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OBS-5+ System

7. Calibration

7.1 Sediment and NTU Calibration

In addition to the concentration, the size, shape, and reflectivity of suspended
sediment particles vary from one location to another and will influence OBS-
5+ measurements. When these sediment characteristics change, they will
produce apparent changes in SSC by themselves unless sediment calibrations
are performed. All sediments produce a unique set of calibration curves like
the examples shown in FIGURE 4-4. The sediment calibration procedure is
complicated, and for a modest fee, we will calibrate an OBS-5+ sensor with
your sediment. Call for a quotation to perform this service.

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Содержание OBS-5+

Страница 1: ...OBS 5 System Revision 11 13 C o p y r i g h t 2 0 0 8 2 0 1 3 C a m p b e l l S c i e n t i f i c I n c ...

Страница 2: ......

Страница 3: ...removing reinstalling and shipping defective products to Campbell Campbell will return such products by surface carrier prepaid within the continental United States of America To all other locations Campbell will return such products best way CIP Port of Entry INCOTERM 2010 prepaid This warranty shall not apply to any products which have been subjected to modification misuse neglect improper servi...

Страница 4: ...ng container Campbell Scientific s shipping address is CAMPBELL SCIENTIFIC INC RMA _____ 815 West 1800 North Logan Utah 84321 1784 For all returns the customer must fill out a Statement of Product Cleanliness and Decontamination form and comply with the requirements specified in it The form is available from our web site at www campbellsci com repair A completed form must be either emailed to repa...

Страница 5: ...s 6 6 Operation 7 6 1 Instrument Setup 7 6 1 1 Mounting Suggestions 7 6 1 2 Surveys 7 6 1 3 Logging Data 8 6 1 4 Battery Installation 8 6 2 OBS 5 Utility Software 9 6 2 1 Software Installation 9 6 2 2 Running the OBS 5 Utility 10 6 2 3 Pull Down Menus 11 6 2 4 Communication Settings 11 6 2 5 Testing Sensors 12 6 2 6 Monitoring Turbidity NTU 13 6 2 7 Water Density and Barometric Corrections 13 6 2 ...

Страница 6: ...s top sensor endcap with copper antifoulant Cu a f collars left and connector endcap right 2 4 2 Schematic of optical system 3 4 3 Sample calibration curves fine and bold lines lookup tables I II and III bold curves and sediment concentrations pf ND open arrow and FD solid arrow peaks 4 4 4 Calibration curves for four different sediments and SSC values for near detector peaks colored arrowheads 5 ...

Страница 7: ...ls 36 10 3 Effects of disaggregation methods 37 Tables 6 1 Working and Maximum Depths 7 7 1 Schedule of Concentrations for Sediment Calibrations 23 7 2 SSC Calculation Spreadsheet 23 9 1 Battery Life in Hours with 100 Power 33 10 1 Relative magnitude of the effects of sediment characteristics on OBS 5 sensitivity 34 iii ...

Страница 8: ...Table of Contents iv ...

Страница 9: ...essure sensor If the maximum depths are exceeded the pressure sensor will rupture and the housing will flood See Section 6 1 Instrument Setup for more information Always orient the unit so that the OBS 5 sensor looks into water clear of reflective surfaces Pad the end caps that contact metal with electrical tape neoprene or expanded polyethylene tubes Never mount the instrument by its end caps or ...

Страница 10: ...ated from water density and barometric pressure entered by the operator FIGURE 4 1 Dimensions top sensor endcap with copper antifoulant Cu a f collars left and connector endcap right 4 1 Optics The heart of the OBS 5 is an optical system comprised of a near infrared NIR laser diode and a photodetector positioned 10 mm from the laser called the near detector ND and one mounted 25 mm from the laser ...

Страница 11: ...s from 0 the ND and FD signals rise to maxima at peak concentrations shown by the red open and blue solid arrowheads above the x axis Beyond the peak sediment concentrations light attenuation is the dominant factor controlling the light level at the detectors and so the ND and FD counts decline The scattered NIR must travel farther to be detected by the FD than by the ND and therefore the peak of ...

Страница 12: ...trations associated with the ND and FD peaks depend on sediment characteristics as shown by the variety of response curves and the colored arrowheads on FIGURE 4 4 Other sediment characteristics being equal such as shape and NIR reflectivity see Section 10 Interfering Factors larger particles produce higher peak concentrations and greater OBS 5 measurement ranges than smaller particles 4 ...

Страница 13: ...datalogger needed Operates up to six months on three C cell batteries Monitors high sediment concentrations up to 200g L Logs depth wave height wave period temperature and salinity Records 200 000 scans of data in the OBS 5 flash memory 5 1 Measurement Range Mud D50 20μm 0 to 50 000 mg l Sand D50 250μm 0 to 200 000 mg l Pressure1 0 to 10 20 50 100 or 200 m Turbidity 0 4 to 1 000 NTU 5 ...

