What the DK Value Reveals About the Measurability
of Media
The dielectric constant (DK value, εᵣ) is a fundamental material parameter in level measurement. It indicates how strongly a medium affects an electric field and is crucial in capacitive measurement methods as well as in signal reflection in radar technologies (FMCW or TDR).
Whether powders, granulates, or liquids: the DK value determines how clearly and consistently a measurement signal is produced — and therefore how reliably level conditions can be detected.
What is Meant by the Dielectric Constant?
The dielectric constant indicates how well a medium can store electrical energy or become polarised in an electric field. It is dimensionless and always specified relative to vacuum.
Formula for calculating the relative dielectric constant
(relative permittivity):
- ε = Permittivity of the material
- ε₀ = Electric field constant (8.854 × 10⁻¹² F/m)
The higher εᵣ, the more strongly the material influences electric fields — an effect that plays a decisive role in level measurement.
How the DK Value Influences Signal Quality in Level Measurement
The higher the DK value, the more significantly the electric or electromagnetic field used for level measurement is affected.
This has a positive impact on:
• Signal strength
• Measurement stability
• Reliable detection despite dust, vapour, internal structures, pipes, or long measuring distances.
Signal Quality as a Function of the DK Value
As the DK value increases, signal strength rises significantly — from weak echoes to clearly defined amplitudes
Examples
DK 1,1 → low signal response; measurement possible, but technically demanding depending on process conditions
DK 3 → noticeably more stable signal variation or reflection
DK 10+ → very clear signals and high measurement reliability, even under challenging conditions
Capacitive Technology:
Measurement Signal Through DK-Dependent Capacitance Change
Capacitive level switches like our and series operate based on the capacitor principle.
As the level rises, the medium displaces the air at the sensor.
The DK value increases, the capacitance changes — and the sensor detects the level or point level accordingly.
Radar: Measurement Signal Through DK-Dependent Reflection
The intensity of the radar echo is likewise influenced by the DK value:
• Low DK values → weaker echoes
• High DK values → strong reflections
Modern FMCW radar sensors such as the operate reliably even at DK values ≥ 1.1.
Guided radar (TDR), used in the is less affected by dust or turbulent surfaces. However, the same principle still applies: A higher DK value results in clearer and more stable signals.
Non-contact radar – Comparison of Real Media
Guided Radar (TDR) – Interface Measurement
With an identical measuring range, water generates a significantly stronger radar echo than EPS due to its high DK value
The signal curve shows two distinct echoes — the level and the interface — resulting from the different DK values of, for example, oil and water
The result: clear measurement points, stable processes, and reliable detection — regardless of the measurement principle used.
DK Values of Typical Materials from UWT Applications
Many industrial media differ significantly in their permittivity, which directly affects measurement behavior.
| Medium | DK Value (approx.) |
| Air | 1,0 |
| EPS / EPP | 1,1 – 1,3 |
| Plastic granules | 1,5 – 3 |
| Wood pellets | ~ 2 |
| Grain, corn, soybeans | 2 – 5 |
| Cement, lime, gypsum | 3 – 6 |
| Coffee / cocoa powder | 2 – 4 |
| Oils | 2 – 4 |
| Alcohol (ethanol) | ~ 25 |
| Milk | 50 – 70 |
| Water | ~ 80 |
DK values vary depending on moisture, temperature, and density — our sensors are specifically designed to operate reliably under these real-world conditions.
Additional DK Values at a Glance
For a more comprehensive overview, our compact PDF is available:
The DK value determines measurement behavior: depending on their permittivity, different materials generate measurement signals of varying strength
Perfectly Matched Sensor Technology – for Every Medium
Capacitive Level Switches (Capanivo® and RFnivo®)
• Measure based on changes in the electric field distribution within the medium.
• Reliable even at low to medium DK values (≥ 1.5).
• Flexible designs for powders, granulates, pasty products, and liquids — from compact vessels to large industrial installations.
Radar Sensors (NivoRadar® and NivoGuide® Series)
• Operate reliably even at very low DK values (≥ 1.1) and benefit from higher DK values through stronger reflections and clearer measurement signals.
• In free-space FMCW sensors, echo quality increases significantly as the DK value increases — ideal for long measuring distances, dust, or turbulent surfaces.
• Guided radar (TDR) is less sensitive to surface turbulence; however, here as well, higher DK values improve signal stability and reflection quality.
• Depending on the model, both technologies are suitable for demanding applications involving bulk solids and liquids.
Echo Curve & Diagnostics with the UWT LevelApp
The UWT LevelApp enables wireless control of level sensors such as NivoRadar® and NivoGuide®. Using a mobile device, all sensor settings are easily accessible for straightforward and intuitive commissioning.
As part of sensor diagnostics, the echo curve is displayed clearly and comprehensively. It shows signal strength over the measuring distance and makes distinct echo peaks as well as potential interference directly.
Level and diagnostic data can be assessed transparently, with all relevant information easily accessible at any time via smartphone or tablet—offering valuable support for commissioning, service, and operation.
Example of an echo curve from the NivoRadar® NR 7:
The distinct echo peak (green) marks the current level and indicates signal quality over the measuring distance.
Level and diagnostic data can be evaluated transparently, and all relevant information is conveniently accessible at any time via smartphone — providing valuable support for commissioning, service, and operation.
Our commitment: Technology. Performance. Partnership.
Our sensors are designed to support industrial processes safely, reliably, and efficiently — across all industries and applications.
