Wet Labs ac-s User’s Guide
Spectral Absorption
and Attenuation Meter
ac-s
User’s Guide
WET Labs, Inc.
P.O. Box 518
Philomath, OR 97370
541 929-5650
www.wetlabs.com
ac-s User’s Guide (ac-s) Revision H 21 May 2008
Attention!
Return Policy for Instruments with Anti-fouling Treatment
WET Labs cannot accept instruments for servicing or repair that
are treated with anti-fouling compound(s). This includes but is not
limited to tri-butyl tin (TBT), marine anti-fouling paint, ablative
coatings, etc.
Please ensure any anti-fouling treatment has been removed prior to
returning instruments to WET Labs for service or repair.
ac-s User’s Guide (ac-s) Revision H 21 May 2008
ac-s Warranty
This unit is guaranteed against defects in materials and workmanship for one year from
the original date of purchase. Warranty is void if the factory determines the unit was
subjected to abuse or neglect beyond the normal wear and tear of field deployment, or in
the event the pressure housing has been opened by the customer.
To return the instrument, contact WET Labs for a Return Merchandise Authorization
(RMA) and ship in the original container. WET Labs is not responsible for damage to
instruments during the return shipment to the factory. WET Labs will supply all
replacement parts and labor and pay for return via 3rd day air shipping in honoring this
warranty.
Shipping Requirements for Warranty and Out-of-warranty Instruments
1. Please retain the original shipping material. We design the shipping container to
meet stringent shipping and insurance requirements, and to keep your meter
functional.
2. To avoid additional repackaging charges, use the original box (or WET Labs-
approved container) with its custom-cut packing foam and anti-static bag to return
the instrument.
• If using alternative container, use at least 2 in. of foam (NOT bubble wrap or
Styrofoam “peanuts”) to fully surround the instrument.
• Minimum repacking charge for ac meters: $240.00.
3. Clearly mark the RMA number on the outside of your shipping container and on
all packing lists.
4. Return instruments using 3rd day air shipping or better: do not ship via ground.
ac-s User’s Guide (ac-s) Revision H 21 May 2008
Table of Contents
1. Instrument Setup and Testing ......................................................................... 1
1.1
Installing WETView ................................................................................................ 1
1.2
Bench Testing .......................................................................................................... 2
1.3
Air Tracking ............................................................................................................. 3
1.4
Cleaning ................................................................................................................... 3
1.5
System Requirements............................................................................................... 5
2. Operation ........................................................................................................... 6
2.1
Basic Power On........................................................................................................ 6
2.2
Mounting and Deploying the Meter ......................................................................... 6
2.3
Data Collection ........................................................................................................ 9
2.4
Care and Maintenance............................................................................................ 10
3. Data Processing .............................................................................................. 11
3.1
Analog Acquisition ................................................................................................ 11
3.2
Analog-to-Digital Conversion ............................................................................... 11
3.3
Digital Processing and Data Output ....................................................................... 11
3.4
Data Format ........................................................................................................... 11
3.5
Post Processing ...................................................................................................... 11
3.6
Temperature-dependent Absorption Correction .................................................... 14
3.7
Scattering Correction ............................................................................................. 15
4. Calibration and Characterization ................................................................... 16
4.1
Temperature Correction ......................................................................................... 16
4.2
Precision ................................................................................................................. 16
4.3
Absolute Calibration .............................................................................................. 17
4.4
Linearity and Dynamic Range ............................................................................... 17
4.5
Air Calibration and Tracking ................................................................................. 17
5. Specifications ................................................................................................. 20
5.1
Connectors ............................................................................................................. 20
5.2
Power Requirements .............................................................................................. 22
6. Technical Reference ....................................................................................... 23
6.1
Mechanical ............................................................................................................. 23
6.2
Optics ..................................................................................................................... 23
6.3
Electronics.............................................................................................................. 26
6.4
Signal Processing ................................................................................................... 26
Appendix A: Data Record Format ...................................................................... 28
Primary Processing ............................................................................................................. 29
Appendix B: Pressure Sensor Use and Care.................................................... 33
Appendix C: Common Mode A/C Induced Noise ............................................. 34
ac-s User’s Guide (ac-s) Revision H 21 May 2008 i
1. Instrument Setup and Testing
This section provides an introduction to the ac-s and describes how to set up and perform air
tracking and bench testing prior to deploying the ac-s.
