Ideal Gas Flow - ABB SM2000 User Manual Supplement

...2 MATH CONFIGURATION
...2.10.1 Liquid Flow – Fig. 2.12
Mass Flow – Derived density correction
This method uses a preset table of temperature and density
values to define the correction, which is calculated as follows:
Qmd = Qc x density correction
a1 x a3 x scaling factor
m3 =
m2
Note. Input a3 is the actual product temperature input
(as a2 in previous examples) but with the density
correction applied using a custom linearizer – see
Section 4.8.1 of the User Guide.
Mass Flow – Measured Density Correction
Qmm = Qc x input from density meter.
a1 x a3 / m2
m3 =
m2
Where a3 is the input from an external density meter.
Note. With all of the above calculations the engineering
range should allow for the extremes of all the input
variables.
14

2.10.2 Ideal Gas Flow

Gas flow is usually measured using a differential pressure device
across orifice plates and wedges.
Corrections can be applied to compensate for variations in
temperature and pressure – see Fig. 2.13.
T
A
Q = Corrected Volumetric Flow
c
Q = Volumetric uncorrected flow
T = Reference temperature in K or ºR
ref
T = Actual temperature in K or ºR
A
P = Reference pressure in Absolute
ref
P = Actual pressure in Absolute
A
Fig. 2.13 Temperature and Pressure Compensation
Where Q = K h the square root extraction and scaling can
be achieved on the DP device or on the input set up of the
instrument.
Let m1 = constant 1 x a3
Qc = m2 = a1 x constant2 x a2/m1
Note. The engineering range should allow for the
extremes of all the input variables.
Ideal Gas Flow
Q
P x T x Q
ref A
P
A
T x P
ref A