OPERATOR’S MANUAL OBS500 Smart Turbidity Meter with ClearSensor™ Technology Revision: 5/14 C o p y r i g h t © 2 0 0 8 - 2 0 1 4 C a m p b e l l S c i e n t i f i c , I n c .
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Precautions DANGER — MANY HAZARDS ARE ASSOCIATED WITH INSTALLING, USING, MAINTAINING, AND WORKING ON OR AROUND TRIPODS, TOWERS, AND ANY ATTACHMENTS TO TRIPODS AND TOWERS SUCH AS SENSORS, CROSSARMS, ENCLOSURES, ANTENNAS, ETC. FAILURE TO PROPERLY AND COMPLETELY ASSEMBLE, INSTALL, OPERATE, USE, AND MAINTAIN TRIPODS, TOWERS, AND ATTACHMENTS, AND FAILURE TO HEED WARNINGS, INCREASES THE RISK OF DEATH, ACCIDENT, SERIOUS INJURY, PROPERTY DAMAGE, AND PRODUCT FAILURE.
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. Cautionary Statements ............................................... 1 3. Initial Inspection ......................................................... 2 3.1 Ships With ............................................................................................
Table of Contents 7.7 7.6.3 Edlog Programming ................................................................... 29 Operation in High Sediment Loads and Sandy Sediments ................ 30 7.7.1 Wiper Removal Procedure ......................................................... 31 8. Factors that Affect Turbidity and SuspendedSediment Measurements .......................................33 8.1 8.2 8.3 8.4 8.5 8.6 8.7 Particle Size ...........................................................................
Table of Contents 7-3. 7-4. 7-5. Settings Editor screen ......................................................................... 16 Terminal Emulator ............................................................................. 21 Normalized response of OBS500 to AMCO Clear® turbidity. The inset shows the response function of a turbidity sensor to high-sediment concentrations. ........................................................ 23 7-6. Position of OBS500 in clean tap water in big black tub ..........
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OBS500 Smart Turbidity Meter with ClearSensor™ Technology 1. Introduction The OBS500 submersible turbidity meter is designed for general pressure measurements. The OBS500 uses ClearSensor™ (U.S. Patent No. 8,429,952), an anti-fouling scheme that uses a shutter/wiper mechanism to protect and clean the optics and a refillable biocide chamber to allow biocide to leach out over the optics continually while in the closed position.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 3. • The probe must be calibrated with sediments from the waters to be monitored. The procedure for calibrating the probe is provided in Section 7.5, Calibration. • Sites with high sediment loads or large sand grains can be problematic for the shutter and its motor. Refer to Section 7.7, Operation in High Sediment Loads and Sandy Sediments, for more information. • The OBS500 will be damaged if it is encased in frozen liquid.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology CAUTION • The most important general precaution is to orient the unit so that the OBS sensor looks into clear water without reflective surfaces. This includes any object such as a mounting structure, a streambed, or sidewalls. The backscatter sensor in the OBS500 can see to a distance of about 50 cm (20 in) in very clean water at angles ranging from 125° to 170°. The side scatter (SS) sensor can only “see” to about 5 cm (2 in) at 90°.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology FIGURE 4-2. Apply tape to protect sensor FIGURE 4-3. Secure with hose clamps. Do not overtighten.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology FIGURE 4-4.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 4.2 Datalogger Programming and Wiring Short Cut is an easy way to program your datalogger to measure the sensor and assign datalogger wiring terminals. The following procedure shows using Short Cut to program the OBS500. 6 1. Install Short Cut by clicking on the install file icon. Get the install file from either www.campbellsci.com, the ResourceDVD, or find it in installations of LoggerNet, PC200W, PC400, or RTDAQ software. 2.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 4. Select Datalogger Model and Scan Interval (default of 5 seconds is OK for most applications). Click Next. 5. Under the Available Sensors and Devices list, select the Sensors | Water | Quality folder. Select OBS500 Smart Turbidity Meter. Click to move the selection to the Selected device window. Temperature defaults to degrees Celsius and the sensor is measured every scan.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 5. 6. After selecting the sensor, click at the left of the screen on Wiring Diagram to see how the sensor is to be wired to the datalogger. The wiring diagram can be printed out now or after more sensors are added. 7. Select any other sensors you have, then finish the remaining Short Cut steps to complete the program. The remaining steps are outlined in Short Cut Help, which is accessed by clicking on Help | Contents | Programming Steps. 8.