Campbell OBS-3+ Product Manual
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Campbell OBS-3+ Product Manual

Suspended solids and turbidity monitors
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OBS-3+ and
OBS300
Suspended Solids and
Turbidity Monitors
Revision: 7/19
Copyright © 2008 – 2019
Campbell Scientific

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Summary of Contents for Campbell OBS-3+

  • Page 1 OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Revision: 7/19 Copyright © 2008 – 2019 Campbell Scientific...
  • Page 3 Quotations for repairs can be given on request. It is the policy of Campbell Scientific to protect the health of its employees and provide a safe working environment, in support of this policy a “Declaration of Hazardous Material and Decontamination”...
  • 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: Area: 1 in...
  • Page 7 • Periodically (at least yearly) check electrical ground connections. WHILE EVERY ATTEMPT IS MADE TO EMBODY THE HIGHEST DEGREE OF SAFETY IN ALL CAMPBELL SCIENTIFIC PRODUCTS, THE CUSTOMER ASSUMES ALL RISK FROM ANY INJURY RESULTING FROM IMPROPER INSTALLATION, USE, OR MAINTENANCE OF TRIPODS, TOWERS, OR ATTACHMENTS TO TRIPODS AND TOWERS...

  • Page 9: Table Of Contents

    Table of Contents PDF viewers: These page numbers refer to the printed version of this document. Use the PDF reader bookmarks tab for links to specific sections. 1. Introduction..............1 2. Precautions ..............1 3. Initial Inspection ............2 4. QuickStart ..............2 Preparation for Use ................2 Use SCWin to Program Data Logger and Generate Wiring Diagram ..2 5.
  • Page 10 Table of Contents 10. Maintenance ............. 22 11. Factors that Affect Turbidity and Suspended- Sediment Measurements ........23 11.1 Particle Size ..................23 11.2 Suspensions with Mud and Sand ............24 11.3 Particle-Shape Effects ................ 24 11.4 High Sediment Concentrations ............25 11.5 IR Reflectivity—Sediment Colour .............26 11.6...
  • Page 11 Table of Contents 11-3. Relative scattering intensities of grain shapes ........25 11-4. Response of an OBS sensor to a wide range of SSC ......26 11-5. Infrared reflectivity of minerals as a function of 10-Munzell value .. 27 C-1. Pin assignments for MCBH and MCIL wet-pluggable connectors ..

  • Page 13: Introduction

    The sensor may be damaged if it is encased in ice. • • Damages caused by freezing conditions will not be covered by our warranty. • Campbell Scientific recommends removing the sensor from the water for the time period that the water is likely to freeze.

  • Page 14: Initial Inspection

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Initial Inspection Upon receipt of the OBS-3+ or OBS300, inspect the packaging and • contents for damage. File damage claims with the shipping company. The sensor is shipped with a calibration sheet and an instruction manual. •...
  • Page 15 OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors In the Available Sensors and Devices box, type OBS-3+ or find the sensor in the Sensors > Water > Quality folder. Double-click OBS- 3+/OBS300 Turbidity Sensor. Select your sensor Low and High NTU Range and Maximum Voltage Output.

  • Page 16: Overview

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors In Output Setup, type the scan rate, a meaningful Table Name, and Data Output Storage Interval. Click Next. Select the output options. Click Finish and save the program. Send the program to the data logger if the data logger is connected to the computer.

  • Page 17: Applications

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Insensitivity to bubbles and organic matter • Ambient-light rejection and low temperature coefficient • Applications OBS sensors are used for a wide variety of monitoring tasks in riverine, oceanic, laboratory, and industrial settings. They can be integrated in water- quality monitoring systems, CTDs, laboratory instrumentation, and sediment- transport monitors.

  • Page 18: Measurement Details

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors FIGURE 5-1. The OBS300 has the same components but they are arranged differently. The OBS light source is a Vertical-Cavity Surface-Emitting Laser diode (VCSEL), which converts 5 mA of electrical current to 2000 µW of optical power.

  • Page 19: Specifications

    Fitted with MCBH-5-FS, wet-pluggable connector—multiple mating • cable length options available Accurate and rugged • • Compatible with Campbell Scientific CRBasic data loggers: CR200(X) series, CR300 series, CR6 series, CR800 series, CR1000, CR1000X, CR3000, CR5000, and CR9000(X) Operating Temperature: 0° to 40°C CAUTION Sensor may be damaged if it is encased in frozen liquid.
  • Page 20 OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Power Voltage output: 5 to 15 VDC/15 mA (Volts outputs) 4-20 mA transmitter: 9 to 15 VDC/45 mA max. (4 to 20 mA output) Operating wave length: 850 ± 5 nm Optical power: 2000 µW Drift: <2% per year...

  • Page 21: Installation

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Installation If you are programming your data logger with Short Cut, skip Section 7.3, Wiring to Data Logger , and Section 7.4, Data Logger Programming (p. 10) (p. 11) Short Cut does this work for you. See Section 4, QuickStart , for a Short (p.

