3. OPERATION
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3.1
GENERAL OPERATING PRINCIPLES
Numerical reference in this section refers to Figure 8.
The purpose of the AMH-38 or AMH-100 system is to automatically load specified values of mass onto
the PG7000 piston. This is accomplished by lifting the complete mass set up off and above the piston-
cylinder to the mass selection position, selecting the individual masses to be loaded and retained, and
then placing the masses to be loaded back onto the piston.
To accomplish the mass lifting, selection and lowering function, the AMH mass handler uses four main
sub-systems. These systems are present in both the AMH-38 and AMH-100 models.
1.
Electronic and electrical controls(7):
The AMH electronic and electrical controls are located
just above the mass lifter, under a protective cap. These support the AMH operating logic, a
proximity sensor to detect mass load position, reading of the main mass selection column
switches, operation of the column rotating motor and actuation of the pneumatic control solenoid
valves.
2.
Mass lifter(8):
The mass lifter is used to lift the entire mass load to the mass selection position
and then to lower the selected masses onto the piston. The mass lifter is pneumatically actuated.
A flexible diaphragm(4) is connected to a lifting assembly(5). A three-way solenoid valve (e.g. 9)
can be actuated to admit or exhaust drive air pressure to and from the volume under the
diaphragm. Admitting drive pressure forces the lifting assembly up. Exhausting the pressure
lowers it. With AMH-38, the pressure is exhausted outside the vacuum chamber, to the AMH
drive vacuum supply when there is vacuum in the chamber.
As the mass lifting assembly (5) rises, it engages a ledge on the mass lifting shaft(6), pushing it
up. The mass lifting shaft is connected to the binary mass carrier(10) and the mass bell(1) sits
on the binary mass carrier. As the mass lifting shaft goes up, it lifts the binary carrier and the bell,
which in turn lifts the main masses(14) and the binary mass tubes(2). When the lifting assembly
reaches the top of its stroke, the entire mass load is lifted completely off the piston cap(12) and
the masses are in the mass selection position. In this position, the ledges on the main mass
selection columns(13) align with the gaps between the main masses and the binary mass
selector pins(e.g. 3) align with the holding grooves in the binary mass tubes. When gas is
exhausted from the volume under the lifting assembly, it descends, lowering the selected masses
onto the piston.
3.
Main mass disc selection columns(13):
The three main mass selection columns are used to
retain the main mass discs(14) that are not to be loaded onto the piston. The columns are
rotated synchronously by a DC motor and a drive belt(11). Contact switches are used to monitor
the column position. Each column has a number of sides equal to the maximum number of main
masses plus one (six sides for AMH-38, ten sides for AMH-100). One side, which retains all the
masses so that none are loaded, has a ledge for each mass. Each subsequent side has one less
ledge, moving from the bottom up. The last side has no ledges and is used to select all the main
masses for loading. When the mass load is lifted to the mass selection position, the motor is
operated to rotate the columns to retain the desired number of masses. The rest of the main
masses are free and are lowered onto the piston when the lifting assembly descends.
Page 19
© 2007 DH Instruments, a Fluke Company
