Level Sensor

a measuring transducer that converts the level measurements of liquids or bulk materials into mechanical, electrical, or pneumatic signals that can then be conveniently transmitted, processed, and recorded. They can be classified as sensors for liquids or for bulk materials, depending on their purpose, and as float, hydrostatic, electric, acoustic, thermal, nuclear, or optical sensors, depending on their operating principle.

Figure 1. Level sensors: (a) float sensor with constant load, (b) hydrostatic sensor, (c) capacitance-measuring sensor; (1) vessel with liquid or bulk material, (2) float, (3) pulley connected to the movable element of a rheostat, (4) rheostat, (5) DC amplifier, (6) measuring instrument graduated in units describing the level H, (7) manometer, (8) insulated tube, (9) electrode, (10) terminals for switching in a capacitance-measuring instrument

In a float sensor (Figure l, a), the float continuously follows the level of the liquid in producing the level measurements. Hydrostatic level sensors (Figure 1, b) use the principle of the dependence of the hydrostatic pressure P of a liquid column (as measured by a manometer) on the level H of the liquid in the vessel: P = Hγ, where γ is the specific gravity of the liquid. The capacitor in a capacitance-measuring sensor (Figure 1, c) functions on the principle of the dependence of its capacitance on the level of the liquid or bulk material in the vessel. If the values of the dielectric constants for air and the liquid or bulk material and the geometric dimensions of the capacitor electrodes are known, the measured capacitance of the sensor can be used to determine the level to which the vessel is filled.