Campbell OBS-5+ Operator's Manual
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Campbell OBS-5+ Operator's Manual

Turbidity and temperature monitoring system
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OBS-5+
Turbidity and Temperature
Monitoring System
Operator's Manual
Issued 7.12.09
©
Copyright
2007-2009 Campbell Scientific Inc.
Printed under licence by Campbell Scientific Ltd.
CSL 729

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Summary of Contents for Campbell OBS-5+

  • Page 1 OBS-5+ Turbidity and Temperature Monitoring System Operator’s Manual Issued 7.12.09 © Copyright 2007-2009 Campbell Scientific Inc. Printed under licence by Campbell Scientific Ltd. CSL 729...
  • Page 3 Note that goods sent air freight are subject to Customs clearance fees which Campbell Scientific will charge to customers. In many cases, these charges are greater than the cost of the repair. Campbell Scientific Ltd,...
  • Page 5 PLEASE READ FIRST About this manual Please note that this manual was originally produced by Campbell Scientific Inc. primarily for the North American market. Some spellings, weights and measures may reflect this origin. Some useful conversion factors: 1 in (square inch) = 645 mm Area: 1 in.

  • Page 7: Table Of Contents

    Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. Introduction ............... 1-1 1.1 Features ....................1-1 1.2 Optics ...................... 1-2 1.3 SSC-Measurement Principle..............1-2 2.
  • Page 8 8. Interfering Factors ............ 8-1 8.1 Particle Size .................... 8-1 8.2 NIR Reflectivity ..................8-2 8.3 Particle Shape, Flocculation, and Disaggregation ......... 8-3 9. References ..............9-1 10. Specifications ............10-1 Appendix A. Turbidity Standards ..........A-1 Figures 1-1. Dimensions (top), Sensor Endcap with Copper Antifoulant (Cu a.f.) Collars (left) and Connector Endcap (right) ........

  • Page 9: Introduction

    Section 1. Introduction ® The manual describes the features of the OBS-5+ as well as its use for surveys and battery-powered, internal-logging operations. Using backscatter from a 780 nm laser diode and a patented dual-detection system (U.S. Patent Number 5,796,481), a calibrated OBS-5+ measures suspended sediment concentrations, SSC, as large as 200 g l , which is about 10 times higher than standard OBS technology.

  • Page 10: Optics

    OBS-5A Turbidity and Temperature Monitoring System 1.2 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, called the far detector (FD), see Figure 1-2.
  • Page 11 Section 1. Introduction Figure 1-3. 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. The concentrations associated with the ND and FD peaks depend on sediment characteristics as shown by the variety of response curves and the coloured arrowheads on Figure 1-4.

  • Page 12: Calibration Curves For Four Different Sediments And Ssc Values For Near-Detector Peaks (Coloured Arrowheads)

    OBS-5A Turbidity and Temperature Monitoring System Figure 1-4. Calibration curves for four different sediments and SSC values for near-detector peaks (coloured arrowheads).

  • Page 13: Instrument Setup

    Section 2. Instrument Setup 2.1 Mounting Suggestions CAUTION Maximum depth for the OBS-5+ is limited by the installed pressure sensor. If the maximum depths are exceeded, the pressure sensor will rupture and the housing will flood. The depth limits are listed in Table 2-1. Table 2-1.

  • Page 14: Logging Data

    OBS-5A Turbidity and Temperature Monitoring System Figure 2-1. Electrical Connections 2.3 Logging Data In applications where a survey cable is impractical or when the OBS-5+ must be attached to an instrument frame, it can be powered by the internal batteries and the data can be logged by the data FLASH memory See instructions for Cyclic Mode sampling in Section 3.

  • Page 15: Battery Installation: A) Endcap Removal, B) Wiping, C) Cable Disconnect, And D) Battery Contact

    Section 2. Instrument Setup Figure 2-2. Battery Installation: A) Endcap Removal, B) Wiping, C) Cable Disconnect, and D) Battery Contact...
  • Page 16 OBS-5A Turbidity and Temperature Monitoring System...