  • Page 22: Cable Ties Or Hose Clamps

    FIGURE show the recommended wiring configuration for connecting the OBS sensor to a Campbell Scientific data logger; wiring to data loggers manufactured by other companies is similar. In this configuration, single-ended analogue inputs are used to measure the OBS voltage signal. The red power wire is connected to a switched 12 V terminal, which allows the OBS sensor to be turned off when it is not making measurements.

  • Page 23: Data Logger Programming

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors FIGURE 7-1. OBS-3+ connected to a CR1000 data logger (OBS300 has the same wiring) NOTE The assignment of terminal (for example, SE1, SE2) vary depending on application. Data Logger Programming Short Cut is the best source for up-to-date data logger programming code. If your data acquisition requirements are simple, you can probably create and maintain a data logger program exclusively with Short Cut.

  • Page 24: Calibration Certificate

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors The CRBasic program should include Delay(0,2,Sec) to provide a 2 s warm-up time, as well as a VoltSE() instruction to measure the high input range and another VoltSE() instruction to measure the low input range. The millivolt measurements are converted to NTU by using the coefficients provided on the Calibration Certificate.

  • Page 25: Calibration Certificate Showing Millivolt Coefficients

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Polynomial for Curve Type Converting to Polynomial for Converting to FIGURE 7-2. Calibration certificate showing millivolt coefficients...

  • Page 26: Calibration

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Polynomial for Curve Type Converting to Polynomial for Converting to FIGURE 7-3. Calibration certificate showing volts coefficients Calibration Turbidity The normalized response of an OBS sensor to styrene divinylbenzene beads (SDVB) turbidity over the range from 0 to 4000 NTU is shown on FIGURE 8-1.

  • Page 27: Normalized Response Of Obs-3+ To Amco Clear ® Turbidity. The Inset Shows The Response Function Of An Obs Sensor To High Sediment Concentrations

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors NTU value with a 2 -order polynomial. This section explains how to do a turbidity calibration. 4000 3000 2000 1000 20000 40000 60000 SSC (mg/l) 1000 2000 3000 4000 Tur bidity (TU) FIGURE 8-1.

  • Page 28: Materials And Equipment

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors The NTU values of the standards will remain the same as long as the ratio of particle mass (number of particles) to water mass (volume) does not change. Evaporation causes this ratio to increase and dust, bacteria growth, and dirty glassware can also cause it to increase.

  • Page 29: Setup

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors 8.1.2 Setup Plug the test cable into the OBS sensor; connect the red and black wires to the battery and place the multimeter test probes on the blue (+) and green (–) wires or connect the blue and green wires to the data logger. Swab sensor with an alcohol-soaked towel to sterilize it.

  • Page 30: Sediment

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Perform 2nd-order polynomial regressions on the calibration data to get the coefficients for converting OBS signals to NTU values. FIGURE 8-3. OBS-3+ (left) and OBS300 (right) in 500-NTU AMCO Clear turbidity standard in 100-mm black polyethylene calibration ®...

  • Page 31: In Situ Calibration

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors after each addition of sediment for the determination of SSC by filtration and gravimetric analyses. 8.2.3 In situ Calibration In situ calibration is performed with water samples taken from the immediate vicinity of an OBS sensor in the field over sufficient time to sample the full range of SSC values to which a sensor will be exposed.

  • Page 32: Procedure

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors from the wall; see FIGURE 8-4. For the OBS300, mount the sensor so that the laser diode is submerged just below the water surface to maximize the distance from the detector and the bottom of the container. FIGURE 8-4.

  • Page 33: Troubleshooting

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors Add enough additional sediment to get one full increment of sediment, Wi ± 5%. Repeat steps 4, 5, and 6. Repeat step 8 until five full increments of sediment have been added or until the OBS signals exceed the output range.

  • Page 34: Maintenance

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors TABLE 9-1. Troubleshooting Chart Fault Cause of Fault Remedy Fails finger wave test No power, dead battery Replace battery and reconnect wires MCIL-5 plug not fully seated Disconnect and reinsert plug. Sensor broken Visually inspect for cracks.

  • Page 35: Factors That Affect Turbidity And Suspended-Sediment Measurements

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors 11. Factors that Affect Turbidity and Suspended- Sediment Measurements This section summarizes some of the factors that affect OBS measurements and shows how ignoring them can lead to erroneous data. If you are certain that the characteristics of suspended matter will not change during your survey and that your OBS was factory calibrated with sediment from your survey site, you only need to skim this section to confirm that no problems have been over...

  • Page 36: Suspensions With Mud And Sand

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors FIGURE 11-2. The apparent change in turbidity resulting from disaggregation methods 11.2 Suspensions with Mud and Sand As mentioned in Section 11.1, Particle Size , backscattering from particles (p. 23) is inversely related to particle size on a mass concentration basis. This can lead to serious difficulties in flow regimes where particle size varies with time.

  • Page 37: High Sediment Concentrations

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors OBS-3+ Plates Cubes Spheres 0.01 Scattering Angle FIGURE 11-3. Relative scattering intensities of grain shapes 11.4 High Sediment Concentrations At high sediment concentrations, particularly in suspensions of clay and silt, the infrared radiation from the emitter can be so strongly attenuated along the path connecting the emitter, the particle, and the detector, that backscatter decreases exponentially with increasing sediment concentration.

