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Summary of Contents for Wet Labs ac-s
- Page 1 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 F 9 Feb. 2006...
- Page 3 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.
- Page 5 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...
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Page 7: Table Of Contents
Signal Processing ....................25 Appendix A: Data Record Format..............28 Primary Processing ......................30 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 F 9 Feb. 2006... -
Page 9: Instrument Setup And Testing
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: •... -
Page 10: Bench Testing
• 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. -
Page 11: Air Tracking
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. - Page 12 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.
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Page 13: System Requirements
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. -
Page 14: Operation
RS-232 connection into the computer and leads that connect to a power supply. Attach the power leads to a stable power source that supplies 10–35 VDC to the ac-s. Make sure the polarity is correct before switching on the power supply. Connect the RS-232 connector to the desired serial port of the data collection computer. - Page 15 1. Do not make direct contact between the ac-s pressure housing and a metal frame or hose clamp. The ac-s is available in one of two pressure-housing materials.
- Page 16 • Secure the ac-s to a sturdy cage or lowering frame that will protect the instrument from striking the deck, ship’s side, or sea bed. Use a dielectric isolator (rubber sheeting or thick tape) to isolate the instrument’s aluminum case from the steel cage.
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Page 17: Data Collection
Data Collection WET Labs offers several output configuration options to provide flexible interfacing to different systems. These various output protocols are discussed at length in the Data Processing Section of the manual. Unless supplied with a custom output protocol the instrument powers up in a free run mode. -
Page 18: Care And Maintenance
WETView or a WET Labs data logger, consult the Data Processing section of this manual for a detailed description of the binary data format. RS-232: Operating across an RS-232 cable, you can obtain binary data from the instrument. -
Page 19: Data Processing
(hex 00). WETView is capable of processing collected binary files in addition to serial data. If you prefer to use your own software to process the ac-s output data, please refer to Appendix A for a description of the ac-s data packet formatting. - Page 20 The following treatment applies to the absorption case if c is replaced by a. The pathlength of the ac-s is fixed at 25 cm. In the case of the ac-s the transmittance is computed by taking the ratio of the signal value to the reference...
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Page 21: Temperature-Dependent Absorption Correction
Absorption of water shows a temperature dependency that is wavelength-dependent. While existent throughout the visible portion of the spectrum, at infrared wavelengths the effect must be taken into account. With regard to the ac-s, the water absorption temperature effect must be considered to correct the absorption and attenuation at wavelengths above 700 nm. -
Page 22: Scattering Correction
(λ). If the shape of the scattering function does not change much as a function of wavelength, we may assume that k a (λ) is not a function of λ. ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006... -
Page 23: Calibration And Characterization
Calibration and Characterization The ac-s is a dual path absorption and attenuation meter whose output values are related to a specific reference medium that is clean water. The instrument is calibrated to provide a reading of 0.0 for all channels in clean fresh water. The offset value, determined during our calibration process, is the number which, when added to the raw instrument output in clean water, provides zeroes for all wavelengths with the meter at a specific temperature. -
Page 24: Absolute Calibration
Nevertheless, pure water is the baseline for all oceanic property measurements. At WET Labs, we produce our calibration water with a custom de-ionization and filtration system. After de-ionization, the water is processed by a series of filters and held in a 60-liter reservoir that re- circulates through an ultra-violet chamber and additional filters. - Page 25 3. Allow the unit to sit open for an hour or two to assure that it dries. 4. Reassemble and insert flow tubes. 5. Turn on meter and allow it to warm up about 5 minutes. ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
- Page 26 7. Remove flow tube and re-clean the windows. The single wipe technique with ethanol will work fine at this point. 8. Repeat steps 4–6 until mean values stabilize over three cycles. Use these values as air calibration values. ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
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Page 27: Specifications
0.001–10 m Connectors The ac-s has two bulkhead connectors mounted on the top flange. The power and data connector has six pins and connects to the sea or test cable. It provides input power to the instrument and data output in RS-232 and RS-485 formats. A second connector with three sockets provides power to the pump (Figure 3). - Page 28 RS 485 - Voltage supplied to the instrument is internally jumpered to provide power output to the pump port connector. Power is applied to the pump connector whenever the meter is powered. ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
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Page 29: Power Requirements
Lamp 1 2.5 watts Lamp 2 2.5 watts CPU board 0.3 watts A/D board 0.5 watts Motor and controller 0.6 watts Other electronics 0.5 watts DC/DC converters 2.1 watts TOTAL 9.0 Watts ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006... -
Page 30: Technical Reference
Technical Reference Figure 10 shows a diagram of the ac-s. The unit consists of two pressure housings separated by an aluminum “unistrut” frame. The “bottom” pressure cylinder houses the light sources, filter wheel, motor controller and transmitter optics. The “top” can houses the receiver optics and the control and acquisition electronics for the unit. - Page 31 72 degree section of the beam path across the filter wheel. The filter wheel rotates at a tightly controlled 8.0 rps, such that the shorter wavelength of each filter section is traversed before the longer wavelength. Figure 6. ac-s filter wheel 6.2.2 c Beam Optics 1 Lamp...