  • Page 17: Operations

    Section 3. Operations 3.1 Software Installation Copy all of the files on the supplied CD to a directory called OBS on your PC hard drive. The program OFW5+.exe is the GUI interface with the OBS-5+. Make a shortcut to this program on the PC desktop. The other files on the CD include the OBS-5+ firmware, a system-maintenance program called HOST5.exe, communication drivers, and an SSC-calibration spreadsheet.

  • Page 18: Pull-Down Menus

    OBS-5A Turbidity and Temperature Monitoring System 4) Connect the OBS-5+ to a PC with the test cable (Figure 2-1). 5) Click Connect/Disconnect to get a green light and synchronize the OBS- 5+ clock with your PC by clicking 3.3 Pull-Down Menus OFW5+ has four pull-down menus for File, OBS-5+, View, and Help.

  • Page 19: Communication Settings

    Section 3. Operations Section 3.7), 4) view a list of calibration tables, 5) switch to RS485 serial communication, or 6) set detector gains (Set Gains). The View menu controls the display on your PC. Switches are provided for: • Toolbar toggles the icons ON and OFF. •...

  • Page 20: Monitoring Turbidity (Ntu)

    OBS-5A Turbidity and Temperature Monitoring System 2) Wave your hand in front of the OBS-5+ sensor; the turbidity and SSC levels on the top plot will fluctuate as data scrolls across the plot. 3) Blow into the pressure sensor or press your thumb on it to compress air on the diaphragm (Figure 1-1).

  • Page 21: Water Density And Barometric Corrections

    Section 3. Operations measure turbidity, the electronic gain of the near detector is set to the calibration value and the active lookup table is overridden. Consequently, the unit cannot simultaneously measure SSC (g l ) and NTU when either g/l or NTU is selected. You must choose one or the other.

  • Page 22: Surveying

    OBS-5A Turbidity and Temperature Monitoring System The main factors to consider when setting up OBS-5+ Cyclic sampling schedules include: • Sampling interval needed to characterize the processes of interest (e.g., water level fluctuations, flood and transport duration, tidal conditions, dredge operations etc.).
  • Page 23 Section 3. Operations 2) Open the Data Window with the View pull-down menu. 3) Click the lookup table icon and select a calibration table for your survey. The last active table will be used otherwise. 4) Click Survey to select: sensors, lines per minute, and depth units (Metres or Feet).

  • Page 24: Cyclic Sampling

    OBS-5A Turbidity and Temperature Monitoring System 6) A file for logging data was created when you started OFW5+. 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 “Excel Spreadsheets”, Section 3.15).

  • Page 25: Data Retrieval

    Section 3. Operations 3.12 Data Retrieval 1) Remove dummy plug and connect OBS-5+ to PC with test cable (Figure 2-1). 2) Run OFW5+. 3) Open the Data Window to verify that the instrument is transmitting data. 4) Click to end data collection and use Offload Data to save data in a file.

  • Page 26: Excel Spreadsheets

    OBS-5A Turbidity and Temperature Monitoring System 2) Click Open and select a file to view. Print will print a graph when Open As Plot is selected. To print a text file, select Open As Text, and use the Word Pad file print functions. For spreadsheet operations, see the next section.
  • Page 27 Section 3. Operations 3-11...

  • Page 29: Troubleshooting

    Section 4. Troubleshooting This section will help you isolate 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 our help.
  • Page 30 OBS-5A Turbidity and Temperature Monitoring System Figure 4-1. Internal Components OBS-5+ or pressure sensor malfunction. • Open unit and inspect for: 1) broken sensor wires, and 2) loose pressure sensor connector (Figure 4-1). • Check sensor power by clicking Survey and selecting all sensors; the green LEDs should illuminate.
  • Page 31 Section 4. Troubleshooting OBS-5+ indicates different NTU values in the field than other turbidimeters. Not all turbidity meters read the same! OBS-5+ sensors are checked with U.S. EPA-approved AMOCO Clear turbidity standards before leaving our factory (see Appendix A). Other turbidimeters will read different NTU values on natural water samples.
  • Page 32 OBS-5A Turbidity and Temperature Monitoring System...

  • Page 33: Maintenance

    Section 5. Maintenance 5.1 OBS-5+ Sensor The sapphire windows over the laser diode and the detectors must be kept clean to make accurate SSC measurements (Figure 1-1and Figure 1-2). A gradual signal decline over a period of days to weeks indicates fouling with mud, oil, or biological material.

