Technical Information

How does it work?

Microwave moisture analysers work on the principle that water has a very high dielectric constant compared to many materials. When microwaves come into contact with moist materials they slow down (and hence change phase) and weaken (attenuate) as the energy is transferred to the material.

The LFM Moisture Analyser is based on this principle. Put simply, it measures the change in phase and attenuation of a microwave passing through a moist material.

Microwaves are influenced in their intensity and speed of propagation by the presence of free water molecules. By measuring the decrease in intensity (attenuation) and the decrease in speed (by the change of phase) it is possible to infer the moisture content.

Since phase shift and attenuation also depend on the amount of material present, a measurement of the mass loading on the belt is required to compensate or “normalise” the microwave measurements. This is generally provided by a beltweigher.

More Information

Advantages of the LFM Moisture Analyser technology

Alternative moisture analysis technologies

Technology Applications Advantages Disadvantages
Microwave Transmission systems
  • Granular material on conveyor belts
  • Managing dust extinction and maximum moisture limits
  • Measuring “dry tonnes” for mass balance reconciliation
  • Measuring critical process applications such as filtration, pelletising and sintering
  • Samples a representative sample eg through material on conveyor belts
  • Low power versions are considered very safe due to low emission of electromagnetic radiation
  • Suitable for conveyor applications
  • Has limits as to the depth of the material being measured
  • Cannot measure chemically combined water
  • Cannot measure thick beds of highly attenuating materials such as coke, pure magnetite or manganese ore
Microwave Resonance Systems
  • Concrete batch plant applications
  • Cheaper than Transmitter Receiver systems
  • Suitable for bin installations
  • Limited in high moisture systems
  • Cannot be used with high attenuation materials eg iron ore
  • Cannot be used with sticky materials
Near Infra Red (NIR)
  • Typically used in the food and tobacco industries. Some multi channel units have wider applications
  • Usually the most generic moisture analysers
  • Can be low cost depending on number of frequencies being analysed
  • Only measures surface moisture. Most suitable applications are in installations within a closed environment where surface moisture is representative of average moisture
  • Readings can be affected by grading of material, atmospheric dust/fog and light penetration of enclosure
Nuclear
  • Best used where material is highly conductive (coke, magnetite) and sinter mixtures
  • Tend to be specialist instruments that can be used where material is highly conductive (coke, magnetite) and sinter mixtures § Work on the principle that fast neutrons are preferentially slowed down by hydrogen atoms
  • Shieldings and warnings are necessary
  • Measures total hydrogen content including chemically bound hydrogen. This leads to difficulties with hydrated oxides of iron eg. hematite and goethite