Key points
Vladislav Snitko from Emerson explains why the latest non-contacting radar transmitters are the best option for level measurement in water and wastewater applications.
High-quality level measurements are essential to help optimise the operational performance of water and wastewater companies. Access to continuous level measurement data improves operational efficiency by optimising wet wells, filter beds or vessel utilisation, and enhancing inventory management.
Safety and sustainability improvements can also be made by preventing overspills and run-dry situations, costly water loss and environmental damage.
By implementing an automated measurement solution, organisations can make immediate gains by eliminating manual rounds, thereby improving worker efficiency. To provide peace of mind, these automated solutions must be very accurate, reliable over a long lifecycle and have low maintenance requirements.
Historically, ultrasonic and hydrostatic measurement technologies have been deployed for level measurement applications in water utilities. However, both of these have certain limitations, including measurement accuracy and device reliability issues.
Ultrasonic devices can be affected by a range of process or environmental conditions, which can lead to inaccurate or unreliable measurements. These include temperature, pressure, foam, turbulence, build-up, the presence of gas in air, wind, dirt and even spiderwebs.
Hydrostatic submersible transmitters are immune to the effects of foam and turbulence, but measurement accuracy can be impacted by changes in density and temperature, as well as build-up on the device itself. Being in direct contact with the media means hydrostatic devices require frequent calibration and maintenance, which increases the total cost of ownership.
Non-contacting radar transmitters, which are applied widely within the oil, gas and petrochemical industries, provide an alternative solution. These devices are extremely accurate, with measurements unaffected by temperature, pressure, light foam, condensation, build-up, wind, dirt or spiderwebs.
No calibration is required and because they do not come into contact with the material being measured, this helps to minimise maintenance and improve long-term reliability.
Although widely regarded as the best technology to meet the requirements of water and wastewater applications, the use of non-contacting radar within the industry has been limited. Principally, this is because they have been considered too large, complex and costly.
Dedicated radars for water applications
The availability of non-contacting radar transmitters designed specifically for water and wastewater applications is creating the opportunity to make improvements.
These new devices, such as the Rosemount™ 1208 Level and Flow Transmitter Series from Emerson, not only provide the high levels of accuracy and reliability expected of radar, but are also very compact, cost-effective and easy to implement and use. As a result, the choice of what level measurement technology to apply becomes very simple.
Meeting the demands of typical water applications, the transmitter also has hazardous area approvals for when methane gases are present; can withstand submersion and outdoor conditions; and has drinking water approvals to ensure that it can be applied throughout the entire water supply chain.
In terms of the accuracy and reliability of level measurements, the radar transmitters surpass that of ultrasonic and hydrostatic devices.
By providing 80 gigahertz (GHz) fast-sweep frequency modulated continuous wave (FMCW) technology on a single electronic chip, this enables very precise measurements to be delivered from a device that is compact and cost-effective.
The fast-sweep FMCW technology and advanced algorithms enable more information to be collected than legacy radar devices. Impressive level measurement accuracy of ± 2 millimetres at a range of 15 metres can be achieved. This can help utility companies to optimise their operational efficiency and ensure compliance with environmental requirements.
Simple integration
Although radar technology offers superior performance, devices must integrate seamlessly with existing data networks and be able to communicate with existing automation systems. This is achieved by providing support for traditional process communications protocols such as 4-20mA and HART®, and also Bluetooth® wireless technology and IO-Link – increasingly used within water and wastewater applications.
HART connectivity provides access to advanced diagnostics from the radar transmitters, which supports predictive maintenance and more effective troubleshooting. IO-Link connectivity also provides access to process insights that can enhance operational performance, while also enabling remote configuration and monitoring.
Water plant increases process efficiency
Radar technology has helped to improve efficiency at a drinking water treatment plant in Eden Prairie, USA. Serving a community of over 60,000 people, the plant can pump up 28 million gallons of water per day and last year treated 2.7 billion gallons of water.
The plant has several wet wells, which receive and store wastewater from pumping stations, a by-product of the water treatment and lime softening process. A submersible hydrostatic pressure level sensor had been used to measure the level in the wet well, but this was problematic because it did not provide reliable measurements.
The level sensor was giving inaccurate level readings due to build-up/caking on the diaphragm. This was restricting the pumping station from operating effectively, as pump starts/stops were configured to certain levels in the wet well, and this was either causing pumps to run dry or creating overflow situations.
A Rosemount 1208 Non-Contacting Radar Level and Flow Transmitter was installed on the side wall of the wet well. The robust and fully submersible housing, combined with drinking water approvals, meant the radar met all the requirements for this application.
The surface-tracking algorithm enabled reliable tracking of the water surface. By simply setting the reference height, the radar transmitter could deliver reliable measurements and disregard the echoes from a cut-out on the cement floor of the wet well without the need for echo-tuning.
In addition, the 80 GHz FMCW fast sweep technology ensures accurate and reliable measurements in this fast fill application. The technology has enabled the Eden Prairie plant to optimise process efficiency by reducing manual rounds and eliminating maintenance tasks. The precise measurements also provide greater protection against pumps running dry and overflow situations.
