Oil Condensing within the Photometer

There are some common causes for oil condensing within the photometer and some less common ones. If operators see liquid in the sample tubing, it is also present inside the unit.

They are, in no specific order, with some detail:

1. Frequent sampling of upstream aerosol concentration
   - Sampling upstream before and after testing
   - Periodically sampling upstream without need
2. Sampling upstream aerosol concentration for prolonged periods of time
   - Sampling upstream for longer than needed to set 100% level
   - Sampling upstream to observe aerosol level
3. Lengthy upstream sample lines
   - Lines > 12 feet lead to aerosol loss during transport
4. Shorter is better
5. Small ID upstream sample lines
   - Sample line ID < 0.25 inches lead to aerosol loss
6. Larger is better
7. Changing in sample tubing diameter
   - Increases and decreases in diameter through sample path will increase aerosol loss
8. High upstream concentrations
   - Upstream sample levels ≥100µg/l
9. Lower upstream aerosol levels decrease the unit exposure
10. 10 to 20 µg/l is sufficient in most cases
    - Sample “raw” aerosol before fully diluted with system air flow
11. One extreme example would be testing the photometer response by directly sampling the generator output

*References to “loss” of aerosol are generally the result of aerosol oil droplets falling out of the airstream and/or impacting the transport tuning surface.
**Items 1 and 2 are the most common. The others occur with varying levels of frequency.