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology • • • Insensitivity to bubbles and organic matter Ambient-light rejection Low temperature coefficient Side scatter sensors have the following advantages: • • 5.1 More accurate in very clean water Fixed measurement volume Applications Turbidity sensors are used for a wide variety of monitoring tasks in riverine, oceanic, laboratory, and industrial settings.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology Historically, most turbidity sensor manufacturers and sensor users labeled the units NTUs, for Nephelometric Turbidity Units. ASTM and the USGS have come up with the following unit classifications that are applicable to the OBS500: Optical Backscatter FBU Formazin Backscatter Unit Side Scatter FNU Formazin Nephelometric Unit Ratio Back and Side scatter FNRU Formazin Nephelometric Ratio Unit The document “U.S.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology The OBS500 has three communication modes: SDI-12, RS-232, or 0 to 5 V. The mode defaults to SDI-12/RS-232 but can be set in our Device Configuration Utility to analog. As an SDI-12/RS-232 sensor, the OBS500 is shipped with an address of 0. With SDI-12 and RS-232, the basic values output by the OBS500 are backscatter turbidity, side scatter turbidity, and temperature.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 6.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 7. Diameter: 4.76 cm (1.875 in) Length: 27 cm (10.625 in) Weight: 0.52 kg (1.15 lb) Maximum Cable Length: 460 m (1500 ft) (1 channel SDI-12 or Analog); 15 m (50 ft) (RS-232) Installation If you are programming your datalogger with Short Cut, skip Section 7.3, Datalogger/RTU Connection, and Section 7.6, Programming. Short Cut does this work for you. See Section 4, Quickstart, for a Short Cut tutorial. 7.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology FIGURE 7-1. Device Configuration Utility After installing the Device Configuration Utility, select the OBS500 in the Device Type selection. Select the correct PC Serial Port and then click Connect (see FIGURE 7-1). The Terminal tab can be used to verify the setup of the OBS500. Select the Terminal tab. Click in the Terminal window and push the Enter key several times. This will wake up the RS-232 mode of the sensor.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology FIGURE 7-2. Terminal Mode using 1 and H commands TABLE 7-2. RS-232 Terminal Commands Terminal Commands Values Returned 1 Identify Serial Number, SDI-12 address, etc.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology Device Configuration allows you to change the configuration of the OBS500. Select the Settings Editor tab. FIGURE 7-3. Settings Editor screen There are three settings that can be changed: SDI-12 address, measurement mode, and side scatter ratio top. Select the desired values and press the Apply button. NOTE 7.3 The SDI-12 address is not used while in analog mode.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology TABLE 7-3. OBS500 Connector Pin-Out MCIL-8-MP/MCBH-8-FS Contact Number Electrical Function Wire Color 1 Power Ground Black 2 SDI-12/RS232 TX/Analog SSBS Control White 3 Power (9.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 7.3.2 RS-232 Wiring Our CR800, CR850, CR1000, and CR3000 dataloggers have COM ports (control port Tx/Rx pairs) that can be used to measure RS-232 sensors. TABLE 7-5.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 7.4 Communication Modes 7.4.1 SDI-12 The OBS500 uses an SDI-12-compatible hardware interface and supports a subset of the SDI-12 commands. The most commonly used command is the aM! command, issued by the datalogger. Here, a represents the sensor address (0 to 9). The communication sequence begins with the datalogger waking the sensor and issuing the aM! command.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology TABLE 7-7.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology The address may also be changed by connecting to the probe in the Device Configuration Utility. Once connected, in the Settings Editor tab click in the address box and enter the new address. Press Apply to save the changes. 7.4.1.2 SDI-12 Transparent Mode The transparent mode allows direct communication with the OBS500. This may require waiting for programmed datalogger commands to finish before sending responses.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology For CR10X and CR510 standard mixed-array dataloggers, the datalogger telecommunications command to enter SDI-12 transparent mode is nX where n is the control port being used for SDI-12. For example, if the selected control port is C1, the command would be 1X. In response, the datalogger opens the link to control port 1 and responds with a prompt. CR10X and CR510 dataloggers reply with “entering SDI-12”.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology universal response curve. However, there is residual nonlinearity that is removed by calibration and by computation of a TU value with a 2nd-order polynomial. This section explains how to do a turbidity calibration. 