Non-contact radar level transmitters and their frequency bands!
Hey, all right? Today we’re learning more about non-contact radar level transmitters, also known as free space radars. Yep, same device, just a different name. And you’ll find that they have various frequency options as well. Which should you choose? Let’s learn a little more!
Frequency of flight?
No, time of flight and frequency. Y’all read my time of flight (ToF) article, so you’re up to speed on that principle, right? Okay, okay, for those of you who missed it, I’ll summarize.
Time of flight means the time it takes the radar signal to reach the surface of your product and return. Radar uses electromagnetic waves, while ultrasonics use mechanical waves. If you want to learn the difference, you can read that article up there. Just come back here when you’re done.
For radar functionality, you’ll see different frequency bands. You can have 6 gigahertz (GHz), 26, and more. But why all the frequencies, and which one will work for your application?
Take a seat and find out the differences between the types of frequency bands. In fact, you’ll also find different sales pitches for these bands, depending on the company. So we’ll analyze these differences and see what happens!
So many frequencies, so little time! You’ll need to pay attention to how they differ to find one to suit your needs. Military equipment uses a specific frequency, as do satellites, so you may have to factor communication into your requirements too.
For example, a radar gun operates on frequencies that change from country to country. The first generation of radar guns used a frequency range from 8 to 12 GHz called the X band. The new generation of radar guns use the K band (18 to 27 GHz), and you can find radar level transmitters using Ka-Band (27 t0 40 GHz).
Radar level transmitters on the market come in four different frequencies. You have radars based on C band (6 GHz), K band (26 GHz), and X band (10 GHz). Then some vendors produce radars on the W band (75-85 GHz). And here comes the drama! Beware the terror of – misalignment! Dun dun dun!
Vendors who offer W-band radar devices have rainbows and kittens in their sales pitches. And companies who don’t will throw tomes of technical explanations at you about why you need to stick to the other bands. We’ll go through this topic later.
What’s all this beam business?
If you read our reviews of the Pulsar R96 and the SITRANS LR200 or their comparison, I mentioned beam angle and beam spread. You need these details to fit a radar for your application. For instance, you can’t use a radar in a tank with an agitator if you have low dielectric constant. The signal will reflect off of it and give a bad reading, however, you have exceptions on the market.
So the beam angle and spread have to do with your transmitter’s antenna and frequency. A low-frequency radar with a common antenna will have a beam angle around 20 degrees. For example, the SITRANS LR200 works with 6 GHz. A 4-inch antenna creates a beam angle of 29 degrees, and an 8-inch antenna has a beam angle of 17 degrees.
The VEGAPULS 62 works on 26 GHz, so you can have a beam angle between 8 and 22 degrees. So you see that higher frequencies can have lower beam angles using small antennas. You can get lower beam angles with low-frequency radar, but you need big antennas, often too big for common processes.
So you get why big antennas don’t work, but why small beam angles? It means that the radar can measure in low tanks, or tanks with interference, or even close to the tank wall. VEGA has a terrific ad showing a device measuring the level of a water bottle. We’d love to replicate this, so VEGA, please send us a demo! 🙂
Endress+Hauser also offers high-gigahertz technology, with options for process and storage applications. The reps say 113 GHz, but that’s just a sum of the frequencies, so don’t get too impressed. Now if you want to impress me, make a video with an 80-GHz radar measuring the level in a beer barrel. Ad protip: People like beer better than water. Just sayin’.
Low or high frequency?
The documents for level measurement from Emerson Automation Solutions make a point – three of them, in fact – of saying why high-frequency devices can give you more headaches than low. On the other side, VEGA and Endress+Hauser sell positive messages for high-frequency radar.
Emerson starts with interference, saying that high frequency devices have problems with vapor, foam, or buildup. Emerson then claims that a radar with a beam angle smaller than 4 degrees can have problems with antenna misalignment and signal loss. Last but not least, apparently waves and ripples will increase signal loss and risk your accurate and reliable level measurement.
VEGA and Endress+Hauser have countered these arguments with videos and recommendations for stilling wells and bypasses. If you go through Emerson’s documents carefully, you’ll notice a decided lack of these options.
Now you’ll scale out the radar level transmitter of your dreams using your process requirements, then check the accuracy and benefits for your application. You’ll also analyze the prices and local support to find the right device for you. So let’s hear it – are you Team Low or Team High?
See y’all soon.