YOKOGAWA vigilantplant DM8, User Manual

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<2. PRINCIPLES OF OPERATION>
2-2
IM 12T03A01-02E
From equation (2) and (3), the density ρx can be obtained.
{ }
(3) ρ
x
=
- 1
B
(t)
A
(t)
f
x
2
The ρx in equation (3) represents the liquid density at measuring temperature. The density ρTB
at the reference temperature can be obtained by the following equation (4):
α : Temperature coefficient of density for measuring liquid (g/cm 3 /°C)
T
x
: Liquid temperature at density measurement (°C)
T
B
: Reference temperature (°C)
(4) ρ T
B
= ρ
x
+ α ( T
x
- T
B
)
2.2 Main Components
2.2.1 Density Detector
Figure 2.2 is a schematic diagram of the density detector.
As shown in the figure, the density detector consists mainly of a vibrator assembly, a capacitance
pickup electrode, and an amplifier.
Preamplifier
Density signal
Temperature signal
Temperature
measuring element
Vibrator
Sample
Piezo-electric element
Pick-up electrode
Vibrator cross sectional view of Density Detector
Figure 2.2 Schematic Diagram of Density Detector
The vibrator assembly consists of a sample path formed by connecting the ends of two thin
tubular vibrators whose upper ends are connected to a base. The connector incorporates
an RTD to measure the sample liquid temperature. The vibrator assembly also contains a
piezoelectric element to maintain vibration corresponding to the sample liquid density.
The capacitance pickup electrode installed between the two vibrating pipes detects the lateral
oscillation frequency of the vibrator.
5th Edition : Dec. 11, 2015-00