Automation has brought significant improvements in safety, efficiency and productivity across process industries. However, unplanned downtime continues to impact overall equipment effectiveness (OEE), with lost production and maintenance costs directly affecting profitability. While critical assets such as pumps and motors are often the focus, measurement instrumentation plays an equally important role. If level measurement becomes unreliable, operators lose visibility, processes are interrupted, and maintenance demands increase.
Solids level measurement remains one of the more challenging areas. Unlike liquids, which settle to a flat and predictable surface, bulk materials behave in far less consistent ways. They form uneven profiles, with peaks and valleys that constantly change during filling and discharge. Phenomena such as ratholing can leave material along vessel walls, creating the false impression of available capacity and increasing the risk of overfilling. In addition, many solids have low dielectric properties, making accurate measurement more difficult for some technologies.
Dust adds another layer of complexity. During filling and discharge, high concentrations of airborne dust can create safety risks and reduce visibility. From a measurement perspective, dust can attenuate signals, generate false echoes, and lead to build-up on sensor surfaces. Over time, this can result in unreliable readings or signal loss, requiring frequent intervention.
Non-contacting radar offers a practical way to overcome many of these challenges. By measuring level without direct contact with the material, it eliminates mechanical wear and build-up associated with contacting technologies. With no exposure to abrasive solids, heavy loads or vibration, reliability is improved and maintenance requirements are significantly reduced—even in dirty or demanding environments.
Modern radar transmitters based on frequency modulated continuous wave (FMCW) technology provide high sensitivity and accuracy, even in dusty conditions and over long measuring distances. Advanced signal processing enables these devices to filter out false echoes from internal structures, while specialized solids algorithms account for uneven material surfaces by calculating a representative average level. In particularly dusty environments, air purging systems can be used to keep the antenna clean, maintaining signal strength and ensuring reliable measurement.
Typical ash storage tanks
A good example of this can be found at a waste-to-energy facility in Europe. Compressed fly ash produced from the incineration process undergoes chemical treatment before being stored in three large vessels, each around 16 meters high. The treated ash is then collected by trucks and used as a construction material in road building.
To maintain efficient operations, the plant operator needs accurate and reliable level measurement to prevent overfilling, manage inventory, and plan refilling, maintenance and cleaning activities. However, the application presents a number of challenges. Fly ash creates a highly dusty environment and tends to adhere to surfaces, leading to build-up inside vessels and on instrumentation. The filling process is also relatively fast, while the material surface remains uneven and constantly changing.
Previously, the company used guided wave radar devices from another supplier. In practice, ash accumulated on the probes, causing them to clog within five to six days. This led to unreliable measurements and required regular manual cleaning. Maintenance teams had to access the vessels frequently, exposing them to dusty conditions and taking the vessels out of service for extended periods. These interruptions affected both the chemical treatment process and truck loading operations.
To resolve the issue, Emerson installed Rosemount™ 3408 non-contacting radar transmitters on each vessel. Although fly ash has a low dielectric constant, the FMCW technology used in the Rosemount 3408 provides the sensitivity required for accurate measurement. A dedicated solids algorithm enables reliable readings despite uneven and changing material surfaces, while an air purging system prevents build-up on the antenna. In addition, built-in signal quality diagnostics alert operators to any abnormal process conditions or potential issues.
Since installation, the transmitters have delivered consistent, maintenance-free operation. There have been no unplanned stoppages related to level measurement, and vessel availability has improved significantly. This has enabled more efficient coordination of both the chemical treatment process and truck loading operations. As a result, the company has achieved annual savings of approximately $80,000, with a return on investment in just one month.
