Radar Level Transmitters: Operating Principle & Applications

Radar level transmitter basically employs electromagnetic waves to determine the fluid level in a tank. It converts level information into a 4-20 mA signal and transmits it to the controller; this signal may then be used in a measurement and control loop to control a process. The level is also displayed by an inbuilt display in the transmitter. Having worked with some of these particular level transmitters in the field (particular the guided wave radar level instruments), I can attest that this is one of the most robust level measurement technologies that can handle difficult liquid conditions like those exhibiting heavy vapors, turbulence, bubbling and form formation however different manufacturers of these instruments offer a variety of options that suit different application specifications.

There are two types of radar level transmitters:

• Non-contact radar level transmitters.
• Guided wave radar level transmitters.

Non-Contact Radar Level Transmitters

Principle of Operation

Short bursts of electromagnetic energy are emitted to a liquid surface. An ultra-high speed timing circuitry measures the time of the signal reflected off the liquid surface-transit time (i.e. the total time taken by the initial pulse to liquid surface plus the time taken by reflected pulse from the liquid surface).  

Complex signal processing filters out false reflections and other background noises. The precise level is then calculated by factoring in the tank height and sensor offset information.

Distance (D) = C(Speed of Light) x T (Transit Time)/2  

Applications of Non-Contact Radar Level Transmitters

Generally non-contact radar is used in media that involve liquids or slurries, hydrocarbons to water-based media. Examples of applications where this technology is used include:

• Pulp and paper process industries (chemical storage, piping vessels etc.).
• Chemical processing (feedstock vessels, catalyst tanks, corrosives and caustics, mixing and blending tanks, waste sumps, day and batch tanks).

Guided Wave Radar (GWR) Level Transmitters

Principle of Operation

This instrument operates by using pulses of electromagnetic energy, which are transmitted down a probe. When a pulse reaches a liquid surface that has a higher dielectric than the air/vapor in which it is traveling, the pulse is reflected.

An ultra-high speed timing circuit accurately measures the transit time and provides a precise measurement of the liquid level or the liquid-liquid interface as shown in the diagram below:

Applications of Guided Wave Radar Level Transmitters

Generally guided wave radar is used in media that involve liquids or slurries, hydrocarbons to water-based media. Typical applications include:

• These instruments find use in applications that involve hydrocarbons (low dielectric media subject to variation such as hexane, butane, LPG, etc.).
• Separators.
• Propane storage and chillers.
• Steam drums.
• Ammonia tanks.
• Molten sulfur.
• Knock out drums (compressor, flare knock out drums, and so on).

You may also read:

• Types of Sensors used in Measurement and Process Control
• Ultrasonic Level Measurement
• Principle of Operation of Magnetostrictive Position Sensors
• Ultrasonic Level Switches
• Key considerations for specifying Displacer Level Transmitters
• Installation Considerations of an Orifice Plate Flow Sensor