A radar level transmitter measures the distance between the transmitter’s installation site and the surface of a distant process material. It measures the distance by measuring the time of flight of the traveling wave.
Radar level transmitters are the most widely used in many critical applications. They accurately measure the levels in the tank, and operate on a relatively simple time-of-flight concept.
Time of flight Principle
Time of flight is when any wave or particle travels through a given medium after being reflected from the object. The total time these waves or particles take is termed the time of flight.
Let t1 = Time taken by a wave from transmitter to target.
t2 = Time taken by the wave to reflect to the receiver
Time of flight( TOF) = t1 + t2
Working of the Radar Level Transmitter
A trans receiver sends and receives waves. It calculates the time the waves go towards the target, reflect from it, and return.
The speed of the waves equals the speed of light( 3 X 108 m/s). The transmitter algorithm calculates the time. Thus, using the above-mentioned formula, the radar level transmitter calculates the distance between the trans receiver and the target.
A trans receiver in the radar-type level transmitter emits the electromagnetic wave signal and receives it after it reflects from the object. As a result, the transmitter calculates the time of flight.
The radar transmitter works by transmitting microwaves (of varying frequencies for different uses) to the vessel or tank and measuring the time it takes to travel to and from the level filled in the vessel or tank. The radar transmitter calculates the distance from the transmitter to the top of the material filled in the tank using the formula distance speed X time.
The important factor in selecting the microwave frequency depends on the dielectric constant of the filler material and vapors and the medium present above the fill level.
The measuring accuracy of the radar level transmitter depends on the object’s dielectric. An object with high dielectric absorbs the microwave more, and the measurement accuracy is lower because of the less-than-well-received signal at the transmitter. Under the circumstances, the microwave frequency must be higher.
Types of the Radar Level Transmitter
There are two types of radar-type level transmitters. One is a non-contact radar level transmitter, and the other is a contact-type radar level transmitter.
- Contact type Radar Level Transmitter
- Non-Contact type Radar Level Transmitter
Contact type Radar Level Transmitter
An antenna or transceiver is attached to a probe at the vessel’s or tank’s end by a contact-type radar transmitter. Through the probe, the antenna or trans receiver sends microwave signals.
When microwave signals strike the surface, they reflect and return to the antenna or transceiver. A portion of the microwave travels to the bottom of the tank and reflects there.
Non-Contact type Radar Level Transmitter
Non-contact radar level transmitters have an antenna, a trans receiver, and a processing circuit. The antenna or trans receiver is protected inside a cone shape for sensing microwaves in a straight path for better measurement accuracy.
The antenna/trans receiver transmits high-frequency microwave signals inside the tank or vessel. These microwave impulses are reflected from the top of the substance they strike. The reflected waves are then received by the transmitter’s receiver. The time between sending and receiving waves is calculated by the transmitter. The distance is calculated by the transmitter using the formula distance = Speed x Time.
If the transmitter’s antenna becomes dusty, the measuring accuracy suffers. Cleaning is required on a regular basis to ensure accurate level measurement. Modern transmitters include an automatic antenna cleaning system.
How Does the Dielectric Constant Affect the Measurement?
The dielectric constant of the filler material and vapors present in the space above the filled level affects the measuring accuracy. The vapor causes interference in the path of microwaves. Therefore, it is important to take these factors into consideration while measuring. This is very significant in determining the actual level.
The dielectric constants of the mediums or fluids present should significantly differ. Because if dielectric constants are near about the same, then there is no significant difference in reflected echoes. This highly depends on the frequency of the microwave in use. The selection of a specific frequency for given dielectrics is fairly common. Before making any adjustments or purchasing a new transmitter, always consult with the vendor.
Different radar level transmitters are available for interface measurement. The minimal dielectric constant difference for successful level measuring is 5.
Advantages of Radar Type Level Transmitter
- Radar level transmitters can measure the levels of liquids, solids, slurries, or interfaces.
- With no moving parts, the maintenance is much less.
- There are no effects on measurement due to liquid turbulence, density change, temperature change, or pressure change.
- Non-contact type radar level transmitters are also most suitable for highly corrosive fluids.
Limitations of Radar Type Level Transmitter
- If there is a change in the material’s dielectric constant, then the readings will vary.
- In using contact-type radar, if any material sticks on the probe, it will form echoes, and we will get the wrong reading. We must pull the probe out, clean it, and reinstall it.
- In non-contact radar, if any material sticks on the antenna, we need to clean it.
- The minimum dielectric constant difference for interference measurement should be 5. Otherwise, we won’t be able to accurately measure interface echo.
Applications of Radar Level Transmitters
- Mining Industry
- Captive Power Plant
- Paper and pulp industry
- Aeronautics industry