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Ultrasonic level sensor versus Radar level sensor

Date: 2019.3.25

Radar level transmitter has been used on several occasions for level measurements making it more popular than ultrasonic level sensors which are more effective in wastewater plants. While radar level technology has, for a long time, been seen as the best method due to its accuracy and performance, it is not in the case of wastewater applications. These applications employ non-contact level measurement, the ultrasonic level meter, which they find to have applicable specific benefits as well as being cost effective. This article gives a comparison between radar sensors and ultrasonic level transmitter as well as gives specific situations where ultrasonic instruments are considered more effective than radar.

Level Instruments

Water and Wastewater plants need time to time measurements is level as well as limit-level detection to ensure water management, process engineering, and safety. Monitoring and controlling the water level helps in optimizing the operations like fluid flow, treatment processes and cost calculation and control.
There is not a single technology that can manage all the processes hence every technology is used for specific task depending on the material, conditions and the environmental conditions. The installation options are another great consideration taken into account while choosing the technology to use. Choosing the best technology for every application is vital for ensuring successful measurement, control, and costs. Multiple technologies can also be used in cases where the costs are not the major consideration.

Ultrasonic level sensor versus radar level sensor

  • Ultrasonic level transmitter and free-space radar are often used in cases where a continuous level of measurement is needed as they offer more advantages than any other technology.
  • Ultrasonic level sensors employ piezo crystals to produce a mechanical pulse launched from sensor membrane. Due to the change in air density and the medium, the sound wave can reflect from the surface of the process medium. The sensor membrane receives the reflected pulse within a time that is similar to the distance between the sensor membrane and the medium surface. Because the empty calibration distance is programmed when the sensor is commissioned, the instrument can give the level by subtracting the distance from the empty calibration distance.
  • The ultrasonic level sensor then submits a pulse to the surface of the liquid or solid to determine the tank level. It also measures the flight time for the signal which is reflected. An ultrasonic pulse needs air as a medium of transmission. It operates according to the speed of the sound in the air. It, therefore, can't be used for level measurement on a vacuum. If there are gases like nitrogen(N2), carbon dioxide(CO2) and methane in the sensor or the surface, it will result in a different velocity sound resulting to large measurement errors.
  • Radar works in the same principle of time flight as ultrasonic level. The difference between them is that it uses high-frequency microwaves that are produced from an antenna. As opposed to sound waves which reflect according to a change in density, microwaves operated according to a change in the dielectric constant of the process medium. Microwaves do not need air as a transmitter since they are electromagnetic. Because of this, radar level transmitter is, therefore, suitable to be used in a vacuum or the presence of other gases apart fro air. A radar level measurement instrument is used to send microwave to a liquid or solid and measure the flight time for the signal reflected to determine the level.

Ultrasonic level transmitter applications

  • Ultrasonic level meter sensors are applicable in many types of applications including rainwater basins, wet wells, and wastewater chemicals. They are flexible need little maintenance.
  • Other users avoided ultrasonic level measurement sensors because in the past they provided erroneous measurements as a result of condensation. However, there are ultrasonic sensors that come with automatic self-cleaning which eliminates the condensation errors. It works by monitoring the sensor amplitude membrane. Condensation is detected by dampening of the amplitude. The unit then increases the piezo frequency crystals hence resulting in the self-cleaning effect that frees the sensor membrane from dampening effect of condensation. This feature, therefore, allows users to use ultrasonic technology without worrying about condensation.
  • A level sensor is also employed in a flume and weir level measurement which transforms it to flow rate using Q-H curve. Many ultrasonic sensors come with a pre-programmed Q-H curve for different flumes and weirs. Other instruments permit manual entry of a table used in non-standard flumes or weirs. This eliminates the extra costs associated with radar technology.
  • Ultrasonic level instruments are also used to measure rainwater basins hence to protect wastewater plants from overloading. It can do this by measuring all the variables together with just a level sensor in the basin connected to a level transmitted connected about 1,000 feet from the sensor.
  • Ultrasonic level meters are small hence can be mounted in tight places such as the ceiling. It can also ensure an indication of high measurement in tube for flooding protection even if it's under water. If used indoors with low temperatures, it should be used with heaters to prevent the formation of ice for reliable measurements.
  • Two level measurement sensors are used with one installed upstream and downstream to measure the level difference when cleaning mechanical bar screens. The resulting levels will be nearly equal when the screen is clean. The upstream, however, rises when the bar screen traps debris and solid.

Radar level meter applications

Radar is considered a better option is some wastewater applications than ultrasonic level sensors. When foam accumulates in the surface, radar is sure to perform better than ultrasonic.
Radar performs perfectly in sludge digestion. This is a process where bacteria can be conducted in aerobic digestion or anaerobic digestion. The sludge in both processes is converted to simpler compounds from proteins and sugars. The digesters used in the process always generate foam and other gases hence ultrasonic level transmitter cannot be used in this process. Since ultrasonic sensors use sound speeds in the air, the empty space can contain other gases apart from the air which can result in large measurement errors. In this case, radar is a better option than ultrasonic  level instruments.
radar level meter

Conclusion

Radar may be an excellent level measurement and a high- performing choice in many applications; however, it might not be a good choice in most wastewater applications. The latest ultrasonic instruments come with features that are suitable for wastewater application. Additionally, they are cost-effective, efficient and safe hence should be selected when choosing instruments for wastewater applications.
radar level meter  Ultrasonic Level meter and Radar level Meter Comparison


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