Overview

RF Admittance Level Switch can detect capacitance as well as impedance between probe and vessel. It is flexible for various applications while consistently demonstrating immunity to buildup, especially for dust, coal ash and other powdery ashes level control. 

Working Principle

The RF700 series probe detects level changes by monitoring variations in capacitance and impedance between the probe and the vessel wall. In the electronic unit, the reactance between the measuring electrode and the wall of an empty vessel forms a balanced bridge circuit, producing a stable oscillation signal. As the medium level rises and covers the measuring electrode, the reactance changes, unbalancing the bridge circuit and stopping the oscillation.

A post-processing circuit senses this change in oscillation and generates an alarm signal. The radio-frequency oscillation is applied not only to the measuring electrode but also to a shield electrode via a 1:1 voltage follower, ensuring both share the same potential, phase, and frequency while remaining electrically insulated. This eliminates potential differences between them, so any reactance change caused by medium buildup on the shield does not affect measurement.

As a result, only reactance changes from the medium between the measuring electrode and the vessel wall are detected, effectively eliminating measurement errors caused by buildup on the probe.

Technical Specifications

Application: Solid/Particles

Measuring range: 20-50mm
Process Connection: DN50 Flange

Sensitivity: 0.3PF
Ambient temperature: -40°C to 80°C 
Power supply: 24VDC/220VAC
Response time: Approximately 0.1 second
Explosion-proof certification: Flameproof: Ex d IIC T1-T5/T6 Ga; Ex ia D 20 T85°C
Protection rating: Aluminum/IP65
Output signal: Relay
Power: Max. 2W
Process pressure: -1 to 25 bar
Probe material: SUS304/SUS316/SUS316L
Insulation material: PTFE