Berthold MicroPolar LB 566, User Manual, Page: 17 / 176

Chapter 3. System Description
MicroPolar (++) LB 566 17
System Description Chapter 3.
3.1
Principle of Measurement
As the microwaves pass through the product, their propagation
velocity is slowed down (= phase shift) and their intensity is at-
tenuated (= attenuation). Figure 3-1 illustrates the principle of
measurement: Compared to a reference signal, the propagation
velocity of microwaves passing through the product is slowed
down (phase shift) and their intensity (attenuation) is reduced.
Phase shift
Messgut
Phase comparison
--> Phase
Amplitude comp.
--> Attenuation
Reference path
Reference signal
Measurement signal
Measured value:
Concentration %DS
HF sources
Receiver
Transmitter
The prerequisite is that the product being measured shows die-
lectric properties. Generally, water is a very distinct dielectric
fluid. The water or dry mass concentration can therefore be de-
termined by measuring the phase shift and/or attenuation.
The concentration to be detected in the product is therefore in
good approximation linearly dependent on the phase shift and
the attenuation. For this reason, we can measure the concen-
tration or the dry matter content of the product using a linear
calibration (see
chapter 3.2 Calculation of Measured Values ).
Figure 3-1:
Schematic diagram:
Change in
microwave by
product