Three beams
are all you need
New ultrasonic meter for the process industry

Any new purchase a company makes represents a compromise between accuracy (if a meter is involved), price, maintenance and upkeep costs, ease of operation and service life. Based on these and other factors, the user builds up a network of pros and cons that provides his framework. Expanding the product range can undoubtedly help a supplier to more accurately
target the user’s requirements profile. Krohne unveiled just such an alternative at Achema.
Years from now, there will still be disagreement over whether a volume-based flow measurement system or a mass flow meter is the better choice. Both alternatives certainly “work” in many process applications, but it is best to avoid temperature and pressure factors if for no other reason than to eliminate uncertainty. So even out into the future, there will still only be a “more suitable” measurement principle, not a “better” one. If you need a precise stoichiometric mol mass in your reactor, you will be happy to have an accurate mass flowmeter. However, if you think in terms of volume because you are involved with polymerization reactions, you will be pleased to see accurate volume flow data. There are a lot of very accurate and very expensive meters on the market that are based on the ultrasonic principle and work with five beams for example. At this year’s Achema, Krohne unveiled a new meter that works with fewer beams but is nevertheless accurate. To be precise, the measuring uncertainty of the triple-beam meter is 0.5%.
So what is the problem with reducing the number of beams to three? As is often the case in the field of engineering, there is a big difference between theory and practice. If you could assume that the flow profile in a measurement tube had uniform turbulence characteristics, the world of meters would be (almost) simple. However, this flow state cannot be guaranteed, and the flow differential between a laminar and a turbulent profile can be 33%.

How many beams are enough?
To give you a comparison, a five-beam meter has no dependency on the Reynolds number, and the dependency of a triple-beam device is less than 0.5% Both meters have the advantage of redundant measurement beams. In contrast to single or dual beam meters, both can correct for non-symmetrical flow profiles, and the five-beam meter can even detect individual eddies. Thus the hierarchy is as follows: one to two percent measurement inaccuracy with a single-beam meter, 0.5% with a triple-beam meter and 0.15% with a five-beam meter. Engineers at Krohne in Dordrecht/Netherlands use the extra information gained about the momentary flow profile to provide more in-depth information from the field. André Boer, Vice-President of Krohne Altometer in Dordrecht, explained that “by using new DSP technology, we can provide more information about volume flow. We exploit this to provide data about product change, for example.” However the development problems have to do with the details. Determining how to arrange the beams around the tube perimeter is definitely not a trivial task. Jankees Hogendoorn, one of the “fathers” of the meter who played a major role in the development of the five-beam meter, had to empirically determine the best position for the sensors. More than 20 test devices had to be built during the course of these investigations.
Cross-talk effects during time measurement also had to be minimized in the design phase. Patented sensors with acoustic de-coupling were developed. These sensors are so small that only small openings are needed for the transducers which cause very little flow disturbance. They are also suitable for high-temperature applications:
- UFM 3030 Standard: 180 °C
- UFM 3030 XT (optional): 220 °C
Additional meter data:
- Viscosity: 100 cST
- sound velocity, density, conductivity: no restrictions
- media temperature: -25 °C to + 220 °C
- ambient temperature: -40 °C to +65 °C
- working pressure: up to 100 bar
- start of measurement at zero flow up to 20 m/sec
- solids up to 5%, gas/air pockets up to 2%
- EX class: Atex zone 1 (optional) FM Div 1/2 (optional)
All we have to do now is look at the future. Where can the user expect to see improvements next? The Dutch flow experts have the answer to this question as well. Boer explained that “our smallest meter at the moment is a DN 25 device, but it won’t be long before we have DN 15 devices in our product range.”j