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1 OVERVIEW
The LQ500 Density Meter measures the density of a substance that flows through a pipe by means
of a phase difference method using microwaves.
This method is little affected by the presence of contamination. It uses no moving mechanical parts
or mechanism that is often used in other measuring methods for cleaning, sampling, or defoaming.
It permits continuous measurement.
The density meter, which outputs measured density in electric current, is suitable for an application
in a process for monitoring and controlling.
1.1 Principle of Measurement
This density meter has adopted a new measuring method called "Phase difference method by
microwaves." When microwaves go through a substance and comes out of it, by measuring the
phase lag of the waves, we get a certain physical property of the substance that is proportional to
the density.
The theory of density measurement based on the phase difference method is shown in Figure 1.1
The difference between the phase lagθ
and the phase lagθ
Δθ ＝ θ
− θ
2
is determined, and since the differenceΔθis in direct proportion to the density, the density of the
object substance is measured.
Phase differenceΔ θ
Phase difference Δ θ = θ
Density =Ｋ・Δ θ (K: Coefficient)
of the microwave received through water (density 0%)
1
of the microwave received through the object substance, that is,
2
1
Microwave
transmission
Substance to
be measured
−θ
Ｗ
Ｓ
Fig. 1.1 Principle of phase angle difference
13
Phase lagθ
Reception
Drinking
water
Phase lag θ s
6 F 8 A 0 5 2 1
W
ｔ
ｔ
ｔ
ｔ
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