Yokogawa DM8C/VD6 Liquid Density Analyzer - Manual (Page 24)

< 2. PRINCIPLES OF OPERATION >
2-2
IM 12T03A01-02E
2.1.2 Density Converter
The density converter computes the liquid density using the oscillation frequency signal and voltage of
the temperature.
Each value of l, E, ρ
1
, D
1
, D
2
or rx in equation (1) is a function of liquid temperature, hence the value
of f
x
is also a function of temperature. To obtain the correct density, the factors A
(t)
and B
(t)
depending
temperature should be previously compensated for the temperature as follows.
where, A (t) = A
1
( 1.0060 - 1.9814 x 10 -4 ‡T - 9.7683 x 10 -8 ‡T 2 )
B (t) = B
1
{ 1 + 4.5 x 10 -5 ( T - 30 ) }
A (t) = ( A + 131072 ) / 100
B 1 = B / 300
T : Liquid temperature (°C)
(2)
A (t)
1 + ρ
x
B (t) ¥
f
x
=
(Note) Both A and B are constants of the detector which has inherent values.
From equation (2) and (3), the density ρ
x
can be obtained.
{ }
(3) ρ
x
=
- 1
B (t)
A (t)
f
x
2
The ρ
x
in equation (3) represents the liquid density at measuring temperature. The density ρT
B
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) ρT
B
= ρ
x
+ α ( T
x
- T
B
)