vi UK Focus - Water / Wastewater
point. The laser beam is focused at a specific location based on water depth and according to how many measurement points are selected. Although one or two velocity points are often enough, multiple points (up to 15) can be used in applications with turbulent, skewed flows or changing flow profiles. Reflected energy from the point of convergence is much higher than energy reflected back from the unfocused sections. The frequency shift between the transmitted and received indicates the flow direction whilst the magnitude of the shift provides velocity. The options for measurement include: (1) single point; (2) multi-depth; (3) multi-point; and (4) multidepth- multipoint. This allows the LaserFlow to measure up to 15 different locations in the flow profile to give very high accuracy
Installation & Maintenance Simplicity is one of the LaserFlow’sTM
strongest
features – a sensor that can be installed facing upstream or downstream using simple adaptable brackets within 15 minutes using a temporary spreader bar or in just an hour or so for permanent installations - without any interruption or adaptations to flow and when the LaserFlowTM
needs removing
or reinstalling then it takes just a few minutes with the Street Level Installation Tool especially useful if the device is in a chamber or difficult location.
The LaserFlowTM has a much wider turn-
down ratio compared to conventional flumes and is a proven candidate for retrofitting to flumes which are incorrectly sized/installed or whereby the uncertainty of measurement is unacceptable.
The capital cost of most instrumentation is outweighed by its maintenance; industry sources commonly use a figure of 50:1 over a 10-year period. It is therefore essential that companies move away from high maintenance instrumentation to instruments that can effectively be “fitted and forgotten” and only require routine verification. The LaserFlowTM
requires
no routine maintenance and is favoured to replace high or even low maintenance flow meters. Where traditional instruments are not maintained, errors occur and trust is lost. Although this is significant but worse still if the instrument are relied on for decision making of major infrastructural development using erroneous data; the associated costs of bad descisions far outweigh the cost of any flow meter installation.
readings. In all applications to date RS Hydro have achieved results to within 1% of MCERTS flumes. The reasons for using these different techniques ultimately depend on how stable the flow conditions are. If very stable conditions exist then a single point measurement may suffice however if the flow profile is changing then multidepth-multipoint can be selected to optimise performance and if the LaserFlow is submerged a TIENet area velocity sensor mounted to the underside of the LaserFlow automatically takes over once submerged conditions are recognised.
Accuracy
It is an understandable thought that “quick and easy” instruments must have a lesser accuracy but not the LaserFlowTM
which provides conservative accuracies of around
1-2% borne out by field tests in the UK compared to high- accuracy MCERT’d flumes. Due to its high accuracy, obvious applications include:
• MCERTS Discharge • STW Inflows • CSOs
• Rivers, Streams & Culverts
Health & Safety Many installations are in sewers, confined spaces or where there is a danger of fast flowing unhygienic water. By installing the LaserFlowTM
costs are minimised. Furthermore as no profiling is required then there is no requirement to go near or in the water body. Installation is therefore very quick and safe and risks of wetted sensors breaking loose and causing blockages or indeed being flushed down sewers are eliminated.
Cost
Costs for repairing or installing traditional concrete flume structures can amount to more than six-figure sums and although wetted area velocity sensors can be used they require high maintenance and also suffer from a higher level of repairs due to their contact nature. It is therefore essential that the initial cost of a flow meter is put into perspective. Metering managers will concede, for one reason or another, meter ‘x’ was not maintained last month due to manpower resources and when they did they found that the sensor had stopped reading a week before or even that it was not actually there due to the ragging that ensued and caused its demise.
Secondary precautions like screens are then introduced at further expense, portable units can only be installed in raw wastewater applications typically for 1-2 weeks at a time due to the same issues and/or battery power but the LaserFlowTM
can be installed as a portable device using the ISCO 2160 flow module or with the permanent SignatureTM
Connectivity The LaserFlowTM
Transmitter. The Signature is a SMART device and provides multiple input and output capabilities using ISCO’s TIENet system. The Signature itself has a USB interface, datalogging (with variable rate logging), provides reports, alarms, Ethernet/ wireless connectivity and is FlowLinkTM
compatible. It is possible
to connect multiple LaserFlows to one Signature. The Signature is SCADA-ready using analogue or digital outputs including Modbus. Furthermore, it is possible to connect modbus/SDI12 sensors along with other ISCO and third party sensors.
Real results from the field
Barry Pike, MCERTS Manager for Wessex Water commented: “We have been working with the LaserFlow and RS Hydro over the last few months and the accuracy and performance has been extremely impressive. We have used it to provide accurate flow measurement on the inlet to a number of our WWTWs. This flow meter has an incredible future in the wastewater industry and it allows Wessex Water to measure applications which could not be considered before. Beyond its accuracy and performance, the device also needs almost no maintenance. The LaserFlow is likely to revolutionise the approach to measuring open channel flow measurement in many applications.”
Released in 2013 to address the demand for a high accuracy device with almost zero maintenance, low health & safety issues and high reliability, the LaserFlowTM
represents a paradigm , entry can be minimised and H&S concerns and
step change in open channel flow measurement and provides metering managers the long overdue ability to measure open channel flows without installing expensive, maintenance intensive flow measurement systems.
The image below shows a LaserFlowTM installed upstream of
a recently MCERT’d flume. The data shows about a 1-2% difference between the meters using only a single point measurement rather than 15 which presents a challenging question- which technology is the most accurate?
If you would like to find out more or arrange a trial, simply log onto our website at
www.rshydro.co.uk.
is
non-intrusive and requires little or no maintenance, even with a battery module, temporary deployments for up to 3 months at a time are practical.
The payback period of a LaserFlowTM traditional installations. The LaserFlowTM risk free and accurate flow measurement.
can be 1/25th of simply provides proven,
IET March / April 2014
www.envirotech-online.com
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