GFS2102™ OPERATION AND MAINTENANCE MANUAL
© 2007 DH Instruments, a Fluke Company
Page 48
4.1.5.1
SETTING UP STARTING AND ENDING SAMPLE
TOLERANCE
While the absolute value of the reference cylinder mass reading is not critical, the
change in mass since the start of the accumulation is the key measurement. At
any given time after the start of the accumulation, the accumulated mass divided
by the elapsed time gives a value of the average mass flow for the accumulation
up to that point. The mass flow would be the slope of a plot (or best fit line of the
plot) of accumulated mass vs. elapsed time. At the beginning of the
accumulation, relatively small variations in the mass or time readings will change
the slope significantly. As more time and mass is accumulated, the slope
becomes more consistent and any contributors to uncertainty in time or mass
measurement become less significant. For this reason, calculated flow values
are not usually displayed at the beginning of an accumulation. The initial
calculated flow values are not meaningful and in the frequent cases where DUT
flow errors are plotted throughout the accumulation, these large early error
values cause scaling problems that do not allow easy viewing of the precise error
values that result later in the accumulation.
To assist the user with determining useful limits on how much mass to deplete
during an accumulation and when useful samples and flow calculations should
begin during the accumulation, the GFS Tools test setup allows the user to select
these starting and stopping points in terms of a predicted uncertainty of the flow
value at that point. There is always an inherent trade off with gravimetric
measurements between flow uncertainty and time taken for a measurement.
This method helps the user get the results desired, maintain practical test times,
and estimate how much mass must be used for each point.
The predicted uncertainty at which the user would like to end the accumulation is
called the
Ending Sample % Rdg Tolerance
. When this value is entered in the
Test Definition Editor, GFS Tools predicts the amount of mass that will be used
for the accumulation and the amount of time needed for it and displays them.
The user can also enter a fixed value of mass to use, and view a calculated
Ending Sample % Rdg Tolerance
. In the same Test Definition Editor tab, the
user selects a
Starting Sample % Rdg Tolerance
, which defines the point at
which the first flow sample is displayed and recorded. The time to reach this
point is also displayed to help determine a reasonable selection. These entries
in the Test Definition Editor are described in detail in Section 5.5.2.6.
4.2
MANUAL GFS TOOLS OPERATION
Using GFS Tools software, GFS2102 users can setup and run fully automated flow tests.
However, since GFS Tools is the main user interface to GFS2102, frequently users will want
to operate and read parts of the system without conducting a full flow test. Below, several
functions are described that may be done manually using GFS Tools.
4.2.1
READING THE BALANCE
It is necessary to read the balance during setup of the GFS2102 system to ensure that it is
communicating correctly and the positioning of the balance and AMH-GFS2102 allows stable
mass indications. At any time, to quickly get a direct indication from the balance, first run a
diagnostic test using
[Run][Run Diagnostic Test]
. During the diagnostic test initialization,
most of the device setups and pre-test operations are automatically skipped to quickly take
you to a point where the balance output and LCM conditions can be viewed. When the test is
initialized, select the
Balance Interface
from the drop down menu option next to the
[GFS]
display toolbar button. Real time output of the balance is displayed.