The ac-s is delivered in a sturdy wooden shipping container with the following components:
• ac-s, with one absorption flow tube and one attenuation flow tube
• four flow sleeves
• four protective black plastic caps
• dummy plug with lock collar
• this manual
• WETView User’s Guide
• additional reference: ac-9 Protocol Document
• WETView software and instrument-specific calibration information
• Ten-foot test cable
• double “Y” de-bubbler tubing
• stainless steel intake screens
Familiarize yourself with the ac-s: remove the black plastic flow tubes by grasping the
flow tube sleeves and sliding them away from the ends of the flow tube (toward the
middle of the flow tube). You only have to slide the collars about ½ in. to unlock the flow
tube from its fixed position. The flow tube will lift out, exposing the transmitter and
detector windows on the lower and upper flanges respectively. Observe the flow tubes.
The attenuation tube is different from the absorption tube. Its flow chamber is plastic and
the two sleeves on the tube are identical. This tube installs on the “c” side of the
instrument (the side with the identical looking windows). The “c” tube has no “up or
down” orientation. The absorption tube is lined with a quartz tube and one of the two
sleeves is flat on top (the lip present on all the other sleeves is missing). This tube installs
on the “a” side of the instrument, which can be identified by the “a” detector on the upper
flange and is the only window, which is clearly different from the other three. The flat
flow tube sleeve goes on this detector.
You may want to mark the tubes and their orientation with tape or marking pen before
using the instrument at sea so there is no confusion upon reinstalling the tubes after
cleaning the optics. Reinstall the flow tubes before bench testing your instrument. If you
have removed the plastic caps from the stainless nozzles, replace them at this time.
1.1 Installing WETView
WETView displays data produced by WET Labs ac meters. It runs on PC-compatible
computers with at least 16 Mb of memory and 3 Mb free hard disk space running
Windows-95 or later operating system.
1. Insert the WETView CD in the host computer.
2. Double-click on the SETUP.EXE icon. Setup will guide you through the rest of the
installation process.
ac-s User’s Guide (ac-s) Revision H 21 May 2008 1
When installed, the following files should be on the hard disk: WETVIEW.EXE,
WETVIEW.UIR, ACSXXX.DEV, AIRXXYYY.CAL. The .DEV and .CAL files are the
calibration files for your particular instrument. They are not installed by setup and will
need to be copied to the hard drive manually.
Caution
If you have old device files from previous calibrations, you should rename them or
archive them in a different directory so that they will not be overwritten.
1.2 Bench Testing
The following items are needed to bench test the ac-s:
• A clean, solid lab table or work bench
• The ac-s with 10-foot test cable (or sea cable)
• A 10–35 volt power supply (the ac-s requires 10–35 VDC)
• A PC with WETView installed.
1. Connect the test cable to COMM1–COMM4 of the computer. Connect the power
leads to the power supply. The black lead is the V+ lead. Before connecting the cable
to the instrument, use a multimeter to check the input power.
2. Connect the ground probe to pin 1 on the pigtail connector (the center pin as you are
looking into the connector). Connect the hot probe to pin 4 (Figure 4). You should
measure the power supply voltage across these two pins.
3. Turn the power supply off.
4. Connect the pigtail to the instrument. Push the connector straight on to avoid
damaging the pins. Apply power to the instrument and allow it to begin warming up.
5. Run WETView. When the interface is displayed, you will need to provide a .DEV file
name. Click on the <O> button in the center top of the screen or choose “Open
Device File” from the File Menu at the top left of the screen. The program will ask
you to choose the proper COMM port. Select COMM1 through COMM4 as
appropriate. Note that WETView supports COMM1 through COMM4 only.
6. Click on the center button or <F1> to start displaying data. After 5–10 seconds,
tabular data should be displayed on the right side of the screen. A real time graph will
begin to develop, depending on the graph parameters set at the time. Refer to the
WETView User’s Guide for details of running the WETView software.
7. After a short time, again click on the center button that will stop the data collection
and ask for a file name to apply to the data if you should want to archive it. Press ESC
if you do not want to save the data. To quit the program, choose QUIT from the File
menu. At this point you have successfully completed a bench test of the instrument.
2 ac-s User’s Guide (ac-s) Revision H 21 May 2008
1.3 Air Tracking
WET Labs provides an air calibration (.CAL) file similar to the device (.DEV) file and
can be applied in WETView in the same manner. The DEV file provides the clean water
offsets so that when measuring clean, fresh water, the instrument’s output should be very
nearly 0.0 for all channels. The .CAL file provides the offsets that provide 0.0 values
when the instrument is clean and dry and measuring air values. This is a useful tracking
tool for catching instrument drift, filter aging and improper cleaning.
