Level measurement of different liquids used on industrial scale is very important for the maintenance of quality standards and to ensure safety and protection of the employees and the industry as a whole. The liquid level indicator has many diverse uses and is used for wide range of different functions.  There are many different types of application in the industry in which the measurement of the liquid level is required.  It could be used to measure the level of liquids or solids as well. Some of the typical uses of liquid level measurement indicators are for waste-water management and treatment system, measurement of bore hole or well level, measuring liquid level in tanks, vessels or containers etc. some of the common usage of solid level measurements could be for dust collectors, pneumatic conveying receivers etc.

The liquid level measurements have been divided into two broad categories; point level measurement and continuous level measurements. The point level measurement is used to detect and control the liquid measurement at some point in the container or vessel. The continuous level measurement keeps a check on the level of the liquid all the time through a level transmitter or a transducer. The output provided by the level transmitters is of 4 to 20 signals, often. This is proportional to the height of the medium or liquid. Mostly, the output of the continuous level is used for controlling the pump or valve that is controlling the level of the medium or liquid, continuously and consistently.

This article will provide a brief overview of some of the popular continuous level measurement techniques which would include; hydrostatic pressure, ultrasonic and radar.

• Hydrostatic pressure technique: it makes use of the differential pressure sensor and is commonly used for sensing the liquids in the huge tanks or liquid reservoirs. The differential pressure sensor in the device measures two pressure inputs; a high pressure and a low pressure port. It provides the difference of the total tank pressure and the head pressure of the liquid in the tank.
• Ultrasonic level indicator: these sensors are used where non contact level sensing is required. The ultrasound waves are transmitted into the material container. The waves reflect back and are gathered by the transmitter. The level of the medium inside the container is measured by calculating the time the ultra sound waves take to travel from the sensor to the material and the reflection of the echo sound back to the sensor.
• Radar:  the radar waves make use of the low energy, high frequency electromagnetic waves which are emitted by the sensor and are transmitted along the probe which is submerged into the into the medium to be measured. The impulses upon hitting the medium are reflected back towards the probe and then to the sensor. The sensor then calculate the liquid level by finding  the time difference between the impulses sent and the impulses reflected. It is also referred to as Time Domain Reflectometry.