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3.2.9.2.
Gas Cells
Sampled air never flows through the FTIR Optics Bench. Instead, the samples flow
through a gas cell. The infrared beam from the FTIR Optics Bench passes through a
window on top of the bench, which is reflected by mirrors and directed into the gas cell.
The infrared beam passes through windows in the gas cell, where the gas molecules in
the sampled air absorb infrared radiation at wavelengths specific to each gas type. Mirrors
focus the beam exiting the gas cell on the Optics Bench to a detector, which collects the
signal for analysis.
Most ACM 150 applications are for TLV-TWA level monitoring, which requires higher
sensitivity. The detection is at the low ppm and, sometimes, sub-ppm levels.
As the path length increases, more gas molecules come in contact with the infrared beam.
For this reason, the path length of the gas cell is directly proportional to the detection
sensitivity. The standard gas cell used in the ACM 150 monitor has a path length of 5
meters. Transfer optics and adjustable mirrors below the cell focus and direct the infrared
beam into the cell and out to the detector.
The beam enters and exits the gas cell through windows at the bottom. It is reflected and
forth by the internal mirrors at the top and bottom, making multiple passes through the gas
cell. The mirrors have a highly reflective gold coating.
The gas cells mount to a plate that bolts to the FTIR Optics Bench.
3.2.10. Touchscreen computer assembly
3.2.10.1.
Computer assembly
The computer is a single assembly panel mounted on a door that swings out for access.
The rear view of the computer assembly below shows the power and interconnecting
cables. The computer connects to the FTIR optics bench via the SBC computer, receiving
its data constantly. Cables connect it to all the valve and relay circuit boards. The computer
directly controls all I/O functions. A connector is provided for interface via TCP/IP to
internal networks or external computers via the Internet.
3.2.10.2.
Touchscreen
The computer has an integral touchscreen on the front, which serves as the user interface
for the ACM 150 monitor. A typical display is shown below. Remote users have the same
computer display but use the mouse instead of touch.
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