VEGA – Radar benefits are out in the open
A key infrastructure
The inland waterways of the East Riding of Yorkshire are important for many reasons and it is this diversity that makes them such a valuable and unique resource. They are important for navigation, recreation and trade, as well as environmentally being a key part of the ‘ecological infrastructure’, providing crucial corridors of green space and a refuge for important wildlife. These waterways also provide benefits to our communities and improve their quality of life, they are used for walking, cycling, angling and boating. This is also an important part of the sustainable transport network and still play a role in supporting trade.
Valuable and unique: Burstwick Drain, Hedon, East Riding of Yorkshire
Inland waterways additionally provide a crucial flood risk management function as part of the land drainage system. Monitoring the current capacity of each waterway at key points is vital for safely managing or providing accurate warnings of flood risk, especially with the advent of more extreme weather events seen in recent years, in combination with urban development and its effect on drainage to water courses.
A key area of this is monitoring the water level, ensuring that regular information is on hand to manage levels both in ‘drought and deluge’. This information needs good reliability, accuracy and availability, East Riding of Yorkshire Council persevered with ultrasonic level and submersible pressure sensor technologies for drainage and open water level measurement for many years. Recently they have turned to VEGA radar sensors to solve issues they have had at a number of sites. Problems encountered included; high maintenance levels, measurement accuracy, sensor replacement and regular ‘loss of measurement’. Their applications are in urban and rural environments – with differing and shared challenges for the sensors. This case study looks at two of the first applications installed, one in each environment.
The measurement sites
The ‘urban’ application is a typical one: a small un-named tributary stream which runs close to and under a housing estate in a built-up area, downstream it feeds into the City of Hull sewer network, so monitoring the flow rate is important. Ensuring that the level and flow is monitored reliably has been highlighted as it is so close to houses and they had flood event in the last year or so. The site consists of a small culvert approximately 2m wide and typically runs at between 0.3 and 0.6m depth, it flows into an concrete underground tunnel structure with an angled metal screen, which prevents larger debris from entering. A nearby industrial estate sited up river has caused occasional large waste items; plastic wrapping, cardboard boxes or even pallets have been known to come from there, thus blocking the flow through the screen. A hydrostatic sensor was previously deployed, however the accuracy, especially at low levels, was not very good. Silting was an issue and they also suffered frost damage at low levels with ice formation literally ‘blowing apart’ the sensitive diaphragm of the sensor. It was then replaced with a non contact ultrasonic sensor, which didn’t suffer the damage, however loss of echo would occur in high winds and even cobwebs would cause unreliable readings. There are existing structures and conduits built to accommodate and mount devices and cables, along with an existing data station installation mounted in a bollard next to the drainage structure, to record and transmit the data to the control centre in Beverley.
The ‘rural site’ is a main river heading towards the coast, approximately 20m wide. The river is tidal influenced and in a navigable section with a flood wall protecting a small rural hamlet with vegetation on both sides of the river. The measurement point is on a road bridge and the span is around 8m above the river with a 3-4m level change. Getting reliable readings would be difficult to achieve with other devices, as their installation would be expensive to engineer and maintain. The flow of the river, potential silting, water traffic and debris would also be unknown factors for any sensor structure or fixing mounted at the side of the river. The measurement point would also need to be inconspicuous in the remote site, although the road bridge was not open to pedestrians.
Process challenges for open water measurement
For level sensors working out in the ‘open environment’; remote, urban or rural, there are many challenges. These can be split into two areas: Operational – weather (wind, ice, sun), corrosion/wear, sensor drift and low power consumption capability. Physical – from plants to spider webs, silting, risk of damage in river flows/floods, vandalism or theft risk. To overcome these, a lot of engineering may be needed and for others regular maintenance visits.
A typical gauging installation in Lincolnshire on a river with a flume, with sensors mounted in stilling tubes inside green cabinets to calm the water surface. This is done to physically protect the instruments and ensure weather conditions do not interfere with the level measurements.
Protection from weather – ultrasonic sensors will lose their signal if the wind is too strong – the signal can be literally ‘blown away’ and disrupted by the surface turbulence. In fog or heavy rain or mist – attenuation can result in loss of echo. Cold days with sun on the sensors can cause significant temperature related accuracy issues too. For submersible pressure sensors, ice can cause issues, particularly in shallow water, initiating drift or damage to the sensor and accuracy/linearity is generally not very good with low water pressure heads. This means that, for the signal and sensor to remain impervious to all conditions, either design of sensor will need mounting in ‘stilling’ tubes or ‘wells’. These installation costs can add significantly to the cost of a ‘cheap’ level sensor.
