Preventive Maintenance
Lamp Replacement
Thermo Fisher Scientific
Model 49
i
Primary Standard Instruction Manual
4-3
2. Loosen the knurled nut around the tube and carefully slide out tube.
3. Push a piece of lens paper down the tube using a 1/4-inch piece of
Teflon® tubing so as not to damage the tube. Use a cotton swab to clean
the window surfaces through the holes that the tube fits into.
4. Both absorption tubes are identical, so they can be replaced in either
position. Replacement of absorption cells is opposite to that of removal.
Since the Model 49
i
Primary Standard is a ratio instrument, and
cleaning the absorption tubes does not affect the calibration, it is not
necessary to recalibrate the instrument every time the cells are cleaned.
5. Re-install the instrument cover.
If windows are severely contaminated, they are best cleaned by removing the
windows from the bench. The windows on the detector side can be removed
by removing the detector block and carefully removing the windows. The
windows on the source side can be removed by removing the source block to
gain access to the windows. It is recommended that the Model 49
i
Primary
Standard be recalibrated if the optical bench has been completely
disassembled. Always leak-check the system after any component removal.
Lamp Replacement
The lamp control system of the Model 49
i
Primary Standard has been
designed to operate the lamp conservatively to increase its life. However, the
lamp should be replaced when any one of the following conditions occur:
•
No light output.
•
Inability to adjust lamp position to obtain an output detection
frequency of 65 kHz.
•
Noisy output signal, which has been traced to an unstable lamp (see the
“Troubleshooting” chapter).
It is not necessary to recalibrate the Model 49
i
Primary Standard since it is a
ratio instrument and replacing the lamp does not affect the calibration.