Eurotherm 6100, User Manual

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100/180MM DISTRIBUTED GRAPHIC RECORDER: USER GUIDE
Page 106 HA029324
Issue 11 Oct 14
4.3.11 FUNCTION (Cont.)
ROOT MASS FLOW
Note: The overall accuracy of a fl ow measurement installation depends on a number of fac-
tors outside the control of the recorder manufacturer. For this reason, the recorder manu-
facturer takes no responsibility for the accuracy of the results obtained using the mass fl ow
equations implemented in the maths pack.
The equation solved is:
where, QM
t
= Mass fl ow (in kg/sec), at time ‘t’
K = Scaling factor (see below)
Rg = Specifi c gas constant in J/kg-K (see below)
Z = Compressibility factor (see below)
DeltaP
t
= Measured value across the orifi ce plate at time ‘t’
AbsP
t
= Absolute pressure of the fl uid at the up-stream tapping at time ‘t’ in kPa(A)
Temp = Temperature of the fl uid at the up-stream tapping in Kelvins
SCALING FACTOR
This is determined from an assumed value of Qm at a known DeltaP, AbsP and Temp. The value is chosen
to give an output within the range low scale to high scale.
SPECIFIC GAS CONSTANT
The specifi c gas constant for any gas is available from published tables. For convenience, the value for a
number of common gases is given in
table 4.3.11a , above.
COMPRESSIBILITY FACTOR ( Z-FACTOR)
Compressibility factor is a density-related measure of how far a particular gas deviates from a ‘perfect’
gas under any set of temperature and pressure conditions, and is give by the equation:
where: Z = Compressibility factor
P = Absolute pressure of the gas in kPa(A)
T = Absolute temperature of the gas (Kelvins)

= gas density at pressure P and temperature T (from published tables)
Z

P
T

1

QM
t

K2
Rg

Z

DeltaP
t

AbsP
t
Temp