Level Sensors and Switches for Bulk Solids

Level sensors and switches for bulk solids (grain, cement, powders, pellets) are instruments designed for accurate point-level detection ("full/empty") or continuous level measurement in silos, hoppers and containers. They operate reliably in harsh conditions (dust, extreme temperatures, pressure) and prevent overfilling or material run-out. The range includes both contacting and non-contacting devices from leading manufacturers (Mollet, ENVEA, KROHNE) with ATEX certification for explosive atmospheres.

Operating Principle

• 80 GHz FMCW Radar: Non-contact continuous measurement using frequency-modulated continuous wave microwaves; highest accuracy and beam focusing even in extremely dusty silos.

• Guided Wave Radar (TDR / reflex radar): Contact/semi-contact measurement along a probe or cable; perfect for very low dielectric constants (εr > 1.4), foam, interface and tall silos up to 75 m.

• Pulse Radar (ToF, usually 26 GHz): Classic non-contact radar using time-of-flight method; suitable for medium-dust conditions up to 30–40 m.

• Ultrasonic: Non-contact measurement with sound waves; cost-effective solution for clean environments without heavy dust.

• Capacitive: Contact/semi-contact, reacts to change in capacitance; universal but sensitive to buildup.

• Rotary Paddle: Mechanical rotating paddle stops when covered; reliable point-level switch for heavy-duty applications.

• Membrane / Pressure Plate: No power required, membrane deforms under material pressure; simple point-level switch.

• Vibrating Fork: Vibration frequency changes when covered; ideal for granules and powders, resistant to buildup.

• Microwave Barrier (Doppler): Non-contact transmitter-receiver barrier; detects flow or presence even through vessel walls.

• Plumb Bob / Yo-Yo (tape type): Mechanical lowering of a weight on a tape; continuous measurement completely independent of dust and dielectric properties.

Main Application Areas

Monitoring of bulk solids in agriculture (grain storage), food & beverage (flour, sugar), cement plants, chemical and pharmaceutical industries, power generation (coal, ash), and woodworking. Used in silos, hoppers, conveyor transfer points for process automation, overfill/empty protection and in explosive (ATEX) zones.

Advantages of Radar Level Transmitters (especially 80 GHz FMCW and Guided Wave Radar)

• Completely non-contact (free-space radar) or guided contact (TDR) – no wear or buildup problems

• Immune to dust, steam, condensation, temperature and pressure extremes (-40…+200 °C, up to 100 bar)

• Extremely high accuracy (1–2 mm) and long ranges (up to 100 m free-space, 75 m guided)

• Suitable for almost all bulk solids, even very low dielectric materials, foam and interface layers

• ATEX/IECEx certified for all explosion zones

• Easy integration via 4–20 mA/HART/Profibus, minimal maintenance, service life > 10 years

• Best price/performance ratio for demanding and dusty applications.