0.8 0.6 0.4 4000 3000 Turbidity (NTU) Normalized OBS-3+ Response (OPV330 VCSEL) 1.0 0.2 A B C 2000 1000 0 0.0 0 20000 40000 60000 SSC (mg/l) 0 1000 2000 Tur bidity (TU) 3000 4000 FIGURE 7-5.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology TABLE 7-9. Calibration Materials and Volumes Side Scatter 90-Degree Materials Calibration Cup Diameter (mm/inches) 8594 - 20TU 100 (~4) 8595 - 40TU 100 (~4) 8596 - 125TU 100 (~4) 8597 - 250TU 100 (~4) 8598 - 500TU 100 (~4) 8599 - 1000TU 100 (~4) OBS Sensor Material 8600 - 125TU 200 (~7.9) 8601 - 250TU 200 (~7.9) 8602 - 500TU 200 (~7.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology TABLE 7-10. Change in TU value resulting from one hour of evaporation of SDVB standard, i.e., loss of water but not particles. Calibration-cup Size φ mm (φ in.) 250 TU 500 TU 2000 TU 4000 TU 100 (4) +0.26 +0.52 +2.10 +4.20 150 (6) +0.60 +1.20 +4.80 +9.70 Materials and equipment: OBS500 with cable, datalogger, large black polyethylene plastic tub (0.5 M I.D. X 0.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 6. Repeat steps 2, 3, 4, and 5 for the other standards. 7. Perform 2nd-order polynomial regressions on the calibration data to get the coefficients for converting OBS signals to TU values. FIGURE 7-7. OBS500 in 500-TU AMCO Clear® turbidity standard in 100-mm black polyethylene calibration cup 7.5.2 Sediment There are three basic ways to calibrate an OBS sensor with sediment. These are described in the following sections.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 7.5.2.2 Wet-Sediment Calibration Wet-sediment calibration is performed with sediment obtained from water samples or from the bed of a river that has not been dried and pulverized. Consolidation and biochemical changes during storage and processing cause some alteration of wet sediment, and for this reason, sediment and water samples should be stored at about 4°C prior to use.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology FIGURE 7-8. Portable Sediment Suspender (left) and OBS beam orientation in suspender tub (right) SSC = Wts [Vw + Wts/ρs]–1, where Wts = total sediment weight in tub in mg, Vw = volume of water in liters, ρ = density of water (ρ = 1.0 kg L–1 at 10° C), and ρs = sediment density (assume 2.65 103 mg L–1) Procedure 28 1. Record and log the clean-water signal as in Step 1, Section 7.5.1, Turbidity; see FIGURE 7-6.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 10. Perform 3rd order polynomial regressions on the data to get the coefficients for converting OBS output to SSC. 7.6 Programming 7.6.1 Using SCWIN SCWIN is the easiest and, typically, the preferred method for programming the datalogger. SCWIN generates a wiring diagram that shows how to connect the OBS500 to your Campbell Scientific datalogger. NOTE The sections that immediately follow are for CRBasic and Edlog.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology Note that Edlog only allocates one input location for Instruction 105. Two input locations are required—one for the pressure measurement and one for the temperature measurement. The additional input location needs to be inserted manually using the Input Location Editor. To get into the Input Location Editor, select Edit/Input Labels or press the F5 key. Once in the Input Location Editor, do the following steps: 7.7 1. Choose Edit/Insert Block. 2.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology the current usage. Therefore, increased current usage indicates that the wiper needs to be cleaned (see step 2). 4. Mount the sensor between 45 degrees pointing down to vertical hanging down. 7.7.1 Wiper Removal Procedure CAUTION 1. Remove the stop screw in the OBS500 housing at the end of the shutter/wiper slot. 2. Remove the 4-40 flat head screw and copper plate to expose the drive shaft access port (FIGURE 7-9). 3.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology Drive shaft access port FIGURE 7-10. Insert screwdriver and rotate clockwise FIGURE 7-11. Shutter disassembled Shutter copper plate Floating nut spacer Floating nut FIGURE 7-12.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology Factors that Affect Turbidity and SuspendedSediment Measurements This section summarizes some of the factors that affect OBS measurements and shows how ignoring them can lead to erroneous data.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology Sonic Probe (Most Aggressive) Sonic Bath Hand Shaking (Least Aggressive) FIGURE 8-2. The apparent change in turbidity resulting from disaggregation methods 8.2 Suspensions with Mud and Sand As mentioned in Section 8.1, Particle Size, light scattering from particles 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.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology OBS-3+ 1 Relative Scattering Intensity Plates Cubes 0.1 Spheres 0.01 0 20 40 60 80 100 120 140 160 180 Scattering Angle FIGURE 8-3. Relative scattering intensities of grain shapes 8.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology FIGURE 8-4. Response of an OBS sensor to a wide range of SSC 8.5 IR Reflectivity—Sediment Color Infrared reflectivity, indicated by sediment color, has a major effect on sensitivity because with other factors remaining constant, it changes the intensity of light scattering. Although turbidity sensors are color blind, tests have shown that “whiteness”, color, and IR reflectivity are correlated.