5-6
Model 3786 Ultrafine Water-based Condensation Particle Counter
H i g h o r L o w P h o t o m e t r i c R e a d i n g s
A good check of the instrument’s “optical health” is the raw “Photo”
value displayed on the status screen. The baseline value should be
between about 150 and 280 when the instrument is warmed-up and
the pump is off (no flow). Lower values than this should only occur
during warm-up when the photo detector has not reached its
operating temperature. Values higher than this range may occur
before the instrument has reached operating temperature or the
optical background light has increased. A typical symptom of water
in the optical system (flooded optics) is a very high photometric
baseline value. High background light can be confirmed by turning
off the laser and observing the resulting baseline value. The laser
can be turned off using a computer connected to the UWCPC that is
running a terminal emulation program. The command SL,0 will “Set
Laser” to off and a SL,1 command will turn the laser on. Powering
up the instrument will also turn on the laser. When the laser is
turned off, there is no background light so if the baseline
photometric value returns to a normal range, it is likely that water or
other contaminates are present in the optical system. Apply the
following steps as the first approach to drying a flooded optical
system:
1.
Drain the UWCPC reservoir.
2.
Remove the wick.
3.
Disconnect the fill bottle.
4.
Disconnect any sample source from the sample inlet.
5.
Operate unit with pump on in a dry environment for at least 10
hours.
Drying the optics should return the baseline photometric value to its
normal range. Flooding of the optical system will likely leave
residues on the optical surfaces which may affect the photometric
calibration. Reinstall the wick, connect the Fill Bottle, and reprime
the unit with water before returning it to operation. For cleaning and
recalibration contact TSI and arrange for factory service.
