Contrec 515, Operation Manual

Page: 11 / 92

Introduction
515 HC04 - 8 June 2007 3
where:
Differential Pressure Equations
This application uses the following general formula for mass flow as per the
ISO 5167 (2003) standard:
where:
For further details of these equations or restrictions of use please refer to the
appropriate standard or relevant documents.
Analog Input Scaling
The analog inputs in this instrument are scaled by the following general
formula:
where:
ρ
flow
= density at flow conditions
h
TF
= Specific enthalpy at feed
temperature
h
TR
= Specific enthalpy at return
temperature
q
m
= mass flow
C = coefficient of discharge
β
= diameter ratio of orifice to pipe
ε
= fluid expansion factor... (for water
ε
= 1.0)
π
= universal constant (3.14159)
d = diameter of orifice (bore)... (for cone type meters substitute d
2
with D
2
β
2
)
D = diameter of pipe
∆
P = differential pressure
ρ
= density at flow conditions
q
m
=
C
1
β
4
–
-------------------
ε π
4
---
d
2
2
∆
P
ρ
P
min
= minimum point (equivalent to offset)
P
max
= maximum point (P
max
– P
min
is equivalent to span)
A* = normalised signal (0 to 1) with correction applied for a flow input
f A
( )
Pmin Pmax Pmin
–
( )
A*
⋅
+ =