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Haverford College
Department of Chemistry

Changing the Internal Desiccant in Perkin-Elmer Spectrum 1000 IR Spectrometers

Introduction

The sealed optics chamber in this instrument is protected from moisture and carbon dioxide build up by the presence four disposable packets containing desiccant that are located in a removable holder in the sealed optics chamber, within the instrument's main housing. The instrument is programmed to provide a screen message upon start up that will inform the user that it is time to replace the old desiccant packets with fresh new ones. The replacement cycle can vary from 4 to 6 months, depending on local environmental conditions, and our instruments are presently set on a 6 month cycle.

Procedure

  1. In order to gain access to the sealed internal optical chamber, it is necessary to loosen the captive Allen head screw that secures the main instrument housing cover in place. This screw is located just under and to the right of the the sample compartment door.

  2. After completely loosening this captive screw, you will note that the main cover is now slightly raised above its normal position, and it can be opened. Before opening the cover, however, slide the entire instrument forward toward the front edge of the bench in order to provide sufficient clearance for the cover to stand open safely and securely without falling.

  3. With the cover open, part of the electronics, including the internal cooling fan, will be turned off by a pressure sensitive switch (white plastic located on the right inside surface of the instrument) that is released when the cover is lifted. If required (this should only be done by trained service personnel), this safety feature can be bypassed by lifting this white plastic switch in an upward direction. This is generally done when the procedure is completed to check and confirm that the laser beam's path has not been blocked during the desiccant changing procedure.

  4. The dessicant packets, as they come from the manufacturer, will not always fit properly into the holder, and it is generally necessary to mold the packages by hand and flatten them before attempting to insert them.

  5. The holder that contains the desiccant in the sealed optics chamber is removed by unloosening the two screws holding the top metal plate of the holder to the plastic optics chamber. Once the screws are loose, lift the holder up and out of the instrument. Open the holder by taking off its one removable side. Remove the four old packets of desiccant aside so you don't mix them up with the new ones. Insert the new desiccant packets into the holder, starting from the right and working towards the left, being certain that no part of the individual packets protrudes through the holes in the holder (doing so will sometimes block the path of the laser beam) and that the plastic tube in the holder is not kinked or otherwise constricted.

  6. Once the four packets have been properly fitted into the holder, replace its removable side, and be certain that both the left and right holding tabs have been snapped back into place securely.

  7. Place the holder containing the fresh desiccant back into the optical chamber, align the screws, and tighten (don't overtighten) them sufficiently to insure that the rubber gasket been compressed enough to seal the optical compartment from the environment. Bypass the electrical switch mentioned above, then open the sample compartment an place an object in the sample path. The red dot that you see on the object indicates that the path of the laser beam has not been obstructed. Turn off the switch, and carefully lower the main housing cover down onto the captive screw that holds it in place. The cover will lower to its normal position as you tighten the holding screw, and the pressure sensitive switch will also be turned on as the cover is lowered into final position. Note that the small orange-yellow indicator light on the front right hand side of the instrument is now glowing once again.

  8. Pull down the "Setup" menu on the Spectrum software screen by clicking on it, then select "Instrument." Within the window that appears, click on "Adjustments," then within the next window, click on the "Clock" icon. In the window that appears, verify that the time and date shown are correct, then in the lower left part of the window click on the open "Desiccant changed" box so an "X" appears with in it. Click on OK to close this dialog, thereby updating the program to show when the next "Change desiccant" will automatically appear on screen.

  9. This completes the procedure, and the instrument is once again ready for routine use.