Level Instruments

Different types of Level Instruments

Ultrasonic Level Measurement

Ultrasonic level instruments can be used to measure most types of liquids and has the advantage of not being effected by the type of liquid. Ultrasonic is non contact by it's very nature and can easily provide fast digital signals to be used in both storage and process applications.  Measurement is achieved by the emitting an ultrasonic sound wave. When the sound wave hit's the surface of a liquid a certain portion of the wave is bounced back to the instrument. Level is calculated by measuring the small time difference between the emitted wave and the returning wave. Therefore an ultrasonic level instrument mounted at the top of a tank, would direct a wave downwards. The longer the time period, the further the surface is from the instrument. More time equals, a lower level.

Float Level Switch

Considered a simple and robust method of determining fixed levels. Float switches consist of a sealed enclosure containing a switch which is triggered by different orientations. When hanging loose the internal switch will indicate one state (off). Once the liquid level rises to the level of the float, it will typically turn (float) on it's side triggering a different state of the internal switch (on). This is an ideal system where only a few levels need to be determined. A measurement of low, medium and high (full) can be achieved by hanging 3 float switches at different fixed levels within the tank. A two float system can be used to turn a pump on and off to refill the tank. A lower level switch will trigger the pump on and the higher level switch will trigger the pump off.

Hydrostatic Level Measurement

Typically used as a method to detect low level conditions, a Hydrostatic level instrument is essentially a pressure gauge. In a deep well application, the instrument would be positioned at the bottom of the well, and a pressure reading would be detected. As the level of the liquid drops, the pressure drops, indicating a low level condition. This system could be used to protect submersed pumps from running when water is not present, preventing damage from 'dry running'.

Pendulum Level switch

Similar to a floating ball valve, positioned at the end of a rod, this type of level switch will be pushed up, engaging a switch as a granular bulk solid material rises and pushes on the 'floating' ball. Used to indicate a full condition. For example a hopper may be filled with any type of granular bulk solid. As the level reaches the instrument, it will physically push the mechanism upwards, triggering a switch at the full level for that hopper.