BRONKHORST
®
9.17.022 page 19
most common gases, which is accurate at both lower and higher flow ranges. Consult Bronkhorst
®
for
applications.
At nominal flow ranges for each instrument, a good approximation is the use of the so-called “CFDirect”
conversion method, which comes with the FLUIDAT software.
Consult FLUIDAT for the most optimal conversion factor.
1.6.3 Liquid Conversion Factors
1) -FLOW models
The general formula for determining the relationship between signal and mass flow reads:
in which:
V
signal
= output signal
Vkc
signal p
m
k = calibration constant
c
p
= heat capacity at constant pressure of the fluid
m
= mass flow
A conversion factor must be used if the liquid flow meter is not used on the calibrated liquid.
This conversion factor reads:
in which:
c
p1
= heat capacity of the calibration liquid
12
mm
Cf
Cf
c
c
p1
p2
c
p2
= heat capacity of the new liquid
For application of this formula consult Bronkhorst
®
2) CTA based LIQUI-FLOW
For the CTA based LIQUI-FLOW liquid mass flow sensor, the transfer function between the liquid mass flow
and the linear output signal can roughly be described with the equation:
mpsignal
cKV
2
V
signal
= output signal
K = calibration constant
c
p
= specific heat
= heat conduction coefficient
m
= mass flow
A conversion factor must be used if the liquid flow meter is not used on the calibrated liquid (reference liquid)
but on another liquid (custom liquid). The conversion factor CF can roughly be calculated with the equation:
FLUIDCUSTOM
p
FLUIDREFERENCE
p
c
c
CF
2
2
For application of this equation, please consult Bronkhorst
®
1.6.4 Software for conversion factor calculation
Bronkhorst
®
gathered the physical properties of over 600 fluids in a database called FLUIDAT
.
Application software, such as FLUIDAT
on the Net (FOTN), enable the user to calculate accurate
conversion factors, not only at 20°C/1 atm (as shown in the conversion table, App.1) but at any
temperature/pressure combination.
Apply to your distributor for more details of this software.
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