2. SYSTEM OVERVIEW
Page 7
© 2007 DH Instruments, a Fluke Company
The reference mass is approximately 2.0 kg, which is close to the mid point between a full 1.1 liter
reference gas cylinder and an empty 1.5 liter reference gas cylinder, so that the balance is checked and
corrected for drift at a mass load that is close to the cylinder mass being measured. The balance
readings are then corrected for any drift that has occurred since the last time a balance zero or AutoZero
were checked.
Figure 3.
AMH reference mass plate
AMH-GFS2102 lifts the reference gas cylinder vertically only 3 mm when unloading it from the balance so
that the gas flow is not disturbed and no unnecessary deflection of the gas conveyance loop takes place.
The standard balance mass tray has been replaced with a custom mass tray that uses a three point
locating system to assure consistent physical placement of the reference gas cylinder on the balance
during and after each balance AutoZero process (see Section 4.1.3).
Figure 4.
Balance mass tray supporting the reference gas cylinder
The reference gas cylinder and reference mass are loaded and unloaded from the balance by two AMH
plates that are keyed to lift one of the components when the plate is raised and allow it to rest on the
balance when the plate is lowered. The plates move vertically along two posts on the AMH base that
orient them, and are raised and lowered by three cams on two shafts in the AMH base which contact
rollers that support each plate. A small motor is included in the AMH base to turn the shafts, which are
actuated by 12V valve drivers in the LCM.