There is a tendency to pit ultrasonic level sensors and radar level sensors against one another when in reality each sensor has advantages and disadvantages that give each sensor its own place. In this blog, we will look at the differences in how these two technologies work and will cover the applications each sensor is best suited for.
Ultrasonic Level Sensors
As the name implies, ultrasonic level sensors operate by emitting a burst of sound waves in very rapid succession. The sound waves emitted from the sensor travel at a known speed (the speed of sound) to the intended target where they bounce off the target and return to the sensor.
Using the amount of time it takes for the sound burst to return to the sensor after being sent, the distance between the sensor and the substance being measured or the level of the substance is calculated. With help from other parameters programmed into the sensor or control system, volume, weight, or other similar measurements can also be calculated from the measured distance.
In order to accurately determine the level of the target substance, ultrasonic sensors require an unobstructed air column between the sensor and the target. Things like physical obstructions, excessive foam, heavy vapors, thick dust, and light powders can all deflect or absorb the signal, or act as a false surface leading to erroneous readings from the ultrasonic sensor.
Common Uses of Ultrasonic Sensors
Liquid Level Measurement
Ultrasonic sensors are most commonly used for measuring the level in a body of liquid, such as in a tank, well, pit, lake, or another body of liquid. Ultrasonic level sensors can also be used to measure liquid in non-linear containers. This usually requires a strapping chart to adjust the reading to a volume as liquid rises and falls.
Solids Level Measurement
Ultrasonic sensors are an excellent choice for solids level measurement, especially in comparison with radar level sensors. The ultrasonic sound waves are much easier to manage and measure than radar’s electromagnetic waves when coming off a substance with an angle of repose. It is important to note that using an ultrasonic sensor for solids level measurement usually reduces the effective range of the sensor by half. Additionally, environments with dusts or powders scatter sound waves, leading to erroneous readings. But an ultrasonic sensor with an appropriate range used in an environment with little to no air-borne particles will provide extremely reliable solids level measurement.
Open Channel Flow
Open channel flow is another application of an ultrasonic level sensor. Open channels are a primary means of transporting, filtering, and metering water, often used in water treatment plants, environmental monitoring, and irrigation canals. Often, in this type of application, ultrasonic level sensors are paired with an appropriate controller for flow calculations.
Presence Detection and Object Profiling
Last but not least, ultrasonic sensors are a great fit for presence detection and object profiling. If object detection is required in dirty or wet environments where the targets are fairly slow-moving, an ultrasonic sensor can be used. They are able to handle harsh conditions, making them a suitable choice.
The car wash industry is the perfect example of using ultrasonic sensors to improve processes and enhance efficiencies. Ever wonder how the sprays, nozzles, and sponges find the exact spots on your car in an automatic car wash? APG’s IRU-2000 Object Detection Ultrasonic Sensor is the answer to that! Learn more about its capabilities here.
Radar Level Sensors
Radar sensors, by contrast, work not with sound waves, but with electromagnetic waves. This is the key difference between ultrasonic and radar sensors. Like the waves from ultrasonic sensors, the waves emitted from the radar sensor bounce off of objects and travel at a known speed (much faster than ultrasonic waves). Unlike ultrasonic sound waves, radar’s electromagnetic waves react differently to certain materials as they are reflected off the surface.
Radar sensors are affected by different variables than other level sensors. Radar level transmitters are affected less by temperature than ultrasonic sensors, improving consistency and accuracy. Radar level sensors are also well suited for specialty applications, such as working in a vacuum, or in higher pressures (as long as the housing can handle it). Radar sensors are also less affected by foam, vapors, powders, and dust that can interfere with signals on ultrasonic sensors and lead to erroneous readings. This can make radar sensors a better choice for these applications.
An important factor for radar sensors is the target material’s dielectric constant. A material with a low dielectric will not reflect an electromagnetic wave, so radar tends to pass right through. These materials are typically non-conductive and have low moisture content, such as dry powders and granules.
To be fair, radar can sense a lot of these materials, but the energy of the returning waves is so small that precise alignment with the signal is paramount. This introduces techniques such as guided wave radar, or special antenna. Measuring materials with a low dielectric constant is not always impossible, just very challenging.
The most common applications for radar sensors are:
- Chemical / Petrochemicals
- Food and Beverages
- Granular Solids
- Plastic Pellets
- Minerals and Mining
- Oil and Gas
- Asphalt Blending Tanks
- Alum and Wax Tanks
- Pulp and Paper
- Sand and Gravel
- Primary and Secondary Sludge
The Bottom Line: Ultrasonic vs. Radar
In the end, if your application is straight-forward, an ultrasonic sensor is a good bet for high-quality performance and excellent longevity. For tanks, wells, channels, or reservoirs, an ultrasonic can be configured to meet your needs.
However, as soon as foam, vapors, powder, dust are introduced to the equation, radar sensors become the answer to your measurement needs. Environmental variables just don't affect radar measurements the way they do ultrasonic sensors.
A necessary caveat here is that good tech will always trump bad tech. Yes, radar sensors are better than ultrasonic sensors in foamy, dusty applications, but a poorly-designed radar sensor is always going to perform poorly. Similarly, ultrasonic sensors are usually cheaper than radar for easier liquid or clean-air solids level measurement, but a cheap ultrasonic will never be anything better than a cheap ultrasonic. Ultrasonic and radar sensors don't compete with each other, they complement each other. Neither one is a one-size-fits-all level measurement solution.