When you install WETView, the latest air .CAL file should be transferred to your
WETVIEW directory. The name of the file takes the form AIRXXYYY.CAL where XX
is the calibration number; YYY is the instrument serial number.
When a .DEV file is opened in WETView, it will display *.DEV in the dialog box, which
will list all the .DEV files on the default drive. If you change the *.DEV to *.CAL, the
available .CAL files will be displayed. Select the latest .CAL file and start collecting
data. Make sure the black plastic caps are installed on the flow tube nozzles so no
ambient light can enter the flow tubes. If the instrument is clean and dry, the values
displayed in WETView should be very close to 0.0 (within 0.005–0.01). If the values are
within this range, the instrument is clean and ready to deploy. If the values are outside
this range, the first step is to re-clean the instrument and then reapply the .CAL file
offsets.
1.4 Cleaning
1. Remove flow tubes and all O-rings. Remove the sleeves from the flow tubes. Wash
the windows with a mild detergent diluted with distilled, reverse osmosis-filtered
(RO) or de-ionized (DI) water and rinse the flow tubes. Use Kimwipes or other lintfree tissues to wash the windows. Rinse the meter off completely with water to ensure
no soap residue is left inside the flow tubes or on the windows.
2. Dry the meter. Place the instrument in a protected area where it can dry completely.
Using a small heater to blow warm air over the meter may help speed the process.
Using dry nitrogen to blow-dry the meter and remove water from the small grooves
around the windows will also help speed the process. It is suggested that the
instrument be left overnight to dry out completely. Reassemble the meter. Carefully
replace O-rings and slide collars back on to the flow tubes. Replace O-rings around
the windows.
3. Clean windows using a Kimwipe or lens paper. Place a couple of drops of methanol
or ethanol on the Kimwipe. With firm pressure, gently wipe the windows with
methanol. This should remove any visible streaks on the windows. If necessary,
follow with a dry wipe in one direction across the window face. Blow off any lint or
dust with a dry air source.
4. Clean the flow tubes by putting a few drops of methanol on a Kimwipe and, using a
wooden dowel rod, carefully slide the Kimwipe through the flow tube. Repeat this
ac-s User’s Guide (ac-s) Revision H 21 May 2008 3
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.
4 ac-s User’s Guide (ac-s) Revision H 21 May 2008
1.5 System Requirements
This section explains the basic system components necessary to operate the ac-s. Note
that components will vary depending on whether the ac-s is used for profiling, on a
mooring, or underway flow.
Instrument
The ac-s and its flow tube assembly form the basic optical sensor.
Pump
The flow-through system will typically require an ancillary pump to assure proper
operation. Pump requirements depend upon desired flow rates, required depth of
operation, power availability, and existing hardware.
Cabling
The ac-s requires a minimum of four conductors for power and RS-485 output. (Three
conductors for RS-232 output).
Power Supply
The ac-s requires a 10–35 VDC supply, capable of providing a minimum of 10 watts
continuous output. Additional wattage will be required to also drive a pump from the
same supply. If a longer cable is used, power losses must be accounted for in determining
the power supply voltage and power requirements.
Serial Communications
Data from the ac-s is transmitted via both RS-232 and RS-485 depending on which
sockets are connected to the instrument’s bulkhead connector. Regardless of the mode of
transmission you use, you must have a serial interface on your computer or data logger
capable of accepting data from the instrument at a rate of 115,200 baud. If you have an
instrument with RS-485 output and are using a computer with standard RS-232
communication ports or USB ports, optional protocol converters can be readily obtained.
Host/Data Logger
The ac-s can be interfaced to any computer or data logger capable of supporting a
115,200 baud rate serial interface. If you plan to use our WETView software acquisition
package you will need a computer running Windows 95 or newer.
Software
The WETView host software package interfaces directly to the ac-s via your computer
serial port. WETView allows real-time graphical visualization of the data in any of
several ways such as a function of time, depth, or wavelength. WETView automatically
applies calibration constants, temperature corrections and generates a tab-delimited
ASCII text file that can be imported into programs such as Excel or MatLab for postprocessing or manipulation.
ac-s User’s Guide (ac-s) Revision H 21 May 2008 5
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