How the latest radar level measurement technology, with new levels of affordability and Bluetooth communications can benefit these sectors
By Doug Anderson, Marketing Manager VEGA UK
Comments from Jürgen Skowaisa, Product Manager - Radar and Ultrasonic VEGA Germany
Across the world, there are tens of thousands of sewage treatment plants and billions of litres of sewage is treated every day
Myriad measuring instruments monitor and measure water or sewage for level, flow, pressure and water quality, as well as controlling increasingly complex biological processes at the treatment facilities themselves.
Level is one of the most common measurements - for example, flow in open channels, flumes and weirs, controlling screening systems, emergency overflows, flood monitoring, settling ponds, sludge, solids handling and dosing systems …along with countless other tasks. Until recently, continuous level measurements in the water processing and monitoring industries mainly relied on non-contact ultrasonic level sensors, particularly on effluent, due to the large amounts of solid material, and submersible pressure transmitters used mainly on the cleaner, water supply side.
Now, a still relatively new contactless level option is using radar technology. It’s already well-established in many process industries, yet water utilities still have comparatively little experience with it, partly due perceived higher cost and perceived complexity, making them a ‘specialist’ solution. Now, thanks to new developments in technology and cost, radar can be considered as a first choice.
Why choose radar level measurement technology?
Mainly due to less influences from process or environment, the excellent reflectivity of water to radar signals, inherent accuracy and repeatability and a more robust measurement technique. at a price competitive to incumbent technologies.
Jürgen Skowaisa is Product Manager for both radar and ultrasonic technology for a market leading level company.
From experience, he considers contactless radar level measurement technology as the future for the water, environmental and sewage sectors, primarily because of its robustness in the face of process and weather influences. He has direct experience of condensation, turbulence, vapours, wind, fog or rain impairing ultrasonic sensors, as well as temperature influence (solar gain) from solar radiation.
Velocity changes of ultrasonic signals are related to temperature changes (1.6% per 10 ‘degrees’ Kelvin). For instance, on an ultrasonic sensor a temperature sensor inside the transducer does the compensation
“As long as it’s cloudy, you get reliable values” explains Skowaisa “But during longer periods of direct sun, temperature on the transducer increases, and the sensor temperature can become much higher than the ambient temperature, thus causing an error “
One solution is a solar shield, or additional temperature sensor, but it doesn’t always mitigate errors, as temperature variations in the air between sensor and liquid surface can’t always be measured and corrected for. This was demonstrated in a test by an environment agency, who installed a radar alongside an ultrasonic sensor (fitted with a temperature sensor and a solar shield) on small bridge. The data showed the ultrasonic sensor still produced noticeable errors, or drift, in certain weather conditions, while the radar device output remained accurate.
Turbulence, waves or foam can also affect ultrasonic sensor performance, reflection signals can scatter and if in the open, wind can take the signal away completely. Radar microwave signals are unaffected – with millions of pulses emitted and the output updated twice each second – which means they can even measure wave height. With surface foam, latest radar sensors also have the focusing and dynamic sensitivity to carry on working and measuring.
Radar delivers accurate, reliable level data even with sensor face condensation or vapours and gases in the vessel. The proliferation of Anaerobic Digestion (AD) units for energy generation and sludge handling plants typically present these environments for level controls. Also, new designs of ‘sealed’ waste treatment plants - to reduce odour in urban areas and facilitate harvesting of gases for energy generation - provide greater potential of these issues arising in future.
What capabilities do the sensors typically have?
A compact 2-wire, (4-20mA) loop-powered ‘water’ radar will typically have an accuracy in the region of 2mm or 5mm, (bulk solids versions level available) with encapsulated antennas with a 10° beam angle (3° options), ranges from around 8 to 15 metres (variants up to 120m), they can feature Bluetooth, Profibus, FF and HART communications for set up and/or data transmission with ATEX and IEC hazardous area approvals along with SIL 2 conformance.
Some resist submersion with flood-proof housings (IP68 to 2 Bar). Basic devices can handle process pressures up to 3 bar, temperatures up to 80 °C – normally ample for most water/environmental sectors (alternatives are capable of 400 Bar and 400°C!). There are tens of thousands of radar based devices already installed in the water industry worldwide, and the adoption looks set to accelerate.
“The technology boasts higher precision in general, it is very easy to use and can offer a great performance alternative to ultrasonic instruments” explains Jürgen.
So what about the price?
“The price differential between ultrasonic and radar measurement technology used to be very high. Today, the cost of radar technology is the same, even lower, depending on the application, so it is actually turning out to be a better all round solution”.