Страница 14: ...ate 2 Hz Data capacity 8 MB 200 000 lines Battery capacity 8 A h Maximum battery life2 3 000 hrs External supply voltage 6 to 18 Vdc External supply current 55 mA Serial data protocols RS 232 RS 485 Maximum housing depth 300 m 984 ft Operating temperature range 0º to 40ºC Storage temperature range 20º to 70ºC 5 5 Dimensions Length diameter 380 mm 15 in 60 mm 2 4 in Weight 2 04 kg 4 5 lb Weight sub...

Страница 15: ...yethylene tubes Never mount the instrument by its endcaps or attach anything to them This could a cause a leak 6 1 2 Surveys The OBS 5 will usually be towed with a cable harness for surveys The serial cable can tow the OBS 5 without a depressor weight or vane as long as the connector is strain relieved Strain relief can be provided by attaching the cable to the stainless steel housing FIGURE 4 1 w...

Страница 16: ...ed during the previous day turn the sensor end up so water around the O rings can drain out when the endcap is removed FIGURE 6 2 A Pull endcap out and disconnect the inline connector B Wipe water from the inside wall of the housing tube with a paper towel C Turn the connector end up and push the ridge on the battery sliding contact until the spent batteries pop out D Insert new batteries with the...

Страница 17: ...RE 6 2 Battery installation A endcap removal B wiping C cable disconnect and D battery contact 6 2 OBS 5 Utility Software 6 2 1 Software Installation Insert the CD and select Install OBS 5 Utility Follow the installation wizard to install the software The OBS 5 Utility is the GUI interface with the OBS 5 As part of the installation there are several additional files included This section explains ...

Страница 18: ...og file and prompt you to accept the name see FIGURE 6 3 Files are automatically named with Greenwich Date and Time as follows OBS5 _20010808_172433 log Or you can create your own file name and destination by choosing No see FIGURE 6 4 Data received from the OBS 5 while it is connected to the PC will be stored in this file FIGURE 6 3 New data log prompt FIGURE 6 4 Designating your own file name an...

Страница 19: ... calibration tables 5 set detector gains Set Gains 6 Retrieve an Active Table 7 Retrieve detector Gains or 8 switch to RS 485 serial communication The View menu controls the display on your PC Switches are provided for Toolbar toggles the icons ON and OFF Status Bar toggles the status bar at the bottom of the screen ON or OFF Data Window pops the data window into view 6 2 4 Communication Settings ...

Страница 20: ...t the OBS 5 information box the baud rate of the unit is synchronized with your PC If you don t get an information box repeat the above procedure until communication is established 6 2 5 Testing Sensors 1 Before daily operations and deployments verify that the instrument works by clicking Open Plot and then clicking Survey Select all sensors and click Start Survey An example plot of data is shown ...

Страница 21: ...t cannot simultaneously measure SSC g L 1 and NTU when either g L 1 or NTU is selected You must choose one or the other 6 2 7 Water Density and Barometric Corrections Instrument depth is estimated from pressure and it is important to set the water temperature and salinity so the OBS 5 can correct for water density and calculate depth correctly The sensor measures absolute pressure so the instrumen...

Страница 22: ...s 2 048 seconds 0 57 hour Rate Rate is the frequency of sampling for the duration of measurements All sensors are sampled at the same rate typically 2 5 10 or 25 times per second Hz Power This indicates the percentage of time over the duration of a sample that sensors are ON Higher power levels mean larger samples and better statistics but shorter battery life Lower levels spare the batteries but ...

Страница 23: ...m to give a size greater than 200 Survey Select the survey mode when operating the unit with a cable connection to a PC and when high data rates are desired Data can be logged with a PC at rates up to 120 lines per minute 2 Hz Cyclic Sampling Use cyclic sampling to record data internally in the 8 MB flash memory at regular intervals for example every 1 5 15 or 30 minutes Depending on the number of...

Страница 24: ...pth units Meters or Feet Set temperature and salinity for the survey area 5 Click Start Survey and check the data flow in the Data Window 6 A file for logging data was created when you started the OBS 5 Utility You can review data at any time with Open and import the log file directly into an Excel spreadsheet for post survey processing and plotting see Section 6 2 15 Excel Spreadsheets 16 ...

Страница 25: ...or your survey area with and activate buttons Step 3 Section 6 2 10 Surveying 4 Click Cyclic Sampling and select sensors statistics depth units meters or feet water temperature and salinity 5 Select Interval Duration Rate and Power level see recommendations in Section 6 2 9 Sampling Modes and Terms 6 Click Start Sampling to begin logging data and watch a few lines as they are displayed in the data...

