylinder 1 (level sensing element) is a hollow long cylinder made of stainless steel, vertically suspended at one end of lever 2 and partially immersed in the medium being measured. It experiences minimal displacement during detection and does not float on the surface of the liquid, which is why it is called a sinker. The other end of the lever 2 is vertically fixed to the torsion tube 3 and one end of the mandrel 4, and is supported by a pivot on the housing. The other end of the torsion tube is fixed to the instrument housing 5 via a flange. The other end of the mandrel 4 is a free end, used to output angular displacement. A torsion tube is a hollow tube made of elastic alloy steel. On the one hand, it separates the medium under test from the external environment; on the other hand, it uses the elastic torsional deformation of the torsion tube to convert the torque applied to one end of the torsion tube into rotational motion (i.e., angular displacement) of the spindle.

A float-type level gauge consists of a level transmitter and a float chamber assembly, a float assembly, a lever assembly, and a torsion tube assembly. The float is submerged in the liquid being tested and is rigidly connected to the torsion tube system. The force acting on the torsion tube is the net value of the buoy’s own weight minus the buoyancy exerted by the liquid on it. Under this combined force, the torsion tube rotates by a certain angle. Changes in the level of the liquid cause changes in the buoyancy of the buoy suspended in that liquid, which in turn alters the torque on the torsion tube and leads to further rotation of the tube. This rotational motion is transmitted to the swinging component of the intelligent transmitter; the magnet attached to this component moves as a result, changing the magnetic field detected by the Hall effect sensor. The transmitter converts this magnetic field signal into a standard electrical signal, thereby allowing the level and interface of the liquid to be measured. To prevent sticking

The cylinder-type level gauge is an early type of variable buoyancy level gauge. It has a simple structure, reliable operation, is not easily affected by the external environment, and is easy to maintain. Compared to differential pressure level gauges, it eliminates the need for isolation and purging in many applications, and there are no issues such as vaporization within the pressure transfer tube or density differences, which is why it remains widely used to this day. Structure of the barrel-type level gauge: The barrel (the level detection element) is a hollow, long cylindrical structure made of stainless steel; it is suspended vertically at one end of a lever and is partially immersed in the medium being measured. It experiences minimal displacement during detection and does not float on the surface of the liquid, which is why it is called a sinker. The other end of the lever is fixed perpendicularly to one end of the torsion tube and the mandrel, and is supported by a pivot on the housing. The other end of the torsion tube is fixed to the instrument housing via a flange. The other end of the mandrel 4 is a free end, used to output angular displacement.