Wet Labs ac-s, User Manual

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4 ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006
procedure with both flow tubes. Examine each flow tube when you are through to
ensure there are no streaks or small pieces of lint left on the inside of the flow tube.
5. Dry the windows. Since small amounts of moisture can affect the air readings, it is
important to ensure the meter is completely dry. Using nitrogen to blow dry the
windows immediately before replacing the flow tubes works very effectively. This
will remove any water or methanol trapped in the small grooves around the window.
6. Replace the flow tubes. Carefully slide the flow tubes into place without sliding dirt
across the windows. Slide the sleeves up around the windows and over the O-rings,
making certain they are firmly in place and aligned correctly. Use small black caps, or
black electrical tape, over each of the nozzles on the flow tube to provide a dark
environment and to keep the meter clean and free of moisture while obtaining data.
7. Turn the meter on and allow it to warm up for at least 15 minutes. When the meter is
stable you should be able to collect 10 minutes worth of data and the values should
not vary more than 0.005 m
-1
over the 10-minute time period.
8. Collect data. Record a one- to two-minute file and save data. Repeat steps 4–6 until
you can collect three data files, cleaning the windows after each file, such that the
average values for each channel vary by no more than 0.005 m
-1
.
The meter is calibrated over a specific range of internal temperatures (refer to your
calibration sheet). If the meter’s internal temperature is higher than the maximum
calibration range, it may be operating out of spec. Setting the meter in a shallow pan of
water (immerse most of the lower can) can help keep the instrument cool. This process
should be repeated until the air values are within specification. This may take three or
more iterations but is very important to be done carefully before taking your instrument
to sea. The air calibration procedure should be done again at the end of a cruise or data
collection period to track the instrument’s performance over time.
Note
The ac-s time averages its dark offsets. If the flow tubes are removed, incoming light
corrupts the dark readings. Following flow tube replacement while the meter is still
running, either wait three minutes for the dark offsets to stabilize, or cycle the power to
the instrument, resetting the dark offsets.