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Radar and Ultrasonic Sensors

Both radar and ultrasonic sensors transmit wavesThere 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 is important, as it affects how sensors are selected and applied.

Ultrasonic Sensors

As the name implies, ultrasonic level sensors operate by emitting a burst of sound waves in very rapid succession. These sound waves hit the intended target, bounce back to the sensor, and travel at known speed (the speed of sound). We can calculate time of flight and come up with a distance.

Other parameters are programmed into the sensor or control system to determine volume, weight, or other similar measurements.

Radar Sensors

Radar, by contrast, works not with sound waves, but with electromagnetic waves. This is the key difference. 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 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).

An important factor 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 Bottom Line

In the end, radar sensors are affected by fewer variables than ultrasonic. This makes them more consistently accurate in most applications (except with low dielectric materials, of course). However, this comes at a price. At around 3 to 4 times more costly than an ultrasonic sensor, radar has a while before it will be practical for most applications.

As for ultrasonics, if you need to measure liquids, or even many solids, in a tank, well, pit, or pile, they’re a good bet.

Have more questions about whether ultrasonic or radar level transmitters are the best fit for you? Our Measurement Experts would love to help you. Give them a call, drop them an email, or live chat with them today.


APG's Guide to Ultrasonic Sensor Programming

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