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THE HAND
A self-centering, four point hand is used to provide a wide tolerance
for variations in the sample container’s dimensions, weight, and
positioning. The hand features a positive close and grasp design, so
that an unexpected power loss will not cause the sample to drop. The
hand senses the absence of a sample when the hand fully closes and a
sample is supposed to be present. This condition is treated as a fault
condition by the software and results in a safe system shut down.
OPERATING MODES
The system has three operating modes: Master, Slave, and Local. Slave
mode is the most typical the whole sample changer is controlled as a
peripheral device with high level commands such as load#1, loadnext,
reset, unload. Control of the spectral acquisition is through the
MCA’s native script/batch/job language. Responsibility for defining
the sample queue and taking control of the MCA system rest with a
Changer Lab Windows program that runs on the MCA computer system.
In the Master mode the
Assistant's
software is in control of the sample queue and runs the MCA system
through MCA batch commands. Local control allows the user to control
all axis movements with easily accessible switches for set up without
a computer.
SAMPLE WALL
With a significant number of samples loaded into a changer tray there
is always the possibility of a hot sample interfering with the
background of a low level sample. This may require more shielding
between the samples in the tray and the sample in the counting
position than is required in the counting shield in general. In this
situation the system can be supplied with an additional shield wall
between the sample tray and the counting shield.
DETECTOR
ACCOMMODATIONS
The system can be configured for either NaI (Tl) or Germanium detector
systems. Any standard detector cryostat can be accommodated. Vertical
dipstick Germanium detectors have the dewar located underneath the
shield inside the system cabinet, while horizontal dipsticks can have
the end cap penetrate the shield side wall. An "in-line" type cryostat
simplifies the installation and removal of the detector. Well
detectors do not represent any special problems as long as the
container is longer than the well depth so that there is a place for
the hand to grab the sample.
Using two detectors at the same time
is possible, as is a split spectrum with low energy and high energy
spectra accumulated simultaneously from a single detector |
