Well, without more details on your process and tank, we can’t give you an accurate answer. Both principles work using the time-of-flight concept. If you want to know more about that, then you can read this post here. But we can highlight the pros and cons of each, and you can figure out the best solution based on those.
In my opinion, ultrasonic devices have become obsolete. Sure, many brands still push this tech. But with the low-cost radars now available, it’s hard to justify. Still, it may be too early to declare the ultrasonic dead.
Anyway, an ultrasonic uses a piezoelectric sensor to emit mechanical waves. As a non-contact level transmitter, it has a simple design compared to other level devices. Unfortunately, it also has a dead zone or blocking distance, a specific length where the device won’t measure. And vapor and foam can cause it to work incorrectly.
Now, radars work with electromagnetic waves, also known as microwaves. If you need a non-contact solution, then you can use a free space radar, whereas a guided radar has the antenna in constant contact with the product. Some vendors say you can apply radar in products with foam and vapor and such, but your mileage may vary on those.
Regardless, changing the working frequency will change the beam spread, making the installation easier in some cases. And a radar measures everything inside the tank, unlike the ultrasonic that stops at the product’s surface.
As for the drawbacks? Well, most radar devices cost more than ultrasonics, although VEGA and Endress+Hauser have a few low-cost options. They take a little more work to set up as well and need a liquid with a minimum dielectric constant.