Capacitive Level Sensor

L = level, Z = impedance, 1 = tank 2 = liquid, 3 and 4 = electrodes.

Working Principle of Capacitive SensorConductivity and capacitive level sensors serve as a continuous and point-level sensors by measuring the impedance between two electrodes immersed in the liquid or between one electrode and the electro conductive tank's wall

Float Type Level SensorL = level, 1 = tank, 2 = liquid, 3 = float, 4 = magnet, 5 = magnetic armature, 6 = contacts, 7 = bellows, 8 = lever.

Working Principle of Float type Level SensorIn a float-type level sensor the buoyancy force holds the float on the surface of the liquid. The float carries a member having a magnetic coupling with a transduction element (coil, magnetic reed), that is mounted on the outside wall of the tank and can be actuated by the proximity of the float. In some designs, the float mechanically links the switching mechanism through the sealing in the wall (e.g., bellows). The switching system can respond to the restraining force developed by a spring element connected to the float

Inductive Level Transducer (a)Variable-inductance type (b) transformer-type level transducer L = level, Z = impedance, 1 = tank, 2 = liquid, 3 = coil, 4 =core

Principle of Inductive level sensorIt is used in application of measurement of the level of liquid metals and other electro conductive liquids. In one of the designs, a coil is wound around a tube containing the liquid. The inductance of this coil changes rapidly as the liquid moves and approaches the coil. In another design, the transducer is introduced by a transformer with a primary coil wound on one limb of a twin-limbed iron core. The other limb is enclosed by a tube containing the liquid and forming one turn of the secondary winding. The effective resistance of this turn is inversely proportional to the height of the liquid column in the tube. The change in the height can be sensed by measuring the power consumption at the primary coil

Photoelectric level sensor(a) Transmittance-mode (b) reflectance-mode L = level, 1 = tank, 2 = liquid, 3 = light source, 4 = photo detector, 5 = prism

Principle of Photoelectric level sensorOperate in transmittance or reflection modes. In the transmittance mode, a sensing system, including a light beam source and a photo detector responds to the interruption of the light beam when the liquid breaks the beam path from the source to the detector. In the reflection mode, an optical prism mounted inside a tank changes the reflectance of the light when it is immersed in the liquid. The construction of the transducer is arranged so that a light source and photo detector for sensing the change in the light's intensity are mounted on the outside wall of the tank. The light beam passes through and is reflected from the faces of the prism

Pressure Type level sensorL = level, 1 = tank, 2 = liquid, 3 = pressure transducer

Working Principle of pressure type level sensorA pressure-type level sensing system contains a pressure transducer mounted at the bottom of a liquid-filled tank. The transducer responds to the pressure developed by the weight of the liquid's column. This pressure is directly proportional to the measured height

Weighing type level sensorL= level, 1 = tank, 2 = liquid, 3 = load cell

Working Principle of weighing type level sensorA weighing sensing system for measuring level determines the level with load cells placed underneath the bottom of the tank or connected to the tank by a mechanical link. If the tank's weight and liquid's density are known, the level is readily calculated using data obtained with the cells.

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