Страница 26: ...collection and use Offload Data to save data in a file 5 Highlight the data with the start and end times you want 6 Click Browse select a destination file and click OK 7 Wait for the progress bar to disappear and examine data as a plot or text file see Section 6 2 5 Testing Sensors 6 2 13 Shutdown From the OBS 5 menu select Sleep 6 2 14 Graphing and Printing 1 Use File menu to select how the data ...

Страница 27: ...to bracket the data you need on the graph Plot Width allows the graph to be sized to fit a PC screen On the depth plot select Max 0 and Min the maximum depth to display depth increasing downward 6 2 15 Excel Spreadsheets To make an Excel spreadsheet from OBS 5 data start Excel and set file type to All Open a data file and select Delimited in Step 1 of 3 of the Text Import Wizard Click Next and sel...

Страница 28: ...asurements When these sediment characteristics change they will produce apparent changes in SSC by themselves unless sediment calibrations are performed All sediments produce a unique set of calibration curves like the examples shown in FIGURE 4 4 The sediment calibration procedure is complicated and for a modest fee we will calibrate an OBS 5 sensor with your sediment Call for a quotation to perf...

Страница 29: ...d click on the Activate button then click View Active The calibration data table contains all the information needed by the OBS 5 to interpolate SSC values from the detector signals From left to right the column lists 1 SSC values g L 1 2 ND counts 3 2nd derivatives for ND curve 4 FD counts and 5 2nd derivatives for FD curve During a calibration the first table highlighted in red is created from t...

Страница 30: ...edule shown in TABLE 7 1 and adapt it to your sediment as required during the calibration procedure Sediment preparation is a critical factor in calibration quality Use dry material whenever possible because it can be accurately weighed Keep in mind that mixing grinding and sieving can produce smaller sediment than you will measure in the field and that the OBS 5 is very sensitive to particle size...

Страница 31: ...in Set the initial ND and FD gain values to 16 starting with the third SSC value in TABLE 7 2 adjust the gain to keep the ND and FD counts in the range of 50 000 to 60 000 While calibration points can be deleted at any time never start a new SSC value until you are satisfied with the current values and gain setting CAUTION The FD counts will peak first at around 2 to 7 g L 1 and the ND will peak b...

Страница 32: ...e Large black neoprene or polyethylene tub 1 gallon 4 l brown Nalgene polypropylene bottle with top cut off 1 liter volumetric flask Hand drill motor manual suspender Mixing propeller manual suspender Scale with 10 mg accuracy Automatic suspender optional Tea cup with round bottom and teaspoon 7 1 3 Procedure for Sediment 1 Put batteries in the OBS 5 and connect it to a PC with test cable using th...

Страница 33: ...number for the sediment calibration 4 Start the calibration with the button and secure the unit in a big black tub filled with clean tap water FIGURE 7 3 The sediment calibration dialog will appear the initial display will not show the red and green symbols FIGURE 7 3 OBS 5 in big black tub of clean water 25 ...

Страница 34: ...data table and the ND red and FD green points will be plotted on the calibration graph If you are satisfied with the data mount the unit in the suspender 6 Position the OBS 5 so that it produces the minimum FD signal in clear water FIGURE 7 4 FIGURE 7 4 OBS 5 in suspender tub 7 Weigh the first increment of sediment with the electronic balance see TABLE 7 1 and transfer it to a tea cup with a round...

Страница 35: ...listed in the table If the data for the current point is unacceptable for any reason too much or too little gain for example highlight the data line number and click the Delete button Adjust the gain and record it again with the same SSC value Do not proceed to the next SSC value until you are satisfied with the current data Once you add sediment to the suspender you cannot remove it CAUTION 13 Re...

Страница 36: ... 6 1 2 Start the OBS 5 Utility software wake the OBS 5 and click the OBS Settings button to verify its response 3 Use the OBS 5 pull down menu select Gain and set ND and FD gain to 2 This is the setting used for the factory calibration 4 Start the calibration with the button and secure the unit in a big black tub filled with clean tap water FIGURE 7 3 The NTU calibration dialog will appear 5 Enter...

Страница 37: ...e problems that can be easily fixed such as cable continuity processor reset and battery replacement or more serious ones such as sensor computer and electronic malfunctions and damaged mechanical parts that will require assistance The problem symptoms are shown in bold text Power failed because of contact corrosion or a broken power wire Check for a broken red wire connecting the battery tube and...

Страница 38: ... check port settings on the serial port tab The default baud rate is 115 2 kbps If the PC is not set to this speed follow the steps in Section 6 2 4 Communication Settings to set it If the OBS 5 still fails to respond try changing PC speeds and clicking OBS Settings until communication is established for example 57 6 38 4 19 6 9 6 kbps etc If this fails switch the PC back to 115 2 kbps and do the ...

