Radar level transmitters have become one of the most reliable technologies for continuous level measurement due to their non-contact operation, high accuracy, and immunity to vapor, dust, and pressure variations. However, certain process conditions—especially temperature, pressure, dielectric constant, turbulence, and foam—still influence measurement reliability.
This article provides a clear technical overview for engineers on how these factors affect radar performance and how to ensure accurate level measurement in real-world applications.
1. Influence of Temperature on Radar Level Transmitters
Radar waves propagate through air independent of temperature changes—the propagation speed of microwaves is almost unaffected by thermal conditions.
However, the temperature limitation lies in the transmitter hardware itself, including the antenna, seal materials, and electronic components.
1.1 Sensor Temperature Limits
Typical operating limits for industrial radar level transmitters are:
–40 °C to +150 °C for standard process connections
Up to 300 °C for special high-temperature designs with extended nozzles or cooling mechanisms
When the medium temperature is high:
The antenna can overheat
Seal materials may degrade
Electronics may drift or shut down
1.2 How to Handle High-Temperature Applications
Common engineering solutions include:
Air or water cooling jackets
Extended standpipes or waveguides to keep the antenna away from the hot vapor zone
Keeping 100–800 mm safety distance between antenna and maximum fill level
Selecting PTFE windows or high-temperature process seals
2. Effect of Process Pressure on Radar Measurement
Radar signals are not influenced by air density, so they function well in:
Vacuum conditions
Pressurized tanks
However, the mechanical design of the transmitter has its own allowable pressure rating. If the vessel pressure exceeds this limit:
Antenna deformation may occur
Seal leakage may develop
Signal quality may be reduced due to mechanical stress
Different manufacturers specify different maximum operating pressures depending on antenna type, flange rating, and sealing material.
3. Media Properties That Affect Radar Performance
Radar measurement depends on the reflection strength of microwaves. Several medium characteristics influence the quality of the returned signal.
3.1 Dielectric Constant (DK / εr)
The dielectric constant determines how strongly the radar signal is reflected at the liquid surface.
High DK (>10 mS/cm conductivity) → strong reflection, stable measurement
Low DK (1.2–2.0) → weak reflection, risk of signal loss
Modern 80 GHz high-frequency radars can measure even very low DK hydrocarbons, but older or low-frequency (6G / 26G) radars may struggle.
Typical Dielectric Constant Values
| Material | Approx. DK |
|---|---|
| Water | 80 |
| Acid/alkali solutions | 30–70 |
| Oils | 2–4 |
| LPG / LNG | 1.3–1.8 |
If the DK is too low, a horn antenna or guided-wave radar may be needed.
3.2 Turbulence, Surface Movement, and Foam
Turbulence
Strong agitation or inlet streams create:
Surface waves
Vortex formation
Scattering of microwaves
This leads to attenuated or unstable readings.
Foam
Foam absorbs and scatters microwave energy.
Wet, conductive foam = usually still measurable
Dry, thick foam = strong attenuation, possible signal loss
Engineering recommendations:
Avoid mounting above the inlet
Use stilling wells or bypass chambers
Select higher-frequency radar for small tanks or short ranges
4. Installation Guidelines for Reliable Radar Performance
Proper installation is crucial for accurate measurement.
4.1 Avoid Disturbance Sources
Do not install above inlets, feed streams, or falling material
Keep away from agitators or paddles
Avoid locations with excessive vortex formation
4.2 Materials and Corrosion Protection
For corrosive or crystallizing media:
Use PTFE windows, PTFE-lined antennas, or separated flange designs
Ensure temperature at sealing materials does not exceed 200 °C for PTFE
4.3 Maintain a Safe Distance
Keep a design distance of 100–800 mm between the antenna and the maximum fill level to reduce thermal influence and avoid coating buildup.
5. Operating Principle of Radar Level Transmitters
5.1 Time-of-Flight (ToF) Radar
The transmitter emits a microwave pulse and measures the time taken for the echo to return:
Where:
-
d = distance to liquid surface
-
c = speed of electromagnetic waves
5.2 Frequency-Modulated Continuous Wave (FMCW) Radar
Uses a swept-frequency signal.
The difference between transmitted and received frequency is proportional to the distance, providing higher resolution and stability.
Conclusion
Radar level transmitters offer exceptional reliability across a wide range of industrial conditions. Understanding the impact of temperature, pressure, dielectric constant, turbulence, and installation location is essential for ensuring measurement accuracy and long-term stability.
By selecting the appropriate radar frequency, antenna type, and installation method, users can achieve highly dependable level measurement even in challenging or dynamic process environments.