Solartron Mobrey 7828 - API Density Referral

7828 Density Transmitter Technical Manual Calculated parameters
78285000_AA B-3
B.2.2 API DENSITY REFERRAL
This calculation uses an iterative process to determine the density at the base
temperature by applying temperature and pressure corrections using the API-ASTM-IP
petroleum measurement tables.
The information required for the API density is:-
• Reference pressure and reference temperature
• Line pressure - this is not measured by 7828, and must be entered as part of the
configuration.
• Product type: Refined product, crude product or user defined.
Density/Temperature Relationship
Correction factors in the revised API-ASTM-IP petroleum measurement tables are based
on the following correlation equations:
ρt / ρ
15
= exp ( -α
15
∆t ( 1 + 0.8 α
15
∆t ) )
where:
ρt = Density at line temperature t°C
ρ
15
= Density at base temperature 15°C.
∆t = (t - 15) °C
α
15
= Tangent thermal expansion coefficient per deg C at base
temperature of 15
°C.
The tangent coefficient differs for each of the major groups of hydrocarbons. It is
obtained from the following relationship:
α
ρ
ρ
15
0115
15
2
=
+KK
where K
0
and K
1
are known as the API factors.
Hydrocarbon Group Selection
The hydrocarbon group can be selected as:
• General refined products
• General crude products
• User defined.
K
0
and K
1
are programmed into the 7828 for the first two groups.