  • Page 34: Pressure Housing

    OBS-5A Turbidity and Temperature Monitoring System Table 5-1. Battery Life in Hours with 100% Power Interval (sec.) 100% 100% 100% > 3000 2050 1180 > 3000 > 3000 1100 2040 > 3000 > 3000 1930 > 3000 1100 1800 > 3000 >...

  • Page 35: Sediment And Ntu Calibration

    Section 6. 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.
  • Page 36 OBS-5A Turbidity and Temperature Monitoring System lists: 1) SSC values (g l ), 2) ND counts, 3) 2 derivatives for ND curve, 4) FD counts, and 5) 2 derivatives for FD curve. During a calibration, the first table, highlighted in red, is created from the rising limb of the near detector response between zero counts and point “a”...
  • Page 37 Section 6. Sediment and NTU Calibration Six to ten calibration points are needed to define each table. For the lookup tables to function properly, the peaks in the ND and FD curves must be within ± 2,500 counts of one another, and to maximize resolution, the peak heights should be between 62,000 and 64,500 counts.

  • Page 38: Equipment And Materials

    OBS-5A Turbidity and Temperature Monitoring System Table 6-2. SSC-Calculation Spreadsheet Grams Total Cs (g/l) Water Sediment Added Grams (g/l) Volume (l) Density (g/l) 0.00 0.00 0.00 2650 1.00 1.00 0.33 2.00 3.00 1.00 3.00 6.00 2.00 4.00 10.00 3.33 Sediment concentrations can also be calculated manually with the following equations: Sediment mass...

  • Page 39: Procedure For Sediment

    Section 6. Sediment and NTU Calibration 6.3 Procedure for Sediment 1) Put batteries in the OBS-5+ and connect it to a PC with test cable using the RS-232 plug (Figure 2-1). 2) Start OFW5+; wake the OBS-5+; and click the OBS Settings button to verify its response.
  • Page 40 OBS-5A Turbidity and Temperature Monitoring System 5) Enter 0.001 in the value box and click the Record button to log the Clearwater data point. The unit will take 1,200 measurements in 60 seconds. When the process is complete, the data appear in the data table and the ND (red) and FD (green) points will be plotted on the calibration graph.
  • Page 41 Section 6. Sediment and NTU Calibration 7) Weigh the first increment of sediment with the electronic balance (see Table 6-1) and transfer it to a tea cup with a rounded bottom. 8) Withdraw about 10 ml of water from the suspender and add it to the tea cup containing the dry sediment.
  • Page 42 OBS-5A Turbidity and Temperature Monitoring System 14) To compute the lookup tables, click the Calculate Fit button and supply the requested information. Referring to Figure 6-2, pick point ‘a’ by counting the number of data points on the ND curve from the origin (0, 0) to the first point beyond where the ND and FD curves cross, 6 in Figure 6-2.

  • Page 43: Turbidity (Ntu) Calibration

    Section 7. Turbidity (NTU) Calibration 7.1 Equipment and Materials • Large black, neoprene or polyethylene tub (www.statelinetack.com, rubber tub, Cat. No. 310290, Rubbermaid wastebasket, RCP 2957 BLA) • 100 mm test cylinder (www.deslinc.com, No. TC-4) • AMCO Clear turbidity standards (GFS No. 8429, 8430, and 8431, www.gfschemicals.com) 7.2 Procedure for Turbidity 1) Put batteries in the OBS-5+ and connect it to a PC with test cable using the...
  • Page 44 OBS-5A Turbidity and Temperature Monitoring System Figure 7-1. OBS-5+ in 100 mm Cup 6) Add enough 250-NTU standard to cover the sensor end (Figure 1-1) and swipe bubbles off the sapphire windows with your finger. Click the Record button. 7) Repeat Step 6 for the 500 and 1,000 NTU standards. 8) Review the data table and graph, and if they look satisfactory, click the Calculate Fit button.