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology FIGURE 8-5. Infrared reflectivity of minerals as a function of 10-Munzell Value 8.6 Water Color Some OBS users have been concerned that color from dissolved substances in water samples, not colored particles as discussed in Section 8.5, IR Reflectivity—Sediment Color, produces erroneously low turbidity measurements.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology more sensitive, by factors of four to six, to mineral particles than particulate organic matter, and interference from these materials can, therefore, be ignored most of the time. One notable exception is where biological productivity is high and sediment production from rivers and re-suspension is low. In such an environment, OBS signals can come predominately from plankton. 9.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology FIGURE 9-1. DevConfig, Send OS 10. Troubleshooting A common cause for erroneous, turbidity-sensor data is poor sensor connections to the datalogger. Problem: Unit will not respond when attempting serial communications. Suggestion: Check the power (Red is +V and Black is Ground) and signal (White is SDI-12 Data) lines to ensure proper connection to the datalogger.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology The following three tests are used to diagnose malfunctions of an OBS500. 1. The Finger-Wave Test is used to determine if an OBS sensor is ‘alive’. Power the OBS sensor and connect datalogger (see Section 7.2, Device Configuration Utility). Wave your finger across the sensor window about 20 mm away from it. The datalogger should show the output fluctuating from a few TU to the full-scale signal.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 11. References Anderson, C.W., 2005, Turbidity (ver. 2.1): U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A6., sec. 6.7, Sept 2005, accessed December 8, 2011, from http://pubs.water.usgs.gov/twri9A6/. Boyd Bringhurst and Jeff Adams. “Innovative Sensor Design for Prevention of Bio-fouling.” Oceans 2011, September 2011. Lewis, Jack. 1996.
OBS500 Smart Turbidity Meter with ClearSensor™ Technology 42
Appendix A. Importing Short Cut Code This tutorial shows: • • How to import a Short Cut program into a program editor for additional refinement. How to import a wiring diagram from Short Cut into the comments of a custom program. A.1 Importing Short Cut Code into a Program Editor Short Cut creates files that can be imported into either CRBasic Editor or Edlog program editor. These files normally reside in the C:\campbellsci\SCWin folder and have the following extensions: • • • • • • • .
Appendix A. Importing Short Cut Code 6. Import wiring information to the program by opening the associated .DEF file. Copy and paste the section beginning with heading “-Wiring for CRXXX–” into the CRBasic program, usually at the head of the file. After pasting, edit the information such that a ' character (single quotation mark) begins each line. This character instructs the datalogger compiler to ignore the line when compiling the datalogger code. A.1.
Appendix B. Example Programs B.1 CR1000 SDI-12 Program Although this is a CR1000 program, other CRBasic dataloggers are programmed similarly.
Appendix B. Example Programs B.2 CR1000 RS-232 Program Although this is a CR1000 program, other CRBasic dataloggers are programmed similarly.
Appendix B. Example Programs B.3 CR1000 Analog Program Although this is a CR1000 program, other CRBasic dataloggers are programmed similarly. 'CR1000 Series Datalogger 'OBS500_analog_O&M.
Appendix B. Example Programs B.4 Examples for High Sediment Loads B.4.1 Normally Open CR1000 Example 'CR1000 Series Datalogger 'OBS500 normally open ‘In normally open mode the OBS500 can make measurement multiple times per minute but the wiper interval could be set to as low as a ‘time or two a day. This mode is also beneficial where the power budget is critical since opening and closing the wiper consumes ‘considerably more power than making the turbidity measurement.
Appendix B. Example Programs B.4.2 Cycle Shutter/Wiper for Each Measurement CR1000 Program The following CRBasic program will: • • Open the shutter if closed, then make a measurement Make a measurement if open, then close Shutter/wiper cycles will be cut by 50%. This will reduce wear and power consumption 50% but still leave the optics shuttered 50% of the time.
Appendix B.
Appendix C. OBS500 Copper Sleeve Kit Installation 1. Remove the Button Head Hex Screw as shown. 2. Slide the Copper Sleeve over the OBS500 and snap it into place. 3. Install the 4-40 x ¼ SS Slot Head Screw.
Appendix C.
Campbell Scientific Companies Campbell Scientific, Inc. (CSI) 815 West 1800 North Logan, Utah 84321 UNITED STATES www.campbellsci.com • info@campbellsci.com 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 Africa Pty. Ltd. (CSAf) PO Box 2450 Somerset West 7129 SOUTH AFRICA www.csafrica.co.za • cleroux@csafrica.co.za Campbell Scientific Ltd.
