Why choose radar technology for water monitoring?

01 June 2021

Control engineering Europe finds out more about the benefits of radar technology for level sensing applications in the water sector.



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According to figures from the Environment Agency, water companies discharged raw sewage into rivers in England more than 400,000 times in 2020. It is figures such as these that make the reliable and accurate monitoring of all discharges into the environment so important. It is also the reason that the Environment Agency places so much emphasis on schemes such as the Monitoring Certificate Scheme (MCERTS) to help ensure that monitoring is done correctly, regularly inspected and properly verified. 

VEGA has recently announced that its 80 GHz compact radar sensor technology has received MCERTS Class 1 approval. But why would you consider using radar technology for simple applications such as water level monitoring? The answer is because it offers measurements that are unaffected by the everyday challenges that are posed by such applications – ambient temperature changes, condensation, foaming surfaces and build up on the sensor – the technology also offers an inherently accurate all-conditions solution. 

For example, the currently used legacy technologies – based on ultrasonic level sensing – require protection from solar gain/air temperature, as any undetected air temperature variations will cause a measurement error. This could mean that multiple sunshades, additional external temperature sensors or even dual measuring heads are needed to achieve the equivalent accuracy to a radar. 

In a first for an MCERTS open channel flow measurement system, there is now the option to use the radar sensors as a ‘standalone’ two-wire loop powered radar transmitter. With no need for a local controller, it is well-suited to use with telemetry systems. The 80GHz compact radar removes the cost, complexity and power needs for installing a remote controller/transmitter box. A choice of digital communication, using HART or current output, also adds to the versatility and accuracy – with local controllers optionally used for additional local display, datalogging, relay and pulse outputs for level alarms, for flow and triggering volume-based samplers. Another useful capability is the single or twin channel measurement, which could be used to measure both flow through a structure and storm water spill level, for example.

A safe solution
Bluetooth set up and retrieval of measurement can be achieved via an App, without the need for a local display. This makes it safer and more convenient. ATEX approvals are also available on both sensors and controllers. 

Explaining why MCERTS approval is so important for radar level sensors, Matt Westgate, water industry specialist at VEGA, said: “This is an exciting ‘coming of age’ for radar in the water industry, showing that it's got the credibility of class one certification. The performance and instrument cost also has the commercial benefits often associated with ultrasonic level systems. We really feel we can outperform ultrasonic level systems head-to-head. MCERTS certification enables just the sensor to be the transmitter of the flow data, which means no extra controller or box on the wall is needed, saving time cost and complexity and offering a much better solution for telemetry data loggers and the like.”

Westgate went on to explain that maintaining an accurate level measurement in direct sunlight and varying ambient temperatures is incredibly important when it comes to electronic distance measurement (EDM) and open channel flow measurements. “Accuracy fluctuations occur when technologies affected by ‘solar gain’ or undetected temperature gradients in the air above the surface cause errors in the level measurement,” he said. “These are then exponentially calculated through flow curves associated with flow structures. There has also been the argument that the flow structures themselves have inherently low accuracy, therefore the ultrasonic based level and flow measurement does not show up its fallibility. However, we believe you should get the best data you can, to minimise errors and maximise data accuracy and therefore exploit its value.”

Areas of application
As a non-contact technology, radar is flexible in how and where it can be applied. A level sensor that fits in the palm of your hand, has no dead-band and can measure up to 15m really covers a vast array of applications. “The radars have a number of ATEX approval options to choose from, so there really are no restrictions as to where it can be mounted,” continued Westgate. “We feel that radar can play the key role in both underground assets and normal open channel flow measurements both in and out of treatment works, but of course the flexibility and capability of radar doesn't stop there, it extends to sludge tanks and hoppers, digester level monitoring, chemical tanks and dosing systems, gravity blet thickeners, as well as clean water distribution. We see the MCERTS certification being a foundation stone in that wall of applications and the final stamp of approval confirming its accuracy.”

Conclusion
“With the continuing development of radar chip technology and the lowering cost, radar sensors look set to become the standard level sensing technology in the water sector in years to come,” argues Westgate. “When you combine that with performance gains – even marginal ones – lower engineering costs to install and easier set up, multiply that by hundreds of sites in the water network, it all adds up to a big potential operational and cost savings, including CO2 though reduced site visits, and materials.”  


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