Revision 1 22 9/10/2019
2.6.1 Rate/Read Aperture Strip and the Rear
Window Assembly
The Rate/Read Aperture strip and the Rear Window are made of a clear plastic to allow the
light from the sensor block to pass through to the tape to correctly measure the rate of color
change on the tape. The sensor block is held onto the sample chamber via clips; by
tightening the screws on the clips, the rear window is pressed into the rear window rubber
gasket and sealed to the sample chamber by pressure from the sensor block above it. The
rate/read aperture strip is sealed to the inside of the sample chamber using silicone grease.
The sample flow through the sample chamber assembly is shown in Figure 2-6.
Figure 2-6: Sample Flow
Clean, humidified, and flow-regulated sample enters the sample chamber from the sample
inlet and passes over the Rate/Read Aperture strip, behind the rear window. Some of the gas
passes through the aperture strip and onto the sesning tape, causing a measurable color
change. The tape is held firmly against the sample chamber by the compression head. The
amount of gas that passes onto the tape is dependent on the size of the aperture strip. After
the gas passes over the tape, it is vented.
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