Real Time information requires a “hands off” approach!

Posted: Wednesday 18th September 2013

Sewer and treatment works flow measurement brings lots of baggage with it, or put another way, ragging, debris, fat, dead sheep etc etc! says Flowline's Mark Davis.

The only reliable way to measure these flows is using non-contact sensors, up to about 15 years ago that meant flumes and weirs with a suitable level measuring device, perfectly acceptable if designed and constructed to the relevant standards, and certified, ideally to mcerts.

Although flumes and weirs are not actually non-contact devices, the primary device still gets dirty and a thin plate weir is certainly not acceptable for sewage flows, the actual level sensor doesn’t touch the flow so essentially they are low maintenance devices.

There are however a couple of problems with flumes and weirs, firstly installation usually requires civil works of some sort which may include over pumping or shut down of flows, secondly flow conditions downstream of the primary device can have a big effect on the readings, the obvious one being backing up of flows causing drowning and a false high flow reading, backing up can be caused by many circumstances, river flooding, sewer blockage, inlet screens blinding.

Measuring level and velocity is a way around this problem, but how? As described above, anything wetted will need cleaning, maybe not every week but certainly routinely, one UK water company spends £5K a year just to clean one system.

Clearly if the future of sewer networks is in real time management and control, reliable flow data is a key requirement.

Ultrasonic and Radar level measurement has existed for any years, in fact a patent existed from 1904 for device similar to a radar level gauge, Saab installed their first radar tank level gauge in 1975. The technology has existed for years, what has changed? In common with virtually any high tech product it’s the price or more importantly, the affordability.

GPS, sat navs, cell phones, computers, have existed for decades, at first only as high priced products, the real transformation came when price reductions brought them to the mass market, and its actually quite recent, anyone fancy paying £2600 for a mobile, that was the 1982 price of a Motorola DynaTAC!

So low cost ultrasonic and radar level is a reality, from £200 for an ultrasonic, to sub £1000 for Vega’s WL61 radar, but that’s just level, we need non-contact velocity as well. Marsh McBirney launched their radar based system, the Flo-Dar over 15 years ago, a compact radar sensor with built in ultrasonic level sensor and remote mounted control unit, over 6000 of these are now in use worldwide but with a potential user base of over 3000 sites in the UK alone its hardly achieved a significant market penetration!

New and therefore, unfamiliar technology certainly plays a part, users rightly require new technology to be proven, robust and reliable, before they entrust it with automatic control of their treatment works, something a mag meter or even a clamp on ultrasonic meter supplier would probably not have to demonstrate.

To return to the subject of Real time sewer control, even a small network requires a lot of sensors, over 40 radars in the small network feeding into Merano STW in South Tyroll, this network has been operating as a remote controlled real time system for over 14 years.

So as all technology must, radar flow measurement has moved on, the Raven-Eye is the new non-contact RADAR area/velocity flow meter for open channel flow measurements from Flow-Tronic. It combines state of the art non-contact measuring technology which measures flow above the water surface with easy integration into existing SCADA or telemetry systems.

Using the latest design, development and production methods, has allowed Flow-Tronic to manufacture a high quality new generation radar sensor at a price that makes it virtually “just another sensor”

But using the latest technology cannot just mean a price reduction, it must give an increase in performance, remember the old Motorola phone, 1 hour talk time anyone? So, better technology now gives improved performance in challenging conditions, disposes of a remote mounted control unit and allows easier integration with existing telemetry systems and of course a significant price reduction!

The combination of these benefits and virtually zero maintenance requirements, give the user a very low “Cost of Ownership”.

But as they say “the proof of the pudding….” To address this point, The Raven has been tested by Anglian Water at Letchworth STW, these tests are in advance of Mcerts site testing, I will let Oliver Grievson of Anglian Water take up the story.

”The Raven-Eye has been trialled against a recently MCERTS certified installation at Anglian Water’s wastewater treatment works at Letchworth and the overall results are good. The unit itself was installed in a challenging position ahead of a downstream pipe,..the Raven-Eye was connected to an internet site.

This had the benefit that the secure site could be accessed from anywhere. This was compared with

the certified final effluent flow meter and produced good results.”

Nothing is perfect, there is no “one solution fits all” instrument, but non-contact Radar flow meters certainly address a lot of the requirements of real time sewer monitoring.

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April 2021

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