  • Page 45: Interfering Factors

    Section 8. Interfering Factors Changes in sediment concentration (SSC) are the primary cause for OBS-5+ output fluctuations in the environment. In some monitoring areas, however, factors other than SSC, will cause the OBS-5+ to indicate SSC variation that are invalid and which the user does not wish to measure. These factors are called interferences because they cause apparent shifts in SSC that are not real.

  • Page 46: Nir Reflectivity

    OBS-5A Turbidity and Temperature Monitoring System Figure 8-1. Effects of Sediment Size 8.2 NIR Reflectivity The output of an OBS-5+ will increase with the NIR-reflectivity of suspended sediment independent of SSC. This can degrade accuracy when unknown reflectivity changes occur during a monitoring campaign. For instance, when a dredge cuts 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.

  • Page 47: Particle Shape, Flocculation, And Disaggregation

    Section 8. Interfering Factors Figure 8-2. Near-infrared Reflectivity of Minerals 8.3 Particle Shape, Flocculation, and Disaggregation Particle shape can be an interfering factor. The sensitivity of an OBS-5+ sensor to plate-shaped particles is about ten times higher than it is to spherical particles. Disaggregation of dry sediment by grinding can cause the sediment to become finer grained than it was in the environment and this will bias a sediment calibration.
  • Page 48 OBS-5A Turbidity and Temperature Monitoring System Figure 8-3. Effects of Disaggregation Methods Finally, flocculation of clay particles in estuaries can affect sensitivity by causing small particles to clump together into larger ones to which the OBS-5+ is less sensitive. For example, when a dredge works into a zone of saline water where flocculation occurs, an OBS-5+ can indicate less than the actual level of SSC.

  • Page 49: References

    Section 9. References Black, K.P., M.A. Rosenberg. 1994. Suspended Sand Measurements in a Turbulent Environment: Field Comparison of Optical and Pump Sampling. Coastal Engineering, 24, pp. 137-150. Conner, C.S. and A.M. De Visser. 1992. A Laboratory Investigation of Particle Size Effects on an Optical Backscatterance Sensor. Marine Geology, 108, pp. 151- 159.
  • Page 50 OBS-5A Turbidity and Temperature Monitoring System...
  • Page 51 Section 10. Specifications RANGE Mud (D =20μm) ........... 0 to 50,000 mg/l Sand (D =250μm) ..........0 to 200,000 mg/l Pressure ..............0 to 10, 20, 50, 100 or 200m Turbidity ..............0.4 to 1,000 NTU ACCURACY Mud ................ 2.0% of reading Sand ................
  • Page 52 OBS-5A Turbidity and Temperature Monitoring System 10-2...

  • Page 53: Turbidity Standards

    Appendix A. Turbidity Standards AMCO Clear, supplied by GFS Chemicals (www.gfschemicals.com), is an approved calibration standard and is the one we use to certify our instruments. It is made from styrene divinylbenzene (SDVB) microspheres. SDVB spheres have a median size and standard deviation of 0.28μm (~1/5 that of formazin particles) and 0.10 μm respectively and a refractive index of 1.56.
  • Page 54 OBS-5A Turbidity and Temperature Monitoring System Recommended formazin storage times are listed in the accompanying table. Working standards are prepared by volumetric dilution of 4000-NTU stock formazin with distilled water. So for example, a 2000 NTU calibration standard is made by mixing equal volumes of stock formazin and distilled water. Turbidity Maximum (NTU)
  • Page 55 Operator’s Manual We must emphasize that unlike SSC, which has physical units, turbidity values (NTUs, FTUs, etc.) do not. Therefore, if you measure water turbidity to be 100 NTU, you cannot directly infer any physical quantities from it. Turbidity values do not represent particular SSC values, indicate light levels at the bottom of a stream, or quantify biological process’.
  • Page 56 CAMPBELL SCIENTIFIC COMPANIES Campbell Scientific, Inc. (CSI) 815 West 1800 North Logan, Utah 84321 UNITED STATES www.campbellsci.com • info@campbellsci.com Campbell Scientific Africa Pty. Ltd. (CSAf) PO Box 2450 Somerset West 7129 SOUTH AFRICA www.csafrica.co.za • sales@csafrica.co.za Campbell Scientific Australia Pty. Ltd. (CSA)

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