FMG HYDRO Humidity mesuarements using capacitive probe
Version Française
English Version

Home / About moisture measurement

About moisture measurement

The FMG moisture measuring probes are designed for on-line measurement of materials varying from rubbles to other not so rough objects. The measuring process determines the actual water content of a mixture. In order to achieve this, the difference between the dielectric constant of water ( e = 80 ) and that of the material in question is estimated. Most materials have a dielectric constant lying in the range of
e = 3…10. The water content of the material results in a widely varying range for the dielectric constant, and a measurement of the changes in the capacitive field permit us the attain a high resolution for the corresponding measured signal. This is then further processed by the electronic inside the probe, and the processed signal is available as the moisture measurement signal at the terminals of the probe.

All current measuring systems (whether based on capacitive, microwave or conductivity measurements etc.) measure the water content of the mediums only indirectly, where a known physical effect is utilized for the purpose.

Some property of the medium changes (in accordance with the physical effect) due to a change in the moisture content, and these changes are then converted by the sensor into a proportionally varying signal [0-10V] or [0(4)-20mA]. As there is no absolute scale of indication, it becomes necessary to calibrate the measuring probe depending on the material in question. This calibration is required, whether the material is moving or not.

This implies that for different materials the probe has to be calibrated separately, and a material specific calibration curve is required for evaluating the signal output at the probe terminals.