What is Time-of-Flight Radar Level Measurement

Radar level measurement based on Time-of-Flight (ToF) is a non-contact method for determining the level of a liquid or solid in a vessel or open channel. The device emits short pulses of electromagnetic waves (microwave pulses), which travel to the surface of the material being measured, get reflected back, and are detected. The time the pulse takes to go and return (round-trip time) is proportional to the distance. Knowing the distance from the sensor to the surface, the level can be calculated (often subtracting from the maximum measurement distance).

Key advantages of ToF radar:

• Non-contact: no parts submerged, so no issues with corrosion, build-up, fouling.
• Works in harsh process conditions (vapors, dust, temperature, pressure).
• Accurate and reliable.

Micropilot FMR20 — Overview

The Micropilot FMR20 is a level measurement instrument by Endress+Hauser using non-contact radar / Time-of-Flight principle.

Here are its main characteristics and applications:

How the Micropilot FMR20 Implements Time-of-Flight

Some specifics about how the FMR20 does ToF measurement:

• Frequency: approx. 26 GHz (K-band). Higher frequency helps with better resolution and smaller beam widths.
• Antenna / Beam-angle: Different antenna sizes (40 mm, 80 mm) which affect the beam divergence. Larger antenna gives narrower beam, which helps focusing and reduces interference from side reflections.
• Blocking / Dead-zone: There is a minimum “blocking distance” or dead zone near the sensor where echoes cannot be reliably examined. The device has to ignore any signal echoes in that zone.
• Signal processing: The FMR20 evaluates echo signals, filters out spurious reflections (from obstructions, internal vessel parts), possibly does mapping of echo strength vs time to ensure correct surface detection. It also does linearization when used for flow via open channels/weirs.

Strengths and Limitations

Strengths:

• Very good accuracy for liquids (±2 mm).
• Non-contact means low maintenance, no issues with material contact.
• Suitable for a wide range of process conditions (temperature, pressure, contaminated or dusty vapors).
• Wireless configuration (Bluetooth) + HART support for integration and set-up flexibility.

Limitations / things to pay attention to:

• For solids or materials with low reflectivity, accuracy drops (±5 mm or more).
• Need relatively clear line-of-sight; obstructions in beam path, turbulence, foam, vapors or heavy dust can interfere with echo detection.
• Dead-zone near sensor: very near surface measurement might not be possible if within blocking distance.
• Installation geometry matters: alignment, antenna shape, mounting height, etc.