Страница 39: ...sor power by clicking Survey and selecting all sensors the green LEDs should illuminate If they do not the sensor power circuit may not be working If the depth sensor reads high and does not change it may need to be cleaned see Section 9 2 Pressure Sensor If the sensors appear to be in working order the digitizer or microcontroller may be damaged Such problems require factory service 31 ...

Страница 40: ...etergent and warm water or a scouring pad will remove most contaminants encountered in the field A cloth with solvent or mineral spirits can be used to remove oil and grease However do not use MEK benzene toluene acetone TCE or electronic cleaners as they could damage the epoxy bond between the sapphire and the optic bushings At the conclusion of each survey or deployment clean the OBS 5 sensor If...

Страница 41: ...0 3000 2050 780 1180 400 900 3000 3000 1100 2040 600 1800 3000 3000 1930 3000 1100 3600 3000 3000 3000 3000 1930 9 4 Pressure Housing The pressure housing and O ring seals require little maintenance other than careful inspection every six months and service before moored deployments 1 Disassemble O ring seals and inspect mating surfaces for pits and scratches 2 Inspect O rings for cuts and nicks r...

Страница 42: ...that is caused when the factor changed over its full range in the environment For example the size of suspended sediment particles in the environment ranges from about 0 5 to 125 μm This range causes relative OBS sensitivity to change from 2 to 0 008 see next section giving a factor of 250 Interfering factors ranked in this way are summarized in TABLE 10 1 The ranking shows for instance that the s...

Страница 43: ...uts through a layer of oxidized light brown reflective mud into an underlying layer of black anoxic mud the OBS 5 will indicate that SSC of mud stirred up by the cutter has dropped even when it has not The relative signal level per unit of SSC varies from a low of about one for dark non reflective sediment to a high of about ten for white reflective sediment FIGURE 10 2 In areas where sediment col...

Страница 44: ...ained than it was in the environment and this will bias a sediment calibration A good example of how much OBS 5 readings can change as a result of the disaggregation is shown in FIGURE 10 3 The slope of each line on the graph indicates the sensitivity of an OBS sensor when calibrated with sediment disaggregated in a particular way The more mechanically aggressive a disaggregation method is the mor...

Страница 45: ...les smaller such as disaggregation or larger aggregation during the calibration process than they will be in the environment will cause SSC to appear to increase or decrease when there has been no actual change 2 Processes in the environment that make sediment particles larger than they were during a calibration will produce an apparent decline in SSC Conversely an environmental process that makes...

Страница 46: ... Analysis Handbook John Wiley Sons New York pp 511 546 Downing John 1998 Suspended Particle Concentration Monitor U S Patent Number 5 796 481 Downing John and Reginald A Beach 1989 Laboratory Apparatus for Calibrating Optical Suspended solids Sensors Marine Geology 86 pp 243 249 Gibbs R J 1978 Light Scattering from Particles of Different Shapes Journal of Geophysical Research 83 pp 501 502 Gibbs R...

Страница 47: ...ise calibration standard giving standard errors less than 1 compared to 2 1 for formazin and better linearity 0 15 NTU compared to 0 32 for formazin Photos courtesy of GFS Chemicals The key benefits of SDVB standards are 1 1 lot to lot variation in turbidity 2 consistent optical properties from 10 to 30 C 3 guaranteed one year stability 4 mixing and dilution are not required and 5 they are not tox...

Страница 48: ...rd is made by mixing equal volumes of stock formazin and distilled water Turbidity NTU Maximum Storage Time 1 10 1 day 2 20 1 day 10 40 1 day 20 400 1 month 400 1 year Besides being the primary standard formazin has two other advantages It is available from several chemical and scientific suppliers www vwrsp com www ColePalmer com www riccachemical com and www labchem net and it is the least expen...

Страница 49: ...mple even the median diameters of the two approved calibration standards differ by a factor of more that five and the shape of SDVB and formazin particles also differ see NTU SSC relationships Reference John Downing 2005 Turbidity Monitoring Chapter 24 in Environmental Instrumentation and Analysis Handbook John Wiley Sons Pages 511 546 2005 Sadar M 1998 Turbidity Standards Hach Company Technical I...

Страница 50: ...Appendix A Turbidity Standards A 4 ...

Страница 51: ......

Страница 52: ...1W7 CANADA www campbellsci ca dataloggers campbellsci ca Campbell Scientific Centro Caribe S A CSCC 300 N Cementerio Edificio Breller Santo Domingo Heredia 40305 COSTA RICA www campbellsci cc info campbellsci cc Campbell Scientific Ltd CSL Campbell Park 80 Hathern Road Shepshed Loughborough LE12 9GX UNITED KINGDOM www campbellsci co uk sales campbellsci co uk Campbell Scientific Ltd CSL France 3 A...

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