KROHNE ALTOSONIC V EN - Manual (Page 58)

ALTOSONIC V
Operating Manual rev02 E 7.30850.34.00 Page 58 of 106
5.2 Mass calculation
For mass calculation without using API standard volume calculations for the proces density it is of
great importance that its measurement conditions are approximately similar to the measurement
conditions of the flow rate in the UFS.
ρ φ φ ⋅ =
v m
Φ m : Mass flow rate [kg/hr], the unit used in UFP is [ton/hr], 1 [ton] is 1000 [kg]
Φ v : Volume flow rate at proces conditions
ρ
: Density at proces conditions [kg/m 3 ]
Any deviation in measured density as function of the measurement conditions is directly proportional in
the calculation of the mass flow rate.
For example: Crude oil with flow measurement at 25 °C and density measurement at 24°C.
Density 25°C: 845.00 kg/m3
Density 24°C: 845.71 kg/m3
This gives a deviation in mass flow rate of:
% 08 . 0 100
845
845 71 . 845
= ⋅
−
So variations of the measurement conditions for densitometer position to flow rate position will effect
linearity and repeatability of the mass measurement.
When this problem occurs it is better to use the API standard volume calculation for its mass
calculation. Its a little more complicated but then there is a correction for the measurement conditions.
5.3 Solartron meter density is calculated as follows:
Density calibration at 20 °C, 1 barA.
Density temperature and pressure corrected:
2 2 1 0 T K T K K D ⋅ + ⋅ + =
) 20 ( 19 )) 20 ( 18 1 ( − + − + = t K t K D D
t
) 1 ( 21 )) 1 ( 20 1 ( − + − + = P K p K D D
t p
Where K20 and K21 are:
) 1 ( 20 20 20 − + = p B K A K K
) 1 ( 21 21 21 − + = p B K A K K
D : Density, uncorrected [kg/m 3 ]
Dt : Density, temperature corrected [kg/m 3 ]
Dp : Density, pressure corrected [kg/m 3 ]
T : Periodic time [µs]
t : Temperature [°C]
p : Pressure [barA]
K0, K1, K2 : Calibration factors, Density calibration at 20 °C, 1 barA.
K18, K19 : Calibration factors, Density calibration at 20 °C, 1 barA.
K20A,K20B : Calibration factors, Density calibration at 20 °C, 1 barA.
K21A,K21B : Calibration factors, Density calibration at 20 °C, 1 barA.
The calibration factors can be altered on-line while the system is operating, by keyboard (CONTROLS
F9, DENSITO F5) or by Modbus control.
But for custody transfer reasons the write access to the density cells can be blocked in the
configuration file CLNT0300.DAT