Incidental occurrences – if you solve the problems for a sensor with a stilling tube, this can instigate other common issues, such as blockages to the tube by debris or silt causing slow flow in and out affecting the level reading until it is physically cleared. Webs and debris collecting inside an ultrasonic sensor has also be known to cause problems for loss of echo. Even a submersible pressure sensor may need the cable fixing to a wall or installing down a tube to protect it from being snagged or washed away, but sometimes when removal is needed, they can get stuck, requiring even more time and money, as well as the safety issues of working close to, or in a water course.
Security from wilful damage – in urban or rural areas sensors can attract attention – whether as a ‘target’, theft or vandalism, all sensors need some level of protection, or at least a good disguise! Many sites have no power, solar panels are difficult to site unless the area is protected, so the ability to operate with battery power over long periods of time is a key attribute too.
How does radar solve it?
VEGA has developed a radar level sensor like no other – with the water industry as its focus. From performance, environment and cost, the benefits of radar are many. For open water applications, a radar level transmitter is an ideal solution, why? Because it needs no extra engineering, like stilling tubes to protect the signal -being contactless, it just needs mounting above and looking down perpendicular to the liquid surface. It has very good focussing, which means it doesn’t need mounting out on long arms. Unlike an ultrasonic it can be mounted out in the open, without fear of measurement interference from wind, rain, mist surface turbulence and sun/solar temperature error, they can 
even measure wave height – as VEGA radars emit 3.6 million pulses a second, a rough water surface can be bought to a standstill. Another ‘small’ but critical problem over come by radar is spiders and insects, they can cause signal loss for ultrasonic sensors with the webs they weave and more importantly the debris that gathers in them. A radar with microwave signals will just look straight through. For the physical challenge it needs to be adaptable for outside use, submersion incidents and vandal resistance. To meet this, the units are submersible IP 68 (2 bar) and compact enough to be mounted inside a 150mm/6” diameter plastic or metal pipe. This means they are ideal for mounting, along with their logger, at a remote site in a very inconspicuous way in a minimal cost, yet robust housing, using standard piping and brackets. For ultimate camouflage, if the ‘pipework’ has a bend and ‘appears’ to come out from a wall, it can look just like an outfall and of little interest to the curious! Good focussing often allows mounting closer to a wall than an ultrasonic sensor, yet still monitor water level reliably, or mounted many metres above the water it can still measure to mm accuracy.
The difference with Radar Technology
Radars use microwaves instead of sound pulses, to reflect off a surface to measure level. The microwave signals are virtually unaffected by temperature (e.g. sun on the transducer with cold air near a water surface), vapours (e.g. mist, rain, fog), air movement (wind). Radar can still measure reliably with challenges like heavy surface turbulence, high levels of foam and they can ‘see though’ non-metallic materials like plastics, vegetation and cobwebs and conversely, they get a high signal return off a water surface. Radar has a very small dead band/blocking distance and is also very accurate, typically providing mm resolution and 2mm precision over almost its whole range of typically 15m (there are other versions up to 75m and can measure liquids or solids). It is capable of being spanned down to measure over a few tens of mm with the sensor mounted several meters away, or used over the whole range. A data logger manufacturer, who did some testing on VEGA radar commented, ‘this is the most accurate sensor we have tested’, another customer said the sensor was ‘too good!’ Talking of data-loggers, VEGA units can work with battery powered GSM/GPRS devices for 2-3 years on a 15 min measure and once a day dial-in. They are also certified to the latest European communications regulations for safe use outside.
The site requirements
Each site in the council’s area utilises an Isodaq Frog GPRS/GSM data logger, they mainly provide the telemetry on battery power, enabling remote harvest of the data on a twice daily basis, ensuring that the data is collected and trended, poling sites to retrieve real time data is also an option. The radar sensors use minimum start up current when ‘awoke’, to maximise the battery capacity, this means they can power the sensors on the 15 minute interval for up to 3 years. If connected to ‘mains’ power, the radar can operate in continuous operation, so they can dial in on ‘timed’ or ‘event’ driven basis, such as flooding or rapid level change. The data loggers are small and ruggedized, with a similar IP68 rating, providing an excellent package for remote monitoring sites. Supplementary power options are also available, for slave batteries, solar panels or micro turbines.
