Sense of purpose15 April 2013

It's instructive to find that, even in 2013, new sensing technologies are being developed that can transform industrial measurements.

Aside from ongoing developments around digital communications, diagnostics and industry-specific functionality – all the result of increasing electronic intelligence – instrumentation is no longer renowned for technical innovations, at least in terms of the sharp end of sensing. So it's remarkable to find two significant developments in the last few weeks for level monitoring alone that could have a significant impact on controls for a range of plant types.

The first involves 3D and 1D laser technology, and has its roots in ABB's acquisition of laser specialist K-Tek a couple of years ago – the technology having been worked up with ABB's Canadian interferometry division. The second is from pioneering technology firm Cambridge Consultants, which calls its device FELT (fringe effect level transducer).

Looking at the former, ABB's level transmitter product manager Alan Hunt concedes that laser devices have been used for point-and-click distance measurements for years, but argues that, to date, the industrial world has been largely overlooked. He also explains that this company's latest (3D) device is designed to automatically scan stock piles (coal, biomass, gypsum, potatoes, sugar, lime, road grit, etc), either on the ground (covering potentially hundreds of cubic metres) or in bunkers, and to derive volumetric inventory measurements to better than 2% accuracy, despite irregular shapes.

Dubbed VM3D, the device's scanner head can rotate through 360 degrees in the horizontal plane and 180 in the vertical. "If it's mounted high up, then the instrument has free reign to scan over a large-scale target and take potentially thousands of point-level measurements, moving in a ring pattern throughout its field of view," explains Hunt. That's clever. However, since lasers are line-of-sight devices – meaning multiple scanners might be required to cover any blind sides – cleverer still is that data from these is then "mashed together" in a computer control box, subtracted from any baseline (the ground, bunker walls, whatever) and the point-level cloud converted to volume.

Sounds expensive? Well, it can be. But prices evidently start at around £20,000 – which, compared to inaccurate, potentially dangerous and certainly time-consuming manual methods, doesn't sound bad. And it doesn't stop there: ABB's 1D version, which was unveiled two years ago, provides a very effective problem-solving technology where even ultrasonics and radar-based level detection and monitoring systems don't work well.

"The beautiful thing about lasers is their very tight beam angle," explains Hunt. "With all other technologies, the further you make the measurement from the device, the larger the beam area – which means there's plenty of opportunity for false echoes. That doesn't happen with lasers, and their incident angle to the surface also doesn't matter. It's such a short wavelength [904nm] that everything looks flat to it."
And we might add its sheer range as another point scorer: ABB's LM80 can measure level over 80 metres and can perform positioning over 400 metres. That's an order of magnitude more than ultrasonics.

LNo fuzzy FELT
Meanwhile, Cambridge Consultants principal engineer Dr Temoc Rodriguez describes its level sensing innovation as "a cost-effective device for accurately measuring liquid levels that requires no calibration". He also says that the firm's new FELT technology has no moving parts, is immune to temperature shifts and changes in fluid composition. It's also, he adds, robust and not affected by interference due, for example, to metal objects, people or electrical noise.

On the face of it, FELT seems remarkably similar to any other liquid level device that relies on detecting some variation in electrical characteristics caused by fluid rising or falling over electrodes. However, this design has three parallel electrodes – one for measurement, the other two reference. What's more, there is no direct contact between the electrodes and the fluid.

Rodriguez explains that an electric field is applied to the electrodes, and the ratio of the charge between the measurement and reference measured. That leads to a determination of liquid level, which is both continuous and accurate. Just as important, it's also highly customisable for depth and configuration.

"We found that other fluid measurement technologies with similar accuracy use radar or ultrasonics and are very expensive, while cheaper devices have accuracy issues and use probes that require careful calibration," states Rodriguez. "FELT uses a novel approach to enable this new, cost-effective, yet remarkably robust sensor platform."

Cambridge Consultants says it now expects "significant demand" – and from a diverse range of industries.

Brian Tinham

Related Companies
ABB Ltd
Cambridge Consultants Ltd

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