It means customers can now choose based purely on best technology, rather than on price.
Like any industry-oriented device, application based set up helps with both quality and speed of commissioning.
“Users in this industry require quick, easy selection for applications such as pumping stations, sludge reception and handling tanks, digesters, flow-rate measurement in open channels and other similar applications typical of this sector. Even flow curves can be programmed into the sensor itself for open channel flow measurement.”
A variety of mounting and communication options are available to make the sensors easy to integrate into existing infrastructures. Straightforward, user-friendly operation and handling, like Bluetooth Apps and PC comms. delivers fast simple set up and diagnostics.
Jürgen adds, “The measurement data can be transmitted either directly to an existing control unit or to a SCADA system (4 … 20 mA, Profibus PA even Foundation Fieldbus), so this makes the technology a true all rounder.” he concluded.
When it comes to approvals, as well as hazardous area certifications, there is a European norm for Level Probing Radar (LPR) level sensors for open air use. Devices must conform to this standard to be used outside.
Reliable data in demanding applications: The following examples show the advantages the new sensors have in daily use in the water sector.
Precision open channel flow measurement: In flow rate measurement in open channels, accuracy is key due to the exponential flow calculations, which can amplify the small errors. According to Jürgen, many users don’t realise that ultrasonic technology can deliver inaccurate results.
“Users simply trust that the values stated in the manual are correct, but in reality, these only apply under ideal measuring conditions.”
Regulators charge businesses for effluent discharge quantities on the basis of these values. Radar technology can deliver better measurement data for all parties involved.
MCERTS Approved radar level measurement for open channel flow measurement
Recently the first radar based system for open channel flow measurement was approved under the MCERTS scheme - overseen by the Environment Agency in the UK. It was assessed for performance, accuracy and quality of manufacture. Radar technology is a perfect choice for this application, unaffected by temperature changes, reliable in all weathers, even with condensation on the sensor face, delivering precision level data for computation into flow. It is now certified for this application under the scheme and offers great advantages for versatility, capability and flow measurement accuracy .
Storm water overflows and sewer flows: SWO or CSO chambers are often sited underground and users can benefit greatly from the technology.
“Because radar technology has no blocking distance, measurement can continue even to very high water levels, and the immunity to condensation on the sensor face also helps reduce misreads or lost readings”. Jürgen mentions another advantage, “Even flooding is no problem, because radar sensors have IP68 protection options. Millimetre measuring precision under all conditions can monitor ‘spill’ more accurately, too.”
Storage of chemicals: some chemicals used for sewerage or water treatment and cleaning give off fumes, condensate and vapours. They require secure, safe handling and measurement when used so close to the water courses and plants. Radar level measurement works with fumes or vapours present and has the great advantage that it can be mounted above/outside a plastic or GRP vessel looking down through the top to provide a reliable, accurate monitoring for inventory. An ideal solution for plastic mobile IBC containers, no fitting required.
Pumping stations, wet wells and shafts: Radar level measurement offers excellent performance, pump shafts are often narrow and filled with many pipes, fixtures and fittings, the pumps themselves are sometimes located directly in the shaft, build up solids is prevalent. Reliability is achieved with focused beam and the very high reflectivity of water to radar signals. On very deep shafts, seen on large-scale schemes, an alternative sensor can be used with only a 3 degree beam angle with ranges up to 120m.
Open waterways Flood risk is increasing, as the result of more concentrated heavy rainfall in some areas and urbanisation in others. In turn, so is flood level monitoring, gauging of rivers, waterways, and estuaries. Non-contact radar sensors, with their immunity to sun, wind, rain and fog etc. really come in useful. They can be mounted anywhere, quickly and easily, out ‘in the open’ without still wells or sounding tubes, of or under bridges and retrofit to existing installations.
With its contradictions of scarcity and deluge, the monitoring of water and flood levels, supply and sewage treatment will continue to grow in the future and it will always place new challenges on technologies.
Meeting these needs in different environmental markets is a challenge in itself: In Europe - upgrades for existing plants, looking for latest technology to automate etc. while in countries like China and Brazil, new sewage plants with latest field bus communications are being built ‘almost daily’.
New radar level measurement technology devices with improved reliability and performance, application based set up, Bluetooth set up, as well as price competitiveness - offer a real alternative to legacy sensors with a choice based on the technology, not just price.
“Future market and environmental requirements can be quickly met with such a capable core technology" concludes Skowaisa, “I am convinced radar instruments will play a major role in achieving this.”
VEGA Controls Ltd
VEGA manufacture level measurement, level switch, interface, density and process pressure instrumentation.