  • Page 38: Ir Reflectivity-Sediment Colour

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors FIGURE 11-4. Response of an OBS sensor to a wide range of SSC 11.5 IR Reflectivity—Sediment Colour Infrared reflectivity, indicated by sediment colour, has a major effect on OBS sensitivity because with other factors remaining constant, it changes the intensity of light scattering.

  • Page 39: Water Colour

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors FIGURE 11-5. Infrared reflectivity of minerals as a function of 10-Munzell value 11.6 Water Colour Some OBS users have been concerned that colour from dissolved substances in water samples, not coloured particles discussed in Section 11.5, IR Reflectivity , produces erroneously low turbidity measurements.

  • Page 40: Biological And Chemical Fouling

    Campbell Scientific sells two wipers from a third-party manufacturer: the Hydro-Wiper C with its own controller, or the Hydro-Wiper D that is controlled by a data logger.

  • Page 41: Terminology

    OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors 13. Terminology 110 Rule: 100 ppm of 100-μm suspended sand will scatter light with the same intensity as 10 ppm of 10-μm suspended silt, other factors, such as size, shape and colour, remaining constant. Backscatter/forward scatter: The interaction of light with suspended particles, water molecules, and variations in refractive index that alters the direction of light transport through a sample without changing the wavelength.
  • Page 42 OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors the concentration of suspended matter increases, so will water turbidity, and as the concentration of dissolved light-absorbing matter increases, turbidity will decrease. Turbidity (operational definition): NTU value is a number ranging from 0 to 10,000 that is computed by a turbidimeter from measurements of the intensity of light scattered from water sample and by interpolation between bracketing SDVB (AMCO Clear...

  • Page 43: Importing Short Cut Code Into Crbasic Editor

    Appendix A. Importing Short Cut Code Into CRBasic Editor Short Cut creates a .DEF file that contains wiring and memory usage information, and a program file that can be imported into the CRBasic Editor. By default, these files reside in the C:\campbellsci\SCWin folder. Import Short Cut program file and wiring information into CRBasic Editor: Create the Short Cut program following the procedure in 4, QuickStart (p.

  • Page 45: Example Programs

    Appendix B. Example Programs B.1 CR1000X Example Program The calibration values used in this program are from the calibration certificate shown in FIGURE 7-3. The example program uses the voltage curve coefficients. Since the coefficients of the voltage curve are used, the multiplier for VoltSE() needs to be 0.001.

  • Page 46: Cr200(X) Example Program

    Appendix B. Example Programs 'Use the low range terminal to get a more accurate measurement. NTU < 250 Then 'The value of 250 was chosen because it is the nominal low range value of 'this OBS sensor. i = 1 VoltSe (NTUX(i),1,mV5000,2,1,0,60,0.001,0) NTUX(i) = A(1) * NTUX(i)^2 + B(1) * NTUX(i) + C(1)
  • Page 47 Appendix B. Example Programs i = 1 'n=10 in this case so ten measurements will be made for both the high and low 'input ranges. A multiplier of 0.001 is used because the coefficients are 'from the voltage calibration sheet VoltSe (NTUarray(i),1,2,0.001,0) NTUarray(i) = A(2) * NTUarray(i)^2 + B(2) * NTUarray(i) + C(2) Next...

  • Page 49: Electrical Connections Details

    Appendix C. Electrical Connections Details FIGURE shows the contact numbers for the MCIL/MCBH-5 connectors and TABLE lists the electrical functions and wire colours. The user need only be concerned with the wire colours for the 8425 cable as the MCBH wires are not accessible.

  • Page 50: Pin Numbers, Electrical Functions And Wire Colour Codes For Obs Sensor Bulkhead Connectors

    Appendix C. Electrical Connections Details TABLE C-1. Pin numbers, electrical functions and wire colour codes for OBS sensor bulkhead connectors. MCBH-5-FS/MCIL-5-MP Electrical Wire Colour Wire Colour Contact Number Function (MCBH) (8425) Power (5 – 15V) Power Ground Black Black Signal Common Green Green High Range Signal (4X)

  • Page 51: Data Logger Connection To A Relay

    Appendix D. Data Logger Connection to a Relay An SPST single-channel solid-state relay can be used instead of the switched 12V terminal. FIGURE shows the relay connections. Black White Blue Green FIGURE D-1. Wiring diagram for connecting an OBS sensor to an external relay and a data logger NOTE The assignment of terminal number (for example, SE terminal 1...
  • Page 52 INFO Global Sales & Support Network A worldwide network to help meet your needs Australia Costa Rica Southeast Asia Garbutt, QLD Australia San Pedro, Costa Rica Bangkok, Thailand Location: Location: Location: 61.7.4401.7700 506.2280.1564 66.2.719.3399 Phone: Phone: Phone: info@campbellsci.com.au info@campbellsci.cc thitipongc@campbellsci.asia Email: Email: Email:...

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