Level sensors measuring fluid play a critical role in the detection, measuring and monitoring of liquids and fluidized solids. Whether the fluid is housed in a compact container or is spread over a large area, there are many specific criteria to selecting the right sensor for the job. First, you must ask yourself some key questions:

What kind of liquid is being measured?
Can the sensor be submerged in the fluid or should it be external?
Does the fluid need constant measurement or can measurements be taken in intervals?
Is direct measurement of the level needed?
Is process shut-down acceptable when sensor removal or maintenance is required?
There are many variables that change the selection for optimal monitoring in industrial and commercial processes. Other factors include temperature, pressure, vibration, density of the fluid, and environmental conditions as well.

Types of Level Sensors
There are 4 kinds of level sensors:

Point and Continuous Level Detection
Point Level Detection
Point Level Detection & Continuous Monitoring
Continuous Level Measurement
 
Point and Continuous 
These sensors are mainly for the point detection of solids. This includes vibrating, rotating paddle, mechanical, radar, and ultrasonic level sensors. 

Point Level Detection of Liquids
The principle behind magnetic, mechanical, cable and other float level transmitter sensors involves the opening and closing of a switch, either through direct contact or a magnetic reed. A permanent magnet sealed inside a float rises or falls to the actuation level. Many factors influence this type of sensor, such as chemical compatibility, temperature, density, buoyancy, and viscosity.

Point Level Detection & Continuous Monitoring
Ultrasonic level sensors are used for non-contact sensing of highly viscous liquids and bulk solids. They are used often in water treatment for pump control and open channel flow measurement. Ultrasonic level sensors are affected by certain factors like turbulence in liquids, foam, stream, vapor and changes in concentration. Correction factors can be applied to the measurement to improve the accuracy.

Continuous Level Measurement
Magnetostrictive level sensors are similar to float sensors, in that a permanent magnet sealed inside a float travels up and down a stem. Ideal for high-accuracy, continuous level sensing applications, this sensor can be used on a wide variety of liquids in storage and shipping containers. However, these sensors require the right choice of float based on the specific gravity of the liquid. Other level sensors used for continuous level measurement are resistive chain level sensors, magnetoresistive float sensors, hydrostatic pressure level sensors, air bubbler systems and gamma ray gauges.  ddfgfg