MICROWAVES jumping on ultrasonics

Latest developments with radar level sensors look set to catapult the technology into the limelight – and overshadow ultrasonics by Brian Tinham

Non-invasive techniques have been the talk of level measurement for years. But radar’s position in this discussion has, until recently, been marred by expense and difficulties of certification in the UK through the DTI’s RadioCommunications Agency. In short, although accepted as offering a potential panacea for level measurement, radar has been reserved by most engineers for those otherwise insurmountable level measurement problems.

But not any longer. Today, licensing is not a problem. And now, all of a sudden we hear first Vega’s Melvin Henry at the May C&I Europe Show talking about the prospect of radar costing sub-£1,000 by the year 2000. And, then at last month’s ACHEMA chemical industry fair in Frankfurt, Saab’s Peter Dragen says that we can expect radar priced at well below that. His view: `Ultrasonics will be dead for level measurement within two years! Because radar will be cheaper.’

Merit in the claims?

It’s a hell of a claim. Particularly since just a year ago we were pointing out the welcome reduction in cost of radar-based level instruments from the then £3,000-£4,000 mark down to around £2,500!And we mustn’t underestimate the significance of radar as a technology for level. From a pure engineering point of view, modern sensitive radar could represent a virtual panacea for level sensing, certainly where water-based media are concerned – but also for most oily fluids, irrespective of the application details.

Remember, radar can measure accurately the most aggressive of media, no matter what the vessel conditions (agitated, pressurised, heated, steamy, foaming) and application (multi-product batching, etc). Equally, if the price was right, it could happily handle benign fluids in simple, small storage tanks.

Sophisticated software

Also, today’s standard radar instrument software can remove false echoes and compensate automatically for oddly shaped vessels, while digital signal processing makes for extreme sensitivity by optimising the use of reflected signals. And in some, calibration is entirely automatic.

Then again, radar frequencies have now been optimised to make the best of the trade-off – narrow enough beams to cut interference from tank equipment, yet long enough wavelength to minimise sensitivity to foam and vapour.

So, are the claims for radar’s imminent future true? Could radar prices fall to make them the mainstream – with instruments emerging to suit the plethora of application types currently fulfilled by the range of other technologies?

Well, apparently, yes. New sensing technologies are the prime key here. Microwave Impulse Radar (MIR) sensing, developed at Lawrence Livermoore National Laboratory in the USA, has already resulted in devices for detecting wall studs down at the $40 mark. Then again, pulsed radar sensors have been re-engineered for low cost. And, according to Dragen, even frequency modulated continuous wave (FMCW) radar sensors are dropping in cost.

Dragen: `Low cost pulsed radar sensors have come first. They’re now small, easy to make and they’re slashing microwave prices. We wouldn’t use this technology yet; it’s too new and not accurate and reliable enough for the kinds of top-end applications we cover. But it’s certainly going to rock the boat for vendors of lower cost ultrasonics-based monitors.’

Volume production

But there’s more. Dragen again: `Satellite TV and the huge growth of the communications industry are leading to much lower cost, mass produced hardware – including radar antennae. So this too will contribute to falling prices in our industry, just as electronics and microcomputing did before. It will literally transform radar for level measurement.’

Already, Vega has previewed its compact Vegapuls 50 radar – at last month’s ACHEMA. The device is being built in Cincinatti, USA, at what’s currently Ohmart’s plant. Henry says: `Vegapuls 50 radar will cost £1,200; it will include our EchoFox Lite software and certainly compete well against ultrasonics in slightly difficult applications.’

Then Endress + Hauser’s ACHEMA launches were Micropilot II and Levelflex. According to Diether Schaudel: `Micropilot II, which is the loop-powered radar instrument, is half the price of its predecessor, at £1,200 in the UK. It has a PTFE rod antenna, is intrinsically safe, and handles temperatures from -40oC to +150oC and pressures to 16bar.’

It also supports HART and Profibus PA fieldbus connection. Schaudel says that it’s limited in range, process conditions and response speed compared to Micropilot I, but at a very attractive and challenging price.

Meanwhile, Endress + Hauser’s Levelflex is an £800 device for solids level measurement, featuring a steel cable detector and time domain reflectrometry technology. It will compete with similar equipment from, for example, Krohne.

As for Saab, its major ACHEMA launch was TankRadar Pro, harnessing advanced FMCW radar technology and operating at 10GHz. Dragen: `We’re marketing TankRadar Pro in Lite, Standard and Gold versions – graded for storage, agitated batch and improved accuracy applications.’

Pricing here is around £1,900 for the Lite, up to £3,000 for the Gold – but we’re talking about very high accuracy, extended depth capability (typically, +/-5mm over 30m, although the device is capable of much greater depths). It’s also top of the range performance for demanding applications. Facilities include, for example, Saab’s EchoFixer and automatic multiple echo tracking (MET) through adaptive, intelligent software, its FHAST fast signal processing surface range filter and automatic, instant self calibration.