【2025 Accumulated Knowledge】11. Issues in measuring level with contactless radar level gauges

The working principles and suitable application conditions of the following 19 types of level gauges are provided for reference. 1. Magnetic flap level gauge: Also known as magnetic float level gauge or magnetic column level gauge. Principle: It operates based on the principle of communicating vessels, as well as the principles of buoyancy and magnetic coupling. When the liquid level in the container being measured changes, the permanent magnet inside the float transmits a magnetic signal to the magnetic flip-column display panel, causing the red and white flip columns to rotate 180°. When the liquid level rises, the flip columns change from white to red; when the liquid level drops, they change from red to white. The point where red and white meet on the panel indicates the actual height of the liquid level in the container, thereby enabling the display of the liquid level.

2. Float level gauge Principle: The structure of a float level gauge is designed and manufactured based on the principles of buoyancy and a static magnetic field. The position of a float with a magnet (referred to simply as a float) in the medium being measured is influenced by buoyancy; changes in liquid level cause changes in the position of the magnetic float. The magnet and sensor (reed switch) inside the float ball cause a change in the number of components connected in series in the circuit (such as fixed resistors), which in turn alters the electrical parameters of the instrument’s circuit system. In other words, changes in the position of the magnetic float cause changes in electrical quantities, and by detecting these changes in electrical quantities, the liquid level inside the container can be determined.

3. Steel strip level gauge Principle: It is designed and manufactured based on the principle of mechanical equilibrium. When the liquid level changes, the original mechanical equilibrium is disrupted by the buoyant force acting on the float, and a new equilibrium is achieved through the movement of the steel strip. The level detection device (float) moves the steel strip in response to the liquid level; the displacement transmission system causes the transmission pin to rotate through the movement of the steel strip, which in turn acts on the counter to display the liquid level.

4. Radar level gauge: Principle – A radar level gauge is a measuring instrument based on the time-of-travel principle. Radar waves travel at the speed of light, and the travel time can be converted into a level signal using electronic components. The probe emits high-frequency pulses that travel along the cable. When these pulses encounter the surface of the material, they are reflected back and captured by a receiver inside the instrument, which then converts the distance signal into a level signal.

5. Magnetostrictive level gauge – Principle: When the sensor of a magnetostrictive level gauge is in operation, its electrical circuit generates a pulsed current in the waveguide wire; as this current propagates along the waveguide wire, it creates a magnetic field of pulsed current around the wire. A float is attached to the sensor rod of the magnetostrictive level gauge; this float can move up and down along the rod as the liquid level changes. Inside the float, there is a set of permanent magnet rings. When the magnetic field generated by the pulsed current meets the magnetic field of the magnetic ring produced by the float, the magnetic field around the float changes, which causes a torsional wave pulse to be generated in the waveguide wire made of magnetostrictive material at the location of the float. This pulse travels back along the waveguide wire at a constant speed and is detected by the detection mechanism. By measuring the time difference between the pulsed current and the torsional wave, the position of the float, that is, the level of the liquid surface, can be determined accurately.

This post was last edited by The one on 2025-12-4 12:08: 9. Pressure level transmitter

10. Capacitive level gauge: Principle: A capacitive level gauge measures the height of the liquid level by detecting changes in capacitance. It is a metal rod inserted into a container filled with liquid; the metal rod serves as one pole of the capacitor, while the container wall acts as the other pole. The dielectric between the two electrodes is the liquid and the gas above it. Since the dielectric constant ε1 of the liquid is different from that ε2 at the liquid surface – for example, ε1 > ε2 – as the liquid level rises, the overall dielectric constant between the two electrodes of the capacitive level gauge increases, thereby increasing the capacitance. Conversely, as the liquid level drops, the ε value decreases, and the capacitance also decreases. Therefore, a capacitive level gauge can measure the liquid level by detecting changes in the capacitance between two electrodes.