Two-Wire FMCW Radar Level Transmitter Advantages

  Christoffer Widahl and Jimmie Soderstrom presented The New Normal for Process Radar—The New Two-Wire FMCW [Frequency-Modulated Continuous Wave] Radars are Here!, at the 2019 Emerson Exchange conference.

Jimmie opened with a question, “Why measure level?” It is to monitor that supplies are sufficient to keep processes running, control processes to run at maximum output and to control safety functions such as overfill prevention. Some of the struggles of level measurement include viscosity changes, dielectric property changes in the fluid and foam may all affect the radar signal. A turbulent surface of the liquid level also scatters the radar signal. Other struggles include physical obstacles in the tank, o-ring and wetted part degradation, poor power supply and grounding, and human error.

Safety functions drive a breadth of requirements. Regulations dictate cumbersome test procedures for safety testing.

Christoffer describe the Rosemount 5408 that is 30 times more sensitive due to FMCW technology for sensitivity and resolution. Instead of a once a second radar pulse, a continuous radar signal is sent down to the liquid level. It handles the struggles much better. Limited power prevented the FMCW for many years, but now can be powered through a two wire loop. It can operate on voltages as low as 12VDC. Power diagnostics monitor supply and warn you when limits are reached.

The Rosemount 5408 has a two-second power reserve to handle power intermittency that may occur. New wetted parts were designed to handle higher temperatures & pressures up to 482degF at 754psi for PEEK and 482degF at 44psi for PTFE. There is a selection of antennas to best fit the intended application. Types include cone, process seal and parabolic antennas.

To simplify installation, non-contacting radar technology can be used. Instructions are available when and where they are needed with foldout instructions and pictorial-based documentation. Markings on the level transmitter guides proper alignment of the transmitter head to ensure proper installation.

Communications are available for HART, Foundation fieldbus and FDI (with Device Descriptions inside for hosts that don’t yet accept FDI). The user interface for the Rosemount Radar Master Plus software is embedded in the FDI package and includes interactive graphics, configuration and diagnostics. The transmitter saves measurements & echo curve data in on-board 7-day memory to aid in troubleshooting.

Jimmie explained that from a safety perspective, that a Rosemount 5408:SIS level transmitter is available to prevent overfills in the safety layer. Remote proof testing can be performed and the SIS transmitter is IEC 61508 certified to SIL 2 for a single device and SIL3 with redundancy.

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