IM 01C25R01-01E
2-7
2. About Multivariable Transmitter
Example 1 : Calculation of Nc
(1) When flow unit is changed.
Nc= (Kg/s) /(Mass Flow unit in use)
Table 2.6 Example of Calculated Nc by Flow Unit
T0206E.EPS
kg/s
kg/h
lb/s
lb/h
Flow unit
(kg/s) / (kg/s) = (1kg/1s) / (1kg/1s)
(kg/s) / (kg/h) = (1kg/1s) / (1kg/3600s)
(kg/s) / (lb/s) = (1kg/1s) / (0.4535924kg/1s)
(kg/s) / (lb/h) = (1kg/1s) / (0.4535924kg/3600s)
Calculation of Nc
1
3600
2.204623
7936.648
Nc
(2) When differential pressure unit is changed.
Nc = (Differential pressure unit)/(Pa)
Table 2.7 Example of Calculated Nc by Differential Pressure Unit
T0207E.EPS
Pa
kPa
inH2O@68degF
∆
p unit
(Pa) / (Pa) = (1Pa) / (1Pa)
kPa/Pa = 1000Pa / 1Pa
inH2O@68degF / Pa = 248.6406Pa / 1Pa
Calculation of Nc
1 = 1
1000 = 31.62278
248.6406 = 15.76834
Nc
(3) When a flow unit and a differential pressure unit are changed.
Nc =(Kg/s) /(Mass Flow unit of use)
(Differential pressure unit of use)/(Pa)
Example 2 : Calculation of Kfactor
When Qm unit = kg/s, Differential pressure unit = kPa
Kfactor =
π
/4
Nc
C/ 1–
4
ε
d
2
2
b
1/K
=0.7853982
31.62278
0.6043 / 1– 0.1296
0.984
0.03162
2
2
1.250380
1/1
=0.02502868
0.02503
Table 2.8 Flow Parameter of Example
T0208E.EPS
C
ε
d
D
ρ
b
Tb
SPb
K
π
/4
Nc
Symbol
0.6043
0.984
0.6
0.03162 m
0.0527 m
1.250380 kg/m
3
273.15K(0 degC)
101.325 kPa abs
1
0.7853982
31.62278
Value
Discharge coefficient Orifice Corner Taps [ISO5167-1 1991] ReD 1
10
6
Expansion factor
=0.6,
∆
=50,000 Pa, SP=1,000,000Pa abs,
=1.399502
Diameter ratio
Bore of orifice
Pipe diameter
Base Density on Tb, SPb Condition (NITROGEN 101,325 Pa abs 273.15K)
Reference temperature unit: K
Reference static pressure unit: kPa abs
Compressibility factor
Unit convert factor when DP unit is kPa kPa/Pa = 1000Pa / 1Pa =31.62278
Description
Example 3 : Calculation of Qm
∆
p = 50kPa, SP = 500kPa abs, T = 293.15K
Qm(kg/s) = Kfactor
∆
p
(Tb / T)
(SP / SPb)
= 0.02503
50
(273.15 / 293.15)
(500 / 101.325)
= 0.3795 (kg/s)