- Page 32 The a beam sample water volume is enclosed by a reflective flow tube. Light passing through the tube is both absorbed by the water itself and by various pigments contained in particulate matter within the sample volume. Forward scattered light is ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
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Page 33: Electronics
Signal Processing The purpose of the ac-s signal processing circuitry is to take a raw optical signal and make it into a physically meaningful measurement ready for output. Signals from the absorption path and attenuation path detectors go through several levels of analog and digital processing before they are registered as output from the unit. - Page 34 “red” filter is sampled prior to the “blue” filter. That means that the 44 output point was actually sampled 6.25 ms before the first output point. Due ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
- Page 35 Currently this is every 4 revolutions, or twice per second. ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
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Page 36: Appendix A: Data Record Format
Appendix A: Data Record Format The ac-s outputs its data as binary records. If you use a terminal emulator program to connect to the ac-s, the incoming data will appear as seemingly random characters. Table 4 shows a sample hexadecimal snapshot of binary data collected from an ac-s. The leftmost column and header rows in are for reference only, and do not appear in the output data. - Page 37 Bytes Data Description ff00ff00 Packet registration Record length of full packet (not including chksum) = 720 02D0 Packet Type 03 and above designates an ac-s meter reserved meter type—53 indicates an ac-s serial number 000002 A reference dark counts 4e1a...
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Page 38: Primary Processing
Primary Processing When receiving binary packets from an ac-s, the first thing to look for is the packet registration, which is four characters. The characters, in hexidecimal notation, are FF 00 FF 00. After successfully receiving these characters, the 2 byte packet length is the next item to be received. - Page 39 16 bit sum of all characters sent in the packet, including the identifier (FF 00 FF 00) and up to the last data byte preceding the checksum field. One pad character (00) is sent following the checksum, before the next packet identifier is sent. ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
- Page 40 Figure 10. ac-s system diagram ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
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Page 41: Appendix B: Pressure Sensor Use And Care
Appendix B: Pressure Sensor Use and Care A pressure sensor is available as optional equipment on the ac-s. It is mounted in the top flange next to the electrical connectors. A plastic fitting and capillary tube, both filled with silicone oil, provide a buffer between the pressure transducer and seawater. The transducer is both sensitive and delicate. -
Page 42: Appendix C: Common Mode A/C Induced Noise
Appendix C: Common Mode A/C Induced Noise The ac-s can be susceptible to common mode noise caused by environmental alternating current (A/C) generated electromagnetic fields. Most typically, this will be caused by 60 Hz A/C power wiring in a laboratory or ship environment. This noise can cause large measurement errors in situations where the meter does not have an adequate earth ground. - Page 43 Add ac-9 Protocol Document to list of delivered R. Watte items (DCR 465) 1/13/06 Clarify warranty statement (DCR 481) A. Gellatly, S. Proctor 2/9/06 Correct output precision value (DCR 486) B. Rhoades, H. Van Zee ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006...
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