Radar-based level measurement instrumentation has experienced a constant rise in the radar frequencies used. But does more always equal better?
Within this interview, Andrew Reese, global industry manager for Primaries & Metal at Endress+Hauser, explains why the answer to the above question is not a simple “yes” or “no”.
Could you explain what impact the frequency has on radar level measurement in general?
Andrew Reese: First and foremost it’s a matter of simple physics; the frequency influences the wavelength of the measuring signal. The higher the frequency, the shorter the wavelength, that means the shorter the distance between two wave crests.
And how does this influence the measurement and the suitability for different applications?
AR: For example, with a higher frequency the microwave beam angle can be much smaller. A narrow beam of only 3° can measure down in to the bottom cone of a silo and is an advantage for level measurement in tall narrow tanks with many obstacles inside, such as strengthening beams, struts, ladders or an aeration system. Also, a higher frequency signal will work reliably on both very small chemical additive tanks and very tall silos compared to lower frequency signals.
Does a higher frequency also have disadvantages?
AR: Yes. For example, a high-frequency signal is more prone to attenuation due to the small wavelength, which means it loses strength when crossing through a medium. In practice this results in high frequency instruments having more trouble with conditions such as dust, foam or vapour. But ripples and waves on liquid mediums can also be a problem - because on such turbulent surfaces the signal tends to get disturbed and scattered. If the wavelength of the signal is smaller than the wavelength of the waves on the surface, that is. If the signal is scattered, however, it also loses power and makes the measurement more unreliable.
So, what is the ideal frequency?
AR: There is no one best frequency for radar level measurement. It all depends on the application and the conditions around the measuring point. That’s why Endress+Hauser decided on a common sense approach rather than claiming “one frequency fits all”. Our portfolio encompasses a set of measuring devices operating at different frequencies, using intelligent application-optimised software such as dust build-up monitoring and related hardware options such as dust purges, silo alignment tools and high-temperature protection. Starting from the challenges of our customers we want to provide them with the ideal solutions based on the industry expertise of employees and clever design of products.
Can you give us more details on other factors customers should have in mind before deciding on a radar level instrument?
AR: Yes, of course. For example, take a holistic approach to selection. Look at the silo design, shape, age, condition and how the medium flows in, through and out. Do you experience poor flow conditions in your solids or powder silos? Do you often suffer from froth spilling over in flotation tanks or overspill from tailings dams or worse, out of dangerous chemical tanks or fuel biomass digesters? Do you get a water cut or emulsion in your fuel oil storage tanks? Depending on these and many other site conditions, installation of a level device could become very complicated.
And what about the trend towards Industry 4.0 or the IIoT?
AR: With mines needing to optimise their processes to raise their effectiveness and lower costs, process automation and digitalisation of course plays a role. We see the smart use of measurement data as a first step towards Industry 4.0. That’s why we developed the innovative Heartbeat Technology that is included in the Micropilot FMR6x series. It ensures trouble free plant operation during the sensor’s entire life cycle by combining self- diagnosis, approved verification and process condition monitoring functions. But with the IIoT trend the functional safety of the instrument is also becoming more relevant.
What do you mean by that?
AR: Industry 4.0 or IIoT means a higher degree of automated processes, which means plant operators must be sure that they can rely on their instruments. Functional safety provides the assurance that the safety-related systems will offer the necessary risk reduction required to achieve safety for the equipment. Integration of field instruments that can be used in HAZOP-defined Safety Instrumented System (SIS) zones is included in this safety guideline under IEC 61511. Each zone and each field instrument has a risk class or Safety Integrated Level (SIL) from 1 to 4. The steel, oil and gas industry, nuclear plants and the machinery sector, to name but a few, all rely heavily on functional safety to achieve safety for the equipment giving rise to the hazards. But I am convinced that this is already changing in the mining industry. We at Endress+Hauser are already prepared for this development as our instruments are developed according to international guidelines and can be used in SIL2 and 3 areas. What this means for our customers is that they can integrate our instruments into their process with minimal certification or testing efforts.
