4. OPERATION
Page 49
© 2007 DH Instruments, a Fluke Company
4.2.2
AMH OPERATION
For several reasons a user may want manual control of the AMH-GFS2102 platform
movement to raise and lower the reference mass or reference gas cylinder. It is helpful to
test the position and movement of the cylinder assembly and AMH during setup of the
system. There are two ways to gain manual control of the AMH, one by using
[Tools][Change GFS AMH State]
within GFS Tools, or to start a diagnostic test as
described above in Section 4.2.1. Select the icon for the GFS display. At the bottom of the
GFS display window the four icons at the right allow access to all three AMH positions, and
an option to continuously cycle the AMH through each position.
4.2.3
BALANCE ZERO AND SPAN ADJUSTMENT
Although the change in mass during an accumulation is more important than the absolute value
of the mass, for a few reasons, it is desirable to zero the balance or to calibrate zero and span on
the balance before the beginning of a test or accumulation. Zeroing the balance before starting
allows easy viewing of the balance’s stability during an accumulation by viewing the size of the
AutoZero correction each time an AutoZero is performed. Running a zero and span ensures that
the slope of the balance output is as accurate as possible in the mass range where it will be
relied on to measure a change in mass.
Icons are available in the GFS Tools, GFS display window that allow a user to quickly run a zero
and span correction on the balance. The reference mass is used for the span and the states of
zero or reference mass loaded are controlled by the AMH automatically so the process is easy
and fast. (See Section 5.1.5.2.3) Users can also set up GFS Tools to automatically perform a
balance zero function before each test or accumulation (see Sections 5.5.2.7, 5.2.2.1), but the
zero and span function is reserved for occasional use and cannot be set to run automatically.
4.3
REFERENCE GAS CYLINDER FILLING
Pressurized gases are potentially hazardous. Energy stored in these gases can be released unexpectedly
and with extreme force. Pressurized systems should be assembled and operated only by personnel who have
been instructed in proper safety practices.
It will be necessary for the GFS2102 user to regularly refill the reference gas cylinders between tests.
Filling of the cylinders is done using the GFS-FS reference gas cylinder fill station. The fill station is
specifically designed for filling the reference gas cylinders at a slow rate so that heating of the cylinder is
minimized. If the cylinder is filled to its working pressure quickly, the cylinder temperature may rise to 50
°
C or more. The cylinders are designed and tested to withstand certain fast filling and levels of heating,
but if the cylinder is heated to extremes the aluminum could separate from the carbon fiber/resin coating
or such temperature instability will cause major GFS flow measurement problems unless the cylinder is
completely cooled. It is better to fill the cylinder slowly and avoid excessive heating. Even after filling
with GFS-FS, the cylinder may require more than one hour to completely cool. Frequent users of the
system will find it efficient to have more than one cylinder of each size that they use so that one can be
refilled and cooled while the other is in use. The following guidelines should be used for reference gas
cylinder refills.
4.3.1
TRANSPORTING THE REFERENCE GAS CYLINDER
ASSEMBLY
The reference gas cylinder assembly is used to contain very high pressure gas and should be
handled with care, especially when it is filled. The risk of high pressure cylinders becoming
projectiles when stems or valves are broken off is well documented. A molded plastic case is
provided with each reference gas cylinder assembly for the purpose of storage and transport.