Level Sensors detect the level of substances that flow, including liquids, slurries, granular materials, fluidized solids, and powders. The substance to be measured can be inside a container or can be in its natural form (e.g. a river or a lake). The level measurement can be either continuous or point values. Continuous level sensors measure level within a specified range and determine the exact amount of substance in a certain place, while point-level sensors only indicate whether the substance is above or below the sensing point. Generally the latter detect levels that are excessively high or low.

Types of Level Sensors for Solid/Liquid Level Detection & Monitoring

  • Level Sensors for Point Level Detection or Continuous Monitoring of Solids
    • Vibrating Point Level Sensor – These detect levels of very fine powders (bulk density: 0.02 g/cm3 – 0.2 g/cm3), fine powders (bulk density: 0.2 – 0.5 g/cm3), and granular solids (bulk density: 0.5 g/cm3 or greater).
    • Rotating Paddle Level Sensor – Rotating paddle level sensors are for bulk solid point level indication.
    • RF Admittance Level Sensor – RF Admittance level sensor uses a rod probe and RF source to measures the change in admittance.
  • Level Sensors for Point Level Detection of Liquids
    • Pulse-Wave Ultrasonic (Non Invasive) Level Sensor – Liquid level is detected using Pulsed-Ultrasonic technology.
    • Magnetic and Mechanical Float Level Sensors – The principle behind magnetic, mechanical, cable, and other float level sensors involves the opening or closing of a mechanical switch, either through direct contact with the switch, or magnetic operation of a reed.
    • Pneumatic Level Sensors – Pneumatic level sensors are used where hazardous conditions exist, where there is no electric power or its use is restricted, and in applications involving heavy sludge or slurry.
    • Conductive Level Sensors – Conductive level sensors are ideal for the point level detection of a wide range of conductive liquids such as water, and is especially well suited for highly corrosive liquids such as caustic soda, hydrochloric acid, nitric acid, ferric chloride, and similar liquids.
  • Level Sensors for Continuous Level Measurement of Liquids
    • Magnetostrictive Level Sensors – Magnetostrictive level sensors are similar to float type sensors, ideal for high-accuracy, continuous level measurement of a wide variety of liquids in storage and shipping containers.
    • Resistive Chain Level Sensors – Resistive chain level sensors are similar to magnetic float level sensors in that a permanent magnet sealed inside a float moves up and down a stem in which closely spaced switches and resistors are sealed.
    • Hydrostatic Pressure Level Sensors – Hydrostatic pressure level sensors are submersible or externally mounted pressure sensors suitable for measuring the level of corrosive liquids in deep tanks or water in reservoirs.
    • Nuclear Gamma Ray Level Sensor Gauge – Nuclear level gauge or gamma ray gauge measures level by the attenuation of gamma rays passing through a process vessel. The technique is used to regulate the level of molten steel in a continuous casting process of steelmaking.
  • Level Sensors for both Point Level Detection or Continuous Monitoring of Solids and Liquids
    • Ultrasonic Level Sensors – Ultrasonic level sensors are used for non-contact level sensing of highly viscous liquids, as well as bulk solids.
    • Capacitance Level Sensors – Capacitance level sensors excel in sensing the presence of a wide variety of solids, aqueous and organic liquids, and slurries.
    • Optical Level Sensors – Optical sensors are used for point level sensing of sediments, liquids with suspended solids, and liquid-liquid interfaces. These sensors sense the decrease or change in transmission of infrared light emitted from an infrared diode (LED).
    • Microwave Radar Level Sensors – Microwave sensors are ideal for use in moist, vaporous, and dusty environments as well as in applications in which temperatures vary.

Level Sensors Selection Guidelines

A variety of level sensors are available for point level detection and continuous level monitoring of solids and liquids. There are many physical and application variables that affect the selection of the optimal level monitoring method for industrial and commercial processes. The selection criteria include the physical: phase (liquid, solid or slurry), temperature, pressure or vacuum, chemistry, dielectric constant of medium, density (specific gravity) of medium, agitation (action), acoustical or electrical noise, vibration, mechanical shock, tank or bin size and shape. Also important are the application constraints: price, accuracy, appearance, response rate, ease of calibration or programming, physical size and mounting of the instrument, monitoring or control of continuous or discrete (point) levels.