Maintenance
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8.2 Emitter and receiver
8.2.1 Cleaning the mirrors and windows
The protective windows are made of quartz, and cleaning causes no problems. Dirt and
grease can be removed using a soft cotton cloth with acetone or pure alcohol.
The mirrors are made of a thin layer of aluminium which is sputtered onto a quartz sub-
strate. To protect the highly reflective aluminium surface from dirt and oxidation, and to
obtain a high reflectance in the short ultraviolet wavelength region, the mirrors are coated
by a layer of magnesium fluoride, MgF
2
.
Magnesium fluoride is a salt which is soluble in most liquids, including water. Therefore,
any dirt finding its way onto the mirrors should remain there. Loose dust may be removed
gently with a dry, soft, cotton cloth or a photographer’s lens brush.
The reflective surface is affected by the moisture which is present in the atmosphere. After
some time, the surface may become somewhat greyish, and this will affect the amount of
light reaching the analyser. Therefore, after a few years, it may be necessary to replace one
or both of the mirrors.
8.3 Autocalibration units
Under normal conditions the calibration unit requires low maintenance. The following ac-
tions are recommended to be taken once a month:
• Check the function of all valves through the software in the gas analyser. Please re-
fer to the software manual for further instructions.
• For each gas, make sure that the gas flow through the flow meter (item 5, figure 3.2)
has not changed.
• Disconnect the output line and check for contamination (oil, grease, dirt etc.). If
found, investigate the reason for it immediately. Replace all contaminated gas lines.
• Leak-check all connections to the unit by means of leak testers or simply by soap
water. Immediately close any gas supply to a leaking line, ventilate the area, and
take corrective actions.
• Ensure that the input pressure is below 3.5 bar (50 psi) on all lines by looking at the
pressure regulators at the gas cylinders.
• Check inside the unit for possible dust, leakage, loose connections, etc.
NOTE: The magnesium fluoride coating on the mirrors is very sensitive. It must not be
touched or cleaned with liquids.
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