10 Product Specifications
10-2. Principle of this product
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10-2-2. Opt-Sonic calculation (specific gravity)
Figure 4 is a graph that shows the correlation between the specific gravity of pure gases and sound speed.
The straight line drawn in this figure represents the function
d
Sonic
that connects the points of paraffinic
hydrocarbon gases.
Figure 5 is a graph that shows the correlation between the specific gravity of pure gases and refractive
index. The straight line drawn in this figure represents the function
d
Opt
that connects the points of
paraffinic hydrocarbon gases.
Figure 4: Correlation between specific gravity and
sound speed
Figure 5: Correlation between specific gravity and
refractive index
If the gas to be measured consists only of paraffinic hydrocarbon gases, an accurate specific gravity can be
obtained by measuring sound speed and refractive index and substituting them into the functions
d
Sonic
and
d
Opt
.
However, if the gas to be measured includes components with sound speed and refractive index that are not
on the straight lines drawn by the functions
d
Sonic
and
d
Opt
, respectively, i.e., N2, O2, CO2, CO etc., these
components act as interference gases that generate errors.
The correlation between the true specific gravity of the measuring gas
d
and the functions
d
Sonic
and
d
Opt
can be expressed by the following formulas (6) and (7).
i
i
Opt
x
k
d
d
(6)
i
i
Sonic
'
x
k
d
d
(7)
where
x
i
represents the volume fraction of interference gas component i, and
k
i
and
k'
i
represent the error
coefficients caused by interference gas component i.
The error coefficients
k
i
and
k'
i
represent the "distances" in a vertical axis direction from the component i to
the straight lines drawn by the functions
d
Sonic
and
d
Opt
in the graphs shown in Figures 4 and 5.
RIKEN KEIKI has discovered a correlation in which the ratio of
k
i
to
k'
i
is approximately constant,
regardless of the types of interference gases.
i
i
'
k
k
(8)
Using the relational formula (8), the formula (6) can be written as follows:
i
i
Opt
x
k
d
d
(9)
Содержание OHC-800
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