Technical Description: Inlet
Rapid Multi-Stream Sampler
Thermo Fisher Scientific
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
C-5
The sample arm is driven by a stepper motor connected via toothed
pulleys and drive belt. The pulleys are positively mechanically
attached to their respective shafts so that slippage is negligible. Inlet
position indexing is achieved by optical encoding. An encoder disc is
attached to the main drive pulley on the RMS. The encoder is a
stainless steel disc with a series of holes close to its circumference,
one for each inlet position (the encoder disc has 64 of these holes so,
on a 32-way inlet, moving over one inlet position corresponds to
moving over two encoder holes). An additional hole (located on a
slightly greater circumference) identifies inlet position #1. A pair of
optical transmitter / receiver sets is used to sense the individual inlet
positions and the inlet #1 position respectively.
This type of encoder does not give absolute position indexing. On
startup, the main shaft is rotated slowly so that position #1 can be
located. To move to other inlets, the controller steps the drive motor
to the calculated correct position. At the same time, the second
sensor counts the number of inlet positions moved. If there is a
mismatch, an error is flagged and the position #1 alignment
procedure is repeated. The motion is always clockwise, and position
#1 is checked each time the inlet rotates through this point. This
procedure has been found to give an extremely high reliability in
terms of the accuracy of inlet selection.
Calibration gases are expensive and required on a relatively
infrequent basis. It would clearly be wasteful to have these gases
flowing continuously so additional gas control is required in the
calibration gas lines.
The main control element is a solenoid valve (24 Vdc, normally
closed), located in the calibration gas line before the RMS. The valve
is energized (and the gas allowed to flow) by the inlet controller only
when the gas is required.
The solenoid valves are in manifolds of six valves, the common port
from each manifold connecting to a port on the RMS. This means
that up to six calibration gases can be handled through one port on
the RMS. The manifolds are fitted to the side of the instrument
enclosure (up to 4
six way modules as required). This minimizes
the line length between the panel(s) and the RMS, which in turn
minimizes the flushing time requirement when sampling a calibration
gas. The default connection is for calibration gas #1 through #6 to be
connected to RMS port 32 (or 64), #7 through #12 to port 31 (or 63),
etc. This keeps the low number ports free for sample gas connection
(Sample Line #1 can connect to Port #1, etc.). The tubing material
used for this connection is FEP. This has excellent chemical
resistance and mechanical properties, is non-porous, and has very
favourable adsorption and permeation properties.
Inlet Selection
Calibration Gas
Control