Sensor set up
No special set up of the radar is needed for standard applications, they are pre configured and ranged. Because of the high accuracy of the sensor, the ranging can be done in the data logger or on the raw data values afterwards. However, if needed, it can be pre-ranged on delivery or re-configured to suit the application parameters via a simple, free to use, PC based FDT/DTM PACTware industry standard software and VEGACONNECT interface. It can connect anywhere on the 4-20mA signal cable and gives access to all configuration settings, uses Windows™ based menus and allows sensor back up files. The low operating voltage of the radar is perfectly compatible with most data loggers.
In the field
At the urban site, the radar was mounted in a tube on a simple arm. Fabrication was done with a simple piece of 150mm black plastic (also good for GPRS/GSM signal) drainage pipe with the bracket arm around 500mm long and the radar approximately 1.8m above minimum level. Despite being close to the bank, it reads the level of the water reliably. Some of the existing cable and conduit was used and the software of the bollard mounted data logger was easily modified and tested with the sensor, to suit the ‘warm up’ time for the radar. Since the set up was finalised, the radar has monitored the level faultlessly every 15 minutes. There are now plans to change the data reading time a higher frequency as this is a ‘mains powered’ site.
Radar level measurement of a stream in the urban environment – mounted in a plastic tube, 2m measuring range close to the screen and edge of the channel, yet follows the water level very reliably.
The rural river site has the radar mounted off a bridge, using a very similar configuration. The bracket was around 450mm long and 150mm diameter tube approximately 0.7m long. This time the data logger is also installed in the tube, directly above the radar, this compact configuration will be the norm for future sites with mains or battery power when no bollard is available. The device is measuring in excess of 10m range as the river is partly tidal at this point.
Rural monitoring site: The radar is mounted off a road bridge on a simple bracket, the assembly is easy to mount, robust and lightweight, easily fabricated and relatively anonymous.
East Riding of Yorkshire Council is planning on rolling out radar technology across a large number of its sites; and has found the integration and installation with existing data loggers easy to do using the 4-20mA signal. Brackets and mounting designs have already been standardised and fabrication costs are minimal using ‘off the shelf’ pipe and brackets.
Benefit Summary
Users of radar technology are seeing high reliability and accuracy of reading with no loss of echo from environmental conditions. Simpler installation – no stilling tubes, cable fixings and special structures and lower maintenance – result in reduced TOPEX costs. The power consumption, especially over longer ranges (10m+) is much lower than an ultrasonic sensor, without sacrificing performance. The high versatility – the same unit for open water applications featured in this case study will also enhance measurement reliability in water, chemical and sewage applications above and below ground; open channel flow, CSO’s, chemical tanks, digesters and sludge tank indication. This means for a large utility provider, lower sensor stocks and fewer model choice decisions, just mechanical mounting. There are models available for even longer ranges (up to 75m) still using the identical low power 4-20mA HART, (many versions have communications capabilities for Profibus, FF, SDI12 and Modbus formats). Compact sensors mean easy integration and space savings in SCADA, telemetry, PLC and pump control panels, no coaxial signal cables and level controller boxes needed. Non contact radar also means no drift and re-calibration visits saving further costs. Certification for ATEX areas is intrinsically safe EX ia IIC T6 for many sensor types – suitable for zone 0, along with ‘SIL 2’ approval options, which adds a safety and security element to the approval portfolio.
Simpler installation. A diagram of radar logger design for installation in standard 150mm heavy duty PVC pipe
Radar sensors are now becoming affordable and every day technology for the water industry and its applications. True, sensor costs may be a little higher in some applications – but lower installation, operational costs, personnel safety and longer sensor lifespans are the result. This technology is being taken forward, seriously, across a number of utilities, applications and processes, where before it was considered a luxury.
The users at East Riding are more than happy to share their experiences of VEGA radar, from installation, set up and operation, perhaps even co-ordinate some site visits. Please inform them you have read this article and would like to know more. For radar or data logger product details and specifications, or to discuss any applications you may have, please contact VEGA directly: info.uk@vega.com or 01444 238850
If you would like to contact EYRC directly their details are:
Gary Harris, Drainage Engineer, Flood & Coastal Erosion Risk Management, e-mail; gary.harris@eastriding.gov.uk
Mike Kitching, Trainee Construction Officer, Flood & Coastal Erosion Risk Management, e-mail mike.kitching@eastriding.gov.uk
| Doug Anderson Marketing Manager | E-Mail: doug.anderson@vega.com |
VEGA Controls Ltd |
Web: www.vegacontrols.co.uk |
| Tel +44 1444 870055 | |
| Fax +44 1444 870080 |
Intended article distribution:
For distribution to process control and instrumentation trade magazine editors as news item and publishing on VEGA websites as news/application/case study article.
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