Since ever moisture measurement is a completely application specific discipline. Qualified services therefore have an enormous importance. Water as medium seems to be quite simple, but in reality water has a very complex nature and appears in broad variety of sha-pes. Rightly water is called one of the four elemental forces.
Because of it´s manyfold shapes water can be met in solids or liquids in different conditions and with different types of chemical binding. The question of appearance of certain states and conditions of water and their contribution to the total water volume is strongly related to the properties of the material under test.
For all indirect moisture measurement methods - microwave moisture measurements included - the question of calibration is following that. In comparison to calibration procedures for other physical properties moisture calibrations are not that simple.
Most calibration curves - showing the relation between the electrical property measured in reality and moisture content - are nonlinear. They can be established only empirical with a sufficient number of samples with different moisture.
Starting with conditioning of the samples great care has to be taken. Already this step can lead to tremendous faults in the calibration.
The properties of the material to be calibrated must be known exactly. In case the reference method is the well known oven drying method, some kinds of materials (like gypsum or tobacco) can only be dried at low temperatures, else they will be destroyed while drying.
hf sensor is well equipped for taking calibration curves of various materials. In the moisture lab of hf sensor modern climate chambers, drying ovens and moisture analyzers are available.
Using different calibration stations the moisture probes best suited for the desired application can be calibrated. The reproducable conditions guarantuee high calibration accuracy.