At initial set-up the optical alignment of the photoacoustic detector to the FTIR infrared beam should be checked and adjusted if necessary. A liquid crystal infrared imager is supplied by MTEC for this purpose. The imager is placed in the sample holder and provides a clear direct image of the infrared beam's focal spot location. The detector should be aligned in the FTIR sample compartment by centering the focal spot in the sample holder. Kinematic detector mount positioners are supplied by MTEC and should be secured in place to register the detector alignment position so that future re-installation does not require alignment. Note that if the FTIR spectrometer in use has provision for automatic alignment of the interferometer, this alignment routine should be done prior to placing the photoacoustic detector in the FTIR. The spectrometer's own detector should be used because it has the correct position and active area size for the alignment procedure.
An FTIR-PAS signal-to-noise performance test should yield a peak-to-peak noise of less than 0.2% at 2000 cm-1 for the conditions given in Table 3.

Some FTIR systems may not allow exact duplication of these parameters and may not perform well enough to fully meet this noise specification. Others will exceed this specification. The adjustments that will most likely improve FTIR-PAS system performance (when necessary) are alignment of the FTIR beam splitter, and tune-up of the FTIR's mirror velocity stabilizing servo-loop at low velocities.
The reproducibility of helium purging can be tested by reloading and purging the carbon black reference several times and comparing the reproducibility of spectra. Purge times of 10 seconds before and after sealing the sample cup at a flow rate of 10 cc/sec of helium are adequate for most applications where the sample has a low moisture level. The reproducibility of sample loading can also be checked by reloading and again comparing the reproducibility of spectra.