There is a tendency, at least in the industrial media, to put Ultrasonic and Radar level measurement technology in the same hat. Even though many people use the terms interchangeably, the two technologies are quite different.
So, at the risk of sounding a bit nit-picky, we feel that defining the differences between ultrasonic and radar sensors is important, as it affects how sensors are selected and applied. In this blog, we will look at ultrasonic vs. radar sensors and explain the difference between the two level transmitter types.
Level Transmitter Types: Ultrasonic 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, we can calculate the distance between the sensor and the substance being measured or the level of the substance. With help from other parameters programmed into the sensor or control system, we can also use the calculated distance to determine volume, weight, or other similar measurements.
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. This leads to erroneous readings from the ultrasonic sensor.
Ultrasonic sensors are most commonly used for measuring the level in a body of liquid. This can be a tank, well, pit, lake, or another body of liquid. Even non-linear containers can use ultrasonic sensors to measure the liquid, it usually just requires a strapping chart to adjust the reading to a volume as liquid rises and falls.
Ultrasonic sensors are also a popular choice for solid level detection, but should be avoided in dusty environments as the powders can affect the signal, leading to erroneous readings. The trick for using ultrasonic sensors for solid level detection is using a sensor with double the needed range. This provides a stronger signal with a better echo off of the usually uneven and soft target.
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.
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.
Level Transmitter Types: Radar Sensors
Radar sensors, by contrast, works not with sound waves, but with electromagnetic waves. This is the key difference between ultrasonic and radar sensors. Like ultrasonics, the waves bounce off of objects and travel at a known speed (much faster than ultrasonic waves), but they react differently to certain materials.
There is a different set of variables that affects how well a radar sensor operates. Unlike other level transmitter types, such as ultrasonic sensors, radar level transmitters are much less affected by temperature, 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).
Unlike ultrasonic sensors, radar is much less affected by temperature, improving consistency and accuracy. Radar is 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, dust, and uneven surfaces. As these substances can interfere with signals on ultrasonic sensors and lead to erroneous readings, this can make radar sensors a better choice for certain 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, or uneven surfaces 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 ultrasonics.