Looking for opinions: Ultrasonic tank fluid level sensors

Working on an industrial wastewater treatment plant... Do any of you have experiences with these? I'm changing our input signal from a physically located float switch to something that will provide real time values via a 4-20mA signal. Do those of you with experience have a preference? Any brands to avoid?

I have personally not had much luck with ultrasonics. They seem to work fine until the day after the warranty expires the do all sorts of weird stuff. I ended up replacing all of them with submersible pressure transducers and haven't had any problems since then.

I have had great success with Milltronics (now part of Siemens) "MultiRanger" wave guided radar sensors. They are a little different from "ultrasonics" and are not fooled by foaming, which is a potential headache for WWTP applications. They are also more expensive, and in fact considerably more expensive than the submersible pressure transducer type mentioned above. The go-to standard for that industry tends to be the submersible transducers, but if it is measuring level in a tank with an agitator, that may be impossible. That's where I went with the wave guided radar.

My new project will include guided wave radars, though I have used ultrasonic in special situation with no problem. I will use radar because of interface on liguids, interfaces and vapors are problems for ultrasonic.

mendonsy said:

I have personally not had much luck with ultrasonics. They seem to work fine until the day after the warranty expires the do all sorts of weird stuff. I ended up replacing all of them with submersible pressure transducers and haven't had any problems since then.

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Some of the newer varieties are a bit better but if this is a black-water tank that gets lots of foam at times you will be disappointed.
Many that I have seen have best luck with pressure switches kept high enough off the bottom to avoid the build up.

I agree

jraef said:

I have had great success with Milltronics (now part of Siemens) "MultiRanger" wave guided radar sensors. They are a little different from "ultrasonics" and are not fooled by foaming, which is a potential headache for WWTP applications. They are also more expensive, and in fact considerably more expensive than the submersible pressure transducer type mentioned above. The go-to standard for that industry tends to be the submersible transducers, but if it is measuring level in a tank with an agitator, that may be impossible. That's where I went with the wave guided radar.

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Unless you have no sludge, no foam, same density and no agitation go with the guided radar. I have tried them all.

we have Endress hauser radars they are pretty good

I appreciate all the input. There is a high potential for foaming, and sludge. The density is unfortunately variable...

I work in clean water treatment plants.

We use a mixture of manufactures for our ultra sonic level instruments, but have mostly settled on Siemens. For simpler applications (filter beds etc) we have the Sitrans LU transducer in a head, loop powered. For slightly more complex or higher accuracy required we have the hydroranger plus or newer hydroranger 200. I have just installed some Sitrans LUT400's in over flow tanks so will see how we get on with those.

We also have installed a range of older types including Mobrey MSP90 and the newer MSP900. The 90's have lasted 25 years or so pretty well, but many are starting to fail. It actually tends to be the mA output stage that fails. There are some Mobery MSP400's in use, and i cant stand them. Similar to the Sitrans LU, but they are not loop powered, have a stupid three way screw system for the lid, that regularly leak and the menu system is atrocious.

One other manufacturer i have recently installed is pulsar. They do a unit that retro fits into the same dimensions as the older mobery units. I quite liked that one, keypad on the box, and very easy to set up.

Every failure of an ultrasonic sensor I have had, has been from Siemens. The PROBE (formerly milltronics) series just dies, the LU series was worse because its failure mode has always been a random ramped up output to full scale and then recovery. Really screws up a process.
I bought their radar variety (not guided radar) because of low cost and only time will tell if they are as bad as the ultrasonics.

I have a couple hydrorangers that have worked fine.

I too have several sensors out in the field to measure liquid level. I use submersible pressure also. Have never had any problems. I always use 4-20ma this way if I get a zero reading I know I have power/broken cable problems.

depends

damica1 said:

I too have several sensors out in the field to measure liquid level. I use submersible pressure also. Have never had any problems. I always use 4-20ma this way if I get a zero reading I know I have power/broken cable problems.

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Just some info if you have to install some, don't assume any problems, I have seen all of these examples screw up readings.

If you use a mixer as the liquid is centrifugally spun to the outside the pressure on the sensor will decrease showing a level less than what you have.

If you get a buildup of sludge or sediment on it, it will not read correctly it may read high or low depending on how much.

If you have a liquid that is not the same as what it calibrated for due to process changes or different liquids coming into tank it will read high or low.
These are just some of the problems pressure transducers can cause.

+1 For the wire guided radar. We recently used an Endress&Hauser one, seems to work very well.

Another thing to watch out for is condensation build up. Are your temperatures variable as well? Ultra Sonic might get messed up with that as well.

My experience is old, but I have had poor luck with ultrasonics. Scum and foam cause false readings. Echoes from tank walls and stilling wells can create problems. In outdoor installations the wind can cause the echo to drift so the sensor misses it.

I have had the best luck with submersible pressure transmitters, including both te types with and without the diaphragm.

http://www.bannerengineering.com/en-US/products/8/Sensors/30/Ultrasonic-Sensors/228/QT50U-DC—Analog

I have had good luck with these units, installed over five years ago and no fails.