Definition. Non-contact, density-independent water content measurement via the interaction between microwaves and water molecules.
Microwaves above 2 GHz pass through or reflect off the material. Water molecules absorb and slow the wave — both effects depend on water content, but differently on density.
From these two independent variables the 2-PMR method computes water content and density simultaneously. Water content becomes density-independent.
Advantages over NIR: volumetric penetration instead of surface only, insensitive to color, dust, atmosphere. Advantages over capacitive: no drift from material variation.
FAQ
What does the microwave actually measure? +
The interaction of microwaves with water molecules in the material. Water molecules absorb and delay microwaves — the method computes water content from these.
Why density-independent? +
Two independent resonance variables (amplitude and phase) allow simultaneous derivation of water content and material amount. Density cancels out.
Where are the limits? +
Very low material quantities below 100 g/m² become inaccurate. GrammageScan with a different sensor setup covers that range.
Practical tip
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Three data points — material, temperature, position — are enough for a first sensor recommendation.
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