
Using ProLink
®
Software with Micro Motion
®
Transmitters
101
Configure Menu: Transmitter Variables
continued
Density units
Configure Menu:
Transmitter Outputs
Configure Menu:
Transmitter Information
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Configure Menu:
Characterize
Configure Menu:
Transmitter Variables
From the operating density (fluid density at line conditions) and
operating temperature of a given petroleum fluid, the standard density
(density at 60
°
F or 15
°
C) can be determined directly from API thermal
expansion tables or by using API equation API-2540:
Where
:
ρ
O
= operating density
ρ
S
= standard density
T = temperature difference from base (standard)
temperature
(60
°
F or 15
°
C)
α = where K
0
and K
1
are constants
The equation requires significant calculation time to generate one
reading. The RFT9739 software uses a simplification of this correlation
to maximize sampling frequency of the measurement. Accuracy of the
Micro Motion correlation is ±0.0005 g/cc relative to the API-2540
equation. After temperature correction to 60
°
F or 15
°
C, the density is
converted to degrees API by the following expression:
Degrees API =
The K
0
and K
1
in the API-2540 equation are constants characteristic of
different types of Generalized Petroleum Products. Separate API tables
exist for crude oils, distillates, gasolines, lube oils, and other products.
The correlation in the RFT9739 software is based on the API constants
for Generalized Petroleum Products.
The API equation used by the RFT9739 is valid for Generalized
Petroleum Products from 2 to 95
°
API over an operating temperature
range of 0 to 300
°
F. As fluid density or operating temperature extends
beyond these values, the RFT9739 correlation error will increase.
Density calibration must be performed in units of g/cc for the API
correlation to be correct.
API standard volume
If degrees API is selected as the density unit, the RFT9739
automatically calculates standard volume at 60
°
F or at 15
°
C based on
the following expression:
ρ
o
ρ
s
α–()∆
T 10.8α∆
T+()[]×=
∆
K
0
ρ
s
2
------
K
1
ρ
s
------+
141.5
Standard specific gravity
-----------------------------------------------------------------
131.5
–
Standard volume
Mass flow
Standard density
---------------------------------------------=
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