Active Shield: Reliable measurement despite material build-up

Kategorie: Wyjaśnienie pomiaru poziomu

Tagi: materiał zbrylający się, detektor min/max, aktywna osłona

Active Shield - Reliable measurement despite material build-up

The protective shield against false switching

Material build-up is one of the most common sources of interference in level measurement. Whether sticky powders, slurries or conductive bulk solids – as soon as material adheres to a probe, the risk of false switching increases. Moisture or condensation on the sensor probe can also cause capacitive interference.

Active Shield refers to an active shielding technique in which an additional protective field prevents false switching caused by material build-up. This is exactly where Active Shield Technology comes into play: it ensures that the sensor reacts exclusively to the actual medium – not to external disturbances. The result is stable, reliable measurement signals, even under demanding process conditions.

Why do material build-ups cause false switching?

In capacitive or RF-based measurement principles, conductive material adhering to the probe can create an unwanted electrical connection to the vessel wall. The sensor then incorrectly interprets this as a “covered” condition – even though the actual level has not yet been reached. The consequences range from false alarms and process disruptions to unplanned plant downtime.

How does Active Shield work?

Active Shield operates with an additional, intelligently controlled protective field surrounding the sensor probe. Unlike purely passive shielding, this technology actively works with a defined electrical potential and dynamically adapts to the respective process conditions.

Simply explained

• The active electrode generates its own measuring field.

• At the same time, Active Shield creates an identical electrical potential – exclusively as a protective field.

• This protective field prevents material build-up or moisture from forming a conductive bridge to ground (the vessel wall).

• False switching is reliably suppressed.

The result:
Even if material or condensate deposits directly on the sensor body, the measurement signal remains stable and unambiguous.

Benefits at a glance

• No false signals caused by material build-up or moisture

• Consistent measurement quality, even with challenging media

• Ideal for sticky, viscous or conductive materials

• Reduced maintenance effort and longer sensor service life

Severe material build-up caused by moist cellulose: A typical challenge for level measurement in the pulp and recycling industry

Reliable measurement with Active Shield: the protective field prevents false switching caused by material build-up

Why is Active Shield often combined with RF technology?

RF technology (radio frequency) offers design-related advantages for demanding applications:

Reliable measurement even in dusty environments
Low sensitivity to material build-up
High flexibility for media with a low dielectric constant
Robust, maintenance-free and durable technology

By measuring the complex electrical impedance, the signal remains stable even when conductive media adhere to the sensor probe. In combination with Active Shield, this creates a particularly reliable solution for applications where conventional capacitive sensors reach their limits.

What happens inside the vessel?

With metallic vessel walls, Active Shield generates an electrical protective field between the electrode and the vessel wall (ground). This protective field has the same electrical potential as the measuring field of the active electrode. As a result, the probe is effectively shielded: material build-up or moisture cannot form a direct connection between the electrode and ground – false switching is reliably prevented.

RF measurement principle: The sensor detects capacitance and electrical impedance – a clear signal change reliably indicates that the level has been reached.