PREVIEW EXHIBITOR
How it works, and why it is better than ever VEGA Controls describes the benefits of using ‘through air’ radar for non-contact measurements
‘CONTACTLESS’ RADAR A
sk any engineer and, given the choice, a non-contact measurement of any
process parameter is always preferred. But how do non-contact or ‘through air’ radars work? While the principle of ‘non contact time
of flight’ measurement of radar is similar to ultrasound – i.e. they both measure distance directly to compute level and volume. Some manufacturers call contactless radars “through air” devices when actually they do not use air at all, they use electromagnetic radio or microwaves. This is because transmission through-air can have its accuracy compromised or signal blocked by conditions like temperature, noise, gases, dust, pressure, even weather, if used outside. There is growing popularity of this technology in other sectors, such as automotive for driver assistance, parking and control. Indeed, VEGA radar devices were used in early tests on autonomous car development.
BASICS OF RADAR LEVEL TECHNOLOGY ‘Contactless’ process radar devices use either Pulse technology or Frequency Modulated Continuous Wave (FMCW). For Pulse, a microwave generator directs a continuous beam of very short, microwave pulses (millions per second), that are transmitted to, and reflected back from a product surface, via a cone, rod, parabolic, planar or ‘flush’ antenna. The elapsed time period between transmission and reception of the signal (at the speed of light) is measured, calculated and converted to a distance, vessel level or volume. FMCW systems use similar antennas and employ a modulating transmission signal and then a frequency shift detection technique to measure. Both offer accurate, continuous and real-time (some several times per second) readings. The measured products’ Dielectric Constant (DK) or Relative Permittivity (r) will have an effect on reflectivity to radar signals. It used to be a major application consideration, but is less of an issue with new 80GHz high-sensitivity radar devices. This property also has advantages, radar sensors can be mounted completely outside looking through ‘low reflectivity’ plastic vessel walls or glass windows. They offer good all round performance from storage tanks to highly agitated, chemical reactors.
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IS THERE ANYWHERE NON-CONTACT RADAR CANNOT GO? Of course there are some areas where a guided wave radar (with a rod, co-axial or cable probe that guides the measurement path) works better. For example, in external side chambers or bridles on vessels, this radar signal format gets less interference from side connections. On interface measurement (e.g. oil and water), guided wave radar is the better solution. But a good full-range radar supplier will advise on this and provide the right technology for your application.
POWER REQUIREMENTS Many years ago, all radar devices required a separate power supply for the electronics just to handle the large amounts of power for signal processing. They could be tricky to set up for end users and often needed service engineers to commission them and got a reputation for being ‘specialist’ and a ‘bit of an art’ to get working. In recent years, like many other technologies, state- of-the-art electronics and processing systems have enabled devices to use infinitely more powerful processors, be loop powered and very simple to set up. There are different licenses to ISM (Industrial Scientific and Medical) frequencies: C band (around 6.2GHz) with a wider beam angle, K band (24/25GHz) – with a narrower beam angle, and now the latest 80GHz is very highly focused. These are all, approved for “through air” microwave transmission in closed vessels and some meet new LPR EN 302729 standard for “open air” applications, like rivers and open storage sites.
ARE ALL RADARS THE SAME? Regardless of the radar level ‘technique’, it is electronic and measures at the speed of light. The difference comes in with quality of components and fundamental design, just like the difference between a low and high quality camera and lens – image quality and sensitivity to light. In a radar, good sensitivity and performance is key to effectively analyse the information gathered, reliably follow and deliver the correct ‘level’ measurement. This also makes setting up a device easier, so in short the ease of use, operation and sophistication varies by manufacturer.
SEPTEMBER 2017 | SENSORS & INSTRUMENTATION 2017
A non-contact radar is virtually the only solution for level application on molten iron in a ladle
WHERE TO NOW FOR RADAR? Latest generation, high sensitivity, highly focused 80GHz non-contact radar level transmitters are working in solids and liquids applications that were previously seen as extremely challenging: foaming surfaces, ‘very low reflectivity’ plastics and hydrocarbons, long nozzles, through valves, fast response for wave height measurement or conveyor positioning, high combustion temperatures and vacuums, to name a few. Although level radars will always be complex in their nature, the most important user benefits must be kept at the forefront of development: simple to use, easy to set up, reliable, predictable performance and a low cost of ownership - which is what the latest generation 80GHz radar products are really focusing on.
80GHz level radars for liquids and solids offer more focusing and with higher sensitivity
More questions on contactless radar? Ask the experts at VEGA Controls on Stand H6 in Hall 1 at Sensors & Instrumentation.
VEGA Controls Limited
www.vega.com/uk T: 01444 870055
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