Level Indicators in a Liquid Tank

Fixed Mechanical Indicators

• Fixed mechanical indicators operate by measuring the level of water within a tank. These level indicators employ a measuring tape having two open ends. One of these ends remains fixed within a casing on the top of tank's wall while the other floats on the surface of the liquid with the help of a hollow material. In this manner, the floating end of the measuring tape goes up and down with the liquid level (surface), and readings are taken manually from the top. Similarly, when the tank fills, the tape completely rolls back in to its fixed casing. This type of level indicator is often used in household water tanks and large containers.

Fixed Electronic Indicators

• These types of indicators operate over digital voltage pulses (or signals) to detect the level of liquid within storage tanks. These indicators come mainly in the form of electronic circuits which are fixed on the walls of containers or tanks at a certain height and indicate the maximum or minimum liquid levels by generating a light beam or an alarm sound through their output panels. These indicators are powered by direct current batteries, which come attached with them. In industrial operations, fixed electronic indicators are either placed at both top and bottom ends of the liquid tank or in a series at different levels of tank height, which allows them to sense more than one level of liquid.

Floating Electrical Indicators

• Floating electrical liquid level indicators function by floating over a liquid surface and sensing its own height with respect to the height of the storage tank. These are often encapsulated (sealed) electrical mechanisms with an array of magnetic switches that change their states with an increase or decrease in the liquid level. Many floating electrical indicators perform their operations in a continuous manner. This is in contrast with fixed electronic indicators, which perform level indication operations in a discrete manner.

Submersible Indicators

• Submersible indicators perform their sensing operations by staying at the bottom of liquid storage tanks. These are the most advanced type of liquid level indicators and are operated as either liquid pressure transmitting devices or as ultrasonic wave transmitting mechanisms. Submersible indicators working as pressure transmitting devices keep measuring the changes in liquid pressure and interpret it with respect to the height of liquid within a tank. In contrast, ultrasonic wave transmitters continuously produce ultrasonic sound above 2,000 KHz (kilohertz) while being submerged at the bottom of storage tanks. This sound is reflected back to the transmitter after a change in medium (liquid to air) is detected, and the transmitter calculates the time sound waves took to reflect back, interpret this in the form of distance or height of the liquid level.