Guided Wave Radar: Nr.1 Alternative to Mechanical Level Measurement

Related Vendors

Glatt Ingenieurtechnik GmbH

Donadon SDD Srl

ProMinent GmbH

Emerson Process Management AG

Improving GWR performance

To extend the application range and performance of GWR installations, manufacturers have added intelligence and signal processing to provide smart diagnostics and increase measurement accuracy and reliability. A good example is Emerson’s patented Direct Switch Technology (DST) which increases the strength of the returned signal by a factor of 2–5 by minimizing losses. This provides a better margin to handle interference from objects close to the probe, coating, foam, vapor and turbulence.

DST enables GWR to handle long measurement ranges (50 m) and media with dielectric constants as low as 1.2 using a single probe. It also enables a single probe to measure interface level — a major advantage for adhesive media. Using single probes minimizes maintenance issues associated with other probe types, such as coaxial and twin probes, in liquids such as dirty oil, which can bridge and so cause false reflections.

Smart diagnostics help with preventive maintenance and provide a better understanding of the process. Emerson also offers the option of Signal Quality Metrics, allowing users to monitor signal strength over time and gain early warning of problems such as fouling and foaming.

GWR technology can also be used for interface level measurements. A Rosemount GWR with advanced signal processing and an inert metal probe suspended in the process medium enables the same transducer to measure the level of both the liquid surface and a liquid-liquid interface. This arrangement works because the pulse is reflected back where there is a change of dielectric constant in the fluid surrounding the probe.

In interface applications with thick emulsion layers, displacer technology may still be the better choice. The displacer averages out density differences to determine the interface level, whereas GWR can be unpredictable in applications where there is no distinct interface.

Special probes with multiple layers of protection are available for extreme temperatures and pressures; Emerson’s GWR can operate at temperatures from –196 °C to 400 °C and pressures up to 345 bar.

Applications involving high-pressure saturated steam and varying pressures and temperatures are challenging for both displacers and GWR. For displacers, density variations can cause errors of up to 30 percent. For GWR, the high dielectric constant of steam can generate errors of up to 20 percent in a standard instrument. Emerson’s GWR with Dynamic Vapor Compensation (DVC) gets around this problem by using a fixed reference reflector to measure the vapor dielectric, yielding a final accuracy of within 2 percent. Applications include boilers, deaerators, boiler feed water heaters and steam drums.

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