Teledyne 6200A - Sulfides analyzer - Manual (Page 201)

TAI Model 6200A SO
2
Analyzer Operator Manual, 02164, Rev. G
9.4 Optical Sensor Module Troubleshooting
9.4.1 PMT
The PMT detects the light emitted by the secondary emission of the SO
2
molecules. It has very
high gain and low noise to detect the weak light source optimally. It is not possible to test the
detector outside of the instrument in the field. The best way to determine if the PMT is working
is by using Optic test. OT operation is described in Section 9.1.3.3.
The basic method to diagnose a PMT fault is to eliminate the other components using ET, OT
and specific tests for other sub-assemblies.
9.4.2 UV Lamp Adjust or Replacement
As the UV lamp output changes, the SO
2
concentration will change. There are four main types of
energy changes or fluctuations associated with the UV lamp:
1. Line voltage changes - UV lamp energy is directly proportional to the line voltage.
Lamp short term drift - Over a period of hours, the UV emitted from the lamp may increase or decrease
slightly.
2. Lamp aging - Over a period of months, the UV energy will show a downward trend, usually
30% in the first 90 days, and then a slower rate, until the end of useful life of the lamp, 2-3
years nominally.
3. Lamp positioning - The physical alignment of the lamp in its holder (which is optimized by
PEAKING the lamp, originally at the factory) may be disturbed.
To adjust or to replace the UV lamp, proceed as followings;
1. Loosen the thumbscrew to allow the lamp to move freely. Replace the lamp if needed.
2. Adjust the POT on the UV reference preamp to the minimum. The preamp assembly is
located at the opposite end of the UV lamp assembly. Remove the cover by loosening two
screws.
3. Slowly rotate or move the lamp vertically while monitoring the UV LAMP display to read
maximum value.
4. Finger tight the thumbscrew.
Adjust the POT to approximately 3500 mV.
Place the cover of UV reference preamp assembly.
5. Perform lamp calibration as described in Section 9.1.6.
9-58